WASTEWATER – TYPES, WASTEWATER – TYPES, CHARACTERISTICS & CHARACTERISTICS & REGULATIONREGULATION

Definition of wastewaterDefinition of wastewater

Water that has been usedWater that has been used

Can be pollutedCan be polluted

Types of wastewaterTypes of wastewater

Domestic: wastewater by residential, Domestic: wastewater by residential, shop houses, offices, schools etc. and shop houses, offices, schools etc. and normally generated from toilets, sinks normally generated from toilets, sinks and bathrooms.and bathrooms.

Industrial: wastewater generated by Industrial: wastewater generated by industries. Quantity and quality industries. Quantity and quality depends on the type of industrydepends on the type of industry

Storm water: rainwater, may contain Storm water: rainwater, may contain pollutantspollutants

Why treat wastewater?Why treat wastewater?

Untreated wastewater harmful Untreated wastewater harmful to healthto health

Breeding sites for insects, pests Breeding sites for insects, pests and micro organismsand micro organisms

Can cause environmental Can cause environmental pollution and affect ecosystempollution and affect ecosystem

Wastewater CharacteristicsWastewater Characteristics

PhysicalPhysical

Chemical Chemical

BiologicalBiological

1.1. Physical CharacteristicsPhysical Characteristics

A. Colour:A. Colour:

depends mainly on the depends mainly on the wastewater constituentwastewater constituent

B. Odour: B. Odour:

not significant if aerobic. not significant if aerobic. Anaerobic wastewater release Anaerobic wastewater release hydrogen sulphide (smells like hydrogen sulphide (smells like rotten egg)rotten egg)

C. Temperature:C. Temperature:

higher than water temperature higher than water temperature due to the microbiological due to the microbiological activitiesactivities

D. Turbidity:D. Turbidity:

caused by the presence of solids caused by the presence of solids mainly suspended solids (SS) mainly suspended solids (SS) from clay, sand, human waste from clay, sand, human waste and plant fibresand plant fibres

6.4 Chemical Characteristics6.4 Chemical Characteristics

A. Organic compounds:A. Organic compounds:

DefinitionDefinition

All organic compounds contain All organic compounds contain carbon in combination with one carbon in combination with one or more elements.or more elements.

Properties of organic compoundsProperties of organic compounds

Usually combustibleUsually combustible

Have lower melting and boiling Have lower melting and boiling pointspoints

Less soluble in waterLess soluble in water

Have very high molecular weightHave very high molecular weight

Most organic compounds can Most organic compounds can serve as a source of food for serve as a source of food for micro-organismsmicro-organisms

Source(s):Source(s):

Nature: fibres, vegetable oils, Nature: fibres, vegetable oils, animal oils and fats, cellulose, animal oils and fats, cellulose, starch, sugar.starch, sugar.

Synthesis: a wide variety of Synthesis: a wide variety of compounds and materials compounds and materials prepared by manufacturing prepared by manufacturing processes. E.g. DDT, polyvinyl processes. E.g. DDT, polyvinyl chloride.chloride.

Fermentation: Alcohols, acetone, Fermentation: Alcohols, acetone, glycerol, antibiotics, acids.glycerol, antibiotics, acids.

Classification of organic matter Classification of organic matter (difference in degradability)(difference in degradability)

Biodegradable organicsBiodegradable organics

Non-biodegradable organicsNon-biodegradable organics

Biodegradable organicsBiodegradable organics

Food for micro-organismsFood for micro-organisms

Fast and easily oxidized by micro-Fast and easily oxidized by micro-organismsorganisms

e.g. starch, fat protein, alcohol, human and e.g. starch, fat protein, alcohol, human and animal waste.animal waste.

Non-biodegradable organicsNon-biodegradable organics

Difficult and much more longer Difficult and much more longer to biodegradeto biodegrade

Or toxic to micro-organismsOr toxic to micro-organisms

e.g. PVC, pesticide, industrial e.g. PVC, pesticide, industrial waste, cellulose, phenol, lignic waste, cellulose, phenol, lignic acid.acid.

