In the trial operation stage of activated sludge method, we need to carry out sludge culture, which is to raise enough microorganisms, which is the key to the subsequent treatment of wastewater. In general, there are two methods for the culture of activated sludge: self-culture and inoculation culture. Today, let's talk in detail about the advantages and disadvantages of the two ways of cultivating bacteria, as well as their respective points of attention.
1. Self-culture bacteria
1. What is Self-culture
Self-culture is a process of direct water intake and aeration to form activated sludge in the aerobic tank.
2. Advantages and disadvantages of self-growing bacteria
Since the self-culture bacteria are used in the factory's specific sewage, the bacteria cultured are more targeted, and the removal efficiency of organic matter is higher than that of inoculation culture; In addition, it is more adaptable to the inhibitory substances present in the water.
The disadvantage is that the cultivation time is long and the energy consumption is large.
3. Pay attention to the process of self-cultivation
1. Control the concentration of sewage and the amount of water entering the biochemical tank
The influent concentration is controlled at about 20% of the design value; The water intake is to fill the biochemical tank at one time within the first 2 days;
2. aeration control
After the biochemical tank is filled with water, it can be bored. At this time, you only need to turn on the horsepower of the aeration equipment, and leave the rest alone. After about 2 days, the stuffy aeration ends and the normal bacteria cultivation stage is entered. At this time, the aeration rate is adjusted to maintain the dissolved oxygen in the aerobic tank at the level of 2 ~ 4PPM.
3. Control of nutrients
Nitrogen and phosphorus can be added according to the ratio of BOD:N:P = 100:5:1, according to the daily monitoring of nitrogen and phosphorus content, what is missing is supplemented.
4. continue to water + normal aeration
After the end of the dull aeration, the influent COD concentration should continue to be 20%, and the influent should be stopped when the secondary sedimentation tank is close to full overflow. The reflux of the secondary sedimentation tank should be turned on (reflux ratio 30-50%). The D0 value of the aeration tank should be monitored twice a day, and the COD value of the supernatant in the secondary sedimentation tank should be monitored once a day.
5. secondary sedimentation tank discharge supernatant (circulating water)
When it is detected that the supernatant of the secondary sedimentation tank meets the discharge standard, the backflow of the secondary sedimentation tank is stopped, and the waste water in the secondary sedimentation tank is drawn out with a temporary pump for discharge, and the liquid level of the secondary sedimentation tank is reduced to 2/5. At this time, continue to water, water concentration is 30% of the design value, repeat step 4; Continue to cycle, each time re-water, influent COD is increased by 10%.
6. From the 7th to 10th day, the MLSS value and SV30 value of the aerobic tank were detected and recorded.
7. After the activated sludge forms a floc, a small amount of mud is discharged, which is to discharge impurities and facilitate the renewal of activated sludge. You can line up twice a day for 10 minutes each time.
8. in about 20 to 30 days, MLSS reaches more than 900PPM, continuous water. The inlet water concentration is taken as the concentration at the time of circulating inlet water, and then the inlet water concentration is increased by 10% every 3 days.
2. Inoculate and cultivate bacteria
1. What is inoculation?
The inoculation culture is to inoculate the sludge of other companies, put it into the aerobic tank, and form activated sludge adapted to the company's waste water after aeration.
2. Advantages and disadvantages of inoculation culture
The advantages of inoculation culture are short time and low energy consumption.
The disadvantage is that it is not as targeted as self-culture bacteria, which may bring filamentous bacteria, and if the treatment is not good, filamentous bacteria may expand in the later stage, which is generally used for the cultivation of industrial wastewater.
3. Pay attention to the process of inoculation and culture
1. Source of inoculated sludge
The sludge near the same type of wastewater treatment plant is preferred to choose the liquid reflux sludge in the secondary sedimentation tank, and the desludge cake containing activated sludge is selected next.
