Biosolids
A solid substance formed from the by-products of wastewater treatment. These solids can be beneficially used by agriculture or forestry.
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Our role in protecting the environment doesn't end with water recycling. We aim to beneficially reuse as many of the by-products of wastewater treatment as possible. In some cases, we can turn waste into valuable products like biosolids and renewable energy.
We produce organic solids (sludge) during wastewater treatment. This sludge is collected and processed. It's converted into a safe, stable, nutrient-rich fertiliser product called biosolids.
NSW Health and NSW Environmental Protection Authority (EPA) have confirmed that biosolids are safe if they're made and used following the EPA's biosolids guidelines.
The National Association of Testing Authorities accredits the laboratories that test all our biosolids for contaminant levels and stability. This determines the grade of the product and how the biosolids should be used. To ensure compliance with regulations, soil scientists and agronomists carry out detailed analysis on biosolid application rates and processes as part of our reuse program.
Biosolids can be used on farms.
Learn more about how biosolids are produced.
You can help us recycle our waste into biosolids by:
Producing biosolids helps us reduce our environmental footprint by:
Considering biosolids as a resource instead of a waste product is a part of our circular economy.
A circular economy is a set of principles that values all things as resources rather than products and waste. It aims to eliminate waste, circulate products and materials so they're used more than once and regenerate nature.
We used to think of the solids left over from wastewater treatment as waste products to be disposed of. But when we look closer, we find that they're full of useful resources – things like organic matter, nutrients and healthy bacteria. Valuing and reusing resources found in wastewater, like biosolids, is part of circular economy thinking.
Can you think of other connections between water, materials and energy? It's something we're working on.
We can draw inspiration from the Earth's natural cycles, including the natural water cycle, nutrient cycles (like the nitrogen cycle in wastewater treatment) and energy cycles.
Uses | Benefits |
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Agriculture and forestry |
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Composting |
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Land rehabilitation |
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We use some biosolids directly without further processing. Some biosolids go on to be processed further for indirect uses.
Around 60% of the biosolids produced from our water resource recovery facilities are directly applied to agricultural soils.
Over 40 farms across the central west and south west of NSW use our biosolids to help improve soil. 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 like sheep and cattle may graze on crops and pastures grown in biosolids. There are withholding periods for farm animals fed on biosolids-treated pastures.
Farmers use special machinery to spread biosolids on the ground.
We send about 30% of our biosolids to forestry for growing timber.
We send the remaining 10% of our biosolids for further processing. Biosolids can be mixed with other materials like green waste and composted further. These products are tested to ensure they're safe for use in the same way as any other composted product.
Composted biosolids are used in agriculture, horticulture, mine rehabilitation, and gardens and parklands within Greater Sydney.
We can use cogeneration and co-digestion to make heat and energy from biosolids to help power the rest of the water resource recovery facility.
Learn more about wastewater treatment and energy management and climate change.
Cogeneration is the production of electricity and heat at the same time.
We can use the electricity and heat to reduce the overall energy demand of a water resource recovery facility.
In a wastewater system, the anaerobic digestion of organic waste can be used to produce methane gas. This gas can be used to power a combustion engine that drives an electricity generator.
The heat generated from the combustion engine can then be used to warm the digester and improve its efficiency.
We already use cogeneration at a number of facilities. We recently installed new cogeneration at our St Marys Water Resource Recovery Facility and increased our cogeneration capacity at the Malabar Water Resource Recovery Facility.
Co-digestion takes liquid organic waste from restaurants and other sources and combines it with solids from the wastewater system. This mix is then digested to produce methane gas and biosolids.
In 2011, we began exploring the possibilities of co-digestion and the benefits of treating organic waste as a resource at the Cronulla Water Resource Recovery Facility.
This work is producing some impressive results with a lot of promise for the future.
The benefits of using co-digestion are:
In 2020, we worked with Australian Native Landscapes to build a garden at our education centre within Penrith Water Resource Recovery Facility.
We used recycled composted biosolids from our water resource treatment facilities and planted drought-tolerant, low-maintenance native plants. We collect and use rainwater to conserve our drinking water.
We'll be watching how the garden thrives over time. It's a great example of how we can contribute to liveable cities.
Biosolids garden