Effect(s):Effect(s):

– Depletion of the dissolved oxygen Depletion of the dissolved oxygen in the waterin the water

Destroying aquatic lifeDestroying aquatic life

Damaging the ecosystemDamaging the ecosystem– Some organics can caused cancerSome organics can caused cancer

Trihalomethane (THM-Trihalomethane (THM-carcinogenic compound) are carcinogenic compound) are produced in water and produced in water and wastewater treatment plants wastewater treatment plants when natural organic compounds when natural organic compounds combine with chlorine added for combine with chlorine added for disinfection purposes.disinfection purposes.

Normally, wastewater has high Normally, wastewater has high organic content. The organic organic content. The organic content are measured by content are measured by Biochemical Oxygen Demand Biochemical Oxygen Demand (BOD) and Chemical Oxygen (BOD) and Chemical Oxygen Demand (COD) and the value is Demand (COD) and the value is about 100 to 400 mg/L.about 100 to 400 mg/L.

What is Biochemical Oxygen What is Biochemical Oxygen Demand (BOD)?Demand (BOD)?

DefinitionDefinition

The quantity of oxygen utilised The quantity of oxygen utilised by a mixed population of micro-by a mixed population of micro-organisms to biologically organisms to biologically degrade the organic matter in degrade the organic matter in the wastewater under aerobic the wastewater under aerobic conditioncondition

BOD is the most important BOD is the most important parameter in water pollution parameter in water pollution controlcontrol

It is used as a measure of It is used as a measure of organic pollution as a basis for organic pollution as a basis for estimating the oxygen needed estimating the oxygen needed for biological processes, and as for biological processes, and as an indicator of process an indicator of process performance.performance.

Organic matter + OOrganic matter + O22 CO CO22 + H + H22O + O + new cellsnew cells

BOD test, BOD test, 5-day at 205-day at 20ooCC

3-day at 303-day at 30ooCC

microorganism

Test method (BODTest method (BOD5 5 @ 20@ 20ooC)C)

1.1. A water sample containing degradable A water sample containing degradable organic matter is placed in a BOD bottle.organic matter is placed in a BOD bottle.

2.2. If needed, add dilution water (known If needed, add dilution water (known quantity). Dilution water is prepared by quantity). Dilution water is prepared by adding phosphate buffer (pH 7.2), adding phosphate buffer (pH 7.2), magnesium sulphate, calcium chloride and magnesium sulphate, calcium chloride and ferric chloride into distilled water. Aerate the ferric chloride into distilled water. Aerate the dilution water to saturate it with oxygen dilution water to saturate it with oxygen before use.before use.

3.3. Measure DO in the bottle after 15 minutes Measure DO in the bottle after 15 minutes (DOi)(DOi)

4.4. Closed the bottle and placed it in incubator Closed the bottle and placed it in incubator for 5 days, at temperature 20oCfor 5 days, at temperature 20oC

5.5. After 5 days, measure DO in the bottle (DOt).After 5 days, measure DO in the bottle (DOt).

BOD bottleBOD bottle

Calculation of BOD,Calculation of BOD,

WhereWhere

BODBODtt = biochemical oxygen demand, = biochemical oxygen demand, mg/Lmg/L

DODOii = initial DO of the diluted wastewater = initial DO of the diluted wastewater sample about 15 min. after preparation, sample about 15 min. after preparation,

mg/Lmg/L

DODOtt = final DO of the diluted wastewater = final DO of the diluted wastewater sample sample

after incubation for five days, mg/Lafter incubation for five days, mg/LPP = dilution factor= dilution factor

P

DODOBOD ti

t

PP = dilution factor= dilution factor

==

waterdistilled of Volume sample of Volume

sample of Volume

Why dilution is needed?Why dilution is needed?

