Dynamical Modeling of Water Flux in Forward Osmosis with Multistage Operation and Sensitivity Analysis of Model Parameters

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. Several types of membrane-based desalination technology, including electrodialysis, membrane distillation, reverse osmosis (RO), and forward osmosis (FO), have been developed [3,4]. Among these, 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. FO can be applied to treat hypersaline streams that are too concentrated for RO [9]. Special cases in which there is no requirement to regenerate draw solution also have high potential, as draw solute: It is possible to use diluted fertilizer for direct fertigation [10][11][12] including wastewater treatment [13] and food concentration [7,8]. One such case is the use of fertilizer.However, there are still many difficult barriers to field implementation of the FO process. Typical problems involve intrinsic, performance-reducing properties, including concentration polarization (CP) and reverse solute diffusion (RSD) [14]. Since both sides of the membrane are in contact with two kinds of solutions, feed solution, and draw s...

The Effect of the Osmotically Active Compound Concentration Difference on the Passive Water and Proton Fluxes across a Lipid Bilayer

“…Specifically, the water flow is driven by the difference in the concentration of osmotically active substances, whereas the lipid pore opening can be driven by the water activity gradient. The water flux, on the other hand, is an entropic effect driven by the osmotic pressure difference between membrane separate aqueous phases [ 72 ]. The spontaneous lipid pore formation can be energetically feasible, even without any external stress [ 30 ], since the energy required for its opening is of the order of a few tenths 10 k B T [ 30 , 72 , 73 ].…”

“…The water flux, on the other hand, is an entropic effect driven by the osmotic pressure difference between membrane separate aqueous phases [ 72 ]. The spontaneous lipid pore formation can be energetically feasible, even without any external stress [ 30 ], since the energy required for its opening is of the order of a few tenths 10 k B T [ 30 , 72 , 73 ]. The probability of the lipid pore opening would depend on spontaneous curvature of the lipid bilayer and its components [ 30 , 31 ] and the Gaussian elastic modulus according to the Helfrich representation of the membrane [ 26 , 74 , 75 ].…”

Selection of substrate manufacturing techniques of polyamine‐based thin‐film composite membranes for forward osmosis process

“…The S parameter depends on the bulk tortuosity ( τ ), bulk porosity ( ε ), and thickness ( δ ) of the FO membrane support layer and defines the mass transport length scale across it. S is expressed as follows [ 39 ] : Regardless of the operating conditions, using the appropriate models can predict the performances of FO membranes through three parameters. [ 38 ]…”

“…The support layer (SL) is also responsible for the internal concentration polarization (ICP) which is considered as the main cause of water flux decline. [ 13,39,55,56 ] ICP, as characterized through the S parameter, is caused by dilution of the DS. [ 13,47 ] This results in a decreased osmotic pressure of the DS near the AL‐SL interface.…”

Theoretical Model for the Prediction of Water Flux during the Concentration of an Olive Mill Wastewater Model Solution by Means of Forward Osmosis

“…On the other hand, more factors can influence the performance of the FO process, including membrane-specific factors (material, structure, surface area, and configuration), FS and DS characteristics, and operating parameters [ 12 ]. Therefore, as indicated by Singh et al [ 13 ], understanding the dynamics of solute and solvent transport through osmotic-driven membranes, although essential, remains an unsolved problem at this time.…”