Evaluation of rate-limiting factors in a biofilter for treating ethylbenzene.

摘要

Biofiltration is an emerging and promising VOC control technology. Important advantages of biofiltration systems over other air-pollution-control technologies include low capital and operating costs, low energy requirements, and the absence of residuals and by-products requiring further treatment or disposal. This biofiltration study focused on gaining a better understanding of the inner environment and destruction mechanisms within a biofilter, more consistent and reliable system operation, and improvement of the elimination capacity of a biofilter. 5-Methyl-2-hexanone (MIAK) was used for the preliminary biofiltration study and ethylbenzene was used as the target air pollutant for the main biofiltration study.; With nine-month time-release fertilizer mixed with composting media, the biofilter was operated for 62 days above the target removal efficiency of 80 percent without any water addition. Initial mixing of the time release fertilizer could eliminate the supplementary efforts to add nutrients and water continually to the biofilter. With this method, the operational cost could be reduced significantly.; Ethylbenzene was not equally degraded over the depth of the biofilter. Instead, small portions of the biofilter were dominant in degrading ethylbenzene for a given time period. The change in the degradation rate was strongly correlated with the water content. The water was redistributed across the depth of the biofilter during each experiment. The optimum water content was at least 130 percent. Higher ethylbenzene degradation rates led to a temperature increase at the location of greatest degradation and microbial activity.; A thermodynamic model which incorporated Gibbs energy dissipation values for growth of various microorganisms on various organic substrates was developed. The thermodynamic model is specific for ethylbenzene but may be adapted to other compounds of concern by changing the physical properties associated with the selected compound. The equation for the heat release from the biodegradation process was an integral part of this model. With the equation, heat released from the biodegradation of substrates can be estimated. This thermodynamic model improves upon the currently available biofilter models making it possible to correlate water distribution and microbial activity and consequent removal efficiency with spatial location in the biofilter.