Water treatment in a new flux-enhancing, continuous forward osmosis design: Transport modelling and economic evaluation towards scale up

A forward osmosis-nanofiltration integrated system was designed for experimental investigation and mathematical modelling for purification of contaminated water in steady state and continuous mode. Unlike the conventional module of a FO scheme, this new design provided different hydrodynamic regimes that very significantly reduced concentration polarization. Dynamic modelling encompassing the effects of pressure, cross flow rate, draw solution, run time and overall hydrodynamics on the efficiency of separation as well as yield of pure water flux was done to capture the most significant transport phenomena during forward osmosis and nanofiltration. The system applied in purification of arsenic-contaminated water produced encouraging results in terms of 99% purification of water at reasonably high flux of 58-60 L/(m(2).h) (LMH). Recovery of draw solute could be done efficiently at the rate of 60 LMH in a steady state continuous operation. The developed model successfully predicted system performance as reflected in the high values of the overall correlation coefficient (R-2 > 0.98), Willmott d-index (>0.95) and low relative error (<0.1). Economic evaluation indicated that such FO-NF system in the proposed new configuration could be quite promising in purifying arsenic-contaminated groundwater at a low cost of $ 1.57 m(-3). (C) 2015 Elsevier B.V. All rights reserved.