Seawater desalination integration

FIGURE 43.1 Integrated membrane system proposed for seawater desalination. (Adapted from Drioli, E., Curcio, E., Criscuoli, A., and Di Profio, G., J. Membr. Sci., 239, 27, 2004.)... 

F. Macedonio, E. Curcio, E. Drioli, Integrated membrane systems for seawater desalination Energetic and exergetic analysis, economic evaluation, experimental study. Desalination 2007, 203, 260-276. 

E. Drioli, A. Criscuoli and E. Curcioa, Integrated membrane operations for seawater desalination, Desalination, 147 (2002) 77-81. 

D.L. Shaffer, N.Y. Yip, J. Gilron, M. Elimelech, Seawater desalination for agriculture by integrated forward and reverse osmosis improved product water quality for potentially less energy, J. Memb. Sci. 415-416 (2012) 1-8. 

Figure 5.4 Process flow diagram and mass balance of a RO-EDR integrated desalination plant. Seawater desalination by ED is rare - used in Japan to recover sea salt.

Integrated membrane process for seawater desalination. MF = microfiltration UF = ultrafiltration NF = nanofiltration MC = membrane contactor RO = reverse osmosis MD = membrane distillation. 

The flow sheet of an ideal integrated process for seawater desalination is depicted in Fig. 7.2. 

El-Zanati and El-Khatib (2007) suggested an IMS consisting of a NF unit as pre-treatment section of an RO unit, while MD was used as a system to concentrate the two brine streams from both NF and RO. The integration of these systems improved the performance of the seawater desalination unit, leading to a water recovery factor of 76.2%. The water production cost was estimated at around 0.92 m. This cost was considered competitive in comparison with those of potable water produced in a RO system for seawater treatment. 

Economic assessment study has been carried out for co-production of electricity and potable water [1-6]. The desalination economic evaluation program (DEEP) was used to evaluate the economics of desalination [1-7]. A 330 MW(th) integral reactor, SMART, has been taken as a nuclear energy option for seawater desalination. 

This issue is very significant for pretreatment systems for seawater desalination plants with open-ocean intakes. Often the source seawater contains small sharp objects (such as shell particles), which can easily puncture the pretreatment membranes and result in a very quick loss of their integrity, unless the damaging particles are removed upstream of the membrane pretreatment system. As discussed previously, to remove sharp seawater particles that can damage the membranes from the source water, the SWRO plant intake system has to incorporate a microscreening system that can remove particles larger than 120 p,m. 

Integration of brackish and seawater desalination systems. In many places brackish water can be found close to the sea. Integrating the two types of desalination may reduce the cost of the final product. 

Figure 7.1 shows the two major treatment options to obtain RO-quality water from sewage and seawater. The key in water reclamation is to first treat the sewage biologically and use MF/UF membrane filtration to remove suspended solids. Two membrane filtration alternatives are available for water reclamation tertiary filtration (TF) of the effluent from a conventional activated sludge (CAS) process and an integrated membrane bioreactor (MBR). For seawater desalination, pretreatment must be provided if the source is open seawater. The current practice involves multimedia filtration, but membrane filtration has also been considered. 

RO is the most relevant membrane-based technique for seawater desalination [98]. Similar to NF, RO is carried out using asymmetric membranes with a nonporous skin layer. Membranes can be integrally skinned or TFC. The most important technique for the preparation of such membranes is IP, which has been already described in Section 1.6.3 devoted to NF membranes. As reported by Lee et al. [99], the studies about the preparation of polymeric membranes for RO application, from 1950 to 1980, focused on the search for optimum membrane materials. Subsequently, the performance of RO membranes was improved by controlling membrane formation reactions and using catalysts and additives. 

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