As part of its $94 million upgrade, the North Head Water Resource Recovery Facility (WRRF) has been installed with two new digestors. 

The digestors are currently being used to produce biosolids for use in compost and on a trial basis in forestry, and are expected to almost double the sludge digestion capacity at the plant.

The North Head WRRF provides wastewater facilities for one million Sydneysiders; from Seven Hills in the west, to Yagoona in the south and Ku-Ring-Gai and Collaroy in the north.

In 2021, Sydney Water began important upgrades to the facility to improve how we process biosolids.

Sydney Water currently uses biosolids produced at North Head for compost in mine rehabilitation and to grow forests for the production of chipboard in rural New South Wales.

More than 100 workers helped build and install two digestors. 

Sydney Water Contract Specialist, Graham Keating, said that Sydney Water produces about 180,000t of biosolids per year.

“Currently 56 per cent of biosolids are directly applied to farmland in Western New South Wales, 29 per cent are used in the forestry market and 15 per cent are composted before being land applied to farms or used in the land rehabilitation of mine sites in the Hunter Valley,” Mr Keating said.

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

Sydney Water Senior Process Engineer, Matt Wood, said that the upgrades are an important step in ensuring that 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 New South Wales,” Mr Wood said. 

“Sydney Water has beneficially reused 100 per cent 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.” 

Sydney Water said that it is constantly looking to reduce its carbon footprint and use alternative and renewable energy sources. At North Head WRRF, almost 45 per cent of the facility’s total energy needs come from renewable sources.

The facility features a hydroelectric generator. The 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.

Featured image: Biosolids treated at Sydney Water North Head WRRF.

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