Microbial Removal of Alkanes from Dilute Gaseous Waste Streams: Kinetics and Mass Transfer Considerations

Abstract

Treatment of dilute gaseous hydrocarbon waste streams remains a current need for many industries, particularly as increasingly stringent environmental regulations and oversight force emission reduction. Biofiltration systems hold promise for providing low-cost alternatives to more traditional, energy-intensive treatment methods such as incineration and adsorption. Elucidation of engineering principles governing the behavior of such systems, including mass transfer limitations, will broaden their applicability. Our processes exploit a microbial consortium to treat a mixture of 0.5% n-pentane and 0.5% isobutane in air. Since hydrocarbon gases are sparingly soluble in water, good mixing and high surface area between the gas and liquid phases are essential for biodegradation to be effective. One liquid-continuous columnar bioreactor was operated for more than 30 months with continued degradation of n-pentane and isobutane as sole carbon and energy sources. The maximum degradation rate observed in this gas-recycle system was 2 g of volatile organic compounds (VOC)/(m3.h). A trickle-bed bioreactor was operated continuously for over 24 months to provide a higher surface area (using a structured packing) with increased rates. Degradation rates consistently achieved were approximately 50 g of VOC/(m3.h) via single pass in this gas-continuous columnar system. Effective mass transfer coefficients comparable to literature values were also measured for this reactor; these values were substantially higher than those found in the gas-recycle reactor. Control of biomass levels was implemented by limiting the level of available nitrogen in the recirculating aqueous media, enabling long-term stability of reactor performance.

A model for treating polluted air streams in a continuous two liquid phase stirred tank bioreactor

“…The operational data (volume of the phases, mass transfer coefficients and biokinetic parameters) are not from any specific operations and have been chosen arbitrarily. It should be noted that these data are in the range of the data that have been reported in the literatures [10][11][12][13][14][15][16]. In all simulation cases presented here, it is assumed that the pollutant and oxygen concentrations in the organic phase do not change along the recycle path (so the first term in 4 and 8 can be deleted).…”

Influence of high biomass concentrations on alkane solubilities

“…The consortium was grown at 30°C using carbon-free mineral medium in the recycle stream with humidified, dilute isobutane and n-pentane gas/air streams serving as the sole carbon and energy source. Further information on these specific bioreactors can be found in Barton et al (1997Barton et al ( , 1998Barton et al ( , 1999). …”

“…Two principal factors relating to improved efficiency in bioremediation filters are kinetics and mass transfer. Several recent studies have been conducted to improve biofilter kinetics, without resulting in consortial overgrowth, through nutrient limitation in the filter's feedstreams (Barton et al, 1997(Barton et al, , 1998(Barton et al, , 1999Hekmat et al, 1997;Rihn et al, 1997;Sorial et al, 1997). A predictive model was also developed for trickle-bed biofilters operating under such conditions (Barton et al, 1998).…”

Biofiltration of gasoline and diesel aliphatic hydrocarbons

“…Yet only a few papers on the biofiltration of gasoline and other diverse hydrocarbon mixtures are available (Leson and Smith, 1997;Barton et al, 1997;Wright et al, 1997;Morales et al, 1998;Namkoong and Park, 2003;Namkoong and Park, 2004;Paca et al, 2007). Even fewer studies have tackled the interactions of aliphatic and more biodegradable aromatic compounds in their mixtures (Schindler and Friedl, 1995;Holubar et al, 1999;Lu et al, 2001;Kim, 2003;Hassan and Sorial, 2010;Halecky et al, 2012).…”