Ditch the nutrients

摘要

All wastewater treatment facilities (WWTFs) in the Chesapeake Bay watershed have been or soon will be subject to strict effluent nutrient loading limits. In Maryland, WWTFs in this watershed with capacities larger than 1900 m3/d (0.5 mgd) are required to achieve new annual average effluent concentration limits of 4.0 mg/L of total nitrogen (TN) and 0.3 mg/L of total phosphorus (TP). Different communities have used a variety of technologies to meet these limits, including oxidation ditches, sequencing batch reactors, membrane bioreactors, and nitrifying activated sludge processes followed by denitrification filters. Two new oxidation ditch systems in Maryland were designed specifically to achieve biological enhanced nutrient removal (ENR). Both systems are of similar design capacity and are operated under similar influent flows and loads and climate conditions.