Research On The Treatment For Micro-Polluted Water By UV/Chlorine And Reverse Osmosis Process

Nowadays,the organic pollution of surface water is very serious.One kind of organic pollution is natural organic materials(NOM)with complex structures.The other is micropollutants,which is difficult to be removed by conventional processes.UV/Chlorine technology is a new advanced oxidation process with good degradation effect on NOM and micropollutants.It combines UV/Chlorine advanced oxidation technology with reverse osmosis process.On one hand,pre-oxidation is used to reduce membrane fouling,on the other hand,by-products can be effectively retained by reverse osmosis membrane.In this study,humic acids were used to simulate NOM in water and benzoic acid was chosen as the target micropollutants.Factors influencing the degradation of humic acids and benzoic acid by UV/Chlorine pretreatment were investigated,including the initial concentration of pollutants,oxidant dosage and the p H of the system.The effect of humic acids as the background on the degradation of benzoic acid was also studied.For humic acids,the degradation rate will not necessarily increase if the initial concentration is decreased or the oxidant dosage is increased,while the degradation rate of benzoic acid increases with the decrease of the initial concentration of benzoic acid and the increase of the oxidant dosage.The lower the p H of the system is,the faster the degradation rate of humic acid and benzoic acid will be.Humic acids as the background in water will inhibit the degradation of benzoic acid.The effect of UV/Chlorine pretreatment on the water flux of the reverse osmosis membrane has been investigated.In addition,the optimal pretreatment parameters were obtained.Because the pretreatment made the humic acids partially mineralized and changed the molecular weight distribution and structure of humi c acids,the flux of the membrane declined more slowly,which means the membrane fouling was improved.When the UV/Chlorine process was operated with oxidant dosage of 400 ?M and p H=7,the decline of the water flux was the smallest and the best operating results were obtained.The ability of RO membranes to retain the(disinfection byproducts)DBPs generated during pretreatment was also investigated.Chloroform chloride(TCM),dichloroacetic acid(DCAA),chloral hydrate(CH)and dichloroacetonitrile(DCAN)were selected as representative DBPs.The experimental results showed that the rejection of DCAA and CH using reverse osmosis membrane could be 90% or above,while only about 50% of TCM and DCAN can be retained.Through ATR-FTIR characterization of the membrane surface and the desalination rate test of the membrane after operation,the results showed that residual chlorine after the UV/Chlorine pretreatment failed to destroy the polyamide separation layer.The treatment performance of the combined UV/Chlorine and reverse osmosis processes on the Songhua River was investigated.After pretreatment(the oxidant dosage was 400 ?M and p H of the system was 7),the degradation of TOC and UV254 were 41.39% and 30.90%,respectively.If raw water which wasn't treated by pretreatment was directly treated by reverse osmosis,the water flux would be declined rapidly.It was 45.72 L/(m2·h)after 8 hours of operation.If raw water was oxidized before entering the reverse osmosis platform,although the initial water flux would be slightly reduced,the decline of flux is extremely slow.After 8 hours of operation,the water flux is 65.45 L/(m2·h).UV/Chlorine pretreatment can effectively improve membrane fouling.