Effect and mechanism of preoxidation using potassium permanganate in an ultrafiltration membrane system

Abstract

The use of potassium permanganate (KMnO 4) for sand filter effluent pretreatment was investigated as well as its performance in combined ultrafiltration (UF) processes. The former process was implemented via direct continuous dosing of KMnO 4 into the influent of a UF system. Investigations into this option indicated that the optimal dose of KMnO 4 was 0.3 mg/L and significant improvements to the efficiency of natural organic matter (NOM) removal during the KMnO 4/UF process were achieved. Due to membrane fouling, the use of KMnO 4 also resulted in lowered total membrane resistance in comparison with results obtained when operating without KMnO 4. The KMnO 4 oxidation of the sand filter effluent to UF also indicated some potential for mitigating transmembrane pressures, due to the changed characteristics of organic pollutants. This observation was confirmed by Attenuated total reflection-Fourier transform infrared spectroscopy analysis (ATR-FTIR). Scanning electron microscopy showed that a significant amount of fouling that had clogged the membrane was very loose and easy to be removed by hydraulic washing during the KMnO 4/UF process. The fouling removal mechanism was demonstrated by energy dispersive X-ray spectroscopy. It was noted that KMnO 4 could oxidize metal ions into metal oxide particles, which were adsorbed on the membrane surface together with the pollutants. These formed loose fragments on the filtration cake that were easy to flush away.