Community diversity and biofilm characteristic response to low temperature and low C/N ratio in a suspended carrier biofilm reactor

A modified anaerobic–anoxic–aerobic reactor was developed to investigate the influence of both a low carbon-to-nitrogen (C/N) ratio and low temperature on microbial community structure and biofilms. The thickness and density of the biofilm on the suspended carriers and production of extracellular polymeric substances decreased with temperature. The biofilm thickness was more obviously affected by temperature than was the biofilm density. The polysaccharide-to-protein ratio at 10°C was remarkably higher than at 18°C, which would suggest that microbes secrete more polysaccharides in low-temperature conditions. Filamentous bulking was observed at 10°C when SVI was above 170 mL/g; however, this phenomenon did not occur at other temperatures. Our experimental data support the hypothesis that low temperature was more likely to lead to sludge bulking than was nutrient limitation. Chao1 values of metagenomic sequencing at 26°C were higher than those at 10°C. Haliscomenobacter, a primary filamentous species, was found to be more numerous in biofilm than in activated sludge at the same temperatures. The bacterial communities in the biofilm were different from those in the activated sludge, suggesting that suspended carriers had a significant effect on microbial community structure and biomass. Additionally, the ability of suspended carriers to inhibit sludge bulking was more significant at low temperature. Achievement of stable operation of a suspended carrier biofilm reactor is highly beneficial in terms of lower carbon requirements to the removal of organics and nitrogen from domestic wastewater.