Critical review of pretreatment on the performance of gravity driven membranes

Ever since the Gravity Driven Membrane (GDM) system was proposed in 2010 as an environmentally friendly and low-carbon water treatment technology, the search for an appropriate pre-treatment measure to combat the low stable flux and membrane fouling has been of great importance for the promotion and development of GDM systems. This review summarized the effects of pre-treatment measures (particulate adsorption, coagulation, oxidation) in existing reports on stable flux, membrane fouling and water quality of GDM systems. Based on the literature reports, the internal mechanism was classified. The effects of different pretreatment conditions on stable flux were evaluated by meta-analysis, and the optimal process conditions to maintain higher stable flux with different pretreatments were predicted. The analysis revealed that appropriate pretreatment selection could improve the performance of the GDM system by removing fouling by the pretreatment itself, reducing bacterial EPS emissions, producing smaller/more hydrophilic pollutant molecules, enhancing bioactivity and generating a looser membrane structure. Moreover, the investment and operating costs of GDM systems can be reduced through suitable pre-treatment measures, thereby expanding their application in decentralized water supply and wastewater treatment. Given the variability and uniqueness of water source conditions, this review aimed to guide the design of pretreatment measures in GDM systems to improve the efficiency of targeted treatment and promote its applicability.