Enhanced transport of bacteria through a soil matrix using colloidal gas aphron suspensions

The influence of an anionic surfactant sodium dodecylbenzene sulfonate (DDBS) in the form of either an aqueous solution or microgas dispersion known as colloidal gas aphron (CGA) on the transport of a Pseudomonas pseudoalcaligenes strain through a saturated soil matrix was examined. The experiments were conducted in 30-cm-long and 6.35 cm internal diameter stainless steel columns packed with a sandy clay loam. A 10-ml pulse (0.033 pore volumes) of a bacterial suspension containing 10¹⁰ colony forming units (cfu) per ml was injected, and the column was eluted with either deionized water, a solution of DDBS, or a CGA suspension at a surface loading rate of 0.16 cm/min. The bacterial distributions within the column were similar after the passage of the water and surfactant solutions; however, the distribution of bacteria in the columns and effluent after the passage of the CGA suspension was markedly enhanced. The bacterial concentration in the lower hail of the column after the passage of the CGA suspension was 2 to 3 orders of magnitude higher than that observed for either the surfactant or water solutions under similar experimental conditions. The final bacterial density in the effluent after the passage of the surfactant solution was one- half order of magnitude greater than that in the effluent produced by passage of water. After the passage of the CGA suspension, the total number of bacteria in the effluent was at least 2 or 3 orders of magnitude greater than that obtained by passage of either surfactant or water as the eluting agent, respectively. The results of the study suggests that CGA suspensions can transport bacteria more efficiently than conventional surfactant solutions or water.