What are the operations for controlled sludge swelling in the activated sludge process?

A variety of chemicals can be used for sludge deep dewatering treatment, and the following common agents will be used for ordinary sludge dewatering: cationic polyacrylamide: this is a polymer flocculant, which can flocculate small particles in the sludge into larger particles through adsorption and bridging, and improve the sedimentation performance and dewatering performance of the sludge.

Polyaluminum chloride: This is an inorganic polymer coagulant, which can coagulate with impurities in the sludge to form an insoluble precipitate, so that the water in the sludge is separated. Lime:

Lime can neutralize with the acidic substances in the sludge, adjust the pH value of the sludge, and promote the cohesion and settlement of the sludge. Diatomaceous earth: Diatomaceous earth has the characteristics of porosity and high specific surface area, which can be used as a filter aid to improve the filtration performance and dewatering performance of sludge.

Things to look out for....

Category 1: Emergency measures.

It is suitable for temporary emergencies, and the main method is to add drugs to enhance the sludge sedimentation performance or directly kill filamentous bacteria. The addition of coagulants such as iron salt and aluminum salt can directly improve the compactness of sludge and ensure the precipitation of water. In addition, adding some chemicals, such as chlorine, to the reflux sludge can also eliminate sludge swelling.

The addition of hydrogen peroxide and ozone can also have the effect of destroying filamentous bacteria.

This method can generally reduce the SVI value quickly, but these methods do not fundamentally control the reproduction of filamentous bacteria, and once the dosing is stopped, the sludge swelling phenomenon can make a comeback. Moreover, the dosing may destroy the microbial growth environment of the biochemical system, resulting in the reduction of the treatment effect, so this method can only be used as a temporary emergency.

The second category: improvement of the biochemical environment.

When sludge expansion occurs in sewage plants, it is generally impossible to solve it from the change of process flow, pool type and aeration mode, and can only inhibit or eliminate the overgrowth of filamentous bacteria by changing the microbial growth environment in the biochemical tank on the basis of the running process. With different processes and water quality, it is difficult to have a one-size-fits-all solution. However, there are several problems that should be paid attention to in biochemical processes.

1) Control of the nature of sewage.

First of all, the pH value should be checked and adjusted, when the pH value is lower than 5, it will not only be beneficial to the sludge expansion, but also will have a certain harm to the normal biochemical reaction, so when the pH value is low, it should be adjusted in time. In addition, in the cold areas of the north, you should pay attention to the water temperature in winter, if the water temperature is low, it should be heated, because low temperature will also lead to the occurrence of sludge expansion. The use of blast aeration can effectively improve the water temperature in winter.

When the nutrients in the sewage are insufficient or unbalanced, they should be supplemented. The content of N and P should be controlled at about BOD:N:P=100:5:1.

If there is digestion before the biochemical system of sewage treatment, the low molecular weight organic acid produced will be conducive to the growth of filamentous bacteria, and the wastewater can be pre-aerated in the conditioning tank to improve. Generally, an air diffuser is used to aerate the regulating tank with an effective water depth of 3-5 meters, and the air supply can be controlled at 3 meters of wastewater. It keeps the wastewater in the regulating tank fresh and effectively prevents odors caused by anaerobic.

2) Maintaining sufficient dissolved oxygen in the pool is particularly important for biochemical systems with high loads, and 3) DO> should generally be controlled at least 2 mg L. 4) The sludge in the sedimentation tank should be discharged or refluxed in time, and 5) the anaerobic phenomenon should be prevented. If anaerobic phenomena occur, 6) the various gases produced will be adsorbed on the sludge, 7) the sludge will also float, and 8) the sedimentation performance will deteriorate.

9) Anaerobic sludge reflux can also lead to the proliferation of filamentous bacteria. In this case, in addition to discharging sludge and removing the dead angle in the sedimentation tank, 10) and shortening the residence time of sludge in the tank, 11) the do value of the aeration tank should also be increased, 12) the water entering and leaving the sedimentation tank should be kept with dissolved oxygen, 13) or the sludge should be aerated and regenerated before returning into the biochemical tank.

