What is the reason for the poor COD degradation effect of air flotation?
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There are introductions to this aspect in the information and on the Haichuan Forum.: The air flotation device can remove more than 90% of COD, but our air flotation device can only remove about 20% of COD (from 1300 mg/l to 1100 mg/l). We add PAC and adjust the concentration several times. The pH value of the incoming water is between 6.5 and 8, but the COD does not drop much. Can you please help me analyze the reason? This post was last edited by Tan Zhaofeng on 2008-2-22 10:54 ]
That depends on your COD composition. If most of it is SCOD, then of course the removal rate will be very low.
The first is a conceptual error. It is not how much COD can be removed by air flotation, but how much COD can be removed through coagulation reaction. After coagulation reaction, air flotation can remove it, and precipitation can also be removed. As mentioned above, the key is whether the COD in the water is soluble or exists as SS or colloidal substances. If it is soluble COD, the coagulation flotation or sedimentation effect will be poor. It is best to use other methods for treatment, such as biological treatment, etc.
The principle of air flotation is to blend air into water through pressurization and then release it in an air flotation tank. Small bubbles can take away a large amount of suspended solids in the water. Such suspended matter includes organic matter and inorganic matter. If there are more organic matter suspended in the water, cod can be effectively degraded. Organic matter in fresh water if dissolved in water. Then this is useless :victory: :victory: :victory: :victory: .
Dear experts, I am a half-way monk when it comes to sewage treatment. I have a lot to learn from you.* . Please feel free to enlighten me. So how should we solve this situation now? . It is estimated that our sewage contains soluble COD, but our biochemical system is not very good at degrading COD. We are now looking for reasons and solutions. Our biochemical system process flow is as follows: Anaerobic tank (retention time 7 hours) + aerobic tank (residence time 10 hours) + secondary sedimentation tank + activated carbon filter. The residence time of the anaerobic pool seems to be shorter, but due to site constraints it cannot be enlarged, and all biochemical pools are iron tanks built on the ground. However, due to the particularity of our company, the volatile phenol in sewage is 150~300mg/l, and the COD is 1000~2000mg/l, so the effluent after treatment is sometimes good or bad.
If most of the water is soluble COD, then the coagulation + flotation effect will definitely be insignificant.
The air flotation in our factory can mainly remove oil. After many experiments, the removal rate of COD is quite low. It can also remove COD that exists in the state of suspended solids in the water body, because part of it can be removed by coagulation after dosing through air flotation.
What is your anaerobic pool used for? ? ? Anaerobic digestion? Acidification and hydrolysis? If the previous time is too short, it is recommended to conduct experiments and determine the hydraulic retention time based on the sludge retention time. The latter part takes too long. For phenol-containing sewage, biochemical methods are prone to problems, and now it is even more troublesome if the retention time is insufficient.
The composite activated water purifier has three major functions: coagulation, oxidation, and adsorption. It is a replacement product of polyaluminum chloride. We have been using this product. Contact 13001778622 to give you a sample for a small test.
See what the poster said about the high concentration of phenol in the biochemical influent. Phenol is a kind of microbial poison. If the concentration exceeds 100mg/l and enters the biochemical system directly, it will definitely cause poor operation of the biochemical system. Is it possible to consider pre-treating the incoming water with macroporous adsorption resin and reducing the phenol concentration before biochemical treatment? This should improve the operation effect of the biochemical system! ! !
With a COD of 1000-2000, it is uneconomical to use anaerobic methods. And based on the 7 hours you mentioned, I guess the design unit built for you is not an anaerobic tank, but a hydrolysis acidification tank. On the contrary, I think your aerobic segment stay time is not enough.
Let’s talk about air flotation first. Air flotation is generally used for pretreatment or biochemical post-treatment. It mainly removes suspended solids, colloidal substances and oils in water. In most cases, it has a good effect on removing SS in water. Of course, the removal effect of oil is also quite good. Air flotation is the transfer of pollutants rather than degradation. It transfers pollutants from water to sludge. From this, it is not difficult to see that if the pollutants in the water are SS or oil, the removal effect of air flotation will definitely be high, which can reach more than 50% or even 70-80%. However, if the pollutants in the water are composed of dissolved organic matter, the effect of air flotation is not so obvious. Of course, this is also related to the coagulant supporting the air flotation. If the coagulant only forms flocs for wrapping, of course, the amount of adsorption is also partial, and the removal rate is not very obvious. Looking at your entire process, anaerobic hydrolysis and acidification play the main function, while methanation is not the main function. Aerobic function should be contact oxidation. From all equipment or modular treatment, aerobic can be divided into secondary aerobic, or strong oxidation can be carried out at the water outlet. You can try it.