Abstract
We compared two representative forward osmosis (FO) modules—spiral-wound (SW) and plate-and-frame (PF)—to provide practical information for the selection of FO element for a large-scale FO process. The FO operating performance of commercially available SW FO and PF FO was explored under different membrane area and flow rate conditions. The performance trend as a function of the membrane was obtained by adjusting the number of serially connected elements. Although SW FO and PF FO elements exhibited comparable feed pressure drops, SW FO demonstrated a significantly higher draw channel pressure drop than PF FO. Furthermore, the significant draw pressure drop in SW FO increased the draw inlet pressure, consequently limiting the number of serially connected elements. For example, the maximum number of serially connected elements for the normal operation was three elements for SW FO (45.9 m2) but nine elements for PF FO (63 m2) when the flow rate of 10 LMP was applied for feed and draw streams. Additionally, a footprint analysis indicated that SW FO module exhibited a slightly larger footprint than PF FO. Under investigated conditions, PF FO exhibited relatively better performance than SW FO. Therefore, this pilot-scale FO study highlighted the need to reduce the flow resistance of SW FO draw channel to take advantage of the high packing density of the SW element.
Highlights
In the past decade, forward osmosis (FO) technology has gained much attention for various applications, such as desalination, wastewater reclamation, food concentration, and microalgae dewatering [1,2,3]
The footprint normalized by the membrane area ranged from 0.0099–0.0083, 0.0097–0.0065, and 0.0077–0.0067 m2/m2 for the SW FO module with one element, three elements, and PF FO module, respectively
The membrane area per element for SW FO and PF FO was different, the direct performance comparison was possible using the pronounced performance trends as a function of membrane area by controlling the number of elements connected in series
Summary
Forward osmosis (FO) technology has gained much attention for various applications, such as desalination, wastewater reclamation, food concentration, and microalgae dewatering [1,2,3]. The main merit of the FO technology is that it utilizes osmotic pressure as the driving force for water transport; the FO process needs lower energy than the pressure-driven membrane process, i.e., reverse osmosis (RO). To commercialize the FO process, there remain challenges, including the development of readily and completely separable draw solutes and improvement of high-performance FO membranes [4,5]. The osmotic pressure difference across a membrane mainly determines the water transport from a diluted solution (i.e., feed solution (FS)) to a concentrated solution (i.e., draw solution (DS)). To utilize the full osmotic pressure difference potential energy and obtain high membrane flux, the membrane should have intrinsic characteristics of high water permeability (A), low solute permeability (B), and low membrane structural parameter (S) [6].
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