Bacterial Deposition in Porous Media Related to the Clean Bed Collision Efficiency and to Substratum Blocking by Attached Cells

Abstract

Deposition of Pseudomonas putida mt2 and Rhodococcus strain C125 during transport through columns packed with Teflon grains was investigated. Deposition was analyzed in terms of the clean bed collision efficiency α0 (the probability of a cell to attach upon reaching a cell-free substratum) and the surface area blocked by attached cells. Blocking was quantified by a blocking factor B, the ratio of the blocked area per cell to the geometric area of a cell. At an average interstitial fluid velocity of 200 μm s-1, α0 is close to unity (0.83 ± 0.01) for both strains, indicating that cell−solid interactions are almost completely favorable for deposi tion. Values for B of 1.6 ± 0.1 and 12.0 ± 0.8 were obtained for Ps. putida and Rhodococcus strain C125, respectively. This difference is consistent with differences in cell size and cell−cell repulsion, which were both smaller for Ps. putida than for Rhodococcus strain C125. At coverages close to saturation, multilayer adhesion and/or pore clogging occurs for the weakly blocking Pseudomonas cells but not for the strongly blocking Rhodococcus cells. The collision-blocking concept succesfully explains the breakthrough of Bacillus cells in coarse sand columns, as reported by Lindqvist and Enfield, for which adhesion is less favorable (α0 = 0.10 ± 0.01) and blocking is relatively strong (B = 5.8 ± 0.8). The general conclusion is that deposition of microbes during their transport through coarse grain media is adequately described by the collision-blocking model in cases of strongly blocking cells or weakly blocking cells at low coverage conditions.

Enhancing bacterial transport for bioaugmentation of aquifers using low ionic strength solutions and surfactants

“…Even if all bacteria injected into the column attached to the media grains, only 0.08% of the surface area would be covered. This is less than that reported to produce clogging or blocking in porous media (Liu et al, 1995;Rijnaarts et al, 1996). The fraction of bacteria removed in the column, R, is related to the volume-averaged concentration of bacteria in the column in¯uent (C 0 ) and euent (C), by R = 1 À C/C 0 .…”

“…Numerous studies have shown that low ionic strength (IS) solutions and surfactants can substantially reduce bacterial adhesion to ultraclean glass and quartz surfaces (Fontes et al, 1991;Gannon et al, 1991;Martin et al, 1992;Rijnaarts et al, 1996). Despite this work, however, it is not well known to what extent these laboratory results, using cm-long columns, can be applied to soils over larger distances necessary for bioaugmentation schemes.…”

“…However, high colloid concentrations can ®ll the soil grain surface and invalidate the assumptions of the cleanbed ®ltration theory used to calculate a (Yao et al, 1971;Liu et al, 1995). Column media can become ®lled, or``jammed'', with colloids with as little as 3% of the soil grain surface area covered, preventing other suspended particles from interacting with soil surfaces (Rijnaarts et al, 1996). When bacteria have extremely low a's, it is dicult to obtain accurate estimates of a from column breakthrough concentrations, unless very long columns are used, since euent concentrations will nearly equal in¯u-ent concentrations.…”

Colloid deposition experiments as a diagnostic tool for biomass attachment onto bioproduct adsorbent surfaces

“…7 Mathematical models of microbial transport in porous media most commonly utilizes the advection-dispersion equation as derived by mass balance principles. 8,9 A common approach to evaluate biomass deposition in laboratory packed-bed experiments employs the 'clean-bed' filtration model or colloid filtration theory (CFT). This model is valid for steady-state systems which are initially free of biomass particles and where axial dispersion can be neglected (Pe ≥ 20).…”

“…This implies that attached biomass particles onto the process surface can effectively reduce deposition by a socalled collector 'blocking' effect. 9 On the other hand, increased biomass attachment can result from cellto-cell aggregation: a phenomena known as system 'ripening'. 12 In this paper we have investigated the factors influencing intact yeast cell deposition onto anion and cation exchangers currently utilized for expanded-bed adsorption of biotechnological products.…”