In September 2014, a one-year design and build project to almost double the capacity of the Mutton Island Waste Water Treatment Plant was completed. Murphy is currently operating and maintaining the facility on a 20-year contract.
The project brief was to increase the capacity of the plant by more than 85 per cent to serve a population of 170,000, while maintaining operation of the existing plant without any outage. The upgraded plant is operated as a non-nitrifying plant, which allows additional aeration capacity, increasing the load that can be treated at Mutton Island.
The project was significantly constrained by Mutton Island sitting within Galway Bay, which is a Natura 2000 site with a Special Protection Area (SPA), designated under the Birds Directive 79/409/EEC and a Special Area of Conservation (SAC), designated under the Habitats Directive 92/43/EEC. It is also a Ramsar Convention Wetlands site and in regular public use for bathing, sailing, fishing and other water-based leisure uses.
A new Combined Heat & Power plant was installed, fired by waste gas released during the treatment process and across the whole installation a new System Control Acquisition of Data and Analysis (SCADA) system was designed and installed by Murphy engineers.
Because of the imperative of maintaining the water quality in the bay, a new overflow catchment system was designed and installed to prevent any noxious discharge in to the bay.
The €5.7m design and build element of the work was completed on time and on budget.
Continued, uninterrupted operation of the existing plant, whilst new facilities were built alongside, was an absolute imperative. At the same time, reliability problems with the existing plant had to be addressed.
In total, five major elements of the existing plant had to replaced or upgraded to ensure the future reliability of both the new and existing plants. These included:
- New inlet screening/conditioning plant replaced and integrated with site-wide SCADA to provide automated control, allowing targeted flushing to eliminate blockages
- Replacement of over-loaded drum thickener plant with largest available model for the plant room, replacement feed pumps, new flocculation tank and automated feed pumps ensuring greater operator flexibility.
- A full mechanical and electrical remodelling of cake centrifuge, pumps and discharge system to reduce load so creating a duty/load system to enhance reliability
- Improved polyelectrolyte dosing system catering for varying sludge flow and concentration.
- A new system of wheel carriages and bridge motors was installed to ensure continued operation of the primary settlement tanks
- Two new pumping stations were constructed in-line with the existing settlement tanks and aeration lanes, both with interchangeable pumps so operation can continue in the event of pump failure
As a result of the upgrade and expansion of the facility by Murphy, the plant has been in continuous operation without any blockage or other failure since July 2015, handling flows in excess of 170,000m3/day in storm conditions.
Project delivery and innovations
- Conversion of two primary settlement tanks to final clarifiers and a switch to a non-nitrifying process allowed an increase in capacity sufficient to serve 170,000 people’s needs every day.
- A thorough review of plant layout and logistics led to a redesign of plant in to a more efficient configuration which requires less intensive use of plant and is designed for in-line maintenance without loss of operating capacity.
- Design and construction in-house of innovative overflow screen incorporating a weir for flow measurement.
- Integration of stand-alone sludge disintegration units to increase the bio-gas production, improving the efficiency of the on-site CHP facility.
- Use of GRP composite and high grade stainless steel components to ensure no degradation of the highly sensitive environment in Galway Bay.
- No reduction in operation of existing plant throughout the design and build phase of the contract
- 85% increase in throughput capacity with increased reliability
- No environmental degradation of bathing water or habitat
- Improved energy output from on-site CHP
- No accidents or RIDDOR incidents on site
- Extensive collaboration between client, design team, specialist suppliers and Murphy to deliver on time and on budget