| Site remediation | (Environmental Engineering) The process of cleaning up a hazardous waste disposal site that has either been abandoned or that those responsible either refuse to cleanup or are financially unable to cleanup. |
| Siting | (Environmental Engineering) Obtaining government (federal, state, and local) permission to construct an environmental processing, treatment, or disposal facility at a given site. |
| Softening | (Environmental Engineering) The removal of divalent cations by precipitation or ion exchange. |
| Source reduction | (Environmental Engineering) The elimination or reduction of the waste at the source by modification of the actual process which produces the waste. |
| Species | (Environmental Engineering) In chemistry, an ion or molecule in solution. |
| Sterilization | (Environmental Engineering) The destruction or inactivation of all microorganisms. See Disinfection. |
| Stratosphere | (Environmental Engineering) The atmosphere from approximately 12 km to 70 km. The temperature of the atmosphere increases in this region.Strong acid |
| Substrate level phosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP) using organic substrates without molecular oxygen. |
| Surface water | (Environmental Engineering) Water which is contained in lakes, rivers, and oceans. |
| Suspended growth reactor | (Environmental Engineering) A reactor in which the microorganisms are suspended in the wastewater. Examples of suspended growth reactors are activated sludge reactors and anaerobic digesters. See attached growth reactor. |