MICROBIAL REMOVAL OF ALKANES FROM DILUTE GASEOUS WASTE STREAMS - KINETICS AND MASS-TRANSFER CONSIDERATIONS

Treatment of dilute gaseous hydrocarbon waste streams remains a curren t need for many industries, particularly as increasingly stringent env ironmental regulations and oversight force emission reduction. Biofilt ration systems hold promise for providing low-cost alternatives to mor e traditional, energy-intensive treatment methods such as incineration and adsorption. Elucidation of engineering principles governing the b ehavior of such systems, including mass transfer limitations, will bro aden 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 hig h surface area between the gas and liquid phases are essential for bio degradation 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 d egradation rate observed in this gas-recycle system was 2 g of volatil e organic compounds (VOC)/m(3).h). A trickle-bed bioreactor was operat ed continuously for over 24 months to provide a higher surface area (u sing a structured packing) with increased rates. Degradation rates con sistently achieved were approximately 50 g of VOC/(m(3).h) via single pass in this gas-continuous columnar system. Effective mass transfer c oefficients comparable to Literature values were also measured for thi s 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.