Answer: The main reasons for sludge swelling are: more carbohydrates in wastewater, insufficient dissolved oxygen, lack of n, and the following control measures can be taken after sludge swelling: (1) Strengthen aeration and maintain the mixture DO not be less than 1

Control of activated sludge swelling.

Answers]: a, c, d

ACD three reasons, sludge swelling: sludge swelling is mainly caused by the malignant multiplication of filamentous bacteria, and there are also concomitant sludge swelling caused by the abnormal increase of bound water in the sludge. Generally, there are many carbohydrates in sewage, lack of nutrients such as nitrogen, phosphorus, iron, insufficient dissolved oxygen, high water temperature or low pH value, etc., which are easy to cause filamentous bacteria to multiply, resulting in sludge expansion.

In addition, sludge expansion can also be caused by overload, long sludge age, or small organic matter concentration gradients. If the sludge discharge is not smooth, it is easy to cause the expansion of the combined water-based sludge.

There are two types of sludge swelling, one is the swelling of sludge filamentous bacteria caused by the reproduction of a large number of filamentous bacteria in activated sludge, and the other is the non-filamentous swelling caused by the accumulation of highly viscous substances or toxic substances in the colloidal bacteria.

The first category: filamentous bacteria swelling is mainly caused by the reproduction of filamentous bacteria, microscopic observation of the expanded activated sludge, there are filamentous organisms proliferation, these filamentous organisms are entangled with each other, hindering the sludge thickening, and the SVI value usually rises to more than 300.

1) Acidic environment: Acidic is easy for filamentous bacteria to grow and multiply.

2) Insufficient oxygen supply.

3) The water temperature is on the high side.

4) Imbalance in carbon-to-nitrogen ratio.

The second type of envy and dust: the swelling of non-filamentous bacteria is due to the physiological activity of mycocolloidal bacteria.

often, it leads to the deterioration of the sedimentation performance of activated sludge. This kind of sludge swelling can be divided into two types: one is because the influent contains a large amount of dissolved organic matter, so that the sludge load is too high, and the influent water lacks enough nutrients such as nitrogen and phosphorus, or the dissolved oxygen in the mixed liquid is insufficient.

Another non-filamentous bacteria is that the influent contains more toxic substances, resulting in activated sludge poisoning, so that the bacteria can not secrete a sufficient amount of viscous substances to mess up the foundation, and cannot form flocs, so that it is impossible to separate the sludge in the secondary sedimentation tank and eventually lead to the disintegration of the sludge.

Control methods: (1) enhanced aeration; (2) adjust the load; (3) Sectional water injection; (4) addition of nitrogen-containing compounds; (5) Add lime and digest sludge; (6) dilution into sewage; (7) If carbohydrates increase, the ** of wastewater should be investigated; (8) When toxic wastewater enters the system, it should be pre-treated; (9) Inoculation of activated sludge.

Sludge expansion is a common abnormal phenomenon in the activated sludge system, which refers to the fact that due to the change of certain factors, the quality of activated sludge becomes lighter, expands, and the sedimentation performance deteriorates, and the SVI value continues to rise, and the normal sludge separation can not be carried out in the secondary sedimentation tank, and the sludge surface of the secondary sedimentation tank continues to rise, which eventually leads to sludge loss, and the MLSS concentration in the aeration tank is excessively reduced, thereby destroying the sludge of normal process operation, which is called sludge expansion. When the sludge expands, the SVI value rises abnormally, sometimes reaching more than 400.

Sludge swelling can be generally divided into two categories: filamentous swelling and non-filamentous swelling. Filamentous bacteria swelling is the sludge swelling caused by the excessive reproduction of filamentous bacteria in the activated sludge flocs, and non-filamentous bacteria swelling refers to the sludge swelling caused by the abnormal physiological activities of the colloidal bacteria themselves and the large production of viscous substances.