For removing pollutants

Adsorption (qv) of gases has been reviewed (40,50) (see also Adsorption, gas separation). Adsorption, used alone or in combination with other removal methods, is excellent for removing pollutant gases to extremely low concentrations, eg, 1 ppmv. When used in combination, it is typically the final step. Adsorption, always exothermic, is even more attractive when very large gas volumes must be made almost pollutant free. Because granular adsorbent beds ate difficult to cool because of poor heat transfer, gas precooling is often practiced to minimize adsorption capacity loss toward the end of the bed. Pretreatment to remove or reduce adsorbable molecules, such as water, competing for adsorption sites should also be considered (41). 

The use of solvent extraction as a unit process operation is common in the pesticide industry however, it is not widely practised for removing pollutants from waste effluents. Solvent extraction is most effectively applied to segregated process streams as a roughing treatment for removing priority pollutants such as phenols, cyanide, and volatile aromatics [7]. One pesticide plant used a full-scale solvent extraction process for removing 2,4-D from pesticide process wastewaters. As a result, 2,4-D was reduced by 98.9%, from 6710 mg/L to 74.3 mg/L. 

Dry deposition can also be a very important mechanism for removing pollutants from the atmosphere in the absence of precipitation. Indeed, even in such places as eastern England, the ratio of dry to wet removal of S02 has been estimated to be 2 1 (Davies and Mitchell, 1983). If this is the case, then in arid and semiarid regions such as much of the western United States dry deposition is clearly important. 

Environmental treatments for removing pollutants include in situ degradation with microorganisms and enzymes, use of biofilters, and extraction and sorption of the pollutants. These and other techniques will be covered in this chapter, but for various reasons, the extraction of contaminants is of particular interest primarily because extraction requires no particular pretreatment of the chemical. Air can be injected into the soil around an aquifer and recovered in sorption towers for concentration and removal from the environment. 

Table 10.1 The aluminum demand and power consumption for removing pollutants from water...

Each technique for removing pollutants from process gas streams is economically feasible under certain conditions. Each specific instance must be carefully analyzed before a commitment is made to any type of approach. 

Testing and Evaluation of Permeable Materials for Removing Pollutants from Leachates at Remedial Action Sites... 

Environment New membranes that can selectively filter contaminants nanostructured traps for removing pollutants from industrial effluents, characterization of the effects of nanostructures in the environment... 

Electrostatic precipitation is a widely nsed process for removing polluting particles from gas streams, for example, in power station fines or in cement kilns. The effluent dust grains become charged as the gas flows between two electrodes, then deposit in a cake on the electrode snrface. This cake sticks to the electrode with a force that rises with the electric field bnt not simply proportional to the square of field strength as expected from the basic electrostatic equation for the cohesive stress a in a dielectric ... 

Trotta, F. and Tumiatti, W. 2003. Cross-linked polymers based on cyclodextrin for removing polluting agents. WO 03/085002. 

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