Digesters installed in North Head WRRF

Two digesters have been installed in the North Head Water Resource Recovery Facility (WRRF), marking an important milestone in its $94 million upgrade.

The digesters produce biosolids which are currently being used in compost and on a trial basis in forestry. They will almost double the sludge digestion capacity at the plant.

The North Head WRRF provides wastewater facilities for one million Sydneysiders, in the west, south and north.

Upgrades to the facility commenced in 2021 by Sydney Water, to improve how it processes biosolids.

Biosolids produced at North Head are currently used for compost in mine rehabilitation and to grow forests for the production of chipboard in rural New South Wales.

The two digesters, recently built and installed by over 100 workers, will almost double the capacity of sludge digestion at the plant.

According to Graham Keating, Sydney Water Contract Specialist, Sydney Water produces about 180,000 tonnes of biosolids per year. 56% of biosolids are directly applied to farmland in Western NSW, 29% are used in the forestry market and 15% are composed before being land applied to farms or mine sites in the Hunter Valley.

Though composted biosolids are ultimately land applied, the direct land application to farms and forestry is better in terms of carbon neutrality. As the quality of the North Head biosolids improves, it is likely they were will be beneficially used in forestry.

Matt Wood, Sydney Water Senior Process Engineer, said the upgrades are an important step in ensuring biosolids continue to be beneficially reused and kept out of landfill.

“We proudly produce biosolids to help reduce society’s environmental footprint and restore and improve soils throughout NSW. Sydney Water has beneficially reused 100% of its biosolids for over 20 years. Not only does this avoid sending them to landfill or out to sea, but their organic, nutrient and microbial content makes them ideal for rejuvenating soils and improving the land’s ability to sequester carbon,” Wood said.

Sydney Water is constantly looking to reduce its carbon footprint and use alternative and renewable energy sources. At North Head WRRF, almost 45% of the facility’s total energy needs come from renewable sources, such as its hydroelectric generator.

As treated wastewater falls down a long drop shaft on its way to the deep-water ocean outfall, the falling water has enough kinetic energy to drive a water-powered generator, producing hydroelectricity.

North Head WRRF also uses cogeneration to meet some of its energy needs. Methane gas (biogas) is captured from the anaerobic digesters and used to power a combustion engine that drives an electricity generator and produces heat to supply the plant’s process heating requirements.

Upgrades to the North Head WRRF are due for completion by late 2024.

Image caption: North Head Water Resource Recovery Facility. Image courtesy of Sydney Water.