| 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. |
| Biofilm | (Environmental Engineering) A film of microorganisms attached to a surface, such as that on a trickling filter, rotating biological contactor, or rocks in natural streams. |
| Biogeochemical cycle | (Environmental Engineering) The cycle of elements through the biotic and abiotic environment. |
| 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. |
| Catabolism | (Environmental Engineering) The production of energy by the degradation of organic compounds. |
| 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. |
| Chemical fixation (or stabilization/solidification) | (Environmental Engineering) A term for several different methods of chemically immobilizing hazardous materials into a cement, plastic, or other matrix. |