Faced with a future mandate to limit phosphorus and nitrogen discharged to Jordan Lake, the City of Mebane (N.C.) expected to upgrade its activated sludge plant to a biological nutrient removal system.Interestingly though, effluent ammonia levels were below 1.0 mg/L even though the aeration basin dissolved oxygen (DO) was below the recommended 1.0-2.0 mg/L for nitrification. Because of the low DO, the plant was also removing some nitrates.Encouraged by the nitrification and denitrification at low DO, the plant staff looked into simultaneous nitrification-denitrification. “We installed timers and started cycling two of the six floating aerators on and off to maintain
