Role of reactive manganese and oxygen species in the KMnO/NaSO process for purification of algal-rich water and membrane fouling alleviation.

Ultrafiltration (UF) is a highly efficient technique for algal-rich water purification, but it is heavily contaminated due to the complex water characteristics. To solve this problem, potassium permanganate (KMnO) oxidation enhanced with sodium sulfite (NaSO) was proposed as a pretreatment means. The results showed that the end-normalized flux was elevated from 0.10 to 0.91, and the reversible fouling resistance was reduced by 99.95%. The membrane fouling mechanism also changed obviously, without the generation of cake filtration. Regarding the properties of algal-rich water, the zeta potential was decreased from -29.50 to -5.87 mV after KMnO/NaSO pretreatment, suggesting that the electrostatic repulsion was significantly reduced. Meanwhile, the fluorescent components in algal-rich water were significantly eliminated, and the removal of dissolved organic carbon was increased to 67.46%. In the KMnO/NaSO process, reactive manganese species (i.e., Mn(V), Mn(III) and MnO) and reactive oxygen species (i.e., SO and OH) played major roles in purifying algal-rich water. Specifically, SO, OH, Mn(V) and Mn(III) could effectively oxidize algal pollutants. Simultaneously, the in-situ adsorption and coagulation of MnO could accelerate the formation of flocs by decreasing the electrostatic repulsion between cells, and protect the algal cells from being excessive oxidized. Overall, the KMnO/NaSO process showed significant potential for membrane fouling alleviation in purifying algal-rich water.