Solid waste
Solid waste in some cases can be a resource. A good example is the factory at Yokohama in Japan which is engaged in converting waste paper into toilet paper. In our country, the mainstreet of Patna city is being illuminated by biogas produced from nightsoil of the city dwellers. In Delhi, the sewage treatment plant produces cooking gas. Fermentation of wastessuch as cattle dung, human excreta, garbage and aquatic weeds like algae and water hyacinth, produces biogas which can be used for a variety of purposes. Fermentation takes place at temperatures between 28° and 40°C and gases produced are predominantly methaneand carbon dioxide with a small quantity of hydrogen sulphide and nitrogen. Slag, a waste product left when the metal has been extracted from its ore, can be powdered and added to cement for construction. Flyash is another material used as a valuable cementing material. It is clear from the above that the solid wastes can serve as very useful resource for providing raw material for our industries, for generating energy and for the production of manure.