Evaluation of Partitioning Electron Donors for Enhanced Bioremediation of Chlorinated Solvent Source Zones

natalie L. Cápiro和Kurt D. Pennell （Tufts University; Medford， MA）最近的研究表明，微生物能够在氯化溶剂源区附近进行生物降解。这种生物活性可以增强（加速）氯化溶剂的水溶液溶解（去除），并有可能提供更有效的源区处理，从而降低潜在的暴露和修复成本。然而，生物修复的性能，更具体地说，生物增强溶解，面临两个挑战；持续释放电子供体（食物来源）并将电子供体递送到预定目标。为了克服这些限制，一种潜在的替代方案是分配电子给体（ped），即相对水溶性的有机化合物（例如乙酸正丁酯），但也会分配成（直接与）氯化溶剂混合。当PED被输送到地下污染源区时，它优先进入有机分离相氯化溶剂中，然后随着污染物慢慢溶解回经过的地下水中。这种电子供体传递策略旨在促进靠近污染源区域的氯化溶剂降解细菌的生长，同时最大限度地减少与氯化溶剂生物修复（例如甲烷生产）无关的微生物过程中电子供体的消耗。本研究的具体目标是评估控制PED输送、传质和消耗的物理、化学和生物过程，以支持氯化溶剂源区微生物的持续生物降解。将以三氯乙烯（TCE）作为代表性污染物进行实验室规模实验和数学模型的结合。该研究计划围绕四个任务进行，这些任务将：(1)基于非生物和生物间歇式反应器研究评估和选择PED进行详细研究；(2)与目前的电子供体传递方法相比，量化含有残余TCE的柱中PED的传递和释放，以及生物增强的溶解和降解速率；(3)测量PED的传递/释放、TCE的溶解和降解的空间分布和时间演变；(4)建立数学模型，从实验数据中获得传质和利用率参数，并预测对不同PED输送策略和地下含水层条件的响应，以支持潜在的扩大到现场应用。美国环保署估计，未来30年将需要2090多亿美元（按2004年的汇率计算），以减轻235,000至355,000个氯化溶剂污染地点的危害，影响美国近30%的饮用水供应。此外，这些成本估算不包括许多易受蒸汽侵入的地点，而蒸汽侵入现在被认为是城市地区的主要暴露途径。从这种新型修复技术的测试和验证中获得的知识将通过改进对强化生物处理的理解，为减少氯化溶剂源区寿命和修复成本提供一种可持续的方法。将实验研究与数学建模相结合，将为从业者和研究人员评估PED在一系列潜在补救方案中的表现提供必要的指导方针和速率参数。此外，该项目将把教育倡议纳入研究人员的研究和教学活动，目的是将获得的知识的影响扩大到期刊出版物和会议报告的传统框架之外。这一目标将通过以下举措实现：(a)纳入本科生进行实验室研究，(b)招募女性和代表性不足的少数民族科学和工程本科生和研究生，(c)向监管机构和受影响的社区传播教学工具。

Evaluation of Partitioning Electron Donors for Enhanced Bioremediation of Chlorinated Solvent Source ZonesNatalie L. Cápiro and Kurt D. Pennell (Tufts University; Medford, MA)Recent studies have demonstrated that microorganisms are capable of biodegradation within close proximity to chlorinated solvent source zones. This biological activity can enhance (accelerate) aqueous dissolution (removal) of chlorinated solvents, and has the potential to provide more effective source zone treatment, thereby reducing potential exposure and remediation costs. However, the performance of bioremediation, and more specifically, biologically-enhanced dissolution, faces two challenges; sustained release of electron donor (food source) and delivery of electron donor to the intended target. To overcome these limitations, a potential alternative are partitioning electron donors (PEDs), organic compounds (e.g., n-butyl acetate) that are relatively water soluble, but also partition into (directly mix with) chlorinated solvents. When a PED is delivered to the subsurface contaminant source zone, it preferentially partitions into the organic separate phase chlorinated solvent, and then slowly dissolves back into the passing groundwater along with the contaminant. This strategy of electron donor delivery is intended to promote the growth of chlorinated solvent degrading bacteria in close proximity to the contaminant source zone, while minimizing consumption of electron donor in microbial processes not associated with chlorinated solvent bioremediation (e.g., methane production). The specific objectives of this research are designed to assess the physical, chemical and biological processes that govern PED delivery, mass transfer, and consumption to support sustained microbial biodegradation in chlorinated solvent source zones. A combination of laboratory-scale experiments and mathematical modeling will be conducted using trichloroethene (TCE) as a representative contaminant. The research program is structured around four tasks that will: (1) evaluate and select PEDs for detailed study based on abiotic and biotic batch reactor studies, (2) quantify PED delivery and release, and rates of bioenhanced dissolution and degradation in columns containing residual TCE in comparison to current electron donor delivery approaches, (3) measure the spatial distribution and temporal evolution of PED delivery/release, TCE dissolution and degradation, and microbial communities in heterogeneous aquifer cells to assess the potential for improved bioremediation under more realistic conditions, and (4) implement mathematical models to obtain mass transfer and utilization rate parameters from experimental data, and predict responses to alternative PED delivery strategies and subsurface aquifer conditions to support potential scale up to field-application. The U.S. EPA estimates that more than $209 billion dollars (in constant 2004 dollars) will be needed over the next 30 years to mitigate hazards at 235,000 to 355,000 chlorinated solvent contaminated sites, impacting nearly 30% of U.S. drinking water supplies. Additionally, these cost estimates do not include many sites susceptible to vapor intrusion, which is now recognized as a key exposure pathway in urban areas. The knowledge gained from the testing and validation of this novel remediation technique will provide a sustainable approach to reduce chlorinated solvent source zone longevity and remediation costs through an improved understanding of enhanced biological treatment. Integration of experimental studies with mathematical modeling will yield guidelines and rate parameters necessary for practitioners and researchers to assess PED performance for a range of potential remediation scenarios. Furthermore, the project will incorporate educational initiatives into the research and instructional activities of the investigators, with the goal of extending the impact of acquired knowledge beyond the traditional framework of journal publications and conference presentations. This goal will be achieved through the following initiatives: (a) the inclusion of undergraduate students conducting laboratory research, and (b) recruitment of female and underrepresented minority science and engineering undergraduate and graduate students, (c) dissemination of instructional tools to regulatory agencies and impacted communities.