Once upon a time, the water washed or flushed down Australia's drains and toilets was considered 'wastewater'.

But in a changing and drying climate, improving how we reclaim and reuse the by-products of our water use is important for future water security.

Biosolids are the organic material left over after sewage treatment. Rich in nutrients and similar to the look and smell of soil once dried, this valuable resource can be applied to maintain productive soils, stimulate plant growth, and fertilise crops.

With a high nutrient value, biosolids can help improve soil quality and crop yields.

There has been an increase in the generation of biosolids in our region as the population grows.

So, we're making essential improvements to the way we manage biosolids and improving our wastewater treatment plants to meet this demand.

Local farmers already using biosolids on their farms have reported a range of benefits, including:

  • Increased yields
  • Reduced water use
  • A boost in carbon levels in their soils
  • Money saved through the use of this cheap and sustainable alternative to other types of fertilisers

More about biosolids

Along with recycled water, biosolids are a major by-product of the wastewater treatment process and must be used in accordance with regulatory requirements set out by the Environmental Protections Authority Victoria (EPA).

When treated and managed appropriately, they can be beneficially reused for a number of purposes.

Biosolids are derived from wastewater sludge, mainly a mix of water and organic materials from teh sewage treatment process. Most wastewater comes from household kitchens, laundries and bathrooms.

Biosolids contain:

  • Macronutrients: Such as nitrogen, phosphorous and sulphur.
  • Micronutrients: Such as copper, zinc, calcium, magnesium, iron, boron, molybdenum, and manganese.

Biosolids can be applied as a fertiliser to improve and maintain productive soils, stimulate plant growth, and rehabilitate mining sites.

Biosolids are a valuable by-product of the wastewater treatment process. Their use represents an appropriate use of a resource and closes the ‘nutrient loop’.

In the face of declining stocks of inorganic (rock) phosphate, biosolids are an increasingly important source of fertiliser.

What you flush down the toilets and drains in your house is treated at one of Coliban Water’s 16 Water Reclamation Plants.

We use a range of treatment processes to produce recycled water and biosolids. During sewage treatment, microorganisms digest (eat) the sewage, completely breaking down the original organic solids that have been discharged into the sewerage system.

This leaves effluent and a solids component, known as sludge.

The water content of the solids is then reduced, usually by passing through mechanical processes.

These solids are then treated to produce biosolids. Biosolids consist of dead microorganisms, a small portion of active microorganisms, and inert solids which have come down the sewer.

Biosolids have their own distinctive odour, depending on how they have been treated. Most have a slightly musty, ammonia odour, usually caused by sulphur and ammonia compounds (both of which are plant nutrients).

After processing and drying, biosolids have an odour similar to organic soils or compost.

The use of biosolids has environmental benefits, particularly in areas of degraded soils. Biosolids use completes the nutrient cycle by returning nutrients to the land from which they were sourced. Organic matter has been used by humans for thousands of years to improve soil fertility and productivity.

Yes. Biosolids have been successfully used in Australia and internationally for many years.

International studies have shown biosolids are safe when treated and managed according to guidelines.

The Australian water industry uses some of the most advanced technology and quality assurance programs in the world, ensuring the safe and sustainable reuse of biosolids.

The Guidelines for Environmental Management: Biosolids Land Application (pub 943) lists the requirements for biosolids treatment and use and provides a multi-barrier approach to managing risks.

We analyse biosolids to ensure they meet quality standards for land application. The frequency of testing is

based on the amount of biosolids generated by the treatment facility.

Dried biosolids are typically the consistency of soil/compost.

Yes. Protecting and enhancing our environment is central to everything we do. Our environmental and sustainability policy outlines our approach to managing our activities and assets in a sustainable manner and meeting our general environmental duty requirements.

All biosolids sites that we operate meet strict technical and environmental guidelines.

Our Biosolids Bases are managed under local planning and EPA requirements. An Environmental Improvement Plan is also in place at each site.

Dunolly Biosolids Base

Our new 10-hectare Biosolids Base at the Dunolly Water Reclamation Plant complements and supports our other Biosolids Base in Elmore.

Works in Dunolly included the construction of access tracks, a concrete tipping point where biosolids will be deposited, and the installation of a new pump station to help catch rain and stormwater run-off.

Biosolids will be air-dried on-site before being made available for beneficial reuse on farmland.

The facility in Dunolly operates with the relevant planning permits, and will be managed in accordance with EPA requirements. The image below shows where the new Biosolids Base is located, in relation to the existing plant.

Key works include:

  • Compacting an area with clay to allow biosolids to be spread
  • Installing gates and internal access roads to a delivery point
  • Installing run-off collection and a reuse system for drying and stockpiling areas (eg a collection sump, pump station, pipework, lagoon storage, power supply and controls)
  • A small amenities office for workers
  • Power
  • Agricultural fencing
  • Washdown facility for trucks.

Construction and operation of a new Biosolids Base will not impact the normal wastewater service received by customers in Dunolly.

Residents may notice increased truck movements in the area as works begin.

We will carry out weekly odour monitoring.

We're confident the pre-treatment of biosolids before they reach the Biosolids Base in Dunolly will limit the incidence of odour. This includes our site selection, preparation, and ongoing good operational practices.

We continue to work with the Environment Protection Authority Victoria (EPA Victoria) on this project. We have received approval from EPA Victoria to construct this new facility.

The Dunolly Water Reclamation Plant has three evaporative lagoons and the wastewater is treated to produce Class C water. Treated wastewater can be reused for flood irrigation on adjacent land.

When operational, the Biosolids Base will operate with a planning permit and will be managed in accordance with EPA requirements for land management, run-off and odour.

Biosolids will be trucked from other water reclamation plants in the region and dropped-off at an approved delivery point.

Deliveries will be made once or twice per week throughout the year.

Once on-site, the truck enters through secure gates along a formed (crushed rock) access road and will reverse up to the delivery point.

An area approximately 30-metres long and 40-metres wide is required for delivery.

The truck unloads the biosolids and the pile gradually displaces from the delivery point.

Trucks are then washed and all washwater contained within the area.

At the start of the warmer months, biosolids are removed from the delivery pile, spread and windrowed. This typically commences in October or November, and continues until March or April depending on the weather.

This is done to reduce the moisture concentration in the solids through open-air evaporation.

At the end of the drying season, dried biosolids are harvested from the windrowing area and stored in piles at approximately three metres. They typically require stockpiling for 12 months (but can be up to three years) before they are suitable for beneficial reuse.

A non-residual herbicide is sprayed over the windrows and stockpiled biosolids as required.