One-stage nitritation - anaerobic ammonium oxidation at low temperatures in a moving bed biofilm reactor

Paper in proceeding, 2013

Bacteria capable of anaerobic ammonium oxidation (anammox) enable autotrophic nitrogen removal. Organic carbon in wastewater can instead be utilized for energy production. However, anammox-based processes are not yet used at any extent for treatment of the main stream at wastewater treatment plants. One of the reasons for this is the challenge for the slow growing autotrophic bacteria to work at low temperatures. Here we investigate one-stage nitritation-anammox at temperatures of 13-16°C in a pilot moving bed biofilm reactor (MBBR) receiving reject water from anaerobic sludge digestion. At a target nitrogen loading rate of 1 g NH4+-N m-2 d-1 the average nitrogen removal rate was 0.81 g NH4+-N m-2 d-1 and 0.55 g NH4+-N m-2 d-1 at 16°C and 13°C respectively. At low temperatures oxygen control is important to avoid oxygen penetration to the deeper parts of the biofilm, which causes inhibition of the anammox bacteria and as a result nitrite accumulation. Hence, the process was operated at conditions to limit the activity of the aerobic ammonium oxidizing bacteria (AOB) by oxygen availability. The biofilm biomass was dominated by anammox bacteria, with 1.0 × 1014 copies m-2 (16S rRNA), with considerably fewer AOB of 2.1 × 1012 copies m-2 (amoA), as measured by quantitative PCR. Cell specific conversion rates of anammox bacteria and AOB were estimated at 0.3-0.5 fmol N cell-1 d-1 and 7-9 fmol N cell-1 d-1, respectively. The study shows the applicability of one-stage nitritation-anammox in MBBRs at low temperatures and highlights the importance of quantification of AOB and anammox bacteria for understanding process performance.