Waste.

Waste can be defined as unwanted materials or substances that are left after you have used something. Waste materials or substances are unwanted because the good part of them has been removed or it is not used.


Types of Waste

According to physical state, wastes can be classified as;

a. Solid wastes
b. Sludge wastes
c. Liquid wastes
d. Gaseous wastes

Solid wastes

These are wastes which comprise of about 73% of the solid wastes. Example of solid wastes include household solid wastes such as vegetable, fruit and garden wastes, papers, cans, plastics, bread wrappers, broken glassware, batteries from watches, radios, mobile phones, etc. and junked automobiles.

Industrial solid wastes

These types of wastes include packaging materials, metal turnings, scrappers, plastics and junked automobiles.

Medical solid wastes

These include packaging, used syringes and soiled dressings.
Market, yard and street sweepings
These are wastes such as paper, glass, cans, plastics, and vegetable wastes.

Sludge wastes

These are semi-solid wastes i.e. wastes which are neither solids nor liquids, for example, a mixture of livestock urine and cow dung.

Liquid wastes

These are wastes which are in the form of liquid or watery materials. They contain less than 25% solid substances. Example of liquid wastes include water from sinks, wash basins and baths, urine, industrial effluent, oil spills and agricultural chemicals e.g. insecticides and pesticides.

Gaseous wastes

These are waste materials which are released into the atmosphere in gaseous state. Examples of gaseous wastes are carbon dioxide, carbon monoxide, sulphur dioxide and nitrogen dioxide.
Most of the gaseous wastes come from industries and automobile exhaust fumes, laboratories and burning of organic materials such as plastics and polythene bags.

Wastes can also be classified as
a. Hazardous waste
b. Non- hazardous wastes

Hazardous wastes:

These are harmful wastes which can endanger the health of living organisms. Examples of hazardous wastes include paints, engine oil, car batteries, used syringes, soiled dressings, organochlorides, radioactive elements and heavy metals e.g. lead and mercury.

Non hazardous wastes:

These are wastes which are not harmful in that they do not endanger the health of living organisms. Examples of such wastes include packing materials, papers, plastics, cans, water from wash basins, baths, etc, vegetable, fruit and garden wastes and glass.

Furthermore, wastes can also be classified as;

a. Recycled wastes
b. Non- recycled wastes

Recycled wastes

These are wastes which can be used to manufacture new products. The used materials are recycled instead of being thrown away. Examples of waste materials which can be recycled include metals, glass, papers, cow dung, beer bottles and plastic bags.

Non- recycled wastes

These are wastes which cannot be used to manufacture new products and cannot be used again e.g. soiled papers and cotton wool.