ENVIRONMENTAL ENGINEERING

441

Lecture 2:

Water Chemistry

Philadelphia UniversityFaculty of Engineering

Department of Civil EngineeringFirst Semester, 2013/2014

PHYSICAL AND CHEMICAL PROPERTIES OF WATER

1 - Organic compounds

2- Inorganic compounds1. Nutrients2. Metal3. Non-Metal

1- ORGANIC SUBSTANCES

The main element of organic compounds is Carbon.

Organic substances may be Natural occurring organic substances includes protein,

lipids, carbohydrates and plant pigments Synthetic organic chemicals

Pesticides and agrochemicals Surface active agent including emulsifier, wetting

agent, foams, detergents Halogenated hydrocarbons ( CHCl3, CHBr3, CHCl2Br,

etc Over 120 toxic organic compounds listed on the

USEPA Priority Pollutant List including pesticides and solvents

2- INORGANIC CHEMICALSA -Nutrients: Two nutrients are essential for the

growth of organisms: Nitrogen Phosphorus Both are indictors of water pollution

NITROGEN (N)

Source (s) Elements for protein, chlorophyll and biological

compounds Decomposition of compounds animals and human wastes, chemicals

(fertilizers)Effect (s)

NO3- poisoning to human specially babies below than 6month old and animals

NO3-> NO2-(in acidic condition) – will substitute O2 in blood vessel

PHOSPHORUS (P)

Exist in a form of “inorganic”, and “organic phosphate”.

Source (s): readily present in soil fertilizers human wastes (“organic phosphate” domestic wastes (element in detergent)

effects (s) Cellular activity and aquatic plants > 0.2 mg/L – disturb coagulation processes in

water treatment plants

INORGANIC CHEMICALSB) Ions – anions and cations

Major Ions (conc. In mg/L) such as Ca, Mg, Na, K, SO2, Cl, NO3, HCO3

Minor Ions: Conc in ug/L such as Al, Cu, Fe, Mn

Source (s):Minerals readily available from nature

Effect (s):Colour, odour, taste and turbidityDeteriorate health (at high concentration)

METALS – NON TOXIC AND TOXIC

C) Heavy metals: such as As, Ba, Cd, Cr, Pb, Hg, Se, Ag

Source (s)human activities such as mining and

industriesEffect (s):

dangerous disease such as cancer, abortion and deformation in newborn baby

SOLIDS(IMPURITIES) TYPES OF SOLIDS

1. Dissolved Solids (in Liquid) cannot be removed from liquid without accomplishing a phase change such as distillation, precipitation, adsorption, extraction or high pressure membrane

2. Suspended solids (filterable solids) those solids that can be filtered by a glass fiber filter disc can be removed from water by physical methods such as sedimentation, filtration and centrifugation.

3. Colloidal particles1. Size in range between dissolved substances and

suspended particles2. Can be removed by high-force centrifugation or

filtration – very small pore size3. Measured by turbidity

SOLID

 Measured in mg/L Sources (s):

Inorganic compounds such as clay, sand Organic compounds such plant fibre, human wast

Effects (s): Aesthetics Adsorption point/centre for chemical and micro-

organism Health aspect

PHYSICAL AND CHEMICAL PROPERTIES OF WATER

To illustrate the quality of a tested water qualitatively and quantitatively.

Physical1. Suspended Solids2. Turbidity3. Odor4. Taste5. Temperature

Chemical TDS Alkalinity Hardness Fluoride Metals Nutrients

Biological Microorganisms

CHARACTERIZATION OF WATER 1- TURBIDITY

Turbidity: The presence of suspended material such as clay, silt, finely divided organic mater, and other particulate material in water

The unit of measure is a Turbidity Unit (TU) or Nephlometric Turbidity Unit (NTU)

It’s a measure of the cloudinessRiver values range from 2 to 200mg/L of SiO2The EU drinking water upper limit is 10mg/L with

a guideline value of 1mg/L

2-COLOR

Color in water is caused by dissolved minerals, dyes or humic acids (decomposition of lignin) from plants. Apparent Color: Color that is partly due to

suspended solids (SS) True Color (water treatment): Color that is

contributed by dissolved solids (DS) after removal of SS

Color itself is not usually undesirable from the stand point of health- it indicates that water needs appropriate treatment

3- ODOR Many organic and inorganic chemicals are

odorous including algae and other organisms H2S – hydrogen sulfide sometimes present in

ground water and wastewater. Threshold odor is determined by diluting a

sample with odor –free water until the last perceptible odor is detectable (dilution factor)

Like odor, may be due to decaying micro-organisms or algae or due to high conc. of salts such as Ca & Mg

4-TASTE

5- TEMPERATURE

One of the most important parameters in natural surface waters.

