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WATER QUALITY WATER QUALITY MANAGEMENTMANAGEMENT

Water quality management is the science that predicts how much waste is too much for a body of water

AssimilatedAssimilated- amount of waste that can be tolerated by a body of water

Determined by knowing the type of pollutants discharged and their effect on water quality

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Major classes ofMajor classes ofWastewater constituentsWastewater constituents

Suspended solids (TSS, VSS, NVSS, etc.)Suspended solids (TSS, VSS, NVSS, etc.)Biodegradable organics (BOD, COD)Biodegradable organics (BOD, COD)Pathogens (bacteria, viruses, protozoa, etc.)Pathogens (bacteria, viruses, protozoa, etc.)Nutrients (N, P)Nutrients (N, P)Organics that donOrganics that don’’t biodegrade (refractory)t biodegrade (refractory)Heavy metals (Cd, Zn, Pb, Hg, Cu)Heavy metals (Cd, Zn, Pb, Hg, Cu)TDSTDSTemperatureTemperature

OxygenOxygen--Demanding MaterialsDemanding Materials

Biodegradable Organic ContentBiodegradable Organic ContentBODBOD55 is the amount of dissolved oxygen consumed by is the amount of dissolved oxygen consumed by

microorganisms during the biochemical oxidation of microorganisms during the biochemical oxidation of organic and inorganic matter to carbon dioxide in 5organic and inorganic matter to carbon dioxide in 5--day day standard test at 20standard test at 20°°C.C.

Total Oxidizeable (Organics & Some Inorganics) Total Oxidizeable (Organics & Some Inorganics) CODCOD is the amount of dissolved oxygen consumed by is the amount of dissolved oxygen consumed by

chemical oxidizing reagents (Kchemical oxidizing reagents (K22CrCr22OO77) during the reaction ) during the reaction with organic and inorganic matter to produce carbon with organic and inorganic matter to produce carbon dioxide in a standard test at 20dioxide in a standard test at 20°°C.C.

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Biochemical Oxygen Demand (BOD)Biochemical Oxygen Demand (BOD)

BOD: Oxygen is removed from water when organic matter is BOD: Oxygen is removed from water when organic matter is consumed by bacteria. consumed by bacteria. Low oxygen conditions may kill fish and other organisms.Low oxygen conditions may kill fish and other organisms.

Sources of organic matter Sources of organic matter Natural inputsNatural inputs---- swamps, leaf fall and vegetation aligning swamps, leaf fall and vegetation aligning waterways. waterways. Human inputsHuman inputs---- pulp and paper mills, meatpulp and paper mills, meat--packing plants, food packing plants, food processing industries, and wastewater treatment plants. processing industries, and wastewater treatment plants. NonNon--point inputspoint inputs---- runoff from urban areas, agricultural areas, runoff from urban areas, agricultural areas, and feedlots.and feedlots.

Purpose of BOD and COD testsPurpose of BOD and COD tests

Test the water quality in lakes and riversTest the water quality in lakes and riversDetermine the amount of oxygen required to Determine the amount of oxygen required to oxidize the organic matter in wastewateroxidize the organic matter in wastewater

Determine the size of treatment system needed Determine the size of treatment system needed (a design factor)(a design factor)

Assess the efficiency of the treatment process by Assess the efficiency of the treatment process by monitoring influent and effluentmonitoring influent and effluent

Determine compliance with wastewater Determine compliance with wastewater discharge permitsdischarge permits

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Biochemical Oxygen Demand (BOD)Biochemical Oxygen Demand (BOD)

Establishes biological Establishes biological ““strengthstrength”” based on based on oxygen uptake by microbes during aerobic oxygen uptake by microbes during aerobic metabolism of organics in wastemetabolism of organics in waste

55--day (BODday (BOD55) and 20) and 20--day (BODday (BOD2020))Carbonaceous (CBOD)Carbonaceous (CBOD)Nitrogenous (NBOD)Nitrogenous (NBOD)Ultimate (UBOD)Ultimate (UBOD)

