| Ethers | (Environmental Engineering) An organic compound which has two hydrocarbon groups bound by an interior oxygen atom. The general formula is R'-O-R". |
| 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. |
| Groundwater | (Environmental Engineering) Water which is contained in geologic strata. Also properly written as two words, ground water. |
| 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. |
| Hydrocarbon | (Environmental Engineering) Any organic compound composed entirely of carbon and hydrogen. Two examples are methane gas and octane. |
| Isomers | (Environmental Engineering) Two or more different compounds with the same chemical formula but different structure and characteristics. |
| Ketones | (Environmental Engineering) Organic compounds with two hydrocarbon groups bonded to a carbonyl group. |
| Landfill | (Environmental Engineering) A legal and controlled area for the placement of wastes into the ground. |