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E nergy is needed in various stages of desalination. Energy consumption directly affects the cost-effectiveness and feasibility of using desalination technologies for drinking water production. This chapter presents energy types, use, methods of conservation, and the potential use of renewable energy resources for desalination. Some of the information provided in this chapter may not be applicable to today's desalination energy issues. However, the information provides a comparison between costs associated with various energy sources as applied to desalination worldwide, and can be used as a reference for future energy development and use for desalination. Energy Needs and ConsumptionEnergy is needed in various stages of desalination. Desalination technologies use pumps in various stages of desalination, i.e., feedwater intake, treatment process, and discharge of product water and concentrate. Pumps consume a significant amount of energy. RO plants use pumps to pressurize feedwater passing through the membranes. Ion exchange plants use pumps to pass the feedwater over the resin, and use backwash pumps to clean and recharge resin beads. In electrodialysis, pumps pressurize feedwater to generate flow across the surface of the membranes. The amount of energy pumps consume depends on the type of process, the TDS concentration in the feedwater, the capacity of the treatment plant, the temperature of the feedwater, and the location of the plant with respect to the location of the intake water and concentrate disposal site.Each desalination technology is unique in design and mode of operation and it is rather difficult to compare energy consumption for different types of desalination technologies. Table 1 is a generalization of typical energy consumption for various technologies.The energy consumption for reverse osmosis plants depends on the salinity of the feedwater and the recovery rate. Seawater reverse osmosis plants require higher amounts of energy due to the higher osmotic pressure of seawater compared to brackish water reverse osmosis plants. The osmotic pressure is related to the TDS concentration of the feedwater. Electrodialysis plants use electric energy to desalt the water. For electrodialysis, the energy required is directly related to the TDS concentration in the water. Electrodialysis is economical only for brackish waters (TDS < 4000 mg/L). Energy Conservation and RecoveryA system's ability to conserve or recover energy is critical for implementing an economical desalination technology. The section below describes various energy conservation and recovery techniques. Methods of Energy ConservationPelton impulse turbines (PIT) and hydraulic turbochargers (HTC) are the most widely used devices for energy conservation in desalination plants (Manth et al. 2003). Reverse running pumps may be found in older facilities, but these pumps are least effective for energy conservation. Figure 1 shows the integration of a PIT with a reverse osmosis plant. Normally, the motor uses electric energy to drive the feed pum...

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