Carbonaceous & Nitrogenous BODCarbonaceous & Nitrogenous BOD

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Influent & Effluent BOD & TSSInfluent & Effluent BOD & TSS

Influent Influent

TSS TSS 100 to 300 100 to 300 mg/Lmg/L

BODBOD5 5 100 to 300 100 to 300 mg/Lmg/L

Effluent standards Effluent standards ((avgavg 3030--d)d)

TSSTSS 30 mg/L30 mg/LBODBOD55 30 mg/L30 mg/L

NOTE: BOD is always less (ca. 0.5) than COD

BOD testBOD test

•Standardized•Needs:

IncubatorBottlesDO meterDilution waterSeed (opt.)Expressed in mg/L

BOD bottles

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BOD testBOD test

1)1) A special 300 mL BOD bottle is filled with a sample of A special 300 mL BOD bottle is filled with a sample of water that has been appropriately diluted and water that has been appropriately diluted and inoculated with microorganismsinoculated with microorganisms

2)2) Blank samples containing only the dilution water are Blank samples containing only the dilution water are also placed in BOD bottles and sealedalso placed in BOD bottles and sealed

3)3) The sealed BOD bottles containing diluted samples and The sealed BOD bottles containing diluted samples and blanks are incubated in the dark at 20blanks are incubated in the dark at 20°°C for the C for the desired number of daysdesired number of days

4)4) After five days has elapsed, the samples and blanks After five days has elapsed, the samples and blanks are removed from the incubator and the dissolved are removed from the incubator and the dissolved oxygen concentration in each bottle is measured.oxygen concentration in each bottle is measured.

BOD testBOD test

BOD5 (mg/l) = __________D0 – D5

P

P is volume fraction of 1 liter used in test(dilution factor = 1/P)

D is dissolved oxygenconcentration at Time=0 and Time = 5 days

Example: Determine the BOD5 for a 15 ml sample that is diluted with dilution water to a total volume of 300 ml when the initialDO concentration is 8 mg/l and after 5 days, has been reduced to 2 mg/l.

D0 = 8D5 = 2P = 15 ml/300ml = 0.05Dilution factor = 300/15 = 20

BOD5 (mg/l) = _______ = 1200.05

8 - 2

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Nutrients: N & PNutrients: N & P

Nitrogen is often the limiting nutrient in ocean Nitrogen is often the limiting nutrient in ocean waters and some streamswaters and some streams

Nitrogen can exist in numerous forms, but Nitrogen can exist in numerous forms, but nitrate (NOnitrate (NO33

--), nitrite (NO), nitrite (NO22--), ammonia (NH), ammonia (NH33) are ) are

most commonly measuredmost commonly measured

Sources: primarily from fertilizers and acid Sources: primarily from fertilizers and acid depositiondeposition

NutrientsNutrientsNitrogenNitrogen

Urea mineralizes rapidly to NHUrea mineralizes rapidly to NH44++

NHNH44+ + oxidizes to NOoxidizes to NO33

-- (NBOD)(NBOD)Nitrifying bacteria use CONitrifying bacteria use CO22--C (HCO3C (HCO3--

alkalinity)alkalinity)Influent N ranges (mg/L as N):Influent N ranges (mg/L as N):

Total: 20 Total: 20 –– 7070Organic: 8 Organic: 8 –– 2525Ammonia: 12 Ammonia: 12 –– 4545No nitrate or nitrite typicallyNo nitrate or nitrite typically

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Forms of nitrogen in wastewaterForms of nitrogen in wastewater

TKN = 40% Organic + 60% Free AmmoniaTKN = 40% Organic + 60% Free Ammonia

Typical concentrations:Typical concentrations:AmmoniaAmmonia--N = 10N = 10--50 mg/L50 mg/LOrganic N = Organic N = 10 10 –– 35 mg/L35 mg/L

No nitrites or nitratesNo nitrites or nitrates

Forms of nitrogen:Forms of nitrogen:Organic NOrganic NAmmoniaAmmoniaNitriteNitriteNitrateNitrate

TKNTotal

N

Nutrients Nutrients (cont(cont’’d)d)

