Robust mitigation of FO membrane fouling by coagulation-floatation process: Role of microbubbles

Forward osmosis (FO) membrane fouling is a big obstacle in real textile wastewater treatment. Herein, a series of pretreatments include coagulation (C), microbubbles (Mbs) and their combination process (Mbs + C) were used to alleviate membrane fouling. Their different effects on flux and rejection rate of FO membrane were also investigated. Satisfactory removal efficiencies for UV254, dissolved organic carbon (DOC), chemical oxygen demand (COD) and antimony (Sb) of 48.27, 47.80, 40.70 and 41.87% were obtained at the optimum polyaluminum chloride (PAC) dosage of 300 mg L-1 and combined treatment time of 15 min. Compared with C alone, combined Mbs + C resulted in smaller flux decrease (similar to 40%) and higher rejection rate (>98%) of FO membrane. This result confirmed the positive effect of Mbs on the combined processes. Fluorescence excitation-emission matrices coupled with parallel factor (EEM-PARAFAC), gel permeation chromatography (GPC) and gas chromatography mass spectrometry (GC-MS) measurements were further carried out to investigate the mitigation effect of pre treatments on membrane fouling. Results exhibited Mbs + C can significantly remove tryptophan-like substance and aliphatic alcohols due to enhanced coagulation-floatation property and oxidation of hydroxyl radicals. This study provides useful insights for fouling mitigation through Mbs and coagulation in actual FO process when dealing with textile wastewater.