| Aerobic process | (Environmental Engineering) A process which requires molecular oxygen. |
| Anaerobes | (Environmental Engineering) A group of organisms that do not require molecular oxygen. These organisms, as well as all known life forms, require oxygen. These organisms obtain their oxygen from inorganic ions such as nitrate or sulfate or from protein. |
| Autotrophic | (Environmental Engineering) Organisms which utilize inorganic carbon for synthesis of protoplasm. Ecologists narrow the definition further by requiring that autotrophs obtain their energy from the sun. In microbiologist parlance, this would be a photoautotroph. See photoautotrophic and chemoautotrophic. |
| Biochemical oxygen demand (BOD) | (Environmental Engineering) The amount of oxygen required to oxidize any organic matter present in a water during a specified period of time, usually 5 days. It is an indirect measure of the amount of organic matter present in a water. |
| Carbonaceous biochemical oxygen demand (CBOD) | (Environmental Engineering) The amount of oxygen required to oxidize any carbon containing matter present in a water. |
| Chemical oxygen demand (COD) | (Environmental Engineering) The amount of oxygen required to oxidize any organic matter in the water using harsh chemical conditions. |
| Clarifier (sedimentation basin) | (Environmental Engineering) A tank in which quiescent settling occurs, allowing solid particles suspended in the water to agglomerate and settle to the bottom of the tank. The solids resulting from the settling being removed as a sludge. |
| Covalent bond | (Environmental Engineering) A bond in which electrons are shared approximately equally by two atoms. |
| Deoxygenation | (Environmental Engineering) The consumption of oxygen by the different aquatic organisms as they oxidized materials in the aquatic environment. |
| Elementary reaction | (Environmental Engineering) A reaction in which the rate expression corresponds to the stoichiometric equation. |