No Persulfate Dosing Of Electro-Fenton Like System And Its Performance Research

Fenton technology is an important branch of advanced oxidation technology (Advanced oxidation processes, AOPs). After H2O2 catalyzed by Fe2+, a highly active hydroxyl radical (·OH, E0=+2.33V～2.8V) can be produced. Recent years, more and more attention was drawn to ·OH, for a complete degradation of the refractory organics in water. Some macro molecules turned into smaller toxic or non-toxic molecules, or even degradation directly into CO2, H2O. However, the traditional technique was limited to the application, because the waste on Fenton catalyst Fe2+ and the final iron mud treatment. Electro-Fenton combined Fenton technology with electrochemical technology, in which Fe2+ get regenerated, thus effectively avoiding the problem of iron sludge treatment and follow-up by controlling the pH and other conditions.Fenton-like reaction refers to persulfate (S2O82-, PS or HSO5- PMS) activated by transition metal ions (Fe2+, Co2+, and Ag+, etc.), then sulfate radical (SO4·-, E0=+ 2.6V～3.1V) can be generated. SO4·- has a longer life (30～40μs) and a stronger oxidation ability compared to ·OH (20ns), so SO4·- has more advantages in the removal of recalcitrant pollutants. Combined Electro-Fenton and Fenton-like reaction, Electro-Fenton like reaction can achieved PS regeneration and Fe2+ regeneration.Because PS can be generated by SO42- with electrochemical preparation, PS can be activated to SO4·- by Fe2+, SO4·- react with pollutants then back again to the reaction with SO42-. Started with the reaction SO42- â†' SO4·-â†' SO42-, this acticle combined in situ electrochemical SO4·- with electro-Fenton like technology, aimed at creating a new kind of electro-Fenton like system (Electro/Fe3+/SO42- system). The new system can complete the generation of PS, and regeneration of the catalyst regeneration of Fe2+ by Fe3+ with cathodic reduction. Therefore, we were on the low concentrations of PS detection, electrochemical performance parameters to generate over two salt study and two model pollutants (RB5 and methylamine (CH3NH2)) degradation to verify the system performance. The detailed contents and results are as follows:(1) The establishment of a method, which detecting PS at low concentration:PS can be produced a stronger oxidizing SO4·- via activated, and the dye methylene blue (MB) likely to be decolorized by a small amount of oxidant. The PS was activated by microwave (MW), for a shortage of reaction time. And the extent of decolorization showed responsible for the concentration of PS. The decolorization reaction is carried out to the end in 1min; the extent of decolorization is not affected by pH of the stock solution; the decolorization extent by various concentrations of PS decreased with increasing MB concentration; a great linear coorelation was achieved beteen PS concentration and extent of MB discoloration, and the correlation coefficent was 0.997.(2) PS generation by electrochemical system:SO42- can be generated to PS in the electrochemical reaction at the anode. The relationship between the generation amount of PS with the electrolyte composition, current density and cell types were investigated. Being a same concentration of total concentration of SO42-, PS amount reduced with increasing proportion of H2SO4 and (NH4)2SO4; the amount of PS are also positively correlated with the current density during experiment; Compared with double-chamber electrolysis cell experiments, single chamber turned to generate more PS, and single chamber own a higher production efficiency.(3) The degradation of RB5 by electro/Fe3+/SO42- system:the effect of type and concentration of iron, electrolyte pH and RB5 dosing on RB5 decolorization rate. It was found that, under the same background conditions, Fe3+ showed a better RB5 decolorization than Fe2+ in the system. What’s more, an excessive amount of Fe2* showed negative influence on decolorization of RBS while an excessive amount of Fe3+ showed no negative influence on decolorization of RB5. The pH of electrolyte increased during RBS decolorization process by electro/Fe3+/SO42- system. The dosing of RBS showed a first order kinetics with RBS decolorization, and with the increasing concentration of RBS dosing, RBS decolorization rate decreases. After few times dosing RBS, RBS decolorization rate did not reduced but increased, indicating recycling system more conducive to the RB5 degradation; RB5 can achieved 83% of mineralization within 200min by electro/Fe3+/SO42- system. And by identification of intermediates during RB5 decolorization process, decolorization path of RB5 were proposed.(4) The continuous degradation of CH3NH2 (g) by electro/Fe3+/SO42- system: the performance of electro/Fe3+/SO42- system during CH3NH2 (g)degradation, and the type and concentration of iron ions during Electro/Fe3+/SO42- system were detected. It is confirmed that persulfate and Fe2+ both were renewable and recyclable in Electro/Fe3+/SO42- system. And by measuring electro/Fe3+/SO42- system active species, the mechanism of Electro/Fe3+/SO42- system were summarized.