Optimization Strategies: BOD to N-removal - OCSD Case Study

The Orange County Sanitation District (OCSD) modified their activated sludge operation from biochemical oxygen demand (BOD) to nitrification-denitrification (NDN) mode to reduce ammonia discharged and sent to the Groundwater Replenishment System (GWRS) operated by Orange County Water District. Aggressive design criteria could be used since there are no regulatory requirement to meet effluent standards while maintaining stable performance. The conversion to NDN was successfully implemented at modest cost and modifications to existing facilities, without adding new aeration basin volume. Aeration basins were reconfigured to achieve stable nitrification and denitrification. Two new clarifiers increased the total number of available clarifiers to 26. Complete nitrification is achieved and settleability improved dramatically. An economic comparison showed that the combined energy (blower plus pumping) and thickening chemical costs for BOD and NDN modes are the same.