Biosolids are produced as part of our wastewater treatment and reuse program and are a valuable agricultural resource. Farmers across the state are now using this product for soil improvement with successful results.
Biosolids are the stabilised organic solid residue produced by the wastewater treatment process. About 25,000 equivalent dry tonnes of biosolids are produced annually at Adelaide’s wastewater treatment plants.
The biosolids are a mix of water and organic matter that are a byproduct of the wastewater treatment process. The majority of wastewater comes from domestic households. Biosolids contain:
- about 4% of organic carbon
- macronutrients such as nitrogen, phosphorus, potassium and sulphur
- micronutrients such as copper, zinc, calcium, magnesium and iron
- traces of other metals such as arsenic, cadmium nickel lead from industrial wastes entering the sewer network.
These nutrients are bound up with the organic and mineral elements in the biosolids. As the organic matter decomposes in the soil, the nutrients become available for uptake by the crops.
Biosolids are generally used in agriculture to improve and maintain productive soils and to stimulate plant growth. They are used to increase soil fertility and as a source of nutrients for various crops. They also provide benefit by improving the water holding capacity of soil.
In South Australia, the CSIRO (Commonwealth Scientific and Industrial Research Organisation) conducted trials over a three year period to assess the agronomic benefits and risks from using biosolids in dryland agricultural production.
The results of the trials indicated that the use of biosolids from the Bolivar Wastewater Treatment Plant provided farmers with a ready supply of plant available nitrogen, phosphorus and micronutrient. They provided modest economic benefits based on grain yield and grain protein content. When applied in accordance with the SA Biosolids Guidelines there was no detrimental uptake of metals.
The use of Biosolids in South Australia is regulated by the South Australian Biosolids Guideline for the safe handling and Reuse of Biosolids and administered by the Environment Protection Authority (EPA).
Farmers in South Australia have been using biosolids from Bolivar since the late 1960s 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 30,000 product tonnes of biosolids are now used annually from SA Water’s metro and country wastewater treatment plants.
Biosolids must not be applied to non permanent plantings (e.g. field crops and vegetables) that are irrigated.
In New South Wales, biosolids are also used extensively. The annual production is about 180,000 wet tonnes and up to 99% is beneficially reused in agriculture, horticulture and landscaping.
SA Water makes these soil improving biosolids at Bolivar available free of charge to farmers wishing to use the product on their properties.
SA Water will also arrange and pay for all soil surveys, analysis and paperwork required for approval for use of biosolids in accordance to the South Australian Biosolids Guidelines administered by the 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.
These biosolids are air dried and milled or screened to make them easy for spreading using common agricultural equipment such has gypsum spreaders.
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 and the approval process is much simpler than with perennial horticultural crop production. There are no site specific approval requirements for using landscaping biosolids, but SA Water needs to ensure that the product will be used in accordance with the EPA guidelines and can discuss the proposed use with the EPA on behalf of consumers.
For more details about biosolids or to enquire about taking biosolids from SA water please contact our Land Manager on 0419 805 629.
Further information about biosolids is available at www.biosolids.com.au.