A Low Cost Conventional BNR Alternative to Oxidation Ditches Results in Big Success for Small Communities

Smaller communities that are required to reduce total nitrogen (TN) and total phosphorus (TP) in wastewater treatment plant discharges pay higher costs per unit flow to construct and operate their wastewater treatment facilities compared to larger facilities. Oxidation ditches are commonly used where nutrient removal is required; however, smaller communities pay a premium for the extended hydraulic retention time and oval tanks typically provided for oxidation ditches. Conventional biological nutrient removal (BNR) in above-ground circular tanks can make nutrient removal more affordable for the customers of small utilities. Several wastewater treatment facilities in the Chesapeake Bay Watershed have recently been upgraded to provide conventional nutrient removal processes in circular tanks similar to traditional plug-flow BNR. Construction costs for these facilities are similar to per gallon construction costs for larger plants. These facilities have performed very well, achieving effluent TN and TP concentrations below 2 mg/L and 0.1 mg/L, respectively.