Effects of unsaturated zone depth, temperature, and alkalinity on biological nitrogen removal in biofilters enhancing nitritation-anammox process

Integration of partial nitrification (nitritation) and anaerobic ammonium oxidation (anammox) in biofilters is a novel process for biological nitrogen removal from wastewater. The unsaturated zone in biofilters provides oxygen for nitritation and supplies inorganic carbon for autotrophic bacteria growth. This study investigated the effects of unsaturated zone depth, temperature, and alkalinity on biological nitrogen removal in biofilters enhancing nitritation-anammox process. The results showed that the highest total inorganic nitrogen removal rate of 20.2 g/m3·d was achieved when the depth ratio of unsaturated zone to saturated zone was 1.14 compared to 0.14 and 0.57. The lower temperatures limited total inorganic nitrogen removal. Marble chips were suitable solid-phase buffers and alkalinity supplement in the biofilters. A kinetic study indicated that when the depth ratio of unsaturated zone to saturated zone was 0.57 and 1.14, ammonium-N removal followed mixed-order model with maximum removal rate constants in the range of 30-42 g/m 3·d.;Key Words: Alkalinity; Anammox; Biofilters; Kinetics; Nitritation; Temperature; Unsaturated zone.