Biochemical tank operation management manual

1. Routine monitoring of water intake in aeration tank

1.1. Temperature

The most suitable temperature range for normal physiological activity of aerobic activated sludge microorganism is 15-30℃. Generally, when the water temperature is lower than 10 ° C or higher than 35 ° C, it will adversely affect the function of aerobic activated sludge. When the temperature is above 40 ° C or below 5 ° C, it will even stop completely.

Within a certain range, with the increase of temperature, although it is not conducive to the transfer of oxygen to water, it can accelerate the biochemical reaction rate, and the microbial proliferation rate will also be accelerated. However, when the temperature rises sharply and exceeds a certain limit, irreversible damage will occur. In contrast, the effect of temperature reduction on microorganisms is less, and there is generally no irreversible damage.

If the decrease of water temperature changes slowly, the microorganisms in activated sludge can gradually adapt to this change, and better treatment effects can be achieved by reducing load, increasing dissolved oxygen concentration and extending aeration time.

Therefore, in the actual production operation, attention should be paid to the sudden change of water temperature, especially the sudden rise of water temperature. In order to prevent the industrial wastewater with high water temperature from adversely affecting the aerobic biological treatment, cooling treatment should be carried out.

1.2. pH value

The optimum pH value of activated sludge microorganism is between 6.5 and 8.5. When the pH value drops below 4.5, all the protozoa in activated sludge will disappear, the activities of most microorganisms will be inhibited, the dominant bacteria are fungi, the activated sludge floc is destroyed, and it is easy to produce sludge bulking phenomenon.

When the pH value is greater than 9, the metabolic rate of microorganisms will be greatly adversely affected, the bacterial micelles will disintegrate, and the sludge bulking phenomenon will occur. When the pH of the sewage is higher than 10 or lower than 5, the pH must be adjusted by acid-base neutralization before entering the aeration tank so that the pH of the sewage entering the aeration tank is at least between 6-9.

The activated sludge mixture itself has a certain buffer effect on pH changes, because the metabolic activities of aerobic microorganisms can change the pH value of their active environment. For example, the use of nitrogen-containing compounds by aerobic microorganisms produces acid due to nitrogen removal, reducing the pH value of the environment; Due to decarboxylation, basic acid is produced, which can increase the pH value. Therefore, after a long time of domestication, activated sludge method can also treat sewage with a certain acidic or alkaline. In addition, the alkalinity of the sewage itself has a certain inhibitory effect on the decline of pH value.

However, the pH value of the sewage changes, such as alkaline sewage into the activated sludge system that has been adapted to the acidic environment, it will have an impact on the microorganisms, and even may destroy the normal operation of the entire system.

Therefore, whether the acid and alkali sewage is neutralized should be determined according to the actual situation, if the pH value of the sewage entering the activated sludge system does not change much, especially when there is only slightly acidic water or slightly alkaline water, neutralization treatment is often not required, and when the pH value changes greatly, neutralization treatment should be carried out in advance to adjust the pH value to neutral.

1.3 COD and BOD5

No matter which activated sludge method is used, there is a certain limit to the organic load that the aeration tank can bear, and beyond the limit, the operation effect of the aeration tank will be difficult to guarantee. For the aeration tank in operation, the maximum influent BOD5 value is fixed. Due to the long BOD5 analysis cycle, COD analysis results are usually used to guide production.

Once the intake organic load of the aeration tank exceeds the standard, measures should be taken immediately to reduce the intake water, increase the sludge return flow, and improve the oxygenation efficiency, so as to avoid the impact on the entire secondary biological treatment system and ensure the quality of the effluent.

If the influent COD value is low, measures should be taken immediately to increase the water intake, reduce the sludge return flow rate, reduce the number of fans, reduce the speed of the table aerator, etc., and reduce the oxygenation efficiency, so as not to cause unnecessary power waste.

1.4. Ammonia nitrogen and phosphate

In theory, the microbial demand for nitrogen and phosphorus should be calculated according to BOD5:N: P-100:5:1, but the actual ratio of BOD5 to nitrogen and phosphorus in the aeration tank water of the activated sludge treatment system is often lower than this value, and the system can also operate normally.

The content of nitrogen and phosphorus varies greatly due to the different types of industrial wastewater treated, and the content of nitrogen and phosphorus in some sewage is very high, and the content of nitrogen and phosphorus in the effluent of the secondary sedimentation tank will exceed the standard without phosphorus removal and nitrogen removal. For the wastewater with very low nitrogen and phosphorus content, if a certain amount of nitrogen and phosphorus can not be supplemented in time, the function of microorganisms will be limited, and the COD and BOD5 of the effluent from the secondary sedimentation tank will be difficult to ensure the standard.

When the industrial wastewater with very low nitrogen and phosphorus content is treated, the ammonia nitrogen and phosphate content in the influent of the aeration tank in operation is about 10mg/L and 5mg/L, respectively, which can meet the needs of mixed liquid microorganisms for nitrogen and phosphorus. If the content of ammonia nitrogen and phosphate in the intake water of the aeration tank is lower than the above values for a long time, the dosage of nitrogen and phosphorus should be increased in time.

1.5. Toxic substances

For specific industrial wastewater, the types of toxic substances are generally unchanged, but the content and displacement are difficult to be constant. In addition to the primary treatment measures such as homogenization regulation, the content of toxic substances in the intake water of the aeration tank must be monitored and controlled.

After the acclimation of activated sludge, the maximum limit of influent toxic substances affecting the biochemical system should be determined according to the adaptation degree of the mixed liquid to the toxic substances in the influent and combined with the operation experience.

If the content of toxic substances in the intake water of the aeration tank exceeds the limit value for a long time, measures such as reducing the intake water, increasing the sludge return flow rate, and improving the oxygenation efficiency should be taken to avoid affecting the treatment effect due to microbial poisoning of the mixed liquid.