Response of sediment microbial communities to different levels of PAC contamination and exposure time

Abstract

Coagulants such as polyaluminium chloride (PAC) are widely used for removing phosphorus from eutrophic water, but its application for water treatment can potentially harm the environment. In this study, a four-timepoint exposure experiment was performed at week 1, 3, 7 and 10 to investigate how microbial communities in lake sediments respond to different concentrations of PAC (RS (raw lake water with nothing added), Low, Medium and High). The results showed that, while PAC can efficiently decrease the amount of C, N and P in lake water, the presence of residual aluminum and aluminum precipitates can greatly affect the microbial communities in lake sediments. In particular, different concentrations of PAC and exposure time affected the microbial diversity and structure of lake sediments, with changes being especially obvious at high concentration of PAC after 10 weeks of exposure. Moreover, the use of PAC significantly increased the relative abundances of Gammaproteobacteria and Competibacter, while reducing those of Thermodesulfovibrionia, Vicinamibacterales, and BSV26 in time- and concentration-dependent manners. Network analysis further showed strong correlations between differential bacterial species of PAC in high concentration at 10 weeks, which further suggested that PAC treatment changed the complex structure of microbiota in lake sediment. Finally, correlation analysis indicated a close connection between water parameters and differential species induced by PAC treatment. Overall, PAC contamination changed the microbial communities at different taxonomy levels and influenced the functional pathways to potentiate the P removal, and the results offered interesting insights into the use of PAC in water treatment and its impact on biogeochemical cycling. These results indicated that more attention need to be paid to the potential impact of chemical phosphorus removing reagents on the environment, including eutrophic water.