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Why is this project needed?

Ringsend Wastewater Treatment Plant Upgrade Project is one of the most important of a number of major investments in both water supply and wastewater that Uisce Éireann will be rolling out in the region to support the economic projections for growth for the Greater Dublin Area.

Wastewater from homes and businesses needs to be collected and treated to ensure it is not a threat to public health or the environment when returned to a river or to the sea.

Ringsend WwTP currently discharges treated wastewater into the Lower Liffey Estuary via an outfall located approximately 1km from the facility. Under the Urban Wastewater Treatment Directive, the Lower Liffey Estuary is designated as a (nutrient) sensitive waterbody.  This designation requires the WwTP to reduce nutrients (nitrogen, phosphorus) to below a specified level before discharging into a nutrient sensitive waterbody.

The Ringsend WwTP is currently operating at levels in excess of its intended design capacity, with wastewater of up to 1.98m population equivalent requiring treatment. In order to treat the current wastewater load to the required standard and to allow for future growth in population and industry, the plant must be upgraded. The need for this upgrade project was highlighted in the Greater Dublin Strategic Drainage Study (2005) and associated Strategic Environmental Assessment (2008). Uisce Éireann has assessed and reaffirmed the need for the Ringsend upgrade project.

This project will allow the Ringsend WwTP to treat the increasing volumes of wastewater arriving at the plant to the required standard and capacity, enabling future housing and commercial development and helping to ensure that Dublin is able to sustain continued growth. When all the proposed works are complete, the Ringsend plant will be able to treat wastewater for up to 2.4 million population equivalent while meeting the standards of the Urban Wastewater Treatment Directive

What solution is now being proposed by Uisce Éireann?

In 2012, Dublin City Council obtained planning consent from An Bord Pleanála under the Strategic Infrastructure Development (SID) provisions of the Planning and Development Acts. The planning consent was to expand the Ringsend WwTP to its ultimate capacity and to relocate the discharge of treated wastewater from the Ringsend plant out into Dublin Bay, through the construction of a 9km undersea tunnel.

In January 2014, the responsibility for the Ringsend WwTP was transferred to us from Dublin City Council. An advanced nutrient reduction treatment technology has been identified that was not available as an option to Dublin City Council in 2012. This technology is known as Aerobic Granular Sludge (AGS) and would allow treated wastewater to remain and be safely discharged at its current location, avoiding the need to construct the 9km long undersea tunnel in Dublin Bay.

In April 2019, An Bord Pleanála granted permission for the works required to facilitate the use of Aerobic Granular Sludge (AGS) technology, to omit the previously permitted long sea outfall tunnel and to upgrade the sludge treatment facilities at Ringsend, Dublin 4, and to provide for a Regional Biosolids Storage Facility in Newtown, Dublin 11.

The project comprises four key elements The project comprises four key elements and underpinning these is a substantial programme of ancillary works:

  1. Provision of additional secondary treatment capacity with nutrient reduction (400,000 population equivalent);
  2. Upgrade of the 24 existing secondary treatment tanks to provide additional capacity and nutrient reduction, which is essential to protect the nutrient-sensitive Dublin Bay area;
  3. Provision of a new phosphorous recovery process; and
  4. Expansion of the plant’s sludge treatment facilities.

What are the benefits of this project?

The use of this AGS technology at Ringsend will maximise treatment capacity and efficiency at the plant.

The impacts of tunnel construction will be entirely avoided, including the 70,000 heavy goods vehicles involved in removing material excavated from the 9km long tunnel. Significant project savings will also be made by not constructing the undersea tunnel.

A much higher treated effluent quality would also be achieved and, even at full future capacity, emissions from the plant would be significantly lower than at present.

The revised project also provides for the recovery of phosphorus (a non-renewable resource), this finite resource would otherwise be discharged to Dublin Bay with the loss of its re-use potential in agriculture.

What is the investment in the project?

