| Corrosive waste | (Environmental Engineering) A waste that is outside the pH range of 2 to 12.5 or a waste that corrodes steel at a rate greater than 6.35 mm (0.25 in) per year. One of EPA's four hazardous waste properties. |
| Covalent bond | (Environmental Engineering) A bond in which electrons are shared approximately equally by two atoms. |
| Cybernetic | (Environmental Engineering) Systems which change in response to feedback. |
| Decomposers | (Environmental Engineering) Organisms which utilize energy from wastes or dead organisms. Decomposers complete the cycle by returning nutrients to the soil or water and carbon dioxide to the air or water. |
| Denitrification | (Environmental Engineering) The anoxic biological conversion of nitrate to nitrogen gas. It occurs naturally in surface waters low in oxygen, and it can be engineered in wastewater treatment systems. |
| Deoxygenation | (Environmental Engineering) The consumption of oxygen by the different aquatic organisms as they oxidized materials in the aquatic environment. |
| Discrete settling | (Environmental Engineering) Settling in which individual particles settle independently, neither agglomerating or interfering with the settling of the other particles present. This occurs in waters with a low concentration of particles. |
| Disease | (Environmental Engineering) Any impairment of the normal function of an organism. |
| Dissolved oxygen (DO) | (Environmental Engineering) The amount of molecular oxygen dissolved in water. |
| Ecology | (Environmental Engineering) The study of living organisms and their environment or habitat. |