Effect of calcification on anaerobic granular sludge: Micro-morphological structure and microbial community

Abstract

In this study, the effect of calcification on methanogenic activity, basic properties, microbial community structure, and microstructure of anaerobic granular sludge (AnGS) was investigated. Results indicated that inorganic crystals were deposited in the sludge in the form of calcite, which increased sludge density and led them to deposit at the bottom of the anaerobic reactor. Calcification markedly reduced the values of volatile suspended solids (VSS) / total suspended solids (TSS) and extracellular polymeric substances (EPS) content by 35.0 % and 27.1 %, respectively. Chloroflexi, Actinobacteria, Firmicutes, and Bacteroidetes were the most dominant functional species in both types of samples, accounting for 69.1 % of the calcified samples and lower than 71.8 % of the uncalcified samples. Compared to uncalcified sludge, the abundance of Methanosaeta (9.7 %) in the calcified sludge decreased by 34.0 %. And calcification reduces the abundance of gene pathway and methane-related enzymes. In addition, the proportion of inorganic crystals in calcified sludge was 180.6 % higher than that in uncalcified sludge, while the proportion of biomass and pores decreased by 11.7 % and 73.8 %, respectively. And the proportion of larger pores was significantly reduced. These factors lead to the cumulative methane production in calcified AnGS decreased by 26.8 %, and the specific methanogenic activity (SMA) reduced by 16.2 %.