Assessment of an integrated membrane system for surface water treatment

With the promulgation of more stringent regulations to guarantee that the drinking water presents minimal health risks, nanofiltration (NF) and low pressure reverse osmosis membrane (RO) processes are nowadays considered for surface water treatment. However, NF and RO spiral wound membranes are sensitive to fouling and an advanced pretreatment such as conventional train, microfiltration (MF) and ultrafiltration (UF) may be necessary to control productivity. Consequently, a study was undertaken to evaluate the efficiency of the combined processes, know as Integrated Membrane Systems, for surface water treatment. Two IMS were evaluated on polluted low salinity water: UF and conventional train prior low fouling reverse-osmosis membranes (LFRO). The one-year study has revealed the efficiency of the IMSs for surface treatment. Both IMSs tested produced water quality that exceeded the most stringent water quality proposed in the new European Directives. However, in case of blending with the pretreated water for remineralization, clarified water has to be disinfected due to its low microorganism removal. In term of hydraulic performances both pretreatments: UF and clarification were found to be effective to control RO fouling. Despite UF reduces the SDI well below the maximum advised by the membrane manufacturer, a slight fouling occurred on the RO membranes at high nux. Organic material plays a role in membrane fouling and therefore reducing SDI may not guarantee a low fouling rate of the RO membranes. Preliminary cost estimation is on-going in order to identify the water cost for both IMSs based on similar final water quality.