2. mud quantity reference value (select one of the following can be)
Dosage of return liquid in secondary sedimentation tank (the concentration of return sludge in secondary sedimentation tank is measured by 4000PPM) : 10m3 per 1000m3 aerobic tank; Sludge cake containing activated sludge: calculated by adding 5 tons per 1000m3 aerobic tank.
3. according to the COD design value of 30% of the concentration of water into the aerobic tank, and mud
4. After 24 hours of stuffy exposure, turn to normal aeration, maintain D0 concentration at 2 ~ 4PPM, and supplement nutrients
5. continue to water + normal aeration
After the end of the dull exposure, the influent COD concentration is 30%, and the influent water is stopped when the secondary sedimentation tank is nearly full, and the secondary sedimentation tank starts the reflux (reflux ratio of 30 ~ 50%). The D0 value of the aeration tank (twice/day) and the COD value of the supernatant in the secondary sedimentation tank (once/day) are regularly monitored.
6. secondary sedimentation tank discharge supernatant (circulating water)
When the detected supernatant of the secondary sedimentation tank meets the discharge standard, the reflux of the secondary sedimentation tank is stopped. Use the temporary pump to draw out the dirty wastewater in the secondary sedimentation tank for discharge, reduce the level of the secondary sedimentation tank to 2/5, pay attention to not lower, so as to avoid pumping activated sludge. Continue to water, water concentration is 30% of the design value, repeat step 5; Continue to cycle, each time re-water, influent COD is increased by 10%.
7. From the second day, the MLSS value and SV30 value of the aerobic tank were detected and recorded
8. the third day to start a small amount of mud, you can row 3 times a day, each time 20 minutes, after the day to increase the mud 10 minutes, the number of mud.
9. in the fifth day or so, MLSS reached more than 900PPM, you can carry out continuous water intake (MLSS value measured 5 days ago is unstable, so it is arranged in the fifth day or so), the intake concentration is taken from the concentration of circulating water, and then every 2 days the intake concentration is increased by 10%.
10. After the 15th day, it is changed to continuous mud mixing, and the mud concentration is controlled to maintain the MLSS at the design concentration value as the standard.
3. Common problems of bacteria cultivation
1. Reasons and countermeasures for failure to form activated sludge after several weeks of cultivation
1. There are problems with the water quality of the incoming wastewater
For influent organic matter concentration is low, need to add substrate concentration, such as methanol, sugar, septic tank water, etc.
For the change of pH value, it is necessary to adjust it well in the physical and chemical section, and do not make the excessive and low pH pollution wastewater enter the bacterial biochemical system by misoperation.
For the inflow of special waste water, its inhibition should be taken into account, and the water should start after the successful cultivation of bacteria.
2. Excessive aeration
Excessive aeration will cause the sludge color to become lighter and the supernatant to become cloudy. At this time, aeration should be stopped.
2. Causes and countermeasures of a large number of bubbles during mushroom cultivation
1. A large amount of white foam is produced in the early stage of cultivation
First of all, this is a normal situation in the early stage of culture, do not worry about it, there are three main reasons.
- In the initial stage of start-up, the sludge in the aeration tank does not adapt to the water quality of the sewage and the growth environment, which is easy to form foam. As the sludge ADAPTS to the water quality, the foam will decrease.
- In the initial stage of start-up, the sludge is relatively small, the sludge load is high, and it is easy to produce foam. As the amount of sludge increases, the foam will gradually disappear.
- At the beginning of start-up, because the sewage contains some surface active substances, it is easy to cause surface foam. However, with the maturity of activated sludge, these surface active substances are biodegraded, and the foam phenomenon will gradually disappear.
2. The inflow of toxic substances
In the later stage of culture, if the incoming waste water contains chemicals that inhibit the current culture activated sludge, it will make the culture activated sludge very easy to die. At this time, the water of the biochemical tank becomes unusually cloudy, and white foam and scum are produced.