Effects of Al3+ on the microbial community, metabolic pathways, and morphological analysis of activated sludge

Abstract

Al3+ generated during aluminum mining, electrolytic industry, and aluminum-based coagulant production enters sewage treatment plants and interacts with activated sludge, interfering with microbial growth and community succession. An anaerobic-anoxic-oxic (A2O) process was used to investigate the effect of Al3+ on biological denitrification, the metal form, and the microbial community structure. The results showed that a low concentration of Al3+ improved removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) as well as biological activity. However, a high concentration of Al3+ reduced the COD and TN removal efficiencies. The removal efficiencies of COD, TN, and NH4+-N were the highest, and the INT-ETS values in the anaerobic, anoxic, and oxic zones were 93.21, 91.36, and 94.44 mg·INTF/(g·TSS·h) in the 10 mg/L Al3+ concentration treatment. Regardless of the change in Al3+ concentration, aluminum in the sludge mainly existed in the form of stable organic aluminum. Microbial richness and diversity decreased under the high concentration of Al3+. However, the relative abundance of Bacteroidetes and Chitinophagales increased, which was coincident with the change in microbial aluminum tolerance capacity. The dominant flora included Proteobacteria, Gammaproteobacteria, Betaproteobacteriales, Rhodocyclaceae, and Thauera. Amino acid and carbohydrate metabolism, as well as membrane transport and replication and repair, were the main metabolic pathways. K03088, K03406, and K02014 exhibited good adaptability under the high Al3+ concentration, which ensured effective removal of COD and TN.