The abnormal problem of activated sludge system and its solution come from Aquasust plastic manufacture--MBBR Media supplier
(1) Abnormal sludge properties, sludge expansion and abnormalities
The amount of suspended solids (ESS) in the effluent will greatly affect the treatment effect. Since most of the SS in the influent water has been removed by pretreatment processes such as grille, grit, and primary sedimentation, the remaining small amount of SS is absorbed by the activated sludge after entering the aeration tank and constitutes a component of the sludge. Therefore, the ESS is actually composed of bleached sludge. The amount of ESS is related to the settling and coagulation performance of the activated sludge and the operating conditions of the secondary settling tank. For a normal treatment system, ESS should be less than 30mg/L or only accounted for less than 0.5% of the activated sludge concentration, that is, when the mass concentration of sludge in the aeration tank is 2～4g/L, ESS should be 10-20mg/L. If it exceeds this limit, it means that the sludge has poor properties, which is often caused by the floating of large or small particles of sludge and the swelling of the sludge.
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
①Fist-sized sludge floats up and down in the sedimentation tank intermittently.
There are two situations that cause a large piece of sludge to float up.
a. Denitrification sludge. The floating sludge is lighter in color, sometimes with rusty color. The reason is that the degree of nitrification in the aeration tank is relatively high. Nitrogen-containing compounds are converted into nitrate through ammoniation and nitrification. The concentration of N03-N is high. At this time, if the sedimentation tank has a too small reflux ratio or poor reflux, etc. The reason is that the sludge level rises, and the sludge cannot be renewed for a long time. The sludge at the bottom of the sedimentation tank can denitrify nitrate due to lack of oxygen.
The improvement method is: increase the reflux ratio to renew the sludge in the sedimentation tank and reduce the sludge layer; reduce the sludge age and discharge more sludge to reduce the sludge concentration; and also appropriately reduce the DO level of the aeration tank. The above measures can reduce nitrification to reduce the source of nitrate.
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
b. Corrupted sludge. The difference between corrupted sludge and denitrified sludge is that the sludge is dark in color and has a strong odor. The cause is that there are dead corners in the secondary settling tank, resulting in sludge accumulation. After a long time, it will be anaerobic and decayed, producing H2S, CO2, H2 and other gases, which will eventually make the sludge float upward.
The solution is to eliminate the sludge in the dead-angle area, for example, compressed air is often used to inflate the dead-angle area to increase the return of sludge. For areas prone to mud accumulation, try to improve in the design.
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
②Floating of small particles of sludge. Small particles of sludge are continuously carried out with the effluent, commonly known as floating mud.
The causes of floating mud can be roughly divided into the following categories.
a. Influent water quality, such as pH value, poisons, etc., make the sludge unable to adapt to or poison, causing deflocculation.
b. The sludge ages due to lack of nutrients or over-oxygenation.
c. The influent ammonia nitrogen is too high and the C/N is too low, which causes the sludge colloid matrix to disintegrate and deflocculate.
d. The pool temperature is too high, often exceeding 40°C.
e. The rotational speed of the mechanical aeration wing wheel is too high, causing the flocs to be broken.
The solution is to clarify the reasons and treat them separately. In the case of sludge poisoning, the entry of toxic wastewater should be stopped; for lack of nutrients, aging sludge and deflocculation sludge, proper nutrition should be added and rejuvenation measures should be taken.
③Sludge expansion In the activated sludge system, sometimes the sedimentation performance of the sludge deteriorates, the density decreases, and the SVI value increases. The sludge is difficult to settle in the secondary sedimentation tank and the mud surface rises. In severe cases, the sludge overflows and is lost, and the treatment effect This phenomenon is called sludge bulking. It is the most difficult problem in the activated sludge process.
a. Physiological characteristics of filamentous bacteria
Large specific surface area, poor sedimentation and compression performance; resistance to low nutrition; resistance to low oxygen; suitable for wastewater with high CAN; certain filamentous bacteria have special requirements for the environment, such as Belle bacteria and sulfur bacteria must contain reducing properties in wastewater It can only grow in large quantities when sulfide.
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
b. Method for controlling filamentous bacteria sludge expansion
Use chemicals to kill filamentous bacteria. Because of the large surface area in contact with the environment, the filamentous bacteria are more sensitive to drugs. When the dosage is appropriate, it can kill the filamentous bacteria without excessively damaging the micelle bacteria, which is obvious in filamentous bacteria. After being restrained, you can stop dosing, add nutrition, and take appropriate rejuvenation measures.
