Pollution control, reverse

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

An industrial organization must decide whether to charge off air pollution control costs as a corporate charge, so that the plant manager does not include them in the accounts or the reverse, so that the plant manager must show a profit for the plant as a cost center, after including costs of air pollution control. 

Leith and First [J. Air Pollut. Control Assoc., 27, 534 (1977) 27, 754 (1977)] studied the collection efficiency of reverse-pulse filters and concluded that once the dust cake has been established, straight-through penetration by dust particles that pass through the filter without being stopped is negligible by comparison with penetration by dust... 

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. 

Reverse osmosis is nsed 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. 

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],... 

In principle, pollution control should be a major application for reverse osmosis. In practice, membrane fouling, causing low plant reliability, has inhibited its widespread use in this area. The most common applications are special situations... 

Process Descriptions Selectively permeable membranes have an increasingly wide range of uses and configurations as the need for more advanced pollution control systems are required. There are four major types of membrane systems (1) pervaporation (2) reverse osmosis (RO) (3) gas absorption and (4) gas adsorption. Only membrane pervaporation is currently commercialized. 

Three different membrane processes, ultrafiltration, reverse osmosis, and electrodialysis are receiving increased interest in pollution-control applications as end-of-pipe treatment and for inplant recovery systems. There is no sharp distinction between ultrafiltration and reverse osmosis. In the former, the separation is based primarily on the size of the solute molecule which, depending upon the particular membrane porosity, can range from about 2 to 10,000 millimicrons. In the reverse-osmosis process, the size of the solute molecule is not the sole basis for the degree of removal, since other characteristics of the... 

T. Matsuura and S. Sourirajan, Studies on reverse osmosis for water pollution control. Water Research 6, 1073-1086 (1972). 

Reverse Osmosis Studied for Sewage Treatment, Water Pollut. Control, 112(4), 15, April (1974). 

TA. Krug and K.R. Attard, Treating oily waste water with reverse osmosis. Water Pollut. Control, 128(5), 16-18, Oct. (1990). 

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 ( ). 

McKee s compendium was published by the state board in 1952. Entitled Water Quality Criteria, it was deeply infused with the policy that the chemical industry had advocated since the 30s and California had enacted in the Dickey Act—to promote waste disposal as a beneficial use of public waters. The deterioration of water quality, McKee later wrote, was a trend that cannot be stopped or reversed... unless the industrial and agricultural development of this Nation is to be curtailed. 25 Water Quality Criteria, and through it the philosophy of the Dickey Act, came to influence water pollution control practice far beyond California s borders. Yet this publication owed its official imprimatur and the influence that flowed from it not to its scientific merits but to a political decision of the California legislature. 

Clearly-defined Objectives. In the case of the EC-WFD, the objectives set down for groundwater quality monitoring are very clear, and require monitoring networks variously sufficient to a) assess the overall chemical status of groundwater bodies, b) evaluate long-term trends in contaminant concentrations and c) determine the effectiveness of pollution control measures (and provide evidence of contaminant trend reversal ). 

The nickel plating industry is a typical candidate for the use of reverse osmosis in pollution control. Figure 4.17 shows a schematic of this industrial application. The workpiece travels from the plating bath with a concentration of 270,000 mg/E to the rinse tanks. There are three rinse tanks in series and rinse water flows countercurrent to the workpiece. The work piece drags out plating bath to the first rinse tank, first rinse tank solution to the second rinse tank and second rinse tank solution to the third rinse tank. Consequently, the first, second and third rinse tanks have concentrations of 3,000 mg/E, 333 mg/E and 37 mg/) , respectively. 

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