Biosolids are the treated sludge which is produced as a result of wastewater treatment process. Sludge is a mix of water and solids (poo). Biosolids are produced once sludge has undergone further treatment which reduces pollutant materials and disease causing pathogens. A stabilized product is produced which is made up of between 15 % to 90 % solids which is called Biosolids. There are a number of different grades of biosolids produced. Regulations determine their final use, for example if they can be used on farming land they must meet minimum requirements.The term biosolids was created in 1991 in an attempt to make the land application of processed sludge more acceptable to the public. It was also intended to make a clear distinction between the untreated sludge and the product produced through processing and treatment.
Biosolids may contain:
- Macronutrients, such as nitrogen, phosphorus, potassium and sulphur and
- Micronutrients, such as copper, zinc, calcium, magnesium, iron, boron, molybdenum and manganese.
Biosolids may also contain traces of synthetic organic compounds and metals, including arsenic, cadmium, chromium, lead, mercury, nickel and selenium.
These contaminants limit the uses to which biosolids can be put, with all applications regulated by appropriate government authorities in each State and federally. Australia has one of the strictest regulatory regimes for biosolids application and use in the world.