I encountered a problem in two projects that I think I need an electrocoagulation expert to solve it! :( We use iron electrodes in electrocoagulation for treatment of two different textile wastewaters for two different projects. In pH about 8-10 the system works not bad (although the removal efficiency should be better) which is because of the high pH. But the problem is when the influent pH is about neutral (7). In this pH the system does not work anything at all! I mean there is no evidence of any green color (which is the proof released Fe 3+) or passivation of cathode and the effluent is the same as the influent. does anybody here know why is it like this!? Because I have not seen such a thing with Al electrodes! And my question is that why with iron electrodes in pH=7 the system does not do anything although it is expected to became better!
Dear Zeinab,
Your observation that electro-coagulation based on corroding iron anodes does not work at neutral pH is consistent with the results of our in-depth assessment of 21 large ETP's on various textile wastewaters in Bangladesh.
At pH 7 and higher (alkaline) there will be no green colored free ferric ions Fe3+ because these react immediately with the water to form iron hydroxides with very low solubility. At pH 7 this ferric and hydroxide production will be (very) low because of lower electro-conductivity as compared to high or low pH.
For optimal results the iron based electro-coagulation shall be operated at acid conditions say pH 4 - 5.
Last-but-not-least both chemical and electro-chemical coagulation remove very little soluble organics including dye color except for some adsorption to the metal hydroxide flocs.
Dear Zeinab
I think that the following review paper about your topic which has been recently published could be helpful for you:
http://www.sciencedirect.com/science/article/pii/S0301479716308106
Regards,
Ata
hello
this link could help you
http://www.tandfonline.com/doi/full/10.1080/21622515.2012.715390
regards
Dear Zeinab
First of all, did you check the removal efficiency at pH of 7? because it is not necessary to develop a noticeable colour during the electrocoagulation process. For example, if the applied current is very high and the concentration of the targeted pollutant is relatively low, the colour development will not be that noticeable thing as the pollutant removal will be very quick.
Secondly, could I ask you is it the initial or final pH value?
you can find some of my published papers on my page.
Regards
Dear Khalid I'm pretty sure that the EC system does not do anything because there is no evidence of iron ion release (green color) in any time! The initial pH of wastewater varies between 7 to 10 and when the initial pH is between 8 to 10 the system works and removes half of COD but when the initiaal pH of wastewater is 7 the outlet COD and color is the same as inlet!
It is a very very weird situation for me myself!
Dear Zeinab
In my opinion, now, we need to know the chemical composition of your wastewater sample, because there is a possibility of presence of a chemical element in your sample, which will be activated at the neutral level of pH. Therefore, the electrochemical reaction will be interfered.
do you have the chemical composition please?
Regards
It is preferred to use the COD measurements for checking whether there is a removal or not. The matter also depends on the type of the pollutants and their contribution and sensitive to pH
Dear Zeinab,
Your observation that electro-coagulation based on corroding iron anodes does not work at neutral pH is consistent with the results of our in-depth assessment of 21 large ETP's on various textile wastewaters in Bangladesh.
At pH 7 and higher (alkaline) there will be no green colored free ferric ions Fe3+ because these react immediately with the water to form iron hydroxides with very low solubility. At pH 7 this ferric and hydroxide production will be (very) low because of lower electro-conductivity as compared to high or low pH.
For optimal results the iron based electro-coagulation shall be operated at acid conditions say pH 4 - 5.
Last-but-not-least both chemical and electro-chemical coagulation remove very little soluble organics including dye color except for some adsorption to the metal hydroxide flocs.
Indeed I recommend the answer of Bruno Peeters. Good results can be obtained in acidic solution that enhances Ferric hydroxide formation. Otherwise alkaline medium enhance Ferrous hydroxide formation. Please refer to the attached paper.
Please check the Pourbiax of metal Iron at which pH the electrode gets passivated and even can you tel me what is the initial alkalinity, chlorides and COD of the wastewater?
Chlorides and Alkalinity of wastewater matters the most for Electrochemical Coagulation,
Dear All,
Thank you for your answers. The initial pH is 7.0. Actually recently I have understood that when the pH of wastewater is 7 it is because of adding NaOH in some parts of the textile process which comes into the wastewater. And the pH is 7 because moreover to NaOH, acetic acid and formic acid and some carbone compounds are added into some parts of process in the factory and so all of these compounds comes into the wastewater!!!! I have first thought of alkalinity but pH of the wastewater is 7! I think that one of these compounds (NaOH, Acetic acid, Formic Acid or carbonate) make trouble!
And the other important thing is that in this case there will be a brownish layer of gelatinous precipitate on the electrodes that with the time they become totall black!
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