In the Desalination Pretreatment Facility, what is the mechanism and chemical reagents used in Dissolved Air Flotation as pretreatment of water?
#DAF #RO #Water #Desalination #pretreatment #membrane
DAF process applied to the primary sewage treatment usually requires pre-addition of chemical reagents. It generally requires coagulation-flocculation.
Coagulation step destabilizes colloids, while flocculation produces suspended solids and destabilized colloids aggregates. On these aggregates or flocs, depressurized air bubbles are able to act. Coagulation is a quick process that requires very low retention, from 0.5 to 3 minutes. It is a process that requires great energy mix. Flocculation is a process of slow mixing with retention times of 10 to 30 minutes. It is a process that requires less energy mixing or agitation. Inorganic salts are typically used in coagulation, such as aluminum polychloride, aluminum sulfate or ferric chloride. In flocculation the most common reagents are poly-electrolytes or polymers of high molecular weight. Coagulant and flocculant doses depend on the characteristics of the wastewater. If for project development there is not a budget for the testing of coagulation and flocculation (jar-test) in order to identify the proper chemicals and their optimal doses, the following minimum doses are commonly considered for design purposes: Coagulant > 50 mg/L Flocculant > 5 mg/L
What stands out from above-mentioned explanation is that the functional mechanism of such chemicals is based on this fact that they are chemical substances which disturb the chemical bonding and electronic charge of the oil-water emulsion in an oily water influent; in other words they are de-emulsifier.
Reza Aminzadeh thank you for your detailed answer :)
Do you have any reference or presentation regarding desalination and wastewater treatment methods?
Dear Shayan,
I am sorry to say that I have only used DAF for industrial projects, so that I have no ready presentation for academic stuff; however, I send you this file, which I believe it presents a good explanation in this regard. Although it is has industrial approach, Different types of DAF are explained straightforwardly.
I believe you also need to know about emulsions and the mechanism of demulsifies or "surfactants", too, in order to better understand the mechanism of coagulants and flocculants. I am sure that you will find their mechanism very simple. To do so, there are so many rheological books and articles in the area of emulsions, micelles, and function of their disturbants that you can use.
Special Thanks for your support, dear Reza Aminzadeh :)
A very detailed report (y)
Here in the link you can find also a good overview about SWRO-Preatretment systems (incl. DAF).
https://www.yumpu.com/en/document/read/30087294/pretreatment-requirements-and-trends-for-desalination
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