Utilization of Microbial Biofilms for Soil Improvement: Roles of Biofilm-mineral Interactions in Geomechanical Behaviors of Soils

岩土工程师关注的关键问题之一是如何改善土壤特性以减轻地质灾害。 本研究探讨了利用矿物表面原位微生物生物膜的形成作为土壤改良的一种手段。 尽管在广泛的工程应用中对生物膜进行了广泛的研究，但目前对地质材料中生物膜-矿物相互作用的认识仍处于起步阶段。 拟议的研究的目标是量化生物膜和土壤矿物之间的相互作用，并确定这种生物膜矿物相互作用对土壤力学性质的影响。主要重点是探讨的假设，由土壤细菌产生的生物膜覆盖土壤矿物和提高土壤的机械强度和刚度，其程度将取决于土壤矿物的物理化学性质，pH值和离子强度的孔隙水，以及围压。 这项研究将是从地质力学角度研究生物膜相关土壤的第一批努力之一，并将使用各种多尺度实验技术，如原子力显微镜，X射线计算机断层扫描，地球物理监测和三轴强度测试。 这些技术的结合将允许检查矿物学和孔隙水化学对生物膜对矿物的粘附力的影响，孔隙空间中的生物膜生长模式，以及进行生物膜生长的土壤的剪切行为。 因此，本研究的具体目标是通过表征矿物表面生物膜的组成和结构来选择模式细菌，在纳米尺度上量化模式细菌生物膜与土壤矿物之间的相互作用，在微观尺度上可视化土壤孔隙中生物膜生长的三维形态模式，并在土壤孔隙中观察生物膜的生长过程。从宏观尺度上研究生物膜的形成对土壤地质力学行为的影响。 建议的研究的成功将推进生物膜形成在提高土壤行为的作用的理解，通过确定与力学行为相关的最相关的因素，调查土壤强度和刚度的增强程度，并提供实验数据的发展生物膜相关土壤的理论力学模型。 社会将受益于对地质介质中生物膜形成的理解的进步以及微生物生物膜的智能使用的发展，以改善非原位和原位土壤性质。 生物膜的使用可以改善水文工程屏障;污染物的受控生物修复方法，以及用于减轻土壤侵蚀、泥石流和边坡不稳定的可持续土壤改良方法。 此外，该研究的结果将对天然和工程多孔介质的工程应用产生广泛的影响，例如农业/农田近地表土壤中的生物量积累，天然石油和天然气生产过程中的生物堵塞，使用选择性堵塞的微生物提高石油采收率，微生物燃料电池中的生物膜开发或生物燃料加工。这项研究的跨学科性质为研究生和本科生提供了独特的经验和机会，将生物科学，表面物理化学和生物物理学与岩土工程相结合。 此外，拟议对高中教师开展的教育和外联活动将扩大代表性不足的群体和少数民族学生对工程学的参与，加强他们的科学和工程学基础，并激发他们对工程学的兴趣。 研究和教育成果将通过在同行评审期刊和专业会议上发表、在区域会议上与高中教师一起展示演示实践模块以及通过大学网站传播演示实践模块的说明等方式，向公众和科学界广泛传播。

One of the key concerns of Geotechnical engineers has been how to improve soil behavior to mitigate geo-hazards. This research addresses the utilization of in-situ microbial biofilm formation on mineral surfaces as a means of soil improvement. Despite extensive research efforts on biofilms in a wide range of engineering applications, current knowledge of biofilm-mineral interactions in geologic materials is still in its infancy. The objectives of the proposed research are to quantify the interactions between biofilms and soil minerals, and to identify the effects of such biofilm-mineral interactions on the mechanical properties of soils. The primary emphasis is to explore the hypothesis that the biofilms produced by soil bacteria coat soil minerals and increase the mechanical strength and stiffness of soils, the extent of which will be dependent on physicochemical properties of the soil mineral, pH and ionic strength of pore water, as well as confining stress. This research will be among the first efforts to investigate biofilm associated soils from a geomechanical point of view, and will use various multi-scale experimentation techniques such as atomic force microscopy, X-ray computed microtomography, geophysical monitoring, and triaxial strength testing. The combination of those techniques will allow examination of the effects of mineralogy and pore water chemistry on adhesion forces of biofilms to minerals, biofilm growth patterns in pore spaces, and shear behavior of soils undergoing biofilm growth. Therefore, the specific aims of the proposed research are to select a model bacterium via characterization of the composition and structures of biofilms grown on mineral surfaces; to quantify the interactions between model bacterium biofilms and soil minerals at the nanoscale; to visualize the three-dimensional morphological patterns of biofilm growth in pore spaces of soils at the microscale; and to identify the effect of biofilm formation on geomechanical behavior of soils at the macroscale. Success of the proposed research will advance the understanding of the roles of biofilm formation in enhancing soil behavior, by identifying the most relevant factor related to mechanical behavior, investigating the extent of enhancement of soil strength and stiffness, and providing experimental data for development of a theoretical mechanistic model of biofilm-associated soils. Society will benefit from the advancement in understanding of biofilm formation in geo-media and the development of the intelligent use of microbial biofilms to improve ex-situ and in-situ soil properties. The use of biofilms may improve hydrologic engineering barriers; controlled bio-remediation methods of contaminants, and sustainable soil improvement methods for mitigating of soil erosion, debris flows, and slope instability. Moreover, the outcome of the research will have broad impact related to engineering applications to natural and engineered porous media, such as biomass accumulation in near-surface soils of agricultural/farm lands, bio-clogging during natural oil and gas production, microbial enhanced oil recovery using selective plugging, biofilm development in microbial fuel cells, or biofuel processing. The cross disciplinary nature of this research gives graduate and undergraduate students unique experiences and opportunities that integrate bioscience, surface physical chemistry, and geophysics with geotechnical engineering. In addition, the proposed educational and outreach activities with high school teachers will broaden the participation of underrepresented groups and minority students in engineering, strengthen their scientific and engineering foundation, and stimulate their interest in engineering. The research and educational results will be broadly disseminated to the public and scientific community through publications at peer-reviewed journals and professional conferences, exhibition of demo hands-on modules with the high school teachers at regional conferences, and dissemination of the description of the demo hands-on modules through university websites.