water quality assessment and pollution control

WATER QUALITY WATER QUALITY ASSESSMENT AND ASSESSMENT AND

POLLUTION POLLUTION CONTROLCONTROL

WMA 318WMA 318Prof. O. Martins and Dr O.Z. OjekunleProf. O. Martins and Dr O.Z. OjekunleDept of Water Res. Magt. & AgrometDept of Water Res. Magt. & Agromet

UNAAB. Abeokuta. Ogun StateUNAAB. Abeokuta. Ogun StateNigeriaNigeria

[email protected]

PROPERTIES OF WATERPROPERTIES OF WATER

Water is a chemical compound of oxygen and hydrogen and Water is a chemical compound of oxygen and hydrogen and in the gaseous state can be represented by the molecular in the gaseous state can be represented by the molecular formula Hformula H22O. The isotopes of hydrogen and three isotopes of O. The isotopes of hydrogen and three isotopes of oxygen exist in nature, and if these are taken into account, oxygen exist in nature, and if these are taken into account, 33 varieties of water are possible.33 varieties of water are possible.

The physical properties of liquid water are unique in a The physical properties of liquid water are unique in a number of respects, and these departure from what might be number of respects, and these departure from what might be considered as normal for such a compound are of the considered as normal for such a compound are of the greatest importance with respect to both the existence of life greatest importance with respect to both the existence of life on earth and the operation of many geochemical processes.on earth and the operation of many geochemical processes.

The boiling point and freezing point of water are both far The boiling point and freezing point of water are both far higher than would be the theoretically expected, considering higher than would be the theoretically expected, considering the low molecular weight of the compound, and the range of the low molecular weight of the compound, and the range of temperature over which water as a liquid is wider than might temperature over which water as a liquid is wider than might be expected. The reason for these and other departures from be expected. The reason for these and other departures from ““normalnormal”” behaviour can be gained by more detailed behaviour can be gained by more detailed consideration of the molecular structure of the compound.consideration of the molecular structure of the compound.

MOLECULAR STRUCTURE MOLECULAR STRUCTURE OF WATEROF WATER

The spheres representing the ions coalesce to some extent, and the The spheres representing the ions coalesce to some extent, and the molecule might be thought of as a sphere having two rather prominent molecule might be thought of as a sphere having two rather prominent bubbles of bubbles of ““blistersblisters”” attached to it. Te bonds connecting the hydrogen attached to it. Te bonds connecting the hydrogen ’’s to s to oxygen describe an angle of 105oxygen describe an angle of 105oo, so that the two hydrogen are relatively , so that the two hydrogen are relatively close together on one side of the molecule.close together on one side of the molecule.

Although this representation of the molecule is somewhat empirical it Although this representation of the molecule is somewhat empirical it helps to explain some of the abnormal features of the behaviour of water. helps to explain some of the abnormal features of the behaviour of water. The molecule has The molecule has dipolar properties dipolar properties because the positive charge because the positive charge associated with the hydrogen are connected on one side of the molecule, associated with the hydrogen are connected on one side of the molecule, leaving a degree of negativity on the opposite side. Forces of attraction leaving a degree of negativity on the opposite side. Forces of attraction thus exist between hydrogens of one molecule and the oxygen bonds. They thus exist between hydrogens of one molecule and the oxygen bonds. They hold molecule together in a fixed pattern in the solid state. In contrast to hold molecule together in a fixed pattern in the solid state. In contrast to the orderly arrangement of molecules in crystal of ice, the molecules of the orderly arrangement of molecules in crystal of ice, the molecules of liquid water are in a chaotic condition of disorder.liquid water are in a chaotic condition of disorder. Hydrogen bonds Hydrogen bonds still still remain an important force but their arrangement is continually shifting remain an important force but their arrangement is continually shifting

The cohesive forces represented by the hydrogen bonds impact to liquid The cohesive forces represented by the hydrogen bonds impact to liquid water is high heat of vaporization. The forces also tend to prevent the water is high heat of vaporization. The forces also tend to prevent the passage to electric currents and impart to the fluid its passage to electric currents and impart to the fluid its high dielectric high dielectric constanconstant. The attraction between molecules of a liquid is shown at a t. The attraction between molecules of a liquid is shown at a liquid surface by the phenomenon called liquid surface by the phenomenon called Surface tension. Surface tension. The surface of The surface of water is 75.6 dynes per centimeter at 0oC and 71.8 dynes per centimeter water is 75.6 dynes per centimeter at 0oC and 71.8 dynes per centimeter at 25at 25ooC, which are very high values compared with the many other liquids C, which are very high values compared with the many other liquids

PROPERTIES OF WATERPROPERTIES OF WATER Chemical Constitution of WaterChemical Constitution of Water 1 Ionic and Non Ionic1 Ionic and Non Ionic Ionic Ionic

AnionAnion CationsCations

2 Major Anions2 Major Anions Bicarbonate, Chloride, SulphateBicarbonate, Chloride, Sulphate

Major CationsMajor Cations Sodium, Potassium, Calcium, MagnesiumSodium, Potassium, Calcium, Magnesium

Non-IonicNon-Ionic SiOSiO22, Dissolved gases, oily Substance, Synthetic , Dissolved gases, oily Substance, Synthetic

detergent, etcdetergent, etc

CHARACTERISTICS OF CHARACTERISTICS OF WATERWATER

HardnessHardness Carbonate (Temporary) Hardness CaCOCarbonate (Temporary) Hardness CaCO33 Non Carbonate (Permanent) Hardness CaSONon Carbonate (Permanent) Hardness CaSO44 Concentration of Hydrogen-ion, which are expressed in pH Concentration of Hydrogen-ion, which are expressed in pH

units. It is theunits. It is the——LogLog1010HH++

Specific Electrical ConductanceSpecific Electrical Conductance - Increases with temperature: values must therefore be related - Increases with temperature: values must therefore be related

to the same temperature (2%)to the same temperature (2%) ColourColour Alkanity: Ability to neutralize acid; due to the presence of OH-, Alkanity: Ability to neutralize acid; due to the presence of OH-,

HCOHCO33--, CO, CO33

2-2-,, Acidity: Water with pH 4.5 is said to have acidity; caused by Acidity: Water with pH 4.5 is said to have acidity; caused by

the presence of free mineral acids and carbonic acidsthe presence of free mineral acids and carbonic acids Turbidity: Measure of transparency of water column; indirect Turbidity: Measure of transparency of water column; indirect

method of measuring ability of suspended and colloidal method of measuring ability of suspended and colloidal materials to minimize penetration of light through water.materials to minimize penetration of light through water.

Dissolved gasses: ODissolved gasses: O22, N, N22, CO, CO22, H, H22S, CHS, CH44, NH, NH33, etc., etc.

PHYSICAL CHEMICAL PHYSICAL CHEMICAL PARAMETER PARAMETER

Since water is not found in its pure in Since water is not found in its pure in nature, it is important to determine its nature, it is important to determine its combined physical, chemical and combined physical, chemical and biological characteristics. This is done biological characteristics. This is done through monitoring of water for its quality.through monitoring of water for its quality.

Physical chemical parameter analyzed in Physical chemical parameter analyzed in natural environments; Atmosphere natural environments; Atmosphere (rainfall), hydrosphere (river, lakes, and (rainfall), hydrosphere (river, lakes, and oceans) and Lithosphere (Groundwater) oceans) and Lithosphere (Groundwater) are similar-are similar-

PHYSICAL CHEMICAL PHYSICAL CHEMICAL PARAMETER (Cont)PARAMETER (Cont)

Temperature:Temperature: Measurement is relevant Measurement is relevant For Aquatic lifeFor Aquatic life Control of waste treatment plantsControl of waste treatment plants Cooling purposes for industriesCooling purposes for industries Calculation of solubility of dissolved gasesCalculation of solubility of dissolved gases Identification of water sourceIdentification of water source Agriculture IrrigationAgriculture Irrigation Domestic uses (Drinking, bathing)Domestic uses (Drinking, bathing) Instrument of measurement is thermometerInstrument of measurement is thermometer pH:pH: Controlled by CO Controlled by CO22/HCO/HCO33

--/CO/CO332-2- Equilibria in natural water. Equilibria in natural water.

Its values lie between 4.5 and 8.5. It is importantIts values lie between 4.5 and 8.5. It is important Chemical and biological properties of liquidChemical and biological properties of liquid Analytical workAnalytical work Measurement is done in the field. Most common method Measurement is done in the field. Most common method

of determination is the electrometric method, involving a pH-of determination is the electrometric method, involving a pH-meter. It is important to calibrate the meter with standard pH meter. It is important to calibrate the meter with standard pH buffer solutionsbuffer solutions

PHYSICAL CHEMICAL PHYSICAL CHEMICAL PARAMETER (Cont)PARAMETER (Cont)

Dissolved Oxygen: Water in contact with the atmosphere Dissolved Oxygen: Water in contact with the atmosphere has measurable dissolved oxygen concentration. It has measurable dissolved oxygen concentration. It values depends onvalues depends on

Partial pressure of OPartial pressure of O22 in the gaseous phase in the gaseous phase Temperature of the waterTemperature of the water Concentration of salt in the water (the higher the salt Concentration of salt in the water (the higher the salt

content in water, the lower the concentration of content in water, the lower the concentration of dissolved oxygen and the other gases). dissolved oxygen and the other gases).

Measurement is important inMeasurement is important in Evaluation of surface water qualityEvaluation of surface water quality Waste-treatment processes controlWaste-treatment processes control Corrosivity of waterCorrosivity of water SepticitySepticity Photosynthetic activity of natural waterPhotosynthetic activity of natural water

MEASUREMENT & RELATIONSHIP OF MEASUREMENT & RELATIONSHIP OF

PHYSICAL CHEMICAL PARAMETERSPHYSICAL CHEMICAL PARAMETERS Temperature:Temperature: Temperature affects the density Temperature affects the density

of water, the solubility of constituents (Such of water, the solubility of constituents (Such as oxygen in water), pH, Specific conductance, as oxygen in water), pH, Specific conductance, the rate of chemical reactions, and biological the rate of chemical reactions, and biological activity of wateractivity of water. Continuous water quality sensor . Continuous water quality sensor measure temperature with thermistor, which is a measure temperature with thermistor, which is a semiconductor having resistance that changes with semiconductor having resistance that changes with temperature. Thermistor are reliable, accurate, temperature. Thermistor are reliable, accurate, and durable temperature sensors that require little and durable temperature sensors that require little maintenance and are relative inexpensive. The maintenance and are relative inexpensive. The preferred water-temperature scale for most preferred water-temperature scale for most scientific work ids the Celcius scale. measure scientific work ids the Celcius scale. measure temperature to plus or minus 0.1 degree celcius temperature to plus or minus 0.1 degree celcius ((ooC) C)

MEASUREMENT & RELATIONSHIP OF MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS PHYSICAL CHEMICAL PARAMETERS

(Cont)(Cont) Specific Conductance:Specific Conductance: Electrical conductivity is a Electrical conductivity is a

measure of the capacity of water to conduct an measure of the capacity of water to conduct an electrical current and is a function of the types and electrical current and is a function of the types and quantities of dissolved substance in water. quantities of dissolved substance in water. As As concentration of dissolved ions increase, concentration of dissolved ions increase, conductivity of the water increases.conductivity of the water increases. Specific Specific conductance is the conductivity expressed in units of conductance is the conductivity expressed in units of Microsiemen per centimeter at 25Microsiemen per centimeter at 25ooC. Specific C. Specific conductance are a good surrogate for total dissolved conductance are a good surrogate for total dissolved solids and total ions concentrations, but there is no solids and total ions concentrations, but there is no universal linear relation between total dissolved universal linear relation between total dissolved solids and specific conductance.solids and specific conductance.

Specific conductance sensors are of 2 types: contact Specific conductance sensors are of 2 types: contact sensors with electrodes and sensor without sensors with electrodes and sensor without electrodes. electrodes.


(Cont)(Cont) Salinity:Salinity: Although Salinity is not measured directly, Although Salinity is not measured directly,

some sondes include the capability of calculating some sondes include the capability of calculating and recording salinity based on conductivity and recording salinity based on conductivity measurement. Conductivity has long been a tool of measurement. Conductivity has long been a tool of estimating the amount of chloride, a principle estimating the amount of chloride, a principle component of salinity in water. Salinity is commonly component of salinity in water. Salinity is commonly reported using the Practical Salinity Scale (PSS), a reported using the Practical Salinity Scale (PSS), a scale developed to a standard potassium-chloride scale developed to a standard potassium-chloride solution and based on conductivity, temperature solution and based on conductivity, temperature and barometric pressure measurement. and barometric pressure measurement.

Before developing the PSS, salinity was reported in Before developing the PSS, salinity was reported in part per thousand/million. Salinity expressed in the part per thousand/million. Salinity expressed in the PSS is a dimensionless value, although by PSS is a dimensionless value, although by convection, it is reported as practical salinity unit. convection, it is reported as practical salinity unit.


(Cont)(Cont) Dissolved Oxygen:Dissolved Oxygen: Sources of DO in surface waters are Sources of DO in surface waters are

primarily atmospheric reaeration and photosynthetic activity of primarily atmospheric reaeration and photosynthetic activity of aquatic plants. DO is an important factor in chemical reactions in aquatic plants. DO is an important factor in chemical reactions in water and in the survival of aquatic organisms. In surface water, water and in the survival of aquatic organisms. In surface water, DO concentration typically range from 2-10mg/l. DO concentration typically range from 2-10mg/l. DO saturation DO saturation decreases as water temperature increases, and DO decreases as water temperature increases, and DO saturation increases with increased atmospheric pressure.saturation increases with increased atmospheric pressure. Occasion of super saturation (greater than 100 percent DO Occasion of super saturation (greater than 100 percent DO saturation) often are related to excess photosynthetic production saturation) often are related to excess photosynthetic production of oxygen by aquatic plants as a result of nutrient (nitrogen and of oxygen by aquatic plants as a result of nutrient (nitrogen and Phosphorus) enrichment, sunlight and warm water temperature.Phosphorus) enrichment, sunlight and warm water temperature.

DO may be depleted in inorganic oxidation reaction or by DO may be depleted in inorganic oxidation reaction or by biological and chemical processes that consume dissolved, biological and chemical processes that consume dissolved, suspended or precipitated organic matter.suspended or precipitated organic matter.

The DO Solubility in saline environments is dependent on The DO Solubility in saline environments is dependent on salinity as well as temperature and barometric pressuresalinity as well as temperature and barometric pressure . DO . DO in water that have specific conductance values of greater than in water that have specific conductance values of greater than 2000 microsiemens/centimeter should be corrected for salinity. 2000 microsiemens/centimeter should be corrected for salinity.

The newest technology for measuring DO is the Luminescent The newest technology for measuring DO is the Luminescent sensor that is based on dynamic fluorescence quenching. sensor that is based on dynamic fluorescence quenching.


(Cont)(Cont) pH:pH: The pH of aqueous solution is controlled by the The pH of aqueous solution is controlled by the

interrelated chemical reactions that produce or consume interrelated chemical reactions that produce or consume hydrogen ions. The pH of a solution is a measure of the hydrogen ions. The pH of a solution is a measure of the effective hydrogen-ion concentration. More specifically, pH is a effective hydrogen-ion concentration. More specifically, pH is a measure that represents the negative base-10 logarithm of measure that represents the negative base-10 logarithm of hydrogen-ion activity of a solution, in moles per liter. Solutions hydrogen-ion activity of a solution, in moles per liter. Solutions having a pH below 7 are described as acidic, and solutions with having a pH below 7 are described as acidic, and solutions with pH greater than 7 are described as basic or alkaline. pH greater than 7 are described as basic or alkaline. Dissolved gases such as carbon dioxide, hydrogen Dissolved gases such as carbon dioxide, hydrogen sulphide and ammonia, apparently affect pH.sulphide and ammonia, apparently affect pH. Dagasification (for example, loss of carbon dioxide) or Dagasification (for example, loss of carbon dioxide) or precipitation of a solid phase (for example, calcium carbonate) precipitation of a solid phase (for example, calcium carbonate) and other chemical, physical, and biological reactions may and other chemical, physical, and biological reactions may cause the pH of a water sample to change appreciably soon cause the pH of a water sample to change appreciably soon after sample collectionafter sample collection. .

