Extended operation and control of biomass overgrowth in biofilters designed for VOC removal

Biofiltration systems have been applied in several industries for treatment of volatile organic compounds (VOCs); however, the systems are poorly understood and are generally implemented as `black boxes'. Common operational problems associated with biofilters include fouling, deactivation, and overgrowth, all of which make biofilters ineffective for continuous long-term use. The objective of this investigation was to develop generic methods for long-term stable operation, in particular by using selective limitation of supplemental nutrients while maintaining high activity and the ability to regenerate biofilter activity. Sustained degradation rates of approximately 50 g/h/m³ for isobutane and n-pentane in air (5000 ppm) were maintained in a trickle bed bioreactor for over 12 months using a nutrient-limited liquid recycle stream. After 5 to 6 months of operation, rates quickly declined to less than 10 g/h/m³, presumably due to extended supplemental nutrient depletion. At this time, the limiting nutrient was reintroduced into the liquid stream and previous removal rates were restored in less than two weeks. Furthermore, biological and transport fundamentals (kinetics and mass transfer) were successfully incorporated into a steady state mathematical model in order to successfully predict operating parameters and thus enable better design. Advances in these areas are particularly important for implementation and extended activity of biofilters in industrial settings and are directly relevant for high priority contaminants.