A pilot study on suspended activated sludge process augmented with immobilized biomass for simultaneous nitrification and denitrification

Concurrent nitrification and denitrification (CND) are natural phenomena in the soil environment that can be applied in wastewater treatment for enhanced total nitrogen removal. However, significant renovation is necessary for existing plants to equip them for nutrient removal. At a domestic wastewater treatment plant, we performed a pilot test by installing bioplates with entrapped biomass in a conventional aeration basin for CND, and investigated the effects of bioplate packing ratio (PR), hydraulic retention time (HRT), dissolved oxygen (DO) level, on/off aeration mode, and supplemental carbon and alkalinity on nitrogen removal. With the pilot aeration basin of 1.3 m3 loaded with mixed liquor suspended solids of 1,500–2,500 mg/L and bioplates at PR of 3.2% (3.2% basin volume) operated at HRT of 6 h and DO of 4–6 mg/L without supplemental carbon or alkalinity, nitrogen in the wastewater was removed to an effluent total nitrogen (TN) of 7.3 mg/L from an influent TN of 28 mg/L, achieving a specific TN removal of 25 g TN/m2/d. The bioplate, consisting of modular, robust cellulose triacetate structure carrying the biomass, shows promise in retrofitting conventional aeration basins for enhanced nutrient removal.