生物炭负载微生物在“地下水抽提淋滤土壤共修复”体系中降解有机污染物的机制

Biochar as a carrier of microorganisms has been used for organic contaminants degradation in soil (Polycyclic aromatic hydrocarbon, Trichloroethylene, etc). Microbe immobilization is proved to be an effective strategy for improving the microbe’s survivability in an adverse environment. Also, biochar could function as a sorbent of pollutants simultaneously. Whereas, the resulting mass transfer resistance weakens the accessibility of organic molecules to microorganisms and the degradation efficiency is still not satisfactory. In this study, a dynamic process “Soil-Groundwater Pumping-Soil Leaching Integrated Remediation” developed by our group independently will be employed for simultaneously remediating organic contaminants both in soil and groundwater. In this system, the groundwater is pumped continually and then leaches through the bulk soil, in which biochar-loaded microorganisms are amended into the upper layer of the soil. With the circulating water flow, an active functional layer will be formed for degrading organic contaminants integrated with physical, chemical and biological processes. This study aims at investigating the influence of the hydrodynamic conditions on pH, redox potential and mass transfer etc., and clarifying the pollutants adsorption or enrichment efficiency by biochar under this dynamic system; To reveal the underlying reasons that biochar as a “shelter” of microorganisms, modern molecular biological analysis techniques including High-Throughput Sequencing and Metagenomics, combined with Fluorescence in Situ Hybridization or Focused Ion Beam Cutting instrument would be utilized to observe the colonization, activity and spacial distribution of microorganisms in biochar. It would be investigated that if water leaching could drive more nutrients to dissolve from biochar and act as cometabolism substrate of bacteria. Besides, perhaps the reinforced mass transfer could optimize the electron shuttle induced by biochar surface functional groups, or it could stimulate the production of reactive oxygen and free radicals. These will be measured by means of Mediate Oxidation or Reduction Electrode and Electron Spin Resonance Spectrum to reveal the underlying mechanisms of biochar in optimizing the colonization and strengthening the organic contaminants degradation. This study aims at providing theoretical basis for the newly developed process “Groundwater Pumping-Soil Leaching Integrated Remediation” and driving the practical application of microbiological remediation technology.

利用生物炭作为固定微生物的载体修复土壤有机污染物（多环芳烃、三氯乙烯等）已有一些探索，证明固定化可提高微生物的环境耐受性，并且生物炭对污染物有显著吸附作用，但由此产生的传质阻力导致降解效率依然不理想。本研究拟采用“地下水抽提”再“淋滤土壤”的动态方式，将生物炭固定化微生物施于土层，形成一层集物理、化学和生物机制为一体的活性净化层。研究水动力条件对体系pH、氧化还原电位和传质的影响，明确生物炭在此动态体系中吸附污染物的效应；利用荧光原位杂交或聚焦离子束切割手段，结合现代分子生物学技术高通量测序和宏基因组学，探明菌落在生物炭颗粒中的分布；阐明水流淋滤是否促进生物炭营养物的溶出为微生物提供基质；分别运用介导氧化还原电极和电子自旋共振测定体系中电子传递效率和活氧自由基的变化，揭示生物炭优化菌群和强化降解的多重机制。研究将为发展“地下水抽提淋滤土壤共修复”工艺提供理论支撑，促进微生物修复技术的应用。

本项目以同步原位修复土壤与地下水中有机污染物为目标，研发“地下水抽提淋滤土壤共修复”工艺，利用生物炭负载微生物作为活性功能层，构建地下水抽出并淋滤至土壤的动态循环修复体系。充分利用生物炭的载体功能、吸附功能、电子传输功能等，形成集“吸附、降解、氧化”为一体的活性净化层，实现对土壤和地下水中有机污染物的高效修复。主要研究的内容涉及：生物炭强化土壤及水体中苯酚的好氧微生物降解；生物炭强化地下水中三氯乙烯的厌氧微生物降解；生物炭耦合微生物修复三氯乙烯和砷共污染地下水的效果；微生物-生物炭强化的反应层降解2,4-二氯酚过程。研究表明，生物炭添加入微生物降解系统，能够显著提高微生物对有机污染物的降解效率，其促进机制是多重的，且在不同的阶段，促进机制不同。初始阶段生物炭快速吸附高浓度有机污染物，使其浓度降低约40%左右，对菌体毒性降低，不仅大大缩短微生物的停滞期，将污染物完全降解的时间从十几天缩短到几天，而且作为菌体生长的载体，使菌体快速增殖。随着降解进行，大量小分子酸产生，pH降低，产生酸抑制，而生物炭的碱性能够缓冲pH降低的冲击，保证了菌体的活性。后期营养物质匮乏的系统中，生物炭溶出的小分子碳，可作为菌体生长的基质，提供碳源。生物炭不仅从多方面促进微生物的降解能力，并且能够在砷等重金属共存的条件下，同时去除砷，实现有机污染物和重金属的共修复。通过构建的“地下水抽提淋滤土壤共修复”装置，创造了良好的动态接触条件，实现了土壤和地下水污染物的同时高效修复。基于项目研究共发表19篇 SCI 收录论文，中文核心期刊论文2篇，项目负责人均为唯一通讯作者。申报发明专利4件，已公开2件。参加国际会议6人次，作大会口头报告4人次。项目负责人担任三个期刊的青年编委，并担任上海市土壤与地下水污染评审专家。培养博士后1名，博士生1名，硕士生6名。目前正在探索生物炭的量产和示范工程，积极进行成果转化和应用。