PhosphorusPhosphorusRaw wastewater contains 4 Raw wastewater contains 4 –– 16 mg/L as P16 mg/L as PEffluent may restrict to less than 1 mg/L as PEffluent may restrict to less than 1 mg/L as PForms areForms are

Orthophosphate: POOrthophosphate: PO4433--, HPO, HPO44

22--, H, H22POPO44--, ,

HH33POPO44

Polyphosphate (polymerized; important Polyphosphate (polymerized; important in in biological phosphorous removal)biological phosphorous removal)Organic phosphorous (low in raw Organic phosphorous (low in raw wastewater)wastewater)

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NutrientsNutrients

Phosphorus is typically the limiting nutrient in Phosphorus is typically the limiting nutrient in lakes, and algae growth is linked to phosphorus lakes, and algae growth is linked to phosphorus inputs. inputs.

P SourcesP SourcesfertilizersfertilizersDetergentsDetergents

P can exist in a variety of chemical forms, so P can exist in a variety of chemical forms, so total P in normally measuredtotal P in normally measured

Effects of nutrient loadingsEffects of nutrient loadings

Algae bloomsAlgae bloomsDO changes, fish killsDO changes, fish killsHasten eutrophication of water Hasten eutrophication of water bodiesbodiesAesthetics (color, clarity, smell)Aesthetics (color, clarity, smell)Uptake and release of toxicsUptake and release of toxics

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POINT SOURCES OF POLLUTANTSPOINT SOURCES OF POLLUTANTS

Point sources include domestic sewage and industrial wastesPoint sources Point sources -- collected by a network of pipes or channels and conveyed to a single point of discharge in receiving waterMunicipal sewage Municipal sewage -- domestic sewage and industrial wastes that are discharged into sanitary sewers - hopefully treatedPoint source pollution can be controlled by waste minimization and proper wastewater treatment

NONPOINT SOURCESNONPOINT SOURCESUrban and agricultural runoff that are characterized by overland dischargeThis type of pollution occurs during rainstorms and spring snowmeltPollution can be reduced by changing land use practices

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OXYGENOXYGEN-- DEMANDING MATERIALDEMANDING MATERIAL

Dissolved Oxygen (DO)Dissolved Oxygen (DO)-- fish and other higher forms of aquatic life that must have oxygen to liveOxygenOxygen-- Demanding MaterialDemanding Material-- anything that can be oxidized in the receiving water resulting in the consumption of dissolved molecular oxygen - BOD, CODAlmost all naturally occurring organic matter contributes to the depletion of DO

NUTRIENTSNUTRIENTS

Nitrogen and phosphorus are considered pollutants when too much present in high conc.High levels of nutrients cause disturbances in the food webOrganisms grow rapidly at the expense of othersMajor sources of nutrients (N, P):

Phosphorus-based detergentFertilizer and agricultural runoffFood-processing wastesAnimal and human waste

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WATER QUALITY WATER QUALITY MANAGEMENT IN RIVERSMANAGEMENT IN RIVERS

Main goal is to control the discharge of pollutants so that water quality is not degraded above the natural background levelControlling waste involves:1) Measuring pollutants levels (x,z, t)2) Predicting their effect on the water quality3) Determining background water quality that

would be present without human intervention

4) Evaluate the levels acceptable for intended uses of the water

RIVER POLLUTION IMPACTSRIVER POLLUTION IMPACTS

Waste Input Receptor

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SIMPLE MASS BALANCESIMPLE MASS BALANCE

Waste Input Qw, Cw

C = Qw Cw + Qs Cs

Input rate - Output rate - decay rate = Accumulation rate

Stream Qs, Cs

Steady state conservative system

Qs + Qw

SIMPLE MASS BALANCESIMPLE MASS BALANCE

Waste Input Qw = 5 m3/sCw = 40 mg/L

C = 20 (10) + 40 (5)

Input rate - Output rate - decay rate = Accumulation rate

Qs = 10 m3/s

Cs = 20 mg/L

Steady state conservative system

(10 + 5)

