| 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. |
| Fixed suspended solids | (Environmental Engineering) (FSS) is the matter remaining from the suspended solids analysis which will not burn at 550°C. It represents the non-filterable inorganic residue in a sample. |
| Groundwater | (Environmental Engineering) Water which is contained in geologic strata. Also properly written as two words, ground water. |
| HAPs | (Environmental Engineering) Hazardous air pollutants. |
| Heterotrophic | (Environmental Engineering) A group of organisms which obtain carbon for synthesis from other organic matter or proteins. |
| Metabolism | (Environmental Engineering) The processes which sustain an organism, including energy production, synthesis of proteins for repair and replication. |
| Organic compound | (Environmental Engineering) Any compound containing carbon except for the carbonates (carbon dioxide, the carbonates and bicarbonates), the cyanides, and cyanates. |
| Organic nitrogen | (Environmental Engineering) Nitrogen contained as amines in organic compounds such as amino acids and proteins. |
| Phototroph | (Environmental Engineering) Organisms which obtain energy from light using photooxidation. |
| Reactive waste | (Environmental Engineering) A waste which; 1) reacts violently with water, 2) forms potentially explosive mixtures with water, 3) is normally unstable, 4) contains cyanide or sulfide in sufficient quantity to evolve toxic fumes at high or low pH, 5) is capable of exploding if heated under pressure, or 6) is an explosive compound listed in Department of Transportation (DoT) regulations. One of EPA's four hazardous waste properties. |