Temperature effects on nitrification in polishing biological aerated filters (BAFs)

Abstract

The effects of temperature on nitrification in a polishing biological aerated filter (BAF) were investigated using a 75‐mm diameter pilot‐scale BAF with a gravel media size of 5 mm and a depth of 1.7 m. Influent soluble chemical oxygen demand (sCOD) and ammonia‐nitrogen (NH3‐N) concentrations were approximately 50 mg/L and 25 mg/L simulating the effluent from an aerated lagoon system. For an influent wastewater temperature of 6.5 °C, approximately 95% of NH3‐N was nitrified at a hydraulic retention time (HRT) of 2 hours. By recirculating 200% of the effluent back into the BAF for a HRT of 1 hour and at 6.5 °C, NH3‐N percentage removal improved from 54% to 92%. For NH3‐N loading larger than 0.9 kg NH3‐N/m3‐day at 24 °C, the mass of NH3‐N removed in kg NH3‐N/m3‐day reached an asymptotic value of 0.63 kg NH3‐N/m3‐day. The NH3‐N concentrations within the column at different temperatures were modelled using zero‐order biotransformation rate kinetics. The results showed that gravel BAF operating at an HRT of 1 hour with 100% or 200% recirculation can be used as an add‐on technology for nitrification for cold weather conditions.