| Epilimnion | (Environmental Engineering) The top layer of a lake. |
| Fermentation | (Environmental Engineering) Energy production without the benefit of oxygen as a terminal electron acceptor, i.e. oxidation in which the net effect is one organic compound oxidizing another. See respiration. |
| Flocculant settling | (Environmental Engineering) Settling in which particle concentrations are sufficiently high that particle agglomeration occurs. This results in a reduction in the number of particles and an increase in average particle mass. As agglomeration occurs higher settling velocities result. |
| Fluidization | (Environmental Engineering) The suspension of particles by sufficient upward velocity of the fluid. During fluidization the gravity force is overcome by a combination of buoyancy and fluid friction. |
| Greenhouse gases | (Environmental Engineering) Gases which trap solar radiation. Of the solar energy entering the earth's atmosphere a portion is reflected back and a portion penetrates onto the earth's surface. The portion reflected back from the earth's surface is at a different wavelength that when it entered. Carbon dioxide and other gases, which pass solar radiation, absorb this reflected radiation, increasing the earth's temperature. This is much like a greenhouse, hence the name. |
| Hindered (Zone) settling | (Environmental Engineering) Settling in which particle concentrations are sufficient that particles interfere with the settling of other particles. Particles settle together as a body or structure with the water required to traverse the particle interstices. |
| Hypolimnion | (Environmental Engineering) The lower layer of a lake. |
| Ion exchange | (Environmental Engineering) An adsorption process in which one ion is exchanged for another ion of like charge. There is an equivalence of exchanged charge. |
| Irreversible reaction | (Environmental Engineering) A reaction in which the reactant(s) proceed to product(s), but the products react at an appreciable rate to reform reactant(s). |
| Landfilling | (Environmental Engineering) The placement of wastes into the land under controlled conditions to minimize their migration or effect on the surrounding environment. |