Synergistic bioleaching by thiobacillus consortia for simultaneous heavy metal removal mechanisms and sludge dewaterability enhancement

This study aimed to develop an enhanced strategy for simultaneous heavy metal (HM) removal and dewaterability improvement in municipal sewage sludge using a composite consortium of Thiobacillus thiooxidans (Tt) and Thiobacillus ferrooxidans (Tf). The novelty of this work lies in the systematic optimization of the Tt:Tf inoculation ratio and the mechanistic investigation that links microbial community succession to process performance. The results demonstrated that the composite consortium significantly outperformed the single-strain treatments. An optimal Tt:Tf ratio of 1:1 achieved the highest HM solubilization. Sludge dewaterability was markedly enhanced, as indicated by a substantial reduction in specific resistance to filtration (SRF). Mechanistically, this improvement was attributed to bioleaching-induced acidification, cell lysis, and restructuring of extracellular polymeric substances (EPS). High-throughput sequencing revealed a dramatic microbial community shift towards dominance by acidophilic γ-Proteobacteria (e.g., Acidithiobacillus, Acidiphilium), whose synergistic functions underpinned the efficient bioleaching process. In contrast, nitrifying bacteria such as Nitrospira were significantly inhibited by the low pH. This work establishes the optimized composite Tt/Tf bioleaching as a highly effective and promising strategy for sludge treatment, providing deeper insights into the microbial ecological mechanisms driving HM detoxification and dewaterability enhancement.