Desludging under way as part of Waiwera wastewater upgrade

Most homes and businesses in Waiwera are connected to an underground wastewater system that quietly carries wastewater away through pipes so it can be treated safely.

At Waiwera, that wastewater has traditionally been treated locally in large open ponds, known as oxidation ponds.

These ponds use sunlight, algae and naturally occurring bacteria to break down wastewater over time, a simple, low energy treatment process used at some smaller wastewater plants across Auckland.

As wastewater sits in the ponds, heavier material naturally settles on the bottom and gradually breaks down into a layer known as sludge.

When this layer builds up and reaches approximately 60 to 70 per cent of a pond’s storage capacity, it must be removed through a routine maintenance process known as desludging.

Crews have now begun desludging the ponds at the Waiwera Wastewater Treatment Plant, marking an important early step in a $45 million upgrade that will permanently end treated wastewater discharges into the Waiwera Estuary.

The desludging work prepares the site for a new wastewater system that will transfer wastewater out of Waiwera altogether, as the oxidation ponds will be converted into storage ponds.

Once complete, wastewater from the Waiwera catchment will be pumped through a new 4.5 kilometre underground pipeline to Hatfields Beach and on to the Army Bay Wastewater Treatment Plant, where it will receive a higher level of treatment before being discharged offshore.

This will allow treated effluent from the Waiwera plant to cease. The project forms part of Watercare’s 10 year, $13.8 billion capital works programme (2025–2034), focused on increasing capacity and improving resilience across Auckland as the region continues to grow.

Hibiscus and Bays Local Board chair Alexis Poppelbaum says the change will deliver lasting environmental benefits for Waiwera.

“Eliminating treated wastewater discharges into the Waiwera Estuary is a major win for water quality and the local environment.

“The new pump station and pipeline will allow wastewater to be treated to a higher standard at Army Bay, while the existing ponds at Waiwera will be repurposed into storage ponds to support the new system.”

Watercare head of wastewater Jon Piggot says desludging is a normal part of managing oxidation ponds and helps keep them working effectively.

“Over time, material settles on the pond floor.

“Removing that sludge restores capacity, improves performance and reduces the risk of odour.

“At Waiwera, around 10 tonnes of dewatered sludge are currently being removed each day and taken offsite.”

Watercare project manager Martin Hughes says the work is critical to preparing the ponds for their future role as storage as part of the new system.

“Completing the desludging allows us to drain the smaller of the two ponds and begin building the new pump station, including connecting the inlet pipe into the pond.

“By reusing the existing ponds, we can maximise their combined storage capacity of 17,500 cubic metres - roughly the equivalent of seven Olympic size swimming pools while helping to minimise odour.

“The ponds will continue to receive wastewater from the Waiwera catchment once the new pump station is commissioned."

Desludging at Waiwera wastewater treatment plant

Watermain and wastewater pipeline installation update:

Hughes says work on the water and wastewater transmission mains are progressing well.

Just over 300 metres of the 840-metre water main on Hibiscus Coast Highway has been laid.

The installation of the wastewater pipeline along Weranui Road and Hibiscus Coast Highway is also progressing well with around 1.7km now installed out of a total of 4.5km.

Auckland Transport is also currently undertaking geotechnical investigations to inform permanent repairs to two slips that occurred in February.

“While the slips have caused some minor disruption, the project remains on track, with the water and wastewater upgrades expected to be completed by the end of the year.

“We understand this work may cause some inconvenience for motorists, and we appreciate your patience as we deliver essential upgrades for Waiwera.”