Reverse osmosis flow scheme

The cross-, co- and counter-flow schemes are illustrated in Figure 4.17, together with the concentration gradient across a median section of the membrane. It follows from Figure 4.17 that system performance can be improved by operating a module in an appropriate flow mode (generally counter-flow). However, such improvements require that the concentration at the membrane permeate surface equals the bulk concentration of the permeate at that point. This condition cannot be met with processes such as ultrafiltration or reverse osmosis in which the permeate is a liquid. In these processes, the selective side of the membrane faces the... 

Figure 5.22 Flow scheme showing the pretreatment steps in a typical seawater reverse osmosis system [50]...

A simplified flow scheme for a brackish water reverse osmosis plant is shown in Figure 5.24. In this example, it is assumed that the brackish water is heavily contaminated with suspended solids, so flocculation followed by a sand filter and a cartridge filter is used to remove particulates. The pH of the feed solution might be adjusted, followed by chlorination to sterilize the water to prevent bacterial growth on the membranes and addition of an anti-sealant to inhibit precipitation of multivalent salts on the membrane. Finally, if chlorine-sensitive interfacial composite membranes are used, sodium sulfite is added to remove excess chlorine before the water contacts the membrane. Generally, more pretreatment is required in plants using hollow fiber modules than in plants using spiral-wound modules. This is one reason why hollow fiber modules have been displaced by spiral-wound systems for most brackish water installations. 

Figure 5.27 Flow scheme showing the use of a reverse osmosis system to control nickel loss from rinse water produced in a countercurrent electroplating rinse tank...

Figure 32.11 shows a scheme of the RO plant for the treatment of the Cs-contaminated liquids. It was equipped with two kinds of spiral wound reverse osmosis membranes high-pressure (HP) and low-pressure (LP) membranes. Before flowing through the membranes, the feed was pretreated using 5 pm sleeve hlters and 0.45 pm cartridge hlters. 

The flow scheme of these facilities is very similar to the one of a conventional water supply facility which treats surface water (in spite of the very different use). It usually consists of a physicochemical treatment (to reduce pollution associated with the colloids that escape from the secondary clarifiers of the WWTF) and a disinfection unit (to remove pathogens and prevent health issues related to the wastewater reuse). The first treatment follows a four-stage scheme coagulation, flocculation, clarification, and filtration. Membrane technology (i.e., reverse osmosis or electrodialysis) is sometimes proposed... 

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