多孔介质中的微生物迁移行为与影响因素研究进展

微生物在地下水和土壤环境中的迁移与地下水资源保护、地下水污染修复及土壤污染防治等息息相关。自然界中多孔介质具有结构复杂性和空间异质性。这导致微生物在其中的迁移易受多重环境因素的影响。本文总结了几种典型多孔介质中微生物迁移模型、理论与研究方法,并对多孔介质中影响微生物迁移行为的3种因素——物理、化学和生物因素进行了梳理。其中物理因素的影响主要包括多孔介质的粒径、表面粗糙度、饱和度、环境温度、水体流速等相关;化学因素主要包含流体pH、离子种类与强度、可溶性有机物含量、多孔介质自身化学性质等;生物因素不但涉及微生物种类、细胞大小和细胞表面特性,还与胞外聚合物的分泌、鞭毛运动及趋化性等相关。本综述旨在总结近年来有关微生物在多孔介质中迁移的相关研究,深入理解微生物在多孔介质中的迁移行为,为其在地下水和土壤污染修复中的实际应用提供理论依据。     

Real time monitoring of biofilm development under flow conditions in porous media

Biofilm growth can impact the effectiveness of industrial processes that involve porous media. To better understand and characterize how biofilms develop and affect hydraulic properties in porous media, both spatial and temporal development of biofilms under flow conditions was investigated in a translucent porous medium by using Pseudomonas fluorescens HK44, a bacterial strain genetically engineered to luminesce in the presence of an induction agent. Real-time visualization of luminescent biofilm growth patterns under constant pressure conditions was captured using a CCD camera. Images obtained over 8 days revealed that variations in bioluminescence intensity could be correlated to biofilm cell density and hydraulic conductivity. These results were used to develop a real-time imaging method to study the dynamic behavior of biofilm evolution in a porous medium, thereby providing a new tool to investigate the impact of biological fouling in porous media under flow conditions.     

Reduction of porous media permeability from in situ Leuconostoc mesenteroides growth and dextran production

In situ growth of bacteria in a porous medium can alter the permeability of that media. This article reveals that the rate of permeability alteration can be controlled by the inoculation strategy, nutrient concentrations, and injection rates. Based on experimental observations a phenomenological model has been developed to describe the inoculation of the porous medium, the in situ growth of bacteria, and the permeability decline of the porous medium. This model consists of two phases that describe the bacteria in the porous medium: (1) the nongrowth phase in which cell transport and retention are occurring; and (2) the growth phase in which the retained cells grow and plug the porous media. Transition from the transport phase to the growth phase is governed by the growth lag time of the cells within the porous medium. The importance of the inoculum injection strategy and the nutrient injection strategy is illustrated by the model. (c) 1996 John Wiley & Sons, Inc.     

Biomass plug development and propagation in porous media

Exopolymer-producing bacteria can be used to modify soil profiles for enhanced oil recovery or bioremediation. Understanding the mechanisms associated with biomass plug development and propagation is needed for successful application of this technology. These mechanisms were determined from packed-bed and micromodel experiments that simulate plugging in porous media. Leuconostoc mesenteroides was used, because production of dextran, a water-insoluble exopolymer, can be controlled by using different carbon sources. As dextran was produced, the pressure drop across the porous media increased and began to oscillate. Three pressure phases were identified under exopolymer-producing conditions: the exopolymer-induction phase, the plugging phase, and the plug-propagation phase. The exopolymer-induction phase extended from the time that exopolymer-producing conditions were induced until there was a measurable increase in pressure drop across the porous media. The plugging phase extended from the first increase in pressure drop until a maximum pressure drop was reached. Changes in pressure drop in these two phases were directly related to biomass distribution. Specifically, flow channels within the porous media filled with biomass creating a plugged region where convective flow occurred only in water channels within the biofilm. These water channels were more restrictive to flow causing the pressure drop to increase. At a maximum pressure drop across the porous media, the biomass yielded much like a Bingham plastic, and a flow channel was formed. This behavior marked the onset of the plug-propagation phase which was characterized by sequential development and breakthrough of biomass plugs. This development and breakthrough propagated the biomass plug in the direction of nutrient flow. The dominant mechanism associated with all three phases of plugging in porous media was exopolymer production; yield stress is an additional mechanism in the plug-propagation phase.     

Geometrical and Physical Modeling of Dilute Adsorbable Gas Flow in Porous Media: An Insider's Account of the Nicholson-Petropoulos Contribution

Abstract

Our joint research grew out of our postdoctoral work with RMB on related topics, namely gas flow in single capillaries (DN) and in porous media (JP); which led us to the realization that the conventional interpretation (in terms of pore models) of gas transport, especially adsorbable gas transport, in porous adsorbents, porous separating barriers and porous catalysts, was rather rudimentary.     

