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Concentrating underground brine using a TFC hollow fiber forward osmosis membrane: effects of cleaning

In this work, underground brine (UGB) with high salinity was concentrated using a thin-film composite (TFC) hollow fiber forward osmosis (FO) membrane. The TFC hollow fiber FO membrane has an active polyamide separation layer at the inner surface; the membrane showed a water permeability coefficient of 1.8 L m−2 h−1 bar−1, a salt rejection of 93%, a structural parameter of 335 μm and a water flux of 15.1 L m−2 h−1 (active layer facing feed solution, AL-FS). Using saturated NaCl solution as the draw solution at the shell side, the increase of the flow rate of the UGB at the hollow fiber from 10 mL min−1 to 280 mL min−1 resulted in an increase in the flux from 0.8 L m−2 h−1 to 12.2 L m−2 h−1. Osmotic backwashing and chemical cleaning were adopted to mitigate membrane scaling and their effects were evaluated. Chemical cleaning using Na2EDTA was found to be more efficient in mitigating membrane scaling than osmotic backwashing, but at the expense of negative influence on the active surface separation performance.