Sewage treatment is the process of removing
contaminants from
wastewater, primarily from household
sewage. It includes physical, chemical, and biological processes to remove these contaminants and produce environmentally safe treated wastewater (or treated
effluent). A by-product of sewage treatment is usually a semi-solid waste or slurry, called
sewage sludge, that has to undergo further
treatment before being suitable for disposal or land application.