Integrated modeling and experimental evaluation of hydrodynamic and microbial controls on DNAPL dissolution and detoxification

基于生物还原性脱卤的原位生物修复是目前对水相氯化乙烯污染场地的一种成熟的修复方法。然而，美国环保署估计，在美国46,000个污染地点，氯化乙烯以致密非水相液体（DNAPL）的形式存在。这些已知或疑似致癌物的DNAPL形式的污染物的存在，是修复工作的主要障碍，对人类和生态健康有着广泛的影响。重要的是，DNAPL在地下水中的非生物溶解是一个缓慢的过程，可能需要几百年的时间才能耗尽DNAPL污染源。几种原位DNAPL处理方法使用物理化学过程来调动并随后捕获和/或破坏污染物，从而加速清理过程。这些方法实施起来困难且成本高，并且可能通过制造不适合微生物生存的条件而妨碍溶解污染物的生物修复。最近，人们对使用脱盐呼吸细菌通过生物增强溶解来处理DNAPLs越来越感兴趣，即通过还原脱氯对dnapl -水界面附近溶解的污染物进行氯化乙烯DNAPLs的大量去除。这种方法很有吸引力，因为它不依赖于DNAPL的动员，并且与使用生物修复技术清除溶解的污染物兼容。虽然生物增强溶解看起来很有希望，但使用“黑箱”方法设计生物DNAPL源处理措施可能无法促进和维持具有最大生物增强溶解率潜力的种群的生长。拟议项目的重点是了解水动力学和不同脱盐种群之间以及其他社区成员之间的竞争在确定DNAPL源区和溶解污染物柱的脱盐种群分布以及由此产生的对生物增强溶解程度和解毒程度的影响方面所起的相互作用。对生物增强氯化乙烯溶解和解毒的流体动力学和微生物控制的评估将使用综合建模和实验方法完成，其中包括以下关键目标：(1)利用数学模型理论预测3种模型情景下微生物竞争、水动力条件和生物增强之间的关系，设计微模型系统研究孔尺度上DNAPL溶解和源区微生物生态。(2)通过实验评估微生物竞争和流体动力学对种群分布、溶解生物增强和烟羽解毒的影响，利用微模型独立估算关键系统参数，并验证模型预测结果。一种创新的荧光原位杂交方法将用于直接可视化和量化微模型中的种群分布。(4)将使用一个中等规模的流动池来测试微模型实验和数学建模是否可以预测放大系统中的生物增强效应。(5)在实验结果的基础上完善数学模型，并用于预测微生物竞争和流体动力学对四种DNAPL配置的DNAPL源区寿命的影响。本研究将促进我们了解在含有DNAPL和溶解污染物的环境中，水动力条件和其他因素如何影响去盐呼吸种群和其他种群对生长基质的竞争分布和结果。这些信息将改变我们如何解释在含有DNAPL源区的许多地点影响污染物行为的生物和物理现象，以及我们如何指导这些地点的修复工作。最重要的是，它将用于确定生物源区处理的合适条件，并设计处理系统，优化DNAPL溶解的生物增强和现场清理目标的实现。将通过让少数族裔服务机构的社区学院学生与马里兰大学本科生合作的研究经验，促进未被充分代表的群体参与科学和工程学科，并为社区学院教师提供培训机会。通过大型生物修复会议提供的短期课程以及基于网络的交互式模拟工具的开发将确保结果得到广泛传播和应用，并促进生物修复从业人员的终身学习。

0934004BeckerIn situ bioremediation based on biological reductive dehalogenation is now an established remediation approach for sites contaminated with aqueous-phase chlorinated ethenes. However, the EPA estimates that chlorinated ethenes are present as dense non-aqueous phase liquids (DNAPLs) at 46,000 contaminated sites in the U.S. The presence of DNAPL forms of these contaminants, which are known or suspected carcinogens, is a major obstacle to remediation efforts that has widespread implications for human and ecological health. Importantly, abiotic dissolution of DNAPLs into groundwater is a slow process and may require several hundred years to deplete the DNAPL source of contamination. Several in situ DNAPL treatment methods use physicochemical processes to mobilize and subsequently capture and/or destroy contaminants and thus accelerate the clean-up process. These methods can be difficult and costly to implement and may preclude bioremediation of dissolved contaminants by making conditions inhospitable to microorganisms.Recently, interest has grown in the use dehalorespiring bacteria to treat DNAPLs through bioenhanced dissolution, i.e., enhanced mass removal from chlorinated ethene DNAPLs through reductive dechlorination of dissolved contaminants near the DNAPL-water interface. This approach is appealing because it does not rely on DNAPL mobilization and is compatible with the clean-up of dissolved contaminants using bioremediation. Although bioenhanced dissolution appears promising, the design of biological DNAPL source treatment measures using a "black box" approach may not promote and sustain the growth of the populations with the greatest potential to bioenhance dissolution rates. The proposed project focuses on understanding the interrelated roles that hydrodynamics and competition among different dehalorespiring populations, as well as other community members, play in determining the distribution of dehalorespiring populations in the DNAPL source zone and dissolved contaminant plume and the resulting impact on the magnitude of bioenhanced dissolution and the extent of detoxification. Evaluation of the hydrodynamic and microbial controls on bioenhanced dissolution and detoxification of chlorinated ethenes will be accomplished using an integrated modeling and experimental approach that includes the following key objectives: (1) Mathematical modeling will be used to theoretically predict the relationships between microbial competition, hydrodynamic conditions, and bioenhancement for three model scenarios and design a micromodel system for studying DNAPL dissolution and source-zone microbial ecology at the porescale.(2) The micromodels will be used to independently estimate key system parameters and test model predictions for the three scenarios by experimentally evaluating the effects of microbial competition and hydrodynamics on population distribution, dissolution bioenhancement and plume detoxification. An innovative fluorescent in situ hybridization approach will be used to directly visualize and quantify population distribution in the micromodel. (4) An intermediate-scale flow cell will be used to test whether the micromodel experiments and mathematical modeling can predict bioenhancement effects in a scaled up system. (5) Mathematical modeling will be refined based on the experimental results and used to predict the effects of microbial competition and hydrodynamics on DNAPL source zone longevities for four DNAPL configurations.The proposed research will advance our understanding of how hydrodynamic conditions and other factors influence the distribution and outcome of competition among dehalorespiring and other populations for growth substrates in environments containing DNAPL and dissolved contaminants. This information will transform how we interpret the biological and physical phenomena affecting contaminant behavior at the many sites containing DNAPL source zones and how we direct our remediation efforts at those sites. Most importantly, it will be used to determine the conditions under which biological source zone treatment is appropriate and design treatment systems that optimize bioenhancement of DNAPL dissolution and the realization of site clean-up goals.Participation of underrepresented groups in science and engineering disciplines will be promoted through research experiences that partner community college (CC) students at a Minority Serving Institution with undergraduate students at the University of Maryland and provide training opportunities for CC faculty. The development of a short course offered through a major bioremediation conference, as well as an interactive Web-based simulation tool, will ensure results are broadly disseminated and applied and promote lifelong learning among bioremediation practitioners.