Mechanical failure

On the morning of Saturday 23 February, 2019 there was an mechanical failure at Ringsend Wastewater Treatment plant which caused a temporary incident whereby a discharge of partially treated wastewater that contained activated sludge entered the Lower Liffey estuary. The discharge was stopped within 20 minutes when the tank was isolated. It is estimated that 100 cubic metres of partially treated wastewater was discharged. This is less than 1% of the hourly flow at the plant.


Irish Water regrets this incident and thanks those engineers on site who worked quickly to limit the damage caused by the mechanical failure at the pipework at the aeration tank. As this was categorised as a low level incident, operators followed agreed protocols and the EPA were notified the next working day, Monday 25 February.

Investigation ongoing

As a result of Irish Water’s ongoing investigations, we now know this mechanical failure may have been a contributing factor to the plume shown in the aerial photograph but it was not the primary cause. The plume was the result of the plant being significantly overloaded. The effluent that was discharged into Dublin Bay over the weekend and formed the plume was not raw sewage as it had already gone through a number of treatment stages.

In the days prior to the formation of the plume, the total solids received at the plant were significantly higher than the design capacity of the plant. The plant is designed to treat an average of 101 tonnes of solids per day. On Friday 22 February 2019, approximately 300 tonnes of solids were received at the plant.


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 and capacity, Irish Water is investing over €400 million in the staged upgrading of Ringsend Wastewater Treatment Plant.

Plant development

Work on an upgrade to add an additional 400,000 population equivalent to the Plant started in February 2018 and in June 2018, Irish Water submitted an application for strategic infrastructure development to An Bord Pleanála to further progress the upgrade of the Plant utilising Aerobic Granular Sludge (AGS) technology.

This upgrade project when completed will enable the plant support the wastewater needs for a population equivalent of 2.4 million, supporting future population growth and ensuring the plant operates to the highest possible environmental standards. Irish Water is committed to safeguarding the environment and ensuring all wastewater is correctly treated and is safely returned to rivers, lakes and sea.

Irish Water is working with the EPA and our colleagues in Dublin City Council to analyse water samples from the discharge point and to agree any actions that might need to be taken as a result.

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