Decreasing lactate input for cost-effective sulfidogenic metal removal in sulfate-rich effluents: Mechanistic insights from (bio)chemical kinetics to microbiome response

High material cost is the biggest barrier for the industrial use of low-molecular-weight organics (i.e. lactate) as external carbon and electron source for sulfidogenic metal removal in sulfate-rich effluents. This study aims to provide mechanistic evidence from kinetics to microbiome analysis by batch modeling to support the possibility of decreasing the lactate input to achieve cost-effective application. The results showed that gradient COD/SO42− ratios at a low level had promising treatment performance, reaching neutralized pH with nearly total elimination of COD (91%–99%), SO42− (85%–99%), metals (80%–99%) including Cu, Zn, and Mn. First-order kinetics exhibited the best fit (R2 = 0.81–0.98) to (bio)chemical reactions, and the simulation results revealed that higher COD/SO42− accelerated the reaction rate of SO42− and COD but not suitable to that of metals. On the other hand, we found that the decreasing COD/SO42− ratio increased average path distance but decreased clustering coefficient and heterogeneity in microbial interaction network. Genetic prediction found that the sulfate-reduction-related functions were significantly correlated with the reaction kinetics changed with COD/SO42− ratios. Our study, combining reaction kinetics with microbiome analysis, demonstrates that the use of lactate as a carbon source under low COD/SO42− ratios entails significant efficiency of metal removal in sulfate-rich effluent using SRB-based technology. However, further studies should be carried out, including parameter-driven optimization and life cycle assessments are necessary, for its practical application. [Display omitted] •Low COD/SO42− ratio achieved almost complete sulfate and metal removal.•Limited lactate entailed tilt advantages of sulfate reducers but confines sulfidogenic metal removal.•Microbial profile transformations caused by COD/SO42− ratio changes are narrow.•Proteobacteria and Firmicutes are leading assemblages in the ecological molecular network.•Sulfate-reduction-related genes are induced by faster lactate degradation while slower SO42− reduction.