集约化畜禽养殖圈舍氨排放特征与产生和转化机制的研究

Airborne fine particulate matter (PM2.5) has become an issue in the global environment due to the health problems and environmental degradation it causes. Ammonia is the major precursors of PM2.5. Swine and broiler housings are important sources of anthropogenic ammonia emissions. However, the monitoring data of ammonia emissions from swine and broiler housings in China are lacking. It decreased the accuracy of emission inventory. The mechanism of ammonia production and transformation within the housings is still obscure, which made the prediction of ammonia emission hardly convincing. The present project plans to use accurate and reliable techniques to monitor ammonia concentration and ventilation rates of typical intensive swine and broiler housings. The monitoring period will last for one year. The activities inside the housings will be recorded. The ammonia emission factors will be calculated and the influence of housing management on ammonia emission will be investigated. At the same time, the mechanism of ammonia production and transformation will be studied, including the hydrolysis of urea and ammonia oxidation processes, in order to clarify the effects of ureolytic microorganisms, pH and temperature on urea hydrolysis rate. The contribution of ammonia oxidation to ammonia mitigation will be studied. The project also intends to discover the urea metabolism of ammonia-oxidizing microorganisms which can reduce ammonia production in the manure. Finally, a mechanistic model will be built to predict the ammonia volatilization rate from manure in housing, including urea hydrolysis, mass transfer and volatilization of ammonia, pH variation and other processes. The results of present project will improve the ammonia emissions inventory from livestock and poultry breeding. It will contribute to the prediction of the ammonia emissions characteristics from housing and the development of ammonia mitigation methods.

大气中的氨是形成对公众健康和生态环境有巨大危害的细颗粒物（PM2.5）的主要前体物。生猪和肉鸡圈舍是我国大气氨排放的重要贡献源。但是，我国圈舍氨排放的监测数据缺乏，影响到排放清单的准确性。圈舍内氨的产生与转化机制也尚未明确，无法准确预测氨的排放特征。本项目以典型集约化生猪和肉鸡圈舍为对象，对圈舍氨浓度、通风率和生产活动等指标进行一年期的准确的跟踪监测和记录，计算圈舍的氨排放系数并分析生产活动对氨排放的影响。同时，对氨的产生与转化机制进行研究，包括尿素水解和氨氧化反应。分析尿素水解微生物、pH值和温度对尿素水解速率的影响。探明氨氧化反应特别是直接代谢尿素的氨氧化微生物对圈舍氨减排的作用。最后，依据实验结果，建立预测畜禽粪便氨挥发的机制模型，包括尿素水解、氨传质与挥发、pH值演化等关键过程。研究结果将有助于完善我国氨排放清单，在预测养殖业氨排放特征和制定减排措施方面具有理论价值和实践意义。

畜禽养殖业是全球最重要人为氨气排放源。随着经济社会发展，我国生猪养殖业的规模不断增长，其氨气排放总量也日益剧增。然而，生猪养殖场的氨气排放规律目前尚不明确，仍然缺乏切实可行的方法控制养殖场氨气排放。传统硫酸酸化可减少氨气排放量，但会导致硫化氢释放等二次污染问题，并影响后继资源化利用。本项目选取典型集约化生猪养殖场对其氨气排放特征进行了在线监测，分析了育肥期生猪固体粪便的脲酶在不同环境条件下的活性，探明了生猪尿液与固体粪便混合后，尿素水解和氨气释放的机制，并进一步对乳酸和酸性废渣代替硫酸酸化猪粪的可行性进行了研究。研究结果发现，生猪养殖场氨气排放呈现夏季高冬季低的现象。日排放量变化与环境温度、生猪进食排泄活动时间点、清粪作业时间点三个因素相关。脲酶在尿素浓度为400 mM、环境温度为35℃、pH值为7.0以及混合速率为821.8 rpm的条件下表现出最高活性。尿素水解最大反应速率和米氏常数分别为26.9±1.2mmol [urea] kg-1 min-1和99.7±3.5mmol [urea] L-1。当生猪尿液和固体粪便接触混合后，尿素的水解主要发生在前8h，但氨气的释放是一个持续的过程。因此，在生猪集中排泄的时间及时分离固体粪便与尿液，避免动物踩踏，可以从源头减少氨气的产生。对硫酸、乳酸和酸渣来讲，将猪粪pH值调整5.5最为经济，并能保证抑制氨气排放。尽管需要添加比硫酸更多的乳酸或酸渣达到pH=5.5，但15天内乳酸组的氨气减排率达83%，高于硫酸组的59%。而且乳酸在15天内会降解93%，不影响后继资源化利用。酒糟或醋渣酸化粪便同样可以减少氨气排放。酒糟组和醋渣组在30天内，氨气减排率分别达61%和57%。而且，酸渣的加入使得粪便中有机物更稳定，便于后继资源化利用。本项目研究成果对畜禽养殖业氨气排放的管控有实践意义。