Effect of immersion time on bacterial community structure and sulfur metabolism in biofilm on concrete surface in sewer environment

This study focuses on an overlooked but critical issue: the composition and functional expression of microbial communities on the concrete surface in different areas of sewer pipes. Three immersion conditions were applied to simulate the duration of concrete in different areas ofsewers exposed to sewage, including short-term (L1), long-term (L2) and permanent immersion (L3). The properties of concrete under different immersion conditions and the bacterial diversity and functional capabilities in biofilms on the concrete surface were analyzed. Results showed that the L1 group was dominated by Halothiobacillus, whereas Desulfomicrobium was prominent in the L3 group. Significant differences in the predominant functional microbial communities and metabolic functional genes further confirmed the strong impact of immersion time on the pathways of microbial sulfur metabolism and concrete performance in sewer environment. Compared with the L2 and L3 groups, the decreased sewage immersion time resulted in an increase in the abundance and metabolic activity of sulfur-oxidizing bacteria in the L1 group. Hence, greater mass loss and gypsum production of concrete was found in the L1 group. The structural and functional differentiation of bacterial communities on the concrete surface observed in this study contributes to a better understanding of the uneven corrosion in real sewer pipes.