Biological Processes for Waste Gas Treatment

The implementation and use of biological techniques for VOC removal at industrial scale is currently growing exponentially. The most commonly used biological waste-gas treatment techniques include bioreactor configurations such as the biotrickling filter, bioscrubber and biofilter. Though the mode of operation for all these configurations is very similar, they are distinguished by the behavior of the liquid-phase (continuously moving or stationary) and by the location of the microorganisms (freely dispersed or immobilized). However while choosing an appropriate treatment technique, focus is placed on the operational and control requirements needed to ensure an optimal chemical and physical environment for mass transfer and biodegradation of the pollutant in order to achieve high removal efficiencies (Kennes and Thalasso 1998; Waweru et al. 2000) . Moreover microorganisms require a steady supply of organic material as a carbon source and O2 as terminal electron acceptor for aerobic metabolism of the contaminant. Generally the pollutant is fed as the sole energy and carbon source to the microbes, where complete mineralization leads to the formation of CO2, H2O, biomass and some amount of heat. This is given by;

Micro organisms

Organic pollutant + O2 ® CO2 + H2O + Heat + Biomass

Innocuous End products (3 1)

(Substrate) (Electron acceptor) (Exothermicity) (Residue) )

Depending on the nature of the pollutant, other end products can also be produced. For example: during the biodegradation of dichloromethane, HCl may appear as one of the end-products. However this reaction (3.1) does not take place as simple as illustrated here, instead involves elaborate degradation pathways at controlled pH, temperature and other necessary conditions.

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