The Republic’s largest sewage plant in Ringsend, Dublin is to be increased in capacity by 50 per cent in a €300 million development by Irish Water.

The company is to seek planning permission this year to extend and upgrade the plant that serves Dublin city and county and parts of Meath. It has been failing to cope with the amount of sewage it receives since it opened in 2003, and has failed EU water quality tests in the last two years.

The extension will give the plant capacity to process the sewage of 2.4 million people and allow it to comply with the EU water quality directives by mid-2020.

The company would not comment on the effect of any decision by a new government to abolish Irish Water., but said the project would continue to be required. An Bord Pleanála has confirmed the planning application would not fall if Irish Water was abolished.

Irish Water has scrapped Dublin City Council’s earlier plans, approved by An Bord Pleanála in 2012, to expand the capacity of the plant by constructing a 9km pipe into the Irish Sea. The council’s €270 million project was due to begin construction in 2014.

Revised estimates

But in May 2014, four months after it took over responsibilty for water services, Irish Water said the council’s scheme would cost €340 million. It said it could achieve the same result without the pipe, using new sludge processing technology, at an estimated cost of €170 million.

The company has now radically revised these estimates and says the council’s pipe project would have cost €500-€600 million, and its project will cost €300 million, not €170 million.

“Detailed project design, from which accurate costs could only be derived for the first time, began in late 2014. The design of the project is now well advanced and realistic cost estimates are continually updated on an ongoing basis,” said a spokeswoman for the company.

“In 2015 and 2016 two independent costings were carried out to verify the likely full cost of the 2012 approved project including the tunnel. This estimated the actual total full project cost to be in the region of €500-€600million . . . the most up-to-date estimate of the upgrade without the tunnel is in the region of €300 million.”

Irish Water project manager Donal O’Connor said new technology, which has come in to use since the council applied for its scheme, will allow the upgrade of the plant to meet EU standards, and its expansion to deal with the equivalent of 2.4 million people’s waste, without the tunnel.

The sewage treatment technology known as Aerobic Granular Sludge (AGS), would allow the discharge of treated waste water to remain at its current location in Dublin Bay, removing the need to build the 9km tunnel, Mr O’Connor said.

The company has initiated an eight-week public consultation process on the projet and will apply for planning permission towards the end of this year.

Construction work is expected to start in 2017 and be completed in two phases by mid-2020.