waste water engineering
♦️ Activated sludge process (ASP)
🔸 Activated sludge :- It is sludge containing large concentration of highly active aerobic micro organisms.
🔸 ASP works on the principle of suspended culture system.
🔸 Components of ASP
A) Primary settling tank :-
~ Detention time - 1.5 to 2 hr.
B) Aeration tank :-
~ Detention time- 4 to 8 hr
C) Secondary sedimentation tank :-
~ Detention time- 1.5 to 2 hr.
D) Sludge thickener & sludge digestion tank
🔸 Activated sludge process parameters
1. Hydraulic retention time (HRT) :- It is the ratio of volume of tank to the rate of sewage flow into the tank.
2. Volumetric loading rate or BOD loading rate :- It is ratio of BOD applied to unit volume of aeration tank.
3. Food to microorganism ratio (F/M) :- It is defined as the ratio of kg of BOD applied per day to kg of MLSS in aeration tank.
4. Mean cell residence time (Sludge age) :- It is defined as mass of cell in the reactors to mass of cells wasted per day.
5. Sludge volume index :- It is the volume occupied in ml by 1 gm MLSS after settling for 30 minute from 1L sewage sample is known as sludge volume index.
🔸 Usual values adpoted
👉 F/M :- 0.4 to 0.3
👉 MCRT :- 5 to 15 days
👉 Efficiency :- 85 - 95%
👉 Recycling ratio :- 0.25 - 0.5
🔸 Operational problems associated with ASP
1. Rising of sludge :- Settled sludge contains large number of live cells. They oxidise the dead cells and release nitrogen. The nitrogen causes the sludge to risep and increases the Xe value.
~ Remedies :- Increase Qr & Decrease Q
2. Bulking of sludge :- Large number of dead cell in settled sludge and growth of filamentous organisms. Occurs when SVI ≃ 150
~ Remedies :- Bring down SVI (≃ 150), Increase pH, Increase DO, decrease F/M ratio.
@Civil_engg_competitive_exam
♦️ Activated sludge process (ASP)
🔸 Activated sludge :- It is sludge containing large concentration of highly active aerobic micro organisms.
🔸 ASP works on the principle of suspended culture system.
🔸 Components of ASP
A) Primary settling tank :-
~ Detention time - 1.5 to 2 hr.
B) Aeration tank :-
~ Detention time- 4 to 8 hr
C) Secondary sedimentation tank :-
~ Detention time- 1.5 to 2 hr.
D) Sludge thickener & sludge digestion tank
🔸 Activated sludge process parameters
1. Hydraulic retention time (HRT) :- It is the ratio of volume of tank to the rate of sewage flow into the tank.
2. Volumetric loading rate or BOD loading rate :- It is ratio of BOD applied to unit volume of aeration tank.
3. Food to microorganism ratio (F/M) :- It is defined as the ratio of kg of BOD applied per day to kg of MLSS in aeration tank.
4. Mean cell residence time (Sludge age) :- It is defined as mass of cell in the reactors to mass of cells wasted per day.
5. Sludge volume index :- It is the volume occupied in ml by 1 gm MLSS after settling for 30 minute from 1L sewage sample is known as sludge volume index.
🔸 Usual values adpoted
👉 F/M :- 0.4 to 0.3
👉 MCRT :- 5 to 15 days
👉 Efficiency :- 85 - 95%
👉 Recycling ratio :- 0.25 - 0.5
🔸 Operational problems associated with ASP
1. Rising of sludge :- Settled sludge contains large number of live cells. They oxidise the dead cells and release nitrogen. The nitrogen causes the sludge to risep and increases the Xe value.
~ Remedies :- Increase Qr & Decrease Q
2. Bulking of sludge :- Large number of dead cell in settled sludge and growth of filamentous organisms. Occurs when SVI ≃ 150
~ Remedies :- Bring down SVI (≃ 150), Increase pH, Increase DO, decrease F/M ratio.
@Civil_engg_competitive_exam