Commonly used drugs and dosages are as follows:
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
The amount of bleaching powder should be added according to the available chlorine 0.5%-0.8% of MLSS;
Add liquid chlorine or bleaching powder to make the bacteria die after 30 minutes when the residual chlorine is 1 mg/L; when the residual chlorine is 5 mg/L, the bacteria die after 120 minutes;
Add waste lye. Increase the pH value of the aeration tank to 8.5-9.0. After maintaining it for a period of time, the filamentous bacteria may shrink and break through microscopic examination.
When the above method is applied in production, it is best to pass a sample test first to determine the appropriate dosage. Due to the strong mutation ability of microorganisms, after using the same drug multiple times, filamentous bacteria tend to have adaptability and lead to the failure of the method.
Changing the water inlet method and the fully mixed activated sludge method (CMAS) for wastewater treatment can easily cause sludge bulking. After research, the use of push-flow (PFR) or sequential batch (SBR) activated sludge method has a good effect on inhibiting sludge expansion.
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Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
To control the DO of the aeration tank, the push-flow (PFR) or sequential batch (SBR) activated sludge method is used to make the sludge alternately undergo anaerobic and aerobic conditions. The micelle bacteria can ingest, transform and store the matrix under anaerobic and aerobic alternate conditions, thereby competitively rejecting filamentous bacteria with poor ability under this condition. To
Adjust the nutrient ratio of wastewater. For treatment systems that increase the SVI value due to lack of N and P and cause sludge expansion, it is necessary to add N/P to the influent water.
Based on the above, when the sludge expands, the environmental conditions of the microorganisms in the aeration tank should be changed in time. In the sludge system where there are two major types of microorganisms-micellar bacteria and filamentous bacteria coexist and compete with each other, Create environmental conditions suitable for the growth of micellar bacteria, so that filamentous bacteria cannot grow in an advantageous manner, so as to achieve the purpose of improving the sedimentation and compression performance of sludge and controlling or preventing sludge expansion. The following table shows the abnormality and analysis of sludge properties.
|
Abnormal symptoms |
Analysis and diagnosis |
solutions |
|
The aeration tank is smelly |
The oxygen supply in the aeration tank is insufficient, the DO value is low, and the ammonia nitrogen in the effluent is sometimes high |
Increase the oxygen supply to make the DO mass concentration of the aeration tank higher than 2mg/L |
|
Black sludge |
If the DO of the aeration tank is too low, the anaerobic decomposition of organic matter releases H2S, which reacts with Fe to form FeS |
Increase oxygen supply or increase the amount of sludge returned |
|
Sludge whitening |
Filamentous bacteria or sessile ciliates multiply |
If there is sludge swelling, refer to swelling countermeasures for other symptoms |
|
The pH value of the inlet water is too low, the pH of the aeration tank is <6, and a large number of filamentous molds are formed |
Increase the pH of the feed water |
|
|
A large piece of black sludge floats up in the sedimentation tank |
The partial mud in the sedimentation tank is anaerobic, producing methane and CO2, and air bubbles are attached to the mud particles to float above. |
Prevent dead spots in the sedimentation tank, flush and clean with compressed air in the dead spots after the mud is discharged |
|
The mud level of the secondary settling tank is raised, the initial effluent is particularly clear, and the sludge overflows in layers when the flow is large |
SV>90%, SVI>200mL/s, filamentous bacteria are dominant in the sludge, and the sludge swells |
Chemical methods such as adding liquid chlorine, sodium hypochlorite, and increasing pH to kill filamentous bacteria; adding granular charcoal, clay, nitrified sludge and other activated sludge "weight agents" to increase DO; interstitial water ingress |
|
The mud level of the second settling pond is too high |
Filamentous bacteria have not grown excessively, and the MLSS value is too high |
Increase mud discharge |
|
Accumulation of deflocculated sludge layer on the surface of secondary sedimentation tank |
The micro-animals die, the sludge deflocculates, the effluent water quality deteriorates, the COD and BOD rise, the OUR is far below 8mg02/(gVSS·h), the concentration of toxic substances in the influent water is too high or the pH value is abnormal |
Stop water intake and add nutrients after the sludge is discharged. It is possible to introduce domestic sewage to rejuvenate or introduce new sludge strains |
|
There are fine sludge floating outside in the second settling tank |
The sludge lacks nutrients; the ammonia nitrogen concentration in the influent is high, and the C/N is inappropriate; the pool temperature exceeds 40℃; the wing wheel speed is too high to break the flocs |
Add nutrients or introduce high BOD wastewater to make F/M>0.1, stop an aeration tank |
|
The supernatant of the secondary sedimentation tank is turbid, and the effluent quality is poor |
