Miniaturized Biotrickling Filters and Capillary Microbioreactors for Process Intensification of VOC Treatment with Intended Application to Indoor Air

Abstract

Typical biofilters and biotrickling filters used for volatile organic compounds (VOCs) control have treatment rates limited to 30-200 g m^-3 h^-1, mostly because they are exposed to dilute VOC streams, have moderate biomass density and activity, and moderate mass transfer coefficients. For these reasons and the concern over releasing bioaerosols and humidity, traditional biofilters and biotrickling filters are not ideal for the treatment of indoor air. Here we report on the development and evaluation of microbioreactors for the intensive treatment of VOCs that could be used for indoor air quality control, when coupled with a VOC microconcentrator (developed separately). The microconcentrator will function to adsorb VOCs from indoor air and release them to the microbioreactor at a higher concentration. The miniaturized bioreactors, with maximized surface area-to-volume ratios, allow for increased mixing and mass transfer of pollutants to the biofilm, resulting in a greater degradation rate of the VOCs. Three different microbioreactors were designed, constructed and their performance for removing vapors of toluene and methanol was assessed. Results showed that they were able to achieve maximum elimination capacities (ECs) for methanol around 1000 g m^-3 h^-1, 780 g m^-3 h^-1, and 12 600 g m^-3 h^-1 for the glass beads packed bed, polyurethane (PU) foam biotrickling filters and capillary microbioreactor, respectively, and around 120 g m^-3 h^-1, 250 g m^-3 h^-1 and 3050 g m^-3 h^-1, respectively, when treating toluene vapors. These values, especially for the capillary microbioreactor, are 40-80 times greater than the rates generally obtained in conventional biofilters and biotrickling filters. The interphase mass transfer coefficient (K_La) was determined. The capillary microbioreactor had values 13-17 times greater than the other two bioreactors, suggesting that improved mass transfer could have contributed to the very high performance observed in the capillary microbioreactor. The results demonstrate that microbioreactors are promising novel technologies for controlling small amounts of organic pollutants.