Desludging underway at Wastewater Treatment Plant

Wastewater Treatment Plant Desludging

We’re trialling a new, environmentally responsible method for managing wastewater sludge. This project transforms sludge from one of our sewerage ponds into a safe, nutrient-rich compost that can be safely used to improve soil health and support land rehabilitation.

Overview

What is sludge?

Sludge is the semi-solid material created during wastewater treatment.

Traditionally, it is processed using complex methods to remove the water before disposal to landfill.

Our approach will naturally compost the sludge on a lime pad, converting it into a beneficial product for disposal to without the need for a resource consent.

How does this composting process work?

Natural composting: The treated sludge is laid out on lime pads and allowed to compost over time. As with normal composting the sludge will be turned and moisture levels maintained to kill harmful pathogens and stabilise the material. Microorganisms also break down the organic matter, transforming it into a soil-like material.

Safe reuse: Once fully composted, the material is suitable for use in land rehabilitation and other non-food applications. It meets environmental safety standards and supports sustainable land management.

Lime pad: The composting sludge is stored on a lime pad which helps maintain moisture levels, and manage any odours from the process.

Testing: The compost will be rigorously tested to ensure quality meets Aa biosolids.

What are the benefits?

Environmentally, this process:

Reduces landfill waste.
Minimises greenhouse gas emissions by turning the compost and reducing anaerobic conditions.
Avoids the need for resource consent due to quality of the Aa biosolid.
Utilises the beneficial nutrients within the sludge for land improvement.

What are we going to do with it?

There are strict regulations around how the final product can be used, even with a high quality Aa biosolid rating. There are a few options we are currently working toward – more info to come!
We’re hopeful that this could be an additional revenue stream for Council in the near future.

Are other places doing this?

Yes. Similar projects around the world have successfully reused treated sludge for land restoration, agriculture (non-food), and energy production.

Our initiative builds on these proven methods while tailoring the process to local needs and environmental conditions.

Other Councils in NZ have already been in touch to find out more.

We’ll keep you updated throughout this trial, both online and through our Project & Policy Committee meetings. If you have any questions, you can always send us an email at info@cdc.govt.nz.