Dezhao Liu

Odorant Emissions from Intensive Pig Production Measured by Online Proton-Transfer-Reaction Mass Spectrometry

Emission of odorous compounds from intensive livestock production is a cause of nuisance in populated rural areas. Knowledge on the chemical composition of odor and temporal variations in emissions are needed in order to identify factors of importance for emission rates and select proper abatement technologies. In this work, a method based on proton-transfer-reaction mass spectrometry (PTR-MS) has been developed and tested for continuous measurements of odorant emissions from intensive pig production facilities. The method is assessed to cover all presently known important odorants from this type of animal production with adequate sensitivity and a time resolution of less than one minute. The sensitivity toward hydrogen sulfide is demonstrated to exhibit a pronounced humidity dependency, which can be included in the calibration procedure in order to achieve quantitative results for this compound. Application of the method at an experimental pig facility demonstrated strong temporal variations in emissions, including diurnal variation. Based on these first results, air exchange and animal activity are suggested to be of importance for emission rates of odorants. Highest emissions are seen for hydrogen sulfide and acetic acid, whereas key odorants are evaluated from tabulated odor threshold values to be hydrogen sulfide, methanethiol, 4-methylphenol, and butanoic acid.

Application of proton-transfer-reaction mass spectrometry to the assessment of odorant removal in a biological air cleaner for pig production.

There is an urgent need to develop odor reduction technologies for animal production facilities, and this requires a reliable measurement technique for estimating the removal of odorants. The purpose of the present experiment was to investigate the application of proton-transfer-reaction mass spectrometry (PTR-MS) for continuous measurements at a biofilter from SKOV A/S installed at a pig production facility. PTR-MS was able to handle the harsh conditions with high humidity and dust load in a biofilter and provide reliable data for the removal of odorants, including the highly odorous sulfur compounds. The biofilter removed 80-99% of carboxylic acids, aldehydes, ketones, phenols, and indoles and ca. 75% of hydrogen sulfide. However, only ~0-15% of methanethiol and dimethyl sulfide was removed. In conclusion, PTR-MS is a promising tool that can be used to improve the development of biological air cleaning and other odor reduction technologies toward significant odorants.

PTR-MS measurement of partition coefficients of reduced volatile sulfur compounds in liquids from biotrickling filters

Biological air filtration for reduction of emissions of volatile sulfur compounds (e.g., hydrogen sulfide, methanethiol and dimethyl sulfide) from livestock production facilities is challenged by poor partitioning of these compounds into the aqueous biofilm or filter trickling water. In this study, Henrys law constants of reduced volatile sulfur compounds were measured for deionized water, biotrickling filter liquids (from the first and second stages of a two-stage biotrickling filter), and NaCl solutions by a dynamic method using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) at a temperature range of 3-45°C. NaCl solutions were used to estimate salting-out constants up to an ionic strength of 0.7 M in order to evaluate the effect of ionic strength on partitioning between air and biofilter liquids. Thermodynamic parameters (enthalpy and entropy of phase exchange) were obtained from the measured partition coefficients as a function of temperature. The results show that the partition coefficients of organic sulfur compounds in the biotrickling filter liquids were generally very close to the corresponding partition coefficients in deionized water. Based on the estimated ionic strength of biofilter liquids, it is assessed that salting-out effects are of no importance for these compounds. For H(2)S, a higher enthalpy of air-liquid partitioning was observed for 2nd stage filter liquid, but not for 1st stage filter liquid. In general, the results show that co-solute effects for sulfur compounds can be neglected in numerical biofilter models and that the uptake of volatile sulfur compounds in biotrickling filter liquids cannot be increased by decreasing ionic strength.

Chemisorption of hydrogen sulphide and methanethiol by light expanded clay aggregates (Leca).

Removal of volatile sulphur compounds from livestock waste air by biological air filtration may be enhanced by application of packing materials with reactive properties. In this study, light expanded clay aggregates (Leca) was tested with respect to sorption and potential chemical degradation of H2S, Methanethiol (MT) and Dimethyl sulphide (DMS). Leca was selected due to its content of minerals, including iron, and due to its high specific surface area. The performance of Leca was evaluated based on breakthrough curves and by comparing the difference between the inlet and outlet gas concentrations. Whereas DMS did not appear to be removed by Leca, both H2S and MT were removed with variable efficiency depending on the specific conditions. Dimethyl disulphide (DMDS) and dimethyl trisulphide (DMTS) were demonstrated to be produced during the degradation process in relatively high yields. A comparison between ambient air and nitrogen gas conditions showed that the chemisorption of H₂S and MT did not necessarily need oxygen to be present. X-ray analysis of Leca showed an abundance of Fe₂O₃. It is therefore hypothesized that Fe₂O₃ in Leca can remove H2S and MT by chemisorption. Both air velocity and moisture content clearly affected the capacity of Leca for removal of H₂S and MT. Lower removal is seen at higher air velocities, whereas higher moisture content enhances removal. However, chemisorption of MT by Leca appears to be limited above a threshold moisture level. Potential reaction mechanisms are discussed in relation to the observed effects. The results implicate that Leca can be used as a filter material with reactive properties provided that moisture content is controlled and that an adequate air velocity is used.

