NH3, N2O, and NO emissions from digested pig slurry stored under different temperatures: Characteristics and microbial mechanisms

Storage temperature is a key factor in determining gas emissions from slurry storage. The reactive nitrogen-related gas (NH3, N2O, and NO) emission characteristics and resulting mechanisms from digested pig slurry stored under different temperatures of 5 (A5), 15 (B15), 25 (C25), and 35 °C (D35) were investigated in this study. Results showed that the temperature increase from 15 to 25 °C was crucial for the changes in the total chemical characteristics of slurry, the increase of gas emissions, and the nitrifiers and denitrifiers accumulation in the slurry. Chemical oxygen demand, total nitrogen (TN), and total ammonia nitrogen content of the slurry decreased while pH increased significantly during storage under C25 and D35, while no obvious changes can be found under A5 and B15. NH3, N2O, and NO emissions increased by 284%, 451%, and 454%, respectively, when the storage temperature increased from 15 to 25 °C. The highest emissions of NH3, N2O, and NO were observed in D35, with the emission factor being 42.3% ± 9.0%, 2.26% ± 0.96%, and 0.11% ± 0.03% of initial TN, respectively; while the lowest emission factor was 4.2% ± 0.2%, 0.04% ± 0.01%, and 0.0003% ± 0.0001% for NH3, N2O, and NO in A5, respectively. The high temperature caused the increased abundance of Nitrosomonas, leading to the high N2O emission in D35. Vulcanibacillus and Thauera were the dominant denitrifiers in the microbial communities, and their increased abundance was another possible explanation for increased N2O emission on C25 and D35. Therefore, regulating slurry temperature to lower than 15 °C can effectively limit the NH3 and N2O emissions, and thus contributed to the air pollution reduction and global warming control. Meanwhile, compared with the cool temperature conditions, extra mitigation options were suggested to be applied to control the gases emissions when slurry was stored under hot conditions such as in summer.