Activated SludgeQuestion 1 of 18

A BNR activated sludge plant is missing both its total nitrogen (TN) and total phosphorus (TP) goals. Field checks show the following: the tank labeled "anoxic" has DO = 0.8 mg/L, and the tank labeled "anaerobic" has nitrate (NO3-N) = 6 mg/L (DO in that tank is near 0.0 mg/L). Mixed liquor is well mixed and alkalinity is adequate. Which operational correction best targets the likely root causes for poor N and poor P removal?

A) Increase DO in the anoxic zone to about 2 mg/L, and allow nitrate to enter the anaerobic zone to improve PAO activity.B) Keep nitrate present in the anaerobic zone for denitrification, and raise DO slightly in the anoxic zone to stabilize floc.C) Focus on lowering DO only in the anaerobic zone, and keep the anoxic zone aerated so nitrification can finish there.D) Reduce DO in the anoxic zone to near 0 mg/L, and keep both DO and nitrate near 0 mg/L in the anaerobic zone.

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