|These pumpkin seedlings have been planted on rows of composted biosolids at community compost education garden.|
The term biosolids refers to solid organic matter that can be extracted from industrial and domestic sludge through the process of treating sewage with wastewater. The term sludge (or slurry) refers to a range of semi-solid/semi-liquid substances or deposits.
As a form of waste disposal, the production of biosolids may be considered an environmentally preferred option compared to incineration and landfilling of municipal sludge. Some of the companies actively involved in the UK biosolids market include Veolia and Thames Water.
 What biosolids can do
Biosolids can be a component of the circular economy. Depending on their level of treatment, biosolids can be used to feed nutrients back into agricultural lands and other depleted environments. As a source of organic matter, biosolids can be used to establish sustainable vegetation and help to replace some toxic substances.
Biosolids have also been used to control soil erosion through a soil regeneration process. They can also play a role in the reclamation of unused mining sites as they assist in the establishment of vegetation and upgrade the mined land.
 Types of biosolids
- Class A biosolids are pathogen-free and can be safely used in applications requiring public contact. Class A biosolids are often produced through anaerobic digestion and additional treatment, such as heating, pasteurisation, composting or newer complementary technologies.
- Class A (EQ) biosolids are Class A biosolids that have been given an "exceptional quality" or EQ rating. These represent the cleanest and safest form of biosolids.
- Class B biosolids have undergone treatment that retains detectable levels of pathogens and may have an unpleasant odour. Their use is restricted, making them better suited to land reclamation or agricultural activity that requires little or no regular human exposure.
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