Unit‐ IIIENV  ENGG  – IIENV. ENGG.  II

Prof S S JAHAGIRDARBE (CIVIL), ME(ENV.)PhD(persuing)g

NK Orchid college of Engg. and Tech. , Solapur

A] SLUDGE TREATMENTThickening DigestionDigestionConditioningDewateringDryingDryingDisposal (Incineration)

1. ThickningReduces moisture content of sludgeTh  t   f thi k iThree types of thickening

1. Gravity thickening1. Gravity thickening2. Air floatation3. Centrifugation

Gravity ThickeningThickening

2. DigestionAerobic or anaerobic decompositionof sludgeof sludgeCan be sent to mechanical filters orsand beds

3. ConditioningConditioning improves the drainability of  digested sludge.Methods adopted –

1. Elutriation (involves passage of air to ( p gseparate particles)

2. Chemical conditioning (addition of g (coagulants)

3. Freezing etc.3 g

4. DewateringPurpose is to reduce volume of sludge andincrease concentrations of biosolids.increase concentrations of biosolids.Dewatering can be achieved on sand dryingb dbeds.

Sludge drying beds

5. Heat dryingReduces water contentT      C Temp  @ 350oC Process carried out in kilnProcess carried out in kiln.Dried sludge used as soil gconditioner

Heat drying unit

6. IncinerationCombustion of sludgeTemp @ 650oC to 750oC  Residual ash is send to landfills

IncineratorIncinerator

B] Anaerobic DigestionConsists of decomposition of sludge from settling tankssludge from settling tanks.Two types of digestersTwo types of digesters

i]  Standard rate or conventionalIi] High rate digester

The process of digestion The process has now been described by the following four steps: g pHydrolysis: large polymers are broken d  b    down by enzymes. Fermentation: Acidogenic fermentations are most important, acetate is the main end product. Volatile acetate is the main end product. Volatile fatty acids are also produced along with carbon dio ide and h drogen  carbon dioxide and hydrogen. 

Acetogenesis: Breakdown of Acetogenesis: Breakdown of volatile acids to acetate and hydrogen. 

Methanogenesis: Acetate  Methanogenesis: Acetate, formaldehyde, hydrogen and carbon dioxide are converted to 

th   d  t  methane and water. 

Cross section of digester

Anaerobic Anaerobic digesters

A bi  Anaerobic digester

Stratification in conventional digesterStratification in conventional digester

T t f di tTwo types of digesters

Two stage ‐ high rate digesterTwo stage ‐ high rate digester

Sludge drying Sludge drying beds

Sludge drying beds

C] DISPOSAL OF DIGESTED SLUDGESpreading on farm landDumping ( in abandoned quarries)Dumping ( in abandoned quarries)Land filling ( Sanitary)Sl d  l iSludge lagooningCompostingp gDisposing in Inland water bodies or Sea  Sea. 

Disposal on l dland‐1

Disposal on l dland‐2

Disposal in ffarms

Disposal into the sea

Sludge L iLagooning

Sludge lagoons

What is sludge digestion? Explain anaerobic digestion. (Nov 2010, 8 marks)Write short note onWrite short note on1. Anaerobic digestion process. (Nov 2009, 6 marks)2. Sludge drying beds (May 2008, 6 marks)

Explain different methods of sludge disposal. (May 2009, 8 marks)E l i l bi di i h k h (M 2008 6Explain low rate anaerobic digester with a neat sketch. (May 2008, 6 marks)Enumerate the methods of sludge dewatering. Explain any one in detail.

(May 2008, 6 marks)Describe anaerobic sludge digester with neat sketch. Also explain various stages ofDescribe anaerobic sludge digester with neat sketch. Also explain various stages of anaerobic digestion of sludge. (May 2008, 8 marks)St t bj ti f l d t t t E t th th d f l d di lState objectives of sludge treatment. Enumerate the methods of sludge disposal.

(May 2007,5 marks )