硫酸盐还原菌体系中纳米零价铁投加量对其生物硫化颗粒界面结构及还原脱氯特性的影响

Role of nano-scale zero valent iron dosage in shaping the interfacial structure and reductive dechlorination performance of sulfate-reducing bacteria-mediated sulfidated nano-scale zero valent iron

摘要:

【背景】 硫化纳米零价铁(sulfidated nano-scale zero valent iron, S-nZVI)作为一种新型铁基还原性反应材料被广泛用于氯代烃污染地下水的修复研究。硫化改性能够提高常规纳米零价铁(nano-scale zero valent iron, nZVI)对氯代烃的还原脱氯活性，同时抑制nZVI与水的副反应，但常用的化学硫化方法存在成本高、工艺复杂等问题，限制了其应用。近年来，基于硫酸盐还原菌(sulfate-reducing bacteria, SRB)的生物硫化途径受到关注，该方法利用SRB代谢产物S²⁻实现nZVI的原位硫化，具有绿色、可持续的优势。然而，目前针对SRB体系中nZVI投加量对生成的生物硫化nZVI (S-nZVI^bio)颗粒界面结构和还原脱氯性能的影响机制仍缺乏系统认识。【目的】 通过构建不同nZVI投加量的SRB培养体系，阐明不同nZVI投加量对S-nZVI^bio界面结构及其对三氯乙烯(trichloroethene, TCE)还原脱氯性能的影响机制。【方法】 在SRB介导的nZVI生物硫化体系中，通过设置0.1、1.0、5.0 g/L 3种nZVI投加条件，获得不同S-nZVI^bio颗粒，利用透射电子显微镜(transmission electron microscopy, TEM)和X射线光电子能谱仪(X-ray photoelectron spectroscopy, XPS)表征其界面结构，并通过批式实验评估TCE的降解动力学、产物分布及电子效率。【结果】 低投加量(0.1 g/L)时Fe²⁺供给不足，颗粒表面形成不完整FeS_x包覆层，并且附着较多的微生物产物，TCE降解速率和电子效率均偏低；高投加量(5 g/L)时因S²⁻相对不足导致硫化不完全，虽表现出最高的TCE降解速率，但电子效率下降；中等投加量(1 g/L)下Fe²⁺与S²⁻供给良好，颗粒表面生成均一致密的FeS_x层，同步实现了较高的TCE降解速率与电子效率。【结论】 SRB介导的生物硫化能够显著提升nZVI的脱氯性能，但其效果受不同nZVI投加量条件下Fe²⁺与S²⁻的供给关系影响。适量投加有利于获得界面结构完整、电子效率与降解性能兼优的S-nZVI^bio。该发现可为“定制”合理高效的nZVI “生物硫化”策略提供理论支持。

Abstract:

[Background] Sulfidated nano-scale zero valent iron (S-nZVI) has been extensively investigated for the remediation of chlorinated hydrocarbon (CAH)-contaminated groundwater due to its high reductive dechlorination activity and enhanced electron utilization efficiency. Sulfidation modification can improve the reactivity of nZVI toward CAHs and suppress parasitic reactions with water. However, conventional chemical sulfidation methods are often costly and complex, which limit their large-scale application. Recently, a biologically mediated sulfidation approach using sulfate-reducing bacteria (SRB) has attracted increasing attention. This strategy employs sulfide metabolites from SRB to achieve in situ sulfidation of nZVI, offering a greener and more sustainable alternative. Nevertheless, the role of nZVI dosage in shaping the interfacial structure and dechlorination performance of the resulting biogenic sulfidated nZVI (S-nZVI^bio) remains unclear. [Objective] To elucidate how different nZVI dosages in SRB systems affect the interfacial structure of S-nZVI^bio and its reductive dechlorination performance toward trichloroethene (TCE). [Methods] SRB-nZVI coculture systems were established with three nZVI dosages (0.1, 1.0, and 5.0 g/L) to obtain distinct S-nZVI^bio particles. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize particle morphology and surface chemistry, while batch experiments were conducted to evaluate TCE degradation kinetics, product distribution, and electron efficiency. [Results] At the low dosage (0.1 g/L), insufficient Fe²⁺ release resulted in incomplete FeS_x shell formation, and more microbial products were attached, leading to slow TCE degradation and low electron efficiency. At the high dosage (5 g/L), the relative scarcity of S²⁻ caused incomplete sulfidation. Although the highest TCE degradation rate was observed, the electron efficiency declined. At the medium dosage (1 g/L), Fe²⁺ and S²⁻ supply was well balanced, enabling the formation of a uniform and dense FeS_x layer, thereby achieving both rapid TCE degradation and high electron efficiency. [Conclusion] SRB-mediated sulfidation significantly enhanced the dechlorination performance of nZVI, while its effectiveness was governed by the Fe²⁺ and S²⁻ supply balance regulated by nZVI dosage. An appropriate nZVI dosage facilitated the formation of well-structured S-nZVI^bio with high dechlorination activity and electron efficiency. These findings provide theoretical support for designing efficient and sustainable biogenic sulfidation strategies of nZVI for groundwater remediation.