Study on the treatment of sudden cadmium pollution in surface water by a polymer enhanced ultrafiltration process

The removal of cadmium(ii) pollution in surface water by a polymer enhanced ultrafiltration (PEUF) process was investigated. Three water soluble polymers, chitosan (CTS), polyvinyl alcohol (PVA) and polyacrylate sodium (PAAS), were selected for this study. Of the three polymers, PAAS had strong interactions with Cd²⁺, and the PEUF achieved a high removal of Cd²⁺; therefore, PAAS was used as a complexing agent for the simulated cadmium pollution experiment. Experiments were performed as a function of the aqueous pH, polymer/Cd²⁺ ratio (P/M), ionic strength and humic acid. Under optimum experimental conditions, the Cd²⁺ removal rate reached 100%. pH was the main factor affecting removal of Cd²⁺, which decreased to 60% at a pH of 4. The Cd²⁺ removal was found to decrease as NaCl and HA were added. The analysis showed that the mechanism of NaCl could be a compressed electric double layer, while the mechanism of HA and H⁺ was competitive complexation. Finally, UF membrane fouling, the dissociation of PAAS-Cd and the regeneration of PAAS were investigated. The results showed that the higher P/M was, the lower the pH, the higher the HA concentration, and the more serious the UF membrane fouling were. The dissociation rate of PAAS-Cd reached 99.8% at a pH of 2.5. When the P/M was 5, the removal rate of Cd reached 99.6% with the addition of 20% new PAAS in the regenerate. This result showed that the PEUF process could be a promising method for removing Cd pollution in surface water.