Effect of potassium permanganate dosing position on the performance of coagulation/ultrafiltration combined process

The effects of potassium permanganate (KMnO4) dosing position on the natural organic matter (NOM) removal as well as membrane fouling were investigated in the coagulation/ultrafiltration combined process. KMnO4 oxidation altered the NOM characteristics in terms of hydrophobicity and molecular weight, and destroyed humic substances originated from terraneous organisms in raw water. The optimal KMnO4 dosage was 0.5 mg·L− 1 in the peroxidation enhanced coagulation process with respect to the dissolved organic carbon (DOC) removal. When KMnO4 was dosed into both upstream and downstream of coagulation, namely in the proposed two-position dosing mode, coagulation and KMnO4 oxidation worked individually on the apparent DOC removal. However, compared to the KMnO4 addition prior to or after coagulation, the two-position dosing mode dramatically alleviated membrane fouling and reduced fouling irreversibility. This was attributed to the change of NOM characteristics as a result of KMnO4 addition prior to coagulation and the presence of MnO2 on membrane surface as a result of KMnO4 addition prior to ultrafiltration. This work may provide useful information for the application of KMnO4 oxidation in the coagulation/ultrafiltration combined system.