Effects of nonionic surfactants on bacterial transport through porous media

Nonionic surfactants of the form CxEy, where x is the number of carbons in the alkyl chain and y is the number of ethylene oxide units in the polyoxye thylene (POE) chain, were studied for their ability to alter the transport of Sphingomonas pacilimobilis through an aquifer sand. The surfactants C12E 4 (Brij 30) and C12E23 (Brij 35) were the focus of this study. Through a sy stematic study, it was shown that these nonionic surfactants were able to e nhance the transport of this bacterial culture through porous media. The ma gnitude of the enhancement increased with decreasing solution ionic strengt h and increasing POE chain length. The mechanism of this enhanced transport appears to be due to expansion of the electric double layer about the bact eria and aquifer sand through displacement of the counterions by the sorbed surfactant. This expanded electric double layer increases the electrostati c repulsion, with a resultant reduction in the collision efficiency and an increase in the Langmuirian blocking parameter. Application of the colloid filtration theory with the experimental parameters of this study shows that nonionic surfactants have the potential to significantly enhance the bacte rial travel distance, especially for low ionic strength systems.