Cotransport of Herbaspirillum chlorophenolicum FA1 and heavy metals in saturated porous media: Effect of ion type and concentration

Predicting the cotransport of functional microorganisms and heavy metals in porous media is essential to both bioremediation and pollutant risk assessment. In this study, batch and column experiments were conducted to explore the cotransport behaviors of functional bacteria (FA1) and heavy metals (Pb2+/Cd2+) in saturated sand media under different conditions. The sorption capacity of heavy metals on FA1 was much greater than that of the sand, while both FA1 and sand showed stronger affinity to Pb2+ than Cd2+. The surface properties, especially zeta potential, of the bacteria and sand were altered by metal adsorption. As a result, the co-existence of Pb2+ decreased the transport of FA1 more significantly than that of Cd2+, and the influence was more significant with higher heavy metal concentration. On the other hand, the co-existence of FA1 inhibited the mobility of Pb2+ and Cd2+ in most scenarios, except when the cotransport concentration of Pb2+ was 5 mg L−1, and the inhibition was more pronounced for Pb2+ than Cd2+. Increase in metal concentrations decreased the FA1-associated Pb2+/Cd2+ in effluents due to the remarkable decrease in FA1 mobility, and free soluble Pb2+/Cd2+ became the major migration species. In addition, due to stronger attractive forces and affinity between Pb2+ and FA1, nearly all presorbed-Pb2+ by sand was remobilized by FA1 and transported mainly in FA1-associated form other than soluble Pb2+. Findings from this study indicated that the cotransport of biocolloids and heavy metals are highly sensitive to the ion type and concentration, and evaluation of their transport in the subsurface should be carefully carried out to avoid inaccurate estimations.