Partial Pit Exhaust Improves Indoor Air Quality and Effectiveness of Air Cleaning in Livestock Housing: A Review

Abstract

Abstract. Ammonia and odor emissions from livestock production systems cause negative impact on atmospheric environment and local society. It is, therefore, important to develop cost-effective methods to reduce these emissions. Air cleaning technologies, including chemical and biological filters, have been proposed to clean the exhaust ventilation air from confined livestock buildings. However, it requires large capacity of the air cleaning unit for the total exhaust air and, consequently, results in high investment and operational costs of the livestock production system. Aiming at emission reduction and optimal indoor air quality of confined farm animal buildings, a concept of partial pit ventilation has been investigated in varied conditions in Denmark. Partial pit ventilation is based on the hypothesis that the most polluted air can be removed by a separate air exhaust near the pollution sources in pit head space, while the room air exhaust is kept as a major ventilation exhaust and controlled according to indoor thermal conditions. The airflow rate of the partial pit air exhaust is designed and controlled as only a small portion of the designed ventilation capacity of the building. By cleaning the pit exhaust air only, the required capacity for a cleaning unit will be significantly reduced. The investigations in Denmark, mostly in growing-finishing pig housing, have shown that partial pit air exhaust can remove a large share of the ammonia, hydrogen sulfide, and odor from the room using a pit air exhaust rate of 10% of the designed ventilation capacity, which is equivalent to 10 m3 h-1 pig-1 for growing-finishing pig housing. This article provides an overview of the investigation results currently available on a partial pit air exhaust (PPAE) system, including both numerical simulations and experimental investigations, to identify important factors that may affect the system performances for removal of ammonia and other pollutants from the animal housing and to address the extension work that may be needed to apply the method in actual production scales. It is shown that PPAE is an effective approach to reduce emissions by combining an effective exhaust cleaner. The system can significantly improve the indoor air quality, because a considerable amount of the concentrated pollutants in the air are removed directly via PPAE. The pollutant removal via PPAE is influenced by airflow patterns, airflow rates, and locations of PPAE openings in pit headspace. Therefore, configuration and control of ventilation systems are crucial for system efficiency. Besides, slatted floor openings, as well as animal lying behavior and location, can also influence the pollutant removal ratio by a PPAE. To achieve an optimal design and control of the system, further systematic investigations, both experimental and numerical, are still needed.