Schematic illustration of a typical wastewater treatment process involving primary treatment (settling of solids), secondary treatment (biological decomposition), filtration, and disinfection of the wastewater to produce water that is clean enough to be discharged as effluent to a nearby stream or river. The solids removed as a result of these treatment processes are sent to an anaerobic digester for further treatment to breakdown and stabilize the organic fraction present in the solids, and to reduce their pathogen content and odour-producing potential. The treated solids resulting from this additional process are referred to as "sewage biosolids" and are transported directly to a farm field for land application as a crop fertilizer, or they are transported to a storage facility where they are temporarily held until they can be applied to land for that purpose.

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