For a valid BOD test, the final DO For a valid BOD test, the final DO should not be less than 1 mg/L. BOD should not be less than 1 mg/L. BOD test is invalid if DOt value near zero.test is invalid if DOt value near zero.

Dilution can decrease organic Dilution can decrease organic strength of the sample. By using strength of the sample. By using dilution factor, the actual value can dilution factor, the actual value can be obtained.be obtained.

Dilution of wastes:Dilution of wastes:

- By direct pipetting into 300 mL BOD - By direct pipetting into 300 mL BOD bottlebottle

BOD AnalysisBOD Analysis

In aerobic processes (OIn aerobic processes (O22 is is present), heterotrophic bacteria present), heterotrophic bacteria oxidise about 1/3 of the colloidal oxidise about 1/3 of the colloidal and dissolved organic matter to and dissolved organic matter to stable end products (COstable end products (CO22 + H + H22O) O) and convert the remaining 2/3 and convert the remaining 2/3 into new microbial cells that can into new microbial cells that can be removed from the wastewater be removed from the wastewater by settling.by settling.

The overall biological conversion The overall biological conversion proceeds sequentially, with proceeds sequentially, with oxidation of carbonaceous oxidation of carbonaceous material as the first step (known material as the first step (known as carbonaceous oxygen as carbonaceous oxygen demand):demand):

Organic matter + OOrganic matter + O22 CO CO22 + H + H22O + new cellsO + new cells

Under continuing aerobic conditions, Under continuing aerobic conditions, autotrophic bacteria then convert the autotrophic bacteria then convert the nitrogen in organic compounds to nitrogen in organic compounds to nitrates (known as nitrification nitrates (known as nitrification oxygen demand)oxygen demand)

andand

Organic-Nitrogen Ammonia-Nitrogen (decomposition)

NH3 - N + O2 Nitrate-Nitrogen (nitrification)

BOD curveBOD curve

1 2 3 4 5 6 7 8 9 10

Ultimate Carbonaceous BOD,Lo

BOD (mg/L)

Day

5-day BOD

Carbonaceous BOD

Nitrogenous BOD

The ultimate BOD (Lo) is defined as the The ultimate BOD (Lo) is defined as the maximum BOD exerted by the waste.maximum BOD exerted by the waste.

The carbonaceous oxygen demand curve The carbonaceous oxygen demand curve can be expressed mathematically ascan be expressed mathematically as

BODBODtt = Lo (1-10 = Lo (1-10-Kt-Kt))

WhereWhere BODBODtt = = biochemical oxygen demand at biochemical oxygen demand at time t, mg/Ltime t, mg/L

LoLo = = ultimate BOD, mg/Lultimate BOD, mg/Ltt = = time, daystime, daysKK = = reaction rate constant, dayreaction rate constant, day-1-1

Determination of BOD K-RateDetermination of BOD K-Rate

Time (day) BODTime (day) BODtt (mg/L) (mg/L) [time/BOD[time/BODtt]]1/31/3

11 X X [1/X] [1/X]1/31/3

22 Y Y [2/Y] [2/Y]1/31/3

33 Z Z [3/Z] [3/Z]1/31/3

From the experiment results of BOD From the experiment results of BOD for various values of t, calculate for various values of t, calculate [time/BOD[time/BODtt]]1/31/3 for each day. for each day.

Plot [t/ BODPlot [t/ BODtt]]1/31/3 versus t versus t

Determine the intercept (A) and Determine the intercept (A) and slope (B) from the plot.slope (B) from the plot.

