Irrigation water is not the only valuable agricultural product flowing from our wastewater reuse program. Farmers across the State are now trialling, with successful results, the use of soil improving biosolids.
Biosolids are the organic solid residue produced by the wastewater treatment process - formerly known as sewage sludge. About 25,000 equivalent dry tonnes of biosolids are produced annually at Adelaide’s wastewater treatment plants.
The biosolids contain organic matter (about 40%), significant quantities of nutrients and about 1% each of nitrogen and phosphorous. They also contain some metals such as cadmium, lead and mercury from industrial wastes entering the sewer network.
In South Australia, trials conducted by the CSIRO (Commonwealth Scientific and Industrial Research Organisation) on durum wheat crops indicated nutrients from biosolids could benefit grain crops without any detrimental uptake of metals.
Biosolids are used to increase soil fertility and as a source of nutrients for various crops. The product can also improve the water holding capacity of soil.
Agricultural Use
Farmers in South Australia have been using biosolids since 1999 as a soil additive and source of nutrients mainly for dry land crops such as cereals and on irrigated crops such as vines, olives and citrus. Approximately 35,000 tonnes of biosolids are now used annually.
In New South Wales biosolids are used extensively as a fertiliser and soil improver for farmers and other users. Annual production is about 180,000 wet tonnes and up to 99% is beneficially reused in agriculture, horticulture and landscaping.
SA Water is making biosolids at Bolivar available free of charge to farmers wishing to use the product on their properties and will also arrange and pay for all soil surveys, analysis and paperwork required for approval for use in accordance to the Biosolids Guidelines administered by the Environmental Protection Agency (EPA).
The only cost to farmers will be the cost of transporting the product from Bolivar and spreading the material on their land provided that an order for at least 100 tonnes is received.
Commercial Landscaping Use
SA Water is also making biosolids available free of charge for the development of significant landscape projects. The only cost to commercial landscapers will be the cost of transporting the product from Bolivar.
Biosolids can be mixed with other inert materials such as clay, sand or loam to provide an improved base for growing grasses, shrubs and trees. Their low cost, availability and stability make them ideal as a filler material. The slow release of nutrients as the organic matter decomposes gives a long term effect from the initial application and appears well suited to native plants and grasses.
Biosolids released for landscaping have been classified as suitable for this use in accordance with EPA guidelines. As the product will not be used for the production of food crops, the approval process is a lot less complex than the site specific approval required for each use of biosolids in agriculture.
There are no site specific approval requirements for using landscaping biosolids. However, we will need to satisfy ourselves the product will be used within the general EPA guidelines. If necessary we will discuss the proposed use with the EPA on your behalf to ensure there are no concerns.