Work has started on a $60 million upgrade of the Rotorua Wastewater Treatment Plant that will cater for future community growth and more effective management of wai tātari (recovered water) for the district.

Originally constructed in 1973, the plant needs to be upgraded to meet higher projected population demand and to ensure ongoing management of wai tātari in an environmentally sustainable and culturally appropriate way and for the ongoing protection of people’s health.

Rotorua Mayor Tania Tapsell says the upgrade will preserve and protect the region’s lakes for present and future generations which is the vision of the Rotorua Te Arawa Lakes Programme.

“Although our current treatment plant is still among the best in the country and treats recovered water to a very high standard, future-proofing is needed to maintain these high treatment standards and meet projected increased demand.”

The plant currently processes 19.7 million litres of wastewater daily which includes sewage, industrial wastewater, contaminated groundwater, stormwater and sediment. The upgrade will enable the plant to treat an average of 25.3 million litres per day with the ability to process 72 million litres during peak inflow periods.

The upgraded treatment process will continue to remove large amounts of nitrogen and phosphorus, and disinfecting the treated water before discharging to Whakarewarewa Forest through an irrigation system ahead of entering the lake at Puarenga Bay (Sulphur Point).

Rotorua Lakes Council Infrastructure and Environmental Solutions Deputy Chief Executive, Stavros Michael, says the short to medium-term discharge solution involves upgrading the treatment plant and the continued use of the forest irrigation system for discharge of wai tātari – with operational improvements – while Council and mana whenua work towards a long-term, new discharge point solution.

“Stage one site works are planned over three years with a comprehensive testing phase undertaken and switching plant processing from old to new seeing the project complete in 2027,” Mr Michael says.

“The upgrade will continue treating wastewater to an extremely high standard, removing pollutants like nitrogen and phosphorus and disinfecting bacteria like E. Coli. The recovered water will continue to meet our water quality targets, sustainability goals and most importantly, future-proofing of our district’s wastewater operations capacity.”

TRILITY won the undertaking through open tendering and was awarded the contract in October 2022 with site works starting in January 2023. Following the plants upgrade, TRILITY will engage a consolidated contract approach to operate, maintain and renew the wastewater’s networks over the next 10 years.

Matt Dawson, TRILITY General Manager Solutions says they’re honoured to build on the mahi tahi (partnership) with Rotorua Lakes Council and entrusted with the upgrade of the Rotorua Wastewater Treatment Plant.

“We acknowledge the mahi of our partners; Fulton Hogan, Stantec and McKay, who, together with Council will work towards a successful project for the Rotorua community.”

The upgrade design includes;

- new inlet screening systems,

- modification of existing ‘Bardenpho’ unit to improve phosphorus and nitrogen removal,

- installation of new membrane reactor units to further clean wastewater and remove nutrients,

- ultraviolet treatment to remove all remaining pathogens and

- addition of wastewater storage capacity to prevent spills from large in-flows that are typically caused by stormwater entering the sewer system.

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