| Biofiltration is fast becoming an established air Pollution control technology for the removal of volatile organic chemicals (VOCs) from waste gas streams. However, the acceptance of this technology in the United States is still uncertain due to the lack of fundamental information. In this study, four trickle-bed biofilters with pelletized media were operated for six years to investigate biofiltration fundamentals under highly controlled conditions. This involved the study of the effects of some major operating parameters, interfacial mass transfer phenomena and biomass dynamics.; The results demonstrated that trickle-bed biofilters were highly effective in treating biodegradable VOCs in gas streams. Major operating parameters that affect biofiltration were identified, which include organic loading, retention time, liquid flow rate, nitrate, backwash strategy and air flow direction.; The non-saturated biofilm structure in a gas phase biofilter was found to play an important role in biofilter performance. As a result, the mass transfer limitation for substrates in the liquid phase is more substantial than that for substrates in the gas phase. Microscopic observations showed that a layered structure with void spaces existed within the biofilm. High oxygen penetration and high dissolved oxygen zones were found inside the biofilm using microelectrode technology. This substantial penetration of oxygen within the biofilm in gas phase trickle-bed biofilters can be attributed to both the low gas-liquid mass transfer resistance and the internal biofilm structure.; A study on the effect of Henry's constant indicated that the VOC removal efficiency generally increases with the decrease of substrate's Henry's constant. However, oxygen transfer may become a rate-limiting step in removing VOCs with low Henry's constants. A theoretical analysis was conducted using a mathematical model, which led to a better understanding of the experimental results and the effect of Henry's constant in general.; Major factors affecting biomass growth and biomass distributions along the biofilters were identified in this study. Two biomass control strategies, periodical biomass removal through backwashing and phosphorus limitation, were investigated. Periodic backwashing was proven to be an effective strategy to maintain a long-term stable operation. |
