Estimation of mass transfer and kinetics in operating trickle-bed bioreactors for removal of VOCs

Long-term, stable operation of trickle-bed bioreactors remains desirable but is difficult to achieve for industrial processes, which generate continuous streams of dilute gaseous hydrocarbons. Mass transfer and kinetics parameters are difficult to measure, complicating predictive estimates. Two methods are presented which were used to predict the importance of mass transfer versus kinetics limitations in operating trickle-bed biofilters. Both methods altered the overall activity of the biofilter and estimated the effective mass transfer coefficient (K_La) by varying the VOC (volatile organic contaminant) loading rate and concentration. The first method altered the total bed temperature of a well-established biofilter to effect a change. The second method, used with developing biofilters possessing low biomass, involved addition of cultured biomass to the recirculating liquid to effect an overall change in VOC removal capacity. Results and modeling from these experiments are presented for a mixed culture trickle-bed bioreactor that is capable of consuming sparingly soluble alkanes, such as pentane and isobutane. Methods to control overgrowth are discussed which were used to operate one reactor continuously for over 24 months with sustained degradation of volatile alkanes with a rate of 50 g h-1 m-3.