Biological Waste Gas Treatments
Profit and protection are two fundamental reasons to clean up waste gas streams. According to the nature of the contaminants and/or the complex mixture of pollutants in the gaseous phase, their concentrations and the flow to be cleaned, removing non-particulate pollutants from a gas stream is achieved by different processes classified into three categories: (i) thermal and/or catalytic oxidation, biological transformation; (ii) transfer into a liquid phase (absorption) or onto a solid phase (adsorption); and (iii) phase change (condensation). Bioprocesses, a relatively recent technology, appear to be a competitive way to treat the waste gas stream before its discharge to the atmosphere. The optimal range of pollutant concentration goes from a very diluted pollutant present in the gas stream (from some μg to mg m−3) to above 1 g m−3. The installation designs cater for an air flow from a few m3 h−1 to more than 100 000 m3 h−1. This chapter describes general approaches for bioreactors used in waste gas stream treatment and more specifically the different biosystems such as biofilters, biological trickling beds and bioscrubbers. The general presentation, operating conditions, yields and industrial applications of these bioprocesses are discussed.