Gao Beibei, Wang Xiaopu, Ford Roseanne M
Department of Chemical Engineering, University of Virginia, Charlottesville, VA 22904, United States.
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong 266580, China.
Sci Total Environ. 2023 Feb 10;859(Pt 1):160004. doi: 10.1016/j.scitotenv.2022.160004. Epub 2022 Nov 8.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, EPA-designated priority pollutants for soil and groundwater, remaining recalcitrant to bioremediation because of limited bioavailability. In this work, we used naphthalene as a model PAH and soil bacteria Pseudomonas putida G7 to investigate the potential role of chemotaxis to enhance access to PAHs in heterogenous porous media. To this aim, we conducted transport experiments and numerical simulations with chemotactic bacteria and naphthalene trapped within a non-aqueous phase liquid (NAPL) mainly in low permeable areas of a dual-permeability microfluidic device. Microscopic imaging showed higher accumulations of chemotactic bacteria, about eight times that of nonchemotactic bacteria, at the junctures between high and low permeability regions. Pore-scale simulations for fluid flow and naphthalene revealed that the junctures are stagnant areas of fluid flow, which generated strong and temporally persistent naphthalene gradients. The landscape and densities of bacterial accumulation at the junctures were strongly regulated by flow profiles and naphthalene gradients especially those transverse to flow. We conducted macroscale simulations using convective dispersion equations with an added chemotactic velocity to account for directed migration toward naphthalene. Simulated results showed good consistency with experiments and pore-scale simulation as normalized bacterial accumulation per mm of NAPL was 7.80, 7.84 and 7.71 mm for experiments, pore-scale and macroscale simulations, respectively. Macroscale simulations indicated that in the absence of grain-boundary restrictions associated with the pore structure bacterial dispersion needed to be increased by 50 % to account for the interplay between chemotactic response and naphthalene gradients at the pore-scale level. Our work details the mechanism of pore-scale chemotaxis in enhancing bioavailability of PAHs and its impact on biomass retention at the system level, which provides a potential solution toward more efficient bioremediation for contaminants such as PAHs with limited bioavailability.
多环芳烃（PAHs）无处不在，是美国环境保护局（EPA）指定的土壤和地下水优先污染物，由于生物可利用性有限，它们对生物修复具有抗性。在这项工作中，我们以萘作为模型PAH，并利用土壤细菌恶臭假单胞菌G7来研究趋化作用在增强多相多孔介质中PAHs可及性方面的潜在作用。为此，我们用趋化细菌和被困在非水相液体（NAPL）中的萘进行了传输实验和数值模拟，该非水相液体主要存在于双渗透微流控装置的低渗透区域。微观成像显示，在高渗透区域和低渗透区域的交界处，趋化细菌的聚集量更高，约为非趋化细菌的八倍。对流体流动和萘进行的孔隙尺度模拟表明，这些交界处是流体流动的停滞区域，会产生强烈且随时间持续的萘梯度。交界处细菌聚集的态势和密度受到流动剖面和萘梯度的强烈调节，尤其是那些垂直于流动方向的梯度。我们使用对流扩散方程并添加趋化速度进行了宏观尺度模拟，以考虑细菌向萘的定向迁移。模拟结果与实验和孔隙尺度模拟结果具有良好的一致性，实验、孔隙尺度模拟和宏观尺度模拟中每毫米NAPL的归一化细菌聚集量分别为7.80、7.84和7.71。宏观尺度模拟表明，在不存在与孔隙结构相关的晶界限制的情况下，细菌扩散需要增加50%，以考虑孔隙尺度水平上趋化反应和萘梯度之间的相互作用。我们的工作详细阐述了孔隙尺度趋化作用增强PAHs生物可利用性的机制及其在系统层面上对生物量保留的影响，这为生物可利用性有限的污染物（如PAHs）提供了一种更高效生物修复的潜在解决方案。
