Municipal biosolids (formerly referred to as sludge) are a byproduct of the wastewater treatment process. Materials removed as part of other processes throughout treatment plant are treated, stored and, eventually, beneficially recycled as fertilizer. Biosolids make an excellent fertilizer since they are high in nutrient content, organic matter and are stringently tested to ensure high quality.

Although the raw flow discharged into the sanitary sewer collection system can include significant quantities of garbage, grit and other debris, those materials are removed immediately as the flow enters the wastewater treatment plant. The biosolids product consists mainly of solids and organic materials that have been treated through an anaerobic digestion process prior to disposal.