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

0934004BeckerIn situ bioremediation based on biological reductive dehalogenation is now an established remediation approach for sites polluted with aquesously-phase chlorinated ethenes. 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。这些污染物的DNAPL形式（已知或疑似致癌物）的存在是补救工作的主要障碍，对人类和生态健康具有广泛影响。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动员并随后捕获和/或破坏污染物，从而加速清洁过程。这些方法实施起来可能困难且昂贵，并且可能通过使条件不适合微生物而妨碍溶解的污染物的生物修复。最近，对使用脱卤呼吸细菌通过生物增强溶解来处理DNAPL的兴趣已经增长，即，通过在DNAPL-水界面附近溶解的污染物的还原脱氯，增强从氯化乙烯DNAPL的质量去除。这种方法是有吸引力的，因为它不依赖于DNAPL动员，并与使用生物修复溶解的污染物的清理兼容。虽然生物增强溶解似乎是有前途的，生物DNAPL源处理措施的设计，使用“黑盒子”的方法可能不会促进和维持增长的人口最大的潜力，生物增强溶解速率。拟议项目的重点是了解流体动力学和不同dehalorespiring种群之间的竞争，以及其他社区成员，在确定DNAPL源区和溶解污染物羽流的dehalorespiring种群的分布，以及由此产生的生物增强溶解的程度和解毒程度的影响发挥相互关联的作用。将采用一种综合建模和实验方法，完成对氯化乙烯生物强化溶解和解毒的流体动力学和微生物控制的评价，其中包括以下关键目标：（1）数学模型将用于理论上预测微生物竞争、水动力条件和生物强化的三个模型方案，并设计了一个微观模型系统，研究DNAPL溶解和源带微生物生态在孔隙尺度。(2)微观模型将通过实验评估微生物竞争和流体动力学对种群分布、溶解生物增强和羽流解毒的影响，用于独立估计关键系统参数和测试三种情景的模型预测。一种创新的荧光原位杂交方法将被用来直接可视化和量化人口分布的微观模型。(4)一个中等规模的流动池将被用来测试微模型实验和数学建模是否可以预测在一个放大的系统中的生物增强效果。(5)基于实验结果，我们将进一步完善数学模型，并用于预测微生物竞争和水动力学对四种DNAPL配置的DNAPL源区寿命的影响。拟议的研究将促进我们对水动力学条件和其他因素如何影响在含有DNAPL和溶解的环境中脱卤呼吸和其他种群之间对生长基质的竞争的分布和结果的理解。污染物。这些信息将改变我们如何解释生物和物理现象，影响污染物的行为在许多网站包含DNAPL源区，以及我们如何指导我们的修复工作在这些网站。最重要的是，它将用于确定生物源区处理的适当条件，并设计处理系统，优化DNAPL溶解的生物增强和实现现场清理目标。通过与社区学院（CC）合作的研究经验，将促进科学和工程学科中代表性不足的群体的参与学生在少数民族服务机构与本科生在马里兰州大学，并提供培训机会，为CC教师。通过一次重要的生物补救会议开设短期课程，并开发一个互动式网络模拟工具，将确保广泛传播和应用成果，并促进生物补救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.