Desalination treatment systems

Figure 23.2 shows a schematic representation of a boiler feedwater treatment system. Raw water from a reservoir, river, lake, borehole or a seawater desalination plant is fed to the steam system. However, it needs to be treated before it can be used for steam generation. The treatment required depends both on the quality of the raw water and the requirements of the utility system. The principal problems with raw water are1,2 ... 

When a membrane-based desalination process is used, seawater is first collected and pumped to the water-treatment plant. Sodium hypochlorite is injected periodically after the intake pumps to prevent biological growth within the water-treatment system. Suspended solids are retained by sand filters or MF. The filtered water is then acidified. 

Several other potential applications of electrodialysis in wastewater treatment systems which have been studied on a laboratory scale are reported in the literature. In most of these applications the average plant capacity, however, is considerably lower than that in brackish water desalination or table salt production. 

The RO system design has been for optimum water production at 28 C, while still maintaining the capability for water production within the design specification of the RO membranes when operating at ambient seawater temperature. Based on the design inputs specified above, the desalination plant, consisting of a UF pre-treatment system and the RO desalination S tem has the following characteristics ... 

Figure 3.34 Lime pre-treatment system plus a RO membrane brackish water desalination plant process flow sheet. Source Cabibbo et al.

Since the 1990s, membrane-based separation processes integrated with traditional treatment systems have been successfully deployed in large desalination, wastewater and municipal water treatment plants [1-4]. More than a dozen large seawater RO (SWRO) plants with product water capacities greater than 200,000 m /day have been commissioned in the last decade. 

Research projects in sanitary engineering include seeking processes and equipment for improved purification efficiency. One example is the development of large, portable water-treatment systems that are suitable for providing clean water to survivors of natural disasters and the bivouac medical units that treat them. Another example is a nanofiltration system that desalinates ocean water for use on naval ships, especially during times of conflict, and extended private offshore operations such as oil drilling. A related nanofiltration system is necessary for oil-spill cleanup. A third example is the specialized absorbent removal of microcontaminants that may be present in small yet detrimental amounts. These may include elements such as arsenic and lead, industrial solvents, and radioactive particles. 

Water treatment systems have now come to include plastics, such as Du Pont s Permasep permeators for reverse osmosis (RO) water desalination, introduced in 1969 (see Figs. 12-5 and 12-6). Since that time such systems have been used in thousands of installations around the world for desalination of brackish water and seawater and to treat waste effluents. These permeators come in four product types, according to the type of water to be treated (see Table 12-1). 

Nogueira, R., Brito, A.G., Machado, A.P., et al., 2009. Economic and environmental assessment of small and decentralized wastewater treatment systems. Desalination Water Treatment 4,16-21. 

Kurihara, M., Matsiika, N., Fusaoka, Y., and Henmi, M. (2(X)3). Newly developed wastewater treatment systems using separation membranes. In Proceedings Water Reuse Desalination Conference, Suntec Singapore, Singapore, Feb. 25-27. 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

The two water desalination applications described above represent the majority of the market for electrodialysis separation systems. A small application exists in softening water, and recently a market has grown in the food industry to desalt whey and to remove tannic acid from wine and citric acid from fruit juice. A number of other applications exist in wastewater treatment, particularly regeneration of waste acids used in metal pickling operations and removal of heavy metals from electroplating rinse waters [11]. These applications rely on the ability of electrodialysis membranes to separate electrolytes from nonelectrolytes and to separate multivalent from univalent ions. 

An UF system utilizing hollow-fiber (FIF) membranes has been successfully used as pretreatment prior to seawater reverse osmosis (SWRO) desalination without any chemical treatments [8]. The quality of UF permeate was good and satisfied the need of SWRO feed water [8]. 

Integrated Membrane Processes for Water Desalination 266 Integrated Membrane Process for Wastewater Treatment 271 Integrated Membrane System for Fruit-Juices Industry 274 Integrated Membrane Processes in Chemical Production 276 Conclusions 281 References 281... 

Wastewater reclamation is a logical extension of desalination technology. Much of the membrane system design is common to both applications, and the membranes available for wastewater treatment are those originally developed for desalination. The first major project designed for... 

The progress made in membrane-based desalination has lead to the substitution of evaporation plants with RO systems in different part of the world. For example, the United States holds the second position in worldwide desalination capacity (15.2% of the world production) and the 78% of their production come from RO treatments. Mediterranean countries, including Spain, Malta, Cyprus, and Israel, have also reverted from traditional multistage flash (MSF) to RO during the past two decades. The water production by reverse osmosis desalination plants passed from 36% of the global desalting capacity in 1996 to 42%... 

J. C. Kruithof, J. C. Schippers, P. C. Kamp, H. C. Fohner, and J. A. M. H. Hofinan, Integrated multi-objective membrane systems for surface water treatment pretreatment of reverse osmosis by conventional treatment and ultrafiltration. Desalination 117, 37 8 (1998). 

---