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What are the factors that affect the metabolism of phosphorus removal bacteria?

In biological phosphorus removal, phosphorus accumulating bacteria release phosphorus in anaerobic state, and excessive phosphorus intake in aerobic state. Phosphorus is removed by discharging phosphorus-rich excess sludge. The factors that affect the metabolism of phosphorus accumulating bacteria include: temperature, pH value, DO in anaerobic tank, nitrate nitrogen in anaerobic tank, sludge age, CP ratio, RBCOD content, glycogen , HRT, etc.

1.Temperature

The effect of temperature on the effect of phosphorus removal is not as obvious as the effect on the biological nitrogen removal process. Within a certain temperature range, when the temperature change is not very large, the biological phosphorus removal can operate successfully. Experiments show that the temperature of biological phosphorus removal should be higher than 10℃, because the growth rate of phosphorus accumulating bacteria will slow down at low temperature.

2.PH Value

When the pH was between 6.5 and 8.0, the phosphorus content and phosphorus absorption rate of phosphorus-accumulating microorganisms remained stable, and when the pH value was lower than 6.5, the phosphorus absorption rate dropped sharply. When the pH value suddenly decreases, the concentration of phosphorus increases sharply in both the aerobic zone and the anaerobic zone. The greater the range of pH decrease, the greater the release amount, which indicates that the phosphorus release caused by the decrease in pH is not the effect of the phosphorus accumulating bacteria itself on the pH change. It is a physiological and biochemical reaction, but a purely chemical "acid-soluble" effect, and the greater the anaerobic release caused by pH drop, the lower the aerobic phosphorus absorption capacity, which indicates that the release caused by pH drop is destructive. Invalid. A slight absorption of phosphorus occurs when the pH is raised.

3.Dissolved Oxygen

Each milligram of molecular oxygen can consume 1.14 mg of easily biodegradable COD, which inhibits the growth of phosphorus-accumulating organisms and makes it difficult to achieve the expected phosphorus removal effect. In the anaerobic zone, a lower dissolved oxygen value should be maintained, which is more conducive to the fermentation of anaerobic bacteria to produce acid, so that the phosphorus accumulating bacteria can release phosphorus better. In addition, less dissolved oxygen is more conducive to reducing the consumption of easily degradable organic matter. In turn, the phosphorus accumulating bacteria can synthesize more PHB.

In the aerobic zone, more dissolved oxygen is needed, which is more conducive to the decomposition of stored PHB substances by the phosphorus accumulating bacteria to obtain energy to absorb the dissolved phosphate in the sewage to synthesize the cellular phosphorus accumulation. The DO in the anaerobic zone should be controlled below 0.3 mg/l, and the DO in the aerobic zone should be controlled above 2 mg/l, so as to ensure the smooth progress of anaerobic phosphorus release and aerobic phosphorus absorption.

4.Anaerobic Pond Nitrate Nitrogen

The existence of nitrate nitrogen in the anaerobic zone consumes organic substrates and inhibits the release of phosphorus by PAO, thus affecting the absorption of phosphorus by phosphorus accumulating bacteria under aerobic conditions. On the other hand, the presence of nitrate nitrogen will be used by Aeromonas as an electron acceptor for denitrification, thereby affecting its fermentation intermediate product as an electron acceptor for acid production, thereby inhibiting the phosphorus release and phosphorus uptake of PAO capacity and synthesis capacity of PHB. Each milligram of nitrate nitrogen can consume 2.86 mg of easily biodegradable COD, resulting in the inhibition of anaerobic phosphorus release, generally controlled below 1.5 mg/l.

5.Mud Age

Since the biological phosphorus removal system mainly realizes phosphorus removal by discharging excess sludge, the amount of excess sludge determines the phosphorus removal effect of the system, and the length of sludge age has a direct effect on the discharge of excess sludge and the uptake of phosphorus by sludge. Impact. The smaller the sludge age, the better the phosphorus removal effect. This is because reducing the sludge age can increase the discharge of excess sludge and the amount of phosphorus removal in the system, thereby reducing the phosphorus content in the effluent of the secondary sedimentation tank. However, for the biological treatment process of simultaneous phosphorus and nitrogen removal, in order to meet the growth requirements of nitrifying and denitrifying bacteria, the sludge age is often controlled to be relatively large, which is the reason why the phosphorus removal effect is unsatisfactory. Generally, the sludge age of the biological treatment system for phosphorus removal is controlled within 3.5 to 7 days.

