Western Wastewater Treatment Plant UV System Renewal
Wellington Water and Wellington City Council are undertaking a programme of works including the renewal of the Plant’s Ultraviolet (UV) disinfection system.
If you have any questions about this work, please contact:
Tiaki Wai, 0800 TIAKI WAI (0800 842 549)
Wellington Water is replacing the ultraviolet (UV) disinfection system, which is the final stage of the wastewater treatment process. The current system is nearing the end of its serviceable life and needs to be upgraded to ensure the plant continues to operate safely and effectively.
This necessary upgrade is to avoid the risk of a system failure. The function of the UV system is to disinfect treated wastewater before it is discharged into the ocean via the Karori long outfall pipe.
Construction is scheduled to begin in January 2026 and is expected to continue through to April 2026.
The long term benefits of this UV system upgrade are that it will improve the plant’s performance and resilience and provide more efficiencies with the UV disinfection of treated wastewater. These upgrades will reduce the risk of equipment failure and support better water quality outcomes for the Karori Stream and wider environment.
The treatment plant's capacity to treat wastewater will not be affected nor will the current UV system which will continue to operate as normal.
There have been some issues with the UV system which was a fault with a transformer that powers the UV system. The transformer was rebuilt and UV system was brought back online. It took longer than expected to fix as once the transformer was rebuilt there was another electrical issue with fuses in the main network line supplying the plant. This issue has been resolved and the UV system is operating again at full capacity.
The plant is currently compliant and meets all guidelines for wastewater quality analysis and effluent monitoring. But during wet weather the plant can reach capacity for treating inflows. To prevent flooding inside the plant, intermittent discharges of treated wastewater to the Karori Stream can happen during peak flows.
Find out more about the Western Wastewater Treatment Plant.
Wellington Water is replacing old Ultra-Violet (UV) equipment at the Western Wastewater Treatment Plant in Karori, Wellington. Ultra-Violet (UV) treatment uses lamps to emit ultraviolet light to deactivate and disinfect bacteria, viruses and protozoa. It’s the final stage of the wastewater treatment plant and an important part in putting safe, healthy water back into the environment. The Western WWTP project is in addition to two other, similar projects at Moa Point and Seaview Wwastewater Treatment Plants.
The existing UV disinfection system was installed when the plant was originally commissioned in 1998, approximately 25 years ago. For this type of electro-mechanical equipment, 25 years is considered to be at the end of its useful life.
The new UV equipment will deliver:
- Greater dose efficiency and control (and therefore improved compliance)
- Better design for access for maintenance
- Improved cleaning system (reduced need for operator input).