environmental engineering - ii r2013

1. DISPOSAL OF SEWAGE AND
SLUDGE MANAGEMENT.
BY
SATHYAN S

2. LAND DISPOSAL:- (219)
• The sewage effluent is generally disposed of by applying it on land. the percolating water may
either join the water table or is collected below by system of under drains.This method can then
be used for irrigation.
• REFER TABLE 8.8 &8.9
• REFER TABLE 8.7
QUALITY STANDARDS:-(222)
DOSAGE(220) METHODS:-
EFFLUENT IRRIGATION
SEWAGE FARMING

3. CONDITION TO ADOPT THIS METHOD
• WHEN NATURAL RIVERS OR WATER COURSE IS NOT AVAILABLE.
• WHEN IRRIGATION WATER IS SCARCELY AVAILABLE.
• WHEN LARGE AREA OF OPEN LAND IS AVAILABLE.
• AREAS HAVING LOW RAINFALL RATE
• THE SOIL IN THE LAND MUST BE POROUS SUCH AS SANDY LOAMY OR ALLUVIAL
SOIL.
• AREAS WITH LOW WATER TABLE AND HIGH PERCOLATION RATE.

5. EFFLUENT IRRIGATION
• CHIEF CONSIDERATION IS
SUCCESSFUL DISPOSAL OF SEWAGE.
• UNDER DRAINS ARE USED
• POROUS TILE PIPE 15-20 CM DIA
SEWAGE FARMING
• CHIEF CONSIDERATION IS
SUCCESSFUL GROWING OF CROPS.
• TO INCREASE THE FERTILITY OF SOIL .
• PRE TREATMENT OF SEWAGE IS
NECESSARY.

6. METHODS
SURFACE IRRIGATION .
a) FREE FLOODING.
b) CHECK FLOODING.
c) BORDER FLOODING.
d) BASIN FLOODING.
e) FURROW IRRIGATION METHOD
SUB-SURFACE IRRIGATION
SPRINKLER ARE SPRAY IRRIGATION.

7. SEWAGE SICKNESS

8. SEWAGE SICKNESS
WHEN THE SEWAGE IS CONTINUOUSLY APPLIED THE SOLID IN THE SEWAGE GETS
CLOGGED AT THE VOIDS IN THE SOIL AND CREATES ANAEROBIC DECOMPOSITION
THUS CREATING FOUL GAS(H2S,CO2,METHANE)
TO PREVENT:-
• PRIMARY TREATMENT OF SEWAGE.
• CHOICE OF LAND.
• UNDER DRAINAGE OF SOIL.
• GIVING REST TO THE LAND.
• ROTATION OF CROPS.
• APPLYING SHALLOW DEPTH.
• PLOUGHING AND BREAKING THE SOIL AND EXPOSING IT TO ATMOSPHERE.

9. SLUDGE CHARACTERIZATION
1.RAW SLUDGE:-
Deposited in a primary sedimentation tank.
It is odorous, contains highly putrescible
organic matter and thus very objectionable.
Moisture content>95%
2.SECONDARY SLUDGE:-
• Deposited in a secondary clarifier.
• It is less objectionable.
• Moisture content 1.trickling filter96%-98%
2.ASTP 98%-99%
SLUDGE THICKENING:-
• The process of reducing the moisture content of the sludge.
• By using sludge thickener or concentrator unit
1.Gravity thickeners
2.Flotation thickeners
3.Centrifugal thickeners

10. SLUDGE DIGESTION
why?

11. SLUDGE DIGESTION
• Contains lot of putrescible organic matter. It may decompose and produces
foul gases and lot of nuisance, pollution and health hazards.
• So it is stabilized by decomposing the organic matter under controlled
anaerobic condition and then disposed of suitably after drying on drying
bed.
• The process of stabilization is called sludge digestion process and the tank
is called sludge digestion tank.

12. IN A SLUDGE DIGESTION PROCESS THE SLUDGE GETS
BROKEN INTO FOLLOWING FORMS.
Digested sludge:-
• Stable humus like solid matter-tary black colour-reduction of 13rd volume of undigested sludge-
quality is better-free of pathogenic bacteria-it may contain cysts eggs of bacteria, protozoa and
worms.
Supernatant liquor:-
• It includes the liquefied and finely divided solid matters and having high B.O.D of 3000ppm.
Gases of decomposition:-
• Methane,CO2, and inert gases like N2 and H2S are evolved.
• The amount of gas produced is equal to 0.9cu.m/kg of volatile solids reduced in digestion.
The digested sludge is dewatered dried up and used as a fertilizer .gases are used as
a fuel .The supernatant liquor contains 1500-3000ppm of suspended solid hence it is retreated at
treatment plant along raw sewage.

