Evaluation of biofilm carrier colonisation in a deammonification moving-bed biofilm reactor

This study focused on the evaluation and characterisation of carrier colonisation of a deammonification moving-bed biofilm reactor (dMBBR) at a low carrier-inoculation ratio (≤5%v/v), applying multiple methodologies. The dMBBR (5 L working volume) was filled with Aqwise carriers (50%v/v filling ratio) and fed with synthetic feedstock. Carrier colonisation was differentially tracked using grey colour for new carriers and white colour for pre-colonised seed carriers. The reactor operated for 190 days at a nitrogen loading of 125-140 gN/m³/d. Multivariant heatmap analysis of the process parameters indicated stable deammonification performance from day 85 onwards albeit some occasional malfunctions occurred, with NH₄⁺ and total nitrogen removal rates amounting to 85% and 61%, respectively. Biofilm development on new carriers, evaluated by bulk density measurements via pycnometry, proved to be a reliable, simple, and non-destructive methodology. Anammox of genus <i>Candidatus Brocadia</i> and ammonia oxidising bacteria of genus <i>Nitrosomonas</i> were well established on the new carriers, in line with theoretical and empirical specific activity tests. This multi-parameter evaluation provides a broad insight into deammonification biomass development on the carriers and may assist in shortening the start-up period of dMBBRs.