Sewage is a liquid waste which has water as its largest component along with various types of impurities like waste water from houses, offices, factories, hospitals etc., is called sewage. It has a complex mixture containing suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes. Discharging untreated sewage into rivers or seas will pollute the water resources. Contaminated water is dangerous for aquatic plants and animals. It also spread many diseases like cholera, typhoid, polio, meningitis, malaria, dengue etc.