基于硫循环介导的生物电化学过程净化页岩气开采水力压裂返排废水的机制与调控

Shale gas exploitation has become an important national energy strategy due to the development of horizontal drilling and hydraulic fracturing technology. A large amount of flow back wastewater was produced from these process which contained high salt content and complex organic matter.The reuse of flowback wastewater in hydraulic fracturing after partially treated was highlighted. In this project, sulfur-cycle mediated bioelectrochemical processes were selected to purify flowback wastewater and recover the resource. The mechanism of sulfur-cycles mediated bioelectrochemical processes coupling with the degradation of complex organic matter were explored. Further more, the mapping relationships between microbial fuel cell (MFC) anode potential and the pathways and rates of different sulfur-cycles occurred in anode were studied and these rules were revealed. The laws of heavy metals removal and sulfur recovery through anodic potential regulation were also investigated. In addition, the mechanisms of flow-back wastewater desalination via microbial desalting cell (MDC) which was mediated with the special sulfate - sulfite cycle was explored and the key factor was discerned as well. The structure and characters of microbial community in sulfur-cycle mediated bioelectrochemical processes were further analyzed and understood. The operation of this project could provide scientific basis and technology choice for the development of new biological electrochemical treatment technology to purify the sulfate contained wastewater with high salinity and complex organics as well as their process regulation.

由于水平钻井和水力压裂技术的发展，页岩气开发已经成为我国重大能源战略。页岩气开采返排废水体积大并含高盐和复杂有机物，经部分处理再用于后期水力压裂是其重要发展方向。申请项目以净化返排废水和回收资源的硫循环介导的生物电化学过程为研究对象，阐明硫循环介导生物电化学过程降解复杂有机物的作用机理，认识和理解微生物燃料电池(MFC)阳极电位与硫循环发生途径和速率的映射关系和规律，探索阳极电位调控去除重金属、回收单质硫的机制和规律，研究在硫酸盐-亚硫酸盐循环下微生物脱盐电池(MDC)强化返排废水部分脱盐的机制和关键因素，分析和掌握硫循环介导的生物电化学系统中的微生物菌群及其特性。研究成果可以为发展净化含硫高盐复杂有机废水的生物电化学处理新工艺和过程调控提供科学依据和技术参考，具有重要科学意义和应用前景。

页岩气开采中产生大量的返排水（FFW）造成环境负担。本研究以去除返排水中复杂有机物、硫酸盐和重金属，脱除返排水的高盐度，并回收单质硫的生物电化学过程为研究对象。通过间歇改变硫酸盐浓度，探究其对微生物燃料电池处理返排水性能的影响。硫酸盐浓度越高，越利于MFC高效去除返排水中的有机物并产生电能。保持高浓度硫酸盐进水的MFC稳定运行后COD去除率为69.8±9.7%。通过硫酸盐还原耦合微生物燃料电池，探究硫循环介导的生物电化学过程同时去除页岩气开采返排水中有机物和铁。总铁的去除率为90.6±8.7%，COD的去除率为72±6%。阳极液中和阳极上分别富集的优势微生物Sulfurovum和unclassified¬¬_Desulfuromonadales对硫化物的生物和电化学氧化形成硫酸盐的过程起关键作用，并因此强化了该系统的硫循环，提高铁去除性能。通过向阳极施加四个不同水平的电位（-0.2, -0.1, 0.0和+0.2 V vs. SHE），探究生物电化学系统阳极电位调控硫循环途径的机制。表明电极电位控制可影响硫酸盐还原过程，硫代硫酸盐为硫循环重要中间产物。催化硫代硫酸盐等氧化为硫酸盐的Sox复合体在-0.1V阳极特殊显著富集，形成了新的硫酸盐-亚硫酸盐/硫代硫酸盐-硫酸盐的隐性硫循环。通过引入双阳极，调控电化学阳极电位（分别为-0.1V, +0.05V, +0.2V vs SHE.）实现同步净化返排水和回收单质硫。结果表明，在-0.1V的电位下调控36h后，有机物去除率为70.0±1.2%；硫酸盐还原产生的部分硫化物通过电化学转化为单质硫得到有效回收，回收率可达75.6±1.8%。研究PMo/CB-MFC处理压裂返排水的性能。当返排水中NaCl浓度为120g/L时，COD的去除率为50.8±15.0%，表明对高盐返排水具备处理能力。开展MDC回收铵和磷酸盐的研究，较高的NH4+浓度对电活性微生物代谢具有促进作用，利用MDC可以去除返排水中的COD并回收部分营养盐。引入流动电极电容去离子技术（FCDI）强化脱盐性能，在施加较低电压水平时，短时间运行对页岩气返排水具有一定脱盐性能，为后续返排水应用过程中盐度脱除提供了新的思路。本研究为生物电化学技术处理含高盐、复杂有机物、重金属和硫酸盐废水提供了新的思路。