The statutory definition of solid waste is not based on the physical form of the material (i.e, whether or not it is solid as opposed to a liquid or gas) but on the fact that the material is a waste. The United State Environmental Protection Agency (USCPA) 2001), define solid waste as any garbage, refuse, sludge from a waste water treatment plant, water supply treatment plant or air deed material, including solid, liquid, semi- solid or contained gaseous material resulting from industrial, commercial mining and agricultural operations and from community activities.
Solid waste can be broadly divided into two heads:
1. Organic or combustible matters
2. Inorganic or mineral or non- combustible matter
Organic or combustible matter: This includes dry animal and vegetable refuse, animal excreta, tree leaves, sticks, rags etc. This waste is subject to decay with time and evolve highly offensive odour and gas with are highly detrimental to health.
Inorganic waste: This consist of non- organic, non- combustible materials such as grit, dust, mud, metal, plastic broken glass, tiles, waste building materials etc. it is not subject to decay and therefore stay so long.