Microbial activity of suspended biomass from a nitritation–anammox SBR in dependence of operational condition and size fraction

Abstract

Single-stage nitritation-anammox combines the growth of aerobic ammonium-oxidizing bacteria (AOB) and anaerobic ammonium oxidizing bacteria (AnAOB) in one reactor. The necessary compromise of their milieu conditions often leads to the growth of nitrite-oxidizing bacteria (NOB). For this study, a sequencing batch reactor (SBR) for nitritation-anammox was operated for 180days with sewage sludge reject water (removal capacity, 0.4kg N m(-3) day(-1)). The growth of NOB was favored by enhanced oxygen supply rather than extended aerobic phases. Suspended-type biomass from this SBR was taken regularly and sieved into three size fractions (all of them <1,000μm). Batch experiments as well as fluorescence in situ hybridization were performed to study the distribution and activity of AnAOB, AOB, and NOB within those size fractions. Both the measured conversion rates and detected abundances decreased with increasing size fraction. The highest anammox conversion rates (15g NH4 (+)-N per kilogram VSS per hour) and the highest abundances of Brocadia fulgida were found in the medium size fraction (100-315μm). The batch experiments proved to be accurate tools for the monitoring of multiple processes in the reactor. The results were representative for reactor performance during the 6months of reactor operation.