Monitoring Methods Research For Harmful Gases In Livestock Production Environment

Harmful gases from livestock and poultry industry are the main part of pollutedgases in agriculture. Air pollution produced during livestock and poultry productiondoes not only reduce the efficiency of livestock and poultry industry, but also affect theglobal air quality. Especially, greenhouse gases from livestock and poultry industryhave been one of the main factors of global warming. Reduce the emission of harmfulgases can improve the global air quality and ease the greenhouse effect. To reduce theemission of harmful gases in livestock and poultry production, effective monitoring ofharmful gases is the first step.Harmful gases can be produced in many processes of livestock and poultryproduction, including feeding, treatment of manure, transportation and so on. Themeasures used to prohibit the emission and production of harmful gases can affect theproduction of harmful gases. To evaluate the effectiveness of different measures andmake selection, monitoring of harmful gases is important. Because of the significantdifference of the composition and distribution of harmful gases in every process oflivestock and poultry production, a single method can not thoroughly monitor theconcentration of harmful gases. In this study, three methods with different dimensions,which include Fixed position, Pathway and Pathway methods, were used to monitorthe harmful gases thoroughly in the main processes which emit harmful gases inlivestock and poultry production. Through the summary and analysis of conventional methods used for monitoringharmful gases and composition and main sources of harmful gases in livestock andpoultry production, odor gases in livestock and poultry houses and methane in openfield were selected as research objects. the monitoring method of the odor level indexinside animal building based on electronic nose, methane monitoring methods based onthe open-path TDLAS and gas concentration distribution reconstruction methods basedon computer tomography technology were introduced, to achieve the monitoring of theharmful gases in livestock and poultry production on multi-scale. The main researchcontents and conclusions include the following four aspects.(1) The composition of harmful gases inside the animal building is complex. Dueto the inability to monitor the concentration of each gas component, the previousresearch mainly uses electronic nose method to measurement the odor level. Becausethe electronic nose belongs to the laboratory instruments which can not be used inpractical production. Monitoring the odor level index inside animal building bymeasuring the concentration of the main malodorous gases component and using of thealgorithms combined with olfactometry method was proposed in this research. Themethod measure the concentration of target components using selectivity sensor toreduce the number of sensors, complexity and cost of the electronic nose system.According to this method, odor level index monitoring electronic nose system foranimal building based on the analysis of the main components of malodorous gasesinside animal building was developed. The system used electrochemical sensors tomeasure the concentration of ammonia and hydrogen sulfide and odor level indexdetermination algorithm to inverse the odor level inside animal building. Comparativeexperiments with olfactometry method proved that this method can accurately monitor the malodor levels of animal building.(2) The composition of harmful gases outside the animal building is simple, butthe distribution range is large and the liquidity is strong. Open path optical methodscan achieve effective monitoring. Relative to the previous Fourier transform infraredspectroscopy method for open path (OP/FTIR) open path tunable diode laserabsorption spectroscopy (OP/TDLAS) simplifies equipment and improves thereal-time monitoring which can be widely used in practical production. In order torealize the monitoring the pathway integration concentration of methane within theproduction environment of livestock and poultry, methane gas monitoring methodbased on OP/TDLAS was put forward according to the characteristics of methane.Implementation of OP/TDLAS methane monitoring system was based on this method.Methane-absorption characteristics line selection, Light modulation, Optical detection，harmonics extraction, data acquisition and processing and optical systemimplementation were introduced. The OP/TDALS methane monitoring system usecalibrated by gas absorption cell and the key performance parameters of the systemwas analyzed in the calibration experiments. The results show that, the detection limitof the system is5ppm and the detection precision is less than20%. The system can beused to monitor the pathway integration concentration of methane within theproduction environment of livestock and poultry.(3) Due to the large area the pathway monitoring method can not accurately reactsthe distribution of harmful gas within livestock manure drying, fermentation tank andother locations in the production environment of livestock and poultry. A monitoringmethod of concentration distribution of methane gas in the region by computertomography (CT) was proposed on the basis of the measurements of the path integration concentration of methane. MLEM and SBFM algorithm was determined touse methane gas distribution graphical reconstruction in the open area of livestockproduction and poultry production according to the gas monitoring requirements. Then,the implementation methods of MLEM and SBFM algorithm were introduced. Graphicreconstruction simulation was carried out by MLEM and SBFM algorithm, and theadvantages and disadvantages of the two algorithms were analyzed and compared.(4) Based on these studies, the application effect of each method was verifiedthrough the on-site application. In the odor level index inside animal buildingmonitoring experiment the odor level inside poultry house was monitoring using theodor level index monitoring system for animal building. The monitoring results showthat the method can obtain the odor level index inside the poultry house stably andaccurately. Methane distribution graphs near the methane fermentation tank werereconstructed by MLEM and SBFM algorithm. And the OP/TDLAS methanemonitoring system was used to get the path integration concentration. From the resultsof the reconstruction, the main parameters of the graph obtained by the two algorithmshave a high consistency which indicating that OP/TDLAS combination with computertomography method can be used in the monitoring of the concentration distribution ofharmful gases in the open area of animal production, and get accurate monitoringresults.