Removal of Membrane Fouling and Control of Halogenated By-Products by a Combined Cleaning Process with Peroxides and Sodium Hypochlorite

Sodium hypochlorite (NaClO) solution is wildly used to remove membrane fouling-derived organic materials and restore membrane flux, which can result in the formation of halogenated by-products. To reduce the halogenated by-products, a combined cleaning process with NaClO and peroxides including hydrogen peroxide (H2O2), peroxydisulfate (PDS), and peroxymonosulfate (PMS) were applied in offline mode to remove the organic fouling. It was found that all the combined cleaning processes could effectively restore the membrane flux. Compared with the process of NaClO cleaning followed by peroxide cleaning (NaClO-peroxide), fewer halogenated by-products were generated in the NaClO post-combined cleaning process (peroxide-NaClO), and the PDS-NaClO cleaning process exhibited the best performance in controlling by-products. Overall, most by-product generation showed a positive correlation with reaction time and temperature.

Automated summary

Sodium hypochlorite solution is commonly used to remove organic fouling and restore membrane flux, but it can lead to the formation of halogenated by-products. To mitigate these by-products, a combined cleaning process with sodium hypochlorite and peroxides (hydrogen peroxide, peroxydisulfate, and peroxymonosulfate) was applied offline. It was found that all the combined cleaning processes effectively restored membrane flux. The process of peroxide cleaning followed by sodium hypochlorite cleaning (peroxide-sodium hypochlorite) resulted in fewer halogenated by-products compared to the sodium hypochlorite post-combined cleaning process (sodium hypochlorite-peroxide), with the PDS-sodium hypochlorite cleaning process demonstrating the best performance in controlling by-products. Overall, the generation of most by-products showed a positive correlation with reaction time and temperature.