Treating wastewater emissions seriously

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New Zealand’s Zero Carbon Act introduced a framework for managing greenhouse gas emissions, including targets to reduce biogenic methane to 24-47% below 2017 levels by 2050.

Water New Zealand

Process emissions knowledge, project managementThe document helps New Zealand wastewater organisations to effectively assess their greenhouse gas emissions

Biogenic emissions from ‘wastewater treatment and discharge’ can be a substantial part of the carbon footprint for organisations operating wastewater treatment plants. Water New Zealand wanted to provide a standardised method for assessing the emissions generated by wastewater treatment processes.


The Zero Carbon Act in New Zealand introduced a framework for managing greenhouse gas emissions, but no sector specific tools. While direct emissions of methane and nitrous oxide form wastewater treatment and discharge only contribute 0.5% of national levels, for councils and council-controlled organisations operating wastewater treatment plants, emissions from wastewater and sludge treatment can be a substantial part of their carbon footprint – in some cases as high as 70%.


Water New Zealand established a climate change special interest group in 2020, including a sub-group focussing on mitigation of emissions. Mott MacDonald played a lead role in chairing and coordinating the group, which soon established the need to create guidance for assessing process emissions from national wastewater treatment plants. To fill knowledge gaps, a standardized approach for determining the wastewater treatment process, discharge and sludge emissions was created. Due to a limited budget, much of our work was completed pro bono.


A guidance document was produced collaboratively that is clear and accessible to asset owners, allowing for informed and low-emission investment decisions, and providing the information necessary to help New Zealand organisations undertaking wastewater treatment to effectively assess their greenhouse gas emissions. The guidelines also set out to improve data collection for improved emissions knowledge nationally.

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