Biosolids are the major by-product of the wastewater treatment process. When treated and managed appropriately, they can be beneficially used. They have high nutrient value and can condition soil, improving its structure and water retention qualities. The highest and best use for biosolids is generally agricultural application, which is discussed on this page. There are other uses for biosolids, with opportunities for beneficial use reflected in the quality of the biosolids produced.
Biosolids are derived from wastewater sludge. Sludge is the major solids component collected from wastewater treatment processes. Sludge normally contains up to around 3% solids. Biosolids are produced once sludge has undergone further treatment to significantly reduce disease causing pathogens and volatile organic matter. Treatment processes produce a stabilised product suitable for beneficial use. Biosolids normally contain between 15% and 90% solids.
Australia currently produces approximately 300,000 dry tonnes of biosolids annually. Approximately 55% is applied to agricultural land and around 30% is disposed of in landfill or stockpiled. The remaining 15% is used in composting, forestry, land rehabilitation or incinerated. Currently, the average cost for biosolids management is in the order of A$300/dry tonne, which equates to about A$90m per year.
Biosolids are a potentially 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 (please see link to the Global Phosphorus Research Institute below), biosolids may become an increasingly important source of fertiliser.
Below is a range of research that explore the use of biosolids in land application (primarily agriculture). When using these papers please cite them correctly.