Learning Centre » Water recycling and sewage » Biosolids


Biosolids are a valuable by-product of modern sewage treatment. Dried biosolids have a range of uses, notably as nutrient rich fertiliser.

Image shows dried biosolids pellets - a nurient-rich fertiliser.

Dried biosolids can be used as fertiliser or an alternative fuel.

What are biosolids?

Modern sewage treatment utilises billions of microscopic bacteria and other organisms to break down and digest sewage to produce recycled water.

In these nutrient rich conditions, the microbes eat, multiply and die. Their dead bodies accumulate at the bottom of sewage treatment tanks and are regularly drained and dried. The resultant product is known as biosolids.

Because biosolids are organic and nutrient rich themselves, they can be recycled as fertiliser. Dried biosolids can also be used as a sustainable, greenhouse friendly alternative fuel.



Producing biosolids

Black Rock Water Reclamation Plant, the region's largest sewage treatment and water recycling facility, creates almost 140 tonnes of biosolids every day. The wet biosolids travel via a raised conveyor to an adjacent drying facility.

Our other water reclamation plants produce biosolids in smaller quantities, which are periodically trucked to the thermal dryer at Black Rock.



Biosolids thermal drying facility

A new facility adjacent to the existing reclamation plant was officially opened in January 2013.

The thermal drying plant produces small biosolids pellets suitable for immediate use as fertiliser, and significantly reduces the greenhouse gas emissions previously associated with the transport and storage of biosolids.

The facility was built by Plenary Group and is operated by TRILITY (formerly Water Infrastructure Group) as a public-private partnership.

  Plenary Group