Understanding aging impact on membrane structure and seasonal variation of natural organic matter in water from a membrane drinking water treatment plant

Abstract

An autopsy of hollow fiber (HF) PVDF membrane samples at different ages from a full-scale drinking water treatment was performed to investigate the membrane aging impact on membrane structures and properties. Scanning electron microscopic images indicated the fouling occurred on membrane surface; diameter of membrane lumen and pore size decreased with an increase in membrane aging. Membrane aging decreased membrane porosity and breaking strength. Clean water test showed the membrane permeability decreased within aging. Contact angle values decreased with an increase in membrane age, and hypochlorite cleaning resulted in a more hydrophilic membrane surface. Chemical cleaning could partially restore membrane permeability and porosity but negatively impact the breaking strength. Organic foulants dominated in membrane fouling. Natural organic matter (NOM) in all surface and groundwater can be problematic during the drinking water treatment and vary spatially and temporally. It can be quantitatively expressed as the concentration of dissolved organic carbon (DOC). By characterizing bulk NOM in feed samples between 30/11/2016 and 29/03/2017, the peak NOM content in raw water occurred on December 7, 2016, and reduced afterward in March 2017 over the sampling period. By separating the NOM using XAD resins into hydrophobic, hydrophilic, transphilic fractions, NOM type of most raw water, membrane permeates, and concentrates is dominated by the hydrophilic fraction (HPI). The DOC concentrations in water samples in Nov and Dec 2016 were generally higher than that from March 2017. NOM removal in this treatment plant seemed to be inefficient.