Numerical Evaluation of a Negative Pressure Ventilation System for Ammonia Emission from a Solid-Covered Manure Storage Tank

Ammonia (NH3) emissions from temporary manure storage tanks represent a significant environmental concern in livestock production systems. While combining solid covers with negative pressure ventilation is a promising strategy to mitigate these emissions, there is currently a lack of systematic research on its design optimization and performance. This study employs Computational Fluid Dynamics (CFD) to evaluate the effectiveness of a solid-covered manure storage tank combined with negative pressure ventilation for controlling NH3 emissions. A validated CFD model was developed to simulate airflow and ammonia transport under open-field and covered conditions. The influences of tank headspace depth, slot type (top and side), and slot location on outlet ammonia concentration were investigated. Results show that headspace depth is one of the important parameters affecting ammonia transport, with deeper headspaces consistently reducing outlet NH3 concentrations. Compared with no-slot scenarios, top slots could increase ammonia emissions by inducing impinging-jet effects, whereas side slots exhibited depth-dependent impacts, reducing emissions at 1.0 and 1.6 m depths but increasing them at 0.4 m depth. All the differences in ammonia emission across the simulations can be attributed to the difference in the near-wall velocity. The findings provide useful guidance for the design and optimization of ammonia mitigation strategies in manure storage systems.