The two-stage biological processes in series offer high efficiency in nutrient removal at minimal costs. The source of wastewater is typical residential customers in the suburb of a large, metropolitan area. The BOD to total phosphorus (TP) ratio averages 55:1. The retrofitted, activated-sludge process consists of an anoxic stage with a 4.8-hour residence time, followed by an aerobic stage in two tanks with a residence time of 11.5 hours. The operating strategy developed at this facility is unique because the sludge blanket at the clarifiers is 3–4 feet deep, and the return activated sludge (RAS) flow rate is maintained at a low (10–25 percent) portion of the plant flow. The second-stage denitrification filters then remove the remaining nitrogen with a methanol feed.