Overview of Traditional Biological Denitrification and Phosphorus Removal Process

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1 Traditional biological nitrogen and phosphorus removal process

It can be seen from the principle of biological phosphorus removal that almost all biological phosphorus removal is activated sludge method, and biofilm method is rare
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As a process of the biofilm method—Linpor-CN process, in an anoxic-aerobic two-stage continuous flow operation mode, it can effectively remove organic matter and total nitrogen, but also effectively remove phosphorus.

However, in most cases, biological phosphorus removal and biological nitrogen removal occur simultaneously in the same treatment process
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The most widely used biological denitrification and phosphorus removal processes include A/O, A2/O, Bardenpho, UCT, Phoredox process (modified Battenpu process), oxidation ditch process and VIP process, etc.

(1) A ₂ /O phosphorus and nitrogen removal process The characteristics of A ₂ /O (Anaerobic/Aerobic/Oxic) process are as follows: the organic combination of anaerobic, anoxic and aerobic in different environmental conditions and different types of microbial flora, It can remove organic matter and phosphorus and nitrogen at the same time
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The A ₂ /O process is simple, the total hydraulic retention time is less than other similar processes, and no external carbon source is needed.

(2) The difference between the UCT process and the A ₂ /O process is that the sedimentation tank sludge is returned to the anoxic tank instead of the anaerobic tank.
At the same time, the anoxic mixed liquid return from the anoxic tank to the anaerobic tank is increased
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This operation mode can reduce the influence of the anaerobic state of the anaerobic tank from the DO and NOx-N carried by the return sludge, and improve the phosphorus removal effect

(3) VIP (Virginia Initiative Plant) process for dephosphorization and denitrification has the following characteristics: ①Each part of the anaerobic, anoxic, and aerobic stages is composed of two or more small completely mixed reaction cells in series.
There is a good matrix concentration gradient distribution in each reaction section, which can fully increase the release of phosphorus in the anaerobic section and the rate of phosphorus uptake in the aerobic section; at the same time, it also contributes to the complete denitrification of the anoxic section, ensuring strict anaerobic section Anaerobic environment
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②The sludge age is short, the load is high, the operating speed is high, and the phosphorus removal effect is good

(4) MSBR process MSBR is a combination of SBR and A ₂ /O process.
Sewage and denitrified activated sludge enter the anaerobic zone together.
Phosphorus accumulation sludge is fully released here, and then the sludge-water mixture alternately enters the anaerobic zone.
The aerobic zone and the aerobic zone respectively complete denitrification, aerobic degradation of organic matter and phosphorus absorption, and finally settle the water in the SBR tank
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2 Problems in the traditional biological nitrogen and phosphorus removal process

For the A ₂ /O process in the continuous flow process , it is difficult to avoid the adverse effects of the nitrate carried by the sludge return on the anaerobic phosphorus release, and the adverse effects of the dissolved oxygen carried during the mixed liquor return on the denitrification.
And the competition between phosphorus-accumulating bacteria and denitrifying bacteria in carbon source and the contradiction between heterotrophic bacteria and autotrophic bacteria in sludge age
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UCT process, MUCT process and VIP process are all improved forms of A ₂ /O process.