Comparison of Chemical Wet Scrubbers and Biofiltration For

Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 80:1170–1179 (2005) DOI: 10.1002/jctb.1308 Comparison of chemical wet scrubbers and biofiltration for control of volatile organic compounds using GC/MS techniques and kinetic analysis James R Kastner∗ and Keshav C Das Department of Biological and Agricultural Engineering, The University of Georgia, Athens, GA, 30602, USA Abstract: Increasing public concerns and EPA air regulations in non-attainment zones necessitate the remediation of volatile organic compounds (VOCs) generated in the poultry-rendering industry. Wet scrubbers using chlorine dioxide (ClO2) have low overall removal efficiencies due to lack of reactivity with aldehydes. Contrary to wet scrubbers, a biofilter system successfully treated the aldehyde fraction, based on GC/MS analysis of inlet and outlet streams. Total VOC removal efficiencies ranged from 40 to 100% for the biofilter, kinetic analysis indicated that the overall removal capacity approached 25 g m−3 h−1, and aldehyde removal efficiency was significantly higher compared with chemical wet scrubbers. Process temperatures monitored in critical unit operations upstream from the biofilter varied significantly during operation, rising as much as 30 ◦C within a few minutes. However, the outlet air temperature of a high intensity scrubber remained relatively constant at 40 ◦C, although the inlet air temperature fluctuated from 50 to 65 ◦C during monitoring. These data suggest a hybrid process combining a wet scrubber and biofilter in series could be used to improve overall VOC removal efficiencies and process stability. 2005 Society of Chemical Industry Keywords: odor; volatile organic compounds (VOC); aldehydes; wet scrubber; biofilter; gas chromatography; mass spectrometry INTRODUCTION and odor complaints have resulted in the need for low Rendering operations convert organic wastes (feathers, cost, effective treatment options. Rendering facilities offals, dead birds, hatchery by-products, etc) from the in non-attainment areas (eg the Atlanta area) are also poultry industry to value-added products such as feed facing EPA regulations, that limit VOC emissions additives, and fertilizer. In poultry-rendering opera- and potentially requires new air pollution control tions feathers are typically hydrolyzed at 140–150 ◦C technology for the industry. Most rendering operations for 20–45 min to break down the keratin (an indi- use wet scrubbers for off-gas treatment and typically gestible protein). The hydrolyzed feathers are then obtain efficiencies of 85–90%, based on odor dilution combined with offal and dried. In both of these to thresholds units, but use chemicals for oxidation (eg steps, volatile organic compounds (VOCs) are gener- ClO2,NaOCl,ozoneorO3). However, recent pilot- ated, some of which are odorous as well. Overhead scale testing of a wet scrubber system for VOC removal vapors from the feather hydrolyzer and driers are indicated very poor performance towards VOCs, passed through condensers to remove some VOCs. specifically branched and straight chain aldehydes.1 The non-condensables are typically passed through Very little information is available about the VOC wet scrubber units to remove the VOC fraction not compositions and concentrations at different points in removed in the condensers. the process and the efficiency of the wet scrubbers for Rendering operations in Georgia and the US have specific compounds. recently come under regulatory scrutiny for odor and Venturi scrubbers, packed-bed wet scrubbers, and VOC air quality issues. Although the industry has a biofilters have been used for odor removal in good track record of minimizing odors, urbanization the rendering industry.2 Venturi and packed-bed ∗ Correspondence to: James R Kastner, Department of Biological and Agricultural Engineering, The University of Georgia, Athens GA, 30602, USA E-mail: [email protected] Contract/grant sponsor: Georgia Research Alliance Contract/grant sponsor: US Poultry and Egg Association Contract/grant sponsor: Poultry Protein and Fat Council Contract/grant sponsor: State of Georgia (Received 12 July 2004; revised version received 18 February 2005; accepted 19 February 2005) Published online 4 May 2005 2005 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2005/$30.00 1170 Biofiltration of aldehydes from poultry-rendering emissions 5 −1 −1 scrubbers are typically coupled together since the k2nd > 2 × 10 Lmol s for ethylmercaptan), but −1 −1 venturi is a single stage scrubber (ie limited mass very slowly with aldehydes (eg k2nd = 2.5Lmol s transfer capabilities) and acts to reduce temperature for propanal).4 Thus, wet scrubbers utilizing chemical and particulate levels. A variety of oxidizing chemicals oxidants appear to have a limited capacity for