I am using a typical 78 cm2 Boron doped diamond, in a electrochemical reactor. My effluent has been submitted to electrochemical treatment applying currents that vary from 5 to 20 mA cm2.
Although my absorbance results are very coherent, my COT results vary akwardly, presenting values that are way of chart, many times superior to the concentration initially present.
The liability of the equipment has been previously tested with the same dye studied, and have been thoroughly used in other readings presenting no problems.
My main suspicion is that there are secondary degradation reactions occuring after the sample collection. Is there any information on the topic ?
Dear Marilia,
We experienced similar far too high COD (DOC) and TOC (COT) results after AOP on various biologically treated wastewater (UV/H2O2, O3). Hence we think that post reactions interfere with the sample analysis.
By the way, we remove dyes and other recalcitrant organics from finishing by advanced biological treatment as demonstrated in 20 large textile WWTP's in Bangladesh. Residual color (light yellowish) is completely removed with a low dose of ozone (O3).
Dear Marilia,
BDD is very powerful electrode to generate hydroxyl radical in situ, and it can also generate sulfate radical or hypochlorite when sulfate or chloride ions inside the water. I suppose that you might add some salts (such as sulfate salt or chloride salt) as electrolyte to increase the conductivity, which may lead to the secondary degradation. Also the dye you choose may contain S or Cl, and may contribute sulfate or chloride during the reaction, and these ions are activated by BDD for your said secondary degradation.
I am confused with your abbreviation. Is COT an organic carbon parameter (like TOC) or chemical oxygen demand (like COD)?
If you experience that chemical oxygen demand increase with treatment I think it is likely that your oxidation produces hydrogen peroxide which can be oxidised and thus contributes to chemical oxygen demand.
It should be impossible to increase organic carbon above the initial, but it is possible that the parameter decreases less than the loss of color as the oxidation might destroy the chromofor of the dye in a partial oxidation without mineralising the dye.
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