The electrometric pH-measurement method, using a hydrogen-The electrometric pH-measurement method, using a hydrogen-ion electrode, commonly is used in continuous water-quality pH ion electrode, commonly is used in continuous water-quality pH sensors. sensors.

A correctly calibrated pH sensor can accurately measure pH to A correctly calibrated pH sensor can accurately measure pH to -+ 0.2 pH units; however, the sensor can be stretched, broken -+ 0.2 pH units; however, the sensor can be stretched, broken or fouled easily. If the streamflow rates are high, the accuracy or fouled easily. If the streamflow rates are high, the accuracy of the pH measurement can be affected by streaming-potential of the pH measurement can be affected by streaming-potential effects.effects.


(Cont)(Cont) Turbidity: Turbidity: Turbidity is defined as an expression of the optical Turbidity is defined as an expression of the optical

properties of a sample that cause light rays to be scattered and properties of a sample that cause light rays to be scattered and absorbed, rather than transmitted in straight lines through a absorbed, rather than transmitted in straight lines through a sample. sample. ASTM further describe turbidity as the presence of ASTM further describe turbidity as the presence of suspended and dissolved matter, such as clay, silt, finely suspended and dissolved matter, such as clay, silt, finely divided organic matter, plankton, other microscopic divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. Implicit in this organisms, organic acids, and dyes. Implicit in this definition is the fact that colour, either of dissolved definition is the fact that colour, either of dissolved materials or of particles suspended in the water also can materials or of particles suspended in the water also can affect turbidity.affect turbidity.

Turbidity sensors operate differently from those for temperature, Turbidity sensors operate differently from those for temperature, specific conductance, DO, and pH, which convert electrical specific conductance, DO, and pH, which convert electrical potentials into the measurement of constituent of interest. potentials into the measurement of constituent of interest. Submersible turbidity sensors typically direct a light beam from Submersible turbidity sensors typically direct a light beam from light-emitting diode into water sample and measure the light that light-emitting diode into water sample and measure the light that scatters or is absorbed by suspended particles in water. scatters or is absorbed by suspended particles in water.

Most commercially available sensors report data in Most commercially available sensors report data in Nephelometric Turbidity Units (NTU)/ with a sensor range of 0-Nephelometric Turbidity Units (NTU)/ with a sensor range of 0-1000 and an accuracy of -+5 percent or 2NTU, whichever is 1000 and an accuracy of -+5 percent or 2NTU, whichever is greater. greater.


POLLUTION POLLUTION CONTROLCONTROLWMA 318 PART 2WMA 318 PART 2

NoteNote For any water body to function For any water body to function

adequately in satisfying the desired use, adequately in satisfying the desired use, it must have corresponding degree of it must have corresponding degree of purity. purity.

Drinking water should be of Drinking water should be of highest highest purity.purity. As the magnitude of demand for As the magnitude of demand for water is fast approaching the available water is fast approaching the available supply, supply,

the concept of management of the the concept of management of the quality of water is becoming as quality of water is becoming as important as its quantityimportant as its quantity. .

ContaminantContaminant

Are physical, chemical, biological or Are physical, chemical, biological or radiological substances found as radiological substances found as unwanted residue in or on a unwanted residue in or on a substance.substance.

Pathogens: Pathogens: Are micro organisms Are micro organisms that can cause diseases e.g bacteriathat can cause diseases e.g bacteria

MetalsMetals (Metals that are harmful in (Metals that are harmful in relatively small amounts are labeled relatively small amounts are labeled toxic)toxic)

Disease caused by Disease caused by contaminantscontaminants

Salmonella Typhi Typhoid feverSalmonella Typhi Typhoid fever Vibro Cholera CholeraVibro Cholera Cholera Entameoba histolytica Amoeba Entameoba histolytica Amoeba

DysenteryDysentery Escherichia Coli (E. Coli) GastroenteritsEscherichia Coli (E. Coli) Gastroenterits Enterovirus PolioEnterovirus Polio Hepatitis Infestious Hepatitis Infestious

HepatitisHepatitis Heavy Metal Cancer Heavy Metal Cancer

Water Purification Water Purification ProcessProcess

Abstraction: Abstraction involves pumping and transportation of raw Abstraction: Abstraction involves pumping and transportation of raw water, a process with high rate of electrical energy consumption. It water, a process with high rate of electrical energy consumption. It occurs at the intake.occurs at the intake.

Screening: Is defined as the process whereby relatively large and Screening: Is defined as the process whereby relatively large and suspended debris is removed from the water before it enters the plant.suspended debris is removed from the water before it enters the plant.

Aeration: Aeration (Air Stripping) is a physical treatment process Aeration: Aeration (Air Stripping) is a physical treatment process whereby air is thoroughly mixed with water to removed dissolved gasses whereby air is thoroughly mixed with water to removed dissolved gasses and odour.and odour.

Coagulation: Addition of chemical to remove suspended solids.Coagulation: Addition of chemical to remove suspended solids. Flocculation: A chemical flocculent, such as aluminium sulphate, is mixed Flocculation: A chemical flocculent, such as aluminium sulphate, is mixed

rapidly with the water to remove mud.rapidly with the water to remove mud. Sedimentation: Also known as clarification- is the gravity-induced Sedimentation: Also known as clarification- is the gravity-induced

removal of particles.removal of particles. Filtration: Involves the removal of suspended particles from water by Filtration: Involves the removal of suspended particles from water by

passing it through a layer or bed of a porous granular material e.g sand. passing it through a layer or bed of a porous granular material e.g sand. The filter water the passed through nozzles, the nozzles and sand in the The filter water the passed through nozzles, the nozzles and sand in the filter beds must be cleaned periodically (This is known as back washing).filter beds must be cleaned periodically (This is known as back washing).

Chlorination: After filtration, the water looks much more cleaner than it Chlorination: After filtration, the water looks much more cleaner than it was in the dam or river but it may not yet be healthy to drink because it was in the dam or river but it may not yet be healthy to drink because it may contain unseen micro-organism (bacteria) that are dangerous to the may contain unseen micro-organism (bacteria) that are dangerous to the human body and can serious illness (such as diahorrea) human body and can serious illness (such as diahorrea)

4.5 liters 4.5 liters –– 1 Gallon. 1 Liter 1 Gallon. 1 Liter –– 100cl. 1 m3 100cl. 1 m3 –– 5 drums or 200 liter volume. 5 drums or 200 liter volume.

WATER QUALITY WATER QUALITY OBJECTIVES AND OBJECTIVES AND REQUIREMENTREQUIREMENT

A major advantage of the water quality A major advantage of the water quality objectives approach to water resources objectives approach to water resources management is that it management is that it focuses on solving focuses on solving problems caused by conflicts between the problems caused by conflicts between the various demands placed on water various demands placed on water resources,resources, particularly in relation to their particularly in relation to their ability to assimilate pollution. The water ability to assimilate pollution. The water quality quality objectives approach is sensitive not objectives approach is sensitive not just to the effects of an individual just to the effects of an individual discharge, but to the combined effects of discharge, but to the combined effects of the whole range of different discharges the whole range of different discharges into a water body.into a water body. It enables an overall limit It enables an overall limit on levels of contaminants within a water body on levels of contaminants within a water body to be set according to the required uses of the to be set according to the required uses of the water.water.

WQ CriteriaWQ Criteria

For some other water quality For some other water quality variables, such as dissolved oxygen, variables, such as dissolved oxygen, water quality criteria are set at the water quality criteria are set at the minimum acceptable concentration minimum acceptable concentration to ensure the maintenance of to ensure the maintenance of biological functions.biological functions.

Examples of the development of national water quality Examples of the development of national water quality criteria and guidelines in Nigeriacriteria and guidelines in Nigeria

In Nigeria, the Federal Environmental In Nigeria, the Federal Environmental Protection Agency (FEPA) issued, in Protection Agency (FEPA) issued, in 1988, a specific decree to protect, to 1988, a specific decree to protect, to restore and to preserve the ecosystem restore and to preserve the ecosystem of the Nigerian environment. The of the Nigerian environment. The decree also empowered the agency to decree also empowered the agency to set water quality standards to protect set water quality standards to protect public health and to enhance the public health and to enhance the quality of waters quality of waters

Background InformationBackground Information FEPA approached this task by reviewing water FEPA approached this task by reviewing water

quality guidelines and standards from quality guidelines and standards from developed and developing countries as well as developed and developing countries as well as from international organisations and, from international organisations and, subsequently, by comparing them with data subsequently, by comparing them with data available on Nigeria's own water quality. available on Nigeria's own water quality.

The standards considered included those of The standards considered included those of Australia, Brazil, Canada, India, Tanzania, the Australia, Brazil, Canada, India, Tanzania, the United States and the World Health United States and the World Health Organization (WHO). These sets of data were Organization (WHO). These sets of data were harmonised and used to generate the Interim harmonised and used to generate the Interim National Water Quality Guidelines and National Water Quality Guidelines and Standards for Nigeria Standards for Nigeria

Background Information Background Information (Cont)(Cont)

These sets of data were harmonised and used These sets of data were harmonised and used to generate the Interim National Water to generate the Interim National Water Quality Guidelines and Standards for Nigeria. Quality Guidelines and Standards for Nigeria. These address drinking water, recreational These address drinking water, recreational use of water, freshwater aquatic life, use of water, freshwater aquatic life, agricultural (irrigation and livestock watering) agricultural (irrigation and livestock watering) and industrial water uses. The guidelines are and industrial water uses. The guidelines are expected to become the maximum allowable expected to become the maximum allowable limits for inland surface waters and limits for inland surface waters and groundwaters, as well as for non-tidal coastal groundwaters, as well as for non-tidal coastal waters. They also apply to Nigeria's waters. They also apply to Nigeria's transboundary watercourses, the rivers Niger, transboundary watercourses, the rivers Niger, Benue and Cross River, which are major Benue and Cross River, which are major sources of water supply in the country. sources of water supply in the country.

THE NATIONALTHE NATIONAL ENVIRONMENTAL ENVIRONMENTAL STANDARDS AND REGULATIONS STANDARDS AND REGULATIONS

ENFORCEMENT AGENCY (NESREA)ENFORCEMENT AGENCY (NESREA) Prior to the dumping of toxic waste in Koko village, in Prior to the dumping of toxic waste in Koko village, in

Delta State, in 1987, Nigeria was ill equipped to Delta State, in 1987, Nigeria was ill equipped to manage serious environmental crisis, as there were no manage serious environmental crisis, as there were no institutional arrangement or mechanisms for institutional arrangement or mechanisms for environmental protection and enforcement of environmental protection and enforcement of environmental laws and regulations in the country.environmental laws and regulations in the country.

Arising from the Koko toxic episode, the Federal Arising from the Koko toxic episode, the Federal Government promulgated the Harmful Waste Decree Government promulgated the Harmful Waste Decree 42 of 1988, which facilitated the establishment of the 42 of 1988, which facilitated the establishment of the Federal Environmental Protection Agency (FEPA) Federal Environmental Protection Agency (FEPA) through Decree 58 of 1988 and 59 (amended) of 1992. through Decree 58 of 1988 and 59 (amended) of 1992. FEPA was then charged with the overall responsibility FEPA was then charged with the overall responsibility of environmental management and protection. It is on of environmental management and protection. It is on record that by the establishment of FEPA, Nigeria record that by the establishment of FEPA, Nigeria became the first in African country to establish a became the first in African country to establish a national institutional mechanism fir environmental national institutional mechanism fir environmental protection.protection.

NESREA (Cont)NESREA (Cont) In the wisdom of Government, FEPA and other relevant In the wisdom of Government, FEPA and other relevant

Departments in other Ministries were merged to form Departments in other Ministries were merged to form the Federal ministry of Environment in 1999, but the Federal ministry of Environment in 1999, but without an appropriate enabling law on enforcement without an appropriate enabling law on enforcement issues. This situation created a vacuum in the effective issues. This situation created a vacuum in the effective enforcement of environmental law standards and enforcement of environmental law standards and regulations in the country.regulations in the country.

To address this lapse, the Federal Government in line To address this lapse, the Federal Government in line with Section 20 of the 1999 constitution of the Federal with Section 20 of the 1999 constitution of the Federal Republic of Nigeria, established the National Republic of Nigeria, established the National Environmental Standard and Regulations Enforcement Environmental Standard and Regulations Enforcement Agency (NESREA), as a parastatal of the federal Agency (NESREA), as a parastatal of the federal Ministry of Environment. By the NESREA Act 2007, the Ministry of Environment. By the NESREA Act 2007, the Federal Environmental Protection Agency Act Cap F10 Federal Environmental Protection Agency Act Cap F10 LFN 2004 has been repealed (NESREA 2007).LFN 2004 has been repealed (NESREA 2007).

Table 1 Definition Related Table 1 Definition Related to Water Quality and to Water Quality and

Pollution ControlPollution Control

Water quality criteria for individual use Water quality criteria for individual use categoriescategories

Water quality criteria have been widely Water quality criteria have been widely established for a number of traditional water established for a number of traditional water quality variables such as pH, dissolved oxygen, quality variables such as pH, dissolved oxygen, biochemical oxygen demand for periods of five biochemical oxygen demand for periods of five or seven days (BODor seven days (BOD55 and BOD and BOD77), chemical ), chemical oxygen demand (COD) and nutrients. Such oxygen demand (COD) and nutrients. Such criteria guide decision makers, especially in criteria guide decision makers, especially in countries with rivers affected by severe organic countries with rivers affected by severe organic pollution, in the establishment of control pollution, in the establishment of control strategies to decrease the potential for oxygen strategies to decrease the potential for oxygen depletion and the resultant low BOD and COD depletion and the resultant low BOD and COD levels.levels.

Development of criteria for Development of criteria for Aquatic DOAquatic DO

Numerous studies have confirmed that a pH Numerous studies have confirmed that a pH range of 6.5 to 9 is most appropriate for the range of 6.5 to 9 is most appropriate for the maintenance of fish communities. maintenance of fish communities.

Low concentrations of dissolved oxygen, Low concentrations of dissolved oxygen, when combined with the presence of toxic when combined with the presence of toxic substances may lead to stress responses in substances may lead to stress responses in aquatic ecosystems because the aquatic ecosystems because the toxicity of toxicity of certain elements, such as zinc, lead and certain elements, such as zinc, lead and copper, is increased by low copper, is increased by low concentrations of dissolved oxygen.concentrations of dissolved oxygen.

High water temperature also increases High water temperature also increases the adverse effects on biota associated the adverse effects on biota associated with low concentrations of dissolved with low concentrations of dissolved oxygen.oxygen.

Criteria for Aquatic Life Criteria for Aquatic Life DODO

The water quality criterion for dissolved oxygen, The water quality criterion for dissolved oxygen, therefore, takes these factors into account. therefore, takes these factors into account. Depending on the water temperature Depending on the water temperature requirements for particular aquatic species at requirements for particular aquatic species at various life stages, various life stages, the criteria values range the criteria values range from 5 to 9.5 mg/l, i.e. a minimum dissolved from 5 to 9.5 mg/l, i.e. a minimum dissolved oxygen concentration of 5-6 mg/l for warm-oxygen concentration of 5-6 mg/l for warm-water biota and 6.5-9.5 mg/l for cold-water water biota and 6.5-9.5 mg/l for cold-water biota. Higher oxygen concentrations are biota. Higher oxygen concentrations are also relevant for early life stages.also relevant for early life stages. More More details are given in Alabaster and Lloyd (1982) details are given in Alabaster and Lloyd (1982) and the EPA (1976, 1986). and the EPA (1976, 1986).

BOD RequirementBOD Requirement

In Nigeria, the interim water quality In Nigeria, the interim water quality criterion for BOD for the protection criterion for BOD for the protection of aquatic life is 4 mg Oof aquatic life is 4 mg O22 l-1 (water l-1 (water temperature 20-33 °C), for irrigation temperature 20-33 °C), for irrigation water it is 2 mg Owater it is 2 mg O22 l-1 (water l-1 (water temperature 20-25 °C), and for temperature 20-25 °C), and for recreational waters it is 2 mg Orecreational waters it is 2 mg O22 l-1 l-1 (water temperature 20-33 °C) (water temperature 20-33 °C) (FEPA, 1991).(FEPA, 1991).