aldehyde have been used as oxidizing agents, including sodium removal. hypochlorite, chlorine gas, chlorine dioxide (ClO2), The primary objectives of this research were to com- and ozone/NaOCl.2 Removal efficiencies based on pare removal efficiencies of individual compounds in odor units ranged from 99% to 93–96% for processes rendering emissions between biofiltration and chem- using a venturi and a packed-bed (water and NaOCl), ical wet scrubber air pollution control devices and and a single packed-bed system treating low intensity assess the impact of upstream temperature pertur- 2 odors (ClO2), respectively. However, optimum bations on biofiltration. Our results indicate clear chemical concentrations and removal efficiencies advantages in coupling physical/chemical processes based on individual and total VOCs were not reported. with a biological process based on independent analy- It is theorized that the chemical oxidizing agents sis of wet scrubbers and an industrial-scale biofilter. used in wet scrubbers react with most of the compounds in rendering emissions to achieve high removal efficiencies. However, there is a general MATERIALS AND METHODS lack of kinetic data specific for the VOCs generated Rendering process and air pollution control in the rendering industry, without which optimal systems scrubber design is impractical.3 Kinetic data indicate Two of the poultry-rendering facilities analyzed dur- that typical oxidizing agents used in wet scrubbers ing this research utilized ClO2 wet scrubbers for 1 (eg ClO2 and ozone or O3) do not react or react air pollution control (Fig 1). A third plant (data slowly with many of the compounds in rendering presented here) was an inedible-poultry-rendering plant waste gases.4–6 Reaction rate constants ranging process, consisting of batch feather hydrolyzers and − from 4 × 104 to 3 × 108(Lmol 1 s−1) are reportedly continuous meat by-product cookers (Fig 2). Vapors required to achieve rapid removal in wet scrubbers.3 generated from the feather hydrolyzer and cookers Recent kinetic analysis indicated that ClO2 does not were condensed in shell (water) and tube (vapors) heat react with hexanal and 2-methylbutanal over a wide exchangers (Fig 2). An open-bed, industrial biofil- range of pH and temperatures.5 Similarly, ozone ter (100 ft L × 40 ft W × 3ftH or 30.5m× 12.2m× rapidly reacts with reduced sulfur compounds (eg 0.91 m), originally sized to handle a flow rate Figure 1. General process flow-sheet for poultry-rendering facility using a wet scrubber system. J Chem Technol Biotechnol 80:1170–1179 (2005) 1171 JR Kastner, KC Das Figure 2. General process flow-sheet for poultry-rendering facility using a biofilter. of approximately 125 000 ft3 min−1 (59 m3 s−1),was Unit operation temperature analysis used to treat non-condensable gases from the meat and The operating temperatures of critical unit operations feather cookers. Portable gas chromatography/mass were monitored in real time via installed thermo- spectroscopy (GC/MS) systems were used to identify couples (T type, Omega Engineering Inc, Stanford VOCs in the non-condensable gases and to determine CT, USA) and data acquisition (Model CR 23X, the efficiency of the air pollution control devices.1 Campbell Scientific, Inc, Logan, UT, USA). Unit Operational wet scrubber details (height, diameter, operation temperatures that were monitored during packing type, etc,) have previously been reported.1 operation included meat cookers, feather hydrolyz- In the process reported here a biofilter was used to ers, overhead condensers (air inlet, cooling liquid treat non-condensable gases and was packed with inlet and outlet), and the high intensity scrubber mulch and bark (3ft or 0.9 m) as the ‘biocatalyst’. treating non-condensable gases (air inlet and outlet, and scrubbing solution). Inlet temperatures to Gas samples were taken from the inlet (entering the biofilter were measured manually at the cen- ductwork) and outlet of the biofiltration system ter of the entering ductwork, typically before each (points 3 and 4, Fig 2), using previously described VOC analysis. Mixing of plant air and the long dis- methods.1 A pitot-static tube (Dywer Instruments, tance (>200 ft) from the condenser to biofilter inlet Michigan City, IN, USA) was used to determine the helped to reduce inlet temperatures to the biofilter cross-sectional velocity profile of the incoming stream ◦ (24–38 C). and subsequently numerically integrated to determine the volumetric flowrate. The outlet sampling system × consisted of 3 ft (0.9 m) diameter 4ft (1.2m) RESULTS height polypropylene barrels with a 1/4 inch (0.6 cm) VOC identification in the plant using a biofilter sampling port at the top. Three of the units were Gas chromatography coupled to MS identified installed

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