生物炭对微生物/铁矿物还原氯代有机物的作用机制

In the anaerobic environment like soil, chlorinated organic contaminants including pentachlorophenol (PCP) are synergistically reduced by microorganism/iron mineral system and this is a main degradation routine for these contaminants. Biochar, which is one of the coexisting substances in the environment of soil, can influence the reduction and degradation of these contaminants by adsorption, complexation and electron transfer in the reaction process. However, the mechanisms are still unclear and ready to study deeply. This work attempts to choose trichloroethylene (TCE) and PCP as model contaminants, and concentrates to investigate the effects and mechanisms of biochar on the synergic reduction of chlorinated organic contaminants by microorganism/iron mineral. For this purpose, we are ready to study the effects of quinones and condensed ring of biochar under different pyrolysis conditions, on the electron transfer between S. decolorrationis and goethite (or chlorinated organic contaminants), and investigate the influence of complex interactions between oxygen-containing groups on these biochars and Fe(II) and the sorption capacities of biochars towards the reactants, on the synergic reduction of chlorinated organic contaminants in the reaction process. Furthermore, the changes in the yields of mineral-bound Fe(II), redox potentials of Fe(III)/Fe(II), and the concentrations of reactants and products are all determined, and the microstructures and components of Fe and secondary mineral on the surface of biochar and mineral are also assayed by in site XAFS, XPS, and XRD, in order to clarify the effects and mechanisms of the biochars with different components and surface properties on the synergic reduction of chlorinated organic contaminants by microorganism/iron mineral. This work can provide a theoretical direction for deeply recognition of the migration, transformation and fate of chlorinated organic contaminants in the soil.

土壤等厌氧环境中，微生物/铁矿物协同降解氯代有机污染物是其迁移转化的主要途径。土壤中的生物炭，可通过吸附、配合和电子传递作用影响微生物/铁矿物对氯代有机物的协同降解。本课题拟以三氯乙烯、五氯酚为模型氯代有机物，研究生物炭在微生物/铁矿物协同降解氯代有机物过程中的影响及作用机制。重点研究不同热解条件和老化的生物炭中醌类物质及稠环结构对微生物与针铁矿（有机物）电子传递性能的影响及机制，含氧基团与Fe(II)的配合作用以及生物炭的吸附富集对体系中氯代有机污染物协同降解的影响。结合分析反应体系中矿物结合Fe(II)量、Fe(III)/Fe(II)氧化还原电位、反应物和产物浓度，原位XAFS、XPS、XRD等考察反应过程中矿物与生物炭表面Fe和次生矿物微观结构和组成的变化，揭示不同组成和表面特性的生物炭对微生物/铁矿物协同降解氯代有机物的作用机制，以更好地认识土壤中氯代有机污染物的迁移转化及归趋。

由于氯霉素结构稳定、生物可降解性差，在土壤、地下水和沉积物中逐渐积累，对生态环境和人类健康造成威胁。厌氧环境中，铁还原菌/铁矿物的异化还原作用参与了有机物、重金属等污染物的转化降解，生物炭作为环境共存组分将对上述还原转化过程产生影响。但迄今，生物炭对铁还原菌的异化还原和抗生素的降解转化的影响研究还未深入。为此，本课题通过研究（1）不同组成和性能的生物炭的制备和表征；（2）生物炭对脱色希瓦氏菌S12还原去除氯霉素的影响及机理；（3）S12/针铁矿还原去除氯霉素的机制；（4）生物炭对S12/针铁矿还原降解氯霉素的影响机制；（5）氯霉素降解途径，揭示S12/针铁矿还原去除氯霉素的反应机理，以及生物炭对其还原降解的影响机制。.主要结果如下：（1）生物炭来源和热解温度对其组成影响很大，稻草来源的生物炭（DBC)酚羟基、醌基等活性基团比木屑来源的生物炭（MBC)高，其中750℃热解得到的稻草生物炭（DBC750)电子传递性能最佳，其次为600℃和450℃。（2）生物炭显著促进S12对氯霉素的还原去除，促进作用依次为DBC750 > DBC600 > DBC450 > MBC750 > MBC450 > MBC600，其中S12/DBC750对氯霉素的去除率达到99%，远高于相同条件下单独S12的去除率（15%），反应速率也是后者的28.6倍。机制研究表明生物炭提高了生物量、增强了S12对氯霉素的电子转移。（3）S12/针铁矿对氯霉素的去除效率为82%，显著高于单独S12对氯霉素的去除率。机理研究表明，S12异化还原针铁矿能产生端羟基结合Fe(II)、促进蓝铁矿的原位生成、提高生物量，从而促进了氯霉素的去除。（4）生物炭对S12/针铁矿还原去除氯霉素具有明显的促进作用，其中DBC600的促进作用最大。通过对影响机制的研究推测，DBC600含有丰富的酚羟基和醌基结构，促进S12对针铁矿的异化还原，提高活性结构Fe(II)的生成量，从而增强了氯霉素的去除效率。（5）利用LC-MS对S12/DBC750还原降解氯霉素的产物分析，推测氯霉素经过硝基还原、脱氯和脱羟基，生成分子量为224和242的降解产物，该产物的毒性明显低于氯霉素，容易被微生物降解。