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.

According to physical state, wastes can be classified as;
Solid wastes
Sludge wastes
Liquid wastes
Gaseous wastes

Solid wastes
These are wastes which comprise of about 73% of the solid wastes. Example of solid
wastes include house hold 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
Hazardous waste
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, organo chlorides, 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;
Recycled wastes
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.
Exercise 3
Visit dumping sites and industrial areas. List and classify the various types of wastes observed
By their physical states
As hazardous and non- hazardous wastes
As recycled and non-recycled wastes.

Waste disposal is the process of getting rid of waste materials that people generate or
the act of getting rid of unwanted materials and items of no value or in excess.

Reducing the amount of waste we produce. For example we do not have to buy plastic bags each time we go shopping. We carry a woven basket instead.

Re-using items instead of throwing them away. For instance we can use an empty margarine container to store sugar.

Recycling waste material. Some wastes can be changed to other products. For example broken glass can be melted and used to make new glass bottles.

Most cities and towns have waste collecting departments or private firms that gather municipal solid wastes from homes and other buildings.

This is the method which involves burning of waste products at high temperatures.

Land disposal
This involves hauling garbage to an area owned by a community or a private firm. Land disposal may range from unsanitary open dumps to sanitary landfills.
Unsanitary open dumps are poor methods of waste disposal because they cause environmental problems such as:
May produce bad odors
Ruin the area’s appearance
Rain water drains through refuse and carry harmful substances to nearby streams and to water used for drinking.
Decomposing wastes produce flammable gas called methane and methane explosions may result.
Sanitary land fills are intended to protect the environment. The waste is packed firmly
by tractors and covered with specially manufactured materials. The covering is done in
order to limit blowing papers, odors, fires and run off of polluted water.
Note: A secure sanitary land fill is lined with materials that prevent water from carrying
leachates (dissolved substances) from the refuse into underground water supplies.

Waste bin collection
This is intended to collect smaller quantities of wastes. The waste bins are placed along
the corridors or in every room or house which in turn is emptied into big waste bins.

Sewage system
Sewage is water that contains waste matter produced by human beings. It is also called waste water. Sewage comes from toilets and sinks of homes, restaurants, office buildings and factories Sewage system involves the use of collection pipes or pit latrines where the sewage is periodically removed and transported to a sewage works where it is treated to make it harmless.

Recycling is the process of reusing the materials instead of throwing them away. The
waste products are used to manufacture the same or different products such as:
Cardboard or cow dung can be used to generate Biogas.
Thermoplastics can be melted and remoulded.
Organic wastes produced domestically or commercially can be composted.
Kitchen refuse can be used to feed animals such as dogs, pigs, cattle, etc.
Newspapers, magazines cartons and packing materials can be used to manufacture
tissue papers.
In Tanzania coffee husks are converted into a form of charcoal which is used for
Coconut and agricultural wastes can be converted into papers.
Jute wastes can be converted into hard boards.
Sewage and factory wastes can be purified to an extent that can be pumped into
storage tanks and used for all domestic purposes.
Glass bottles can be used for storing specimens or medicines.

Waste generation reduction
Waste reduction is deliberate effort to produce fewer wastes. For example, people can
reduce waste by buying items that can last longer or have less packing.

The following are some of the effects of poor waste disposal;
Produce bad odors
Ruin the areas appearance
Decomposing wastes produce flammable gas called methane and this may result to
explosion of the gas which may cause a loss of material property and human life.
Rain water drains through refuse and carry harmful substances to nearby streams and
water used for drinking which may later lead to eruption of diseases like cholera and
may kill organisms found in water
Poor disposal of clinical wastes on land fill site may encourage bacterial breeding leading to possible infections in the area
Unregulated dumps where waste is burned in the open can cause smoke and foul smelling air.
Burning may also result into production of air pollutants which may affect the ozone layer and possible cause of respiratory diseases.

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