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THE GROUP MEMBERS ARE,
TESSY S ALEX (UR12CE115)
ANJALI KUMARI (UR12CE013)
SURENDAR N (UR12CE111)
SUJITH ALEN S (UR12CE110)
JAESON ANTONY A (UR12CE046)
UNIT – IV Sewage Disposal and Sludge ManagementMethods of sewage disposal, sewage farming
Sewage sickness and its preventive measures
Final products in Sludge Digester : stagesFactors affecting sludge digestion and controlDesign of sludge digestion tank
Sludge thickening
Sludge conditioning and dewatering
Final disposal of digested sludge
Bioremediation: constructed wetlands, stabilization pond
Self purification and oxygen sag curveAnalysis
Secondary
OrganicInorganic
Wastewater PreTreatment
RockGritPlasticEtc.
PrimarySedimentation Tank
SettleableSuspendedDissolved
SuspendedDissolved
SecondarySedimentation Tank
Effluent
Digester
Sludge
SludgeGas
Digested SludgeRecycled Water(Supernatant)
(Stabilized)
Pre treatment
• Screening-for removal of objects Eg: wood logs ,cloths, chappals etc….
• Grit Chamber For removing high density inorganic particles by discrete settling principle Eg: Removal of sand, silt etc….
• Primary settling tank For removal of low density organic
solids
Post treatment
• Secondary settling tank-for biomass settling.
• Sludge from primary and secondary settling tanks is sent to sludge treatment unit.
[ ODOURLESS , DISPOSABLE IN NATURE WITHOUT POLLUTING OR
HARMING ]
SLUDGE IS STABILISED BY DECOMPOSING THE ORGANIC MATTER UNDER CONTROLLED
ANAEROBIC CONDITION.[The decomposition of organic and inorganic matter in the absence of molecular oxygen.]
THE MAIN TOPICS TO BE DISCUSSED IN THIS PRESENTATION ARE,
(A) FINAL PRODUCTS IN SLUDGE DIGESTER.
(B) STAGES IN SLUDGE DIGESTION PROCESS.
&(C) FACTORS AFFECTING SLUDGE DIGESTION AND THEIR CONTROL.
AS DAYS PASS SLUDGE BREAKS INTO 3 COMPONENTS.
STABILISED SLUDGE/ DIGESTED SLUDGE/
RIPENED SLUDGE
SLUDGE BREAKS 2.SUPERNATANT LIQUOR
3. DECOMPOSITION OF GASES
1.
1. DIGESTED SLUDGE
• HUMUS LIKE SOLID MATTER.
• TARY BLACK IN COLOR.
• REDUCED MOISTURE CONTENT.
• QUALITY IS MUCH BETTER THAN UNDIGESTED SLUDGE.
• FREE OF PATHOGENIC BACTERIA.
3. DECOMPOSITION OF GASES
• METHANE (65 – 75%)
• CARBON DIOXIDE (30%)
• NITROGEN
• HYDROGEN SULPHIDE.
STAGES
1. ACID FERMENTATION/ACID PRODUCTION STAGE
2.ACID REGRESSION
3. ALKALINE FERMENTATION
STABILISED SLUDGE /DIGESTED SLUDGERIPENED SLUDGE+ SUPERNATANT LIQUOR + METHANE GAS
1 . ACID FERMENTATION / ACID PRODUCTION STAGE
FRESH SEWAGE SLUDGE
ANAEROBIC +
FACULTATIVE BACTERIA HYDROLYSIS
SOLUBLE PRODUCTS FERMENT
VOLATILE ACIDS ORGANIC ALCOHOLS OF LOW MOLECULAR WEIGHT LIKE PROPIONIC
ACID AND ACETIC ACID
ACID FORMERS / ACIDOGENS
GASES LIKE &
2 . ACID REGRESSION
• INTERMEDIATE STAGE.• VOLATILE ORGANIC ACIDS + NITROGENEOUS COMPOUNDS (ATTACKED BY BACTERIA)
ACID CARBONATES + AMMONIA COMPOUNDS +HYDROGEN SULPHIDE + CARBO DIOXIDE
FIRST STAGE
• HIGHLY OFFENSIVE ODOUR ARE EVOLVED FOR 3MONTHS.
• PH INCREASES TO ABOUT 6.8. HOW?• DECOMPOSED SLUDGE ENTRAPS THE GASES
OF DECOMPOSITION. IT BECOMES FOAMY AND RISES TO THE SURFACE TO FORM SCUM.
• BOD REMAIN HIGH.
3. ALKALINE FERMENTATION
• FINAL STAGE OF SLUDGE DIGESTION.• PROTIENS
+ ORGANIC ACIDS
(ATTACKED BY ANAEROBIC BACTERIA CALLED METHANE FORMERS / STRICT ANAEROBER)
AMMONIA + ORGANIC ACIDS + GASES
HIGH RESISTANT MATERIALS
• THE LIQUID SEPARATES OUT FROM SOLIDS TO FORM DIGESTED SLUDGE.
• THE SLUDGE IS GRANULAR AND STABLE .
• DOES NOT GIVE OFFENSIVE SMELL.
