Influent and Effluent Quality

1. Influent to Aeration Tank

Q_Ave = 10 mgd

BOD₅ into primary settling tank = 200 mg/l

SS into primary settling tank = 200 mg/l

30% of BOD₅ removed in primary settling tank

55% of SS removed in primary settling tank

BOD_5in = 200 (1 - 0.3) = 140 mg/l

SS_in = 200 (1 - 0.55) = 90 mg/l

2. Effluent out of Settling Tank: According to Secondary Treatment eff. Criteria

According to EPA effluent criteria,

i). BOD₅ of eff. < 30 mg/l, removal efficiency > 85%

ii). SS of eff. < 30 mg/l, removal efficiency > 85%

BOD_5eff = 25 mg/l < 30 mg/l

Therefore,

MLVSS/MLSS = 0.8

MLVSS � Mixed-liquor volatile suspended solid (mg/l)

MLSS � Mixed-liquor suspended solid (mg/l)

SS_eff = 25 mg/l < 30 mg/l

Soluble BOD₅ = 25 - SS � VSS/SS � 1.42 � 0.68 = 25 - 25 � 0.8 � 1.42 � 0.68 = 6 mg/l

3. Removal Efficiency

For activated sludge process based on soluble BOD₅ effluent

 

BOD₅ into Aeration Tank, S₀ (mg/l): Soluble BOD₅ eff., S (mg/l):

(%)

Overall efficiency, E,  for system based on BOD₅ of effluent (primary + bio)

BOD₅ inf. (mg/l): Soluble BOD₅ eff. (mg/l):

(%)