Osberstown (Naas) WWTP
Client: Kildare County Council
Engineer: TJ O'Connor & Associates
Architect: N/A
Value: c €21M
Period: March 1999 - March 2001


The Stage II upgrading of the Osberstown WWTP began construction in 1999 and was completed in 2001. The plant was designed and built by a joint venture of EarthTech Ltd and SIAC Construction Ltd (SETJV). The work was the first 'design and build' operation conducted by a local authority in Ireland. The design was to upgrade the existing 40,000pe plant to an 80,000pe plant to reach certain BOD, COD and SS targets, incorporating nutrient reduction on the liquid stream. In addition, the sludge produced was to be treated by anaerobic digestion followed by dewatering.

Part of the existing works, built in 1981, was incorporated into the new design, with the retention of the primary settlement tanks as part of the liquid treatment and the use of the final clarifiers as storm tanks. In essence, a new inlet works/screening/degritting area, SBR aeration tanks (CASS® Tanks), digestion facilities and sludge dewatering facilities were constructed. Also, an administration building incorporating a training room, offices and laboratories was provided for in the contract.

SIAC’s scope included all the civil engineering and building works, including all associated pipeworks, storage and settlement tanks, structures, buildings and a road improvement of approximately 1km adjacent to the site entrance.