Drinking Water CriteriaDrinking Water Criteria Quality criteria for raw water generally follow Quality criteria for raw water generally follow

drinking-water criteria and even strive to attain them, drinking-water criteria and even strive to attain them, particularly when raw water is abstracted directly to particularly when raw water is abstracted directly to drinking-water treatment works without prior storage. drinking-water treatment works without prior storage. Drinking-water criteria define a quality of water that Drinking-water criteria define a quality of water that can be safely consumed by humans throughout their can be safely consumed by humans throughout their lifetime. Such criteria have been developed by lifetime. Such criteria have been developed by international organisations and include the WHO international organisations and include the WHO Guidelines for Drinking waterGuidelines for Drinking water Quality Quality (WHO, 1984, (WHO, 1984, 1993) and the EU 1993) and the EU Council Directive of 15 July 1980 Council Directive of 15 July 1980 RelatingRelating to the Quality of Water Intended for Human to the Quality of Water Intended for Human Consumption Consumption (80/778/EEC), which covers some 60 (80/778/EEC), which covers some 60 quality variables. These guidelines and directives are quality variables. These guidelines and directives are used by countries, as appropriate, in establishing used by countries, as appropriate, in establishing enforceable national drinking-water quality standards.enforceable national drinking-water quality standards.

IrrigationIrrigation

Poor quality water may affect irrigated Poor quality water may affect irrigated crops by causing accumulation of salts in crops by causing accumulation of salts in the root one, the root one, by causing loss of by causing loss of permeability of the soil due to excess permeability of the soil due to excess sodium or calcium leaching, or by sodium or calcium leaching, or by containing pathogens or containing pathogens or contaminants which are directly contaminants which are directly toxic to plants or to those consuming toxic to plants or to those consuming them. them.

IrrigationIrrigation

Even when the presence of pesticides Even when the presence of pesticides or pathogenic organisms in irrigation or pathogenic organisms in irrigation water does not directly affect plant water does not directly affect plant growth, growth, it may potentially affect the it may potentially affect the acceptability of the agricultural acceptability of the agricultural product for sale or consumptionproduct for sale or consumption. . Criteria have been published by a Criteria have been published by a number of countries as well as by the number of countries as well as by the Food and Agriculture Organization of Food and Agriculture Organization of the United Nations (FAO) the United Nations (FAO)

Irrigation Criteria Takes Irrigation Criteria Takes into Accountinto Account

Water quality criteria for irrigation water generally Water quality criteria for irrigation water generally take into account, amongst other factors, such take into account, amongst other factors, such characteristics as characteristics as crop tolerance to salinity, sodium crop tolerance to salinity, sodium concentration and phytotoxic trace elements. concentration and phytotoxic trace elements.

The effect of The effect of salinitysalinity on the osmotic pressure in the on the osmotic pressure in the unsaturated soil zone is one of the unsaturated soil zone is one of the most important most important water quality considerationswater quality considerations because this has an because this has an influence on the availability of water for plant influence on the availability of water for plant consumptionconsumption. .

Sodium in irrigation waters can adversely Sodium in irrigation waters can adversely affect soil affect soil structure andstructure and reduce the rate at which water reduce the rate at which water moves into and through soils.moves into and through soils. Sodium is also a Sodium is also a specific source of damage to fruits. specific source of damage to fruits.

Phytotoxic trace elements such as boron, heavy Phytotoxic trace elements such as boron, heavy metals and pesticides may stunt the growth of metals and pesticides may stunt the growth of plants or render the crop unfit for human plants or render the crop unfit for human consumption or other intended usesconsumption or other intended uses..

Livestock wateringLivestock watering

Livestock may be affected by poor quality water Livestock may be affected by poor quality water causing death, sickness or impaired growth. causing death, sickness or impaired growth. Variables of concern include Variables of concern include nitrates, nitrates, sulphates, total dissolved solids (salinity), sulphates, total dissolved solids (salinity), a number of metals and organic a number of metals and organic micropollutants such as pesticidesmicropollutants such as pesticides. In . In addition, bluegreen algae and pathogens in addition, bluegreen algae and pathogens in water can present problems. water can present problems.

Some substances, or their degradation Some substances, or their degradation products, present in products, present in water used for livestock water used for livestock may occasionally be transmitted to may occasionally be transmitted to humanshumans. .

The purpose of quality criteria for water used The purpose of quality criteria for water used for livestock watering is, therefore, for livestock watering is, therefore, to protect to protect both the livestock and the consumer.both the livestock and the consumer.

Livestock Water Livestock Water StandardStandard

Criteria for livestock Criteria for livestock watering usually take watering usually take into account the type of into account the type of livestock, the daily water livestock, the daily water requirements of each requirements of each species, the chemicals species, the chemicals added to the feed of the added to the feed of the livestock to enhance the livestock to enhance the growth and to reduce the growth and to reduce the risk of disease, as well as risk of disease, as well as information on the information on the toxicity of specific toxicity of specific substances to the substances to the different species different species

Recreational useRecreational use

Recreational water quality criteria are used to assess Recreational water quality criteria are used to assess the safety of water to be used for swimming and other the safety of water to be used for swimming and other water-sport activities. The primary concern is to water-sport activities. The primary concern is to protect human health by preventing water pollution protect human health by preventing water pollution from from faecal material or from contamination by faecal material or from contamination by microorganisms that could cause gastro-microorganisms that could cause gastro-intestinal illness, ear, eye or skin infections.intestinal illness, ear, eye or skin infections.

Criteria are therefore usually set for indicators of Criteria are therefore usually set for indicators of faecal pollution, such as faecal coliforms and faecal pollution, such as faecal coliforms and pathogens. There has been a considerable amount of pathogens. There has been a considerable amount of research in recent years into the development of other research in recent years into the development of other indicators of microbiological pollution including indicators of microbiological pollution including viruses that could affect swimmers. As a rule, viruses that could affect swimmers. As a rule, recreational water quality criteria are established by recreational water quality criteria are established by government health agencies.government health agencies.

Amenity useAmenity use

Criteria have been established in some Criteria have been established in some countries aimed at the protection of the countries aimed at the protection of the aesthetic properties of water. These criteria are aesthetic properties of water. These criteria are primarily orientated towards visual aspects. primarily orientated towards visual aspects. They are usually narrative in nature and may They are usually narrative in nature and may specify, for example, that waters must be free specify, for example, that waters must be free of floating oil or other immiscible liquids, of floating oil or other immiscible liquids, floating debris, excessive turbidity, and floating debris, excessive turbidity, and objectionable odours. The criteria are mostly objectionable odours. The criteria are mostly non-quantifiable because of the different non-quantifiable because of the different sensory perception of individuals and because sensory perception of individuals and because of the variability of local conditions.of the variability of local conditions.

Commercial and sports Commercial and sports fishingfishing

Water quality criteria for commercial Water quality criteria for commercial and sports fishing take into account, and sports fishing take into account, in particular, the bioaccumulation of in particular, the bioaccumulation of contaminants through successive contaminants through successive levels of the food chain and their levels of the food chain and their possible biomagnification in higher possible biomagnification in higher trophic levels, which can make fish trophic levels, which can make fish unsuitable for human consumption. unsuitable for human consumption.

In India, the Central Pollution Control Board In India, the Central Pollution Control Board (CPCB) has developed a concept of designated (CPCB) has developed a concept of designated

best use.best use.

Designated Best Use Class Criteria

Drinking Water Source without conventional treatment but after disinfection

A 1.Total Coliforms Organism MPN/100ml shall be 50 or less 2. pH between 6.5 and 8.5 3. Dissolved Oxygen 6mg/l or more 4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or less

Outdoor bathing (Organised) B 1.Total Coliforms Organism MPN/100ml shall be 500 or less 2. pH between 6.5 and 8.5 3. Dissolved Oxygen 5mg/l or more 4. Biochemical Oxygen Demand 5 days 20 C, 3mg/l or less

Drinking water source after conventional treatment and disinfection

C 1. Total Coliforms Organism MPN/100ml shall be 5000 or less 2. pH between 6 and 93. Dissolved Oxygen 4mg/l or more 4. Biochemical Oxygen Demand 5 days 20 C, 3mg/l or less

Propagation of Wild life and Fisheries

D 1. pH between 6.5 and 8.5 2. Dissolved Oxygen 4mg/l or more 3. Free Ammonia (as N) 4. Biochemical Oxygen Demand 5 days 20 C, 2mg/l or less

Irrigation, Industrial Cooling, Controlled Waste disposal

E 1. pH between 6.0 and 8.5 2. Electrical Conductivity at 25 C micro mhos/cm, maximum 2250 3. Sodium absorption Ratio Max. 26 4. Boron Max. 2mg/l

Below-E Not meeting any of the A, B, C, D & E criteria

A colour coding frequently A colour coding frequently used to depict the quality of used to depict the quality of

water on maps water on maps Blue water This water can be directly used for drinking, industrial use, etc.

Green water Water contained in soil and plants is termed as green water

White water Atmospheric moisture is white water

Brown or grey water Various grades of wastewater are shown by brown or grey colour

Water Quality CriteriaWater Quality CriteriaCharacteristics Designated best use

A B C D E

Dissolved Oxygen (DO)mg/l, min 6 5 4 4 -

Biochemical Oxygen demand (BOD)mg/l, max 2 3 3 - -

Total coliform organisms MPN/100ml, max 50 500 5,000 - -

pH value 6.5-8.5 6.5-8.5 6.0-9.0 6.5-8.5 6.0-8.5

Colour, Hazen units, max. 10 300 300 - -

Odour Un-objectionable - -

Taste Tasteless - - - -

Total dissolved solids, mg/l, max. 500 - 1,500 - 2,100

Total hardness (as CaCO3), mg/l, max. 200 - - - -

Calcium hardness (as CaCO3), mg/l, max. 200 - - - -

Magnesium hardness (as CaCO3), mg/l, max. 200 - - - -

Copper (as Cu), mg/l, max. 1.5 - 1.5 - -

Iron (as Fe), mg/l, max. 0.3 - 0.5 - -

Manganese (as Mn), mg/l, max. 0.5 - - - -

Cholorides (as Cu), mg/l, max. 250 - 600 - 600

Sulphates (as SO4), mg/l, max. 400 - 400 - 1,000

Nitrates (as NO3), mg/l, max. 20 - 50 - -

Fluorides (as F), mg/l, max. 1.5 1.5 1.5 - -

Phenolic compounds (as C2H5OH), mg/l, max. 0.002 0.005 0.005 - -

Mercury (as Hg), mg/l, max. 0.001 - - - -

Cadmium (as Cd), mg/l, max. 0.01 - 0.01 - -

Salenium (as Se), mg/l, max. 0.01 - 0.05 - -

Arsenic (as As), mg/l, max. 0.05 0.2 0.2 - -

Cyanide (as Pb), mg/l, max. 0.05 0.05 0.05 - -

Lead (as Pb), mg/l, max. 0.1 - 0.1 - -

Zinc (as Zn), mg/l, max. 15 - 15 - -

Chromium (as Cr6+), mg/l, max. 0.05 - 0.05 - -

Anionic detergents (as MBAS), mg/l, max. 0.2 1 1 - -

Barium (as Ba), mg/l, max. 1 - - - -

Free Ammonia (as N), mg/l, max - - - 1.2 -

Electrical conductivity, micromhos/cm, max - - - - 2,250

Sodium absorption ratio, max - - - - 26

Boron, mg/l, max - - - - 2

Suspended particulate Suspended particulate matter and sedimentmatter and sediment

The attempts in some countries to develop The attempts in some countries to develop quality criteria for suspended particulate quality criteria for suspended particulate matter and sediment aim at achieving a water matter and sediment aim at achieving a water quality, such that any sediment dredged from quality, such that any sediment dredged from the water body could be used for soil the water body could be used for soil improvement and for application to farmland.improvement and for application to farmland.

Another goal of these quality criteria is to Another goal of these quality criteria is to protect organisms living on, or in, sediment, protect organisms living on, or in, sediment, and the related food chain. Persistent and the related food chain. Persistent pollutants in sediments have been shown to be pollutants in sediments have been shown to be accumulated and biomagnified through accumulated and biomagnified through aquatic food chains leading to unacceptable aquatic food chains leading to unacceptable concentrations in fish and fish-eating birds.concentrations in fish and fish-eating birds.

NOTE: SEE VARIOUS TABLE FOR DATANOTE: SEE VARIOUS TABLE FOR DATA


POLLUTION POLLUTION CONTROLCONTROLWMA 318 PART 3WMA 318 PART 3

TYPES OF WATERTYPES OF WATER

Water is commonly described either Water is commonly described either in terms of its in terms of its nature, usage, or nature, usage, or originorigin. . The implications in these The implications in these descriptions range from being descriptions range from being highly specific to so general as to highly specific to so general as to be non-definitivebe non-definitive. Ground waters . Ground waters originate in subterranean locations originate in subterranean locations such as wells, while surface waters such as wells, while surface waters comprise the lakes, rivers, and seas.comprise the lakes, rivers, and seas.

TYPES OF WATER (Cont)TYPES OF WATER (Cont)

Fresh Water Fresh Water (precisely less than 0.5%)(precisely less than 0.5%) Fresh water may come from either a Fresh water may come from either a surface or surface or

ground source, and typically contains less than ground source, and typically contains less than 1% sodium chloride1% sodium chloride. It may be either ". It may be either "hardhard" or " or ""softsoft," i.e., either ," i.e., either rich in calcium and rich in calcium and magnesium saltsmagnesium salts and thus possibly forming and thus possibly forming insoluble curds with ordinary soap. Actually, insoluble curds with ordinary soap. Actually, there are gradations of hardness, which can be there are gradations of hardness, which can be estimated from the estimated from the Langelier or RyznarLangelier or Ryznar indexes or accurately determined by titration indexes or accurately determined by titration with standardized chelating agent solutions with standardized chelating agent solutions such as versenates.such as versenates.


Brackish WaterBrackish Water Brackish water contains between 0.5 or 1 and Brackish water contains between 0.5 or 1 and

2.5% sodium chloride, either from natural 2.5% sodium chloride, either from natural sources around otherwise fresh water or by sources around otherwise fresh water or by dilution of seawater. Brackish water differs dilution of seawater. Brackish water differs from open seawater in certain other respects. from open seawater in certain other respects. The biological activity, for example, can be The biological activity, for example, can be significantly modified by higher concentrations significantly modified by higher concentrations of nutrients. Fouling is also likely to be more of nutrients. Fouling is also likely to be more severe as a consequence of the greater severe as a consequence of the greater availability of nutrients.availability of nutrients.

The main environmental factors The main environmental factors responsible, singly or in combination, for responsible, singly or in combination, for these differences are these differences are the salinitythe salinity, , the the degree of pollutiondegree of pollution, and the , and the prevalence of prevalence of siltsilt..


SeawaterSeawater Seawater typically contains about 3.5% sodium Seawater typically contains about 3.5% sodium

chloride, chloride, although the salinity may be although the salinity may be weakened in some areas by dilution with fresh weakened in some areas by dilution with fresh water or concentrated by solar evaporation in water or concentrated by solar evaporation in othersothers. Seawater is normally more corrosive . Seawater is normally more corrosive than fresh water because of the than fresh water because of the higher higher conductivity and the penetrating power of the conductivity and the penetrating power of the chloride ion through surface films on a metal.chloride ion through surface films on a metal. The rate of corrosion is controlled by the The rate of corrosion is controlled by the chloride content, oxygen availability, and chloride content, oxygen availability, and the temperature. the temperature.

SalineSaline

Water is classified as "saline" when it becomes a risk for growth Water is classified as "saline" when it becomes a risk for growth and yield of crops. Saline water has a relatively high and yield of crops. Saline water has a relatively high concentration of dissolved salts (cations and anions). Salt is not concentration of dissolved salts (cations and anions). Salt is not just "salt" as we know it - sodium chloride (NaCl) - but can be just "salt" as we know it - sodium chloride (NaCl) - but can be dissolved calcium (Cadissolved calcium (Ca2+2+), magnesium (Mg), magnesium (Mg2+2+), sulfate (SO), sulfate (SO44

22-), -), bicarbonate (HCObicarbonate (HCO3-3-), Boron (B), and other compounds.), Boron (B), and other compounds.

