Image of wastewater treatment facility with WASTEMISSION text and the Trinity College Dublin Logo, as well as the Environmental Protection Agency Logo

Project Team

  1. Professor Laurence Gill
  2. Professor Aonghus McNabola
  3. Professor Muhammad Ali
  4. Alejandro Criado Monleon


Research will be conducted from Trinity College Dublin, but research sites are located nationwide in Ireland.


Human activities, particularly the release of greenhouse gases (GHGs) from various sources, have contributed to climate change. In response to this global crisis, international conferences known as COPs have been organised to address climate-related issues. The pivotal COP21 led to the creation of the Paris Agreement in 2015, a legally binding treaty aiming to limit global warming to 2 degrees Celsius above pre-industrial levels. The preferred target, however, is a 1.5-degree increase. Signatory countries, including Ireland, commit to monitoring and reducing GHG emissions through National Inventory Reports (NIRs), aligning with global efforts to combat climate change.

Ireland, in line with various national and international agreements, has set targets to reduce emissions. The European Union's Effort Sharing Decision establishes binding annual targets for Member States, and Ireland's commitment includes a 20% reduction in emissions compared to 2005 levels. Methodologies and procedures have been developed to report GHG emissions, providing a basis for analysing trends and implementing mitigation measures.

National Inventory Reporting (NIR) is a crucial tool used by UNFCCC member states to analyse emission categories, trends, and uncertainties associated with raw emission data. The approach varies from generic Tier 1 methods to country-specific Tier 2 and Tier 3 methods, with higher tiers offering more accurate reporting. The NIRs provide insights into key polluters, contributing to the development of effective mitigation strategies.

In Ireland, the latest NIR published in 2022 reveals that CO2, CH4, and N2O are major contributors to GHG emissions. While total emissions increased by 6.1% from 1990 to 2020, the waste category, including wastewater treatment, experienced a significant drop of 41.8%. Wastewater treatment contributes to CH4, and N2O emissions, accounting for 8.8% and 17.7% of total emissions from the waste sector, respectively. However, estimations are considered uncertain due to limited case studies and reliance on secondary assumptions.

The study also highlights GHG emissions from wastewater treatment processes, emphasizing the complexity of microbial processes involved. Most research has focused on large-scale centralised systems, and few studies have directly measured emissions from decentralised or on-site systems. In Ireland, over one third of the population relies on on-site domestic wastewater treatment systems (DWWTS), contributing to approximately 9.99 kg-CO2eq per person per year. The project aims to provide a detailed understanding of emissions from both centralised and on-site systems, informing strategies for reducing their impact.

In conclusion, this research seeks to address Ireland's commitments to climate agreements by improving the accuracy of GHG emissions reporting and developing effective mitigation strategies, ultimately contributing to the global effort to combat climate change.

Funding Agency

Environmental Protection Agency Research Grant


This research project addresses the critical need to advance our understanding of greenhouse gas (GHG) emissions from wastewater in Ireland, encompassing both domestic and industrial sources. With Ireland facing challenges in meeting ambitious 2030 GHG reduction targets, this study aims to improve the accuracy of existing emission databases, integrate advanced methodologies into analyses, and propose strategies for future emissions reduction.

The research, led by the Environmental Protection Agency (EPA), targets the gaps in current estimates of non-carbon dioxide GHGs, such as methane and nitrous oxide, from wastewater treatment. It takes a comprehensive approach, examining both centralised wastewater treatment plants and on-site domestic wastewater treatment systems. Notably, the study explicitly includes septic tanks in its analysis, recognizing its significance in the emissions landscape.

By investigating the impact of various treatment processes on GHG emissions and conducting field measurements across Ireland, the project aims to provide updated emission factors for diverse wastewater treatment processes, covering both municipal and industrial sources. This approach is expected to yield more accurate estimates, reduce uncertainties, and enhance our understanding of the sources of GHG emissions in the country.

The research is interdisciplinary, involving collaboration with experts in environmental microbiology, process engineering, and sewer network understanding. Stakeholder knowledge from organizations like Irish Water and the EPA will be leveraged to ensure a holistic approach. The project emphasizes engaging with homeowners of on-site systems and addressing unique challenges associated with municipal and industrial wastewater to formulate informed strategies for mitigating GHGs and other air pollutants from wastewater treatment plants.

Additionally, the project includes a trial to validate and optimise GHG surveying methodologies, aiming to improve reporting on emissions within wastewater treatment facilities. The trial will generate emission profiles for different wastewater treatment systems, utilizing direct measurements from chamber surveys.

The research aligns with the broader national trends, where GHG emissions from wastewater treatment systems have increased over the years. The current estimation methods, relying on generic inputs and secondary assumptions, introduce significant uncertainties. The WASTEMISSION project aims to reduce these uncertainties, offering more accurate inventories of greenhouse gas emissions from municipal sites, normalized to Kg CO2eq per person per year for CH4 and N2O.

In summary, the project endeavours to provide Ireland with the knowledge and tools necessary to move towards more accurate Tier 3 methodologies for calculating wastewater emissions, ultimately facilitating informed strategies to mitigate GHGs and air pollutants from wastewater treatment systems.

Expected Project Benefits

This research holds immense significance for Ireland's commitment to climate mitigation by advancing our understanding of greenhouse gas (GHG) emissions from wastewater treatment. Beyond accurate reporting methodologies and identifying key contributors, the study aims to explore ways to improve treatment operational designs. By focusing on both centralised and on-site systems, the research seeks to provide actionable insights for enhancing treatment processes, potentially reducing GHG emissions. The outcomes have the potential to inform operational designs that not only align with global climate objectives but also contribute to more sustainable and environmentally friendly wastewater treatment practices. Ultimately, this research promises tangible benefits, including improved climate action planning, reduced uncertainty in emission estimates, and the development of innovative strategies for a greener future.


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