1. Characteristics of wastewater
Prepared By Brian Patel
Enrollment No

2. Introduction Two types of wastewater Domestic wastewater (Sewage)
Industrial waste water
Wide variation in quality of Industrial waste water
Less variation in the characteristics of sewage

3. Composition of Sewage
Contain organic & Inorganic matter, some gases & living organisms (mainly micro-organisms)
Organic & Inorganic matter may be in suspended, colloidal & dissolved form.
Organic matter include
Carbohydrate like cellulose, starch, Sugar, cotton etc.
Fats & Oil received from kitchen, garbage
Nitrogeneous compound like protein & their decomposed product, including waste from urea, animal, fatty acid etc.
Inorganic matter consist of salt & mineral like sand, gravel, dissolved salts, chlorides, sulphates etc.

4. Decomposition of Sewage
Chemical process
Biological Process
Two type of Biological Process
Aerobic Biological Process
COHNS + Bacteria + O2  CO2 + H2O +Bacteria + Energy
Anaerobic Biological Process
In the absence of Oxygen & end product is Methane, H2S & ammonia.

5. Characteristics of Sewage
Physical Characteristics
Colour :
Fresh sewage brown & yellowish colour
With the passage of time it become septic -black colour
Odour
Fresh sewage not offensive odour
Stale sewage – offensive odour ( All the oxygen disappeared from the sewage)

6. Temperature
Higher temperature –biological Activity more means demand of oxygen more but solubility of DO at higher temp. decrease
Turbidity
Due to suspended solids
Measured by Jackson turbiditymeter
Nephelometric turbidity meter

7. Chemical Characteristics
Solids :
Sewage contain 99.9 % sewage & 0.1 % solid
Solids may be organic or inorganic
T.S. = S.S + D.S.
45% organic solids & 55 % inorganic solids
pH :
pH > 7 Alkalinity
pH< 7 Acidic
pH = 7 Neutral
Fresh sewage is alkaline, with the passage of time acidic
pH determination is important in biological treatment, Chemical coagulation, chlorination(Disinfection)

8. Nitrogen Compound
One or more of the following form
Free amonia – First stage of decomposition
Organic Nitrogen – Total Organic nitrogen
Nitrite – Partly decomposition of organic matter
Nitrate – fully decomposition of organic matter
Chloride content
Main sources in sewage kitchen waste, human feces & urinary discharge
Industry like ice-cream plant, meat salting etc.

9. Fat, Oil & grease
Main sources – from garage, kitchen of hotel & restaurant, discharge of animal & vegetable matter
Major problem in biological process – due to scum on the surface & affect oxygen diffusion
Toxic Compound
Copper, lead, silver, Chromium, Arsenic, Phenol, boron, Cyanide etc are toxic compound
Major source – Industrial wastewater
Affect biological treatment

10. Sulphide, sulphate & Hydrogen Sulphide Gases
In Aerobic decomposition
Sulphur  Sulphide  Sulphate
In Anaerobic Decomposition
Sulphur  Sulphide with H2S + CH4
Dissolved Oxygen
Amount of oxygen dissolve in water
For the survival of Dissolve oxygen minimum 4 mg/lit dissolve oxygen is essential
It prevent the formation of obnoxious odour
Factor affect D.O.
Temperature
TDS of water

11. BOD (Biochemical Oxygen Demand) Two type of organic matter
Biodegradeable & Non biodegradable
BOD means amount of oxygen required by bacteria for the decomposition of biodegradable organic matter under aerobic condition
Widely used to determine the pollution strength of domestic & industrial waste
Useful in the design of wastewater treatment plant
First stage BOD- related to the carbonaceous organic matter
Second stage BOD – Related to the nitrogeneous matter
Measured for 5 days at 20 degree centigrate or 3 day 27 degree centigrate
degrr

12. Equation for the first stage BOD
Yt = L [1- (10)-kdt]
(Kd)t = (Kd)20.[1.047]t-20
Limitation of BOD
Measure only biodegradable organic matter
Very long duration i.e. 5 days
Pretreatment is needed if toxic
COD (Chemical Oxygen Demand)
Measure both biodegradable & Non biodegradable organic matter
Takes 3 hrs
Value is always higher than BOD

13. BOD/COD ratio
If BOD/COD > 0.6 biological treatment is feasible.
If BOD/COD between 0.3 to 0.6 acclimatization is essential
If BOD/COD is < 0.3 Biological treatment is not possible
Relative Stability
S = 100( ) t20
S = 100( ) t37

14. Characteristics of Industrial wastewater
Organic substance
Inorganic substance
Acid & alkalies
Toxic Substances
Color producing substance
Oil

15. Treatment of Industrial waste water
Equalization – to get uniform quality of wastewater
Neutralization- Neutralize excess acidity or alkalinity
Physical treatment
Sedimentation- For the removal of settalable solid
Biological Treatment
If BOD/COD > 0.6 highly biodegradable
If BOD/COD < 0.3 Biological treatment is not feasible
If BOD/COD between 0.3 to 0.6 acclimatization is needed for the biological treatment
Chemical Treatment
Chemical coagulation
Adsorption
Chemical Oxidation

16. Disposal of Sewage Disposal of sewage by
Natural method – Dilution, on Land
Artificial Method
Screening & detritus removal
Sedimentation with or without chemical
Biological Treatment
Types of receiving water body
Ocean or Sea – More dilution factor, high TDS
Lakes – Stagnant water
Perennial river- Flowing water
Estuaries

17. Self Purification of Natural Stream
Normal Biological cycle in stream

18. Natural force Dilution – Higher dilution ratio– Aerobic condition exit
Sedimentation – Concentration of wastewater get reduced
Sunlight – stimulate the growth of algue
Oxidation – continue till complete oxidation of organic matter take place.
Most important action responsible for effecting self purification

19. Factors Affecting Self Purification
Temperature
Velocity
Rate of re-aeration
Amount & type of organic matter
Available initial DO
Types of micro-organism present

20. Factors Affecting Self Purification
Temperature - Higher temp. biological activity more but solubility of dissolved oxygen less
Velocity – if high- Oxygen diffusion rapidly
if low – oxygen diffusion slowly
Rate of re-aeration – Greater the rate, rapid the self purification
Amount & type of organic matter – more biodegradable organic matter , more oxygen demand- D.O. decrease

21. Available initial DO – Greater at the time of discharge earlier the self purification
Types of micro-organism present – Algue present with bacteria – Oxygen added by algue

22. Zone of Pollution in River or Stream
Zone of degardation
Zone of Active Decomposition
Zone of recovery
Zone of clear water

23. Zone of Pollution

24. Oxygen Sag Curve

25. Oxygen Sag Curve Deoxygenation & Reoxygenation occur simultaneously
If deoxygenation > Reoxygenation  Oxygen deficit incresing
If deoxygenation = Reoxygenation Critical Point
If deoxygenation < Reoxygenation  Oxygen deficit decreasing & ultimately goes to Zero

26. Sewage Sickness
Clogging of soil pore
Measure to prevent sewage sickness
Primary treatment of sewage – Sedimentation
Choice of land – Sandy soil
Giving rest to the land
Rotation of crop
Applying shallow depth