Study On Treatment Of Reverse Osmosis Concentrated Water By Pervaporation Desalination Technology

Due to the mature application of reverse osmosis technology in the field of desalination,its water treatment capacity accounts for about 80%of the capacity in the field of desalination,and the global reverse osmosis water production is over 70 million tons per day.However,the residual reverse osmosis concentrated water(ROC),which accounts for about 30%of the produced water,has become a new source of pollution.Due to its high salt content,complex composition and other problems,it is difficult to handle,and direct discharge will destroy the environment.Pervaporation(PV)is a heat-driven selective evaporation process.Its hydrophilic dense selective layer can treat high concentration feed liquid while maintaining high salt rejection rate.It is hoped to solve the problem of reverse osmosis concentrated water.This work focuses on the study of the pollution resistance and membrane cleaning conditions of the new PV desalination membrane in the ROC treatment process,so as to provide reference and help for the early industrialization of PV.The research contents include:Two typical ROC were treated with self-made PV desalination membrane.According to the content of each component in the feed liquid,the composition of precipitated crystalline salt was predicted by salt concentration ratio table.The pollution mechanism of PV membrane in desalination process was analyzed,and the feasible cleaning scheme was explored.At the same time,the effects of feed flow rate on concentration polarization,flux and cleaning efficiency were studied.The results showed that when PV treated ROC with high salinity,the flux decreased to 40%of the initial value after 2 hours.Subsequently,the flux can be recovered to 99.2%of the initial value after 30min of cyclic cleaning with 0.2wt%hydrochloric acid.When ROC with high COD value is treated,increasing the concentration of feed liquid will lead to the initial flux decrease and accelerate the rate of flux decrease.Increasing the flow rate of feed will increase the initial flux of the membrane,slow down the rate of flux decrease and improve the cleaning efficiency.Washing with 0.1 wt%hydrochloric acid for 10 min at the flow rate of 2.2 m/s can restore the flux 100%.In addition,when PV desalination membrane is used to treat oily wastewater,increasing the cross-linking density of dense layer can effectively reduce the COD value of produced water,but at the same time it will lead to a decrease in flux.The combination of PV and nanofiltration can also reduce the COD value of produced water.