Pilot-scale demonstration of efficient ammonia removal from a high-strength municipal wastewater treatment sidestream by algal-bacterial biofilms affixed to rotating contactors

This report details our investigation of a novel, fixed-biofilm algal and bacterial system for the treatment of high-strength municipal anaerobic digester filtrate. Each reactor in the pilot-scale system comprises multiple Algaewheel™ rotating algal contactors (RACs) that help efficiently oxygenate the anaerobic digester filtrate being treated in a shallow tank. Total ammonia nitrogen (TAN) removal by microbial oxidation and anabolic uptake varied between 45 and 60% at hydraulic retention times (HRTs) of 0.5–2 days. Of the TAN removed during treatment, >95% was oxidized to nitrite with 27–36% subsequently evolved as N₂ and only 3–11% oxidized to nitrate. The low extent of nitrate formation makes biological nutrient removal less costly, since nitrite reduction demands less oxygen, by 25%, and organic carbon, by 40%, than nitrate reduction. In addition, due to the efficient aeration by RACs, it should be possible to design systems for sidestream treatment of digester filtrate that require up to 80% less electricity than are typical for aerobic ammonia oxidation.