Water biological phosphorus removal process, the anaerobic section of the type of organic substrate, content and nutrients required by microorganisms and the ratio of phosphorus in the wastewater is an important factor affecting the effect of phosphorus removal. The anaerobic release of phosphorus and aerobic uptake effects are different when different organic matter is the substrate. Smaller molecular weight easily degradable organic matter (such as volatile fatty acids, etc.) can be easily utilized by polyphosphorus bacteria to decompose and release phosphorus from the polyphosphate stored in its body, which induces stronger phosphorus release, while high molecular weight difficult to degrade organic matter induces poorer phosphorus release ability of polyphosphorus bacteria. The fuller the release of phosphorus in the anaerobic stage, the greater the uptake of phosphorus in the aerobic stage. In addition, the energy generated by phosphorus release in the anaerobic stage of B. polyphosphoribacteria is mainly used for its uptake of low molecular organic substrates as the basis for survival under anaerobic conditions.
2, RBCOD (easy to degrade COD)
Research shows that when the acetic acid, propionic acid and formic acid and other readily degradable carbon sources as a phosphorus release substrate, the phosphorus release rate is larger, the release rate has nothing to do with the concentration of the substrate, but only with the concentration of the activated sludge and the microbial composition of the phosphorus release of the substrate can be used to express the zero-level reaction equation. And other types of organic matter to be utilized by the polyphosphorus bacteria, must be converted into such small molecules of easily degradable carbon source, the polyphosphorus bacteria can be used to metabolize.
3, glycogen
Glycogen is a large molecule polysaccharide with branches composed of multiple glucose, is the storage form of intracellular sugar. As shown in the figure above, glycogen is formed in the aerobic environment of the polyphosphorus bacteria, and stored energy in the anaerobic environment to metabolize and form the raw material for the synthesis of PHAs, NADH, and to provide energy for the metabolism of the polyphosphorus bacteria. Therefore, in the case of delayed aeration or over-oxidation, the effect of phosphorus removal will be very poor, because excessive aeration will consume part of the glycogen in the body of A. polyphosphoria in aerobic environment, resulting in insufficient raw material NADH for the formation of PHAs in anaerobic environment.
4, reflux ratio (R)
A / O process to ensure that the effect of phosphorus removal is extremely important point, is to make the system sludge in the aeration tank, "carrying" enough dissolved oxygen into the secondary sedimentation tank, the purpose of which is to prevent the sludge from anaerobic release of phosphorus in the secondary sedimentation tank, but if you can't drain quickly, the secondary sedimentation tank mud layer is too thick. However, if the sludge can not be discharged quickly, the mud layer in the secondary sedimentation tank is too thick, and then high DO can not guarantee that the sludge does not release phosphorus anaerobically, therefore, the reflux ratio of the A/O system should not be too low, and it should be maintained at a sufficient reflux ratio, so as soon as possible, the sludge will be discharged from the secondary sedimentation tank. However, too high reflux ratio will increase the energy consumption of reflux system and aeration system, and it will shorten the actual residence time of sludge in the aeration tank, affecting the removal effect of BOD5 and P. How to minimize the reflux ratio under the premise of ensuring rapid sludge discharge needs to be repeatedly figured out in actual operation. It is generally believed that R in the range of 50~70% can be.
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