Transport and interaction of cadmium and active sludge extracellular polymeric substances in saturated sand influenced by ionic strength and composition.

Artificial groundwater recharge with reclaimed water (secondary effluent from wastewater treatment plants) has become an important approach to solving water scarcity worldwide. Microorganisms in activated sludge can secrete many extracellular polymeric substances (EPS). However, information on the impact of EPS on the movement of heavy metals in porous media and their environmental effects on underground networks is limited. To assess this risk, we extracted EPS from the aerobic section of a wastewater treatment plant using hot sodium hydroxide and conducted experiments using one-dimensional sand columns to investigate how ion composition and strength affect the movement and interaction of cadmium (Cd) and EPS in porous media. The results showed that EPS facilitated Cd migration in porous media. Sodium (Na) and calcium (Ca) ions promoted the migration of Cd in porous media and EPS-Cd complexation. The effect of Ca was more significant than that of Na. As the Na adsorption ratio increased, the migration ability of Cd in porous media and the complexation ability of EPS with Cd decreased. Therefore, when estimating the migration of EPS and Cd in subsurface environments, careful consideration should be given to prevent the risk of groundwater pollution.