Waste water facilities in Tullamore are being upgraded in order to provide additional capacity and meet the requirements of the Wastewater Discharge Licence.
Offaly County Council are behind the project to construct a new waste water treatment plant (WWTP) for Tullamore town and a sludge treatment centre (STC) to service the entire county. The council purchased an additional 5 ½ acres of Greenfield land adjacent to the existing treatment plant site in order to accommodate the new facilities. The site is located close to the town, adjacent to a nearby railway embankment and Tullamore River.
When the project is complete, the fully licensed plant will meet the required effluent discharge standards of 8 milligrams per litre biochemical oxygen demand (BOD), 125 milligrams per litre chemical oxygen demand (COD) and a total phosphorous limit of 5 milligrams per litre.
The existing plant was designed to provide water treatment services for a population equivalent (PE) of 16,000 but is currently having to provide treatment for up to 25,000 PE. The new plant will provide waste water treatment capacity of 45,000 PE in a modular design that can accommodate expansion to 60,000 PE if required in the future. Boasting the capacity to provide for 80,000 PE, the new sludge treatment centre will cover the requirements of the entire county of Offaly.
Construction work began on the site in May 2010 under a Design Build and Operate (DBO) contract with the DB element worth €20 million. The contractor is a joint of venture of SIAC Construction Ltd and EPS Pumping and Treatment Systems, whilst the consulting engineer is T J O’Connor & Associates. Once the site has been commissioned, EPS Pumping and Treatment Systems will take over the operation of the plant under a 20-year operate contract valued at €17 million.
Work has included the construction of a new two-storey preliminary treatment works building and an administration building. The inlet works building is constructed of reinforced concrete with a structural steel roof; the administration building is constructed of block work and both buildings are clad with Kingspan insulated panels.
Preliminary treatment consists of mechanical screening, grit removal and grease removal. Primary settlement is then provided by two 25.4m diameter circular tanks, constructed with precast concrete and post tensioned sections. The tanks are covered to facilitate odour removal and contain rotating half bridges with bottom scrapers and sludge removal pipe work.
Following primary treatment, the wastewater is discharged to a reinforced concrete tank containing three aeration lanes, each of circa 1900m3 volume, with an operating depth of 5m. Diffused air is provided through proprietary plate diffusers, rather than the more common dome type diffusers, to provide a more efficient system. Storm storage of 3,600m3 is provided by the construction of two reinforced concrete tanks adjacent to the aeration tanks with shared end walls. The storm tanks are also covered to facilitate odour removal.
Final settlement of the wastewater is provided via two circular concrete tanks of 27.8m diameter, with rotating half bridges, bottom scrapers and sludge removal pipe work. A proprietary filtration system is also being used to provide tertiary treatment.
The STC is a structural steel frame building clad with Kingspan insulated panels. The WWTP will process waste sludge to the STC, which will also have facilities to accept imported cake and liquid sludge from other plants in the county. Imported and indigenous sludge is blended and thickened in preparation for final treatment, which consists of Mesophilic Anaerobic Digestion followed by a process of thermal drying.
Comprehensive odour control measures have been included throughout the plant to meet the employers’ requirements in respect of the odour concentration at the site boundary.
Improvements have also been made to inlet sewers in order to upgrade the influent entry system for the plant. On the existing site, influent entered via a single sewer inlet under a railway embankment, with a diameter of 750mm. However, this has now been replaced with a 1200mm diameter sewer which was pipe jacked under the railway embankment close to the existing inlet sewer. A second 450mm diameter inlet sewer has been provided in the northern boundary of the site whilst a third 900mm diameter inlet sewer has been constructed under the Tullamore River. For this third sewer inlet to be constructed, the flow of water from the Tullamore River had to be diverted until the construction was complete.
Offaly County Council Senior Engineer for Water Services, Tom Shanahan said:
“A project like this is very important for the future development of Tullamore as not only does it provide more than adequate facilities for waste water treatment, but the inclusion of a sludge treatment centre enables us to dispose of all our sludge in an environmentally acceptable manner.”
The existing plant will be completely decommissioned but Offaly County Council will maintain the buildings for storage and general usage, meaning the former facility will not go to waste.
Civil and mechanical works are now almost complete and the plant is currently in the stages of process proving and commissioning.
Landscaping will include the planting of indigenous trees and hedges, whilst an earth mound will be used to help screen the facility.
The waste water treatment plant and sludge treatment centre will be fully operational by July 2012.