Te Anamata me te Toka Koiora o Tāmaki Makaurau
Auckland's Biosolids Future
Every time you flush or shower, your wastewater begins an important journey. It travels through a network of pipes to a treatment plant, where it’s carefully cleaned before being returned to nature. During this treatment process, soil-like material called biosolids are produced. By 2035, we’ll need a new way of managing biosolids in Auckland – so planning is getting underway now.
Why are we talking about this?
All of Tāmaki Makaurau’s wastewater treatment plants produce biosolids. We have a range of options available for their disposal, which include trucking them to certified commercial landfills or turning them into compost for use as a fertiliser. While these have been serving us well, we need to explore other options for managing biosolids in the long term, to ensure we have reliable and resilient servicing solutions in place for our growing city.
At our largest wastewater treatment plant in Māngere, where three quarters of Tāmaki Makaurau’s wastewater is treated, we are using biosolids to rehabilitate an area on Te Motu a Hiaroa (Puketutu Island) that was quarried from the 1950s until the early 2000s.
It's working well but it won’t last forever. By 2035, we predict the quarry on the island will be full and the rehabilitation of the previous island contours will commence. At this time Auckland will need a new proven and reliable solution in place that is capable of handling more than 175,000 tonnes of biosolids each year.
What's the timeline?
This shows the key steps from:
- 2025-26: Exploring options: We'll narrow down the broad options to specific areas.
- 2027-28: Refining the path: We'll have decided what the solution is and where it will be.
- 2029-30: Formal steps: Statutory approval and final design.
- 2031-34: Bringing solutions to life: Design and construction begin to deliver the agreed solution.
- 2035: Commissioning: The solution is ready to serve future generations.
What are biosolids?
Biosolids are a soil-like material produced as part of the wastewater treatment process. They come from treated wastewater (sewage) and the naturally occurring microorganisms (or ‘good bugs’) that help clean our wastewater. These microorganisms play an important role by breaking down organic matter and nutrients like carbon, nitrogen, and phosphorus.
During treatment, this material goes through a digestion process (like composting). This produces methane gas, which is captured and used to generate energy, which we use to run the wastewater treatment process at Māngere. The remaining stabilised material is biosolids. Due to the digestion process undertaken, biosolids meet safety and environmental standards before reuse or disposal.
What's the biosolids challenge?
Over the next year, we’ll be assessing our options for managing biosolids and we want you to help shape our plan.
Each approach has benefits and trade-offs. That's why your feedback matters – because it will help us to understand what Aucklanders value most as we decide on a solution.
Watch this video to learn more:
Read our Engagement Summary Report 2026
In late 2025, we asked Aucklanders and our mana whenua partners to share their views on the biosolids challenge. Our early engagement included workshops, surveys, community events, and online activities. The purpose was to help the people of Tāmaki Makaurau understand the issue and to learn what matters most to them.
This summary explains the biosolids challenge, who we spoke with, what we heard, and how this feedback will guide the next phase of planning. It reflects our commitment to involving Aucklanders early, listening carefully, and considering environmental, cultural, social, and economic factors in sound decision-making.
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