How are biosolids generated?

Modern sewage treatment processes lead to the production of water that can be recycled or discharged to the environment and most produce biosolids. The sewage treatment process separates solid material from sewage. These solids, known as sludge, are then further treated using biological processes. The resulting biosolids are a combination of treated sewage sludges and the dead micro-organisms used in the biological treatment process. Biosolids may be further dewatered or composted depending on the use to which they will ultimately be put. Regulators, such as State departments of Health and Environment strictly control the application, production and quality of biosolids. The term biosolids is derived from the most common method of its production: the biological treatment of sewage solids.

The sewage treatment process also produces grit and screenings which are solids removed during either the initial treatment process – where floatable materials are skimmed from the surface or filtered out using coarse screens – or which later settle. Grit and screenings are typically landfilled.