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12. REVERSE OSMOSIS SYSTEM DESIGN AND PRETREATMENT
FIGURE 12.4
Single-pass SWRO system.
FIGURE 12.5
Conventional full two-pass SWRO system.
12.4.1 Single-Pass SWRO Systems
Single-stage SWRO systems (Fig. 12.4) are designed to produce desalinated seawater (permeate) in one step using only a single set of RO trains operating in parallel. In general, between 800 and 900 SWRO-membrane elements installed in 100e150 vessels are needed to produce 10,000 m3/day (2.6 MGD) of permeate suitable for potable use in a single-stage SWRO system.
Under a typical single-stage SWRO-system configuration, each RO train has a dedicated sys- tem of transfer pump for pretreated seawater followed by a high-pressure RO feed pump. The high-pressure feed pump motor/operation is coupled with that of energy-recovery equipment.
Single-stage SWRO systems are widely used for production of drinking water. However, these systems have found limited industrial application mainly because of the water-quality limitations of the produced permeate. Even if using the highest-rejection RO-membrane ele- ments commercially available today (nominal minimum rejection of 99.85%), the single-stage
