Biological Phosphorus and Ammonia Nitrogen Removal at a Small Wastewater Treatment Facility

Attaining new and more restrictive limitations for phosphorus and ammonia nitrogen is a large challenge facing numerous municipalities throughout the country. It is even more challenging when the size of the municipality is small due to the potential capital costs to construct new facilities and the potential additional operating costs. Additional challenges facing the City of Brodhead, Wisconsin, was to meet new limitations throughout a cold weather climate when wastewater temperatures drop to as low as 7°C for two to three months per year.The City of Brodhead constructed and began operating a new wastewater treatment facility in July 1998. The new treatment facility includes extended aeration operated oxidation ditches, biological phosphorus removal process basins, aerobic sludge digestion and supplemental chemical addition equipment. Since initial facility start-up, the operations of the various processes have been optimized dependent upon the waste loads received at the facility and the temperatures of the wastewater.The optimization of the operation of the treatment facility has been very successful. The facility has consistently produced water quality well below permitted limitations of 1.7 mg/l phosphorus and 5.8 mg/l ammonia nitrogen. The operating costs for attaining these new limitations have been kept as low as 0.60/lb phosphorus. The operating biology of the system has been very stable allowing the operators to make necessary adjustments depending upon waste loads received by the facility.