Structure and composition of biofilm communities in a moving bed biofilm reactor for nitritation–anammox at low temperatures

It is a challenge to apply anaerobic ammonium oxidation (anammox) for nitrogen removal from wastewater at low temperatures. Maintenance of anammox- and aerobic ammonia oxidizing bacteria (AOB) and suppression of nitrite oxidizing bacteria (NOB) are key issues. In this work, a nitritation–anammox moving bed biofilm pilot reactor was operated at 19–10 °C for 300 d. Nitrogen removal was decreasing, but stable, at 19–13 °C. At 10 °C removal became unstable. Quantitative PCR, fluorescence in situ hybridization and gene sequencing showed that no major microbial community changes were observed with decreased temperature. Anammox bacteria dominated the biofilm (0.9–1.2 × 1014 16S rRNA copies m−2). Most anammox bacteria were similar to Brocadia sp. 40, but another smaller Brocadia population was present near the biofilm-water interface, where also the AOB community (Nitrosomonas) was concentrated in thin layers (1.8–5.3 × 1012 amoA copies m−2). NOB (Nitrobacter, Nitrospira) were always present at low concentrations (<1.3 × 1011 16S rRNA copies m−2).