Māngere Wastewater Treatment Plant Central Interceptor Odour Beds

Between August 2021 and May 2023, Watercare tasked us with the removal and reinstatement of earth filter beds 3 and 4 at the Māngere Wastewater Treatment Plant. We also supplied and mixed the media (biofilter material) for the beds.  

The filter beds (also known as odour beds) are among the largest to be constructed in New Zealand. Each bed needed to be rebuilt within three months to enable Watercare to maintain its renovation programme.  

The structures – which measure 1220 sqm and 1378 sqm and are 950mm deep – had be in full compliance with clean air regulations to reduce harmful emissions and nuisance odours. Foul air from the treated water is pumped into the base of the beds and percolates up through the biofilter media, where it is purified by bacteria.

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All trades and equipment self-performed

Our team first removed the old earth filter bed, then installed rows of new ducts. Once laid, the ducts cannot be trucked over. As Seipp Project Manager Chad Gulliver explains, ‘The only way to get material into place once the ducts are laid is with a long-reach machine.’ We used an extended dipper arm, together with cranage, to lay down the fresh media across the duct field.

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Locally-sourced materials for the biofilters

Our work also involved sourcing the media blend for the filter beds, to client specifications. The beds themselves were formed with gravel sourced from a local quarry. While the biofilter material of woodchips was largely from pine trees grown in the Kaingaroa Forest and processed at the Kinloch and Tokoroa sawmills, bark mulch and bark nuggets – both by-products of the timber industry – also form layers in the beds.

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Providing a quality product

For this build-only project, Seipp provided a lump-sum budget, which it delivered to. Chad adds, ‘In terms of what was required, our team provided the best product, and even improved on it.