Effects of low temperature on the microbial community of MBBR filler biofilm

Moving bed biofilm reactors can purify urban domestic sewage through microbial biodegradation. High-throughput sequencing was used to study the response mechanism of the biofilm microbial community to temperature. The effluent quality of the reactor declined with the decrease in temperature. <i>Proteobacteria</i>, <i>Bacteroidota</i>, and <i>Nitrospirota</i> were the dominant bacteria, accounting for 59.2, 11.9, and 9.4%, respectively. <i>Gammaproteobacteria</i> (38.3%), <i>Alphaproteobacteria</i> (23.2%), and <i>Bacteroidia</i> (12.4%) were the dominant bacteria at the class level. Low temperature had an obvious directional domestication effect on microbial flora, and the composition of the bacterial community was more similar. <i>Pseudomonas</i> was one of the dominant bacterial groups at 5 °C. <i>Nitrospira</i> (<i>p</i> < 0.001) and <i>Trichococcus</i> (<i>p</i> < 0.05) were significantly negatively correlated with effluent ammonia nitrogen and significantly positively correlated with NO₃^- (<i>p</i> < 0.05) at low temperature. Functional bacteria related to chemoheterotrophy (25.88%) and aerobic_chemoheterotrophy (21.56%) accounted for a relatively high proportion. The bacteria related to nitrate reduction only accounted for 2.62%. Studies have shown that low temperatures can inhibit the growth of nitrogen-cycling bacteria, and few domesticated and selected nitrogen-cycling bacteria play a major role in the removal and transformation of ammonia nitrogen. The degradation of chemical oxygen demand can still be achieved through the adsorption and degradation of dominant functional bacteria.