| Disinfection | (Environmental Engineering) The destruction or inactivation of pathogenic microorganisms. See sterilization. |
| 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. |
| Fixed solids | (Environmental Engineering) (FS) are the solids that do not volatilize at 550°C. |
| 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. |
| HAPs | (Environmental Engineering) Hazardous air pollutants. |
| 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. |
| Kerogen | (Environmental Engineering) A fossilized organic material present in oil shale and some other sedimentary rocks. |
| Landfilling | (Environmental Engineering) The placement of wastes into the land under controlled conditions to minimize their migration or effect on the surrounding environment. |
| Mass balance | (Environmental Engineering) An organized accounting of all inputs and outputs to an arbitrary but defined system. Stated in other terms, the rate of mass accumulation within a system is equal to the rate of mass input less the rate of mass output plus the rate of mass generation within the system. |
| Nitrogenous oxygen demand (NOD) | (Environmental Engineering) The amount of oxygen required to oxidize any ammonia present in a water. |