Abstract
To mathematically predict the behavior of a forward osmosis (FO) process for water recovery, a model was constructed using an asymmetric membrane and glucose as a draw solution, allowing an examination of both phenomenological and process aspects. It was found that the proposed model adequately described the significant physicochemical phenomena that occur in the FO system, including forward water flux, internal concentration polarization (ICP), external concentration polarization (ECP), and reverse solute diffusion (RSD). Model parameters, namely the physiochemical properties of the FO membrane and glucose solutions, were estimated on the basis of experimental and existing data. Through batch FO operations with the estimated parameters, the model was verified. In addition, the influences of ECP and ICP on the water flux of the FO system were investigated at different solute concentrations. Water flux simulation results, which exhibited good agreement with the experimental data, confirmed that ICP, ECP, and RSD had a real impact on water flux and thus must be taken into account in the FO process. With the Latin-hypercube—one-factor-at-a-time (LH–OAT) method, the sensitivity index of diffusivity was at its highest, with a value of more than 40%, which means that diffusivity is the most influential parameter for water flux of the FO system, in particular when dealing with a high-salinity solution. Based on the developed model and sensitivity analysis, the simulation results provide insight into how mass transport affects the performance of an FO system.
Highlights
Water shortages have become a key issue facing humanity
After a parameter estimation process, the model was found to be capable of describing significant physio-chemical phenomena during the forward osmosis (FO) process, such as the internal (ICP) and external concentration polarization (ECP), as well as diffusion of the reverse draw solute
The simulation results indicate that the influences of the internal concentration polarization (ICP), ECP, and reverse draw solute flux must be taken into account for FO systems
Summary
Water shortages have become a key issue facing humanity. According to the United NationsWorld Water Development Report in 2019, over 2 billion people suffer from severe water shortage, and the global demand for fresh water has been increasing by about 1% annually since the 1980s [1].much effort has been made to secure water, in particular safe water, with low energy consumption. FO-based water desalination, of which the driving force is an intrinsic osmotic pressure gradient, has a unique position because (1) it is highly resistant to membrane fouling [5], (2) it requires much lower energy [6] and exerts higher driving force than conventional physical separation methods if proper draw solutes are used, and (3) it does not deteriorate the physical properties of feed solution (e.g., color, taste, aroma, and nutrition) [7,8] For these reasons, FO is viewed as workable especially for difficult feed water with high salinity or foulants. Special cases in which there is no requirement to regenerate draw solution have high potential, as draw solute: It is possible to use diluted fertilizer for direct fertigation [10,11,12]
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