Impact of anaerobic digestion on reactive nitrogen gas emissions from dairy slurry storage. (15th August 2022)

• Record Type: Journal Article
• Authors: Wang, Yue; Liang, Lina; Liu, Jingyi; Guo, Dongpo; Zhu, Zhiping; Dong, Hongmin
• Is Part Of: Journal of environmental management. Volume 316(2022)
• Publication Date: 2022-08-15
• Subjects: Reactive nitrogen gas -- N balance -- Nitrogen transformation -- Microbial community -- Functional genes; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2022.115306
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Biogas digesters are commonly used to treat animal manure/slurry, and abundant digested slurry is generated during the digestion process. Gas emissions from digested and raw slurry may vary with the change in slurry parameters after digestion, but the mechanism is not well understood. Gas emissions from raw dairy slurry (RS) and digested dairy slurry (BS) during 98 days of storage were investigated in this study to evaluate the effects of anaerobic digestion on reactive nitrogen emissions from slurry storage. Results showed that much higher N2 O and NO emission and lower NH3 emission was achieved in BS than in RS. The mean gaseous emission of RS and BS accounted for 27.8% ± 6.9% and 17.1% ± 2.3% of the initial TN for NH3, 0.1% ± 0.1% and 3.5% ± 1.6% of the initial TN for N2 O, and 0.0% ± 0.0% and 0.2% ± 0.0% of the initial TN for NO, respectively. Among all detected N2 O-forming and reducing microbial genes, the abundance of amoA genes was the most closely related to N2 O flux (r = 0.54, p < 0.01). More aerobic conditions occurred in BS, and dissolved oxygen (DO) increased to 0.4–1.6 mg L −1 after 35 days because the low organic matter of BS resulted in good infiltration of surface air into the slurry. The increased DO stimulated the growth of Nitrosomonas and the increase in amoA gene copies and contributed to the high N2 O and NO emissions in BS through the nitrification process. Vulcanibacillus, Thauera, Castellaniella, and Thermomonas were the major denitrifying bacteria that occurred in BS and caused an incomplete denitrification process, which could be another reason for the increase in N2 O and NO emissions from BS. Our study indicated that anaerobic digestion reduced the organic matter content of the slurry and caused an active microbial environment that facilitated the transformation of slurry N to N2 O in BS storage, thus lowering the NH3 emission compared with RS storage. Therefore, aside from NH3, N2 O should also be preferentially mitigated during BS storage because N2 O is a greenhouse gas with high global warming potential. Graphical abstract: Image 1 Highlights: BS emitted lower NH3 (50%) but higher N2 O (24.4 times) and NO (2.9 times) than RS. Low slurry OM was key reason for DO increase and N2 O emissions in BS. amoA gene functioned to N2 O emission with correlation factor of 0.54 (p < 0.01). Nitrification and incomplete denitrification dominated N2 O emission in BS. Nitrosomonas and Vulcanibacillus were key bacteria functioned in N2 O emission.