The boilers, biogas, and big changes underway at Moa Point

Inside the facility, two types of boilers will soon be installed to play a vital role. 

The first will be steam boilers to pasteurise sludge, heating it just enough to eliminate harmful bugs.  

The second is a hot water boiler to heat the thermal drier, a big oven, in which the sludge is dried.  

Use of both steam and hot water in the sludge minimisation facility enables us to produce a final product that is greatly reduced in volume from the existing sludge treatment process and is 95 percent dry and odourless.  

This drastic reduction in volume means less material to transport and dispose of. 

In fact, the new process will shrink the volume of sludge we produce by up to 80 percent and cut carbon emissions from sludge treatment by up to 60 percent. 

Currently more than a million litres of sludge per day is piped 9km from the existing wastewater treatment plant at Moa Point to Carey’s Gully sludge dewatering plant at the Southern Landfill. The dewatering plant at the landfill removes most of the water, leaving 40-50 tonnes to be buried with landfill waste each day.  

The facility will help us deliver on two critical targets the Council has set for reducing waste and carbon emissions in Wellington City. Without it, we cannot reduce how much waste goes to landfill.  

What is biogas and how will it be used in the new facility?  

As sludge naturally decomposes in the huge concrete digesters, it produces biogas - a mix of methane and other gases that create a valuable source of renewable energy.  

Instead of letting that decomposition happen in a landfill (which releases emissions into the atmosphere), the new facility captures it on site. 

The biogas is stored in gas bags perched atop the digesters, ready to be used as clean fuel for heating the boilers and generating steam. Any leftover biogas will be used to produce electricity to help keep the plant running.  

The boilers are due to be ‘skidded’ into the facility before the building is fully complete.  

Skidding them in early gives the crews the opportunity to push forward with the install of the equipment and associated pipework and controls earlier.  

What’s coming up next? 

On top of this, there’s plenty happening on the ground as the facility continues to take shape. The steel structure has reached its peak height, and the concrete floor of level three has been poured (it will have four levels in total). Behind the wrap around the building, crews are painting the steel with a special paint that will protect the building in the unlikely event of a fire. 

May promises even more progress, with the roof structure going on, level four slab being poured, and precast panels wrapping the outside. Around the digesters, platforms and stairways will start to appear.  

Speaking of digesters – the two large tanks that can now be seen on site – they have been tested for leaks and are getting a protective inner coating.  

It’s going to be an exciting year for Te Whare Wai Para Nuku, as the project starts to see some of its unique mechanical equipment arriving on site and being installed – ready for the facility to be operational in late 2026. 

Find out more on the project page.