Evaluation of Biological Air Filters for Livestock Ventilation Air by Membrane Inlet Mass Spectrometry

Abstract

Biological air filters have been proposed as a cost-effective technology for reducing odor emissions from intensive swine production facilities. In this work we present results from the application of membrane inlet mass spectrometry (MIMS) for continuously monitoring the removal of odorous compounds in biological air filters. The sensitivity and selectivity were tested on synthetic samples of selected odorous compounds, and linearity and detection limits in the lower ppb range were demonstrated for all compounds tested (methanethiol, dimethyl sulfide, carboxylic acids, 4-methylphenol, aldehydes, indole, and skatole) except trimethylamine. The method was applied in situ at two full-scale filters installed at swine houses. The results have been compared with analyses by thermal desorption gas chromatography-mass spectrometry (TD-GC/MS), and odor was measured by olfactometry. By comparison with TD-GC/MS, observed MIMS signals were assigned to 4-methylphenol, 4-ethylphenol, indole, skatole, the sum of volatile reduced organic sulfur compounds (ROS), and three subgroups of carboxylic acids. The removal rates were observed to be related to air-water partitioning with removal efficiencies in the range of 0 to 50% for low-soluble organic sulfur compounds and high removal efficiencies (typically 80-100%) for more soluble phenols and carboxylic acids. Based on the results and published odor threshold values, it is estimated that the low removal efficiency of ROS is the main limitation for achieving a higher odor reduction.

Butyric Acid- and Dimethyl Disulfide-Assimilating Microorganisms in a Biofilter Treating Air Emissions from a Livestock Facility

“…The pig stable-air emission and removal efficiencies of each biofilter compartment were analyzed by using thermal desorption gas chromatography-mass spectrometry (TD-GC/MS) and membrane inlet mass spectrometry (MIMS; QMG 422; Balzers, Liechtenstein) according to a previously developed method (11). Briefly, insulated polyterafluoroethylene tubes of equal length were installed in (i) the ventilation channel before the biofilter, (ii) between the two filter sections, and (iii) after the filter used for air sampling.…”

“…The custom-built membrane inlet (Mikrolab, Denmark) was holding a poly-(dimethylsiloxane) sheet membrane (130 m thickness; Technical Products, Lawrenceville, GA). The inlet temperature was held at 50°C, and the sample flow over the membrane was 300 ml min Measurement of dimethyl disulfide in the Randers filter was conducted together with the analysis of methanethiol, dimethyl sulfide, and H 2 S by proton transfer reaction mass spectrometry (PTR-MS) analysis at a single time point (11). Briefly, 5 liters of air were collected in nalophan bags and transported directly to the laboratory.…”

“…An Agilent GC/MS (Agilent 6890N GC and 5973N MS) was used for chromatographic separation using a temperature programmed DB5-MS column (30 m; inner diameter, 0.25 mm; 0.25-m film thickness; J&W Scientific) and for compound detection and identification by full-scan MS. Calibration was performed by injection of known amounts of odorants dissolved in pentane or methanol onto sorbent tubes. A significant fraction of methanethiol will be converted to dimethyl disulfide during sampling and analysis (11). The measured dimethyl disulfide concentration is therefore due to a combination of converted methanethiol and dimethyl disulfide originally present in sampling air.…”

“…Biological airfilters have proven useful in reducing a wide range of compounds emitted from pig production facilities (11). Biofilters rely on the versatile metabolic pathways of microorganisms, which are exposed to air contamination and transform these compounds into biomass, carbon dioxide, and water, as well as waste products.…”

“…Commonly detected sulfur compounds include methanethiol (odor threshold value, ϳ1 ppb), dimethyl sulfide (odor threshold value, ϳ2 ppb), and dimethyl disulfide (DMDS; odor threshold value, ϳ12 ppb), and these represent intermediates of the methionine and cysteine degradation (43). Full-scale biofiltration of emissions from a pig facility revealed stable removal of carboxylic acids in the range of 70 to 90%, whereas the reduction of reduced organic sulfur compounds fluctuated between Ϫ20 to 50% (11). Removal efficiencies of DMDS ca.…”