Wastewater biological phosphorus removal is the use of phosphorus excess phosphorus absorption phenomenon. Polyphosphate bacteria release anaerobic phosphorus under anaerobic conditions. After entering the aerobic zone, polyphosphate accumulating PHB aerobic decomposition, the release of a large number of energy available for phosphorus accumulation and growth of bacteria.
Microorganisms absorb much more phosphorus under aerobic conditions than phosphorus released under anaerobic conditions. As the system often discharges excess sludge, phosphorus that is ingested excessively by the bacteria will also be discharged from the system, resulting in better phosphorus removal.
02 affect the phosphorus removal factors
1, dissolved oxygen
First, anaerobic areas must be controlled strictly anaerobic environment. This is directly related to the growth of polyphosphate bacteria, phosphorus release capacity and the ability to use organic substrates PBH synthesis.
Secondly, it is necessary to provide sufficient dissolved oxygen in the aerobic zone. To meet the polyphosphate bacteria stored PHB degradation, release sufficient energy for its excessive use of phosphorus, in order to effectively absorb phosphorus in wastewater.
The general anaerobic DO should be strictly controlled at 0.2mg / L or less, two aerobic DO should be controlled at 2mg / L or more.
2, nitrate content
The presence of nitrate nitrogen also consumes the organic matrix and inhibits the release of phosphorus by the polyphosphate bacteria, which in turn affects the absorption of phosphorus by the polyphosphate bacteria under aerobic conditions. In addition, the presence of nitrate nitrogen will be part of the polyphosphate as an electron acceptor for denitrification, thus affecting its fermentation products as electron acceptors for fermentation acid production, inhibition of phosphorus-releasing phosphorus and phosphorus-capturing capacity and PBH Synthesis ability.
3, temperature
In general, in the range of 5 ~ 30 ℃, can receive better phosphorus removal effect
4, PH value
PH value of 6 to 8, the release of phosphorus is relatively stable
5, BOD5 load and organic properties
Generally believed that the influent BOD5 / TP greater than 15, we can get the ideal phosphorus removal. For this purpose, a partial inflow of water and a method across the primary sedimentation tank can be used to obtain the amount of BOD5 required for phosphorus removal.
6, mud age
The general purpose of phosphorus removal biological treatment system to control the sludge age 3.5 ~ 7d.
03 sewage biological phosphorus removal process
Phosphorus removal process can be divided into the main process of phosphorus removal process and the side of two types of phosphorus removal process.
In the anaerobic section of mainstream phosphorus removal process, the representative processes include A / O, A2 / O, Bardenpho, Phoredox, UCT, modified UCT, SBR and oxidation ditch.
Flow anaerobic phosphorus removal process is not in the direction of flow, but in the return flow of the measured flow on the sludge. Such as Phostrip process.
Biological phosphorus removal process advantages: phosphorus removal effect is good, and can improve sludge settling performance, reduce the phenomenon of activated sludge expansion. Here are a few commonly used processes.
1, A2 / O process
A2 / O process is based on the A / O process adds an anoxic phase, so that the mixture in the aerobic zone back to the anoxic zone denitrification and denitrification, so that the combination of phosphorus and nitrogen removal. Narrow the aeration zone volume.
However, due to the internal circulation, only a small part of the remaining sludge discharged by the system has undergone a complete phosphorus-phosphorus uptake process, and the rest basically enters the aerobic zone directly from the anoxic zone without being anaerobic, Adverse. And in order to reduce the nitrate in the return sludge, the reflux of the mixture must be increased to increase the power consumption.
2, Phostrip process
The process combines biological and chemical phosphorus removal method, part of the return sludge (about 10% to 20% of the influent flow) diverted to the anaerobic phosphorus pool, the sludge in the anaerobic pool usually stay 8 ~ 12 h, phosphorus accumulation in the anaerobic pond phosphorus release, dephosphorization of the sludge back to the aeration tank to continue phosphorus. The phosphorus-containing supernatant into the chemical sedimentation tank, adding lime precipitation. Its phosphorus removal efficiency can reach more than 90%, phosphorus content in treated effluent can be lower than 1mg · L-1, adaptability to influent water quality fluctuation is less affected by influent BOD, and phosphorus is mostly used as lime The form of sludge is removed by sedimentation, so that the sludge treatment is not as complex as the excess phosphorus sludge.
3, oxidation ditch process
Oxidation ditch process due to its special mode of operation, the formation of space oxygen, aerobic alternating changes, to achieve the purpose of nitrification, denitrification and biological phosphorus removal. It can run at low load and longer mud-age conditions, saving 10% to 20% more energy than conventional processes due to no back-flow. If the water volume or load is high, the process will account for the ground will be great.
All biological phosphorus removal system has the following characteristics: to ensure that the anaerobic zone really in an anaerobic state, there is neither free dissolved oxygen, there is no nitrate and other bound oxygen, such as by changing the sludge return and path In order to avoid nitrate into the anaerobic zone, and to prevent denitrification in anaerobic zone of phosphorus anaerobic phosphorus release of the competitive inhibition; to ensure that the anaerobic zone of water biodegradable organic content, so that poly phosphorus Bacteria in the competition with other bacteria on foodstuffs dominance, such as water can be added in the initial sludge acidic fermentation broth.
04 phosphorus removal facilities management of the operation of what matters
1, anaerobic section is the most critical part of biological phosphorus removal, the volume generally determined by the hydraulic retention time 0.5 ~ 2h, if the water content of biodegradable organic matter is higher, you should try to reduce the hydraulic retention time to ensure that aerobic Section into the water BOD5 content.
2, if the phosphorus emission standards are high, and the selected phosphorus removal process can not meet the effluent requirements, you can add chemical phosphorus removal or filtration to remove low levels of phosphorus remaining in the water.
3, in the sludge treatment process if an anaerobic state, the remaining sludge in the phosphorus will be re-released. Concentration of gravity prone to anaerobic state, phosphorus removal requirements of the remaining sludge can not use this method, but should use the air concentration, mechanical concentration, belt gravity concentration and other non-anaerobic enrichment method. If only gravity concentration is the only option, a chemical precipitation facility must be added to the process to remove the phosphorus contained in the concentrated supernatant.
4, mud age is an important factor affecting biological nitrogen and phosphorus removal. The higher denitrification requirements, the longer the required sludge age, the more detrimental to phosphorus removal. Especially in the water BOD5 / TP is less than 20, the muddy age to control the shorter the better. However, if the influent BOD5 is low and the activated sludge grows slowly, it is impossible to control the mud age too short, at this time, chemical phosphorus removal is required.
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