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 Candidatus Brocadia and ammonia oxidising bacteria of genus Nitrosomonas 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.