Sewage sludge

Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term "septage" also refers to sludge from simple wastewater, but is connected to simple on-site sanitation systems, such as septic tanks.

After treatment, and dependent upon the quality of sludge produced (for instance, with regard to heavy metals content), sewage sludge is most commonly either disposed of in landfills, dumped in the ocean, or applied to farmland for fertilizer.

In the United States, the term "biosolids" is sometimes used as an alternative to "sewage sludge", particularly in conjunction with the re-use of sewage sludge as fertilizer after sewage sludge treatment. Biosolids can be defined as organic wastewater solids that can be reused after stabilization processes such as anaerobic digestion and composting. Opponents of sewage sludge use on farms reject this term as a euphemistic public relations term.