Desalination of sea water is often the only viable option for providing safe drinking water in many arid, coastal regions or isolated locations such as small islands! Another important issue is the sewage's treatment, that 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.