| 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. |
| Colloids | (Environmental Engineering) Small particles which have a negligible settling velocity. These particles have a very small mass so gravitational force is low compared to surface frictional forces. Typical colloidal sizes range from 10-3 mm to 1 mm. |
| Compression settling | (Environmental Engineering) Settling which occurs in the lower reaches of clarifiers where particle concentrations are highest. Particles can settle only by compressing the mass of particles below. |
| Consumers | (Environmental Engineering) Organisms which consume protoplasm produced from photosynthesis or consume organisms from higher levels which indirectly consume protoplasm from photosynthesis. |
| Conversion | (Environmental Engineering) The fraction of a species entering a system which is converted to product. |
| 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. |
| 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. |
| Disinfection | (Environmental Engineering) The destruction or inactivation of pathogenic microorganisms. See sterilization. |
| Electronegativity | (Environmental Engineering) The potential of an atom to attract electrons when the atom is bonded in a compound. The scale is 0 to 4 with 0 being the most electropositive (low attraction) and 4 being the most electronegative (high attraction). |
| Elementary reaction | (Environmental Engineering) A reaction in which the rate expression corresponds to the stoichiometric equation. |