Biological method of nitrogen and phosphorus removal of the basic principles, factors affecting and what are the basic processes

Nitrogen and phosphorus are important nutrient sources for organisms. With the widespread use of chemical fertilizers, detergents and pesticides, the nitrogen and phosphorus content in natural water bodies has increased dramatically, and the cyanobacteria and green algae in the water bodies have proliferated, and the lack of oxygen and the production of toxins in the water bodies have worsened the quality of the water, which is a great harm to the aquatic organisms and human health. However, China's existing municipal wastewater treatment plants are mainly focused on the removal of organic matter, sewage (wastewater) water primary treatment is only to remove the sand and gravel in the water and suspended solids; in aerobic biological treatment, domestic wastewater by biological degradation, most of the soluble carbonaceous organic matter is removed.

At the same time produce NH3-N , and and, of which 25% of nitrogen and about 19% of phosphorus is absorbed by microorganisms synthesized cells, through the discharge of sludge to get rid of; the secondary biological treatment is to remove the soluble organic matter in the water, can effectively reduce the sewage and , but the N, P and other nutrients can only be removed by 10% to 20%, and the result is far from reaching the secondary discharge standards. Therefore, the research and development of economic, efficient, suitable for the existing sewage treatment plant transformation of nitrogen and phosphorus removal process is particularly important.

Biological denitrification and phosphorus removal mechanism

Biological denitrification mechanism

The basic principle of biological denitrification of sewage is that, on the basis of organic nitrogen converted to ammoniacal nitrogen, the first use of aerobic nitrification by nitrification, nitrifying bacteria and nitrifying bacteria synergistic effect, ammoniacal nitrogen through nitrification into nitrous nitrogen, nitrified nitrogen, i.e., will be converted to and . Under anoxic conditions, nitrate nitrogen is converted into nitrogen by denitrification, i.e., nitrogen is reduced to nitrogen by denitrification and denitrification, which is released into the atmosphere, and participates in the nitrogen cycle in nature. Nitrogen-containing substances in the water are reduced in large quantities, reducing the potential danger of the effluent and achieving the purpose of nitrogen removal from wastewater.

The removal of nitrogen from wastewater also includes the conversion of nitrogen into cellular protoplasmic components by the assimilation of microorganisms. The main process is as follows: ammonification is organic nitrogen in the role of ammonia bacteria into ammonia nitrogen. Nitrification is further converted to nitrate nitrogen under the action of nitrifying bacteria. Among them, nitrite bacteria and nitrate bacteria are aerobic autotrophic bacteria, taking inorganic carbon compounds as carbon source, and obtaining energy from the oxidation reaction of or . where the optimum temperature for nitrification is 25-35°C in pure culture and 30-40°C in soil, and the optimum pH is alkaline. Denitrification is denitrifying bacteria (most of them are heterotrophic parthenogenetic anaerobes, DO<0.5mg/L) in anoxic conditions, nitrate nitrogen as electron acceptor and organic matter as electron donor for anaerobic respiration, reducing nitrate nitrogen to N2 or NO2- while degrading organic matter.

Biological phosphorus removal principle

Phosphorus exists in nature in two states: soluble or particulate. The so-called phosphorus removal is to convert dissolved phosphorus into particulate phosphorus in water to achieve phosphorus water separation. Wastewater in biological treatment, in anaerobic conditions, the growth of polyphosphorus bacteria is inhibited, in order to their own growth will be released from their cells in the polyphosphate, at the same time produce the use of wastewater in the simple dissolved organic substrates required for the energy, said the process for the release of phosphorus. After entering the aerobic environment, their vitality is fully restored, and they take up a large amount of dissolved orthophosphate from the wastewater while making full use of the substrate, thus completing the process of phosphorus aggregation. The purpose of phosphorus removal can be achieved by removing these microorganisms from the wastewater that have taken up a large amount of phosphorus.

The process of anaerobic release of phosphorus

Polyphosphorus bacteria in anaerobic conditions, the decomposition of the body of polyphosphate to produce ATP, the use of ATP in an active mode of transport to absorb the three types of substrates provided by the acid-producing bacteria to enter the cell synthesis of PHB. at the same time, released out of the environment.

Aerobic phosphorus uptake process

Polyphosphorus bacteria in aerobic conditions, decomposition of PHB and exogenous substrates in the body, the production of a proton drive to transport the outside of the body into the body to synthesize ATP and nucleic acids, and polymerization of excess into the cellular store: polyphosphate (heterochromatic particles).