Research On Concentrated Dye Wastewater By Ultrafiltration-nanofiltration Integrated Process

In this paper,the PES hollow fiber ultrafiltration membrane was prepared by dry-wet spinning process.The effects of polymer concentration,porogen concentration,coagulation bath temperature,concentration of DMAC in the bore liquid,dry spinning process and winding speed on the rejection rate,flux,structure and mechanical properties of hollow fiber ultrafiltration membrane were studied.The nanofiltration composite membrane was prepared by using the self-made PES hollow fiber ultrafiltration membrane as the base membrane and its performance was studied.The concentration and recovery of dye wastewater by the integrated ultrafiltration-nanofiltration process were studied.The effects of different polymer PES concentration,porogen PEG400concentration,coagulation bath temperature,DMAC concentration in the bore liquid,dry spinning process,and winding speed on the properties and structure of hollow fiber ultrafiltration membranes were studied.The composition of casting liquid and spinning process parameters were considered comprehensively.When PES concentration is 20%,PEG400 concentration is 8%,coagulation bath temperature is20?,DMAC concentration in the bore liquid is less than 20%,dry spinning path is50mm,winding speed is 0.17m/s,the rejection rate of PES hollow fiber membrane is more than 90%,and the flux is 200 L/(m~2h)?300 L/(m~2h).Hollow fiber composite nanofiltration membranes were prepared by interfacial polymerization using piperazine(PIP)and trimesyl chloride(TMC).The concentration of PIP was 2wt%,the soaking time was 2min,and the TMC concentration was 0.5wt%,The performance of nanofiltration membrane is best when the soaking time is 1min.With the increase of operating pressure,the retention rate of the nanofiltration membrane does not change much,the water flux increases by 54%,and the influent salt concentration increases,and the retention rate and water flux of the nanofiltration membrane decrease.When the inlet water temperature rises above40°C,the salt rejection rate begins to decrease,and the water production increases with the increase of temperature.Nanofiltration membranes can achieve high retention of positively charged dyes,but depending on the purity of the dye,the salt content,and the purity of the by-products,the nanofiltration membranes have different retention rates for the dyes.Under the condition of changing salt concentration,the nanofiltration membrane's retention rate of dye is basically unchanged,the retention rate of salt is decreasing,and the water flux is also decreasing.As the dye concentration increases,the system's rejection rate for dyes continues to increase,and the rejection rate for salts remains at a relatively stable state.Under the condition of increasing operating pressure,the water flux of the system rose rapidly,and the system's retention of dye remained basically unchanged.After 9 days of short-term running experiments,no degradation occurred during the process of nanofiltration membrane treatment of dyes,and the stability of the nanofiltration membrane was good.