Abstract
To explore the main behavior and mechanism of minimizing nitrous oxide (N2O) emission through intermittent aeration during wastewater treatment, two lab-scale sequencing batch reactors operated at intermittently aerated mode (SBR1), and continuously aerated mode (SBR2) were established. Compared with SBR2, the intermittently aerated SBR1 reached not only a higher total nitrogen removal efficiency (averaged 93.5%) but also a lower N2O-emission factor (0.01–0.53% of influent ammonia), in which short-cut nitrification and denitrification were promoted. Moreover, less accumulation and consumption of polyhydroxyalkanoates, a potential endogenous carbon source promoting N2O emission, were observed in SBR1. Batch experiments revealed that nitrifier denitrification was the major pathway generating N2O while heterotrophic denitrification played as a sink of N2O, and SBR1 embraced a larger N2O-mitigating capability. Finally, quantitative polymerase chain reaction results suggested that the abundant complete ammonia oxidizer (comammox) elevated in the intermittently aerated environment played a potential role in avoiding N2O generation during wastewater treatment. This work provides an in-depth insight into the utilization of proper management of intermittent aeration to control N2O emission from wastewater treatment plants.
Highlights
Nitrous oxide (N2 O) is considered to be the dominant contributor to the deterioration of the ozone layer [1,2] and act as a greenhouse gas (GHG) with a stable-state lifetime of 114 years and global warming potential 298 times greater than that of carbon dioxide (CO2 ) [3]
N2 O-emission factors could achieve up to 95% and 14.6% for lab-scale and full-scale wastewater treatment plants (WWTPs), respectively [8]
Another reactor (SBR2) was operated with each cycle consisting of 2 h anoxic period and 4-h continuous aeration with an airflow rate of 90 mL/min, followed by the same settling, withdrawal and idle periods as SBR1
Summary
Nitrous oxide (N2 O) is considered to be the dominant contributor to the deterioration of the ozone layer [1,2] and act as a greenhouse gas (GHG) with a stable-state lifetime of 114 years and global warming potential 298 times greater than that of carbon dioxide (CO2 ) [3]. It is of great importance to identify anthropogenic sources of N2 O for the purpose of emitting less GHG to the global atmosphere [4,5]. GHG emission [6] and make up for 3.2–10.2% of the anthropogenic source of N2 O [7]. The. N2 O-emission factors (emitting amount of N2 O-N divided by the nitrogen load) could achieve up to 95% and 14.6% for lab-scale and full-scale WWTPs, respectively [8]. For WWTPs, N2 O is mainly produced in biological nitrogen removal (BNR) via nitrification and denitrification, including three main pathways: (1) nitrifier denitrification (ND)—the canonical ammonia-oxidizing bacteria (AOB) utilize nitrite as an alternative electron acceptor instead of oxygen (O2 ) to produce N2 O as a byproduct under anoxic conditions or high nitrite concentrations [10,11]; (2) heterotrophic denitrification (HD)—the imbalanced activities of nitrogen-reducing enzymes in heterotrophic denitrifiers result in
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