分离自活性污泥的硫酸盐还原菌用于铅锌冶炼渣重金属污染修复

3 讨论与结论

硫酸盐还原菌能够固化铅锌冶炼渣中的重金属，具有很好的工业应用前景，研究其对重金属修复的可行性具有很重要的意义。Cabrera等发现从污泥中分离的硫酸盐还原菌在厌氧环境中修复重金属尾矿效果显著^[28]；Joo等将脱硫菌(Desulfovibrio desulfuicans)应用到含有镉、镍和铬多种重金属环境中修复实验结果表明，其去除率分别可达到99.90%，98.31%和74.20%，并生成重金属硫化物沉淀^[29]。通过对铅锌冶炼渣化学成分和矿物组成分析可知，该渣样主要成分为硫酸盐类物质，其中包括硫酸钙(CaSO₄)、硫酸锌(ZnSO₄)和硫酸铁类物质(Fe(SO₄)₂(OH)₅H₂O)等；该结果与冶炼过程中所选的药剂和渣样前期添加还原剂处理有关(硫化物及铁系盐)，但由于受环境中各因子及土著氧化菌的影响，往往会造成重金属的再次“返溶”。为了实现持久稳定地固化冶炼渣中的重金属，本研究接种硫酸盐还原菌于铅锌冶炼渣中，在修复过程中，系统中环境电位降低、pH 升高且各重金属化学形态及浓度发生变化，各重金属稳定态含量增加，可交换态含量减少，所以系统溶液中各离子浓度降低。冶炼渣中硫酸盐还原过程主要是硫酸盐还原菌通过传递电子给系统中的硫酸根，产生为S²⁻，S²⁻具有还原性，其与冶炼渣中重金属结合生成金属硫化物沉淀^[30-31]是一个耗酸的过程，从而引起 pH的升高，环境电位降低。尾矿堆和冶炼渣场中存在多种微生物^[32-35]，包括氧化菌(Acidithiobacillus ferrooxidans、Leptospirillum ferrooxidans、Leptospirillum ferriphilum)和还原菌(SRB、Pseudoobactrum sacolyticum、Stenotrophomonas sp.)等^[36-38]，其中在嗜酸氧化菌的作用下会源源不断地溶出重金属形成恶性循化。本实验取不同修复时段样品，对微生物群落结构变化进行分析^[39-40]，所测样品的 Desulfovibrio 的含量从32.22%增加至63.72%，成为冶炼渣修复过程中的优势菌，且原渣样中主要菌群(Bacillus、Exiguobacterium 和Acidithiobacillus)含量逐渐减少^[41]。该过程硫酸盐还原菌成为主要菌群，将铅锌冶炼渣中恶性循环变为良性循环。综上所述，硫酸盐还原菌可用作重金属污染修复的固化药剂。

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