Application of the multi-wavelength UV-LED/chlorine process to improve reverse osmosis membrane performance for reused water treatment in the steel industry

Membrane fouling is a prominent issue that affects the stable and efficient operation of reverse osmosis (RO) in reused water treatment. In this study, a zero-discharge RO system was adopted to treat the ultrafiltration permeate from a steel plant with the combined multi-wavelength UV-LED/chlorine process, focusing on organic structure modification and membrane fouling control. The results showed that the UV-LED/chlorine process could not only efficiently remove the dissolved organic carbon and the total nitrogen of the RO influent but also alter the organic substances from large molecules to small ones. In addition, the longer wavelength of a 295 nm UV-LED/chlorine process exhibited a greater RO permeate flux of 158 LMH, as compared to the shorter wavelength of 255 nm with the flux of 152 LMH. Moreover, compared to the single-wavelength, the dual-wavelength UV-LED/chlorine process played a more significant role in RO filtration performance, which induced a looser and thinner foulant structure, resulting in an 8% larger permeate flux and recovery at 275 + 295 nm than at 295 nm. This study demonstrated that the combined UV-LED/chlorine process could effectively alleviate RO membrane fouling. Our findings can provide theoretical and technical support for the sustainable development of membrane-based reused water treatment in the steel industry.