20-06-2023

Five Q&As on N2O reduction at wastewater treatment plants

Recently, we hosted a successful webinar on how to mitigate laughing gas (N2O) emissions with Advanced Process Control (APC), where we shared our preliminary results from our pilot study at Soest wastewater treatment plant (WWTP), which showed over 30% reduction in nitrous oxide emissions.

With over 12 years’ experience in this field of work, conducting research and pilots, our wastewater experts Valerie Sels & Otto Icke also shared their key learnings and insights. As we still receive a lot of questions related to this topic, we selected the five most frequently asked questions, and the answers from our experts.

1. Do Wastewater Treatment Plants (WWTPs) for BOD removal-only, also produce N2O?

There is a high risk of N2O production in carbonaceous-only WWTPs, since – especially in summer – some nitrification will occur. As the WWTP is not optimised for denitrification, N2O will be emitted. When carbonaceous plants start to nitrify, they will also typically be operating at a higher load than a fully optimised nitrifying ASP, which is likely to further increase the N2O factor. Further data is required to fully quantify the emissions factors (EFs) from these plants, and improved process control may be recommended to mitigate these issues.

2. Which process step (nitrification or denitrification) typically stands for the highest N2O-emission potential?

Typically, one of the two processes tends to be the main pathway for N2O emission per plant (or per season!), but which one depends on the configuration of the WWTP

3. Do you think the over – or too aggressive – aeration could encourage the accumulation of Hydroxylamine (NH2OH) and subsequently result in higher N2O formation, particularly in early mornings when the flow and load is low?

Yes, we think that over-aeration is one of the causes of nitrous oxide emission via the NH2OH route. We observed this at several plants in the Netherlands. The theory behind it is that at higher oxygen levels, the ammonium conversion rate is increasing and subsequently the ‘leakage’ of N2O is enhanced. This leakage always exists but will increase at higher conversion rates.

Missed our webinar on N2O reduction?

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4. Is N2O always formed no matter what we do?

N2O is always formed during denitrification, so in practice, zero dissolved N2O is not possible if you want to have full nitrogen removal of N2 gas. The target is to limit the N2O emission to air as much as possible.

5. Have you considered the difference in emissions from domestic and industrial wastewater?

We have focused mostly on WWTPs receiving domestic wastewater, since the wastewater characteristics and configurations are often comparable. An industrial wastewater site requires an individual approach, but we’re happy to discuss this further.

Do you have a specific question related to this topic or would you like to get more clarification on a specific answer? Reach out to our Water Technology experts!

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