Application of heat-activated peroxydisulfate process for the chemical cleaning of fouled ultrafiltration membranes

NaClO has been widely used to restore membrane flux in practical membrane cleaning processes, which would induce the formation of toxic halogenated byproducts. In this study, we proposed a novel heat-activated peroxydisulfate (heat/PDS) process to clean the membrane fouling derived from humic acid (HA). The results show that the combination of heat and PDS can achieve almost 100% recovery of permeate flux after soaking the HA-fouled membrane in 1 mmol/L PDS solution at 50 °C for 2 hours, which is attributed to the changes of HA structure and enhanced detachment of foulants from membranes. The properties of different treated membranes are characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS), demonstrating that the reversible and irreversible foulants could be effectively removed by heat/PDS cleaning. The filtration process and fouling mechanism of the cleaned membrane were close to that of the virgin membrane, illustrating the good reusability of the cleaned membrane. Additionally, heat/PDS which can avoid the generation of halogenated byproducts shows comparable performance to NaClO on membrane cleaning and high performance for the removal of fouling caused by sodium alginate (SA), HA-bovine serum albumin (BSA)-SA mixture and algae, further suggesting that heat/PDS would be a potential alternative for membrane cleaning in practical application.