Why do many coal gasification wastewater design processes include air flotation, but do not start it in actual operation?
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It is understood that many chemical industry units (coal gasification or coking plants) have air flotation processes in their designs, because gasification wastewater generally has a high oil content (some as high as 200mg/L), but why are not many of them started normally in actual operation?
Among the several coking wastewater treatment equipment I have seen, air flotation has always been running normally. As for why it is not running, it is related to the special water quality.
I think it is mainly due to equipment corrosion, because coal chemical industry or coking wastewater contains a large amount of sulfide, thiocyanate and cyanide, which are highly corrosive to carbon steel materials. Therefore, no matter which pressure dissolved air flotation is used, it will cause equipment corrosion.
There is such an understanding: Because the oil in wastewater under normal conditions is mainly polymeric organic matter (extractants and aromatic compounds) rather than actual grease, these substances are difficult to remove through conventional physical and chemical methods. Similar performance in actual operations has proven that these substances are biodegradable. In that case, there is no need to add air flotation?
Oil substances are harmful to the stability of the system, so if the content is too high, pretreatment is required. Recently, a coking incident caused a large amount of foam in the anaerobic-aerobic system. One of the reasons is that the oil
personal opinion: One of the main reasons why the coal chemical wastewater does not use the air flotation pretreatment process, or does not start it even if it is used, is that a large amount of thick foam is generated that cannot be removed, which makes the equipment unable to operate normally, and also has a serious impact on the aesthetics of the entire plant.
Foam should be caused by substances such as surfactants, not oil. However, foam will definitely occur after the dissolved gas is released (if there is a surfactant).
Agree with the point above, foam is caused by surfactant components (such as fatty acids) in sewage. Thick foam is produced during aeration. After the foam is generated and removed, new foam will no longer be generated.
After reading your posts, I have another question. Where does the surfactant you mentioned come from? The fatty acids mentioned on the 8th floor are also surfactants? Can you explain it in detail? Thanks. Because my understanding is that surfactants are only produced in domestic sewage due to the use of detergents, etc. Welcome to continue the discussion.
Our company does not have air flotation and grease traps because the oil content in our incoming water is only 25 mg/L.