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Commissioning of biological aerated filter tank

Jul. 30, 2021

Commissioning of biological aerated filter tank

Before the biological aerated filter tank is put into operation, it must be debugged to make the microbial membrane with metabolic activity grow on the filter material. The biological aerated filter tank can be put into normal operation only after the membrane is hung on the surface of the filter material.

1. Preparation before filter commissioning

(1) Before the filter commissioning, you must be familiar with the sewage treatment process and understand the function and expected effect of each unit.

(2) Check whether all pipelines and valves are intact and meet the design requirements.

(3) Water inlet inspection: according to the requirements of "water inlet commissioning", the water inlet shall be carried out slowly, pay attention to the elimination of air in the filter material, and pay attention to whether the air distribution of the aerator is uniform.

(4) Check the water inlet of the aerator and check whether the air distribution of the aerator is uniform.

(5) The filter material shall be continuously flushed after water inlet inspection. Remove the dust on the filter material. The flushing shall be carried out according to the requirements of "backwashing" until the outlet water becomes clear.

(6) Run general or special equipment with load and check its safe operation.

(7) Before introducing sewage into the filter, the following preparations shall be made: confirm that all valves of the filter are in working state; Confirm that the load index of sewage meets the requirements of engineering design.

2. Operation and commissioning of biological aerated filter tank

1. Packing film

The process of fixing and growing microbial sludge with metabolic activity on the filler in the biological treatment system is called membrane hanging. Membrane hanging is the process of cultivation and domestication of membrane sludge in biofilm treatment system.

When the biofilm process is put into operation, it needs a film hanging stage. There are two purposes: one is to make microorganisms grow and reproduce until the filler surface is covered with biofilm, in which the number of microorganisms can meet the requirements of sewage treatment; On the other hand, it is also necessary to make microorganisms gradually adapt to the water quality of the treated sewage, that is, domesticate microorganisms. In the process of membrane hanging, the effluent from the sedimentation tank and the sludge at the bottom of the tank can promote the early completion of the membrane.

The methods used in the film hanging process generally include direct film hanging method and indirect film hanging method.

In various forms of biofilm treatment facilities, biological contact oxidation tank and tower biofilter can use direct membrane hanging method because they have aeration system and large filler amount and filler gap; However, facilities such as ordinary biofilter and biological rotary table need to use indirect membrane hanging method.

a. Direct film hanging method

The method is to make the treatment system continuously feed water and operate normally under appropriate environmental conditions such as water temperature and dissolved oxygen and water quality conditions such as pH, BOD5 and C / n.  For domestic sewage, urban sewage or industrial wastewater mixed with a large proportion of domestic sewage, the direct film hanging method can be adopted. Generally, the film hanging process can be completed after 7 ~ 10 days.

b. Indirect film hanging method

For non degradable industrial wastewater, especially when using ordinary biofilter, biological rotary table and other facilities for treatment, in order to ensure the smooth operation of membrane hanging, the corresponding activated sludge can be pre cultured and domesticated, and then added to the biofilm treatment system for membrane hanging, that is, distributed membrane hanging. The usual practice is to cultivate activated sludge from domestic sewage or its mixed sewage with industrial wastewater, then put the sludge or sludge from other similar sewage treatment plants together with industrial wastewater into a circulating tank, and then pump it into the biofilm treatment facility, and the effluent and precipitated sludge return to the circulating tank.

After the biofilm is formed by circulating operation, it is operated with water and added with industrial wastewater to be treated. 20% of industrial wastewater can be added first. After analyzing the water quality of inlet and outlet water and the biofilm has a certain treatment effect, the proportion of industrial wastewater can be gradually increased until it is all industrial wastewater. Domestic sewage mixed with a small amount (20%) of industrial wastewater can also be used to directly cultivate biofilm. After successful membrane hanging, gradually increase the proportion of industrial wastewater until it is all industrial wastewater.

2. Cultivation and Domestication

1. When starting to hang film, the inlet water flow shall be less than the design value, and the operation can be started according to 20% ~ 40% of the design flow.  It can be seen from the appearance that when the existing biofilm is formed, the flow can be increased to 60% ~ 80%. When the effluent effect meets the design requirements, the flow can be increased to the design standard.

2. In the biological rotary table method, the film hanging time of the rotary table used for nitrification should be increased by 2 ~ 3 weeks, and it should be noted that the influent BOD should be less than 30mg / L. due to the long generation time and slow propagation and growth of autotrophic nitrifying bacteria, if the influent organic matter is too high, heterotrophic bacteria in the membrane can dominate, thus inhibiting the growth of autotrophic bacteria.

3. When nitrite appears in water, it indicates that the nitrification process on biofilm has begun; When nitrite in the effluent decreased and a large amount of nitrate appeared, it showed that nitrifying bacteria had an advantage on the biofilm, and the film hanging work was over.

4. The environmental conditions required for film hanging are the same as those for activated sludge culture. The influent is required to have appropriate nutrition, temperature, pH, etc., especially the amount of nutrient elements such as nitrogen and phosphorus must be sufficient, and a large number of poisons must be avoided.

5. Due to the small amount of membrane in the initial stage, the oxygen charge in the reactor can be slightly less. Make the dissolved oxygen not too high; At the same time, the way of low load water inflow is adopted to reduce the scouring effect on the biofilm and increase the film hanging speed of the filler or filler.

6. The whole cycle of film hanging at 13 ℃ in winter is 2 ~ 3 times longer than that in warm season.

7. During biofilm culture and film hanging, due to the poor adaptability of the newly grown biofilm, a large number of membrane sludge will fall off, which can be said to be normal, especially when industrial wastewater is used for domestication.

8. Pay attention to control the thickness of biofilm, keep it at about 2mm, prevent excessive growth of anaerobic layer, and make biofilm fall off evenly by adjusting hydraulic load (changing reflux water). At the same time, microscopic examination shall be carried out at any time to observe the changes of biofilm biofacies, and pay attention to the changes of species and quantity of characteristic microorganisms.

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