Treatment Of Heavy Meatal-containing Wastewater Using Micellar-enhanced Ultrafiltration At Low Surfactant Concentration

Micellar-enhanced ultrafiltration (MEUF) is a new treatment process developed recently to remove heavy metals from wastewater, which combines ultrafiltration with surfactant technology. This method is of the following advantages: high removal efficiency; low-energy requirements; simple equipment; easy operation; less expensive. In the study, MEUF was applied to treat zinc-containing wastewater, cadmium-containing wastewater, plumbum-containing wastewater and mixed wastewater using anionic surfactant sodium dodecyl sulfate (SDS) at low concentrations. The modified polysulphone hollow-core fibre ultrafiltration membrane is used. Separation and recovery of surfactant sodium dodecyl sulfate and heavy metal ions from the retentate of MEUF by adding EDTA followed by ultrafiltration was also investigated.The results of the study are shown as below. (1) The Zn²⁺ adsorption to SDS micelle reached equilibrium after 3h. (2) When the initial concentration of heavy metal was constant and the initial concentration of SDS was below the critical micelle concentration, not only the dosage of SDS could be reduced but also the rejection of heavy metal and the permeate flux were high. Along with the increase of the initial SDS concentration, the permeate flux decreased gradually and the permeation concentration of SDS increased. Whatever was the concentration of SDS in the feed, the SDS concentration in the permeation was lower than CMC. Consequently the loss of SDS was small. (3) In mixed solution, when the initial concentration of SDS was below or equal to 2.25g·L^-1, the rejection of Zn²⁺ was slightly higher than that of Cd²⁺. When the initial concentration of SDS was higher than 2.25g·L^-1, the rejection of Zn²⁺ was slightly less than that of Cd²⁺. The rejection of Pb²⁺ was less than that of Zn²⁺ and Cd²⁺ with the variation of the initial SDS concentration except for 1.125g·L^-1. When the initial SDS concentration was equal to1.8g·L^-1, the rejection of Zn²⁺ was slightly higher than that of Cd²⁺ with the increase of the total heavy metal concentration. The rejection of Pb²⁺ was less than that of Zn²⁺ and Cd²⁺ when the total heavy metal concentration was below or equal to 50mg·L^-1, the rejection of Pb²⁺ was higher than that of Zn²⁺ and Cd²⁺ when the total heavy metal concentration was higher than 50mg·L^-1. (4) In the separation and recovery process, the appropriate conditions of operation were obtained:δ=1, pH=4. Under these conditions, the recovery ratio of heavy metal and SDS were higher than 92.2% and 61.4% respectively, and the enrichment ratio of SDS was higher than 12.0. The competitive coordination to EDTA among various heavy metal ions was also studied. Whenδwas below 1, the competitive coordination was evident, showing the order of R3Pb²⁺>R3Zn²⁺≈R3Cd²⁺. Whenδwas higher than or equal to 1, there was no competitive coordination to EDTA among various heavy metal ions, the recovery ratio of Zn²⁺, Cd²⁺ and Pb²⁺ are almost equal to each other. When pH was above 3, the competitive coordination was weak, and the recovery ratio of Pb²⁺ was slightly higher than that of Zn²⁺ and Cd²⁺, and R3Zn²⁺≈R3Cd²⁺. When pH was below or equal to 3, there was no competitive coordination to EDTA among various heavy metal ions, the recovery ratio of Zn²⁺, Cd²⁺ and Pb²⁺ are almost equal to each other.The removal of heavy metal ions from wastewater with low heavy metal concentration is very efficient using micellar-enhanced ultrafiltration at low surfactant concentration. The separation and recovery of heavy metal ions and surfactant from the retentate of MEUF using EDTA is also very efficient. The study provides foundation for application and popularization of heavy metal–containing wastewater treatment by MEUF.