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This study considers the potential advantages of applying intermittent ultrasound to the ultrafiltration (UF) process to control long term membrane fouling in the context of water treatment. By means of parallel, bench-scale tests using traditional coagulation pre-treatment prior to UF, and intermittent ultrasound during the operation (3 min/10 min every 3 days), the development of fouling material, and its nature (e.g. hydrophilic and hydrophobic), within the cake layer and membrane pores, have been evaluated in detail. In particular, the impact of intermittent ultrasound on bacteria growth and the production of extracellular polymeric substances (EPS) have been investigated. The results have shown that, compared to a control UF process, intermittent ultrasound reduces both reversible and irreversible fouling, with a 50% reduction in transmembrane pressure development over 60 days of operation. The intermittent ultrasound led to a much thinner cake layer which contained less EPS/biopolymers in the form of polysaccharides (g/g) and protein, as well as DNA concentrations. Material removed from the UF membrane by ultrasound was predominantly of high molecular weight (~100 kDa) and hydrophilic in nature. Compared to the control membrane, pore deposits in the membrane receiving intermittent ultrasound contained much less high molecular weight, biopolymer-type substances, which was consistent with the reduced extent of irreversible fouling observed

The Mekong River is the tenth largest river in the world in terms of water discharge, representing a substantial source of organic matter to the South China Sea. However, the composition and variation of dissolved organic matter (DOM) remain poorly studied in this international river flowing through contrasting climates and severely affected by cascade reservoirs. Herein, using biomarkers, optical spectroscopy, and ultrahigh-resolution mass spectrometry analyses, we present a benchmark investigation of DOM evolution in the upper Mekong (Lancang) River. We show that terrestrial plantderived DOM accumulates in the wet season but degrades downstream in the dry season in the upper natural reach of Lancang. In contrast, terrestrial DOM decreases consistently in both wet and dry seasons along the lower reach affected by reservoirs, accompanied by decreases (instead of increases) in lignin oxidation indices (i.e., acid-to-aldehyde ratios) and high-oxygen highly unsaturated compounds. While photo-and microbial oxidation is considered to partly contribute to terrestrial DOM removal, we employ a series of batch sorption experiments to further show that sorption to finesized mineral particles may explain the decreasing lignin acid-to-aldehyde ratios in DOM. Given the high abundance of fine-sized suspended particles and long residence time in the Lancang reservoirs, removal via sorption (and possibly flocculation) is a potential important pathway for terrestrial DOM in the Lancang River. Cascade reservoirs hence are a hot spot of DOM processing, and an in situ quantitative assessment of sorptive removal of DOM therein warrants closer attention.