ABSTRACT
We define a biological reaction as a reaction mediated by organisms. It encompasses both the organisms and the underlying chemical reactions. To fully apply the knowledge of biological reactions to the treatment of water and wastewater, the chemical nature of these reactions must be given center stage. In other words, to control the process of removing nitrogen by nitrification-denitrification, the intrinsic chemical reactions must be unraveled and fully understood. The organisms only serve as mediators (i.e., the producer of the enzymes needed for the reaction). Thus, on the most fundamental level, nitrogen removal is a chemical process (more accurately, a biochemical process), and the treatment for removal of nitrogen by nitrificationdenitrification as used in this textbook is chemical in nature and the process is a chemical unit process. In fact, nitrification-denitrification removal of nitrogen can be effected by purely enzymatic means by providing the needed enzymes externally without ever using microorganisms.
