硫酸盐还原菌对酸性废水中重金属的生物沉淀作用研究

在小型连续搅拌槽式反应器（CSTR）中，研究了持续低pH条件下，硫酸盐还原菌的生物沉淀作用对人工配制酸性重金属废水的处理效果。试验设置反应器进水pH值依次为4-3，3．5和2．6三个处理，进水中Cu^2＋、Zn^2＋和Cr^3＋含量分别为65、36和10mg·L^-1，SO4^2-含量约为6200mg·L^-1，接种物为经耐酸驯化的混合硫酸盐还原菌，试验时控制水力停留时间为36h，通过定期测定反应器出水pH、氧化还原电位（ORP）、碱度、SO4^2、S^2-以及重金属含量变化等指标来考察废水生物沉淀的处理效果。研究结果表明：对于进水pH值为2．6～4.3的酸性重金属废水，硫酸盐还原菌的生物沉淀作用均有较好的处理效果。处理后，反应器出水pH值大幅升至6．5～8．0，碱度由起始的300～2000mg·L^-1增至7500-4600mg·L^-1，废水中S041-还原率达72％～80％，Cu^2＋和Zn^2＋的去除（沉淀）率达99．9％，Cr^3＋去除率达99．1％。此外，随着进水pH值由413降至2．6，反应器出水pH和碱度均呈现逐步下降的趋势，而S04}的生物还原和重金属的去除效果变化不大。从反应器运行稳定性考虑，控制酸性重金属废水的进水pH值为3．5较适宜今后的实际应用。

Bio-precipitation of heavy metals from a synthetic acidic wastewater by sulfate-reducing bacteria in a bench scale continuous-flow stirred tank reactor

The aim of this study was to investigate the performance of bioprecipitation of heavy metals from a synthetic acidic heavy metals-laden wastewater by the mixed acid-tolerant sulfate-reducing bacteria. Three influent samples with pH levels from 4.3 to 2.6 containing 65 mg·L~(-1) of Zn~(2+), 36 mg·L~(-1) of Cu~(2+), 10 mg·L~(-1) of Cr~(3+), 6 200 mg·L~(-1) of SO_4~(2+) were sequentially introduced into a bench-scale continuous-flow stirred tank reactor amended with sodium lactate as energy substrate. During the whole experimental periods, hydraulic retention time was controlled at 36h, and the temperature of reactor was kept at (32±1)～℃. The results showed that the bioprecipitation process by sulfate-reducing bacteria resulted in a sharp increase in the effluent pH from the initial pH 4.3～2.6 to pH 8.0～6.5, and 72% ～80% of sulfate reduction, and removal efficiencies greater than 99.9% for Zn, Cu, and 99.1% for Cr, respec-tively. Changing influent pH level from 4.3 to 2.6 decreased substantially the effluent alkalinity from ～7 500 to ,-4 600 mg·L~(-1), but had no marked adverse influence on the percentages of sulfate reduction and final removal of heavy metals. The recommended in-fluent pH level applied for the future larger-scale bioprecipitation process with sulfate-reducing was pH 3.5. The results of this work demonstrate that the bioprecipitation process by sulfate-reducing bacteria is of interest for its potential to remediate highly acidic heavy metals contaminated wastewaters.