Nanofiltration range desalination by high flux graphene oxide impregnated ultrafiltration hollow fiber mixed matrix membrane

Abstract

In this work, a novel graphene oxide impregnated ultrafiltration grade hollow fiber membrane was prepared having capability of salt rejection in the range of nanofiltration. Sodium sulfate showed higher rejection (40%–50%) than the other salts, magnesium sulfate and sodium chloride. Charge-charge interaction is the major salt retention mechanism. Optimum operating conditions were identified as 55 kPa transmembrane pressure drop and 5 L/h cross-flow rate. Increasing the solution pH from 5 to 9 augmented the rejection of sodium sulfate from 43% to 51% at relatively high permeate flux 0.25 L/m².h.kPa. In case of filtration of actual sea water, the permeate flux is lowered to 0.20 L/m².h.kPa due to presence of other fouling agents. Rejection of total dissolved solids was 30% for seawater. Beyond 11 h (breakthrough time) the rejection decreases due to screening of charge effects of the membrane surface. Pretreatment by activated carbon delayed the breakthrough time to 14 h and improved permeate flux 0.22 L/m².h.kPa. Thus, ultrafiltration grade hollow fiber mixed matrix membrane offers equivalent salt rejection of nanofiltration membrane at a much higher throughput.