RESUMO
In this study, we quantified the attachment and detachment of bacteria during transport in order to elucidate the contributions of reversible attachment on bacterial breakthrough curves. The first set of breakthrough experiment was performed for a laboratory sand column using leaching solutions of deionized water and mineral salt medium (MSM) of 200 mM with reference to KCl solution by employing Pseudomonas putida as a model bacterium. In the second set of experiment, the ionic strengths of leaching solutions immediately after bacterial pulse were lowered to tenfold and 100-fold diluted system (2 and 20 mM MSM) to focus on the influence of physicochemical factor. Results have shown that bacterial retention occurred in the sand column due to the physical deposition and physicochemical attachment. The physicochemical attachment was attributed to the high ionic strength (200 mM MSM) of leaching solution and the formation of primary energy minimum. Replacing the 200 mM leaching solution with the lower ionic strengths after pulse resulted in the increased tailing of breakthrough curve due to the detachment from the attached bacteria. The detachment could be well explained by DLVO theory, which showed the formation of energy barrier and disappearance of the secondary minimum as the ionic strength gradually decreased. Analysis of mass recovery revealed that 12-20% of the attachment was due to physical and physicochemical attachment, respectively, where the latter consisted of 25-75% of irreversible and reversible attachment respectively.
RESUMO
In this study, the deposition and transport of Pseudomonas aeruginosa on sandy porous materials have been investigated under static and dynamic flow conditions. For the static experiments, both equilibrium and kinetic batch tests were performed at a 1:3 and 3:1 soil:solution ratio. The batch data were analysed to quantify the deposition parameters under static conditions. Column tests were performed for dynamic flow experiments with KCl solution and bacteria suspended in (1) deionized water, (2) mineral salt medium (MSM) and (3) surfactant + MSM. The equilibrium distribution coefficient (K(d)) was larger at a 1:3 (2.43 mL g(-1)) than that at a 3:1 (0.28 mL g(-1)) soil:solution ratio. Kinetic batch experiments showed that the reversible deposition rate coefficient (k(att)) and the release rate coefficient (k(det)) at a soil:solution ratio of 3:1 were larger than those at a 1:3 ratio. Column experiments showed that an increase in ionic strength resulted in a decrease in peak concentration of bacteria, mass recovery and tailing of the bacterial breakthrough curve (BTC) and that the presence of surfactant enhanced the movement of bacteria through quartz sand, giving increased mass recovery and tailing. Deposition parameters under dynamic condition were determined by fitting BTCs to four different transport models, (1) kinetic reversible, (2) two-site, (3) kinetic irreversible and (4) kinetic reversible and irreversible models. Among these models, Model 4 was more suitable than the others since it includes the irreversible sorption term directly related to the mass loss of bacteria observed in the column experiment. Applicability of the parameters obtained from the batch experiments to simulate the column breakthrough data is evaluated.
