Improved sulfate reduction efficiency of sulfate-reducing bacteria in sulfate-rich systems by acclimatization and multiple-grouting

The acclimation of sulfate-reducing bacteria (SRB) was performed to improve its adaptation in sulfate-rich systems with high sodium sulfate as a solution for disposing of soil salinization. The effects of pH, temperature, and carbon–sulfur ratio (CSR) on the activity and reduction efficiency (RE) of SRB were analyzed, and the influence of grouting times (GTs) on RE was studied. The impact of different sulfate-rich systems (i.e., sulfate-rich solution and soil) with different salinity on the RE of SRB was investigated. Results show that the optimum temperature and pH for the best activity and RE of SRB were 30°C and 7.0, respectively. The multiple acclimations for SRB significantly improved the activity and RE of SRB at high CSR. The RE of SRB decreased with increasing salinity since high salinity could inhibit SRB activity. The maximum RE of SRB-200 in sulfate-rich soils with 2% salinity is 40%, which may be due to the significant salinity tolerance degree of SRB-200, which is higher than SRB-150 and SRB-175. In addition, the RE of SRB in sodium sulfate solution was higher than that in sulfate-rich soil due to the soil having a complex skeletal structure. The RE of SRB significantly increased after low GTs (<5) and then remained constant after high GTs (>5). The optimal GTs obtained by SRB-150, SRB-175 and SRB-200 were 4, 4 and 5, respectively, corresponding to the final cumulative REs of 37.2%, 45.2% and 55.2%, respectively. The SEM results shows the formation of sulfides verified the reliability of SRB reduction in sulfate-rich systems. All results provide an important reference for the effective utilization of SRB in sulfate-rich systems.