Water pollution desalination

Thanuttamavong M., K. Yamamoto, J.I. Oh, K.H. Choo, and S.J. Choi (2002). Rejection characteristics of organic and inorganic pollutants by ultra low-pressure nanoliltration of surface water for drinking water treatment. Desalination 145 257-264. 

Many of the scientific aspects of water resources are described in several entries in this encyclopedia. See also Connate Water Desalination Groundwater and Water Pollution. 

Osmosis has other important uses. In some parts of the world, potable water is a precious commodity. It can be obtained much more economically by desalinizing brackish waters, through a process called reverse osmosis, than by distillation. When an ionic solution in contact with a semipermeable membrane has a pressure applied to it that exceeds its osmotic pressure, water of quite high purity passes through. Reverse osmosis is also used to control water pollution. 

R.O. systems utilizing externally wound tubular membrane element in modular assemblies have been used in the desalination of brackish and sea waters, the treatment and/or concentration of industrial waste waters, the separation/concentration of fluid food, pharmaceuticals and chemical solutions, and the manufacture of water purifiers for domestic use. Generally, externally wound tubular membrane systems have been found to be highly suitable for ultrafiltration applications in the processing Industry and in water pollution control applications. 

Bajza, Z. et al. (2004) Influence of different concentrations of 2(804)3 and anionic polyelectrolytes on tannery wastewater flocculation. Desalination, 171(1), 13-20. SBN 0011-9164. Cooper, D.R. et al. (1984) The treatment of waste water from the leather industry. Water Pollution Control, Southern African Branch, Biennial Conference, pp. 450-454. 

Other plant-scale applications to pollution control include the flotation of suspended sewage particles by depressurizing so as to release dissolved air [Jenkins, Scherfig, and Eckhoff, Applications of Adsorptive Bubble Separation Techniques to Wastewater Treatment, in Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972, chap. 14 and Richter, Internat. Chem. Eng, 16,614 (1976)]. Dissolved-air flotation is also employed in treating waste-water from pulp and paper mills [Coertze, Prog. Water TechnoL, 10, 449(1978) and Severeid, TAPPl 62(2), 61, 1979]. In addition, there is the flotation, with electrolytically released bubbles [Chambers and Cottrell, Chem. Eng, 83(16), 95 (1976)], of oily iron dust [Ellwood, Chem. Eng, 75(16), 82 (1968)] and of a variety of wastes from surface-treatment processes at the maintenance and overhaul base of an airline [Roth and Ferguson, Desalination, 23, 49 (1977)]. 

Concentrate can be harmful to the environment due to either its higher than normal salinity, or due to pollutants that otherwise would not be present in the receiving body of water. These include chlorine and other biocides, heavy metals, antisealants, coagulants and cleaning chemicals. Of particular concern is the effect of pollutants on delicate ecosystems and endangered or threatened species. However, with appropriate measures in place, the discharge of concentrate to surface water can remain a viable method for seawater desalination plants. 

One can also recognize that application of sufficient pressure (above the equilibrium osmotic pressure n) to the right-hand chamber in (7.67) must cause the solvent flow to reverse, resulting in extrusion of pure solvent from solution. This is the phenomenon of reverse osmosis, an important industrial process for water desalination. Reverse osmosis is also used for other purification processes, such as removal of H20 from ethanol beyond the azeotropic limit of distillation (Section 7.3.4). Reverse osmosis also finds numerous applications in wastewater treatment, solvent recovery, and pollution control processes. 

Approximately one-half of the reverse osmosis systems currently installed are desalinating brackish or seawater. Another 40 % are producing ultrapure water for the electronics, pharmaceutical, and power generation industries. The remainder are used in small niche applications such as pollution control and food processing. A review of reverse osmosis applications has been done by Williams et al. [52],... 

The term desalination has lately started to include diverse treatments to purify different water sources, from slightly polluted water, through wastewater and... 

In principle, two solutions can be adopted by water agencies facing long-tem salinization of water resources—dilution and desalination. Dilution is the cheapest solution for pollution. 

Grimm J, Bessarabov D, Maier W, Storck S, and Sanderson RD. Sol-gel film-preparation of novel electrodes for the electrocatalytic oxidation of organic pollutants in water. Desalination 1998 115(Suppl. 8) 295-302. 

Reverse osmosis is used as a method of desalting seawater, recovering wastewater from paper mill operations, pollution control, industrial water treatment, chemical separations, and food processing. This method involves application of pressure to the surface of a saline solution, thus forcing pure water to pass from the solution through a membrane that is too dense to permit passage of sodium and chlorine ions. Hollow fibers of cellulose acetate or nylon are used as membranes, since their large surface area offers more efficient separation. See dialysis membrane diffusion desalination. 

Reverse osmosis, although originally developed for water desalination ( ), has been applied to numerous pollution control and concentration problems, including industrial (2 and municipal O) wastewaters, pulp and paper waste streams ( ), food processing liquids ( 5), and dairy wastes ( ). 

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