Kinetic evaluation of removal of odorous contaminants in a three-stage biological air filter.

Biofiltration is a cost-effective technology for removing air contaminants from animal facilities. Kinetic analysis can be helpful in understanding and designing the process but has not been performed on full-scale filters treating complex mixtures. In this study, kinetics was investigated in a full-scale biological filter treating air pollutants from a pig facility. Due to the high air flow rates used in the filter, both a plug flow model and a model based on complete mixing were tested with respect to kinetic order and Michaelis-Menten kinetics. Application of these models only gave poor to moderate agreement with air filter removal data. Two alternative kinetic models (Stover-Kincannon model and Grau second-order model) adopted from wastewater biofiltration process analysis were introduced to analyze contaminant removal in the biological air filter. Data analysis demonstrated the applicability of these two models with a high degree of precision on contaminant removal in the biological air filter. Whereas the Stover-Kincannon model demonstrated that pollutant removal rates were related to the mass loading rates, the Grau second-order kinetic model indicated that the removal efficiencies were dependent on air loading rates. Therefore, the kinetic data can be used for comparing biofilter performances and for design purposes.

Evaluation of clay aggregate biotrickling filters for treatment of gaseous emissions from intensive pig production

Treatment of ventilation air from livestock production by biological airfiltration has emerged as a cost-effective technology for reduction of emissions of odorants and ammonia. Volatile sulfur compounds from livestock production include H2S and methanethiol, which have been identified as potentially important odorants that are not removed sufficiently by biological air filters. Light-expanded clay aggregates (Leca(®)) is a biotrickling filter material that contains iron oxides, which can oxidize H2S and methanethiol, and thus potentially may help to remove these two compounds in biological air filters. This study used on-line PTR-MS measurements to investigate the performances of two Leca(®) biotrickling filters (abraded Leca(®) filter and untreated Leca(®) filter) for removal of odorants and ammonia emitted from an experimental pig house. The results indicated that the abraded Leca(®) filter had a similar or slightly better capability for removing odorants than the untreated Leca(®) filter. This may be due to the enlargement of the surface area by the friction process. The volatile sulfur compounds, however, were not removed efficiently by either of the two Leca(®) filters. Kinetic analysis of a ventilation controlled experiment during the first period indicated that Grau second-order kinetics could be applied to analyze the removal of sulfur compounds and other odorants, whereas the Stover-Kincannon model could only be applied to analyze the removal of odorants other than sulfur compounds, partly due to the limitation of mass transfer of these compounds in the biotrickling filters. In the last measurement period, a production of dimethyl disulfide and dimethyltrisulfide coinciding with strongly enhanced removal of methanethiol was observed for the untreated filter. This was assumed to be enhanced by an incidence of low local air velocity in the filter and indicated involvement of iron-catalyzed reactions in the removal of sulfur compounds.

Real-Time Measurement of Volatile Chemicals Released by Bed Bugs during Mating Activities

In recent years, bed bug (Hemiptera: Cimicidae) problems have increased dramatically in many parts of the world, leading to a renewed interest in their chemical ecology. Most studies of bed bug semiochemicals have been based on the collection of volatiles over a period of time followed by chemical analysis. Here we present for the first time, a combination of proton transfer reaction mass spectrometry and video analysis for real-time measurement of semiochemicals emitted by isolated groups of bed bugs during specific behavioural activities. The most distinct peaks in the proton transfer reaction mass spectrometry recordings were always observed close to the termination of mating attempts, corresponding to the defensive emissions that bed bugs have been suspected to exploit for prevention of unwanted copulations. The main components of these emissions were (E)-2-hexenal and (E)-2-octenal recorded in ratios between 1∶3 and 3∶1. In the current study, the quantity varied over 1000 fold for both of the compounds with up to 40 µg total release in a single emission. Males also emit defensive compounds due to homosexual copulation attempts by other males, and no significant differences were observed in the ratio or the amount of the two components released from males or females. In summary, this study has demonstrated that combining proton-transfer-reaction mass spectrometry with video analysis can provide detailed information about semiochemicals emitted during specific behavioural activities.

The Power of Online Proton Transfer Reaction - Mass Spectrometry (PTR-MS) Measurement of Odorous Emissions from a Pig House

Online monitoring of odorous compounds in the ventilation air was applied in an experimental pig house in Denmark. The measurements were executed by proton-transfer-reaction – mass spectrometry (PTR-MS) while grab samples are used to confirm the identity of the compounds. Sorbent tubes samples were analysed by gas chromatography – mass spectrometry analysis (GC-MS) and Tedlar bags samples by gas chromatography – sulfur chemiluminescence detector (GC-SCD). For three target odorants, dimethyl sulfide, propanoic acid and p-cresol, the reproducibility after averaging over 1 hour was in the same order of magnitude for both grab and continuous sampling (<16 %). However, the detailed information on the concentration variations during the day provided by online measurements, can never be obtained by any analytic method requiring sample collection. The results emphasize the importance of a suitable strategy when taking grab samples for odour evaluation, for example for olfactometric measurements. Concentrations of odorants can easily differ by a factor of two within one week with similar weather circumstances and identical pigs.