Wet Scrubber Analysis of Volatile Organic Compound Removal in the Rendering Industry

Abstract

The promulgation of odor control rules, increasing public concerns, and U.S. Environmental Protection Agency (EPA) air regulations in nonattainment zones necessitates the remediation of a wide range of volatile organic compounds (VOCs) generated by the rendering industry. Currently, wet scrubbers with oxidizing chemicals are used to treat VOCs; however, little information is available on scrubber efficiency for many of the VOCs generated within the rendering process. Portable gas chromatography/mass spectrometry (GC/MS) units were used to rapidly identify key VOCs on-site in process streams at two poultry byproduct rendering plants. On-site analysis was found to be important, given the significant reduction in peak areas if samples were held for 24 hr before analysis. Major compounds consistently identified in the emissions from the plant included dimethyl disulfide, methanethiol, octane, hexanal, 2-methylbutanal, and 3-methylbutanal. The two branched aldehydes, 2-methylbutanal and 3-methylbutanal, were by far the most consistent, appearing in every sample and typically the largest fraction of the VOC mixture.A chlorinated hydrocarbon, methanesulfonyl chloride, was identified in the outlet of a high-intensity wet scrubber, and several VOCs and chlorinated compounds were identified in the scrubbing solution, but not on a consistent basis. Total VOC concentrations in noncondensable gas streams ranged from 4 to 91 ppmv. At the two plants, the odor-causing compound methanethiol ranged from 25 to 33% and 9.6% of the total VOCs (v/v). In one plant, wet scrubber analysis using chlorine dioxide (ClO 2 ) as the oxidizing agent indicated that close to 100% of the methanethiol was removed from the gas phase, but removal efficiencies ranged from 20 to 80% for the aldehydes and hydrocarbons and from 23 to 64% for total VOCs. In the second plant, conversion efficiencies were much lower in a packed-bed wet scrubber, with a measurable removal of only dimethyl sulfide (20-100%). INTRODUCTIONPoultry rendering operations convert organic wastes (feathers, offal, dead birds, blood, hatchery byproducts, etc.) to products such as feed additives and fertilizer. In poultry rendering operations, feathers are typically hydrolyzed in batch mode at 140-150 ºC (276-345 kPa) for 20-45 min to breakdown the keratin, 1 and the meat byproducts or offal are typically treated at 121-135 ºC (172-517 psig) with varying residence times depending on the mode of operation, batch or continuous. 2,3 In some cases, the hydrolyzed feathers are then combined with offal and dried. In both of these steps, volatile organic compounds (VOCs) are generated, some of which are odorous. Overhead vapors from the feather hydrolyzer and driers are passed through condensers to remove some VOCs. The noncondensable gases typically are passed through wet scrubber units to remove the VOC fraction not removed in the condensers.

Comparison of chemical wet scrubbers and biofiltration for control of volatile organic compounds using GC/MS techniques and kinetic analysis

“…These results were similar to previous results at two other rendering facilities, except that hexanal and methanethiol were consistently detected and dimethyldisulfide periodically appeared in the non-condensable process streams. 1,7 These results clearly reinforce the need to characterize emission streams when designing air pollution control devices.…”

“…Portable gas chromatography/mass spectroscopy (GC/MS) systems were used to identify VOCs in the non-condensable gases and to determine the efficiency of the air pollution control devices. 1 Operational wet scrubber details (height, diameter, packing type, etc,) have previously been reported. 1 In the process reported here a biofilter was used to treat non-condensable gases and was packed with mulch and bark (3ft or 0.9 m) as the 'biocatalyst'.…”

“…1 Operational wet scrubber details (height, diameter, packing type, etc,) have previously been reported. 1 In the process reported here a biofilter was used to treat non-condensable gases and was packed with mulch and bark (3ft or 0.9 m) as the 'biocatalyst'. Gas samples were taken from the inlet (entering ductwork) and outlet of the biofiltration system (points 3 and 4, Fig 2), using previously described methods.…”

“…However, recent pilotscale testing of a wet scrubber system for VOC removal indicated very poor performance towards VOCs, specifically branched and straight chain aldehydes. 1 Very little information is available about the VOC compositions and concentrations at different points in the process and the efficiency of the wet scrubbers for specific compounds.…”

Degradation of Isobutanal at High Loading Rates in a Compost Biofilter

“…Other processes, however, like composting, animal rendering, and food processing, cause emissions with variable VOC concentrations. In rendering plants, for example, total VOC concentrations from 4 to 91 ppm v have been measured in the noncondensable gas streams, 4 whereas during aerobic composting of biowaste, individual VOC concentrations up to 103 ppm v were observed. 5 On the other hand, in the blower exhaust from a composting facility processing anaerobically digested sludge, individual VOC concentrations remained Ͻ1 ppm v .…”