Transport of vanadium (V) in saturated porous media: effects of pH,ionic-strength and clay mineral

Vanadium, a hazardous pollutant, has been frequently detected in soil and groundwater, however, its transport behavior in porous media were not clearly understood. In this study, the effects of solution pH, ionic strength (IS) and the effect of clay mineral on the transport of vanadium in saturated porous media were investigated. Laboratory experiments using a series of columns packed with quartz sand were carried out to explore the retention and transport of vanadium with a range of ionic-strength (0.001–0.1 M) and pH (4–8) and two different types of clay minerals montmorillonite and kaolinite. Results of the breakthrough experiments showed that vanadium was highly mobile in the saturated porous media. The increase in pH rendered a higher transport of vanadium in saturated porous media. The study also indicated an easier transfer of vanadium with an increase in IS. Montmorillonite enhanced the mobility of vanadium in the column when compared to kaolinite. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions was used to describe the retention and transport of vanadium in the columns very well.     

Transport of bacteria in porous media and its enhancement by surfactants for bioaugmentation: A review

The success of bioaugmentation processes for groundwater bioremediation requires efficient transport of bacteria in the subsurface environment. In this paper, the factors that influence transport of bacterial cells in porous media are reviewed and the effects of surfactants on the transport are discussed. Movement of bacterial cells in porous media is a process driven by advection and hydrodynamic dispersion forces of fluids. Immobilization of bacterial cells takes place due to processes such as adsorption and straining. Blocking and ripening along with bacterial migration process decrease and increase the retention of cells in porous media, respectively. Physicochemical properties of the porous media, groundwater chemistry, and properties of the bacterial cells affect the transport behavior. Surfactants have the potential to modify bacterial surface properties for both bacterial cells and medium solids, and thus enhance bacterial transport.     

Development and evaluation of an experimental protocol for 3-D visualization and characterization of the structure of bacterial biofilms in porous media using laboratory X-ray tomography

The development of a reliable model allowing accurate predictions of biofilm growth in porous media relies on a good knowledge of the temporal evolution of biofilm structure within the porous network. Since little is known about the real 3-D structure of biofilms in porous media, this work was aimed at developing a new experimental protocol to visualize the 3-D microstructure of the inside of a porous medium using laboratory X-ray microtomography. A reliable and reproducible methodology is proposed for (1) growing a biofilm inside a porous medium, and (2) X-ray tomography-based characterization of the temporal development of the biofilm at the inlet of the biofilter. The statistical analysis proposed here also validates the results presented in the literature based on a biofilm structure single measurement.     

Kinetic analysis of microbial sulfate reduction by desulfovibrio desulfuricans in an anaerobic upflow porous media biofilm reactor

An anaerobic upflow porous media biofilm reactor was designed to study the kinetics and stoichiometry of hydrogen sulfide production by the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans (ATCC 5575) as the first step for the modeling and control of formation souring (H(2)S) in oil field porous media. The reactor was a packed bed (50 x 5.5 cm) tubular reactor. Sea sand (140 to 375 mum) was used as the porous media. The initial indication of souring was the appearance of well-separated black spots (precipitates of iron sulfide) in the sand bed. The blackened zones expanded radially and upward through the column. New spots also appeared and expanded into the cone shapes. Lactate (substrate) was depleted and hydrogen sulfide appeared in the effluent.Analysis of the pseudo-steady state column shows that there were concentration gradients for lactate and hydrogen sulfide along the column. The results indicate that most of the lactate was consumed at the front part of the column. Measurements of SRB biomass on the solid phase (sand) and in the liquid phase indicate that the maximum concentration of SRB biomass resided at the front part of the column while the maximum in the liquid phase occurred further downstream. The stoichiometry regarding lactate consumption and hydrogen sulfide production observed in the porous media reactor was different from that in a chemostat. After analyzing the radial dispersion coefficient for the SRB in porous media and kinetics of microbial growth, it was deduced that transport phenomena dominate the souring process in our porous media reactor system. (c) 1994 John Wiley & Sons, Inc.     

