Encapsulated Cell Bioremediation: Evaluation on the Basis of Particle Tracer Tests

Abstract

Microencapsulation of degradative organisms enhances microorganism survivability (Stormo and Crawford 1994). The use of encapsulated cell microbeads for in situ biodegradation depends not only on microorganism survival but also on microbead transport characteristics. Two forced‐gradient, recirculating‐loop tracer experiments were conducted to evaluate the feasibility of encapsulated cell transport and bioremediation on the basis of polystyrene microsphere transport results. The tracer tests were conducted in a shallow, confined, unconsolidated, heterogeneous, sedimentary aquifer using bromide ion and 2 μm, 5 μn, and 15 μm microsphere tracers. Significant differences were observed in the transport of bromide solute and polystyrene microspheres. Microspheres reached peak concentrations in monitoring wells before bromide, which was thought to reflect the influence of aquifer heterogeneity. Greater decreases in microsphere C/Co ratios were observed with distance from the injection wells than in bromide C/Co ratios, which was attributed to particle filtration and/or settling. Several methods might be considered for introducing encapsulated cell microbeads into a subsurface environment, including direct injection into a contaminated aquifer zone, injection through a recirculating ground water flow system, or emplacement in a subsurface microbial curtain in advance of a plume. However, the in situ use of encapsulated cells in an aquifer is probably limited to aquifers containing sufficiently large pore spaces, allowing passage of at least some encapsulated cells. The use of encapsulated cells may also be limited by differences in solute and microbead transport patterns and flowpath clogging by larger encapsulated cell microbeads.

Recirculating tracer test in fractured basalt

“…The smaller the pore space or fracture aperture, the fewer large-sized particles are transported. This was demonstrated in forced gradient tests by Harvey et al (1989), Petrich (1998), andBrown (1998), who employed different sized particles during their experiments. They discovered that the particle recovery varied inversely with particle size.…”

“…Bales et al (1989) ? Virus-bacteriophage Sandy soil and fractured tuff Harvey et al (1989) Bromide Bacteria Microspheres Sandy aquifer Gannon et al (1991) Chloride Reimus et al (1994) Iodide Microspheres Fractured tuff Petrich et al (1998) Bromide Microspheres Sandy aquifer Pang et al (1998) Chloride and rhodamine WT Spores-Bacillus subtilis Alluvial gravel aquifer Brown (1998) Bromide Spores-Clostridium bifermentans Microspheres Sandy aquifer mechanisms. These mechanisms include the surface roughness of the fracture, fluid dynamics, substratum chemistry, and solute chemistry (Harvey et al, 1993).…”

Bioaugmentation potential of free and formulated 2,6-dichlorobenzamide (BAM) degrading Aminobacter sp. MSH1 in soil, sand and water

“…Specific organisms for introduction into the environment have been combined with different types of carrier materials, such as agar, peat, alginate, alginate-clay and fluid gels (Stromo and Crawford 1994 ; Petrich et al 1998 ). Some carriers, for example, allow a high concentration of cells to be incorporated into the contaminated environment, and this might act as a hot spot with a slow release of viable cells into the surrounding environment (Mertens et al 2006 ).…”

Transport of Gellan Gum Microbeads in Soil Columns of Various Grain Size Distributions

“…have been mostly used in deep-bed fi ltration studies, or as tracers of bacteria in transport studies under laboratory or fi eld conditions. In an earlier study, the transport of 2-, 5-, and 15-µm polystyrene microspheres with neutral surface characteristics was investigated through forced-gradient tracer experiments in a confi ned unconsolidated heterogeneous aquifer to evaluate the feasibility of using encapsulated cell microbeads for in-situ bioremediation (Petrich et al, 1998). Microsphere concentrations decreased substantially within a 1.5 to 6 m distance from the injection wells.…”

“…Transport of microbeads is controlled by the fi ltration effect of the soil matrix, which is infl uenced by various factors including the carrier fl uid characteristics (solution chemistry such as ionic strength and surfactant concentration), the suspension of particles characteristics (particle size distribution, particle shape, surface charge, and hydrophobicity), and the porous medium characteristics (grain size distribution, grain shape, and surface charge). A number of previous reports (Harvey et al, 1989;Harvey et al, 1993;Moran et al, 1993aMoran et al, , 1993bHarmand et al, 1996;Bales et al, 1997;Jegatheesan and Vingeswaran, 1997;Reddi and Bonala, 1997;Petrich et al, 1998) have discussed the effect of grain and particle size distributions, and granular media heterogeneity and depth on transport of particles through granular media. Monodisperse micrometer-and submicrometer-sized synthetic polymer microspheres * Author to whom correspondence may be addressed.…”