Water can be both saline and sodic, or saline-sodic. If water has Water can be both saline and sodic, or saline-sodic. If water has an EC greater than 4 (2 for horticulture) and a Sodium an EC greater than 4 (2 for horticulture) and a Sodium Adsorption Ration (SAR) greater than 12, it is considered Adsorption Ration (SAR) greater than 12, it is considered saline-sodicsaline-sodic

The concentration is usually expressed in The concentration is usually expressed in parts per million (ppm) of salt. of salt.

If water has a concentration of 10,000 ppm of dissolved salts, If water has a concentration of 10,000 ppm of dissolved salts, then one percent (10,000 divided by 1,000,000) of the weight of then one percent (10,000 divided by 1,000,000) of the weight of the water comes from dissolved salts. the water comes from dissolved salts.

Classification of SalinityClassification of Salinity

Slightly saline water contains around 1,000 to 3,000 Slightly saline water contains around 1,000 to 3,000 ppm. 0.1-0.3%ppm. 0.1-0.3%

Moderately saline water contains roughly 3,000 to Moderately saline water contains roughly 3,000 to 10,000 ppm.10,000 ppm. 0.3-1% 0.3-1%

Highly saline water has around 10,000 to 35,000 ppm Highly saline water has around 10,000 to 35,000 ppm of salt. 1-3.5%of salt. 1-3.5%

Seawater has a has a salinity of roughly 35,000 ppm, of roughly 35,000 ppm, equivalent to 35 g/L. 3.5-5.0%equivalent to 35 g/L. 3.5-5.0%

Brine Greater 50,000 ppm. 5.0% aboveBrine Greater 50,000 ppm. 5.0% above

Salinity in Different Water BodiesSalinity in Different Water Bodies

Water salinity based on dissolved salts in parts per thousand (ppt)Water salinity based on dissolved salts in parts per thousand (ppt)

Fresh water Brackish water Saline waterSaline water Brine

< 0.5< 0.5 0.5 0.5 –– 30 30 30 30 –– 50 50 > 50> 50

Relationship between Tidal and SalinityRelationship between Tidal and Salinity

Salinity variations of the tidal water irrigating the rice fields at Warri Salinity variations of the tidal water irrigating the rice fields at Warri mangrove swamp were studied for one calendar year. It was found that mangrove swamp were studied for one calendar year. It was found that the mean pH is 7.24 for low tides and 7.14 for high tides, and pH is the mean pH is 7.24 for low tides and 7.14 for high tides, and pH is highest in July for both high and low tides. Sodium, calcium and highest in July for both high and low tides. Sodium, calcium and magnesium, the major cationic constituents of the soluble salts in the magnesium, the major cationic constituents of the soluble salts in the saline tidal irrigation water, as well as potassium a minor ionic saline tidal irrigation water, as well as potassium a minor ionic constituent were all found to be highest in June at both low and high constituent were all found to be highest in June at both low and high tides. Also, both the Electrical Conductivity (EC) and the derived tides. Also, both the Electrical Conductivity (EC) and the derived Sodium Adsorption Ration (SAR) were highest in June. Salinity at both Sodium Adsorption Ration (SAR) were highest in June. Salinity at both high and low tides is highest in June but lowest in September for high high and low tides is highest in June but lowest in September for high tides and in October for low tides. The indications are that the adverse tides and in October for low tides. The indications are that the adverse effects of salinity are largely responsible for the poor initial growth and effects of salinity are largely responsible for the poor initial growth and survival of the rice variety during early seedling stage. From salinity survival of the rice variety during early seedling stage. From salinity point of view, it would appear that October is the most favourable point of view, it would appear that October is the most favourable month to transplant rice at the Warri mangrove swamp.month to transplant rice at the Warri mangrove swamp.

Effects of SalinityEffects of Salinity

Saline water reduces plant growth to varying degrees, with grass and Saline water reduces plant growth to varying degrees, with grass and grain crops generally showing less sensitivity and field crops being most grain crops generally showing less sensitivity and field crops being most sensitive. Aside from biomass reduction, salinity can have additional sensitive. Aside from biomass reduction, salinity can have additional effects on plants. For example, in a study by Bauder et al., both effects on plants. For example, in a study by Bauder et al., both inoculated and non-inoculated alfalfa were grown with irrigation waters inoculated and non-inoculated alfalfa were grown with irrigation waters of progressively higher salinity levelsof progressively higher salinity levels

Correction of SalinityCorrection of Salinity There are no amendments, chemicals, or additives available There are no amendments, chemicals, or additives available

commercially that can be added to saline water to make the salt go away. commercially that can be added to saline water to make the salt go away. Dilution with a non-saline water or salt precipitation with an evaporation Dilution with a non-saline water or salt precipitation with an evaporation process which leaves the salt behind and traps the evaporated water can process which leaves the salt behind and traps the evaporated water can be used. Dilution of saline irrigation water is only possible if there is a be used. Dilution of saline irrigation water is only possible if there is a source of non-saline water with which to dilute the saline watersource of non-saline water with which to dilute the saline water


The combination of The combination of high conductivity and high conductivity and oxygen solubility is at a oxygen solubility is at a maximum at this point maximum at this point (oxygen solubility is (oxygen solubility is reduced in more reduced in more concentrated salt concentrated salt solutions). The solutions). The corrosion of numerous corrosion of numerous metals in a wide range metals in a wide range of saline waters is of saline waters is reported in the reported in the following Tablefollowing Table..

Effect of velocity on the corrosion of metals in seawater


Distilled or Demineralized WaterDistilled or Demineralized Water The total mineral content of water can The total mineral content of water can

be removed by either distillation or be removed by either distillation or mixed-bed ion exchange. In the first mixed-bed ion exchange. In the first case, purity is described qualitatively in case, purity is described qualitatively in some cases (e.g., triple-distilled water), some cases (e.g., triple-distilled water), but is best expressed, for both but is best expressed, for both distilled and demineralized water, distilled and demineralized water, in terms of specific conductivity.in terms of specific conductivity. Water also can be demineralized by Water also can be demineralized by reverse osmosis or electrodialysis.reverse osmosis or electrodialysis.


Steam CondensateSteam Condensate Water condensed from industrial Water condensed from industrial

steam is called steam condensate. It steam is called steam condensate. It approaches distilled water in purity, approaches distilled water in purity, except for contamination (as by DO except for contamination (as by DO or carbon dioxide) and the effect of or carbon dioxide) and the effect of deliberate additives (e.g., deliberate additives (e.g., neutralizing or filming amines).neutralizing or filming amines).


Boiler Feedwater Make-upBoiler Feedwater Make-up The feedwater make-up for boilers The feedwater make-up for boilers is always is always

softened and subsequently deaerated.softened and subsequently deaerated. It It may vary in quality from fairly high dissolved may vary in quality from fairly high dissolved solids (e.g., Zeolite-Treated), to very pure solids (e.g., Zeolite-Treated), to very pure demineralized feed for high-pressure boilers. demineralized feed for high-pressure boilers. It It tends to be highly corrosive, because of its tends to be highly corrosive, because of its softness, until thoroughly deaerated.softness, until thoroughly deaerated. This This term is more precise than term is more precise than ““boiler feedwaterboiler feedwater””, , which may include recirculated steam which may include recirculated steam condensate in various ratios to fresh make-up condensate in various ratios to fresh make-up water.water.


Potable WaterPotable Water Potable water is fresh water that is Potable water is fresh water that is

sanitized with oxidizing biocides such sanitized with oxidizing biocides such as chlorine or ozone to kill bacteria and as chlorine or ozone to kill bacteria and make it safe for drinking purposes. By make it safe for drinking purposes. By definition, certain mineral constituents definition, certain mineral constituents are also restricted. For example, the are also restricted. For example, the chlorinity will be not more than 250 chlorinity will be not more than 250 ppm chloride ion in the United States ppm chloride ion in the United States or 400 ppm on an international basis.or 400 ppm on an international basis.


Process or Hydrotest Water/FirewaterProcess or Hydrotest Water/Firewater These terms are essentially non-definitive, These terms are essentially non-definitive,

since the water employed may be of since the water employed may be of almost any chemistry, ranging from almost any chemistry, ranging from demineralized water to quite saline demineralized water to quite saline fresh water or even seawater in some fresh water or even seawater in some cases.cases. ““Produced waterProduced water”” is that which is that which originates in oil and gas production, originates in oil and gas production, emanating from geological sources with emanating from geological sources with the hydrocarbons.the hydrocarbons.


Cooling Water Cooling water is another undefined Cooling water is another undefined

term, although term, although it implies that any it implies that any necessary treatment against necessary treatment against excessive scaling or corrosion has excessive scaling or corrosion has been applied, or corrosion-resistant been applied, or corrosion-resistant material selectedmaterial selected. This may include . This may include anything from fresh water to seawater, anything from fresh water to seawater, and may comprise either an open- or and may comprise either an open- or closed-loop system, or a once-through closed-loop system, or a once-through system.system.


Waste WaterWaste Water By definition, waste water is any water that is By definition, waste water is any water that is

discarded after use. Sanitary waste from discarded after use. Sanitary waste from private or industrial applications is private or industrial applications is contaminated with fecal matter, soaps, contaminated with fecal matter, soaps, detergents, etc., but is quite readily handled detergents, etc., but is quite readily handled from a corrosion standpoint. Industrial wastes from a corrosion standpoint. Industrial wastes from chemical or petrochemical sources can from chemical or petrochemical sources can contain strange and specific contaminants contain strange and specific contaminants which greatly complicate materials selection, which greatly complicate materials selection, especially in the uses of plastics and especially in the uses of plastics and elastomers.elastomers.

WATER QUALITY WATER QUALITY ASSESSMENT ASSESSMENT

AND POLLUTION AND POLLUTION CONTROLCONTROLWMA 318 PART 4WMA 318 PART 4

SOURCES OF WATER SOURCES OF WATER POLLUTIONPOLLUTION

The surface water and groundwater The surface water and groundwater systemssystems

Surface water is the water we see in Surface water is the water we see in streams, rivers, wetlands, and lakes streams, rivers, wetlands, and lakes across the country. Every square mile of across the country. Every square mile of ground drains into one of these bodies of ground drains into one of these bodies of water. The area drained is known as a water. The area drained is known as a watershed. As smaller creeks and rivers watershed. As smaller creeks and rivers feed into larger ones, the size of the feed into larger ones, the size of the watershed increases.watershed increases.

SOURCES OF WATER SOURCES OF WATER POLLUTION (Cont)POLLUTION (Cont)

While surface water is found in the form of While surface water is found in the form of rivers and lakes, rivers and lakes, groundwater groundwater is stored in is stored in aquifersaquifers. Aquifers are formations of cracked . Aquifers are formations of cracked rock, sand, or gravel that hold water and yield rock, sand, or gravel that hold water and yield enough water to supply wells or springs. More enough water to supply wells or springs. More than 95 percent of the worldthan 95 percent of the world’’s usable water s usable water resources are stored in its groundwater.resources are stored in its groundwater.

Approximately third-quarter of all Nigerians Approximately third-quarter of all Nigerians depends on groundwater for their drinking depends on groundwater for their drinking water. In most times, 80 percent of all water. In most times, 80 percent of all Nigerians depend on groundwater for their Nigerians depend on groundwater for their drinking water, and more than 97 percent of drinking water, and more than 97 percent of all rural Nigerians, depend on groundwater all rural Nigerians, depend on groundwater for their drinking water supplies.for their drinking water supplies.


As people pump and use water from these As people pump and use water from these underground aquifers, the water must be replaced. underground aquifers, the water must be replaced. Aquifers are replenished or recharged by water Aquifers are replenished or recharged by water seeping down through the soil from surface water seeping down through the soil from surface water supplies. In some parts of the country, groundwater supplies. In some parts of the country, groundwater supplies are very deep, and pollutants may be filtered supplies are very deep, and pollutants may be filtered out by layers of soil, sand, and gravel.out by layers of soil, sand, and gravel.

In parts of Nigeria, there are more direct links to the In parts of Nigeria, there are more direct links to the groundwater. In some parts of north-central and south groundwater. In some parts of north-central and south of Nigeria, the groundwater supply may come within a of Nigeria, the groundwater supply may come within a few meters of the soil surface. Thatfew meters of the soil surface. That ’’s why this area of s why this area of south is covered with wetlands and prairie potholes. In south is covered with wetlands and prairie potholes. In these areas, there is much less filtration by the soil and these areas, there is much less filtration by the soil and a greater risk of contamination by animal wastes, a greater risk of contamination by animal wastes, pesticides, and other pollutants. In other parts of the pesticides, and other pollutants. In other parts of the country, like the east and some part of the south west country, like the east and some part of the south west corner, limestone sits just below the soil surface. This corner, limestone sits just below the soil surface. This limestone layer, or karst, can crack, erode, and form limestone layer, or karst, can crack, erode, and form caverns that allow water and any pollutants to travel caverns that allow water and any pollutants to travel with little filtering from the soil.with little filtering from the soil.


Non-point source pollution Non-point source pollution refers to refers to pollutants that come from a widespread pollutants that come from a widespread area and cannot be tracked to a single area and cannot be tracked to a single point or source. Soil erosion, chemical point or source. Soil erosion, chemical runoff, and animal waste pollution are all runoff, and animal waste pollution are all examples of non-point source pollution. examples of non-point source pollution. Non-point source pollution is major Non-point source pollution is major water quality problem by sheer volume water quality problem by sheer volume and in terms of current and future and in terms of current and future economic costs to the nation.economic costs to the nation.


Point source pollutionPoint source pollution –– also known as also known as ““the the end of the pipe pollutionend of the pipe pollution”–”– can be traced to a can be traced to a specific source, such as a leaking chemical specific source, such as a leaking chemical tank, effluents coming from a waste treatment tank, effluents coming from a waste treatment or industrial plant, or a manure spill from a hog or industrial plant, or a manure spill from a hog confinement lagoon. Although this may seem confinement lagoon. Although this may seem easy to control, there are economic, political, easy to control, there are economic, political, and other factors involved. For known point and other factors involved. For known point source pollution threats, households, source pollution threats, households, communities, industry, and agribusiness must communities, industry, and agribusiness must deal with the problem of disposing of wastes deal with the problem of disposing of wastes and by-products. and by-products.

TREATMENT OF TREATMENT OF POLLUTANTSPOLLUTANTS

TREATMENT METHODSTREATMENT METHODS There are various levels of treatment that prevent There are various levels of treatment that prevent

dumping raw waste products from being dumped into dumping raw waste products from being dumped into surface waters. Industrial wastes may require special surface waters. Industrial wastes may require special treatment to remove harmful chemicals before treatment to remove harmful chemicals before reentering the water system.reentering the water system.

For the more common problem of organic wastes, For the more common problem of organic wastes, the the three main treatment methods for treating waste water three main treatment methods for treating waste water areare

septic systems, lagoons, and sewage treatment plants. septic systems, lagoons, and sewage treatment plants. Each method must be properly sized so that the Each method must be properly sized so that the

treatment system is able to handle the volume of treatment system is able to handle the volume of waste entering it.waste entering it.

Septic systems are designed for individual Septic systems are designed for individual households,households,

lagoons may meet the needs of small towns, and lagoons may meet the needs of small towns, and sewage treatment facilities are necessary for sewage treatment facilities are necessary for

controlling pollution. controlling pollution.

TREATMENT OF TREATMENT OF POLLUTANTS (Cont)POLLUTANTS (Cont)

Septic systemsSeptic systems Septic systems are generally used in rural areas to Septic systems are generally used in rural areas to

handle household wastes. They usually use a large handle household wastes. They usually use a large tank buried in the ground to contain and break down tank buried in the ground to contain and break down household sewage. Attached to the tank is a series of household sewage. Attached to the tank is a series of perforated pipes that are buried in a drain field and perforated pipes that are buried in a drain field and are usually surrounded by crushed rock or gravel to are usually surrounded by crushed rock or gravel to facilitate drainage. Fats, oils, and grease, as well as facilitate drainage. Fats, oils, and grease, as well as large waste particles, are stored and later pumped large waste particles, are stored and later pumped out of the holding tank, while the water and out of the holding tank, while the water and suspended solids in the water flow into the soil suspended solids in the water flow into the soil through the perforated pipes. The soil around the through the perforated pipes. The soil around the septic system filters many harmful compounds, and septic system filters many harmful compounds, and bacteria break down organic matter.bacteria break down organic matter.