Uisce Éireann is investing over €500 million in the staged upgrading of Ringsend Wastewater Treatment Plant. This investment will allow the plant to treat the increasing volumes of wastewater arriving at the plant to the required standard and capacity, enabling future housing and commercial development and helping to ensure that Dublin is able to sustain continued growth.

When will upgrade works at Ringsend be complete?

Uisce Éireann is investing over €500 million in the staged upgrading of Ringsend Wastewater Treatment Plant. This investment will allow the plant to treat the increasing volumes of wastewater arriving at the plant to the required standard and capacity.

This project will enable future housing and commercial development and ensure that Dublin is able to sustain continued growth. The works will be undertaken on a phased basis.

Uisce Éireann is working to provide infrastructure to achieve compliance with the Urban Wastewater Treatment Directive for a population equivalent of 2.1 million in the second half 2023. When all the proposed works are complete in 2025, the Ringsend WwTP will be able to treat wastewater for up to 2.4 million population equivalent while meeting the required standards. 

What is AGS technology?

AGS technology is based on a naturally-occurring treatment process that takes place in our lakes, rivers and estuaries where micro-organisms and bacteria breakdown biodegradable pollutants. AGS technology allows for the breakdown of biodegradable pollutants at a faster rate than would happen in the natural environment. The process is carefully controlled at a wastewater treatment plant to achieve the required effluent water quality standards set by the Environmental Protection Agency, in accordance with relevant EU Directives. AGS is an advanced nutrient removal technology that is a further development of the activated sludge process.

Why is AGS technology being proposed?

AGS technology was not available for consideration at the time of the original planning application in 2012. Since this time, wastewater treatment plants using AGS technology have also come into operation in the Netherlands, Portugal, South Africa and most recently, in Clonakilty and Carrigtohill, Co. Cork.

We have conducted detailed testing and trials of the technology since April 2015 to treat the wastewater being received at the Ringsend plant. These trials have proved successful; confirming that wastewater treated by AGS technology can be safely discharged to the Lower Liffey Estuary and Dublin Bay.

What happens when there is a storm water overflow?

The sewer system in Dublin was built in the 1900s and, as was typical at the time, it carries both wastewater from homes and businesses and water that is drained off roads and pavements. When more rain and wastewater than the plant can process arrives, the excess is held in storm water holding tanks. Normally, when the rain has passed, the excess in the storm water holding tanks enters the plant for treatment. 

When there is unusually heavy and sustained rainfall, such as during a yellow weather warning, the amount of water entering the sewer network can be more than the capacity of the plant and the holding tanks. In that case, to prevent the sewer network from backing up and causing flooding of roads and properties, the storm water is released from the holding tanks to the environment. The storm water tank overflow contains wastewater that is highly diluted with rainwater and has been screened and settled to remove debris – a form of primary treatment.

The current upgrade of Ringsend means that the capacity will be increased and these incidents will be fewer in number although in extreme weather conditions they could still occur.

Uisce Éireann would like to reassure people that there should be no lasting effects on bathing waters. The tide will wash out the spill and the salt water and sunlight acts to clean the water. Uisce Éireann apologises for any inconvenience caused and regrets the impact that overflow incidents may have on beach users. 

Why is there sometimes a smell?

When emptied following a rainfall event it is necessary to clean out the storm water holding tanks to prevent odours.  Any debris or sediment is moved into the treatment plant, where it is treated as normal. The tanks are also washed down manually. Unfortunately, the process of removing the debris from the tanks may create a certain amount of odour and Uisce Éireann apologises to people in the area for any inconvenience caused.

What happens if there is an incident or overflow?