Study of Displacement Efficiency and Flow Behavior of Foamed Gel in Non-Homogeneous Porous Media

Field trials have demonstrated that foamed gel is a very cost-effective technology for profile modification and water shut-off. However, the mechanisms of profile modification and flow behavior of foamed gel in non-homogeneous porous media are not yet well understood. In order to investigate these mechanisms and the interactions between foamed gel and oil in porous media, coreflooding and pore-scale visualization waterflooding experiments were performed in the laboratory. The results of the coreflooding experiment in non-homogeneous porous media showed that the displacement efficiency improved by approximately 30% after injecting a 0.3 pore volume of foamed gel, and was proportional to the pore volumes of the injected foamed gel. Additionally, the mid-high permeability zone can be selectively plugged by foamed gel, and then oil located in the low permeability zone will be displaced. The visualization images demonstrated that the amoeba effect and Jamin effect are the main mechanisms for enhancing oil recovery by foamed gel. Compared with conventional gel, a unique benefit of foamed gel is that it can pass through micropores by transforming into arbitrary shapes without rupturing, this phenomenon has been named the amoeba effect. Additionally, the stability of foam in the presence of crude oil also was investigated. Image and statistical analysis showed that these foams boast excellent oil resistance and elasticity, which allows them to work deep within formations.     

Flowing biofilms as a transport mechanism for biomass through porous media under laminar and turbulent conditions in a laboratory reactor system

Abstract

Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 μm h^?1 in the turbulent flow cell and 1.0 μm h^?1 in the laminar flow cell.     

Real time monitoring of biofilm development under flow conditions in porous media

Biofilm growth can impact the effectiveness of industrial processes that involve porous media. To better understand and characterize how biofilms develop and affect hydraulic properties in porous media, both spatial and temporal development of biofilms under flow conditions was investigated in a translucent porous medium by using Pseudomonas fluorescens HK44, a bacterial strain genetically engineered to luminesce in the presence of an induction agent. Real-time visualization of luminescent biofilm growth patterns under constant pressure conditions was captured using a CCD camera. Images obtained over 8 days revealed that variations in bioluminescence intensity could be correlated to biofilm cell density and hydraulic conductivity. These results were used to develop a real-time imaging method to study the dynamic behavior of biofilm evolution in a porous medium, thereby providing a new tool to investigate the impact of biological fouling in porous media under flow conditions.     

Mathematical model for characterization of bacterial migration through sand cores

The migration of chemotactic bacteria in liquid media has previously been characterized in terms of two fundamental transport coefficients-the random motility coefficient and the chemotactic sensitivity coefficient. For modeling migration in porous media, we have shown that these coefficients which appear in macroscopic balance equations can be replaced by effective values that reflect the impact of the porous media on the swimming behavior of individual bacteria. Explicit relationships between values of the coefficients in porous and liquid media were derived. This type of quantitative analysis of bacterial migration is necessary for predicting bacterial population distributions in subsurface environments for applications such as in situ bioremediation in which bacteria respond chemotactically to the pollutants that they degrade.We analyzed bacterial penetration times through sand columns from two different experimental studies reported in the literature within the context of our mathematical model to evaluate the effective transport coefficients. Our results indicated that the presence of the porous medium reduced the random motility of the bacterial population by a factor comparable to the theoretical prediction. We were unable to determine the effect of the porous medium on the chemotactic sensitivity coefficient because no chemotactic response was observed in the experimental studies. However, the mathematical model was instrumental in developing a plausible explanation for why no chemotactic response was observed. The chemical gradients may have been too shallow over most of the sand core to elicit a measurable response. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 487-496, 1997.     

Migration,clogging, and carbon source release of nano emulsified vegetable oil in porous media,evaluated by column experiments

To effectively solve the problem of aquifer clogging in the process of in situ bioremediation of groundwater pollution by micron emulsified vegetable oil (Micron EVO), Nano emulsified vegetable oil (Nano EVO) was prepared to replace conventional micron EVO, and three one-dimensional laboratory columns packed with medium or fine sands were conducted to simulate migration, clogging, and carbon source release of EVO in porous media. Column experiment results show that micron and nano EVO resulted in a 20.40% and 3.20% reduction in permeability of medium sand, respectively. Correspondingly, the interception of micron and nano EVO in medium sand were 28.51% and 20.15%, respectively. Obviously, EVO interception is an important reason for permeability loss, and reducing EVO droplet size can effectively alleviate permeability loss in porous media. The COD ratios (dissolved COD/total COD) of micron and nano EVO in medium sand were 87.61% and 61.95%, respectively. The release effect of nano EVO was better than that of micron EVO. Effective longevity of micron and nano EVO were 243.17 d and 98.80 d, respectively. The effect of fine sand media on EVO indicated nano EVO can be used in a finer granular media, and its longevity can also be extended in this media.     

Diagnostics of fast processes in laser plasmas after the irradiation of low-density media in the mishen facility

New experimental data on the laser irradiation of low-density porous materials in the Mishen facility are presented and discussed. A wide set of optical and X-ray diagnostics was used to analyze the physical processes in porous media with different microstructures and specific densities of 1–30 mg/cm³ exposed to laser pulses with λ=1.054 µm, τ=3 ns, and I=10¹³–10¹⁴ W/cm². The features of laser absorption and scattering and the processes of energy transfer in porous media were investigated for different average densities, thicknesses, and microstructures of the targets and different incidence angles of the laser beam. It was found that the material microstructure (chaotic or quasi-ordered) significantly affected the formation and dynamics of a plasma produced inside the irradiated samples that model the components of the advanced targets used in inertial confinement fusion research.     

