Modeling the effects of systematic variation in ionic strength on the attachment kinetics of Pseudomonas fluorescens UPER‐1 in saturated sand columns

Abstract

Abstract. We report the effects of salt type and concentration on the change in attachment kinetics when bacteria are pumped through a column of water-saturated clean sand over relatively long periods of time (up to 35 pore volumes). The species Pseudomonas fluorescens UPER-1 was found to exhibit three different kinds of attachment kinetics: first order, second order, and an intermediate order. The attachment kinetics of bacteria was modeled by using the advection-dispersion equation coupled with a set of equations for each kind of attachment kinetics while using colloid filtration theory to predict collector efficiencies. At low or zero salt concentrations (-<10 -4 M) a second-order kinetics model ("blocking"), a "first-order" kinetics model, and an intermediate-order kinetics model ("ripening"), were all found to fit the data equally well. At intermediate and high salt concentrations (_> 10 -3 M) the ripening model was found to fit the data best. We report values for collision efficiencies of bacteria in the range 0.01-0.2, depending upon the salt type and concentration. This study points out the importance of long-term experiments to study the effect of ionic strength on bacteria attachment kinetics in saturated porous media and the phenomenon of cell-to-cell attachment at high ionic strength. This study further points out the range of kinetics to expect when bacteria attach to natural porous media and suggests a modeling framework. IntroductionThe study of transport and attachment of bacteria has received increasing attention from researchers over the last decade. The impetus for this research comes from the need to understand the processes that control transport and attachment of bacteria and to apply that knowledge toward a better understanding of subsurface bioremediation, biocorrosion and biofouling, pathogenic microbial fate in the environment, and biomedical applications. For example, the technology of bioaugmentation involves injecting specific bacteria into the subsurface to accelerate remediation of vadose zone and ground- Prior Modeling ApproachesAnalysis of breakthrough results obtained from column studies and their use in modeling the kinetics of attachment and detachment has been confined primarily to inorganic colloids. Saiers et al. [1994] have reported first-order (attachment rate constant with time) and second-order "blocking" (attachment rate decreases with time) kinetic approaches to modeling their breakthrough data. In low ionic strength suspensions, they found that a similarly charged colloid-porous media sys- 1619

Retention and Remobilization of Stabilized Silver Nanoparticles in an Undisturbed Loamy Sand Soil

“…In this study, β = 1.532 was chosen for simulation instead of 0.432 that was applied in AgNP transport in sand. 33 The first term on the right side of eq 3 accounts for time dependent blocking/ filling of retention sites using a Langmuirian approach, 38 while the second term on the right side describes depth dependent retention (e.g., a decreasing retention rate with depth).…”

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

“…The column used in the studies was a glass chromatography column (Adjusta-Chrom; Ace Glass Inc.) with an internal diameter of 2.5 cm. The column was always packed to a settled bed height of 30 cm in such a way as to minimize the trapping of air bubbles (3). A schematic diagram of the experimental setup (Fig.…”

“…Examples of experimental techniques to study the deposition of cells and other colloids in porous media are (i) packedbed technique (3,4,5,7,9,18), (ii) stagnation point flow technique (4), (iii) rotating disk system (17), and (iv) parallelplate channel technique (4); however, the packed-bed technique has been the most widely used. The influence of various physical and chemical factors on microbial transport through packed-bed porous media was studied by Fontes et al (5).…”

“…Turbidity is further defined as ϭ N C s (3) where N is the number concentration of the bacteria and C s is the scattering cross section of the bacteria. C s depends on the size and refractive index of the bacteria and on the wavelength of the incident light (6).…”

“…The concentration of the bacteria in the effluent stream of a packed-bed column can be measured with either of the following techniques: (i) counting of CFU (2,10,23), (ii) acridine orange direct microscopic counting (8), (iii) radiolabeling of cells followed by scintillation counting (13,14,16), and (iv) spectrophotometric analysis (3,4). Microscopic counting is tedious, prone to the researcher's judgment, and not amenable to a large number of samples.…”