We're replacing the fire-damaged trickling filters with an activated sludge reactor.

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Once up and running, the new reactor will fix the long-standing odour issues experienced since the fire. It will also significantly reduce greenhouse gas emissions and accommodate the needs of our growing population.

We can build the activated sludge reactor without disrupting current operations. In the meantime, we’re working hard to keep the damaged plant operating with minimal odour and will keep the community updated on progress.  

Contractor appointed for activated sludge reactor 

The main construction contract for the Christchurch Wastewater Treatment Plant's activated sludge reactor has now been awarded to HEB Construction, marking a major milestone for the upgrade.

We’re working closely with the contractor to get the site established as soon as possible, with construction expected to start early in the new year. 

This work follows the demolition of the fire-damaged trickling filters earlier this year, clearing the way for the new reactor. Construction is expected to take about three years, with commissioning targeted for 2028.

The new reactor will be a substantial structure, 67m x 67m and 7m high, housing a blower room to mix air with incoming wastewater. The design process has been accelerated by working closely with contractors and using 3D design technology. Once construction begins, our goal is to move quickly, with commissioning of the plant currently targeted for 2028.

In March 2025, we completed demolition of the fire-damaged trickling filters to make way for the conventional activated sludge reactor. 

Check out this time-lapse video to see the demolition from start to finish. 

Estimated timeline for design and construction

September 2024

Design consultant engaged

Aecom has been engaged to provide the detailed design of the Activated Sludge Plant. 

November 2024

Demolition of trickling filters begins

Work to demolish the trickling filters started on 21 November 2024. Southern Demolition is carrying out the work, which is expected to take around five months to complete.

February 2025

Design scope confirmed

All relevant design elements confirmed. 

March 2025

Demolition of trickling filters complete

Demolition of the trickling filters was expected to be complete by April. 

May 2025

Site prepared for construction

The site will be prepared and made safe, ready to be handed to the main contractor. 

May 2025

Structural design complete

The majority of the activated sludge reactor design is complete and ready for tender. 

September 2025

Mechanical and electrical design complete

The entire design for the activated sludge reactor, including mechanical and electrical components, is complete. 

November 2025

Main contractor awarded

The main construction contract awarded to HEB Construction.

January 2026

Site establishment

The main contractor will set up on site in preparation for construction. 

February 2026

Construction begins

Construction of the activated sludge reactor will begin. 

January 2028

Commissioning process begins

We'll start the process of decommissioning the temporary plant and commissioning the new plant. This will take until the end of 2028.