After the completion of the sewage treatment project, it does not mean that the project has ended. Do you know what another important stage is? That's biochemical debugging! It is an important stage in sewage engineering, and the success or failure of debugging directly determines the success or failure of the entire project!
Do you know the first step of adding sludge for debugging, and the addition of sludge for biochemical debugging?
According to the source of sludge, it can be divided into three categories:
1、 Using dry sludge for addition
According to the specific situation, the amount of dry sludge added is generally calculated based on the sludge concentration:
For example, if the capacity of the aerobic tank is 1000 cubic meters and the normal sludge concentration in the aerobic tank is 3000 mg/l, which is 3 kilograms per cubic meter, the required amount of dry sludge is 3 * 1000=3000 kilograms based on the capacity of the aerobic tank.
Dry sludge is generally obtained by dewatering and pressure filtration, with a moisture content between 75-85%, usually calculated as 80%. Therefore, the required amount of dewatered dry sludge is 3000/20%=15000 kg=15 tons.
Therefore, 15 tons of sludge will be produced after dewatering this time.
Main advantages: Less dosage and convenient transportation.
Disadvantages: Generally, coagulants are added for sludge removal, which is not conducive to cultivation. In addition, activation is required when adding dry sludge.
When adding sludge using the A/O method, the volume of tank A should also be included in the aerobic tank volume.
2、 Using aerobic pool mixed solution for addition
If conditions permit, the mixed solution from the aerobic tank of similar sewage treatment plants can be added, and the amount of addition is generally based on the tank capacity. The amount of addition is about 2/3 of the aerobic tank capacity and transported by tanker truck.
Advantages: Good sludge activity, no need for activation, can greatly shorten the debugging time.
Disadvantages: Large added volume, round-trip transportation cost
Larger.
3、 Using a secondary sedimentation tank to concentrate sludge for addition
This addition method is generally determined by experience due to the difficulty in determining the concentration of concentrated sludge, and is usually added at 10% of the tank capacity.
Advantages: Sludge activity is better than adding dry sludge, and transportation costs are suitable.
Disadvantages: The added volume is larger than that of dry sludge, and the sludge activity is worse than that of the aerobic tank mixture.
How to shorten the sewage biochemical debugging?
It is of great significance to shorten the commissioning time as much as possible for large-scale sewage treatment facilities, so that the treatment subject can be put into normal operation as soon as possible in the actual operation process.
Initial stage (3D)
① Firstly, inject a certain amount of clean water and some of the wastewater to be treated into the biochemical tank, and then pour the sludge into the material processing tank. Generally, 20m3 of sludge is added for the first time, along with nutrients such as feces. After mixing with water, they are evenly added to each biochemical tank in proportion. The quality concentration of COD in the biochemical tank should be controlled at 300mg/L when adding culture materials. Then add calcium superphosphate proportionally (as adding feces does not require additional nitrogen sources).
② Sealed exposure: Conduct sealed exposure after feeding. The volume of water vapor is controlled at 1: (5-10). On the first day of aeration, a 6-hour oxygenation and 4-hour shutdown method was adopted.
③ Re feeding: After 1 day of exposure, the mass concentration of COD decreased to around 100mg/L on the second day. Re feeding is required, and 10-15 m3 of sludge can be added to the chemical tank for the second time (leaving some as backup). At the same time, the culture medium mainly containing feces was added, and the standard for adding the culture medium was still to control the mass concentration of COD in the biochemical tank at 200-300mg/L. Add phosphorus as needed and then expose to air.
④ Silent aeration: Silent aeration on the second and third days can reduce downtime, and biochemical aeration can be controlled to start 6 and stop 2.
Mid term (4-7 days)
After 2-3 days of exposure, a small amount of protozoa may be observed through microscopic examination. In principle, at this time, adding carbon sources at regular intervals every day will gradually focus on using ground flour as the main source. Simultaneously add calcium superphosphate and urea to supplement phosphorus and nitrogen sources. The standard for supplementing carbon sources is still based on the mass concentration of COD in the biochemical tank being around 200mg/L.
At this stage, in order to eliminate biochemical metabolites, the biochemical pool needs to be replaced with an appropriate amount of water, while continuing to perform aeration. At this stage, to accelerate the formation of sludge microbial flocs, a suitable amount of powdered PAM can be added to the biochemical tank.
Later stage (7-10d)
After 7-10 days of exposure, the biochemical sludge appears pale yellow, and the settling ratio of the sludge reaches about 10% after 30 minutes. Through microscopic examination, it can be found that there are many active protozoan nematodes, ciliates, as well as post protozoan rotifers, nematodes, etc. At this point, the biochemical sewage treatment can enter the domestication and load adjustment stage.
Load adjustment is generally carried out by increasing the sewage load by one-fifth every 2 days. After one week, it can basically operate at full load. To ensure a smooth transition, depending on the specific situation, some ground flour can be added as a carbon source for several days of increased load.
Debugging precautions
The debugging of biochemical facilities requires special attention to the following points.
① It is necessary to set up a chemical material pool and equip it with a material conveying system for large-scale sewage treatment facilities.
② The added sludge should be decomposed as much as possible to avoid garbage entering the biochemical tank and reduce the efficiency of sludge utilization.
③ When adding, it is necessary to clean up the garbage to avoid it entering the conveying pump, otherwise it is easy to cause blockage of the conveying pump.
④ It is necessary to constantly monitor the changes in COD and dissolved oxygen in the biochemical tank, promptly supplement carbon sources, and adjust gas supply.
⑤ During the debugging period, it is best to control the pH value of the biochemical tank between 7 and 8.5, and promptly identify the cause and take remedial measures in case of any abnormalities.
