Study on emission and distribution characteristics of ammonia emission from anaerobic digesters in typical industrial pig farm

Abstract: The problem of environmental pollution caused by large-scale development of livestock and poultry breeding is increasingly prominent in China, which has large amount of livestock and poultry. It is predicted that the fecal production of livestock and poultry in China will reach 42.44 billion ton in 2020, and the fecal pollution ranks first among the agricultural sources. Greenhouse gases and odorous odors released by livestock manure are important sources of air pollutants, and ammonia is one of the main gases released by livestock and poultry manure. Ammonia is not only a threat to the health of surrounding population of livestock and poultry farms, but also an important part of the atmospheric acid deposition which can lead to soil acidification and eutrophication, and further can become a serious threat to the ecological environment. Therefore, it is a great significance to carry out a study on the characteristics of ammonia emissions from typical large-scale pig farms, clarify the current situation of ammonia emissions from typical agricultural sources, which can provide the foundation for controlling the atmospheric particulate matter pollution and improving regional air quality. Biogas produced by anaerobic fermentation is a common method for treatment of fecal pollution in large-scale livestock and poultry farms. The process can not only generate clean energy and reduce fecal stench, but also recycle nutrients in the form of fertilizer. Therefore, the treatment model centering on large-scale biogas project has developed rapidly. At present, there is still a lack of in-situ monitoring and research on ammonia discharge at the node of the typical fecal treatment process, and there is still a lack of systematic research on the impact of the anaerobic fermentation biogas production facility on the release of pig fecal ammonia. A typical methane project of large-scale pig farms in Yangtze river delta was used as the research object. Ammonia emission was synchronous monitored for 3 consecutive days in each emission node of the biogas engineering facilities (cesspool, regulating pond and biogas tank). The results showed that the average daily emission rate of ammonia in cesspool, regulating pond and biogas tank respectively was 1.48, 3.08 and 1.47 g/(d·m2). The ammonia emission of each node had an obvious daily change process, this process was generally manifested as the fluctuant increase of ammonia emission in the morning, decrease in the afternoon and keep the low-value emission at night. The cesspool and regulating pond in the turnover period of fecal pollution appeared daily emission peak; the ammonia emission rates of the cesspool, regulating pond and biogas tank were positively correlated with the temperature in stable stage, while was negatively correlated with the humidity. The daily ammonia emissions of cesspool, regulating pond and biogas tank were 13.44, 38.72 and 5 275.4 g/d, respectively. This study selected typical large-scale pig farms of anaerobic fermentation biogas production facilities and constructed the field monitoring technology method to measure each discharge ammonia concentration of treatment facilities node. By calculating the excreta ammonia emission rate of each emission node, the characteristics of ammonia emission of each emission node were analyzed, and the main influencing factors of ammonia emission were identified. The results provide a reference for the calculation of ammonia emissions from livestock and poultry breeding in the region and the formulation of ammonia emission reduction measures.