Question

a) Due to faulty functioning of the secondary settling tank (SST), some VSS is washed out with the effluent. Highlight possible effects of VSS washout. b) Activated Sludge Process is operating with . of 11.76 days and F/M of 0.3 d. For Y of 0.5 and k, of 0.05 d', estimate the effluent BOD5 if s, is 200 mg/L. c) The Activated Sludge Process of Question b is designed for effluent BOD5 of 20 mg/l. However, due to faulty functioning of SST, some VSS is escaping with the treated effluent. Due to this, BOD5 of the effluent is estimated as 28 mg/L. Considering that 66% of VSS is biodegradable, estimate the VSS escaping in the effluent d) Why biogas composition usually is 55% methane?

Answer 1

Ans(a) : The secondary settling tank is being used for the basins Or the clarifiers at the time of waste water treatment process. It allows various microorganisms and the other different solids to settle down at the time of treatment and so it is known as secondary settling tank. The sludge that is produced is also raw in nature and as if it is said that some amount of Volatile Suspended Solid is being washed out. There will be some effects if the solids are being washed out with the effluents and these are being listed below :

• The quality of water provided will be less and hence the functioning is also known as faulty.
• Aeration rate is effected and is decreased.
• Retention time of the tank is being increased and then then the amount of sludge formation will be high.
• The stirring speed of the tank will be reduced due to less amount of VSS and the temperature at the time of operating will also be affected.

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