6.COD/TP

In the biological phosphorus removal process of sewage, the type and content of organic substrates in the anaerobic stage and the ratio of nutrients required by microorganisms to phosphorus in sewage are important factors affecting the effect of phosphorus removal. The anaerobic release and aerobic uptake effects of phosphorus are different when different organic matter is used as the substrate. The easily degradable organic compounds with small molecular weight (such as volatile fatty acids, etc.) are easily utilized by phosphorus accumulating bacteria, decompose the polyphosphates stored in the body to release phosphorus, and have a strong ability to induce phosphorus release, while the macromolecular refractory organic compounds induce phosphorus. Phosphorus-accumulating bacteria have poor ability to release phosphorus. The more adequate the release of phosphorus in the anaerobic stage, the greater the uptake of phosphorus in the aerobic stage.

In addition, the energy generated by the phosphorus-accumulating bacteria releasing phosphorus in the anaerobic stage is mainly used for its absorption of low-molecular-weight organic substrates as the basis for survival under anaerobic conditions. Therefore, whether the influent water contains enough organic matter is an important factor related to whether the phosphorus accumulating bacteria can survive smoothly under anaerobic conditions. It is generally believed that the COD/TP of the influent water should be greater than 15 to ensure that the phosphorus accumulating bacteria have enough substrates, so as to obtain the ideal phosphorus removal effect.

7.RBCOD (Readily Degradable COD)

Studies have shown that when the easily degradable carbon sources such as acetic acid, propionic acid and formic acid are used as the phosphorus release matrix, the release rate of phosphorus is relatively large, and the release rate has nothing to do with the concentration of the matrix, but is only related to the concentration of activated sludge and the composition of microorganisms. , the release of phosphorus caused by this type of matrix can be represented by a zero-order reaction equation. To be utilized by phosphorus-accumulating bacteria, other types of organic matter must be converted into easily degradable carbon sources of such small molecules before phosphorus-accumulating bacteria can utilize their metabolism.

8.Glycogen

Glycogen is a branched macromolecular polysaccharide composed of multiple glucoses and is the storage form of intracellular sugars. As shown in the figure above, glycogen in the phosphorus accumulating bacteria is formed in an aerobic environment, and the stored energy is metabolized in an anaerobic environment to form NADH, the raw material for the synthesis of PHAs, and provide energy for the metabolism of the phosphorus accumulating bacteria. Therefore, in the case of delayed aeration or peroxidation, the phosphorus removal effect will be very poor, because excessive aeration will consume part of the glycogen in the phosphorus accumulating bacteria in an aerobic environment, resulting in insufficient NADH, the raw material for the formation of PHAs in anaerobic conditions. .

9.HRT

For a well-run biological nitrogen and phosphorus removal system for urban sewage, it generally takes 1.5-2.5 hours and 2.0-3.0 hours for phosphorus release and phosphorus absorption, respectively. Overall, it seems that the phosphorus release process is more important. Therefore, we pay more attention to the residence time of sewage in the anaerobic section. The HRT in the anaerobic section is too short to ensure the effective release of phosphorus. Facultative acidifying bacteria cannot fully decompose macromolecular organic matter in sewage into lower fatty acids that can be ingested by phosphorus accumulating bacteria,and will also affect the release of phosphorus; HRT is too long and unnecessary, which not only increases infrastructure investment and operating costs, but also Some side effects may occur.

In short, phosphorus release and phosphorus absorption are two interrelated processes. Only after sufficient anaerobic phosphorus release can phosphorus accumulating bacteria absorb phosphorus better in the aerobic section, and only phosphorus accumulating bacteria with good phosphorus absorption will be able to absorb phosphorus in the anaerobic stage. Excessive phosphorus release in the oxygen segment, and proper regulation will form a virtuous circle. The data obtained by our factory in the actual operation are: the HRT of the anaerobic section is 1 hour 15 minutes to 1 hour 45 minutes, and the HRT of the aerobic section is suitable for 2 hours to 3 hours and 10 minutes.

10.Reflux Ratio (R)

The most important point of the A/O process to ensure the effect of phosphorus removal is to make the system sludge "carry" enough dissolved oxygen into the secondary sedimentation tank in the aeration tank. The purpose is to prevent the sludge from being disgusted in the secondary sedimentation tank However, if the sludge cannot be quickly discharged, the sludge layer in the secondary sedimentation tank is too thick, and no matter how high DO is, it cannot ensure that the sludge does not release phosphorus anaerobic. Therefore, the reflux ratio of the A/O system should not be too low, and a sufficient reflux ratio should be maintained to discharge the sludge in the secondary sedimentation tank as soon as possible.

However, an excessively high reflux ratio will increase the energy consumption of the reflux system and the aeration system, and will shorten the actual residence time of the sludge in the aeration tank, affecting the removal effect of BOD5 and P. How to reduce the reflux ratio as much as possible on the premise of ensuring rapid sludge discharge needs to be repeatedly explored in actual operation. It is generally considered that R may be in the range of 50 to 70%.

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