Effects of biogenic nanopalladium precipitation on the performance and microbial community structure of anaerobic granular sludge

Abstract

Biogenic nanopalladium (BioPd) catalysts have drawn increasing attentions recently as a combination of metal catalyst over the support of biomass. Anaerobic granular sludge (AGS), as a special microbial granule, demonstrates a strong potential to reduce Pd(II) and precipitate Bio-Pd in the sludge body. The problem how the Bio-Pd precipitates would influence the function and microbial community of the Pd hosting AGS (Pd-AGS) remains unknown. In this study, Pd-AGS with different Bio-Pd loadings (1.7, 3.0, 4.4 and 8.0 wt% of Pd) was obtained through bio-reduction at different Na₂PdCl₄ concentrations. Effects of Bio-Pd precipitates on acidogenesis and methanogenesis of AGS were assayed. Response of bacterial and archaeal community of AGS towards Bio-Pd precipitation were also revealed based on high-throughput sequencing data on Illumina Miseq platform. Results showed that Bio-Pd precipitates affected the acidogenesis and methanogenesis process of the Pd-AGS, as the produced total volatile fatty acids (VFA) and methane were reduced by 25.8-53.0% and 33.9-87.7%, respectively, comparing to the native AGS. Bio-Pd precipitation resulted in microbial community shift and a decrease in the microbial diversity. The bacterial community suffered more influence than the archaeal community. Hydrogenotrophic methanogens were more sensitive to the toxicity of Pd(II)/Bio-Pd than acetotrophic methanogens. Overall, when the heterogeneous Pd-AGS catalyst is designed to possess both the function of microbial metabolism and Pd catalysis, it is necessary to control a suitable Pd(II) concentration during reduction process and the final Bio-Pd loading in AGS (<4.4 wt% of Pd).

Keywords: Anaerobic granular sludge; Biogenic nanopalladium; Methanogenic process; Microbial community.