Using modelling approach to validate a bench scale forward osmosis pre-treatment process for desalination

Forward osmosis (FO) has recently attracted growing attention in wastewater, brackish groundwater and seawater desalination, and power generation. This study evaluates the potential of using a batch laboratory-scale FO system as a pre-treatment for the reverse osmosis (RO) process. FO is a low pressure-driven process that offers many advantages compared to the conventional pre-treatment for RO especially for brackish water with high potential of scaling and fouling. FO can help to reduce the RO process cost by avoiding RO membrane fouling and achieving higher water recovery. An experimental modelling has been employed to describe the FO process taking into account water flux, water recovery and final draw solution. Based on this experimental modelling, the energy consumption for RO has been estimated. It has been found that the treatment time for the FO process and the initial draw solute concentration are important parameters that have an interrelated effect on FO and RO efficiency. The optimal conditions for this FO pre-treatment process are determined by modelling and are experimentally validated by using real brackish water as feed in a bench-scale FO system. © 2014 Elsevier B.V. All rights reserved.

The objective of this study was to evaluate the possibility of using the FO system as a pre-treatment for the RO process. The different parameters affecting the FO process were investigated using a batch laboratoryscale system. Time and initial concentration of draw solution are important parameters that influence the efficiency of the FO process. However, if we consider this process as a pre-treatment for the RO process, these parameters have contradictive effects. A response surface methodology was used to describe the FO process by modelling; it determined the optimal outcomes in terms of water flux, water recovery and final draw solute concentration prior to RO filtration. A theoretical modelling has been conducted to estimate the energy consumption of RO process using the experimental data from FO process. The optimal conditions have been determined by coupling FO water flux and water recovery and RO energy consumption models. The FO system with lower fouling and scaling tendency appears to be a very efficient onestep RO pre-treatment particularly for desalinating high scaling potential brackish water. The permeate obtained from this pre-treatment is free of organics, scaling agents and biological compounds, and can thus protect RO membranes from fouling as well as achieve higher RO water recovery. This study has demonstrated that the modelling methodology employed for the optimisation of the experimental conditions was successful. The application of the FO process on real brackish water has validated the modelling results. A continuous-mode FO operation will be tested in a future study by directly coupling these two processes (FO– RO) and taking into account the energy cost.