Zhang Ke, Zhang Shaojian, Liao Peng, Zhao Yuanxin, Gan Min, Zhu Jianyu
School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha 410083, PR China; State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China.
Water Res. 2023 Oct 15;245:120589. doi: 10.1016/j.watres.2023.120589. Epub 2023 Sep 10.
Elemental sulfur (S) plays a vital role in the coupled cycling of sulfur and iron, which in turn affects the transformation of carbon and various pollutants. These processes have been well characterized under static anoxic or oxic conditions, however, how the natural redox fluctuations affect the bio-mediated sulfur cycling and coupled iron cycling remain enigmatic. The present work examined S disproportionation as driven by natural microbial communities under fluctuating redox conditions and the contribution of S disproportionation to ferrihydrite transformation. Samples were incubated at either neutral or alkaline pH values, applying sequential anaerobic, aerobic and anaerobic conditions over 60 days. Under anaerobic conditions, S was found to undergo disproportionation to sulfate and sulfide, which subsequently reduced ferrihydrite at both pH 7.4 and 9.5. Ferrihydrite promoted S disproportionation by scavenging biogenic sulfide and maintaining a suitable degree of sulfate formation. After an oxic period, during the subsequent anoxic incubation, bioreduction of sulfate occurred and the biogenic sulfide reduced iron (hydr)oxides at a rate approximately 25 % lower than that observed during the former anoxic period. A 16S rDNA-based microbial community analysis revealed changes in the microbial community in response to the redox fluctuations, implying an intimate association with the coupled cycling of sulfur and iron. Microscopic and spectroscopic analyses confirmed the S-mediated transformation of ferrihydrite to crystalline iron (hydr)oxide minerals such as lepidocrocite and magnetite and the formation of iron sulfides precipitated under fluctuating redox conditions. Finally, a reaction mechanism based on mass balance was proposed, demonstrating that bio-mediated sulfur transformation maintained a sustainable redox reaction with iron (hydr)oxides under fluctuating anaerobic-aerobic-anaerobic conditions tested in this study. Altogether, the finding of our study is critical for obtaining a more complete understanding of the dynamics of iron redox reactions and pollutant transformation in sulfur-rich aquatic environments.
元素硫（S）在硫和铁的耦合循环中起着至关重要的作用，进而影响碳和各种污染物的转化。这些过程在静态缺氧或有氧条件下已得到充分表征，然而，自然氧化还原波动如何影响生物介导的硫循环和耦合铁循环仍然是个谜。本研究考察了在波动的氧化还原条件下由天然微生物群落驱动的硫歧化作用以及硫歧化作用对水铁矿转化的贡献。样品在中性或碱性pH值下孵育，在60天内依次应用厌氧、好氧和厌氧条件。在厌氧条件下，发现硫发生歧化反应生成硫酸盐和硫化物，随后在pH值7.4和9.5时还原水铁矿。水铁矿通过清除生物源硫化物和维持适当的硫酸盐形成程度促进硫歧化反应。在有氧期之后，在随后的缺氧孵育期间，发生了硫酸盐的生物还原，生物源硫化物还原铁（氢）氧化物的速率比前一个缺氧期观察到的速率低约25%。基于16S rDNA的微生物群落分析揭示了微生物群落响应氧化还原波动的变化，这意味着与硫和铁的耦合循环密切相关。显微镜和光谱分析证实了硫介导的水铁矿向结晶铁（氢）氧化物矿物（如纤铁矿和磁铁矿）的转化以及在波动的氧化还原条件下沉淀的硫化铁的形成。最后，提出了基于质量平衡的反应机制，表明在本研究测试的波动厌氧-好氧-厌氧条件下，生物介导的硫转化与铁（氢）氧化物维持了可持续的氧化还原反应。总之，我们的研究结果对于更全面地理解富硫水生环境中铁氧化还原反应和污染物转化的动态至关重要。