• IT HAS MUSTY EARTHY ODOUR.
• DIGESTED SLUDGE IS COLLECTED AT THE BOTTOM OF THE DIGESTION TANK AND IS CALLED RIPENED SLUDGE.
• IT IS ALKALINE IN NATURE.
• PH ≥ 7
• METHANE (60 % – 75%), (30%),
• THIS STAGE EXTENTS TO A PERIOD OF 1 MONTH.
• BOD IS REDUCED.
CONCLUSION OF STAGES IN THE SLUDGE DIGESTION PROCESS(NATURALLY)
• 4 MONTHS ARE REQUIRED FOR THE COMPLETE PROCESS OF SLUDGE DIGESTION TO TAKE PLACE UNDER NATURAL , UNCONTROLLED CONDITION AT ABOUT .
• DIGESTION DEPENDS ON MANY FACTORS LIKE TEMPERATURE .
• IF THE FACTORS AFFECTING SLUDGE DIGESTION ARE CONTROLLED , QUICKER AND EFFECTIVE DIGESTION CAN BE DONE.
THE IMPORTANT FACTORS AFFECTING SLUDGE DIGESTION ARE ,
1 . TEMPERATURE
2 . PH VALUE
3 . SEEDING WITH DIGESTED SLUDGE AND
4 . MIXING AND STIRRING OF THE RAW SLUDGE WITH DIGESTED SLUDGE.
THE MINOR FACTORS ARE,
• QUALITY OF WATER SUPPLIED.
• PRESENCE OF – COPPER, FLUORIDES, RADIO ACTIVE SUBSTANCES.
1. TEMPERATURE
• HIGHER THE TEMPERATURE , HIGHER IS THE RATE OF DIGESTION .
• THE 2 DISTINCT TEMPERATURE ZONES ARE, - (a) ZONE OF THERMOPHILIC DIGESTION. - (b) ZONE OF MESOPHILIC DIGESTION.
(a) ZONE OF THERMOPHILIC DIGESTION
• THERMOPHILIC ORGANISMS MEAN HEAT LOVING ORGANISMS.
• -
• OPTIMUM THERMOPHILIC TEMPERATURE =
• DIGESTION PERIOD – 10 TO 15 DAYS
• IT IS NOT PREFFERED BECAUSE OF ODOUR AND OPERATIONAL DIFFICULTIES.
(b) ZONE OF MESOPHILIC DIGESTION
• OPTIMUM MESOPHILIC TEMPERATURE =
• DIGESTION PERIOD – 30 DAYS
• EXTERNAL HEATING DEVICES IS FIXED IN DIGESTION TANK TO CONTROL TEMPERATURE.
2. PH VALUE
• VOLATILE ACIDS METHANE FORMERS METHANE GAS
• IF METHANE FORMERS WERE NOT PRESENT IN THE SLUDGE DIGESTER ,PH VALUE WILL GO BELOW 5 . IT WILL INCREASE THE ACIDITY, AND THUS SUPPRESS FURTHER BACTERIAL ACTION.
• IN INITIAL STAGE (ACID FERMENTATION/ACID PRODUCTION STAGE) PH VALUE OF 6.5 HAVE TO BE MAINTAINED.
• SO THAT IN FINAL STAGE (ALKALINE FERMENTATION STAGE) PH VALUE OF 7.2 – 7.4 WILL BE MAINTAINED.
• ACIDITY INCREASES DUE TO
- OVERDOSING OF RAW SLUDGE .
- OVERWITHDRAWAL OF DIGESTED SLUDGE.
• REMEDY
- ADD HYDRATED LIME (2.3- 4.5 ) IN RAW SLUDGE.
• FOR THE MAINTENANCE OF OPTIMUM VALUE OF PH
- WEIGHT OF RAW SLUDGE TO BE ADDED SHOULD BE 2 - 3% WEIGHT OF DIGESTED SLUDGE WHICH IS REMOVING FROM
THE SLUDGE DIGESTER.
SEEDING WITH THE SLUDGE DIGESTER
WHAT IS SEEDING ?*A SLUDGE DIGESTION TANK .
*WHEN FIRST PUT IN OPERATION –
*DIGESTED SLUDGE FROM OLD SLUDGE DIGESTER IS KEPT IN IT FOR SOME DAYS .
• WITHOUT SEEDING , IT MAY TAKE A FEW MONTHS TO GET A TANK TO OPERATE PROPERLY.
• PROPER SEEDING CAN GIVE GOOD RESULTS QUICKLY.
MIXING AND STIRRING OF THE RAW SLUDGE WITH THE DIGESTED SLUDGE• RAW SLUDGE + DIGESTED SLUDGE
(MIX WELL)
HOMOGENEOUS MIXTURE
*HELPS IN DECOMPOSITION OF ORGANIC MATTER QUICKLY.
*MIXING IS DONE IN SLUDGE DIGESTOR USING AGITATOR / OTHER DEVICES.
*THIS REDUCES SCUM AND INCREASES THE PRODUCTION OF GAS.
*EXCESSIVE STIRRING WILL KILL USEFUL BACTERIAS.