| Ductility: | (english) Ductility generally refers to the amount of inelastic deformation which a material or structure experiences before complete failure. Quantitatively, ductility can be defined as the ratio of the total displacement or strain at failure, divided by the displacement or strain at the elastic limit. |
| Dynamic equilibrium: | (english) Equilibrium which includes inertial forces. |
| 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. |
| Disinfection | (Environmental Engineering) The destruction or inactivation of pathogenic microorganisms. See sterilization. |
| Dissolved oxygen (DO) | (Environmental Engineering) The amount of molecular oxygen dissolved in water. |
| Dump | (Environmental Engineering) An illegal and uncontrolled area where wastes have been placed on or in the ground. See Landfill. |