26.67 mg/L

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TRANSPORT CHARACTERISTICS TRANSPORT CHARACTERISTICS THAT AFFECT CONCENTRATIONTHAT AFFECT CONCENTRATION

• Velocity

• Dilution (mixing)

• Dispersion

• Degradation (mass loss)

• Adsorption (to soils)

• Sedimentation (to bottom)

• Aquatic Life (attached)

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EFFECT OF OXYGENEFFECT OF OXYGEN--DEMANDING DEMANDING WASTES ON RIVERSWASTES ON RIVERS

Depletes the dissolved oxygen in waterThreatens aquatic life that require DOConcentration of DO in a river is determined by the rates of photosynthesis of aquatic plants and the rate of oxygen consumed by organisms

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BOD KINETICSBOD KINETICS

Aerobic decompositionAerobic decomposition-- when organisms use oxygen to consume wasteThe rate at which oxygen is consumed is directly proportional to the concentration of degradable organic matter remaining at any timeBOD is a first order reaction Lo-Lt = BODt

dL/dt = -kLLt = Lo e-kt where Lo = ultimate BOD

TEMPERATURE EFFECTTEMPERATURE EFFECT

The BOD rate constant is adjusted to the temperature of receiving water using this:

kT=k20(θ)T-20

• T= temperature of interest (in °C)• kT= BOD rate constant at the temperature of

interest(in days -1)• k20= BOD rate constant determined at 20 °C

(in days -1)• θ= temperature coefficient.

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BODBOD

Ultimate BODUltimate BOD--maximum amount of oxygen consumption possible when waste has been completely degradedNumerical value of the rate constant k of BOD depends on:

Nature of waste and TAbility of organisms in the system to use the waste

NATURE OF THE WASTENATURE OF THE WASTE

Materials that are rapidly degraded have large BOD constantsMaterials that degrade slowly are almost undegradable in the BOD testBOD rate constant depends on the relative proportions of the various componentsEasily degradable organics are more completely removed than less readily degradable organics during wastewater treatment

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ABILITY OF ORGANISMS TO ABILITY OF ORGANISMS TO USE WASTEUSE WASTE

Many organic compounds can be degraded by only a small group of microorganismsThe population of organisms that can most efficiently use wastes predominatesBOD test should always be conducted with organisms that have been acclimated to the wasteThis created a rate constant that can be compared to that in the river

TEMPERATURETEMPERATURE

Oxygen use speeds up as the temperature increases and slows down as the temperature decreasesOxygen use is caused by the metabolism of microorganismsBOD rate constants depend on:1) Temperature of receiving water

throughout the year2) Comparing data from various

locations at different T values

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DISSOLVED OXYGEN DODISSOLVED OXYGEN DO

If the discharge of oxygen-demanding wastes is within the self-purification capacity, the DO is highIf the amount of waste increases, it can result in detrimental changes in plant and animal lifeAquatic life cannot survive without DOObjective of water quality management is to assess the capability of a stream to absorb waste

DO SAG CURVEDO SAG CURVE

DO concentration dips as oxygen-demanding materials are oxidized and then rises as oxygen is replenished from atmosphere and photosynthesisMajor sources of oxygen:

Reaeration from the atmospherePhotosynthesis of aquatic plants

Factors of oxygen depletion:BOD of waste dischargeDO in waste discharge is less than that in the riverNonpoint source pollutionRespiration of organisms and aquatic plants

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Use of Ponds for Water Quality

Oxygen Deficit EquationDefine deficit D = DOs - DO in mg/L

L = ultimate BOD (mg/L)

V (dD/dx) = kd L - kr D

Where kd = deoxygenation rate constant (day-1)

kr = reaeration rate constant (day-1)

Since t = x / V, can write the above in time as

dD/dt = kd L - kr D (reaeration vs oxygen use)

Solution to this eqn gives the DO sag curve

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Oxygen Deficit EquationAt t = 0, D = Da and L = La - Initial values

Solving the equation for Dt = deficit at any time t

Dt = kdLa e-kd t - e-kr t + Da e-kr t

Kr - kd

Dt = DOs - DO

DO

X

Critical DO