Ringsend WwTP (2026)

Retrofitted Blocks 2 & 3 back in operation - Courtesy of Uisce Éireann

Ringsend Wastewater Treatment Plant, owned by Uisce Éireann, is located on the Poolbeg peninsula and treats the majority of wastewater generated in Dublin, along with additional flows from parts of counties Kildare and Meath; accounting for approximately 40% of all wastewater produced in Ireland. As the largest wastewater treatment plant in the country, it represents a critical piece of infrastructure serving Dublin and its surrounding areas. Originally designed for a population equivalent (PE) of 1.64 million, the plant has undergone a €550m capital investment programme in recent years to refurbish and expand its capacity to 2.4 million PE. This upgrade ensures that the facility can accommodate ongoing economic and population growth within the Greater Dublin Area, while also safeguarding the sensitive habitats of Dublin Bay Special Area of Conservation.

Drivers & process selection

Ringsend WwTP was not capable of meeting the Urban Wastewater Treatment Directive (UWWTD) standards due to overloading and insufficient nutrient removal capacity. To address this, upgrading the secondary treatment process stage was identified as key intervention, and this was to be delivered under the following five separate contracts:

1. The Process Proving Contract.
2. Capacity Upgrade Contract.
3. Block 2 full Nereda^® retrofit.
4. Block 3 full Nereda^® retrofit.
5. Hybrid 2 (hybrid Nereda^® retrofit of remaining 4 blocks).

Upgraded secondary treatment blocks – Courtesy of Uisce Éireann/Murphy

Nereda^® Aerobic Granular Sludge (AGS) Technology is biological wastewater treatment which has been developed in the Netherlands under a unique public-private partnership between the Delft University of Technology, the Dutch Foundation for Applied Water Research (STOWA), the Dutch Water Boards and Haskoning. Within a Nereda^® reactor, throughout a simple three-step cycle, the purifying biomass in Nereda^® grows naturally as compact aerobic granular sludge, with superb settling properties. An important feature of the granules is that aerobic and anoxic/anaerobic zones co-exist. This enables a large variety of biological processes to happen simultaneously, like nitrification, denitrification and biological phosphate removal.

There were several advantages for introducing Nereda^® treatment technology to Ringsend WwTP. The plant already had a Sequencing Batch Reactor (SBR) system for secondary treatment with minimal space for expansion and the Nereda^® system could be retrofitted to the internals of the 24 existing SBR tanks.

The Nereda^® process also provides improved nutrient removal (nitrogen and phosphorus) which was required to comply with the EPA Wastewater Discharge Licence for the plant.

Ringsend WwTP Secondary Treatment: Project Delivery Partners

• Design consultant & ER (all contracts):
  • TJ O’Connor & Associates Ltd
  • Egis Group
  • Haskoning Group
• Process Proving main contractor: Celtic Anglian Water
• CUC main contractor: PJ Hegarty/Veolia Water Ireland JV
• Block 2 main contractor: FaCT3 Consortium:
  • Celtic Anglian Water
  • TES
  • Farrans
• Block 3 main contractor: Ward & Burke Construction
• Hybrid 2 main contractor: Murphy Process Engineering

Ringsend WwTP Site – secondary treatment upgrade in progress – Courtesy of Uisce Éireann

Process Proving Contract

Given the specific requirements of the upgrade project, the Nereda^® Aerobic Granular Sludge Treatment technology provided a potentially promising solution, however, it had not been proven on a plant the scale of Ringsend WwTP.

To confirm the application of the Nereda^® AGS treatment process specifically to this plant and allow for optimisation of the application in the existing reactor cells, a process proving programme was implemented.

This contract consisted of retrofitting one of the four existing SBR cells in Block 3 with Nereda^® internals and Nereda^® control process optimisation to validate the retrofit design and proposed treatment process. The Process Proving Contract was completed by the existing plant operator, Celtic Anglian Water (CAW), as a variation to their Design, Build, Operation and Maintenance contract for an overall contract value of circa €10m.

Capacity Upgrade Contract

The €70m Capacity Upgrade Contract (CUC) was the first upgrade for the secondary treatment at Ringsend and was completed by PJ Hegarty/Veolia Water Ireland JV.

The design and build element of the CUC involved the piled construction of six new reinforced concrete treatment tanks in a two-tier arrangement with three tanks in the upper tier and three tanks in the lower tier. The six treatment tanks have a total volume of approximately 50,000m³, and have been designed and constructed to use the Nereda^® biological treatment technology.

The Capacity Upgrade Contract scope also included the design and construction of a new pumping station and various ancillary elements. This upgrade increased the plant’s capacity by 400,000 PE (from 1.64 million to 2.14 million PE).