13. STAGES IN SLUDGE DIGESTION
1. ACID FERMENTATION .
2. ACID REGRESSION.
3. ALKALINE FERMENTAION.

14. ACID FERMENTATION /ACID PRODUCTION STAGE:-
• The fresh sewage-sludge begins to be acted upon by anaerobic and facultative bacteria, called
acid formers.
• These organisms solubilize the organic solids through hydrolysis.
• The soluble products are fermented to volatile acids and organic alcohols of low molecular
weight like propionic acid, acetic acid, etc. gases like methane, CO2 and H2S are evolved.
• Intensive acid production makes the sludge highly acidic, and lowers the pH value to >6.
• High putrefactive odours are evolved and continues for 15 days and B.O.D also get increases to
some extent.

15. ACID REGRESSION STAGE
• The volatile organic acids and nitrogenous compounds of the first stage, are attacked by the
bacteria, so as to form acid carbonates and ammonium compounds.
• The decomposed sludge has very offensive odour, and its pH value rises to about 6.8.
• The decomposed sludge also entraps the gases of decomposition, becomes foamy and rises to
surface to form scum.
• This stage continuous for about 3 months or so @21°C .
• B.O.D even increases high.

16. ALKALINE FERMENTATION STAGE
• In this stage more resistant materials like proteins and organic acids are attacked and broken up
by anaerobic bacteria, called methane formers, into simple substances like Ammonia and gases.
• during this stage the liquid separates out from solid and the digested sludge is formed.
• The sludge granular and stable, and does not give offensive odour (it has musty earthy odour).
• The digested sludge is collected at the bottom of the digested tank and called ripened sludge.
• The digested sludge is alkaline in nature, and pHvalue rise about 7.5 .
• Large volume of methane gas along with small amount of CO2 and nitrogen are evolved.
• This stage continuous for about 1 months or so @21°C.
• The B.O.D of the sludge rapidly falls down.

17. ANY DOUBTS ?

18. FACTORS AFFECTING SLUDGE DIGESTION AND
THEIR CONTROL:
• TEMPERATURE.
• pH VALUE .
• SEEDING WITH DIGESTED SLUDGE .
• MIXING AND STIRRING OF RAW SLUDGE WITH DIGESTED SLUDGE.

19. TEMPERATURE
• ZONE OF THERMOPHILIC DIGESTION
• ZONE OF MESOPHILIC DIGESTION

20. ZONE OF THERMOPHILIC
DIGESTION
• Digestion is done by thermophilic organisms.
• temperature = 40-60 optimum 54
• Digestion period 10-15 days.
• Not suits for sewage sludge because of odours
and other operational difficulties.
ZONE OF MESOPHILIC
DIGESTION
• MESOPHILIC ORGANISM
• temperature = 25-40 optimum 29
• Digestion period 30 days.
• It depends upon local climatic conditions.

21. pHvalue.
• If the methane formers are not working properly ,an accumulation of volatile acids may occur,
causing the pH value to drop below 5.
• Acidity increases with 1.with the over dosing of raw sludge: 2.with the over withdrawal of
digested sludge: 3.with sudden admission of industrial waste.
• The remedy is to add hydrated lime in doses of 2.3-4.5kg.per 1000persons to the raw sludge.
• The weight of raw sludge to be added daily, should also be limited to 3-5% of the weight of
digested sludge removed.
SEEDING WITH DIGESTED SLUDGE

22. MIXING AND STIRRING OF RAW SLUDGE WITH
DIGESTED SLUDGE
• PROPER MIXING BY METHOD OF AGITATION
• STIRRING BY SLOW MOVING MECHANICAL DEVICE OR PASSING GASES FROM
BOTTOM TO TOP
• EXCESSIVE STIRRING MAY KILL BACTERIA
• IN COLD COUNTRIES STIRRING MAY HELP THE DIGESTION TANK TO ATTAIN
OPTIMUM MESOPHILIC TEMPERATURE BY TRANSMITTING HEAT FROM HEATING
COIL TO THE TANK:

23. SLUDGE DIGESTION TANK OR DIGESTORS

24. C U TOMORROW