Role of pre-oxidation, using potassium permanganate, for mitigating membrane fouling by natural organic matter in an ultrafiltration system

An ultrafiltration (UF) system was used as an advanced treatment, following the conventional sand filter process, to purify raw water from the Yangtze River. Potassium permanganate was used as a pre-oxidant to oxidize the UF system influent for controlling the membrane fouling. The process was implemented by directly dosing KMnO4 into the UF system influent, i.e. the sand filter effluent. The optimal dosage of KMnO4 was 0.4 mg/L in terms of both the trans-membrane pressure (TMP) and product water quality. Compared to the results obtained when using a UF system without KMnO4, the preoxidation of the feed water by KMnO4 was found to result in a lower cake layer resistance. The pretreatment of the feed water by KMnO4 also indicated that some advantages in terms of mitigating TMPs were achieved by transforming molecular weight distribution of organic pollutants, which were mainly from hydrophilic and hydrophobic organic matter. The analysis of attenuated total reflection-Fourier transform infrared spectra of the cake layer showed that KMnO4 oxidized macromolecules of hydrophobic natural organic matter (NOM) to lower-molecular-weight hydrophilic organic matter, which mitigated the membrane fouling caused by the organic matter. Scanning electron microscopy indicated that loose fragments were formed on the filtration cake in the KMnO4/UF system, which was easily removed by hydraulic washing.