It influences the number and type of microorganism species present and their rate of activities; affect most chemical reactions; affect solubility of gases e.g oxygen decrease with

increase temp. Conc of O2 around 8mg/L @ 25 degree Celsius

In WWTP, T above 36oC, the aerobic MO population tends to be less effective as WW purifiers

In rivers, as increased water temp reduces the amount of oxygen in water, thereby making river less desirable for fish, particularly salmonoids.

PH

The negative log of the hydrogen ion concentration

pH of most mineral waters is 6 to 9 If pH is out side the range 6 – 9, it might kill off

the active microbiological population including the aquatics organisms

pH is important in ensuring proper chemical treatment

ALKALINITY Alkalinity measures the buffering capacity of

the water against changes in pH; measuring the amount of acid needed to lower the pH in a water sample to a specific endpoint (4.5).

Water that has a high alkalinity can accept large doses of acids or bases without altering the pH significantly.

Waters with low alkalinity, such as rainwater or distilled water, can experience a drop in the pH with only a minor addition of an acid or base.

Alkalinity is expressed as mg (CaCO3)/L

In water the only significant contribution to alkalinity are carbonate species and free H+ and OH_

Acid base reaction H2CO3 H+ +HCO3

HCO3- H+ + CO3

2-

ELECTRICAL CONDUCTIVITY/ CONDUCTIVITY

It is a measure of the ability of an aqueous solution to carry an electric current by the movement of ions.

The higher the numbers of ions, the higher magnitude of conductivity

Pure water has 0.05uS/cm (microsiemens/cm)

Sea water has about 40000 uS/cm Groundwater 200-1500

TOTAL HARDNESS

The sum of the divalent metallic cations (Ca & Mg). These cations reacts with soap to form precipitate and with other ions present in water to form scale in boilers.

Measured as mg CaCO3/L Two kinds of hardness:

carbonate hardness; temporary in characteristics, precipitated through boiling

non-carbonate hardness- chloride and sulfate; permanent in characteristic, eliminated through chemical softness / ion exchange

WT goal is to provide water with a hardness of less in the range of 75 to 120mg/L as CaCO3 by using softener

HARDNESS

Measure of “multivalent” cations in water such as Ca2+,Mg2+, Fe2+, Mn3+

Ca2+ and Mn2+are very important Source (s):

natural mineral on earth effect (s):

excessive soap usage (a waste !) precipitate form on hardware precipitate in pipe – temperature and pH increases

DISSOLVED OXYGENOne of the most important measures of water quality is dissolved oxygen. Oxygen, although poorly soluble in water, is fundamental to aquatic life. Without free dissolved oxygen, streams and lakes become uninhabitable to aerobic organisms, including fish and most invertebrates. It is found that the concentration of DISSOLVED OXYGEN in water is SMALLDissolved oxygen is inversely proportional to temperature, andthe maximum amount of oxygen that can be dissolved in water at 0°C is 14.6 mg/L to 7.6 at 30C.

FLUORIDE

Source (s): Minerals

Effect (s): not good for health if it is taken in high

concentration concentration of 1 mg/L is good for the growth of

children teeth excessive concentration – color on teeth and

problem in bone growth Fluoride

ODOUR

Source (s) inorganic compounds such asminerals,

metals, salts organic compound from petroleum

and/or degradation of organic matter  Effect(s)

Aesthetici health problems [reaction from sources and

other chemicals such as chlorine (Cl)

Dissolved oxygen in water is consumed by the oxidation of dissolved ammonia (NH3)and ammonium ion (NH4+)to form the nitrate ion (NO3 ).⎯ NH3(aq) + 2O2(aq) + OH-----NO3-(aq) + 2H2O(aq)

