| 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. |
| Hydrocarbon | (Environmental Engineering) Any organic compound composed entirely of carbon and hydrogen. Two examples are methane gas and octane. |
| In situ treatment | (Environmental Engineering) Treatment of a waste in place, as opposed to pumping or digging the waste up and then treating it. |
| Infectious disease | (Environmental Engineering) A disease caused by pathogenic organisms. |
| Influent | (Environmental Engineering) The fluid entering a system, process, tank, etc. An effluent from one process can be an influent to another process. See effluent. |
| Kerogen | (Environmental Engineering) A fossilized organic material present in oil shale and some other sedimentary rocks. |
| Metabolism | (Environmental Engineering) The processes which sustain an organism, including energy production, synthesis of proteins for repair and replication. |
| Nitrification | (Environmental Engineering) The biological oxidation of ammonia and ammonium sequentially to nitrite and then nitrate. It occurs naturally in surface waters, and can be engineered in wastewater treatment systems. The purpose of nitrification in wastewater treatment systems is a reduction in the oxygen demand resulting from the ammonia. |
| Nitrogenous oxygen demand (NOD) | (Environmental Engineering) The amount of oxygen required to oxidize any ammonia present in a water. |