Bacterial clogging of porous media: A new modelling approach

A comparison is made between existing mathematical models and experimental data that relate the reduction of the saturated hydraulic conductivity (K) of a porous medium to the porosity reduction caused by microbial growth. The models yielded a realistic prediction of a data set obtained with a model porous medium consisting of millimeter‐size glass spheres, but failed to predict the clogging behaviour observed in smaller‐than‐1‐mm sand. A new modelling approach, semi‐mechanistic in nature, is proposed that gives good predictions of fine sand media as well. It relaxes the assumption about uniformly‐thick biofilms by allowing a second arrangement to occur, i.e. discrete plugs filling the pore lumen. The new model requires input data on two intrinsic properties of the system, which renders it sufficiently flexible as to fit very different data sets. The two model parameters are K_min, the minimum K value when all porosity is filled with microorganisms, and B_c, the biovolume fraction at which most cell detachment from biofilm occurs.     

Transport of bacteria in porous media: II. A model for convective Transport and growth

A model is presented for the coupled processes of bacterial growth and convective transport of bacteria has been modeled using a fractional flow approach. The various mechanisms of bacteria retention can be incorporated into the model through selection of an appropriate shape of the fractional flow curve. Permeability reduction due to pore plugging by bacteria was simulated using the effective medium theory. In porous media, the rates of transport and growth of bacteria, the generation of metabolic products, and the consumption of nutrients are strongly coupled processes. Consequently, the set of governing conservation equations form a set of coupled, nonlinear partial differential equations that were solved numerically. Reasonably good agreement between the model and experimental data has been obtained indicating that the physical processes incorporated in the model are adequate. The model has been used to predict the in situ transport and growth of bacteria, nutrient consumption, and metabolite production. It can be particularly useful in simulating laboratory experiments and in scaling microbial-enhanced oil recovery or bioremediation processes to the field. (c) 1994 John Wiley & Sons, Inc.     

Modeling biofilm accumulation and mass transport in a porous medium under high substrate loading

A packed bed biofilm reactor inoculated with pure culture Pseudomonas aeruginosa was run under high substrate loading and constant flow rate conditions. The 3.1-cm-diameter cylindrical reactor was 5 cm in length and packed with 1-mm glass beads. Daily observations of biofilm thickness, influent and effluent glucose substrate concentration, and effluent dissolved and total organic carbon were made during the 13-day experiment. Biofilm thickness appeared to rech quasi-steady-state condition after 10 days. A published biofilm process simulation program (AQUASIM) was used to analyze experimental data. Comparison of observed and simulated variables revealed three distinct phases of biofilm accumulation during the experiment: an initial phase, a growth phase, and a mature biofilm phase. Different combinations of biofilm and mass transport process variables were found to be important during each phase. Biofilm detachment was highly correlated with shear at the biofilm surface during all three phases of biofilm development. (c) 1995 John Wiley & Sons, Inc.     

Transport of bacteria in porous media: I. An experimental investigation

The convective transport of concentrated suspension of bacteria in porous media is of interest for several processes such as microbial enhanced oil recovery and in situ bioremediation. The parameters which affect the transport of the bacterium Bacillus licheniformis JF-2, a candidate microorganism for microbial enhanced oil recovery, were investigated experimentally in sandpacks. Bacteria retention and permeability reduction occurred primarily in the first few centimeters upon entering the porous medium. In downstream sections of the sandpack, the permeability reduction was low, even in cases in which high cell concentrations (10(8) cfu/mL) were detected in the effluent. The effect of (i) addition of a dispersant, (ii) linear velocity of injection, (iii) cell concentration, (iv) salinity (v) temperature, and (vi) the presence of a residual oleic phase were determined experimentally. A lower reduction in permeability and a higher effluent bacterial concentration were obtained in the presence of dispersant, high injection velocities, low salinities, and at a higher temperature. Macroscopic measurements at different linear velocities and in the presence or absence of dispersants suggest that the formation of reversible microaggregates and multiparticle hydrodynamic exclusion may be the primary mechanisms for bacterial retention and permeability reduction. (c) 1994 John Wiley & Sons, Inc.     

Xanthan degragation by biofilm in porous media

Biological activity in oil reservoirs can cause significant problems such as souring and plugging. This study focuses on the problem of polymer degradation and permeability reduction due to biofilm formation during polymer injection for improved oil recovery. Polymers are included in injection fluids to increase their viscosity. Results relating biological processes and polymer degradation to fluid‐dynamic conditions in a laboratory model porous medium are presented.

A transparent flow cell with an etched two‐dimensional network of pores served as a model porous medium. A sterile xanthan polymer and natural sea water solution were continuously injected into the porous medium. A bacterial culture capable of xanthan degradation was introduced into the cell by a single injection. Some of the cells from this culture attached to the pore walls forming an immobile bacterial culture, termed biofilm. The development of this biofilm, its xanthan degradation and its effect on permeability were measured.

The effects of injection rate and rate transitions were analyzed. Injection fluid viscosity was reduced by 30% after 5 min flow through the porous medium at the maximum steady state degradation rate observed. Permeability was significantly reduced by the xanthan degrading biofilm, causing an increase in pressure drop through the porous medium of up to 80%. Polymer injection in oil reservoirs may, therefore, have negative effects on oil recovery, unless efficient biofouling control is applied. The methodology presented may serve as a tool in the development of biofouling control measures in porous media.     

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.     

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.     

Use of 1H NMR to study transport processes in porous biosystems

The operation of bioreactors and the metabolism of microorganisms in biofilms or soil/sediment systems are strongly dictated by the transport processes therein. Nuclear magnetic resonance (NMR) spectroscopy or magnetic resonance imaging (MRI) allow nondestructive and noninvasive quantification and visualisation (in case of MRI) of both static and dynamic water transport phenomena. Flow, mass transfer and transport processes can be measured by mapping the (proton) displacement in a defined time interval directly in a so-called pulsed field gradient (PFG) experiment. Other methods follow the local intensity in time-controlled sequential images of water or labelled molecules, or map the effect of contrast agents. Combining transport measurements with relaxation-time information allows the discrimination of transport processes in different environments or of different fluids, even within a single picture element in an image of the porous biosystem under study. By proper choice of the applied NMR method, a time window ranging from milliseconds to weeks (or longer) can be covered. In this paper, we present an overview of the principles of NMR and MRI techniques to visualise and unravel complex, heterogeneous transport processes in porous biological systems. Applications and limitations will be discussed, based on results obtained in (model) biofilms, bioreactors, microbial mats and sediments. Journal of Industrial Microbiology & Biotechnology (2001) 26, 43–52. Received 20 April 2000/ Accepted in revised form 14 August 2000     

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.