Application Of Integrated Membrane Technology In Resource Utilization Of Industrial Wastewater

Due to the increasing water pollution and the shortage of freshwater worldwide, reclamation of industrial wastewater becomes an important approach to control water pollution and increase freshwater resources. Membrane technology has widely applied in the treatment of industrial wastewater because of its superior performance. However, the relatively high capital and operational costs as well as the disposal of membrane concentrate stream are the two key problems to be solved. Resource utilization of wastewater provides a new alternative to reduce the cost of wastewater treatment and solve the problem of membrane concentrate discharge, while there has few reports regarding the resource utilization of wastewater using membrane technology in practical effluents. In this work, the integrated membrane technology was applied for the treatment of perfluorooctanoate (PFOA) wastewater and soybean soaking water in order to achieve the resource utilization. The effect of process parameters on the wastewater treatment efficiency was investigated. The pilot-plant tests were also carried out, and the membrane system for PFOA recovery was designed and optimized, and finally such membrane-based application was successfully industrialized.Firstly, the rejection performance of PFOA by two commercial nanofiltration (NF) membranes was evaluated with PFOA model solution. NF90 membrane was further chosen to investigate the effect of PFOA concentration, stirring speed, pH, permeate flux on membrane separation performance. By optimizing the operating parameters, the highly concentrated PFOA could be obtained by NF-concentration. This bench-scale results can provide fundamental data for the recovery of PFOA from the practical industrial wastewater.Secondly, the adsorption behaviors of PFOA on the membrane surface were studied by static adsorption experiments, and the adsorption mechanism was investigated by comparing the contact angles before and after adsorptions. The PFOA concentration at the membrane surface was predicted by concentration polarization (CP) model, and the effect of CP on the formation of PFOA micelles was clarified. The distribution of trans-membrane resistances was analyzed by osmotic pressure model.Thirdly, the practical wastewater containing a low concentration of PFOA discharged from fluoropolymers manufactory was treated by the integrated membrane technology. The feasibility of PFOA recovery from the wastewater was verified by the pilot-scale experiments, and the recycling process of permeate water was also studied. Industrial-scale membrane system was designed, fabricated and applied in the practical production, and the economic and environmental benefits were evaluated.Fourthly, ultrafiltration (UF)-osmosis reverses (RO) integrated process was applied in the treatment of soybean soaking wastewater released from soybean processing to achieve the resource utilization and the membrane process was optimized. The main components in RO permeate were analyzed and its effect on soybean soaking process was also evaluated. The RO permeate was reused for soybean soaking and the effect of recycling times on the soaking efficiency was investigated. The pilot-plant test for the soybean soaking wastewater treatment was finally carried out successfully.