Performance and Microbial Diversity of a Trickle-Bed Air Biofilter under Interchanging Contaminants By Z. Cai, D. Kim, G. A. Sorial*, P. Saikaly , M. M. Zein, and D. B. Oerther DOI: 10.1002/elsc.200620111 A trickle-bed air biofilter (TBAB) was evaluated under conditions of interchanging the feed volatile organic compounds (VOCs) in the sequence methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK), styrene, and then back to MEK. The obtained performance results revealed that the biofilter provided high removal efficiency within the critical load- ing of each VOC, which was previously defined in the non-interchanging VOC fed biofilter. The biofilter easily acclimated to the oxygenated compounds (MEK and MIBK), but re-acclimation was delayed for the aromatic compounds (toluene and styrene). Ratios of the molar mass of CO 2 produced per molar mass of VOC removed were investigated. It has been found that the ratios for the aromatic compounds closely resembled the theoretical complete chemical oxidation based ratios while larger differences were encountered with the oxygenated compounds. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes was used to assess the impact of interchanging VOCs on the bacterial community structure in the biofilter. The results from denaturing gradient gel electrophoresis (DGGE) showed that the structure of the microbial community in the biofilter was different after each interchange of VOCs. 1 Introduction Biofiltration technology has recently emerged as an effi- cient and cost-effective technology for the control of volatile organic compounds (VOCs) emission. However, fluctuations in concentration and variation in the waste air composition is the most common situation encountered in the chemical industry, which challenges the application of biofiltration technology. During the past decade, numerous studies were performed at the bench, pilot, or pilot-field scale reactors to evaluate the effect of inlet concentration on biofiltration performance [1–13]. Target contaminants included hydrocarbons (e.g., benzene, styrene, hexane, toluene, and naphthalene), oxyge- nated hydrocarbon (e.g., methanol, ethanol, diethyl ether, acetone, and methyl ethyl ketone), chlorinated hydrocar- bons (e.g., chlorobenzene and o-dichlorobenzene), and sul- fur compounds (e.g., hydrogen sulfide). Factors affecting the decontamination efficiency include: nature of the contami- nants, packing materials and biofilter configurations, empty bed retention time, volumetric loading rates, nutrient feed flow rates, nutrient solution pH, and flow patterns of air. Jorio et al. [14] and Sorial et al. [15] studied the effect of variation of styrene inlet concentration and gas flow rate on the overall biofilter performance. They found that excess biomass accumulated within the biofilter decreased the over- all biofilter performance when the employed inlet concen- tration exceeded the removal capacity of the biofilter. Deshusses et al. [5] studied the transient behavior of a biofil- ter under step change of MEK and MIBK concentrations. They found that the biofilter adapted rapidly (2–5 hours) to the new operating conditions. Cai et al. [3, 4] studied the bio- filter behavior in removing oxygenated compounds, and they observed that the biofilter could maintain high removal effi- ciency when the employed loading rate did not exceed its elimination capacity. They also found that oxygenated com- pounds favored biomass growth, which would cause channel- ing in the biofilter and lead to a decrease of biofilter perfor- mance. Periodic backwashing operation with media fluidization was necessary for removing the excess biomass in order to maintain a stable high performance. Further- more, biofilter re-acclimation after backwashing or non-use due to shutdown for factory retooling or equipment repair, or during weekends and holidays is an important factor in biofilter operation. To obtain consistent performance and to control the biofilter more effectively, some researchers have focused on biofilter re-acclimation. Torronen et al. [16] noted that 2–4 hours were required following a two-day peri- od of non-use and that five hours were required following a five-day period of non-use, for removal efficiency to return to previous levels for hexane and phenolic compounds. Togna and Frisch [17] reported styrene re-acclimation peri- ods after two or more days without chemical contact. Stan- defer and van Lith [18] reported that biofilter removal effi- ciency returned to previous levels after one hour following a two-day period of non-use and after 5–8 hours following a seven-day period of non-use. Martin and Loehr [19] report- ed biofilter re-acclimation after restart-up from two inter- mittent periods. Moe and Qi [20] found out that weekend shut-down periods caused varying effects on removal effi- ciency for different compounds. Cai et al. [3, 4] and Kim et al. [1, 2] observed that non-use periods did not have noticeable adverse effects on removal efficiency when the employed loading rates did not exceed the elimination capacity of the biofilters and non-use operation could be Eng. Life Sci. 2006, 6, No. 1 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 37 – [*] Z. Cai, D. Kim, G. A. Sorial (author to whom correspondence should be addressed, e-mail: George.Sorial@uc.edu) P. Saikaly, M. M. Zein, D. B. Oerther, University of Cincinnati, Department of Civil and Environmental Engineering, Cincinnati, 45221, OH, USA. Eng. Life Sci. Biological VOC Removal Eng. Life Sci.