Pollutants decontamination reduction

Table 21.2 Hypothetic example of decontamination reduction of various pollutants...

S02 and NOx in flue gas from coal combustion contribute to smog and acid rain. Methods to remove these pollutants include alkaline wet scrubber systems that fix S02 to solid CaS04, and selective catalytic reduction by metal/metal oxide systems of NO/NOz to N2 and steam in the presence of ammonia. Particulate active carbons have also been used in flue gas decontamination, especially as they avoid costly scrubber processes and can operate at lower temperatures. The potential of active carbon fibers in this application has been explored by a... 

Electroremediation using electrical current is the final purification method discussed in this chapter. Here, an array of anodes are placed in the soil opposite an array of cathodes. When electric potential is apphed the following processes occur electrolysis of water in the soil, dissolution of polluting ions, migration of ions under the influence of the apphed potential field, and reduction or pH based precipitation at the cathode [68,69]. This technique, also known as electroreclamation or electrochemical soil decontamination, does not require a membrane however, improved electroremediation has been reported when ion-exchange membranes were incorporated into the system [70]. The function of the membrane is to retain OH ions produced at the cathode. Migration of these OH ions is prevented to avoid precipitation of the heavy metal ions in the sod. 

The cost of the added contaminant is important in this regard, which in this case was charcoal. For the reductions illustrated in example given, the cost at 5 g/L is about 1.31/m. To achieve removal concentration reductions of 98% or greater of the listed pollutants, the added charcoal required would be 20 g/L, and thus 5.23/ m. Although such costs are far from trivial, the entire process of decontamination is critically important and can be the controlling issue as far as the success of a project is concerned. 

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