Summarized the mechanism of phosphorus and nitrogen removal from wastewater

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The mechanism of biological nitrogen removal in wastewater consists of two parts: 1. Assimilation by microorganisms to form new cells (a relatively minor process); 2. Conversion of organic nitrogen through ammonification, nitrification, and denitrification into molecular nitrogen, which is then released into the atmosphere (the main process). Organic substances such as proteins and urea enter the biological nitrogen removal system along with the wastewater; under the action of protein hydrolyases, they are broken down into amino acids. Amino acids undergo deamination under the action of deaminases, converting organic nitrogen into ammonium nitrogen (ammonification reaction). Part of this ammonium nitrogen is utilized by microorganisms for the growth of bacterial cells, while the remaining part is further decomposed and oxidized by nitrifying bacteria. First, it is converted into nitrite nitrogen under the action of nitrite-oxidizing bacteria, and then into nitrate nitrogen under the action of nitrate-oxidizing bacteria. At this point, the oxidation process of nitrogen in the wastewater is complete; all these processes take place in the aerobic tank. As the wastewater enters the anoxic (or facultatively anaerobic) tank, denitrification takes place. In the presence of molecular oxygen, denitrifying bacteria oxidize and break down organic matter, using molecular oxygen as the final electron acceptor. In the absence of molecular oxygen, nitrate and nitrite serve as electron acceptors, while oxygen molecules act as hydrogen acceptors to produce H2O and OH-. Organic matter provides energy as a carbon source and electron donor, thereby being oxidized and stabilized. During denitrification, the conversion of nitrate and nitrite is accomplished through both the assimilation and dissimilation processes carried out by denitrifying bacteria. Assimilation is the process in which nitrate and nitrite are reduced to NH3 for the synthesis of new cells. Dissimilation is the process in which nitrate and nitrite are reduced to gaseous substances such as N2 or N2O, NO, with N2 being the main product. The mechanism of biological phosphorus removal in wastewater: Simply put, microorganisms release phosphorus from their cells under anaerobic conditions; then they enter aerobic conditions, where they absorb more phosphorus than they released under anaerobic conditions. In other words, by taking advantage of the microorganisms’ ability to absorb excess phosphorus, this phosphorus is stored in the sludge. This post was last edited by johncom on 2009-3-19 16:29]