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47 ENHANCEMENT OF BIOFILTRATION PROCESS FOR AIR PURIFICATION Brian C. Shade, Research Assistant Walter J. Maier, Professor Civil and Mineral Engineering Department University of Minnesota Minneapolis, Minnesota 55455 INTRODUCTION Biofiltration is a biologically mediated process for purifying air contaminated with organic vapors. Early applications by sanitary engineers focused on filtering odorous gases through soil beds to eliminate odors from septic tanks.4 Microbes were found to be the purifying agents. U.S. Utility Patent 2,793,096 was granted to R.D. Pomeroy in 1957 for a soil bed which enhanced the "deodorizing of gas streams by the use of microbial growth." This patent expired in 1974, but design patents are currently held by others for design modification, such as composition of packing materials, configuration of packed beds, and gas delivery systems. Several investigators have studied the unique properties of soils in related applications. Rapid disappearance of cyanide in aerobic soils is an example. Dioxin and other halogenated hydrocarbons have been found to oxidize at slower rates in air and water than in soil. As regards industrial applications for controlling emission of volatile organics, West Germany and the Netherlands are leaders in the field with more than 500 plants in operation. Biofiltration is currently viewed as BACT (best available control technology) in West Germany and the Netherlands.9 However, there is growing interest in biofiltration for industrial applications in the United States.2,5,6>7 A recently published survey3 lists ethanol and butylaldehyde removal from dryer air at Monsanto Chemical Company, removal of pharmaceutical odors at Upjohn Company, and hydrocarbon vapors removal from fuel storage tanks at Esso of Canada. This diversity of applications suggests that there are numerous potential industrial applications. The major features of biofiltration have been described in the literature. Gas flow through the filter (packed-bed) is characterized as plug flow with minimal back mixing.13 At the mass loadings of air commonly applied to biofilters, air flow is in the turbulent flow regime and mass transport rates in the air phase are correspondingly rapid. However, surface transfer of organic vapors from the air phase to the stationary packing phase is dependent on the physical-chemical properties of the packing surfaces, their moisture content, and the physical chemical properties of the chemical, namely, its affinity for adsorption on surfaces, its solubility in water, and its volatility. At high hydrocarbon concentrations, removal rates are reported to be zero order." Kampbell reported increasing rates of removal with increasing hydrocarbon concentrations8 which implies that removal follows first order kinetics. A number of investigators have suggested that the rate limiting step may be either the rate of reaction within the biofilm, or the rate of diffusion in the biofilm.15,16 Zero order kinetics imply that 100 percent removal is possible for any biodegradable compound.14 However, it is unlikely that zero order kinetics will prevail at very low concentrations. Studies of removal rates at low concentrations are needed. Also a more precise description of the interrelated effects of transport, adsorption, and microbial kinetics are needed. Two important questions that have not been described adequately in the literature concern the effectiveness of biofilters under variable loading conditions and the stability of biofilters operating at high removal efficiencies to achieve essentially complete removal of chemicals at low concentrations. The answer to these questions are closely tied to the dynamics of cell mass production and accumulation of active cells throughout the reactor. This paper describes the initial results of a systematic pilot plant study to examine the effects of different air flow rates and mass loadings of chemical under constant and variable loading conditions. The objective is to generate process data at precisely defined operating conditions. The paper also 49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 425
Object Description
Purdue Identification Number | ETRIWC199447 |
Title | Enhancement of biofiltration process for air purification |
Author |
Shade, Brian C. Maier, Walter J. |
Date of Original | 1994 |
Conference Title | Proceedings of the 49th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,44602 |
Extent of Original | p. 425-436 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
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Description
Title | page 425 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 47 ENHANCEMENT OF BIOFILTRATION PROCESS FOR AIR PURIFICATION Brian C. Shade, Research Assistant Walter J. Maier, Professor Civil and Mineral Engineering Department University of Minnesota Minneapolis, Minnesota 55455 INTRODUCTION Biofiltration is a biologically mediated process for purifying air contaminated with organic vapors. Early applications by sanitary engineers focused on filtering odorous gases through soil beds to eliminate odors from septic tanks.4 Microbes were found to be the purifying agents. U.S. Utility Patent 2,793,096 was granted to R.D. Pomeroy in 1957 for a soil bed which enhanced the "deodorizing of gas streams by the use of microbial growth." This patent expired in 1974, but design patents are currently held by others for design modification, such as composition of packing materials, configuration of packed beds, and gas delivery systems. Several investigators have studied the unique properties of soils in related applications. Rapid disappearance of cyanide in aerobic soils is an example. Dioxin and other halogenated hydrocarbons have been found to oxidize at slower rates in air and water than in soil. As regards industrial applications for controlling emission of volatile organics, West Germany and the Netherlands are leaders in the field with more than 500 plants in operation. Biofiltration is currently viewed as BACT (best available control technology) in West Germany and the Netherlands.9 However, there is growing interest in biofiltration for industrial applications in the United States.2,5,6>7 A recently published survey3 lists ethanol and butylaldehyde removal from dryer air at Monsanto Chemical Company, removal of pharmaceutical odors at Upjohn Company, and hydrocarbon vapors removal from fuel storage tanks at Esso of Canada. This diversity of applications suggests that there are numerous potential industrial applications. The major features of biofiltration have been described in the literature. Gas flow through the filter (packed-bed) is characterized as plug flow with minimal back mixing.13 At the mass loadings of air commonly applied to biofilters, air flow is in the turbulent flow regime and mass transport rates in the air phase are correspondingly rapid. However, surface transfer of organic vapors from the air phase to the stationary packing phase is dependent on the physical-chemical properties of the packing surfaces, their moisture content, and the physical chemical properties of the chemical, namely, its affinity for adsorption on surfaces, its solubility in water, and its volatility. At high hydrocarbon concentrations, removal rates are reported to be zero order." Kampbell reported increasing rates of removal with increasing hydrocarbon concentrations8 which implies that removal follows first order kinetics. A number of investigators have suggested that the rate limiting step may be either the rate of reaction within the biofilm, or the rate of diffusion in the biofilm.15,16 Zero order kinetics imply that 100 percent removal is possible for any biodegradable compound.14 However, it is unlikely that zero order kinetics will prevail at very low concentrations. Studies of removal rates at low concentrations are needed. Also a more precise description of the interrelated effects of transport, adsorption, and microbial kinetics are needed. Two important questions that have not been described adequately in the literature concern the effectiveness of biofilters under variable loading conditions and the stability of biofilters operating at high removal efficiencies to achieve essentially complete removal of chemicals at low concentrations. The answer to these questions are closely tied to the dynamics of cell mass production and accumulation of active cells throughout the reactor. This paper describes the initial results of a systematic pilot plant study to examine the effects of different air flow rates and mass loadings of chemical under constant and variable loading conditions. The objective is to generate process data at precisely defined operating conditions. The paper also 49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 425 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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