| Stiffness: | (english) This is a general term which may be applied to materials or structures. When a force is applied to a structure, there is a displacement in the direction of the force; stiffness is the ratio of the force divided by the displacement. High stiffness means that a large force produces a small displacement. When discussing the stiffness of a material, the concept is the same, except that stress substitutes for force, and strain substitutes for displacement; see modulus of elasticity. |
| Transmissibility: | (english) The principle stating that a force has the same external effect on an object regardless of where it acts along its line of action. |
| 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. |
| Amine | (Environmental Engineering) A functional group consisting of "-NH2." |
| Amino acid | (Environmental Engineering) A functional group which consists of a carbon with a carboxylic acid, "-COOH" and an amine, "-NH2." These compounds are the building blocks for proteins. |
| Attached growth reactor | (Environmental Engineering) A reactor in which the microorganisms are attached to engineered surfaces within the reactor. Examples of attached growth reactors are the trickling filter and the rotating biological contactor. See suspended growth reactor. |
| Biochemical oxygen demand (BOD) | (Environmental Engineering) The amount of oxygen required to oxidize any organic matter present in a water during a specified period of time, usually 5 days. It is an indirect measure of the amount of organic matter present in a water. |
| Biofilm | (Environmental Engineering) A film of microorganisms attached to a surface, such as that on a trickling filter, rotating biological contactor, or rocks in natural streams. |
| Carbonaceous biochemical oxygen demand (CBOD) | (Environmental Engineering) The amount of oxygen required to oxidize any carbon containing matter present in a water. |
| Chemical oxygen demand (COD) | (Environmental Engineering) The amount of oxygen required to oxidize any organic matter in the water using harsh chemical conditions. |