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The U.S. egg industry is the world’s second-largest egg producer with an annual production of 5.6 billion kilograms of eggs and provides 81,515 jobs and $22.77 billion to the economy. Due to the very large-scale and concentrated operations, the egg industry is facing crucial challenges in reducing its significant environmental impacts and solving indoor air quality problems. Egg production is a significant contributor of air emissions to the atmosphere, especially ammonia (NH3) emission, which has caused serious concerns on health and the environment, such as soil and water acidification, visibility impairment, and respiratory diseases. Effective management and mitigation of NH3 emissions from layer operations are urgently needed but are limited because of the lack of effective tools for estimating NH3 emissions. It is also in the egg industry’s and the public’s interests to understand the health and environmental impacts of NH3 on the neighboring communities. The U.S.EPA regulatory air dispersion model AERMOD needs to be evaluated for its performance in estimating NH3 dispersion after being emission from layer houses. In addition, heat stress is a serious problem in layer houses with annual losses of $61-98 million nationwide due to impaired egg production. Global warming further worsens the heat stress problem due to increasing events of hot weather and heavier precipitation. Exposure to high-concentration NH3 is another risk to layers and workers. It damages layers’ immune system and egg production and affects workers’ health. The problems of heat stress and NH3 exposure are aggravated in layer houses due to non-uniform airflow resulted from current ventilation systems. The knowledge of the spatial and temporal distribution of heat stress and NH3 concentrations inside layer houses is essential for assessing the associated risks of layers and workers and developing mitigation strategies, but is not yet available.This dissertation aims to fill the gap by developing new knowledge and tools for managing the indoor environment to improve animal welfare and production performance and reduce adverse impact of NH3 emission on health and the environment. Specifically, the temporal and spatial variations in thermal air conditions and NH3 concentrations distribution inside manure-belt layer houses and the associated risks were simulated using developed computational fluid dynamics (CFD) models. Ammonia emission factors for manure-belt layer houses were measured to fill the gap of the existing emission factor inventory and to develop and validate NH3 emission estimation models. A mechanistic NH3 emission model was developed using a laboratory-scale wind tunnel chamber for understanding the fundamental mechanisms involved in NH3 release processes. Based on the mechanistic model, a farm-scale quasi mechanistic NH3 emission model was developed to estimate NH3 emission from manure-belt layer houses. The model can be easily adopted by producers and regulators. The U.S.EPA regulatory air dispersion model, AERMOD, along with a dynamic air dispersion model, CALPUFF, were preliminarily evaluated for their applications in estimation of NH3 dispersion and deposition after emission from the layer houses. Collectively, the results of the dissertation contribute to enhancing indoor environmental quality and effective management and mitigation of NH3 emissions from manure-belt layer houses for the sustainability of the egg industry in the U.S. |