STANDARD: Septic systems are most popular in rural STANDARD: Septic systems are most popular in rural and suburban areas and must be located in soils that and suburban areas and must be located in soils that meet standards for meet standards for percolation percolation or the ability to or the ability to drain away water. standards require a maximum drain away water. standards require a maximum percolation rate of one inch of water in 60 minutes. A percolation rate of one inch of water in 60 minutes. A slow percolation rate allows soil bacteria to break slow percolation rate allows soil bacteria to break down wastes as they move into soil layers.down wastes as they move into soil layers.

CONCERN: Septic systems are generally a greater CONCERN: Septic systems are generally a greater source of concern for groundwater pollution than for source of concern for groundwater pollution than for surface water pollution. However, septic systems are surface water pollution. However, septic systems are a real concern for surface water pollution when they a real concern for surface water pollution when they are located near lakes, rivers, and streams. Of are located near lakes, rivers, and streams. Of particular concern are lakes with high concentrations particular concern are lakes with high concentrations of tourist homes.of tourist homes.

Note: 1 Cube Inch is equal 16.34 cmNote: 1 Cube Inch is equal 16.34 cm3, 3, Multiple inch by 2.54 to get Centimetre Multiple inch by 2.54 to get Centimetre


LagoonsLagoons Many communities, feedlot operators, and industries Many communities, feedlot operators, and industries

use lagoons to control wastes. A use lagoons to control wastes. A lagoon lagoon is simply one is simply one or a series of shallow holding pits into which wastes or a series of shallow holding pits into which wastes are pumped and treated. In a well-designed lagoon are pumped and treated. In a well-designed lagoon system, the material is aerated so bacteria can break system, the material is aerated so bacteria can break down the organic matter. down the organic matter.

STANDARD: In municipal lagoons, the water generally STANDARD: In municipal lagoons, the water generally stays in the stays in the lagoon for at least 30 dayslagoon for at least 30 days for this process for this process to be completed. Then the water is removed and to be completed. Then the water is removed and treated with chlorinetreated with chlorine as needed to destroy remaining as needed to destroy remaining bacteria. The remaining solids must be disposed of by bacteria. The remaining solids must be disposed of by spreading on farm fields or burying. spreading on farm fields or burying.

CONCERN: Lagoons are inexpensive to construct and CONCERN: Lagoons are inexpensive to construct and operate compared to other systems. However, poorly operate compared to other systems. However, poorly constructed lagoons and lagoons built where the constructed lagoons and lagoons built where the water table is very high have been found to leak. The water table is very high have been found to leak. The most often found contaminant tends to be nitrates.most often found contaminant tends to be nitrates.


Treatment plantsTreatment plants We require two levels of sewage treatment. We require two levels of sewage treatment. Primary sewage treatment Primary sewage treatment simply filters out unwanted simply filters out unwanted

items suchitems such as sticks, stones, garbage, and other debris that as sticks, stones, garbage, and other debris that arrive at thearrive at the treatment plant and allows time for the solid treatment plant and allows time for the solid materials tomaterials to settle out.settle out.

Secondary treatment Secondary treatment uses aeration anduses aeration and aerobic aerobic, or , or oxygen-using, bacteria to break down organicoxygen-using, bacteria to break down organic wastes. The wastes. The water is then treated with chlorine to killwater is then treated with chlorine to kill bacteria and bacteria and discharged into adjacent rivers and streams.discharged into adjacent rivers and streams.

Treatment plants remove approximately Treatment plants remove approximately 90 percent of the organic waste and suspended solids, 90 percent of the organic waste and suspended solids, less than 70 percent of the toxic metals and synthetic organic chemicals, less than 70 percent of the toxic metals and synthetic organic chemicals, 50 percent of the nitrogen in the form of nitrates, and 50 percent of the nitrogen in the form of nitrates, and 30 percent of the phosphorus in the form of phosphates30 percent of the phosphorus in the form of phosphates. . CONCERN: This remaining discharge is still high in nutrients CONCERN: This remaining discharge is still high in nutrients

and is not pure water entering the surface water. More and is not pure water entering the surface water. More advanced treatment systems are available, but they are advanced treatment systems are available, but they are rarely used due to their high cost. The remaining sludge is rarely used due to their high cost. The remaining sludge is sent to a landfill as waste or applied to the land as a soil sent to a landfill as waste or applied to the land as a soil additive.additive.

Wastewater Treatment Wastewater Treatment ProcessProcess

TREATMENT OF TREATMENT OF POLLUTANTS SUMMARYPOLLUTANTS SUMMARY

Runoff pollution is difficult to control. The best method of Runoff pollution is difficult to control. The best method of control is limited use of chemical pesticides.control is limited use of chemical pesticides.

The speed and amount of movement depends on The speed and amount of movement depends on whetherwhether

the pesticide is water-soluble, the pesticide is water-soluble, the soil type, the soil type, the amount of rain, and the amount of rain, and the proximity of the water table to the surfacethe proximity of the water table to the surface. . Over time, nearly all pesticides break down to other Over time, nearly all pesticides break down to other

chemicals as they are exposed to sunlight and air. chemicals as they are exposed to sunlight and air. Generally, it is these base chemicals that are detected in Generally, it is these base chemicals that are detected in groundwater. groundwater.

Some agricultural drainage wells provide direct Some agricultural drainage wells provide direct pathways for pollutants to enter groundwater.pathways for pollutants to enter groundwater.

The forms of nitrogen that cause problems as The forms of nitrogen that cause problems as pollutants are the nitrate and ammonium forms. The pollutants are the nitrate and ammonium forms. The nitrate form is water-soluble and moves with the nitrate form is water-soluble and moves with the water into surface water or groundwater. The water into surface water or groundwater. The ammonium form attaches to soil particles.ammonium form attaches to soil particles.

MAINTAINING AND MAINTAINING AND IMPROVING WATER IMPROVING WATER

QUALITYQUALITY Cultural, Cultural, Mechanical, Mechanical, Biological and Biological and Chemical ControlChemical Control

The best solution is The best solution is preventionprevention

Just as there is no single source of water pollution, Just as there is no single source of water pollution, there is no single answer to solve the problem. Once there is no single answer to solve the problem. Once water has become contaminated, it is very difficult, water has become contaminated, it is very difficult, if not impossible, to clean.if not impossible, to clean. Surface water flows quickly, and a Surface water flows quickly, and a pollutant will generally be diluted as it enters larger bodies of water. However, pollutant will generally be diluted as it enters larger bodies of water. However, even large bodies of water, such as the Gulf of Mexico near the mouth of the even large bodies of water, such as the Gulf of Mexico near the mouth of the Mississippi River, cannot tolerate many years of eroded soils, increased Mississippi River, cannot tolerate many years of eroded soils, increased nutrients, and chemical pollution.nutrients, and chemical pollution.

Groundwater, however, moves very slowly. In heavy clay layers or in bedrock, Groundwater, however, moves very slowly. In heavy clay layers or in bedrock, water might only move several inches per year. Even in gravel and sand water might only move several inches per year. Even in gravel and sand aquifers, groundwater may move only several hundred to a thousand feet per aquifers, groundwater may move only several hundred to a thousand feet per year. year. Once the water is polluted, it will spread out Once the water is polluted, it will spread out slowly over a period of many yearsslowly over a period of many years..

Some problems, such as hazardous waste sites, require massive, expensive Some problems, such as hazardous waste sites, require massive, expensive clean-up procedures. With other problems, such as large manure spills, little clean-up procedures. With other problems, such as large manure spills, little can be done but let the wastes become diluted as they reach larger bodies of can be done but let the wastes become diluted as they reach larger bodies of water.water.

However, there are steps to take to reduce some of However, there are steps to take to reduce some of the most serious problems such as siltation from the most serious problems such as siltation from erosion is erosion is passed legislative law to warn passed legislative law to warn deterrentdeterrent

Other Methods Are Other Methods Are No-till and minimum-till farming: No-till and minimum-till farming: Most of the Most of the crop crop

residues - residues - the stalks and leaves of the harvested crop - the stalks and leaves of the harvested crop - are left on the surface of the field with no-till and are left on the surface of the field with no-till and minimum-till farming. Crops are planted into the crop minimum-till farming. Crops are planted into the crop residue the next year. This may reduce soil loss by up to residue the next year. This may reduce soil loss by up to 90 percent. The residue helps keep raindrops from 90 percent. The residue helps keep raindrops from directly hitting the soil and breaking it into small directly hitting the soil and breaking it into small erodible particles.erodible particles.

With no-till or minimum-till farming, crop residue With no-till or minimum-till farming, crop residue remains to protect the soil from rain or wind.remains to protect the soil from rain or wind.

Contour farming: Contour farming: Contour farming involves planting Contour farming involves planting crops in rows that circle around a hill in contours rather crops in rows that circle around a hill in contours rather than in straight rows that go up and down the hill. than in straight rows that go up and down the hill. These contours help break the water flow. With These contours help break the water flow. With conventional farming methods, straight rows encourage conventional farming methods, straight rows encourage the water to run down the row and wash along soil.the water to run down the row and wash along soil.

Other Methods Are Other Methods Are (Cont)(Cont)

Terraces: Terraces: For very steep hillsides, terraces may be For very steep hillsides, terraces may be required. Terraces are constructed by planting a short required. Terraces are constructed by planting a short slope with grass or other cover crops and then slope with grass or other cover crops and then planting the level area with crops. This pattern of planting the level area with crops. This pattern of short slopes and planting areas follows the hillsides. short slopes and planting areas follows the hillsides. This practice breaks up the steep hill into a This practice breaks up the steep hill into a series of shorter slopes and level areas and slows series of shorter slopes and level areas and slows down the water flow.down the water flow. Since the terraces are Since the terraces are planted in grass, they hold the slope in place and planted in grass, they hold the slope in place and reduce erosion. Terracing provides good reduce erosion. Terracing provides good protection for steeper slopes, especially if protection for steeper slopes, especially if combined with low-till or no-till farming.combined with low-till or no-till farming.

Grassed waterways: Grassed waterways: Where concentrated water Where concentrated water runoff occurs due to the sloping of several hills or runoff occurs due to the sloping of several hills or along bottom slopes, planting grass or hay is along bottom slopes, planting grass or hay is recommended. As water collects and runs along these recommended. As water collects and runs along these erosion-prone areas, the denser root systems of the erosion-prone areas, the denser root systems of the grasses help hold the soil in place to prevent these grasses help hold the soil in place to prevent these areas from washing out and forming gullies.areas from washing out and forming gullies.

Other Methods Are Other Methods Are (Cont)(Cont)

Grasses and filterstrips: Grasses and filterstrips: Stream Stream banks and road ditches also need to banks and road ditches also need to be protected. Plants growing on be protected. Plants growing on banks and slopes help hold the soil. banks and slopes help hold the soil. Along stream and river banks, filter-Along stream and river banks, filter-strips of grasses and trees help slow strips of grasses and trees help slow down water run-off and help prevent down water run-off and help prevent soil from washing into waterways.soil from washing into waterways.

Filter strips help reduce erosion Filter strips help reduce erosion along stream and river banks.along stream and river banks.

Good pest management Good pest management dependsdepends

Since polluted groundwater is nearly Since polluted groundwater is nearly impossible to clean, prevention is the impossible to clean, prevention is the onlyonly solution. For pesticides, this means reducing solution. For pesticides, this means reducing the use of chemicals and focusing on an the use of chemicals and focusing on an integrated pest management program that integrated pest management program that controls weeds and insects by more natural controls weeds and insects by more natural means whenever possible and resorting to means whenever possible and resorting to pesticides only as a last resort.pesticides only as a last resort.

Good pest management depends on Good pest management depends on four methods of s control: cultural, four methods of s control: cultural, mechanical, biological, and chemical.mechanical, biological, and chemical.

CULTURAL CONTROLCULTURAL CONTROL

Cultural control relies on Cultural control relies on planting factors such as planting factors such as crop rotation and planting after weeds have crop rotation and planting after weeds have been killed following germination. Good been killed following germination. Good management starts with scouting fields on a management starts with scouting fields on a regular basisregular basis. Keeping records of past problem . Keeping records of past problem areas helps control pests, as well as the need for areas helps control pests, as well as the need for chemical means of controlling pests. chemical means of controlling pests.

The first step is to determine the seriousness of The first step is to determine the seriousness of the infestation of weeds or insects.the infestation of weeds or insects. This is where This is where trade-offs take place. trade-offs take place.

Will the potential loss of crop yield be greater than Will the potential loss of crop yield be greater than the cost of chemical treatment? the cost of chemical treatment?

Are there other options that might be cheaper and Are there other options that might be cheaper and less environmentally dangerous? less environmentally dangerous?

There are no set answers since each farm is There are no set answers since each farm is different and each year brings new challenges.different and each year brings new challenges.

MECHANICAL CONTROLMECHANICAL CONTROL

Mechanical weed control or cultivation is one Mechanical weed control or cultivation is one of the oldest forms of control. Tools like the of the oldest forms of control. Tools like the rotary hoe are used when plants are small, rotary hoe are used when plants are small, while a cultivator is used on larger plants. while a cultivator is used on larger plants. Although mechanical control requires the use Although mechanical control requires the use of fuel to pull the implement across the of fuel to pull the implement across the fields, fields,

it results in reduced chemical control. it results in reduced chemical control. Most farmers substituting mechanical Most farmers substituting mechanical

control for herbicides estimate that it costs control for herbicides estimate that it costs them about half of what their neighbors them about half of what their neighbors spend on chemical control.spend on chemical control.

BIOLOGICAL CONTROLBIOLOGICAL CONTROL Biological control introduces insects and plant Biological control introduces insects and plant

diseases that target specific weed or other pest diseases that target specific weed or other pest populations. populations. One example in the Midwest is the One example in the Midwest is the introduction of the musk thistle weevil which feeds introduction of the musk thistle weevil which feeds on musk thistles.on musk thistles. Thistles are tough weeds to control, Thistles are tough weeds to control, and the weevil appears promising in controlling pest and the weevil appears promising in controlling pest populations.populations.

Insect control is best suited for pasture land Insect control is best suited for pasture land rather than crop land Cultivation tends to rather than crop land Cultivation tends to disrupt the life cycle of the insects.disrupt the life cycle of the insects.

Researchers are also developing microbial controls. Researchers are also developing microbial controls. These microbes are essentially plant diseases that These microbes are essentially plant diseases that occur naturally. occur naturally. The microbes are cultured in labs The microbes are cultured in labs and sprayed on fields where they select the weeds and sprayed on fields where they select the weeds but not the crops. but not the crops.

One major advantage of biological control is One major advantage of biological control is that the diseases can adapt to changing weeds that the diseases can adapt to changing weeds so they canso they can’’t build up resistance or tolerances, t build up resistance or tolerances, which has occurred with herbicides and insects.which has occurred with herbicides and insects.

Musk thistle weevils are used as a biological Musk thistle weevils are used as a biological control on thistles.control on thistles.

CHEMICAL CONTROLCHEMICAL CONTROL

Farmers using other controls methods must Farmers using other controls methods must occasionally resort to chemical control for tough occasionally resort to chemical control for tough cases. However, even when chemical control is cases. However, even when chemical control is required, itrequired, it’’s possible to reduce the amounts of s possible to reduce the amounts of chemicals used. chemicals used.

Careful calibration or setting of the sprayer is Careful calibration or setting of the sprayer is essential to not over-apply chemicals.essential to not over-apply chemicals.

