| Aromatic | (Environmental Engineering) A form of bonding in which ring compounds share electrons over more than two atoms. The electrons are delocalized. This leads to unusual ring stability. |
| Attached growth reactor | (Environmental Engineering) A reactor in which the microorganisms are attached to engineered surfaces within the reactor. Examples of attached growth reactors are the trickling filter and the rotating biological contactor. See suspended growth reactor. |
| 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. |
| Bacteria | (Environmental Engineering) One celled microorganisms which do not have a nuclear membrane. |
| 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. |
| Biosynthesis | (Environmental Engineering) Catabolism, the production of new cellular materials from other organic or inorganic chemicals. |
| Carbonaceous biochemical oxygen demand (CBOD) | (Environmental Engineering) The amount of oxygen required to oxidize any carbon containing matter present in a water. |
| Carbonyl | (Environmental Engineering) A functional group with an oxygen atom double bonded to a carbon atom. |
| Cell | (Environmental Engineering) A unit of varying dimensions in a landfill which is isolated from the environment by 6 to 12 inches of soil cover. A cell is one day's waste or less. A cell is covered with soil at the end of each day. |
| CFCs | (Environmental Engineering) Chlorofluorocarbons, chemicals which result in a depletion of the ozone layer in the upper atmosphere. |