Activated SludgeQuestion 1 of 18

An activated sludge plant notices a sudden increase in final effluent turbidity. Microscopic exam shows mostly tiny pin-point floc particles and dispersed growth with very few larger, compact flocs. Settleometer data shows a low SVI of 65 mL/g. Process data shows MCRT is very high at 28 days and F:M is very low at 0.08. Effluent BOD tests indicate most of the remaining BOD is particulate (from fine suspended solids) rather than soluble. Which operational change is the best first step to correct the cause of this effluent turbidity?

A) Increase aeration and raise DO to stop bulking and improve clarifier settling.B) Reduce wasting (lower WAS rate) to increase sludge age and improve settling by producing heavier floc.C) Add more return activated sludge (increase RAS rate) to prevent sludge blanket rise and carryover.D) Increase wasting (raise WAS rate) to reduce MCRT and bring F:M back toward a healthier range so floc can rebuild.

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