The effects of grain geometry on waterflooding and viscous fingering in micro-fractures and porous media from a lattice Boltzmann method study

The study of fluid fronts formed in porous media is important for enhanced oil recovery. The purposes of this study are to simulate waterflooding and to investigate influential factors on the fluid front movement through a micro-fracture and through simple porous media with different grain geometries. This study used the Shan–Chen form of the Lattice Boltzmann Method (LBM). An increase in the velocity is found to result in viscous fingering, whereas an increase in the wettability of the displacing fluid and the dynamic viscosity ratio creates a piston form of the fluid front. In porous media with the same porosities, various geometries act differently as obstacles against fluid flow from the inlet to the outlet. By enlarging the cross-sectional area of grains in the fluid paths and making them more tortuous, narrower and more twisted films of viscous fingering are formed. The sweep efficiency was also determined under various conditions: with a fixed capillary number, neutral wettability and different viscosity ratios; and with a fixed capillary number, viscosity ratio of (1/3) and wet or non-wet conditions. In all cases, the best sweep efficiency was obtained with grains of diamond geometry. Generally, the least sweep efficiency occurs with grains of star geometry. Simulation results verified the strength and accuracy of LBM predictions.     

Permeability of a growing biofilm in a porous media fluid flow analyzed by magnetic resonance displacement‐relaxation correlations

Biofilm growth in porous media is difficult to study non‐invasively due to the opaqueness and heterogeneity of the systems. Magnetic resonance is utilized to non‐invasively study water dynamics within porous media. Displacement‐relaxation correlation experiments were performed on fluid flow during biofilm growth in a model porous media of mono‐dispersed polystyrene beads. The spin–spin T₂ magnetic relaxation distinguishes between the biofilm phase and bulk fluid phase due to water–biopolymer interactions present in the biofilm, and the flow dynamics are measured using PGSE NMR experiments. By correlating these two measurements, the effects of biofilm growth on the fluid dynamics can be separated into a detailed analysis of both the biofilm phase and the fluid phase simultaneously within the same experiment. Within the displacement resolution of these experiments, no convective flow was measured through the biomass. An increased amount of longitudinal hydrodynamic dispersion indicates increased hydrodynamic mixing due to fluid channeling caused by biofilm growth. The effect of different biofilm growth conditions was measured by varying the strength of the bacterial growth medium. Biotechnol. Bioeng. 2013; 110: 1366–1375. © 2012 Wiley Periodicals, Inc.     

An Improved Spectrophotometric Method To Study the Transport, Attachment, and Breakthrough of Bacteria through Porous Media

This study reports an improved spectrophotometric method for studying bacterial (Pseudomonas fluorescens UPER-1) transport and attachment in saturated porous media (silica sand). While studying the effect of ionic strength by the traditional packed-column spectrophotometric method, we encountered an artifact. The absorbance of a well-stirred bacterial suspension was found to decrease with time in the presence of high concentrations of sodium and potassium phosphate salts (≥10⁻² M) as the cells continued to age in a resting stage. Our results show that collision efficiency and a bed ripening index will be in error by as much as 20% if breakthrough is measured by the traditional spectrophotometric technique. We present an improved experimental technique that will minimize the artifact and should substantially advance the understanding of bacteria transport in porous media.     

微生物在多孔介质中渗流的数学模型

建立了一个完整的描述微生物在地层多孔介质中渗流的数学模型,模型中考虑了微生物的生长、营养物的消耗和微生物的存在对多孔介质物理性质的影响．此外,提供了该方程的求解过程和方法。实例计算结果表明,该方法能较好的描述微生物在多孔介质中的运移状况。     

An improved spectrophotometric method to study the transport, attachment, and breakthrough of bacteria through porous media

This study reports an improved spectrophotometric method for studying bacterial (Pseudomonas fluorescens UPER-1) transport and attachment in saturated porous media (silica sand). While studying the effect of ionic strength by the traditional packed-column spectrophotometric method, we encountered an artifact. The absorbance of a well-stirred bacterial suspension was found to decrease with time in the presence of high concentrations of sodium and potassium phosphate salts (> or = 10(-2) M) as the cells continued to age in a resting stage. Our results show that collision efficiency and a bed ripening index will be in error by as much as 20% if breakthrough is measured by the traditional spectrophotometric technique. We present an improved experimental technique that will minimize the artifact and should substantially advance the understanding of bacteria transport in porous media.