Critical renewals under way at Rosedale Wastewater Treatment Plant

Watercare is working behind the scenes to deliver a complex $25 million renewal project at the Rosedale Wastewater Treatment Plant, upgrading critical infrastructure for the first time in 25 years.

The project is essential to protecting public health, safeguarding the environment, and ensuring wastewater treatment services continue to operate safely and efficiently for Auckland's growing population.

Since May, Watercare has been working alongside Cassidy Construction and GRIT Engineering to renew three of the plant's four anaerobic digesters. Digesters play a vital role in the treatment process, stabilising the solids removed from wastewater so they can be converted into biosolids.

Watercare programme director Rob Burchell says the renewals are part of Watercare's wider $600 million, 10-year Rosedale Upgrade Programme at the Rosedale Wastewater Treatment Plant.

"As Auckland grows, we need to continue investing in the critical infrastructure that underpins public health, protects the environment and supports thriving communities.

"Much of this work happens behind the scenes, but it is essential to keeping wastewater services running effectively while preparing for future growth across the North Shore and west Auckland.

"The wider Programme will increase treatment capacity, improve efficiency, reduce emissions and make better use of renewable energy generated on site."

Burchell says the work presents a rare opportunity to inspect, maintain and refurbish assets that spend decades in continuous operation.

"These are hard-working assets that typically only come offline once every 25 years, so carrying out these refurbishments, maintenance activities and modifications is essentially a once-in-a-generation opportunity.

"One of the biggest challenges with projects like this is that we don't always know the full extent of the work required until the mixed liquor exchanger and digester have been drained, inspected and condition assessments completed.

"Only then can we fully understand the scope of any issues and determine what additional repairs or modifications may be needed."

Burchell says the investigations uncovered issues that could only be identified once the assets had been taken out of service.

"Some of the challenges only became visible once work was underway. We had to adapt quickly, develop practical solutions to emerging issues as they were identified, and maximise the value of the investment.

"When you're working within a live treatment plant, flexibility is critical. Our teams worked through complex challenges while maintaining a focus on the long-term outcome, building greater resilience and reducing future risks.

“A significant part of the digester renewal project has involved replacing ageing components with modern materials and systems designed to improve performance and extend the life of critical assets.

"To date, Watercare has completed renewals on two of the three digesters, with work on the third scheduled to begin in November.

"While largely unseen by the public, projects like these play a critical role in keeping Auckland functioning every day.

"By investing in the renewal of essential infrastructure, Watercare is helping ensure reliable wastewater services, environmental protection and capacity for future growth across the region."

New mixer blades installed in the Mixed Liquor Exchange (MLE) at Rosedale Wastewater Treatment Plant.