Experimental Study On The Reuse Of Dye Wastewater And Its Equipment Design Based On Photocatalysis And Membrane Separation Technology

Nowadays, China faces a severe shortage of water resources and more than 61% of the cities are short of water, of which about 31% are serious water shortages. Hence, it is extremely important to find other sources of water supply, which includes the reuse of wastewater. In recent years, few publications have reported the combined use of photocatalysis and membrane separation technology to treat the dye wastewater, however, the majority of photoreactors described in the literature are slurry photoreactor, in which TiO2 is suspended in the reaction mixture. The slurry type photoreactor has several disadvantages, such as easy to reunite in aqueous solution, narrow range of application, hard to reclaim. Therefore, this paper combined three dimensional foam nickel photocatalytic net and membrane separation for the reuse of dye wastewater, and the experimental conditions, process parameters, the deactivation and regeneration of materials and the optimization design of key components were studied. On the basic of practical engineering application and numerical simulation method, depth purification device for the reuse of dye wastewater has been designed. Using fluent 14.5 to optimize photoreactor and membrane module, it can provide valuable scientific theoretical basis and industrial application for the reuse of dye wastewater.Firstly, the three dimensional foam nickel photocatalytic net was prepared by composite electroplating method. An advanced treatment system which can treat the dye wastewater to the standard of reuse water is described. The system is formed by coupling photocatalytic oxidation process and membrane separation. Important parameters affecting the treatment, such as irradiation time, pH and work pressure, were investigated. Water quality and extent of fouling were measured. The results showed that the highest activity for congo red degradation was reached under pH 4 in about 90 min of irradiation time. In membrane separation, when pH 10, the decline of the UF membrane flux was slower. However, the decline of the RO membrane flux was slower when pH 4. Taking into accounts of the power saving and efficiency,0.5 MPa was used as the work pressure of RO. Photocatalysis as a pre-treatment for 2 hours can reduce the membrane flux decline of UF and RO membrane by about 12% and 8%, respectively. After being treated by photocatalysis, UF and RO, the experimental results of removal of congo red, chemical oxygen demand (COD), hardness and conductivity in the effluent are about 99.2%,20.12 mg/L,28.03 mg/L and 88.3 μs/cm, respectively. All the results exceed the standard value of supply water in central air conditioning system and the quality standard of reuse water for textile industry.Secondly, the regeneration experiments of the deactivation of photocatalytic net, UF membrane and RO membrane were studied. The results showed that:the highest restoration effect of the photocatalytic net was reached after cleaning by lactic acid and ultrasonic. And its removal rate of congo red was almost the same as the new photocatalytic net’s. After cleaning by caustic wash and oxidation, most of flocculent pollutants on the UF membrane surface have been eliminated, and its membrane flux recovery rate reached 95%. After cleaning by caustic wash and pickling wash, most of grain pollutants on the RO membrane surface have been eliminated. Its membrane flux recovery rate reached 90% and its desalination rate recovered to 97%.Last, depth purification device for the reuse of dye wastewater has been designed and key components were studied by numerical simulation method. Fluent 14.5 was used to optimize photoreactor and membrane module. The optimization simulation results of photoreactor showed that arranging baffles can increase the chaos of internal flow field and undermines the stability of the flow field. On the other hand, it can increase the residence time of fluid, so it can reduce the cycles of the photoreactor and save power. When the baffle distance is 120 mm, each individual photoreactor can form two eddy current. The optimization simulation results of the spiral-wound membrane module showed that compared to the circular grid and the rectangular grid, the triangular grid can produce larger vortex. Al/h=3 is the most suitable grid spacing, because the vortex can get a full development and it can make full use of the role of transport of particles. When Al/h=5 and △l/h=8, the grid spacing are too long, which can lead to overdevelopment of the vortex wake zone. Thereby they can weaken the effect of vortex transport of particles.