High sludge load, incomplete oxidation of organic matter |
Reduce the flow of water in, reduce the sludge discharge |
|
Scum appeared on the surface of the aeration tank, like thick porridge covering the surface |
Excessive growth of Nocardia or ciliates in the scum or excessive detergent content in the influent water |
Remove the scum, avoid the scum to continue to circulate in the system, and increase the sludge discharge |
|
The sludge is immature, the flocs are thin, the effluent is turbid, and the water quality is poor; there are many small motile flagellates |
The composition and concentration of the water have changed too much, the nutrition in the wastewater is unbalanced or insufficient; the wastewater contains toxic substances or the pH value is inappropriate |
Balance the composition, concentration and nutrition of wastewater, and appropriately supplement the lack of nutrients |
|
Difficulties in sludge filtration |
Sludge deflocculation |
Dispose of according to different situations |
|
Mud cakes after sludge dewatering |
Organic spoilage |
Timely disposal of sludge |
|
Insufficient addition of coagulant |
Increase the dose |
|
|
Excessive foam in aeration tank, white color |
Too much detergent in the water |
Drop defoamer |
|
The aeration tank foam is not easy to break and sticky |
The influent load is too high and the decomposition of organic matter is not complete |
Reduce load |
|
Aeration tank bubble tea or gray |
The sludge is aging, the sludge age is too long, and the deflocculated sludge is attached to the foam |
Increase mud discharge |
You could contact us:
Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
(2)Biological foam and its control foam are common phenomena in the operation of activated sludge process.
There are two types of foam, one is chemical foam and the other is biological foam.
Chemical foam is formed by the detergent in sewage and some industrial surface active substances under the action of aeration and blowing off. In the initial stage of activated sludge cultivation, there are many chemical bubbles, and sometimes foam mountains up to several meters are formed on the surface of the aeration tank. This is mainly because the activated sludge has not yet formed in the initial stage, and all foam-producing substances have formed foam under the action of aeration. With the increase of activated sludge, a large amount of detergent or surface substances will be absorbed and decomposed by microorganisms, and the foam will gradually disappear. In a normal operating activated sludge system, due to some reasons, a large amount of sludge is lost, which leads to a sharp increase in F/M and chemical foam. Chemical foam treatment is easier, you can use water to defoam, or you can add defoamer. The more difficult thing to deal with is biofoam, which is formed by a type of filamentous bacteria called Nocardia. The chemical foam is milky white, while the biological foam is brown. It can accumulate very high on the aeration tank and enter the secondary settling tank to flow away with the water, causing a series of problems. First of all, the bio-foam spread to the walkway board, making the operator unable to maintain it normally. In addition, bio-foam can freeze in winter, making it extremely difficult to clean up. In summer, bio-foam will drift with the wind and form an unpleasant odor. Nocardia is very likely to become a human pathogen. If surface aeration equipment is used, the biological foam can also prevent normal aeration and oxygenation and reduce the D0 of the mixture. Bio-foam can also enter the mud zone along with the sludge and interfere with the operation of the thickening tank and digestion tank. The bio-foam cannot be washed away with water, and the defoamer has little effect. Because Nocardia is produced inside the activated sludge flocs, trying to use chlorine to solve the problem cannot fundamentally solve the problem. Increasing sludge drainage and lowering SRT sometimes have a slight effect, but it can only remove the part of Nocardia that has a long generation period. The fundamental measure of bio-foam control is to start from the root and focus on prevention.
You could contact us:
Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
①Conditions for the production of biofoam Nocardia is the main reason for the formation of biofoam. This filamentous fungus is a dendritic filament, the waxy lipid compound content in its cell is as high as 11%, and the cytoplasm and cell wall contain a large amount of lipid material, which has strong hydrophobicity and low density. Nocardia is prone to multiply in an environment with high temperature (above 20C) and rich in lipids. People flow sewage with a lot of oil and lipids or incomplete removal of scum in the primary sedimentation tank, which is easy to produce bio-foam. Bio-foam is easier to produce in summer than in winter. The generation period of most Nocardia bacteria is more than 9 days, so it is easier to produce bio-foam in the activated sludge system with ultra-low load.
②Diagnosis and control of foam problems Like sludge expansion, when foam occurs, careful observation and analysis should be made to confirm the type and cause of the foam, and prescribe the right medicine, otherwise it will not be able to control the foam.
Phenomenon 1-- White, viscous air bubbles are produced on the surface of the aeration tank, and sometimes large waves appear.