Capacity Upgrade Contract in operation – Courtesy of Uisce Éireann

Block 2 Retrofit

The Block 2 Retrofit was completed by CAW/TES/Farrans Consortium (FaCT3) for an overall contract value of circa €50m. This involved retrofitting the four existing SBR cells in Block 2 on the upper deck of the existing secondary treatment units with Nereda^® treatment process technology along with an upgrade to the intermediate pumping station. The full scope of this contract included:

• Phased retrofit of the high lift pumps serving the upper deck SBRs located in the intermediate lift pumping station.
• Phased retrofit of the existing aeration system manifold pipework serving the upper deck SBRs.
• Modification to Block 2 centre core and provision of inlet and selection shafts for Block 2.
• Retrofit of Block 2 (Cells 2A, 2B, 2C and 2D) with Nereda^® Aerobic Granular Sludge Technology equipment.
• Provision of sludge buffers and water level correction buffers within Block 2.
• Electrical and instrumentation, control and automation equipment.
• Metal salts dosing distribution system.
• Odour control treatment and associated collection system.
• Miscellaneous items including SAS discharge, washwater utility, compressed air, hoisting facilities, drains etc.

Retrofitted Block 2 back in operation – Courtesy of Uisce Éireann/Murphy

Block 3 Retrofit

The €40m Block 3 Retrofit was completed by Ward & Burke Construction. This involved retrofitting three of the four existing SBR cells in Block 3 on the upper deck of the existing secondary treatment units with Nereda^® technology. The fourth cell had been previously retrofitted as part of a process proving advanced works contract. The full scope of this contract included:

• Phased retrofit of the existing aeration system manifold pipework serving the upper deck SBRs.
• Modification to Block 3 centre core.
• Retrofit of Block 3 (Cells 3A, 3C and 3D) with Nereda^® AGS technology equipment and upgrading of Reactor (Cell) 3B which has already been fitted with Nereda^® equipment.
• Provision of additional sludge buffers and water level correction (WLC) buffers within Block 3; 3A and 3C only.
• Electrical and instrumentation, control and automation equipment.
• Metal salts dosing distribution system.
• Odour control extraction/ collection system.
• Miscellaneous items including SAS discharge, washwater utility, compressed air, hoisting facilities, drains etc.

Hybrid 2

The €70m Hybrid 2 Contract was completed by Murphy Process Engineering Ltd, which involved retrofitting sixteen existing SBR cells in Block 1 on the upper deck and Blocks 4, 5 and 6 on the lower deck of the existing secondary treatment units with hybrid Nereda^® process technology.

The works consisted of the installation and implementation of replacements or upgrades to the existing elements of the SBR reactors to maintain or modernise their functionality and to provide robustness for the future. The full scope of this contract included:

Civil works

• Survey of existing tank structure.
• Inspection/replacement of movement joints.
• Remedial works after demolishing the existing walkways, aeration grid and other plant.

Mechanical works

• Replacement of walkways.
• Replacement of equipment (RAS pump, mixers).
• Replacement of valves and piping.
• Replacement of air mains and aeration grid.
• Replacement of surge boxes.

Sludge coolers – Courtesy of Uisce Éireann

Electrical works

• Replacement of MCC at centre core.
• Replacement of some instruments.
• Replacement of cables and cable containment.
• Replacement of building services (lighting, etc.).

Automation works

• Reprogramming of Block PLCs.
• Reprogramming of Hybrid Nereda^® controllers.
• Integration in SCADA system.

Construction interfaces/complexities

The five contracts were delivered with the added complexity of working within Ireland’s largest WwTP, which remained operational throughout. The secondary treatment upgrades were undertaken alongside significant upgrades to sludge treatment and ancillary systems, including biogas, UV, CHP, and SCADA.

To ensure all upgrade contracts maintained progress and the plant was operational at all times required a great deal of interface coordination between the contractors and the existing operator of the plant. All work activities and plant shutdowns (partial and full) were planned and discussed well in advance. The projects could not have been successfully delivered without the level of collaboration that was achieved between all stakeholders.

Upgraded secondary treatment blocks – Courtesy of Uisce Éireann/Murphy

Summary

The secondary treatment upgrade at Ringsend WwTP was completed in December 2025 with the completion of the Hybrid 2 contract. All projects have been successfully delivered on programme and within budget which is a great achievement by all stakeholders.

The plant’s capacity has been upgraded from 1.64 million PE to 2.4 million, and can now accommodate increased demand from the growing requirements of the Greater Dublin Area. The success of the Nereda^® Aerobic Granular Sludge treatment process has ensured that Uisce Éireann are now compliant with their obligations under the UWWTD for nutrient removal.