CHARACTERIZATION OF A COMPOST BIOFILTRATION SYSTEM DEGRADING DICHLOROMETHANE

The effects of acclimatization of microbial populations, compound conc entration, and media pH on the biodegradation of low concentration dic hloromethane emissions in biofiltration systems was evaluated. Greater than 98% removal efficiency was achieved for dichloromethane at super ficial velocities from 1 to 1.5 m(3)/ m(2).min (reactor residence time s of 1 and 0.7 min, respectively) and inlet concentrations of 3 and 50 ppm(v). Although acclimatization of microbial populations to toluene occurred within 2 weeks of operation start-up, initial dichloromethane acclimatization took place over a period of 10 weeks. This period was shortened to 10 days when a laboratory grown consortium of dichlorome thane degrading organisms, isolated from a previously acclimatized col umn, was introduced into fresh biofilter media. The mixed culture cons isted of 12 members, which together were able to degrade dichlorometha ne at concentrations up to 500 mg/L. Only one member of the consortium was able to degrade dichloromethane in pure culture, and the presence of the other members did not affect the rate of biodegradation in sol ution culture. Although high removal efficiencies for dichloromethane were sustained for more than 4 months in a biofilter column receiving an inlet gas stream with 3 ppm(v) of dichloromethane, acidification of the column and resulting decline in performance occurred when a 50-pp m(v) inlet concentration was used. A biofilm model incorporating first order biodegradation kinetics provided a good fit to observed concent ration profiles, and may prove to be a useful tool for designing biofi ltration systems for low concentration VOC emissions. (C) 1994 John Wi ley & Sons, Inc.