In addition, many farmers use banding techniques In addition, many farmers use banding techniques that spray chemicals in a narrow band over the crop that spray chemicals in a narrow band over the crop row and rely on cultivation for the weeds between row and rely on cultivation for the weeds between rows. An Iowa State University research study shows rows. An Iowa State University research study shows that this method reduces the amount of chemicals that this method reduces the amount of chemicals used by 50 to 67 percent, while maintaining the corn used by 50 to 67 percent, while maintaining the corn yield on 99 percent of the fields tested.yield on 99 percent of the fields tested.

Controlling nitrate pollutionControlling nitrate pollution

General management practices may help ease the General management practices may help ease the problem of nitrate pollution, but they also rely on problem of nitrate pollution, but they also rely on trade-offs that protect both the economic interests trade-offs that protect both the economic interests of the farmer and the natural environment. of the farmer and the natural environment.

The bottom line is not to apply more nitrogen The bottom line is not to apply more nitrogen based fertilizers, either artificial or natural animal based fertilizers, either artificial or natural animal byproducts, than the crops need for that growing byproducts, than the crops need for that growing season. season.

Since ammonia may be lost to the air and nitrates Since ammonia may be lost to the air and nitrates may be moved with the water, it is economical for may be moved with the water, it is economical for the farmer to apply only the amount of nitrogen the farmer to apply only the amount of nitrogen needed and only at the time it is needed by the needed and only at the time it is needed by the plants.plants.

SUMMARYSUMMARY

Storm water, drainage systems in Storm water, drainage systems in town and city are also considered town and city are also considered to be dispersed sources of many to be dispersed sources of many pollutant, because, even though pollutant, because, even though the pollutant are often convene the pollutant are often convene into streams or lakes in drainages into streams or lakes in drainages pipes or storm sewer, they are pipes or storm sewer, they are usually many of these discharges usually many of these discharges scattered over a large area.scattered over a large area.

SUMMARY (Cont)SUMMARY (Cont)

Pollutants from dispersed sources are Pollutants from dispersed sources are much more difficult to control. Many much more difficult to control. Many people think that sewage is the people think that sewage is the primary culprit in water pollution primary culprit in water pollution problems, but dispersed sources cause problems, but dispersed sources cause a significant fraction of the water a significant fraction of the water pollution in Nigeria. The most effective pollution in Nigeria. The most effective way to control the dispersed sources is way to control the dispersed sources is to set appropriate restriction on land to set appropriate restriction on land use. use.

SUMMARY (Cont)SUMMARY (Cont) In addition to being classified by there origin, In addition to being classified by there origin,

water pollutant can be classified into group of water pollutant can be classified into group of substances base primarily on there substances base primarily on there environmental or health effect. E.g., the environmental or health effect. E.g., the following lists identify 9 specific types of following lists identify 9 specific types of pollutants.pollutants.

Pathogenic organismPathogenic organism Oxygen-demanding substancesOxygen-demanding substances Plant nutrientsPlant nutrients Toxic organicsToxic organics Inorganic chemicalsInorganic chemicals SedimentsSediments Radioactive substancesRadioactive substances HeatHeat OilOil

SUMMARY (Cont)SUMMARY (Cont) Domestic Sewage is a primary source of the first Domestic Sewage is a primary source of the first

three types of pollutant. three types of pollutant. Pathogen or diseases causing micro-organism are Pathogen or diseases causing micro-organism are

excreted in the feaces of infected person and may excreted in the feaces of infected person and may be carried into water receiving sewage discharges. be carried into water receiving sewage discharges. Sewage from communities with large population is Sewage from communities with large population is very likely to contained pathogen of some type. very likely to contained pathogen of some type.

Sewage also carries oxygen demanding substanceSewage also carries oxygen demanding substance——the organism waste that exert a biochemical oxygen the organism waste that exert a biochemical oxygen demand as they are decomposed by microbes. BOD demand as they are decomposed by microbes. BOD changes the ecological balance in a body of water changes the ecological balance in a body of water by depleting the Dissolved Oxygen DO content.by depleting the Dissolved Oxygen DO content.

Nitrogen and phosphorus, the major plant nutrients Nitrogen and phosphorus, the major plant nutrients are in sewage, too, as well as in runoff from farm are in sewage, too, as well as in runoff from farm and from suburban lawns. and from suburban lawns.

SUMMARY (Cont) SUMMARY (Cont) SOLUTIONSOLUTION

Conventional Sewage treatment processes Conventional Sewage treatment processes significantly reduce the amount of pathogens significantly reduce the amount of pathogens and BOD in sewage, but do not eliminate and BOD in sewage, but do not eliminate them completely. Certain virus, in particular, them completely. Certain virus, in particular, may be somewhat resistant to the sewage may be somewhat resistant to the sewage disinfection processes. (A virus is an disinfection processes. (A virus is an extremely small pathogenic organism that extremely small pathogenic organism that can only be seen with electron microscopes). can only be seen with electron microscopes). To decrease the amount of Nitrogen and To decrease the amount of Nitrogen and Phosphorus in sewage, usually some form of Phosphorus in sewage, usually some form of advanced sewage treatment must be applied.advanced sewage treatment must be applied.

Toxic ChemicalToxic Chemical Toxic organic chemical, primary pesticide may Toxic organic chemical, primary pesticide may

be carry into the water in the surface runoff be carry into the water in the surface runoff from agricultural areas. Perhaps the most from agricultural areas. Perhaps the most dangerous type is the family of chemical called dangerous type is the family of chemical called Chlorinated hydrocarbons. Common examples Chlorinated hydrocarbons. Common examples are known by there common chemical names are known by there common chemical names as chlordane, Dieldrin, Heptachlor, and the as chlordane, Dieldrin, Heptachlor, and the famous DDT., which has been banned all over famous DDT., which has been banned all over the world. They are very effective poison the world. They are very effective poison against insect that demand agriculture crops. against insect that demand agriculture crops. Unfortunately, they can kill fish, birds, and Unfortunately, they can kill fish, birds, and animals, including humans. And they are not animals, including humans. And they are not very biodegradable, taking more than 30 years very biodegradable, taking more than 30 years in some cases to dissipate from the in some cases to dissipate from the environment. environment.

Inorganic and OilInorganic and Oil Poisonous inorganic chemical, specifically Poisonous inorganic chemical, specifically

those of the heavy metal group, such as lead, those of the heavy metal group, such as lead, mercury, and chromium, also usually originate mercury, and chromium, also usually originate from industrial activities and are considered from industrial activities and are considered hazardous waste. hazardous waste.

Oil is washed into surface water in ruoff from Oil is washed into surface water in ruoff from road and parking lot, and groundwater can be road and parking lot, and groundwater can be polluted from leaking underground tanks, polluted from leaking underground tanks, accidental oil spills from large transport accidental oil spills from large transport tankers at a sea occasional occur, causing tankers at a sea occasional occur, causing significant environmental damage. Blow out significant environmental damage. Blow out accident at offshore oil wells can release many accident at offshore oil wells can release many thousand of tonnes of oil in a short period of thousand of tonnes of oil in a short period of time. Oil spills at sea may eventually move time. Oil spills at sea may eventually move towards shore, affecting aquatic life and towards shore, affecting aquatic life and damaging recreational areas.damaging recreational areas.

CALCULATIONSCALCULATIONS

EXPRESSING EXPRESSING CONCENTRATIONCONCENTRATION

The properties of solutions, suspensions and colloids depend to large The properties of solutions, suspensions and colloids depend to large extent on their concentrations. A dilute or weak solution has a extent on their concentrations. A dilute or weak solution has a relatively small amount of solute dissolved in the solvent. It has a relatively small amount of solute dissolved in the solvent. It has a characteristic different from those concentrated or strong solution of characteristic different from those concentrated or strong solution of the same substances, in which a relatively large amount of solute is the same substances, in which a relatively large amount of solute is present. Since concentrations need to be expressed quantitatively, present. Since concentrations need to be expressed quantitatively, instead of qualitatively terms like dilute or strong, concentration are instead of qualitatively terms like dilute or strong, concentration are usually expressed in terms of mass per unit volume, part per million or usually expressed in terms of mass per unit volume, part per million or billion, or percent.billion, or percent.

MASS PER UNIT VOLUME:MASS PER UNIT VOLUME: One of the common types of One of the common types of concentration is milligram per liter (mg/L). For example, if a mass of 10 concentration is milligram per liter (mg/L). For example, if a mass of 10 mg of oxygen is dissolved in a volume of 1 L of water, the concentration mg of oxygen is dissolved in a volume of 1 L of water, the concentration of that solution is expressed simply as 10mg/L. If 0.3g of salt is of that solution is expressed simply as 10mg/L. If 0.3g of salt is dissolved in 1500mL of water, then the concentration is expressed as dissolved in 1500mL of water, then the concentration is expressed as 300mg/1.5L=200mg/L, where 0.3g = 300mg and 1500mL = 1.5L 300mg/1.5L=200mg/L, where 0.3g = 300mg and 1500mL = 1.5L (1g=1000mg/L; 1L=1000mL).(1g=1000mg/L; 1L=1000mL).

Very dilute solutions are more conveniently expressed in term of Very dilute solutions are more conveniently expressed in term of micrograms per liter (g/L). For example, a concentration of 0.004mg/L micrograms per liter (g/L). For example, a concentration of 0.004mg/L is preferably written as its equivalent 4g/L. Since 1000g=1mg, e.g., a is preferably written as its equivalent 4g/L. Since 1000g=1mg, e.g., a concentration of 1250g/L is equivalent to 1.25mg/L.concentration of 1250g/L is equivalent to 1.25mg/L.

In air, concentrations of particulate matter of gases are commonly In air, concentrations of particulate matter of gases are commonly expressed in terms of micrograms per cubic meter (g/m3).expressed in terms of micrograms per cubic meter (g/m3).

PART PER MILLION:PART PER MILLION: One liter of water has a mass One liter of water has a mass of 1kg. But 1kg is equivalent to 1000g or 1 million of 1kg. But 1kg is equivalent to 1000g or 1 million mg. therefore, if 1 mg of a substance is dissolved in 1 mg. therefore, if 1 mg of a substance is dissolved in 1 L of water, we can say that there is 1 mg of solute per L of water, we can say that there is 1 mg of solute per million mg of water. In other words, there is million mg of water. In other words, there is one part one part per million (1 ppm) per million (1 ppm)

Neglecting the small changes in the density of water Neglecting the small changes in the density of water as substances are dissolved in it, we can say that, in as substances are dissolved in it, we can say that, in general, a concentration of 1 mg per liter is general, a concentration of 1 mg per liter is equivalent to one part per million: 1mg/L=1ppm. equivalent to one part per million: 1mg/L=1ppm. Conversion is very simple; for example, a Conversion is very simple; for example, a concentration of 17.5 mg/L is identical to 17.5ppmconcentration of 17.5 mg/L is identical to 17.5ppm

The expression mg/L is preferred over ppm just as The expression mg/L is preferred over ppm just as the expression g/L is preferred over its equivalent of the expression g/L is preferred over its equivalent of ppb. But both types of units are still used and the ppb. But both types of units are still used and the student should be familiar with each.student should be familiar with each.

PERCENTAGE CONCENTRATION:PERCENTAGE CONCENTRATION: Concentrations Concentrations in excess of 10000mg/L are generally expressed in in excess of 10000mg/L are generally expressed in terms of percent, for conveniences. For practical terms of percent, for conveniences. For practical purposes, the conversion of 1 percent = 10000 mg/L be purposes, the conversion of 1 percent = 10000 mg/L be used even though the density of the solutions are used even though the density of the solutions are slightly more than that of pure water (10000mg/L = slightly more than that of pure water (10000mg/L = 10000mg/1000000mg = 1 mg/100 mg = 1 percent).10000mg/1000000mg = 1 mg/100 mg = 1 percent).

The concentration of salts in seawater is about The concentration of salts in seawater is about 35000mg/L. To convert to percent salts, divide by 35000mg/L. To convert to percent salts, divide by 10,000 obtaining 3.5 percent. The concentration of 10,000 obtaining 3.5 percent. The concentration of wastewater sludge may be about 3 percent solids. To wastewater sludge may be about 3 percent solids. To convert this to mg/L, multiply by 10,000 getting convert this to mg/L, multiply by 10,000 getting 30000mg/L solids.30000mg/L solids.

A concentration expressed in terms of percent may be A concentration expressed in terms of percent may be also computed using the following expression. also computed using the following expression. Percent Percent = (Mass of Solute (mg)/ Mass of Solvent (mg)) X = (Mass of Solute (mg)/ Mass of Solvent (mg)) X 100100

U.S CUSTOMARY UNITS:U.S CUSTOMARY UNITS: The expression The expression grains per gallon (gpg) are sometimes used for grains per gallon (gpg) are sometimes used for concentrations of certain substances in water. concentrations of certain substances in water. One grain per gallon is equivalent to a One grain per gallon is equivalent to a concentration of 17.1 milligrams per liter: concentration of 17.1 milligrams per liter: 1gpg=17.1mg/L1gpg=17.1mg/L

The expression pounds per million gallon is The expression pounds per million gallon is also used in US customary unit of also used in US customary unit of concentration for water treatment applications. concentration for water treatment applications. Since 1 gallon of water weighs 8.34lb, 1 gal/mil Since 1 gallon of water weighs 8.34lb, 1 gal/mil gal is the same as 8.34 lb/mil gal. Or we can gal is the same as 8.34 lb/mil gal. Or we can say that 1mg/L = 8.34 mil gal to convert from say that 1mg/L = 8.34 mil gal to convert from mg/L to lb/mil gal, multiply by 8.34; to go from mg/L to lb/mil gal, multiply by 8.34; to go from lb/mil gal to mg/L. divide by 8.34lb/mil gal to mg/L. divide by 8.34

EXAMPLE:EXAMPLE: A 500-mL aqueous solution has 125mg of salt A 500-mL aqueous solution has 125mg of salt dissolved in it. Express the concentration of this solution in terms dissolved in it. Express the concentration of this solution in terms of (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil galof (a) mg/L, (b)ppm, (c)gpg (d) Percent and (e) lb/mil gal

SolutionSolution (125mg/500mL)X1000mL/L = 250mg/L(125mg/500mL)X1000mL/L = 250mg/L 250mg/L = 250 ppm250mg/L = 250 ppm (250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpg(250 mg/L X 1gpg)/17.1 mg/L = 14.6 gpg Applying this equation Percent = (Mass of Solute (mg)/ Mass of Applying this equation Percent = (Mass of Solute (mg)/ Mass of

Solvent (mg))X 100Solvent (mg))X 100 Percent = 0.125g/500g X 100 = 0.025 percent Or divide Percent = 0.125g/500g X 100 = 0.025 percent Or divide

250mg/L by 10,000 to get 0.025 percent250mg/L by 10,000 to get 0.025 percent 250 mg/L X 8.34 = 2090 lb/mil gal250 mg/L X 8.34 = 2090 lb/mil gal EXAMPLE:EXAMPLE: How many pounds of chlorine gas should be How many pounds of chlorine gas should be

dissolved in 8 mil gal of water to result in a concentration of 0.2 dissolved in 8 mil gal of water to result in a concentration of 0.2 mg/Lmg/L

Solution Solution 0.2 mg/L X 8.34 = 1.67 lb/mil gal0.2 mg/L X 8.34 = 1.67 lb/mil gal And 1.67 lb/mil gal X 8 mil gal = 13 lbAnd 1.67 lb/mil gal X 8 mil gal = 13 lb

BIOCHEMICAL OXYGEN DEMAND: BIOCHEMICAL OXYGEN DEMAND: Bacteria and other Bacteria and other microorganisms use organic substance for food. As they microorganisms use organic substance for food. As they metabolize organics are broken down into simpler metabolize organics are broken down into simpler compounds, such as CO2 and H2O, and the microbes use the compounds, such as CO2 and H2O, and the microbes use the energy released fro growth and reproduction.energy released fro growth and reproduction.

