Using FO as pre-treatment of RO for high scaling potential brackish water: Energy and performance optimisation

Abstract

In this study, high scaling potential brackish water was used as feed water. To avoid rapid and severe scaling on the RO membrane, a forward osmosis stage was used as a pre-treatment of RO stage to remove scaling ions and organic matter. First, a modelling approach has been developed to optimise the operational conditions of FO–RO train. Both water flux and energy consumption have been considered. Then, experiments were conducted using spiral wound TFC FO membranes. Then, results confirmed that FO was a very efficient pre-treatment for RO process where FO demonstrated much lower scaling tendency than RO. Bench scale observation of scaling on FO membrane has confirmed that loosely packed visible scaling was formed on the surface of FO membrane; however, the water flux of FO was almost not affected by scaling. By carrying out FO–RO pilot plant experiments, the energy consumptions of FO–RO process were compared with that of the RO process only; the results indicated that, when treating the high scaling potential brackish water, FO–RO hybrid was more sustainable and feasible in terms of energy consumption and operations. FO appeared to be the ultimate pre-treatment solution that removes both scaling and fouling agents. Nevertheless, the application of this combined FO and RO process can only be justified for treating the brackish water with high scaling potential, when using RO directly is not feasible due to the rapid scaling beyond the control of antiscalent and frequent chemical cleaning.