| Organic nitrogen | (Environmental Engineering) Nitrogen contained as amines in organic compounds such as amino acids and proteins. |
| Oxidative phosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP) using a chemical substrate and molecular oxygen. |
| Phenyl- | (Environmental Engineering) A benzene ring named as a constituent group, C6H5-. |
| Phosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP). |
| Photophosphorylation | (Environmental Engineering) The synthesis of the energy storage compound adenosine triphosphate (ATP) from adenosine diphosphate (ADP) using solar energy. |
| Primary standards | (Environmental Engineering) Required drinking water quality standards related directly to human health. These standards are required and enforceable by the U.S. EPA. See secondary standards. |
| 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. |
| 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. |
| Recycling | (Environmental Engineering) The recovery and reuse of a product which would otherwise be thrown away. |
| Refuse derived fuel (RDF) | (Environmental Engineering) A fuel derived from the combustible portion of municipal solid waste. The fuel is often processed into small briquettes, similar in size to charcoal. |