Sewage Treatment plan Enviornment epidemiology

1. SEWAGE TREATMENT PLANT
PRESENTED BY
DR.ATHIRA MENON
MPH ,JIPMER

2. SEWAGE
Sewage is waste water from a community, containing solid and liquid excreta, derived
from houses, street and yard washings, factories and industries..(Park 25th ed)
Dry Weather Flow:The average amount of sewage which flows through the sewerage
system in 24 hours

3. Health aspects:
a) unsightliness and unpleasant odours.
b) breeding of flies and mosquitoes
c) soil and water pollution
d) contamination of food
e) increase in the incidence of disease

4. Composition of Sewage
a) 99.9% Water+ 0.1% solids (organic/inorganic in suspension/solution).
b) 1g faeces: 1000 million E. coli
10-100 million faecal streptococci
1 to 10 million Cl. perfringens spores

5. Biological Oxygen Demand Chemical Oxygen Demand
dissolved oxygen required by aerobic
organisms to breakdown organic
materials, during a specified period days,
at a specified temperature.
oxygen equivalent of that portion of
organic matter in a sample which is
susceptible to oxidation by strong
chemical oxidizer
Slow : five days required Fast: takes just two hours to complete
300 mg/L and above : "strong“
100 mg/L: "weak"
*COD and BOD can be indicated as mg/L or ppm (parts per million).
Expression of strength of sewage

6. Suspended Solids :
a) The amount of suspended solids in domestic sewage
b) vary from 100 to 500 mg/L
c) 100 mg/L, the sewage is said to be weak : if the amount is 500 mg/L the sewage is said
to be strong.

7. Decomposition of organic matter
In sewage, decomposition of organic matter takes place by 2 ways:
1. Aerobic: Most efficient method
Require continuous supply of free dissolved oxygen
Organic matter Bacteria, fungi & protozoa CO2, H2O, Ammonia,
nitrates & sulphate
2. Anaerobic: Effective when sewage is highly concentrated with plenty of solids
Slower Extremely complex mechanism
Methane, ammonia, CO2 and H2

8. MODERN SEWAGE TREATMENT

9. Treatment divided into 2 stages:
1.Primary 2.Secondary
screening and sedimentation Aerobic oxidation
& Anaerobic digestion

10. PRIMARY TREATMENT
1 . SCREENING
a) Sewage passed through a metal screen
b) Vertical or inclined steel bars usually set 5 cm (2 in) apart
c) Necessary to prevent clogging
d) Fixed type and moving type.
e) The screenings are removed from time to time and disposed off by trenching
or burial.

11. 2 . GRIT CHAMBER
a) Passed through grit chamber or detritus chamber.
b) 10 to 20 metres in length
c) Two important types of Grit Chambers
(i) Horizontal rectangular flow
(ii) Aerated Grit Chamber.
d) Allow the settlement of grits sand, gravel and other heavy solid
materials

12. e) The grit is removed periodically or continuously, and
disposed off by plain dumping or trenching.
f) Grit chamber
i. prevents unnecessary abrasion and wear of mechanical equipment
ii. grit deposition in pipelines and channels
iii. accumulation of grit in anaerobic digesters and aeration basins.

13. 3 . Primary sedimentation
a) flow very slowly at a velocity of 1- 2 feet per minute
b) spends about 6-8 hours in the tank
c) purification by sedimentation of suspended matter.
d) 50-70% solids settle down
e) reduction of 30 to 40 % of coliform organisms

14. g) sludge is removed mechanically
h) Complex organic matter broken down to
simpler soluble substances and ammonia.
i) Fats and grease rise on the surface, Scum is
removed

15. SECONDARY TREATMENT
1.Aeorobic Oxidation
a) Trickling filter method
b) Activated sludge process

16. a) TRICKLING FILTER METHOD

18. b) ACTIVATED SLUDGE PROCESS
I. The heart, Aeration tank
II. Effluent mixed with sludge from final settling tank (activated sludge)
III. Activated sludge: effluent : 20-30%
IV. Mixture in aeration chamber for 6-8 hrs.
V. Aeration by Mechanical agitation or by compressed air from bottom
(diffused aeration)
VI. Organic matter CO2, nitrates and water

20. 2. Secondary sedimentation
I. It is detained for 2-3 hours.
II. 'Aerated sludge’ or activated sludge
III. It is a valuable manure, if dehydrated.
IV. Rest pumped into the sludge digestion tanks
for treatment an disposal.

21. Sludge digestion
I. One million gallons of sewage produces 15- 20 tons of sludge.
II. methods of sludge disposal :
a) Digestion:
1. incubated under favourable conditions of temperature and ph
2. anaerobic auto-digestion
3. complex solid water, CO2, methane and ammonia.
4. Takes 3-4 weeks to complete.
5. In-offensive, sticky and tarry mud, dry readily & form excellent manure

22. b) Sea disposal: By pumping into sea
c) Land: composting with town refuse

23. Disposal of effluent
1. By dilution: Rivers and streams
a) Diluting capacity depends on dissolved oxygen contents of receiving bodies.
b) Effluent should not have more than 30 mg/l suspended solids and BOD should not
exceeds 20 mg/l ( 8:1 dilution)----Royal commission of England 5th report.
2. Disposal on land: irrigation

24. S. No. Parameter
Required
Standards
1 pH 6.5-8.5
2 BOD(5th day) <10mg/l
3 COD <50mg/l
4 Suspended Solids <10mg/l
5
Ammonical
Nitrogen
<5mg/l
6 Total Nitrogen <5mg/l
7 Fecal Coliform <100 MPN/100 ml
Treated Sewage Standards
*CPCB

25. • There are 1,631 STPs (including proposed STPs) with a total capacity of
36,668MLD covering 35 States/UTs*.
• Out of 1,631 STPs, 1,093 STPs are operational, 102 are Non-operational,
274 are under construction and 162 STPs are proposed for construction.
• Sewage generation from urban centers estimated as 72,368 MLD.
STPs in India

26. *CPCB

27. Estimated sewage generation for the State of Puducherry is 161 MLD and total treatment
capacity (including proposed) is 59 MLD.
STPs in Puducherry