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250 12. REVERSE OSMOSIS SYSTEM DESIGN AND PRETREATMENT
12.5.1.3
12.5.1.4
Adsorption of Organics by Activated Carbon Gentle Removal of Algal Biomass Form Source Water
274 274
274
12.5.2.2 Bacterial
Growth Control by
Reduction of
Oxygen 275
Creation of Favorable Hydrodynamic Conditions in the SWRO Membrane
Elements 276
276
12.5.2 Reduction of the Bacterial Content of Source Water
12.5.2.1 Bacterial Growth Control by Microbial
12.5.3
References
Oxidation and UV Inactivation 275
12.1 OVERVIEW OF TYPICAL SWRO DESALINATION SYSTEM
Fig. 12.1 depicts typical configuration of large SWRO system. Filtered water that is pro- duced by the desalination plant’s pretreatment system is conveyed by transfer pumps from a filtrate water storage tank through cartridge filters and into the suction pipe of the high- pressure RO feed pumps. As indicated in Chapter 5, the main purpose of the cartridge fil- ters is to protect the RO membranes from damage. Cartridge filters are typically used only for desalination plants with granular media filtration systems. Pretreatment systems employing MF or UF membranes typically do not have cartridge filters.
The high-pressure feed pumps are designed to deliver the pretreated water to the RO membranes at pressures required for membrane separation of the freshwater from the salts, which typically are 55e85 bars. The actual required feed pressure is site-specific and is mainly determined by the source water salinity, temperature, permeability of the selected SWRO membranes, and the configuration of the RO system.
The RO-membrane elements are installed in pressure vessels, which usually house 6e8 elements per vessel (see Fig. 12.2). Multiple pressure vessels are arranged on support struc- tures (racks), which form RO trains. Each RO train is typically designed to produce between 10% and 20% of the total amount of the membrane desalination product water flow. Fig. 12.1 depicts one RO train with its key componentsdfilter effluent transfer pump, cartridge filter, high-pressure pump, and membrane rack with vessels.
12.2 SWRO MEMBRANE ELEMENTSdKEY TYPES AND PRETREATMENT CONSIDERATIONS
The “engine” of every SWRO plant is the RO-membrane element. The two types of mate- rials used to manufacture SWRO membrane elements today are (1) polyamide, and (2) cellu- lose acetate and its derivatives. RO membranes made of polyamide are also referred to as