Pilot Evaluation Of Floating Media Biological Aerated Filters (BAFs) To Achieve Stringent Effluent Nutrient Discharge Requirements

This paper presents the results of a two-year pilot evaluation of floating media biological aerated filters (BAFs). The pilot consists of two stages - tertiary nitrification (N) filter followed by post denitrification (DN) filter. The focus of the pilot study was to determine the BAFs’ capacity to meet stringent tertiary treatment requirements in treating the effluent from a conventional activated sludge process. It was demonstrated that the two-stage BAF system, on a 30-day average basis, is capable of achieving 1) a total nitrogen (TN) requirement less than 3 mg/L, 2) a total phosphorus (TP) requirement less than 0.3 mg/L with chemical addition, 3) a zero net COD increase under methanol addition conditions, and 4) a TSS concentration less than 5 mg/L. Biological growth in the DN stage was not limited with an influent ortho-P less than 0.3 mg/L. Complete nitrification was achieved at loading rates up to 2.0 kg/m³/d with an oxygen-to-ammonia mass ratio of 30 g/g or above. High rate denitrification was observed at methanol-to-NOx ratios between 2.8 to 3.0 g/g. Methanol dosages greater than 3.4 g/g resulted in increased effluent NOx concentrations, and the increase probably resulted from unstable methanol dosing control. Water temperature down to 80C was shown to minimally affect both nitrification and denitrification performance.