Foam Emulsion Bioreactor

The mechanism of pollutant removal in a foam emulsion bioreactor (Fig. 3.15) is analogous to that of a two-liquid-phase reactor. The bioreactor consists of an emulsion of highly active pollutant degrading microorganisms and water-immiscible organic phase, which is made into foam by passing the waste-gas. The amount of organic phase is low and it uses a biocompatible surfactant for foam production (Shahna et al. 2010). There are only a few reports on foam-emulsion bioreactor for waste-gas treatment, and these results suggest that the foam-emulsion bioreactors could be an interesting alternative to conventional biological treatment systems, if high performance is desired (Kan and Deshusses 2003, 2005, 2006; Shahna et al. 2010). According to Kan and Deshusses (2005), the foam is continuously collapsed and the cells with the emulsion are reused after the desired level of biotreatment is achieved in the reactor. Besides, the foam-emulsion bioreactor gave high oxygen

Treated air

Foamed emulsion bed reactor

Treated air

Foamed emulsion bed reactor

Foam Emulsion Bioreactor

Reservoir for liquid collection/recycle

Polluted air

Fig. 3.15 Schematic of foam-emulsion bioreactor; the process relies on the emulsion of an organic phase with a suspension of an actively growing culture of pollutant-degrading microorganisms, made into a foam with the air undergoing treatment (Kan and Deshusses 2003)

Reservoir for liquid collection/recycle

Polluted air

Fig. 3.15 Schematic of foam-emulsion bioreactor; the process relies on the emulsion of an organic phase with a suspension of an actively growing culture of pollutant-degrading microorganisms, made into a foam with the air undergoing treatment (Kan and Deshusses 2003)

and pollutant mass transfer rates due to the large interfacial area between gas and liquid of the fine foam, and a high partitioning of pollutants into the organic phase.

For stable operation of the foam-emulsion bioreactor, foam stability, and cell activity are of prime importance. Besides, replacing and replenishing part of the culture would also be required to maintain high biodegradation activity and high pollutant removal in this reactor configuration. During short-term experiments (2-8 h), for gas-phase toluene removal, the foam-emulsion bioreactor reached an EC of 280 g/m3.h, with 95% RE, at a gas residence time of 15 s, and still higher EC was reported (408 g/m3.h) with 77% RE, when pure oxygen was added to the inlet air stream (Kan and Deshusses 2003). However, during long-term operations, the RE ranged from 89% to 94%, with EC value <226 g/m3.h. For long-term bioreactor stability, it has been suggested to operate the bioreactor by replacing 20% of the culture with a concentrated nutrient solution, so as to maintain optimal cell growth, activity and to avoid nutrient limitations.

Continue reading here: Other Novel Bioreactor Configurationsfor Volatile Organic Compound Treatment

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