A Central Wisconsin municipal treatment plant (WWTP) with a significant industrial contribution and seven (7) years of Rotating Biological Contractor (RBC) operation was the demonstration site for process modifications which provided significant biological nutrient removal (BNR). The study was conducted June-October, 1990. The plant was near 70% of hydraulic design load and averaged 90% of organic design load, with numerous excursions above organic design load. The BOD:P ratio was above 20:1, and the BOD:TKN ratio was above 10:1. Process modifications resulted in total phosphorus and total nitrogen reductions of 60-90% without chemical addition. Other benefits realized include increased clarity of the secondary effluent and an approximate 50% reduction of RBC shaft biomass weight.

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