Solids recycling

Soil in gloved hands

Biosolids are nutrient rich and safe to use.


Our role in protecting the environment doesn't end with recycling water.

We aim to beneficially re-use as many of the by-products of wastewater treatment as possible.

In some cases, we can even turn waste into renewable energy.

How do we recycle solids?

In the first wastewater treatment step, we use screens to remove large solids like plastics, wipes, food scraps and rags.

This kind of waste is made up of things that shouldn't be put down toilets, drains and sinks. Find out more about the need to keep wipes out of the pipes.

We also remove grit in the early stages of wastewater treatment. Grit is made up of sand, gravel, bone, seeds, coffee grounds and eggshells.

We collect the screenings and grit in large bins and send it to commercial composting facilities for processing and recycling.

After composting, this material can be used in:

  •  landscaping
  •  horticulture
  •  mine site rehabilitation
  •  agriculture.

What are biosolids?

We produce organic solids (sludge)during wastewater treatment.

This sludge is collected and processed to convert it into a safe fertiliser product called biosolids.

Biosolids can be used in farming and gardening as an economic alternative to conventional fertilisers.

How are biosolids produced?

Our solids handling processes convert sludge into a stable, nutrient rich product that can be re-used as fertiliser.

Biosolids production steps

  1. Sludge thickening – mechanical and chemical methods are used to reduce the water content and thicken the sludge.
  2. Sludge digestion - uses either aerobic or anaerobic digesters to break down and stabilise the sludge. This makes nutrients available to plants, reduces pathogens to low levels and reduces odour.
  3. Dewatering - high speed centrifuges or belt press machines remove water from the biosolids. This helps make it lighter for easy transport in trucks.


How are biosolids used?

Over 40 farms across the central west and south west of NSW use our biosolids to help improve soil, mainly in broad-acre farms.

These large farms grow canola, wheat, oats, barley and pastures.

The biosolids are spread and mixed into the soil before sowing the crops. The harvested parts of these crops don’t come into direct contact with the soil/biosolids mixture.

Some animals, such as sheep and cattle, may graze on crops and pastures grown in biosolids. There are withholding periods for farm animals fed on biosolids-treated pastures.

Some biosolids are mixed with other materials and further composted. These products are tested to ensure they're safe for use in the same way as any other composted product.

How safe are biosolids?

NSW Health and NSW Environmental Protection Authority (EPA) have confirmed biosolids are safe if produced and used when following the NSW EPA’s Biosolids Guidelines.

The National Association of Testing Authorities accredit the laboratories that test all our biosolids for contaminant levels and stability. This determines the grade of product and how the biosolids should be used.

What are the environmental benefits of producing biosolids?

Producing biosolids helps us reduce our environmental footprint by:

  • producing gas that we use to generate electricity to power our treatment plants
  • minimising the discharge of solids to our oceans and rivers
  • recycling a valuable resource that helps minimise disposal to landfill.

When we produce biosolids using anaerobic digestion, we can capture methane gas.

This gas can be used to generate electricity and heat for use at wastewater treatment plants.

Learn more about energy management and climate change.