When this process occurs in water, the oxygen consumed is When this process occurs in water, the oxygen consumed is the DO. If oxygen is not continually replaced in the water by the DO. If oxygen is not continually replaced in the water by artificial or natural means, then the DO level will decrease as artificial or natural means, then the DO level will decrease as the organic are decomposed by the microbes. This need for the organic are decomposed by the microbes. This need for oxygen is called oxygen is called Biological Oxygen DemandBiological Oxygen Demand. In effect, the . In effect, the microbes microbes ““demanddemand”” the oxygen for use in the biochemical the oxygen for use in the biochemical reactions that sustain them. Organic waste in sewage is one reactions that sustain them. Organic waste in sewage is one of the major types of water pollutants. It is impractical to of the major types of water pollutants. It is impractical to isolate and identify each specific organic chemical in these isolate and identify each specific organic chemical in these wastes and to determine its concentration. Instead, the BOD wastes and to determine its concentration. Instead, the BOD is used as an indirect measure of the total amount of is used as an indirect measure of the total amount of biodegradable organics in the water. The more organic biodegradable organics in the water. The more organic material there is in the water; the higher the BOD exerted by material there is in the water; the higher the BOD exerted by the microbes will be.the microbes will be.

In addition to being used as a measure of the amount of organic pollutant In addition to being used as a measure of the amount of organic pollutant in streams or lakes, the BOD is used as a measure of the strength of in streams or lakes, the BOD is used as a measure of the strength of sewage. This is the most important parameters for design and operation sewage. This is the most important parameters for design and operation of water pollution control plant. A strong sewage has a high of water pollution control plant. A strong sewage has a high concentration of organic material and a correspondingly high BOD. The concentration of organic material and a correspondingly high BOD. The complete decomposition of organic material by microorganisms takes complete decomposition of organic material by microorganisms takes time, usually 20d or more under ordinary circumstances. The amount of time, usually 20d or more under ordinary circumstances. The amount of oxygen used to completely decompose or stabilize all the biodegradable oxygen used to completely decompose or stabilize all the biodegradable organics in a given volume of water is called organics in a given volume of water is called Ultimate BODUltimate BOD, or BODL for , or BODL for example, if a 1-L volume of municipal waste requires 300 mg of oxygen example, if a 1-L volume of municipal waste requires 300 mg of oxygen for complete decomposition of the organics, the BODL would be for complete decomposition of the organics, the BODL would be expressed as 300mg/L. One liter of waste from an industrial or food expressed as 300mg/L. One liter of waste from an industrial or food processing plant may require as much as 1500 mg of oxygen for complete processing plant may require as much as 1500 mg of oxygen for complete stabilization of the waste. In this case, the BODL would be 1500mg/L, stabilization of the waste. In this case, the BODL would be 1500mg/L, indicating a much stronger waste than ordinary municipal or domestic indicating a much stronger waste than ordinary municipal or domestic sewage. In general, then, the BOD is expressed in terms of mg/L of sewage. In general, then, the BOD is expressed in terms of mg/L of oxygen.oxygen.

The BOD is a function of time. At the very beginning of a BOD test, or The BOD is a function of time. At the very beginning of a BOD test, or time = 0, no oxygen will have been consumed and the BOD = 0. As each time = 0, no oxygen will have been consumed and the BOD = 0. As each day goes by oxygen is used by the microbes and the BOD increase. day goes by oxygen is used by the microbes and the BOD increase. Ultimately, the BODL is reached and the organics are completely Ultimately, the BODL is reached and the organics are completely decomposed. A graph of the BOD versus time has the characteristic shape decomposed. A graph of the BOD versus time has the characteristic shape called the BOD Curve.called the BOD Curve.

The BOD curve can be expressed mathematically by The BOD curve can be expressed mathematically by the following equation:the following equation:

BODt = BODL X (1 BODt = BODL X (1 –– 10-kt) 10-kt) Where BODt = BOD at any time t. mg/LWhere BODt = BOD at any time t. mg/L BODL = Ultimate BOD, mg/LBODL = Ultimate BOD, mg/L k = constant representing the rate of BOD reactionk = constant representing the rate of BOD reaction t = time, dt = time, d The rate at which oxygen is consumed is expressed The rate at which oxygen is consumed is expressed

by the constant k. the value of this rate constant by the constant k. the value of this rate constant depend on the temperature, the type of organic depend on the temperature, the type of organic material, and the types of microbes exerting the BOD. material, and the types of microbes exerting the BOD. For the ordinary domestic sewage at a temperature For the ordinary domestic sewage at a temperature of 20oC, the value of k is usually about 0.15/dof 20oC, the value of k is usually about 0.15/d

Example: Example: A sample of sewage from a town is found to have a BOD after 5 A sample of sewage from a town is found to have a BOD after 5 d (BODd (BOD55) of 180mg/L. Estimate the Ultimate BOD (the BOD) of 180mg/L. Estimate the Ultimate BOD (the BODLL) of the ) of the sewage assuming that k = 0.1/d for this waste water.sewage assuming that k = 0.1/d for this waste water.

SolutionSolution BODt = BODL X (1 BODt = BODL X (1 –– 10 10-kt-kt)) 180 = 180 = BODt = BODL X (1 BODt = BODL X (1 –– 10 10-kt-kt) , It implies that ) , It implies that 180 = BODL X (1-180 = BODL X (1-

1010-0.1X5-0.1X5)) Therefore 180 = BODL X (1- 0.316) ; 180 = BODL X 0.684Therefore 180 = BODL X (1- 0.316) ; 180 = BODL X 0.684 Rearranging terms to solve for BODL givesRearranging terms to solve for BODL gives BODL = 180/0.684 = 260 mg/L Rounded off.BODL = 180/0.684 = 260 mg/L Rounded off. This is particularly true when the BOD data are used to monitor the This is particularly true when the BOD data are used to monitor the

efficiency of a water pollution control plant. It has been found that more efficiency of a water pollution control plant. It has been found that more than two-third of the BODL is usually exerted within the first 5d of than two-third of the BODL is usually exerted within the first 5d of decomposition. For instance, in the preceding example, the 5d BOD is decomposition. For instance, in the preceding example, the 5d BOD is 180/260 = 0.69, or 69% of the ultimate BOD. For practical purposes, the 180/260 = 0.69, or 69% of the ultimate BOD. For practical purposes, the 5d BOD, or BOD5, has been chosen as a representation of the organic 5d BOD, or BOD5, has been chosen as a representation of the organic content of water or waste water. For standardization of results, the test content of water or waste water. For standardization of results, the test must be conducted at a temperature of 20must be conducted at a temperature of 20ooC.C.

In summary, the parameter of BODIn summary, the parameter of BOD55 is the amount of dissolved oxygen is the amount of dissolved oxygen used by microbes in the 5 d to decompose organic substances in water at used by microbes in the 5 d to decompose organic substances in water at 20oC.20oC.

Measurement of BOD5Measurement of BOD5 The traditional BOD test is conducted in the standard 300-mL The traditional BOD test is conducted in the standard 300-mL

glass BOD bottlesglass BOD bottles. The test for 5-d BOD of water sample . The test for 5-d BOD of water sample involves taking two DO measurements: an initial measurement involves taking two DO measurements: an initial measurement when the test begins, at time t = 0, and a second when the test begins, at time t = 0, and a second measurement, at t = 5, after the sample has been incubated in measurement, at t = 5, after the sample has been incubated in the dark for 5 d at 20oC. The BOD5 is simply the difference the dark for 5 d at 20oC. The BOD5 is simply the difference between the two measurements.between the two measurements.

For example consider that a sample of water from a stream is For example consider that a sample of water from a stream is found to have an initial DO of 8.0 mg/L. It is placed directly found to have an initial DO of 8.0 mg/L. It is placed directly into a BOD bottle and incubated for 5 d at 20oC. After the 5 d, into a BOD bottle and incubated for 5 d at 20oC. After the 5 d, the DO is determined to be 4.5mg/L.The BOD is the amount of the DO is determined to be 4.5mg/L.The BOD is the amount of oxygen consumed, or the difference between the two DO oxygen consumed, or the difference between the two DO readings. That is, BOD5 = 8.0 readings. That is, BOD5 = 8.0 –– 4.5 = 3.5mg/L. 4.5 = 3.5mg/L.

Very clean bodies of surface water usually have a BOD5 of Very clean bodies of surface water usually have a BOD5 of about 1 mg/L due to the presence of naturally occurring from about 1 mg/L due to the presence of naturally occurring from decaying leaves and animal wastes. BOD5 values in excess of decaying leaves and animal wastes. BOD5 values in excess of 10 mg/L, however usually indicate the presence of sewage 10 mg/L, however usually indicate the presence of sewage pollution.pollution.

EXPERIMENTATION:EXPERIMENTATION: When measuring the BOD5 When measuring the BOD5 of sewage, it is necessary to first dilute the sample of sewage, it is necessary to first dilute the sample in the BOD bottle. Domestic sewage usually has a in the BOD bottle. Domestic sewage usually has a general BOD value of 200 mg/L. If the sample were general BOD value of 200 mg/L. If the sample were not diluted, the entire DO will be completely not diluted, the entire DO will be completely depleted and it would not be possible to get a DO depleted and it would not be possible to get a DO reading on the fifth day. Computation of the BOD5, reading on the fifth day. Computation of the BOD5, using this using this dilution methoddilution method in a 300-ml BOD bottle, in a 300-ml BOD bottle, is done by using the following equation:is done by using the following equation:

Where DO0 = Initial DO at t = 0Where DO0 = Initial DO at t = 0 D05 = DO at t = 5dD05 = DO at t = 5d V = Sample volume, mLV = Sample volume, mL

V

XDODOBOD

300_ 50

5

EXAMPLEEXAMPLE: A 6.0-ml sample of wastewater is : A 6.0-ml sample of wastewater is diluted to 300 mL with distilled water in a standard diluted to 300 mL with distilled water in a standard BOD bottle. The initial DO in the bottle is BOD bottle. The initial DO in the bottle is determined to be 8.5 mg/L, and the DO after 5d at determined to be 8.5 mg/L, and the DO after 5d at 2020ooC is found to be 5.0 mg/L. C is found to be 5.0 mg/L.

Determine the BODDetermine the BOD55 of the wastewater and compute of the wastewater and compute its BODits BODLL. Assume that . Assume that kk = 0.1/d = 0.1/d

SOLUTION: SOLUTION: BOD5 = ((8.5-5.0) X 300)/ 6.0 = 3.5 X 300/6.0 = 180 BOD5 = ((8.5-5.0) X 300)/ 6.0 = 3.5 X 300/6.0 = 180

mg/Lmg/L Now applying BODt = BODL X (1 Now applying BODt = BODL X (1 –– 10 10-kt-kt)) 180 = BODL X (1 180 = BODL X (1 –– 10 10-0.1X5-0.1X5) and) and BODL = 180/0.684 = 260mg/LBODL = 180/0.684 = 260mg/L

CHEMICAL OXYGEN CHEMICAL OXYGEN DEMANDDEMAND

The BOD test provides a measure of the biodegradable organic The BOD test provides a measure of the biodegradable organic material in water, i.e., of the substance that microbe can readily material in water, i.e., of the substance that microbe can readily use for food. There might also be non biodegradable or slowly use for food. There might also be non biodegradable or slowly biodegradable substance that will not detected by the convectional biodegradable substance that will not detected by the convectional BOD test. BOD test.

TheThe Chemical Oxygen Demand, COD Chemical Oxygen Demand, COD is another parameter of is another parameter of water quality which measures all organics, including the non water quality which measures all organics, including the non biodegradable substances. It is a chemical test using a strong biodegradable substances. It is a chemical test using a strong oxidizing agent (Potassium Dichromate), sulphuric acid and heat. oxidizing agent (Potassium Dichromate), sulphuric acid and heat. The result of the COD test can be available in just 2hours, a The result of the COD test can be available in just 2hours, a definite advantage over the 5d required for the standard BOD test.definite advantage over the 5d required for the standard BOD test.

COD values are always higher than BOD values for the same COD values are always higher than BOD values for the same sample, but there is generally no consistent correlation between sample, but there is generally no consistent correlation between the two tests for different wastewater. In other word, it is not the two tests for different wastewater. In other word, it is not feasible to simply measure the COD and then predict the BOD. feasible to simply measure the COD and then predict the BOD. Because most waste water treatment plant are biological in their Because most waste water treatment plant are biological in their mode of operation, the BOD is more representative of the mode of operation, the BOD is more representative of the treatment process and remains a more commonly used parameter treatment process and remains a more commonly used parameter than the COD.than the COD.

SOLIDS: SOLIDS: Solids occurs in water either in solution or in Solids occurs in water either in solution or in suspension. These 2 types of solid are distinguish by passing suspension. These 2 types of solid are distinguish by passing the water sample through a glass-fibre filter. By definition, the water sample through a glass-fibre filter. By definition, the the Suspended SolidSuspended Solid are retain on top of the filter and the are retain on top of the filter and the Dissolved Solid Dissolved Solid pass through the filter with the water. pass through the filter with the water.

If the filtered portion of the water sample is placed in a small If the filtered portion of the water sample is placed in a small dish and then evaporated, the solid in the water remain as a dish and then evaporated, the solid in the water remain as a residue in the evaporating dish. This material is usually called residue in the evaporating dish. This material is usually called Total Dissolved SolidTotal Dissolved Solid TDSTDS. The concentration of TDS is . The concentration of TDS is expressed in term of mg/L. it can be calculated as follows.expressed in term of mg/L. it can be calculated as follows.

Where A = equal to weigh of dish plus residue. MgWhere A = equal to weigh of dish plus residue. Mg B = Weight of empty dishB = Weight of empty dish C = Volume of sample filtered mL.C = Volume of sample filtered mL.

C

XBATDS

1000)-(≡

Example: The weight of an empty evaporating dish is Example: The weight of an empty evaporating dish is determined to be 40.525g. After a water sample is filtered, determined to be 40.525g. After a water sample is filtered, 100mL of the sample is evaporated from the dish. The weight 100mL of the sample is evaporated from the dish. The weight of the dish plus dried residue is found to be 40.545g. Compute of the dish plus dried residue is found to be 40.545g. Compute the TDS concentrationthe TDS concentration

= 200mg/L= 200mg/L

In drinking water, dissolved liquid may caused taste problems. In drinking water, dissolved liquid may caused taste problems. Hardness, corrosion, or aesthetic problem may also Hardness, corrosion, or aesthetic problem may also accompany excessive TDS concentration. In wastewater accompany excessive TDS concentration. In wastewater analysis and water pollution control, the suspended retained analysis and water pollution control, the suspended retained on the filtered are of primary importance and are referred to on the filtered are of primary importance and are referred to as as TOTAL SUSPENDED SOLID TSS.TOTAL SUSPENDED SOLID TSS.

The TSS concentration can be computed using the TDS The TSS concentration can be computed using the TDS equation, equation,

where A represent the weight of the filtered plus retained solidwhere A represent the weight of the filtered plus retained solid B represent the weight of the clean filterB represent the weight of the clean filter C represent the volume of the sample filteredC represent the volume of the sample filtered

C

XBATDS

1000)-(≡ 100

1000)525.40-545.40( XTDS ≡

Hardness is usually expressed in term of Hardness is usually expressed in term of milligram per liter of calcium carbonate, milligram per liter of calcium carbonate, CaC03; grains per gallon are also used to CaC03; grains per gallon are also used to express hardness concentration. Water with express hardness concentration. Water with more than 300mg/L of hardness is generally more than 300mg/L of hardness is generally considered to be hard, and water with less than considered to be hard, and water with less than 75mg/L is considered to be soft. Very soft 75mg/L is considered to be soft. Very soft water is undesirable in public supply because it water is undesirable in public supply because it tends to increase corrosion problem in metal tends to increase corrosion problem in metal pipes; also, some health official believe it to be pipes; also, some health official believe it to be associated with the incident of the heart associated with the incident of the heart disease.disease.

