Mechanism And Application Research On Cadmium-containing Wastewater Treatment With Micellar-enhanced Ultrafiltration

Micellar-Enhanced Ultrafiltration (MEUF) is a powerful treatment process developed recently to remove heavy metals from wastewater, which combines ultrafiltration with surfactant technology. This study focuses on mechanisms and application of cadmium-containing wastewater treatment with MEUF. Sodium dodecyl sulfate (SDS) was applied as the surfactant and polysulfone hollow fibre was adopted as the ultrafiltration membrane. Influences of operation factors on separation process were systemically investigated. Conditions of separation process were optimized. In addition, mechanisms of MEUF were analyzed by dynamics, energetics, adsorption rules, as well as microcosmic detection.(1) Cadmium pollution, cadmium-containing wastewater treatment technology, application of ultrafiltration and surfactant technology in environment protection, along with current research of MEUF technology were reviewed, and purpose of this investigation were put forword. (2) Variety rules of critical micelle concentration and micelle characteristic of SDS in the wastewater was studied. Mixing nonionic surfactant with SDS efficiently decreases the critical micelle concentration. (3) Retention rate of Cd2+ is above 97% by cadmium-containing wastewater treatment with MEUF. Adsorption process of Cd2+ on SDS micelle follows the law of second-order kinetics, and accords with Langmuir Isotherm. Adsorption is a spontaneous endothermic process, in which adsorption force is principally the attraction of opposite electric charge. (4) MEUF was applied to treat cadmium-containing wastewater, zinc-containing wastewater, plumbum-containing wastewater and mixed wastewater. Results show that the sequence of adsorption of bivalence heavy metal ions to SDS micelle is Pb2+>Cd2+>Zn2+. With the wastewater containing a variety of bivalence heavy metal ions, competitive adsorption to SDS exists among various ions, and the sequence of competitive adsorption is Pb2+>Zn2+>Cd2+. (5) Permeation flux model based on membrane fouling characters was set up. Relationships between permeation flux und operation parameters and membrane parameters were described. Moreover, this model can exactly forecast variety rule of permeation flux by MEUF and the error is 4.77%~12.85% compared with experiments. (6) MEUF with the mixture of nonionic surfactant and SDS was experimented. Dosage of SDS reduces obviously and residue of SDS in permeation decreases. (7) Permeation by MEUF was advanced treated by MFF (Micropore Foam Flotation), and Cd2+ in effluent meets the requirement of the highest concentration limit of the first category contaminants in"Integrated Wastewater Discharge Standard".The Study shows that cadmium-containing wastewater is efficiently and quickly purified with MEUF, and Cd2+ can meet the requirement of the wastewater discharge standard with the combination of MEUF and MFF. Advanced removal of cadmium ions and surfactant from wastewater is simultaneously achieved with tiny air bubble. Moreover, the combination of MEUF and MFF was adopted to reduce the surfactant dosage. Permeation flux model based on membrane fouling was set up, which can overcome the problem of difficulty by measuring the resistance of gelatin layer and membrane in application. Microcosmic detection was used to analyze the interaction between micelle and heavy metal ions for the first time and to detect the adsorption mechanisms between micelle and heavy metal ions on microcosmic level.Above study discusses the key technology of aggregation and self-assembly control of micelle, interaction mechanisms between micelle and heavy metal ions in cadmium-containing wastewater treatment by MEUF. The study provides foundation for application and popularization of heavy metal-containing wastewater treatment by MEUF.