Richard Lab:Review of biofilters
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|EPA. 1998. Analysis of Composting as an Environmental Remediation Technology. Available at: http://www.epa.gov/epaoswer/non-hw/compost/analysis.txt. Accessed August 2006.||
Odors result from the incomplete oxidation of volatile solids produced during the decomposition of biodegradable materials. Biofilters are used to mitigate odors in many operations, from wastewater treatment plants to odor-generating food processing plants, and animal facilities as well (Leson, 1991). Compost has been used as a biofiltering media (Devinny, 1994; Bohn, 1975; Haug, 1993). Compost biofilters can remove 97% of the odor units (Carlson, 1966; Finn, 1997; Leson, 1991; Segall, 1995). The typical gas composition from composting includes 1) Terpenes, 2) organic solvents (see Eitzer (1993) for 1 and 2), and the biological products 3) short chain organic acid, 4) amines, 5) aldehydes (see Wilber (1990) and Miller (1993) for 3,4 and5). Volatiles from composting facilities reach a concentration of 20 to 150 mg VOC / m3 of air (Kissel, 1992). High odor intensity was observed in composting (Bidlingmaier, 1996). The VOC spectrum in manures is described in Kreis (1978). Conrad (1995) reports trial and error methods of designing compost matrices for biofilters. In compost biofilters, there's an opportunity for improved design, better performance, and better reliability. CBF (compost Biofilters) remove 83 to 99% of H2S and other aromatics (Ergas 1995), when 2 CBF were used in parallel (and for some reason the concentration of aromatics at the second outlet was higher than the concentration at the first outlet). In this study CBF filtered chlorinated the measured aliphatic solvents except tricholoromethane and tetrachloroethylene. Other chlorinated aliphated solvents, Benzene, Toluene, m and p Xylene, and o-Xylene were removed at high rates. H2S was successfully removed as well. In Watwood (1995), a large scale CBF degraded trichloroethylene (TCE) only when a methane or propane supplement was used, because TCE degrading microbes need it as a co-substrate (Lu, 1995). The compost type affects the efficiency of TCE removal, and so does the choice of ether methane or propane as a co-substrate. In Watwood (1995) TCE was removed by adsorption and/or transfer into micropores because actual TCE degradation took 10 to 20 days. CBF's can remove VOC's generated during the recycling of punctured spray cans (Conrad, 1995). When gas is streamed through a multistage CBF, 99% of solvents and propellants can be removed. The maximum allowable VOC concentration is 5000 mg / l of air, beyond which microbial activity is inhibited (Leson, 1991). A multistage biofilter would allow a VOC input of 25,000 mg / l of air. CBF's have also been used for filtering contaminated water, in a commercial storm water filter (Conrad, 1995; Stewart, 1994), for the removal of oil, grease and toxic metals from storm water runoff. CBF's have operation requirements. The characteristics of a successful CBF (Leson, 1991; Ottengraf, 1986; Haug, 1993; Williams, 1993; Ernst, 1987; Toffey, 1997) include high porosity and waster holding capacity. A CBF must not loose pore spaces as it is being watered, which could cause back pressure a require greater pump power when streaming the gas through the CBF. As CBF's age, their performance should increase due to the natural selection of microbes tolerant to shock loads and with high growth rates. Moisture must remain between 50-70% for high microbial activity. In most CBF's incoming air must be humdified. Temperature must be maintained between 20 degrees celsius, the threshold for microbial activity, and 35 degrees C, the threshold for mesophilic microbes. The temperature of incoming air must be hot enough to affect CBF effectiveness, or its moisture content. Residence time through the filter must be at least 30 seconds, to treat low velocity and / or low volume air streams. CBF depth should be 1 meter, more increases compaction and less reduces efficiency. A CBF must be designed for uniform air distribution and the filter must be stable to prevent air channeling. Channeling decreases residence time, and the % of active CBF.
|Goschl, R. “Odor Stabilization in Waste Disposal Sites.” In: In Situ Aeration: Air Sparging, Bioventing, and Related Remediation Processes, edited by R.E. Hinchee, R.N. Miller, and P.C. Johnson, 289-295. Columbus, OH: Battelle Press, 1995.||Compost biofilters can be used on a field scale to degrade methane and odorous compounds. Methane is not water soluble nor easily adsorbed, so if a biofilter reduces methane emissions, it must be due to microbial degradation. This was evident in Goschl (1995) by the increase in CO2 and decrease in oxygen at the outlet of the filter, which is consistent with microbial degradation.||Hala|
|Morgenroth, E., Schroeder, E.D., Chang, D.P.Y. and Scow, K.M. 1996. Nutrient limitation in a compost biofilter degrading hexane. J. Air Waste Manage. Assoc., 46, 300–308||CBF require nutrient inputs, since composts have 1-2% N by weight, and most not bioavailable. Morgenroth (1996) found that biofilter degradation of hexane vapors improved dramatically by adding nutrients.||Hala|
|Bohn, H. L., Bohn, K. H., Gostomski, P.A. (Editor). 1999. Moisture in biofilters. Environmental progress - Special biofiltration issue, 18 (3), 156-161.||high microbial activity in biofilters occurs at water potentials of -0.2 to -3 bars.||Hala|