Effects of complex sulphur substrates on sludge bioleaching to improve heavy metal removal and microbial community diversity.

In this study, HS was used as a partial replacement nutrient substrate for sludge bioleaching. The effects of different combinations of HS/sludge load and monomeric sulphur on heavy metal removal and microbial communities were investigated. Changes in pH, oxidation-reduction potential (ORP), SO concentration, heavy metal removal, and the content of heavy metal states during bioleaching were investigated, and community diversity analysis was performed. Daily introduction of HS three times (at an interval of 8 h) at a gas flow rate of 2 ml/min and an HS/sludge load of 15 ml/L with 5 g/L FeSO·7HO and 2 g/L monomeric sulphur as a nutrient substrate significantly accelerated both the bioleaching process and the pH drop in the sludge system, promoted the production of SO, and maintained a higher redox potential. The combination of HS and monomeric sulphur had a significant effect on the leaching of heavy metals. Compared with the experimental group containing only HS or monomeric sulphur, the removal rates of Zn, Ni, Pb, and Cr increased by 4.63%/13.8%, 8.5%/20.07%, 3.84%/9.5%, and 4.24%/8.02% respectively, while promoting the transformation of various heavy metal states to labile states, improving heavy metal stability, and reducing sludge ecotoxicity. High-throughput sequencing analysis showed that introducing the HS gaseous matrix accelerated the decreasing trend of species number, bacterial abundance, and community diversity in the sludge system, promoting Proteobacteria as the dominant phylum, Acidithiobacillus, Metallibacterium, and Thiomonas as the dominant genera, and improving the bioleaching treatment effect.