Module-scale simulation of forward osmosis module-part B: Modified Spiral-Wound

Abstract

Forward osmosis (FO) is an attractive technology that offers advantages especially for treatment of challenging feeds in comparison to other membrane technologies. Substantial developments of membrane material have been shown recently. To support further development of FO process, a larger scale study via membrane module development is required to accurately envisage the most critical factors to be exploited to realize the promises. In this study, we applied a mass-transfer model coupled with the mass conservation and area discretization to simulate the performance of modified spiral-wound (MSW) modules (10 sheets of 1x1m). The study focuses on the spatial flux profile in a full-scale module as function of operational mode: co- vs counter cross current and membrane orientations (active-layer facing feed (ALFS); solution and active layer facing draw solution, (ALDS)). Results show that all modes offer almost similar average flux of about 9-10 L/m2h, but the co-current flows have much higher flux ranges (≈43%). The latter is expected to worsen membrane fouling resistant due to mal distribution in hydraulic loading. An operation with counter current and ALFS and counter current flow is then recommended because it offer similar flux but lower spatial flux ranges (7%).

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

“…Both experimental and computational fluid dynamics, working at the module scale, demonstrated the need to improve the understanding of process limitations that could be affected both by channel design and pressure balance in FO modules [ 237 , 244 , 245 , 246 , 247 , 248 , 249 , 250 , 251 , 252 ]. Further studies are required with specific focus on the concentration process with regard to practical operation and limitations.…”

“…One recommendation is to operate FO in counter current mode to maintain a more constant osmotic pressure over the module(s) ( Figure 5 ; [ 224 ]). Such an approach of operating offers the double benefit of (i) avoiding elevated flux at the start of the concentration process, limiting the fouling propensity and (ii) to still maintain a flux at the end of the concentration process instead of having difficulties when reaching the osmotic equilibrium [ 248 , 249 ]. Phuntsho et al demonstrated that operating in counter-current allows for a higher average permeation flux and water extraction rate for the same filtration area [ 250 , 254 ].…”