| Advanced wastewater treatment | (Environmental Engineering) The removal of any dissolved or suspended contaminants beyond secondary treatment, often this is the removal of the nutrients nitrogen and/or phosphorus. |
| Cell | (Environmental Engineering) A unit of varying dimensions in a landfill which is isolated from the environment by 6 to 12 inches of soil cover. A cell is one day's waste or less. A cell is covered with soil at the end of each day. |
| Covalent bond | (Environmental Engineering) A bond in which electrons are shared approximately equally by two atoms. |
| Disinfection | (Environmental Engineering) The destruction or inactivation of pathogenic microorganisms. See sterilization. |
| Equivalent | (Environmental Engineering) The mass of the compound which will produce one mole of available reacting substance. Thus, for an acid, this would be the mass of acid which will produce one mole of H+, for a base, one mole of OH-. |
| Facultative | (Environmental Engineering) A group of microorganisms which prefer or preferentially use molecular oxygen when available, but are capable of suing other pathways for energy and synthesis if molecular oxygen is not available. |
| 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. |
| Mixed liquor suspended solids (MLSS) | (Environmental Engineering) The total suspended solids concentration in the activated sludge tank. |
| Mixed liquor volatile suspended solids (MLVSS) | (Environmental Engineering) The volatile suspended solids concentration in the activated sludge tank. |
| Primary treatment | (Environmental Engineering) Treatment which includes all operation prior to and including primary treatment, e.g., bar screening, grit removal, comminution, and primary sedimentation. |