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Treating biosolids

What are biosolids? 

Biosolids are the nutrient rich, organic solid residues produced through the wastewater treatment process. Watercare’s objective is to use biosolids beneficially to the greatest extent practicable.


What happens to Auckland’s biosolids?

Watercare is successfully using biosolids to rehabilitate a small part of the old oxidation ponds at the Mangere Wastewater Treatment Plant. Biosolids from other treatment plants are currently being disposed of in commercial landfills. Watercare continues to review options for the long-term beneficial use or disposal of biosolids. Watercare is carrying out its own investigations into how biosolids could be used to benefit the environment and also draws on the experiences of wastewater utilities around the world. 

We continue to work with local iwi and businesses to explore other beneficial-use options for biosolids.​

Planning for the future

Watercare has undertaken trials on company-owned land adjacent to the Mangere plant to test dried biosolids suitability for turf farming, floriculture, and pasture rejuvenation. The possibility of using biosolids as a forestry soil conditioner is also under investigation. Watercare plans to set up a trial with the Forest Research Institute to look at nutrient uptake in trees, as well as surface and groundwater effects, transportation issues, storage, and spreading.

Watercare is also participating in an industry working group looking at national environmental standards for biosolids used on land.