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Biosolids
Recycling for a better environment
Biosolids are the nutrient rich organic material resulting from the treatment of wastewater. Sydney Water produces about 170,000 wet tonnes of biosolids annually which are 100% beneficially used mainly in agriculture or composted. Sydney Water supports the Australian and New Zealand Biosolids Partnership, which is managed by the Australian Water Association and promotes sustainable, beneficial use of biosolids in Australia and New Zealand.
How are they produced?
Sydney Water treats wastewater from 4.6 million people at its wastewater treatment plants located in the Sydney, Illawarra and the Blue Mountain regions. The liquid and solids are separated during the treatment process. After processing, the liquid (effluent) is released into receiving waters or recycled. The solids are further processed and the end product is called biosolids. Biosolids are tested, classified and beneficially used or further processed to achieve higher grade biosolids products.
Biosolids contain organic matter (>60%) nutrients such as nitrogen (2-4%), phosphorus (1.5-3%) and potassium, plant essential trace elements and small amounts of other chemicals.
All biosolids produced by Sydney Water have undergone a treatment process to reduce pathogens, vector (insect and vermin) attractants and odours within the product.
Guidelines for the beneficial use of biosolids
Biosolids beneficial use is regulated by the NSW Environment Protection Authority (EPA) through the Environmental Guidelines: Use and Disposal of Biosolids Products (1997).
An interdepartmental committee using Australian experience and research conducted in Australia and abroad developed these guidelines ensuring the protection of the environment, as well as human and animal health.
The Environmental Guidelines encourage best management practices to ensure the development of sustainable and cost-effective biosolids management. The Environmental Guidelines require a thorough environmental assessment of biosolids land application sites. This includes soil sampling and analysis, as well as assessing the impact of biosolids on surface and ground waters and other significant features.
Why use biosolids?
Biosolids in agriculture
For many years, farmers have recognised biosolids products for their nutrient rich organic material, which provides benefits to depleted agricultural soils. The nutrients in biosolids are released slowly during plant growth which increases crop production and closes the nutrient loop by replacing what cropping takes away from the soil. Applied at agronomic rates, biosolids are an excellent soil conditioner providing superior water holding properties that can improve pastures, reduce nutrient runoff and increase crop yields. More than 50% of available biosolids are used in the agricultural sector. Sydney Water biosolids are applied on suitable farms throughout the Central West and South West of New South Wales.
Biosolids in composting
Composted biosolids are mixed with other organic materials such as green waste, shredded timber and sawdust and formed into windrows (lines of compost material heaped together for processing). The windrows are turned to allow for aeration and to create an even blend. The natural processes of composting raise temperatures above 55 degrees Celsius, destroying most unwanted organisms and breaking down the organic material.
Like any other fertiliser, composted biosolids are generally applied and mixed into the soil, promoting efficient water usage due to the natural water holding capacity of the compost.
Biosolids in land rehabilitation
Mining practices, excessive farming and industrial activities often result in degraded soils that may have poor soil structure leading to erosion, depleted nutrients, acidity and salinity. These soils are often unable to support plant growth. Due to their high levels of plant nutrients and organic compounds, biosolids are fast becoming an alternative soil ameliorant and have been used to successfully revegetate mine sites and degraded agricultural land.
How can you help
To help improve the quality of biosolids, Sydney Water has developed a number of strategies to keep unwanted substances such as chemicals and paints out of the wastewater system and the environment. The trade waste program, which targets industrial and commercial customers, sets standards and charges for the amount and type of substances discharged to the wastewater. It encourages industry and small business to treat wastewater before discharging it to the wastewater system.
There are many ways you can help improve the quality of biosolids. These include:
- don't wash paint, pesticides, medicines or other chemicals down the sink or toilet. Put them in the bin or take them to a chemical collection point
- use low phosphorous or phosphorous-free detergents and pesticides, and only use the recommended amount of detergent for your washing machine and dishwasher
- don't pour grease, oil or milk down the sink.
By improving the quality of waste entering the wastewater, you ultimately improve what returns to the environment after treatment.
To learn more read the fact sheet (PDF - 87KB) .