Uisce Éireann notifies Local Authorities and the EPA of any incidents or overflow that occur at the plant that could impact the receiving waters. During the Bathing Water season, 1 June – 15 September, Local Authorities and the EPA monitor and report on the quality of designated bathing waters. This is to protect public health and to ensure that water users can be confident that designated areas meet the strict standards for bathing waters set out by the EU.  
Bathing water quality can be impacted by a number of factors, such as unlicensed discharges and dog fouling. The Local Authority collects information on bathing water quality on a regular basis and, in consultation with the HSE, provides information and guidance on using bathing waters and about any prohibitions. It is important for water users to check the Local Authority website or or notice boards on beaches for the latest information. 

Why does discolouration occur / what is the cause?

Currently the Ringsend wastewater treatment plant treats approximately 40% of the country’s wastewater load. In order to treat the increasing volumes of wastewater arriving at the plant to the required standard Uisce Éireann is investing over €400 million in the staged upgrading of Ringsend.

The effluent is treated to the highest standards currently achievable at the existing plant.

Uisce Éireann is increasing the capacity of the plant and we are working with holders of trade effluent licences to ensure that inappropriate materials are not being disposed of through the sewer network.

It should be noted that even after all the upgrade works have been completed there will always be a colour variation where the two water bodies meet.

Is it safe to use the water in the bay or the beaches when or after discoloured water is visible?

Uisce Éireann notifies the Local Authority of any incidents or overflows that occur at the Ringsend plant that may impact bathing waters. The Local Authority, in consultation with the Health Service Executive, provides information and guidance on using bathing waters and notifies the public about prohibitions. 

Water users should be aware that the Bathing Water season starts on the 1 June and ends on the 15 September. It is important for water users to check the Local Authority website and notice boards on beaches for the latest information on bathing water quality. 

It is important to note that the Bathing Water Regulations do not apply to beaches/waters that are undesignated, such as waters around the outfall pipe for the Treatment plant, Shelley Banks beach, the South Bull Wall and the North Bull Wall near Dollymount Strand. 

You can find further information at and on

How long does a discolouration last for?

A number of factors influences formation of discoloured water and how long it will last such as the composition of the discoloured water, the tides and the weather. 

What is an EIAR?

An Environmental Impact Assessment Report (EIAR) is an analysis of the likely effects (good and bad), that a proposed development may have on the environment. This includes any likely effects on people, flora, fauna, soil, water, air, landscape and cultural heritage.

What is an EIA?

An Environmental Impact Assessment (EIA) is the process of identifying, predicting, evaluating and mitigating the possible effects on the environment of a project before a decision is made whether or not to proceed with that project. The steps in the EIA process are set out in national and EU legislation. Most large-scale infrastructure projects are subject to EIA as part of their planning consent process.

When a project proposer submits its application for consent to An Bord Pleanála it must include an Environmental Impact Assessment Report (EIAR) describing the project and its anticipated effects on the environment. A period of public consultation then follows, during which the public and any interested body may make comments and observations to An Bord Pleanála on the project and its environmental effects. An Bord Pleanála must then undertake an environmental impact assessment of the project before making its determination on the application.

What is an NIS and Appropriate Assessment (AA)?

The Birds and Habitats Directives of the European Union (EU) set out various procedures and obligations including the establishment of Special Protection Areas (SPA) and Special Area of Conservation (SAC) for the protection of specific habitats and species. Collectively, the SPAs and SACs established throughout the EU comprise a network known as Natura 2000.

The Habitats Directive imposes a duty on Member States to consider the possible nature conservation implications of any project on the Natura 2000 site network before any decision is made to allow that project to proceed. This assessment procedure is known as Appropriate Assessment and is quite similar to the EIA procedure. It is normally undertaken at planning consent stage by An Bord Pleanála.

Like the EIA procedure, a document is prepared by the project proposer and submitted with its application for project consent. This document is known as a Natura Impact Statement (NIS). While there is significant overlap between the EIA and AA processes, it should be noted that the NIS and AA only consider and assess impacts on the Natura 2000 network and that AA is a separate legal consent process distinct from EIA.

How can I view the application documents?

The application may be viewed/downloaded at