Research On Effect Of Ultrafiltration PRE-Treatment And Calcium Ion For Nanofiltration Performance

Advanced treatments of water supply like nanofiltration(NF) have found their application and been researched since the water resource is widely polluted and it is more important to ensure population’s access to safe drinking water. This study, with NF as the core, focuses on the influence of ultrafiltration as pre-treatment and characteristics of membrane fouling with calcium ion in the aspect of flux and Pharmaceutical and Personal Care Products’(PPCPs) rejection.Firstly, the efficiency of NF for pollutant with UF pre-treatment was investigated. The results showed that UF pre-treatment reduced load of NF and a majority of organic pollutant in high molecular weight could be removed by UF. The reject rate of dissolved organic carbon(DOC) was more than 55%, meanwhile the rate of middle molecular weight organics(tannin) was about 15%. Low molecular weight organics like PPCPs and ions were hardly removed by UF. With the change of pollutant concentration, UF stabilized the feed of NF and significantly decreased membrane fouling by removed organics. After physical and chemical clean of contaminated NF membrane, the NF flux was recovered more from the effect of UF pre-treatment.Secondly, the effect of calcium in feed solution to membrane fouling was investigated. The results showed that the concentration of Ca2+ was closed related to membrane fouling. Ca2+ could intensify membrane fouling. It was observed that 4mmol/L Ca2+ made the more serious fouling than more or less Ca2+. Divalent ions aggravated membrane fouling as well as made NF membrane flux difficult to be recovered.At last, the effect of membrane fouling on rejection of two types of PPCPs(bisphenol A and sulfamethazine) was discussed and analyzed with concentration polarization model. The results showed that there was slightly influence on rejection of PPCPs by membrane fouling with low concentration of Ca2+, on the contrary, membrane fouling caused by high concentration of Ca2+ observably restrained the rejection of PPCPs. Then according to concentration polarization model, the observed rejection of micro-organic pollutant was divided to real rejection and mass transfer coefficient. And it was investigated that the effect of steric from membrane fouling was the main reason for decreasing of reject rate.