The most common substance oxidized by oxygen in water is ORGANIC MATTER OF BIOLOGICAL ORIGIN

Such organic matter (such as dead plant material like polymerized carbohydrate below), is oxidised by dissolved oxygen. e.g. CH2O+O2(aq) ------ CO2(g) + H2O(aq)

Under oxygen free (anaerobic) conditions dissolved organic matter will decompose if appropriate bacteria are present:

2CH2O ----CH4+ CO2

Such anaerobic conditions are common in SWAMPS and at the bottom of deep lakes

The Methane (CH4) produced in this process bubbles up towards the surface of the swamps and is the reason that methane used to be known as ‘marsh 'or ‘swamp 'gas

ANALYSIS OF ORGANIC SUBSTANCES

Various parameters are used as a measure of the organic strength of wastewater: BOD –Biochemical oxygen demand COD –Chemical oxygen demand  TOC –Total organic carbon VSS –Volatile suspended solid

BIOCHEMICAL OXYGEN DEMAND

The quantity of oxygen utilized by a mixed population of micro organisms to biologically degrade the organic matter in the wastewater under aerobic condition.

BOD is the most important parameter in water pollution control.

it is used a measure of organic pollution as a basis for estimating the oxygen

Needed for biological processes, as and indicator of process performance

Expressed in milligrams of oxygen required per liter of wastewater (mg/L).

BIOCHEMICAL OXYGEN DEMAND

BOD : BOD5: is the amount of dissolved oxygen used up from the water by microorganisms as they break down organic material at 20C over a 5-day periods. BOD5 for Rivers if > 5 mg/L, they considered

polluted BOD For MWW range 150-1000mg/L

CHEMICAL OXYGEN DEMAND

COD- Determine the amount of oxygen needed to oxidize

the organics in a water or wastewater using a strong oxidizing chemical agent- Potassium dichromate rather than using micro-organisms as in BOD

It measures the total organic carbon with the exception of some aromatics such as benzene which are not oxidized in the reaction.

Indirectly measure amount of organic matter in the water sample

Faster determination of oxygen demand in a water sample, than BOD

It takes shorter time ( 2hrs) compared to 5 days for BOD5

The EU upper limit of 125mg/L for treated wastewaters prior to discharge to rivers

RELATION BETWEEN COD AND BOD

COD > BOD COD ~ ultimate BOD COD/BOD ~ 2, biodegradable organic COD >> BOD, non-biodegradable organic

TOTAL ORGANIC CARBON- TOC

TOC- : measures all carbon as CO2 in mg/L

Inorganic carbon ( HCO3, CO2, CO3, etc) must be removed prior test by acidifying and aerating the sample.

Theoretically the COD is 2.66 times greater than TOC

SOLIDS- Sources of Suspended Solids

Suspended Solids

Immiscible liquids-Oils-Grease

Source- Surface waters; Domestic WW and Industrial WW

Organic-Plant Fiber-Biological Solids (Algae Cells; Bacteria;)

Source – Surface Waters; Domestic WW; Industrial WW

Inorganic-Clay-Silt

Source – Surface Waters; Domestic WW; Industrial WW

MICROBIOLOGICAL CHARACTERISTICS

Water must be free from diseases-producing organisms (pathogen). These organisms include viruses, bacteria, protozoa, helminthes (worms)

Techniques for comprehensive bacteriological examination are complex and time consuming

Indicative tests were developed to indicate the relative degree of Microbial contamination: Escherichia Coli (E. Coli)- intestinal Tracts Aerobactor aerogenes- Urinary tracts Total Coliform test

Two protozoa Giardia cysts Cryptosporidium oocycts Both pathogens carried by animal and cause

gastrointestinal illness

BIOLOGICAL

Indicator microorganism

Their presence shows that pollution has occurred and suggests the TYPE and LEVEL of pollution.

Indicator microorganism properties:  Can be used for all types of water   Always present when pathogen is present  Always absent when pathogen is absent  Easily experimented and give reliable results Typical indicators used are coliform group

Coliform group: fecal coliform e.g.E.Coli

Total coliform e.g. fecal coliform, Soil coliform and others