Potential of nitrous oxide recovery from an aerobic/oxic/ anoxic SBR process

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Courtesy of IWA Publishing

Nitrous Oxide (N2O) is a kind of greenhouse gas which has a great influence on the global warming. And it is also a powerful oxidant in combustion reactions, which can improve the output power of biogas power generation from 5.7% to 7.3%. It is generally known that the amount of N2O emitted from wastewater treatment is 3% of the total global emissions of N2O. So it is of great significance for environment protection and energy recycling to investigate the potential of N2O recovery from the wastewater treatment process.

During biological wastewater treatment, processes such as autotrophic nitrification and heterotrophic denitrification, have been identified as major sources of N2O. Therefore, a single sequencing batch reactor (SBR) with an operating mode of anaerobic/oxic/anoxic (A/O/A) was developed to investigate the potential of N2O recovery.

In the nitritation process, a total N2O production of 9.6 mg/L was obtained. And the vast majority of N2O produced during nitritation was released as a gas into the air; only a small amount of this compound remained in the liquid as a dissolved material.

To investigate the role of heterotrophic denitritation in N2O production, several tests had been devised at the key points during the nitritation process. This finding demonstrates that the function of heterotrophic denitritation in N2O production in the nitritation reactor is considerable, especially under lower DO concentrations and exhaustion of the available organic carbon. Meanwhile, when the operating mode of the single SBR was A/O/A, the majority of the nitrite transformed from ammonia nitrogen during nitritation process could be converted into N2O in the later anoxic period by heterotrophic denitritation with a conversion rate of 77%.

Several different COD/N ratios were selected to investigate their effects on N2O production by heterotrophic denitritation in the later anoxic phase of the A/O/A SBR. The results indicate that COD/ N was greater than 2.2 in the influent might be necessary for completely denitrifying nitrite to N2O in the later anoxic phase.

As a result, the A/O/A SBR presents potential ability to produce and recover N2O from wastewater containing ammonia and organic carbon.

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