Treatment of VOC Mixture in a Trickling-bed Air Biofilter Integrated with Cyclic Adsorption/Desorption Beds

摘要

Biofiltration has emerged as a reliable and cost-effective technology for the control of volatile organic compounds (VOCs) emissions. However, fluctuations in concentration and variation in the waste air composition is commonly encountered in the chemical industry, which challenges the application of biofiltration technology. An integrated technology by coupling cyclic adsorption/desorption beds with a trickling-bed air biofilter was proposed and studied for contaminated air with single solute in our previous studies. The integrated system was found to be able to reduce concentration fluctuation and maintain long-term high removal efficiency. However, many industrial air emissions contain mixtures of VOCs that possess various physical and chemical properties affecting their biological treatment. Therefore, this study expands the application of the integrated technology to VOC mixture. Toluene, styrene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) were selected as the target VOCs in the mixture. The content for the four VOCs in the mixture is based on point source air emission in EPA 2003 toxic release report for chemical industries with the ratio of 0.448: 0.260: 0.234: 0.058 for toluene: styrene: MEK: MIBK, respectively. To compare the performance of the integrated system, the air stream was divided equally into two sub-air streams. One steam passed the 2-bed cyclic adsorption/desorption unit followed by Biofilter "A", and the other stream passed directly through the control system- a stand alone biofilter (Biofilter "B"). Square wave influent concentrations were employed on the integrated and control systems as fluctuating conditions. Backwashing once a week with duration of one hour was employed as the biomass control for both systems. Biofilter "A" maintained long-term 99% removal efficiency due to the effective dampening effect of the 2-bed cyclic adsorption/desorption unit. However, performance for Biofilter "B"fluctuated in removal performance according to the fluctuations in the feed.