Activated SludgeQuestion 1 of 18

You are operating a conventional activated sludge plant that normally nitrifies. Shortly after a reported industrial discharge to the collection system, the plant experiences the following over one shift: effluent NH3-N jumps from 1 mg/L to 18 mg/L, effluent CBOD also increases, aeration basin DO remains 2.0–2.5 mg/L, and the aeration basin MLSS drops from 2,800 mg/L to 2,100 mg/L. Clarifier blanket is light and floc appears pin-point/weak. Which operator action is the best immediate response to protect the process and restore nitrification?

A) Increase RAS rate to the maximum to rapidly return more solids and immediately restore nitrification, even if clarifier blanket starts to rise.B) Increase WAS rate immediately to remove the upset biomass and improve effluent quality by lowering solids inventory in the aeration basin.C) Identify and isolate the toxic source, minimize wasting to retain remaining nitrifiers, maintain aeration, and allow time for biomass recovery.D) Decrease aeration to reduce oxygen uptake and prevent filament growth, then wait for ammonia to come back down on its own.

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