Waste water engineering

Sludge Treatment

🔸 Sludge Treatment is aimed to achieve volume reduction & strength reduction.

🔸 Volume & strength reduction of sludges are achieved by

👉 sludge Thickening :- By concentrating the sludge by expulsion of water.

👉 Sludge digestion :- By anaerobic decomposition to reduce strength.

👉 Sludge conditioning :- To improve drainblility of sludges

👉 Sludge dewatering and drying :- Remove remaining moisture from sludge.

♦️ Strength reduction

👉 Strength reduction of sludge i.e. BOD removal is carried out by anaerobic decomposition known sludge digestion.

👉 Sludge digestion occur in two stages i.e. Acids fermentation and Methane fermentation.

🔸 Sludge digester

👉 Sludge are anaerobically digested by using a reactor known as sludge digester.

👉 Diameter of tank :- 3 to 60m

👉 Height of tank :- 6 to 12m

👉 Digestion period depends upon type of microorganisms

~ mesophilic organisms :- 30 to 60 days (Temperature 20℃ - 40℃)

~ Thermophilic organisms :- 15 to 25 days (Temperature 45℃ - 60℃)

👉 Gas production

~ 70% Methane

~ 30% Carbon dioxide

👉 Calorific value (energy content) :- 5200 to 5800 kcal/m3 of CH4

🔸 Digested sludge are dewatered and dried by using solar drying beds known as sludge drying bed.

🔸 Elutriation :- Washing of sludge before dewatering by mechanical driers.

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