1. Impact of aerobic granular sludge sizes and dissolved oxygen concentration on greenhouse gas N2O emission.
- Author
-
Nguyen Quoc, Bao, Cavanaugh, Shannon K., Hunt, Kristopher A., Bryson, Samuel J., and Winkler, Mari K.H.
- Subjects
- *
GREENHOUSE gases , *SLUDGE management , *ANOXIC zones , *SEWAGE disposal plants , *CARBON dioxide , *OXYGEN , *DISSOLVED oxygen in water - Abstract
• Small AGS (212–1000 μm) emitted higher N2O than large AGS (>1000 μm) at DO >2 mgO2/L. • Higher DO levels resulted in elevated N2O emissions for both small and large size fractions. • N2O reductase genes (nosZ) were more abundant in smaller granules. • Nitrification exhibited a positive correlation with N2O emission rates across all granule sizes. Aerobic granular sludge (AGS) at wastewater treatment plants (WWTPs) are known to produce nitrous oxide (N 2 O), a greenhouse gas which has a ∼300 times higher global warming potential than carbon dioxide. In this research, we studied N 2 O emissions from different sizes of AGS developed at a dissolved oxygen (DO) level of 2 mgO 2 /L while exposing them to disturbances at various DO concentrations ranging from 1 to 4 mgO 2 /L. Five different AGS size classes were studied: 212–600 µm, 600–1000 µm, 1000–1400 µm, 1400–2000 µm, and > 2000 µm. Metagenomic data showed N 2 O reductase genes (nosZ) were more abundant in the smaller AGS sizes which aligned with the observation of higher N 2 O reduction rates in small AGS under anaerobic conditions. However, when oxygen was present, the activity measurements of N 2 O emission showed an opposite trend compared to metagenomic data, smaller AGS (212 to 1000 µm) emitted significantly higher N 2 O (p < 0.05) than larger AGS (1000 µm to >2000 µm) at DO of 2, 3, and 4 mgO 2 /L. The N 2 O emission rate showed positive correlation with both oxygen levels and nitrification rate. This pattern indicates a connection between N 2 O emission and nitrification. In addition, the data suggested the penetration of oxygen into the anoxic zone of granules might have hindered nitrous oxide reduction, resulting in incomplete denitrification stopping at N 2 O and consequently contributing to an increase in N 2 O emissions. This work sets the stage to better understand the impacts of AGS size on N 2 O emissions in WWTPs under different disturbance of DO conditions, and thus ensure that wastewater treatment will comply with possible future regulations demanding lowering greenhouse gas emissions in an effort to combat climate change. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF