Abstract
Forward osmosis (FO) technology has increasingly attracted attention owing to its low operational energy and low fouling propensity. Despite extensive investigations on FO, very few module-scale FO studies on the operation and design of the FO process have been conducted. In this paper, a simple and practical FO process design parameter called normalized membrane area is suggested based on a performance analysis of spiral-wound FO elements. The influence of operation factors on operating pressures and water recovery was investigated using 8-inch spiral wound elements in the continuous operation mode. The membrane area was adjusted by series connection of FO elements to a maximum value of 46 m2 (three elements). The feed and draw flow rates were varied between 5 and 15 LPM under various feed (10, 20, and 30 g/L) and draw (58.4 and 233.8 g/L) concentration combinations. The analysis of flow rates (feed, draw, and permeate flow rates) indicated not only high flow channel resistance on the draw side but also high permeate flow rates can induce higher operating pressures owing to strong mutual interaction of the feed and the draw streams. Feed water recovery was focused on as a key performance index, and the experimental recovery (RExp) and theoretical maximum recovery (RTh) values were compared. The results revealed the significance of the feed flow rate and the membrane area in terms of enhancing the water recovery performance. In addition, a clear relationship was observed between the membrane area normalized by the initial feed flow rates and the water recovery ratio (RExp/RTh), even though the applied operation conditions were different. Finally, an empirical equation to estimate the required membrane area of spiral-wound FO was proposed for the FO process design. The equation can be used to predict water recovery of FO systems as well, for example, if an FO system is operated at 0.08 m2L−1h of the normalized membrane area, the system is expected to offer 78% of the RTh value.
Highlights
Energy consumption is an important criterion governing the selection of water treatment processes [1]
The results revealed the significance of the feed flow rate and the membrane area in terms of enhancing the water recovery performance
The present study aims to analyze the performance of spiral-wound (SW) forward osmosis (FO) elements for FO
Summary
Energy consumption is an important criterion governing the selection of water treatment processes [1]. FO membranes with greater selectivity, smoother active layers, and special porous support layers have been developed [23,24] These researches on FO have demonstrated that FO technologies require low amounts of energy, and the fouling problem is not as severe as that in the case of RO because of the low hydraulic operating pressures involved [25]. Most modeling-based module-scale studies did not consider the actual configuration of FO membrane elements and cannot estimate the operating pressures affected by interactions between the feed and draw streams. The present study aims to analyze the performance of spiral-wound (SW) FO elements for FO process design and identify critical operating parameters that affect operating pressures and water recovery.
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