Calculate K = 2.61 (B/A)Calculate K = 2.61 (B/A)

BOD rate constant, per dayBOD rate constant, per day

K (base 10)K (base 10)

k (base e)k (base e)

K = k/2.3K = k/2.3

Ktt

o

BODL

101

ktt

o e

BODL

1

Effects of Temperature on Effects of Temperature on Reaction Rates and Ultimate BODReaction Rates and Ultimate BOD

Reaction Rate Constant, KReaction Rate Constant, K

- most biological processes speed - most biological processes speed up as the temperature increases up as the temperature increases and slow down as the and slow down as the temperature drops. The rate of temperature drops. The rate of utilization is affected by utilization is affected by temperature temperature

the relationship for the change in the the relationship for the change in the reaction rate constant (K) with reaction rate constant (K) with temperature is expressed astemperature is expressed as

WhereWhere

KKTT = reaction rate constant at temperature = reaction rate constant at temperature T, per dayT, per day

KK2020 = reaction rate constant at 20 = reaction rate constant at 20ooC, per dayC, per day = temperature coefficient = 1.047= temperature coefficient = 1.047T = temperature of biological reaction, T = temperature of biological reaction, ooCC

)20(20

TT KK

Ultimate BOD (Lo)Ultimate BOD (Lo)

wherewhere

TTLoLo == ultimate BOD at temperature ultimate BOD at temperature T,T,

mg/Lmg/L

2020LoLo == ultimate BOD at 20ultimate BOD at 20ooC, mg/LC, mg/L

)]20(02.01[20 TLL ooT

Example:Example:

A BOD test was conducted on a domestic wastewater at 30oC. The wastewater portion added to a BOD bottle was 20 mL and the dissolved oxygen values listed below were measured.

Time (days)Time (days) DO (mg/L)DO (mg/L)

00 7.47.4

11 5.55.5

22 4.54.5

33 3.73.7

44 2.52.5

55 2.12.1

- Calculate values of BOD- Calculate values of BOD33

– Determine the BOD rate constant, Determine the BOD rate constant, KK3030

– Calculate values of BODCalculate values of BOD55 at 20 at 20ooCC

SolutionSolution

What is Chemical Oxygen Demand What is Chemical Oxygen Demand (COD)?(COD)?

DefinitionDefinition

The quantity of oxygen needed to The quantity of oxygen needed to chemically oxidize the organic chemically oxidize the organic compound in sample, converted to compound in sample, converted to carbon dioxide and water.carbon dioxide and water.

Commonly used to define the Commonly used to define the strength of industrial wastewatersstrength of industrial wastewaters

Test ProcedureTest Procedure

Add measured quantities of Add measured quantities of potassium dichromate, sulphuric acid potassium dichromate, sulphuric acid reagent containing silver sulphate, reagent containing silver sulphate, and a measured volume of sample and a measured volume of sample into a flask. into a flask.

The mixture is refluxed (vaporized The mixture is refluxed (vaporized and condensed) for two hours. The and condensed) for two hours. The oxidation of organic matter converts oxidation of organic matter converts dichromate to trivalent chromium,dichromate to trivalent chromium,

Organic matter Organic matter COCO22

++ + +

CrCr22OO772-2- HH22O O

++ + +

HH++ 2Cr2Cr33++

The mixture is titrated with The mixture is titrated with ferrous ammonium sulphate ferrous ammonium sulphate (FAS) to measure the excess (FAS) to measure the excess dichromate remaining in sample.dichromate remaining in sample.

A blank sample of distilled water A blank sample of distilled water is carried through the same COD is carried through the same COD testing procedure as the testing procedure as the wastewater sample.wastewater sample.

COD is calculated from the following equation:COD is calculated from the following equation:

Normality of Normality of Fe(NHFe(NH44))22(SO(SO44))22

Where:Where:

COD = chemical oxygen demand, mg/LCOD = chemical oxygen demand, mg/L

a = amount of ferrous ammonium sulphate a = amount of ferrous ammonium sulphate

titrant added to blank, mLtitrant added to blank, mL

bb = amount of titrant added to sample, mL = amount of titrant added to sample, mL

= volume of sample, mL= volume of sample, mL

8000 = multiplier to express COD in mg/L of oxygen8000 = multiplier to express COD in mg/L of oxygen

)(8000 baCOD

Example:Example:

The results of a COD test for raw The results of a COD test for raw wastewater (50 mL used) are wastewater (50 mL used) are given. Volumes of FAS used for given. Volumes of FAS used for blank and the sample are 24.53 blank and the sample are 24.53 mL and 12.88 mL, respectively. mL and 12.88 mL, respectively. The normality of FAS is 0.242. The normality of FAS is 0.242. Calculate the COD concentration Calculate the COD concentration for the sample.for the sample.

