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Underpinning Auckland's growth

More than 1.5 million people live in Auckland and the population is forecast to be almost 1.9 million by 2035. As New Zealand’s most populace city grows its infrastructure needs to keep pace, and in a sustainable way.

Project Rosedale wastewater treatment plant, Auckland, New Zealand

ClientWatercare Services Ltd

ExpertiseConcept and detailed design

The Rosedale wastewater treatment plant (WWTP) serves about 17% of Aucklanders and is the region’s second largest. A programme of upgrades to the facility, will raise capacity by a third, enough to treat waste from 320,000 people, with peak flows of up to 4m3/s. Our original design included primary sedimentation and a modified activated sludge plant to increase liquid stream capacity as well as a new digester to improve the anaerobic digestion process. We have since developed the design for a thermal hydrolysis plant with partners Stantec. The upgrades to Rosedale will improve its resilience, reduce waste solids and greenhouse gases, and raise biogas yield to help power the plant.

The upgrade includes expanding the primary tanks, renewing the odour control equipment, modifying the bioreactor and digester, and improving the UV disinfection and associated electrical infrastructure – essential to ensuring the environment and waterways are kept clean, and drinking water is of the highest quality.


people served by upgraded plant

The new thermal hydrolysis plant will improve biogas yield and the destruction of solids. Electricity from biogas currently provides more than half the power needs of Rosedale. We are now supporting the integration of sustainable practices, including reducing aeration for biological nutrient removal, an energy-intensive process – helping Watercare achieve its goal of running the plant on 100% self-generated electricity by 2025. 

Rosedale is one of the top five most energy-efficient plants in Australasia. It also reuses treated water onsite, freeing up fresh supplies for Auckland’s burgeoning population. The thermal hydrolysis facility will be completed in 2022, enabling biosolids from the treatment process to be sterilised to create fertiliser that can be used by the agricultural sector.

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