Plant gives back clean water to Dublin Bay

People who swim in Dublin Bay later this month will do so in waters which are cleaner than they have been for almost 100 years.

The clean-up of Dublin Bay which has already resulted in Blue Flags being awarded to Sandymount and Merrion strands, as well as the once notoriously polluted Dollymount strand, will finally see the end of the dumping of raw sewage into the bay.

The work, known for almost a decade as the Dublin Bay Project, is part of a €300 million investment in upgrading the water quality of the bay.

The project involved replacing the old treatment works at Ringsend, much of which was constructed in 1906, with a new three-stage treatment plant while the existing plant remained open.

Sewers as far apart as Bulloch in Dalkey and the nose of Howth were tied in a new pumping station built in Sutton. When switched on later this month, it will drive north Dublin's waste water under the bay through the largest undersea waste water pipeline in the world, to Ringsend.

The Dublin Bay clean-up represents the largest civil engineering project of its kind in Europe. The Ringsend site has already become something of a visitor attraction to engineers from EU applicant countries.

State agencies in the applicant countries view the plant - which supplies 60 per cent of its own energy through the extraction of methane gas - as an effective use of what will be available to them under EU structural funds.

The plant uses only natural methods to purify the waste water, avoiding large-scale disinfectants or any antibacterial contamination which would harm the anaerobic process involved.

The waste water is first run through a screen which removes visible debris, then a series of aerating and decanting processes to separate sludge. Sludge is dried and heated to several hundred degrees, which removes any pathogenic contamination, and is sold to the agricultural industry where it is used as fertiliser throughout Leinster.

The remaining water can then be run through a tertiary treatment stage involving ultra-violet light which eliminates any residual contamination before being released into the bay.

The result is a remarkable turnabout in the quality of the bathing water in the bay and at little cost to the taxpayer.

Dublin City's Council's deputy chief engineer, Mr Battie White, who has overseen the project since its inception, says it was about 80 per cent funded by Europe, with the remainder coming from a levy on commercial interests in the city which are large water users.

According to Mr White, the original cost of the scheme in 1994 was about £200 million (€254 million), but additional works at Ringsend to install another dryer alongside additional aeration capacity pushed the cost up towards €300 million.

Massive inflation in the construction industry down the years has had little effect on the cost of the plant, which now has the capacity to handle Dublin's projected population increase until 2020.

This is due to the "design and build" nature of the contract, said Mr White.

"Our obligation was to hand over the agreed price, and be given ownership of the facility."

In fact, according to Mr White, when construction industry inflation of about 104 per cent over the last nine years is factored in, there is a substantial reduction in the real cost of the project.