pH-adapted culture and performance study of sulfate-reducing bacteria in an acid mine drainage substrate in Chongqing, China

Acid mine drainage (AMD) poses a serious threat to the ecological environment due to its strong acidity, high sulfate and heavy metal content. The application of sulfate-reducing bacteria (SRB) for the remediation of AMD holds considerable promise. However, the enrichment behavior and adaptation mechanisms of SRB to varying initial pH conditions have not been the subject of systematic study. Objective This paper aims to systematically study the effects of different initial pH values on SRB enrichment characteristics and wastewater treatment efficiency. Method In this study, we enriched indigenous SRB in Postgate medium with gradient pH (3, 4, 5, 6, 7) on AMD substrate from a coal mine in Chongqing. Result The study showed that the initial pH significantly affected the enrichment efficiency of SRB. Neutral to weakly acidic was achieved at pH 6, 25 days at pH 5, and no enrichment was achieved at pH 3～4. SRB conditions (pH 5～7) were more favorable for SRB growth, and the fastest enrichment (12 days) metabolism resulted in an increase in system pH (from initial 5～7 to eventually 6.7～7) and a substantial decrease in redox potential (from initial 268 mV to -400 mV), confirming its reducing activity. At pH 6～7, SRB removed >98% of Fe²⁺ (concentration <1.2 mg/L at 44 days) and 68%～73% of sulfate (down to 446～522 mg/L), while soluble sulfide concentrations rose above 90 mg/L. Removal efficiencies were delayed but eventually approached under pH 5 conditions. Microbial community analysis indicated that SRB were successfully enriched at an initial pH of 5～7. The dominant SRB genus was Desulfosporosinus (relative abundance 11%～34.5%), which was most active at pH 6. Further studies showed that the indigenous strains (CQ@pH5, CQ@pH6, and CQ@pH7) grew best under neutral conditions (pH 6～7), had the highest rate of sulfate reduction (soluble sulfide yield up to 38.8 mg/L in 12 days), and 100% Fe²⁺ removal, but the extreme acidic environment (pH≤4) completely inhibited their activity. Conclusion This study elucidates the mechanism by which pH affects the enrichment and functional performance of indigenous SRBs, reinforces their application basis in in situ remediation of acidic mining areas, and provides a theoretical basis and practical reference for the optimization of SRB-driven AMD remediation technologies.