SolutionSolution

B. Inorganic compounds:B. Inorganic compounds:

DefinitionDefinition

When placed in water, inorganic When placed in water, inorganic compounds dissociate into compounds dissociate into electrically charged atoms electrically charged atoms referred to as ions.referred to as ions.

All atoms linked in ionic bond.All atoms linked in ionic bond.

Source(s):Source(s):May cover heavy metals, nutrients May cover heavy metals, nutrients (nitrogen and phosphorus), alkalinity, (nitrogen and phosphorus), alkalinity, chlorides, sulphur, and other inorganic chlorides, sulphur, and other inorganic pollutants.pollutants.

Effect(s):Effect(s):i.i. DiseasesDiseases - NO- NO22

-- “blue baby syndrome” “blue baby syndrome”ii.ii. AestheticAesthetic - Si- Si+4+4 turbidity turbidityiii. Disturb human activity such as the iii. Disturb human activity such as the formation of scale in boiler system formation of scale in boiler system

and and excessive usage of soapexcessive usage of soap - Ca- Ca+2+2, Mg, Mg+2+2 hardness hardness

3. Biological Characteristics3. Biological Characteristics

The principal groups of The principal groups of microorganisms found in microorganisms found in wastewater are bacteria, fungi, wastewater are bacteria, fungi, protozoa, microscopic plants and protozoa, microscopic plants and animals, and viruses. Most animals, and viruses. Most microorganisms (bacteria, microorganisms (bacteria, protozoa) are responsible and are protozoa) are responsible and are beneficial for biological treatment beneficial for biological treatment processes of wastewater.processes of wastewater.

Pathogenic organisms are usually Pathogenic organisms are usually excreted by humans from the excreted by humans from the gastrointestinal tract and discharge gastrointestinal tract and discharge to wastewater. Water-borne disease to wastewater. Water-borne disease include cholera, typhoid, paratyphoid include cholera, typhoid, paratyphoid fever, and diarrhea. The number of fever, and diarrhea. The number of pathogenic organisms in wasteaters pathogenic organisms in wasteaters is generally low in density and they is generally low in density and they are difficult to isolate and identify.are difficult to isolate and identify.

Therefore, indicator bacteria such as Therefore, indicator bacteria such as total coliform (TC) and fecal coliform total coliform (TC) and fecal coliform (FC) are used as indicator organisms.(FC) are used as indicator organisms.

6.6 Wastewater Quality Standards6.6 Wastewater Quality Standards

Regulations in Environmental Regulations in Environmental Quality (Wastewater and Quality (Wastewater and Industrial Effluent), 1978:Industrial Effluent), 1978:

Sets standards for wastewater Sets standards for wastewater discharged from wastewater discharged from wastewater treatment plant and industrial treatment plant and industrial effluenteffluent

Standard A and Standard BStandard A and Standard B

STANDARD A APPLIES

The catchment areas referred to in this regulation shall be the areas upstream of surface or above sub-surface water supply intakes, for the purpose of human consumption including drinking.

STANDARD A - UPSTREAM

BOD mg/l

SS mg/l

COD mg/l

Oil / grease - not detectable

STANDARD B - DOWNSTREAM

BOD mg/l

SS mg/l

COD mg/l

Oil / grease 10 mg/l

UPSTREAM

DOWNSTREAM

STREAM

WATER INTAKE POINTSEWAGE TREATMENT PLANT

RAW WATER IS PUMPED TO WATER TREATEMENT PLANT

DISTRIBUTION OF WATER SUPPLY