The diagnostic procedure is as follows:
If this phenomenon occurs during the sludge cultivation process, it is a normal situation and no attention is needed. As the sludge increases, the foam will disappear naturally. In the activated sludge in normal operation, if the above phenomenon occurs, first check whether the MLVSS is reduced. If sludge loss is caused by the effluent from the secondary sedimentation tank, resulting in a decrease in MLVSS, the cause of the loss should be analyzed and dealt with. If the MLVSS decreases due to excessive sludge discharge, the sludge discharge should be reduced. If MLVSS does not decrease, proceed to the following steps. To
You could contact us:
Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
Check the oxygen consumption rate SOUR of the sludge. If SOUR is lowered, it means that the sludge is poisoned, and the cause of the poisoning should be analyzed and treatment measures should be taken.
If there is foam in some aeration tanks but the others do not, check whether the water distribution between each tank is even, and whether the return sludge entering each tank is evenly distributed. If a certain aeration tank enters a lot of sewage, but distributes less return sludge, the tank is prone to foam.
Phenomenon 2-- A fine dark brown foam is formed on the surface of the aeration tank.
The diagnostic procedure is as follows:
Check the oxygen consumption rate SOUR of the sludge. If SOUR is lowered, it means that the sludge is poisoned, and the cause of the poisoning should be analyzed and treatment measures should be taken.
If there is foam in some aeration tanks but the others do not, check whether the water distribution between each tank is even, and whether the return sludge entering each tank is evenly distributed. If a certain aeration tank enters a lot of sewage, but distributes less return sludge, the tank is prone to foam.
Phenomenon 2-- A fine dark brown foam is formed on the surface of the aeration tank.
The diagnostic procedure is as follows:
You could contact us:
Contact name: Jasmine
Contact email: Kate@aquasust.com
Whatsapp number: 8618868159881.
(3) List of abnormal equipment operation and analysis (see table)
|
unusual phenomenon |
Analysis and diagnosis |
solutions |
|
The motor is noisy |
The bearing is damaged, the bearing is not lubricated well, and the pump is blocked |
Disassembly and maintenance |
|
Large fan vibration |
The bearing is damaged, the bearing is not lubricated, and the transmission belt is loose |
Disassemble and repair, replace the transmission belt |
|
Motor overheated |
The bearing is damaged, the bearing is not lubricated, the motor is overloaded |
Disassembly and maintenance |
|
Pump leakage |
Poor sealing and corrosion |
|
|
Surface exposed wing wheel blockage |
Poor lifting, so that the aeration tank is deposited, MLSS is extremely low |
Clean and remove debris |
|
Surface aerator dehydration |
Surface exposure machine is immersed too deeply, MLSS is normal, DO is low |
Adjust the position of the wing wheel |
|
The surface aeration wing wheel water jump becomes smaller, the wing wheel is submerged too deeply, the MLSS is normal, the DO is low, the bubbles in the diffuse air aeration system are not uniformly turned, and there are clusters of bubbles rising |
Air distribution pipe, aerator blocked or cracked |
Repair cleaning cloth air pipe and aerator |
|
The pH of the effluent drops |
Anaerobic treatment load is too high, organic acid accumulation |
Reduce load |
|
Low load in aerobic treatment, nitrification of ammonia nitrogen |
Increase load |
|
|
There is a layer of floating mud on the surface of the secondary settling tank, which is poisoned by the sludge; the sludge is expanded |
Sludge rejuvenation |
|
|
Elevated ESS |
Insufficient mud discharge, MLSS is too high |
See expansion countermeasures |
|
Mud in the secondary sedimentation tank, denitrification or corruption |
Increase mud discharge |
|
|
Turbid effluent |
Load is too low, sludge cohesion is poor, sludge deflocculate |
Increase nutrition |
|
Sludge poisoning |
Stop water ingress and rejuvenate sludge |
|
|
The filter medium of the subsequent fast filter is contaminated, activated carbon and the load is too high |
Increase recoil |
|
|
Incomplete decomposition of organic matter |
Reduce load |
|
|
The chromaticity of the effluent rises |
Sludge deflocculation, high influent color |
Improve sludge shape |
|
SV rise |
Sludge expansion, or insufficient sludge discharge |
Refer to expansion countermeasures |
|
MLSS drops |
The return pump is blocked or the wing wheel is blocked, the sludge is expanded or poisoned; a large amount of sludge is lost |
Take corresponding measures according to the actual situation |
|
High ash content of sludge, greater than 50% |
Poor operation of grit tank and primary sedimentation tank; too much mud and sand in the influent water, or too high salinity |
Improve the operation status of grit tank and dust removal |
|
Low DO of aeration tank |
The influent is too thick and the load is too high; the influent is too much inorganic reducing substances |
Reduce load |
|
Blocked aerator |
Disassembly and repair
|