DilutionDilution In water pollution control, it is often necessary to predict In water pollution control, it is often necessary to predict

the BOD concentrations and the DO levels downstream the BOD concentrations and the DO levels downstream from a sewage discharge point. One of the first from a sewage discharge point. One of the first computations needed for this involves the effect of computations needed for this involves the effect of dilution. Assuming that pollutant is completely mixed in dilution. Assuming that pollutant is completely mixed in the streamflow (at a point just below the end of the mixing the streamflow (at a point just below the end of the mixing zone), one can calculate the diluted concentration of any zone), one can calculate the diluted concentration of any water quality parameter using the following mass balance water quality parameter using the following mass balance equation:equation:

cd = (csQs + cwQw)/(Qs + Qw)cd = (csQs + cwQw)/(Qs + Qw) where cd = diluted concentration or temperaturewhere cd = diluted concentration or temperature cs = original stream concentration or temperaturecs = original stream concentration or temperature cw = waste concentration or temperaturecw = waste concentration or temperature Qs = stream dischargeQs = stream discharge Qw = waste dischargeQw = waste discharge

A fundamental concept in science is the A fundamental concept in science is the law of conservation of matterlaw of conservation of matter. This . This means that when there is no appreciable conversion of mass into energy, the means that when there is no appreciable conversion of mass into energy, the sum of the masses of substances entering into a reaction must always equal sum of the masses of substances entering into a reaction must always equal the sum of the masses of products of reaction. Even if there in no chemical the sum of the masses of products of reaction. Even if there in no chemical reaction occurring, the law of conservation underlies the concept of reaction occurring, the law of conservation underlies the concept of mass mass balance balance (also called material balance), and is useful in environmental (also called material balance), and is useful in environmental technologytechnology

Mass balance calculations play an important role in the design and Mass balance calculations play an important role in the design and operation of water, sewage, air and solid waste treatment processes. In operation of water, sewage, air and solid waste treatment processes. In treatment systems, the physical, chemical, and biological processes usually treatment systems, the physical, chemical, and biological processes usually occurs in vessel or tanks called occurs in vessel or tanks called reactors,reactors, and the particular reactions or and the particular reactions or processes are referred to as processes are referred to as unit processesunit processes. In the simplest case, it can be . In the simplest case, it can be said that the input must equal the output, or, in other words, said that the input must equal the output, or, in other words, ““what goes in what goes in must go out.must go out.”” If this does not occur, there must be an accumulation If this does not occur, there must be an accumulation (depletion) of the material in the reactor equal to the difference between the (depletion) of the material in the reactor equal to the difference between the input and output, or input and output, or accumulation = input-output.accumulation = input-output. Since, in this kind of Since, in this kind of situation, the composition of material in the reactor changes with time, it is situation, the composition of material in the reactor changes with time, it is referred to as an referred to as an unsteady-stateunsteady-state operation. In the operation. In the steady statesteady state operation, it operation, it can be assumed that the rates of input and output are constant, as is the can be assumed that the rates of input and output are constant, as is the composition of the completely mixed reactor.composition of the completely mixed reactor.

Suppose, for example, two pipes containing salt solutions discharge into a Suppose, for example, two pipes containing salt solutions discharge into a tank in which the two solutions are completely mixed, and the third pipe tank in which the two solutions are completely mixed, and the third pipe carries the mixture out of the tankcarries the mixture out of the tank

The solution in the first pipe has a concentration of c1 mg/L and The solution in the first pipe has a concentration of c1 mg/L and that in the second pipe has a concentration of c2 mg/L. the flow that in the second pipe has a concentration of c2 mg/L. the flow rate of the pipes are Q1 and Q2 respectively. The concept of rate of the pipes are Q1 and Q2 respectively. The concept of mass or material balance can be applied to determine the mass or material balance can be applied to determine the concentration of the mixed solution discharged from the tank concentration of the mixed solution discharged from the tank because under steady-state conditions, the total amount of salt because under steady-state conditions, the total amount of salt entering the tank must be equal to the total amount leaving the entering the tank must be equal to the total amount leaving the tank. In other words, since the salt neither decays nor reacts tank. In other words, since the salt neither decays nor reacts with other substance (in this example), the concentration of salt with other substance (in this example), the concentration of salt in the mixture in the tank stay constant over time.in the mixture in the tank stay constant over time.

The product of concentration of volume flow rate equals the The product of concentration of volume flow rate equals the mass flow rate because mass flow rate because mg/L X L/d = mg/dmg/L X L/d = mg/d where the volume where the volume flow rate in this example is expresses in terms of liter per day, flow rate in this example is expresses in terms of liter per day, or L/d. for convenience here, consider that the time interval is 1 or L/d. for convenience here, consider that the time interval is 1 day. Then the product of c1 X Q must equal the mass of salt day. Then the product of c1 X Q must equal the mass of salt entering the vessel in 1 d from the first pipe. Similarly, c2 X Q entering the vessel in 1 d from the first pipe. Similarly, c2 X Q equals the mass of salt entering the tank from the second pipe. equals the mass of salt entering the tank from the second pipe. The total mass of salt entering the tank in 1 d, that is, The total mass of salt entering the tank in 1 d, that is, the inputthe input, , must be equal to the sum from the two pipes, or input = c1 X Q1 must be equal to the sum from the two pipes, or input = c1 X Q1 + c2 X Q2.+ c2 X Q2.

The The total masstotal mass of salt leaving the tank equals of salt leaving the tank equals the the productproduct of the concentration in the mixture c3 and the of the concentration in the mixture c3 and the volume flow rate leaving the tank. Because water is volume flow rate leaving the tank. Because water is actually incompressible, however, that flow rate must actually incompressible, however, that flow rate must be Q1 + Q2. Therefore, the output of salt is c3 X (Q1 + be Q1 + Q2. Therefore, the output of salt is c3 X (Q1 + Q2). Because the concept of mass or material balance Q2). Because the concept of mass or material balance applies here and output = input, the following applies here and output = input, the following relationship is obtained:relationship is obtained:

c3 X (Q1 + Q2) = c1 X Q1 + c2 X Q2c3 X (Q1 + Q2) = c1 X Q1 + c2 X Q2 Solving the above equation for c3 by dividing both Solving the above equation for c3 by dividing both

sides by (Q1 + Q2), we obtained the following mass sides by (Q1 + Q2), we obtained the following mass balance equation balance equation

c3 = (c1 X Q1 + c2 X Q2)/Q1 + Q2c3 = (c1 X Q1 + c2 X Q2)/Q1 + Q2 Mass balance calculation can be applied to the natural Mass balance calculation can be applied to the natural

environmental systems, such as streams, rivers, lakes environmental systems, such as streams, rivers, lakes and even the atmosphere e.g Stream pollution.and even the atmosphere e.g Stream pollution.

EXAMPLE:EXAMPLE: The BOD5 of an effluent from a municipal sewage The BOD5 of an effluent from a municipal sewage treatment plants is 25mg/L and the effluent discharge is 4 ML/d. the treatment plants is 25mg/L and the effluent discharge is 4 ML/d. the receiving stream has a BOD5 of 2 mg/L and the stream flow is 40 ML/d. receiving stream has a BOD5 of 2 mg/L and the stream flow is 40 ML/d. compute the combined 5-day BOD in the stream just below the mixing compute the combined 5-day BOD in the stream just below the mixing zone.zone.

SOLUTION: Applying cd = (csQs + cwQw)/(Qs +Qw)SOLUTION: Applying cd = (csQs + cwQw)/(Qs +Qw) cd = (2 X 40 + 25 X 4)/ 40 X 4 = 180/44 = 4.1mg/Lcd = (2 X 40 + 25 X 4)/ 40 X 4 = 180/44 = 4.1mg/L Where cd represent the diluted BOD5 in the combined flowWhere cd represent the diluted BOD5 in the combined flow EXAMPLE:EXAMPLE: A river has a dry-weather discharge of 100 cfs and a A river has a dry-weather discharge of 100 cfs and a

temperature of 25oC. Compute the maximum discharge of cooling temperature of 25oC. Compute the maximum discharge of cooling water at 65oC that can be discharged from a power plant into the water at 65oC that can be discharged from a power plant into the stream. Assume the legal limit on the temperature increase in stream stream. Assume the legal limit on the temperature increase in stream is 2oCis 2oC

SOLUTIONSOLUTION: The maximum allowable stream temperature is 25 + 2 = : The maximum allowable stream temperature is 25 + 2 = 27oC27oC

Applying mass balance equation cd = (csQs + cwQw)/(Qs +Qw)Applying mass balance equation cd = (csQs + cwQw)/(Qs +Qw) 27 = (25 X 100 + 65 X Qw)/100 + Qw 27 = (25 X 100 + 65 X Qw)/100 + Qw 200 = 38Qw : 200 = 38Qw : Qw = 5.3 cfsQw = 5.3 cfs The discharge of warm water cannot be exceed 5.3 ft3/s if the stream The discharge of warm water cannot be exceed 5.3 ft3/s if the stream

temperature is not to increase more than 2oC temperature is not to increase more than 2oC

COMPUTATION OF MINIMUM DOCOMPUTATION OF MINIMUM DO

It is important to be able to predict the minimum dissolved oxygen It is important to be able to predict the minimum dissolved oxygen level in a polluted stream or river. For Example, if a new sewage level in a polluted stream or river. For Example, if a new sewage treatment plant is to be discharge its effluent into a trout stream, it treatment plant is to be discharge its effluent into a trout stream, it is possible that conventional (secondary) treatment levels will not is possible that conventional (secondary) treatment levels will not remove enough BOD to prevent excessively low DO downstream. To remove enough BOD to prevent excessively low DO downstream. To determine if some form of advanced treatment is required to determine if some form of advanced treatment is required to preserve the stream for trout spawning and survival, it is necessary preserve the stream for trout spawning and survival, it is necessary to compute the minimum DO caused by the sewage effluent and to to compute the minimum DO caused by the sewage effluent and to compare it to the allowable value for trout streams.compare it to the allowable value for trout streams.

One technique used to describe and predict the behaviour of a One technique used to describe and predict the behaviour of a polluted stream uses the so-called Streeter-Phelps equation. This polluted stream uses the so-called Streeter-Phelps equation. This equation is based on the assumption that the only two processes equation is based on the assumption that the only two processes taking place are deoxygenation of BOD and the reaeration by taking place are deoxygenation of BOD and the reaeration by oxygen transfer at the surface, as previously discussed. Two key oxygen transfer at the surface, as previously discussed. Two key formulas from the Streete-Phelps model of stream pollution and formulas from the Streete-Phelps model of stream pollution and oxygen sag follow. Figure 5.11 illustrate some of the variables in oxygen sag follow. Figure 5.11 illustrate some of the variables in these equations. The minimum DO in the stream is the difference these equations. The minimum DO in the stream is the difference between the saturation DO level and the critical oxygen deficit. The between the saturation DO level and the critical oxygen deficit. The formulas are formulas are

COMPUTATION OF MINIMUM DO COMPUTATION OF MINIMUM DO (Cont)(Cont)

Tc=Tc= Dc=Dc= Where tc = Time it takes for the critical Where tc = Time it takes for the critical

oxygen deficit or minimum DO to develop, doxygen deficit or minimum DO to develop, d Dc = Critical oxygen deficit, mg/LDc = Critical oxygen deficit, mg/L Di = Initial oxygen deficit at time t = 0 just Di = Initial oxygen deficit at time t = 0 just

below the point of waste discharge into the below the point of waste discharge into the stream, mg/Lstream, mg/L

BODL = Ultimate BOD in the stream just BODL = Ultimate BOD in the stream just below the point of waste discharge, mg/Lbelow the point of waste discharge, mg/L

k1 = Deoxygenated rate constant, d-1k1 = Deoxygenated rate constant, d-1 k2 = The reaeration rate constant, d-1k2 = The reaeration rate constant, d-1

]_

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The value of k1 if generally taken to be the same as the rate The value of k1 if generally taken to be the same as the rate constant for the BOD reaction in this equation constant for the BOD reaction in this equation BODt = BODL BODt = BODL X (1-10-kt);X (1-10-kt); it can be determined in the laboratory. The value it can be determined in the laboratory. The value of k2 depends on the velocity and the depth of the flow and can of k2 depends on the velocity and the depth of the flow and can be determined from field studies or by an appropriate formula. be determined from field studies or by an appropriate formula. The reaeration rate constant k2 can be vary from about 0.1 for The reaeration rate constant k2 can be vary from about 0.1 for the sluggish to about 4.0 for a swallow turbulent stream. Both the sluggish to about 4.0 for a swallow turbulent stream. Both rate constants, k1 and k2 depend on temperature.rate constants, k1 and k2 depend on temperature.

The equation tc and Dc look complicated, and they are. They The equation tc and Dc look complicated, and they are. They are presented here to illustrate the power of mathematics as a are presented here to illustrate the power of mathematics as a tool for modeling the environment and helping solve water tool for modeling the environment and helping solve water pollution problems. But as complicated as they may appear, pollution problems. But as complicated as they may appear, the Streeter-Phelps equations are not completely accurate the Streeter-Phelps equations are not completely accurate representations of the oxygen profile in a polluted stream or representations of the oxygen profile in a polluted stream or river. Other factors that affect the oxygen balance include river. Other factors that affect the oxygen balance include photosynthesis and respiration of rooted plants and algae and photosynthesis and respiration of rooted plants and algae and the oxygen demand of benthic (bottom) deposits. Equations the oxygen demand of benthic (bottom) deposits. Equations that have been developed to include these factors are even that have been developed to include these factors are even more complicated than the equation tc and Dc more complicated than the equation tc and Dc


EXAMPLE: EXAMPLE: The BODL in a stream is 3 mg/L and the DO is The BODL in a stream is 3 mg/L and the DO is 9.0 mg/L. The streamflow is 15mgd. A treated sewage 9.0 mg/L. The streamflow is 15mgd. A treated sewage effluent with BODL =50mg/L is discharged into the stream effluent with BODL =50mg/L is discharged into the stream at a rate of 5 mgd. The DO of the sewage effluent is 2 at a rate of 5 mgd. The DO of the sewage effluent is 2 mg/L. Assuming that k1 = 0.2, k2 = 0.5, and the saturation mg/L. Assuming that k1 = 0.2, k2 = 0.5, and the saturation DO level is 11 mg/L, determine the minimum DO level in DO level is 11 mg/L, determine the minimum DO level in the stream. For a stream velocity of 0.5 ft/s, how far the stream. For a stream velocity of 0.5 ft/s, how far downstream does the minimum DO occur?downstream does the minimum DO occur?

SOLUTION: SOLUTION: First, it is necessary to compute the diluted First, it is necessary to compute the diluted BODL and DO using the Mass Balance EquationBODL and DO using the Mass Balance Equation

BODL = (15 X 3 + 5 X 50)/15 + 5 = 295/20 BODL = (15 X 3 + 5 X 50)/15 + 5 = 295/20 = 14.8mg/L= 14.8mg/L DO = (15 X 9 + 5 X 2)/15 + 5 = 145/20 DO = (15 X 9 + 5 X 2)/15 + 5 = 145/20 = 7.3 mg/L= 7.3 mg/L Now compute the initial oxygen deficit as Now compute the initial oxygen deficit as Di = saturation DO Di = saturation DO –– Initial DO = 11.0 Initial DO = 11.0 –– 7.3 = 7.3 =

3.7mg/L3.7mg/L Applying the Streeter-Phelps Model Equations for tcApplying the Streeter-Phelps Model Equations for tc


Tc= = Tc= = ==(0.33)log 1.56 = (0.33)log 1.56 =

0.64 d0.64 d

It will take about 0.64 d (roughly 15hours) for the It will take about 0.64 d (roughly 15hours) for the minimum DO to occur.minimum DO to occur.

Now applying next Streeter-Phelps Model Now applying next Streeter-Phelps Model Equation for Dc givesEquation for Dc gives

Dc= =Dc= = 9.87 X (0.745 9.87 X (0.745 –– 0.479) + 3.7 X 0.479 = 2.63 + 1.78 = 4.4 mg/L0.479) + 3.7 X 0.479 = 2.63 + 1.78 = 4.4 mg/L

The minimum DO in the stream is the difference between The minimum DO in the stream is the difference between saturation DO and the critical oxygen deficit, or 11.0 saturation DO and the critical oxygen deficit, or 11.0 –– 4.4 = 4.4 = 5.6 mg/L. At a velocity of 0.5 ft/s, in 0.64 d the distance 5.6 mg/L. At a velocity of 0.5 ft/s, in 0.64 d the distance downstream for the minimum DO is 0.64 d X 24 h/d X 3600 downstream for the minimum DO is 0.64 d X 24 h/d X 3600

s/h X 0.5 ft/s = 27659 ft approximately 5 million.s/h X 0.5 ft/s = 27659 ft approximately 5 million.

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