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  • Glossary
| Last Updated:12/12/2023



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air pollution

five major classes of pollutants are discharged into the air: carbon monoxide, particulates, sulfur oxides, hydrocarbons, and nitrogen oxides. In addition to the automobile, other major sources are from combustion of fuel in electric power plants, industrial processes, and space heating, from the combustion in solid-waste disposal, coal-waste fires, and agricultural burning.

aeration Tank

an aeration tank is a place where a liquid is held in order to increase the amount of air within it. The most common uses of aeration tanks are in wastewater recovery, as the high oxygen levels will increase the speed at which the water is cleaned. There are two main methods of aerating liquid: forcing air through the liquid or forcing liquid through the air.

atomic absorption spectroscopy

atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state.


afforestation is the planting of trees for commercial purposes, usually on land supporting non-forest veld types, e.g. grassland or fynbos.

atomic energy

energy released in nuclear reactions. When a neutron splits an atom's nucleus into smaller pieces it is called fission. When two nuclei are joined together under millions of degrees of heat it is called fusion.


the 500 km thick layer of air surrounding the earth which supports the existence of all flora and fauna.


the controlled rearing of fish or shellfish by people or corporations who own the harvestable product, often involving the capture of the eggs or young of a species from wild sources, followed by rearing more intensively than possible in nature.

ancient forest

a forest that is typically older than 200 years with large trees, dense canopies and an abundance of diverse wildlife.

alternative transportation

modes of travel other than private cars, such as walking, bicycling, roller blading, carpooling and transit.

alternative fibers

fibers produced from non-wood sources for use in paper making.


(sustainability) an ecologically based farming system, that, through the integration of trees in farms, increases social, environmental and economic benefits to land users.

agenda 21 global sustainable development

the global sustainable development agenda set out in the Rio Declaration on Environment and Development, which was established at the Earth Summit in 1992. Agenda 21 consists of 40 chapters, and at its roots are 27 principles. There are four broad sections which cover a range of issues: social and economic dimensions; conservation and management of resources for development; strengthening the role of major groups; and implementation. Agenda 21 highlights the importance of national strategies with international cooperation. It concludes proposals for the integration of environment and development issues in decision making and provisions for international institutional arrangements and legal mechanisms. Agenda 21 is an important document which has broad support among nations on all aspects of environment related to social and economic growth.

aerobic digester

an aeration tank that is used to treat waste activated humus or primary sludges or a mixture of them, usually in a small plant with extended aeration or contact stabilization treatment. A typical operational problem associated with an aerobic digester is pH control. For example, when pH drops, this may indicate normal biological activity or low influent alkalinity. This problem is corrected by adding alkalinity, i.e. lime, bicarbonate, etc.


a suspension of small liquid or solid particles in gas.

alternative energy

energy that is not popularly used and is usually environmentally sound, such as solar or wind energy (as opposed to fossil fuels).


in the legislative sense, a bill or measure passed by both houses of Congress; a law.

acid rain

the precipitation of dilute solutions of strong mineral acids, formed by the mixing in the atmosphere of various industrial pollutants -- primarily sulfur dioxide and nitrogen oxides -- with naturally occurring oxygen and water vapor.

alternative energy sources

energy that does not come from fossil fuels (such as coal, oil, gas), for example wind, flowing water, solar energy and biomass.

algal blooms

sudden spurts of algal growth, which can affect water quality adversely and indicate potentially hazardous changes in local water chemistry. (Source: US EPA)


simple rootless plants that grow in sunlit waters in proportion to the amount of available nutrients. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals. (Source: US EPA)

air quality

 a measure of the level of pollution in the air.


 a corrosive solution with a Ph of less than 7 (Source: US EPA)