Removal of glyphosate from water by electrochemically assisted MnO2 oxidation process

Glyphosate, one of the organophosphate herbicides, has been widely used in the word. The removal of glyphosate was comparatively investigated by MnO2 oxidation, electrochemical oxidation, and electrochemically assisted MnO2 oxidation (electro-MnO2) processes. The effects of MnO2 dosage, current density, and solution pH on glyphosate removal and Mn2+ release were examined. The results indicated that the removal of glyphosate by MnO2 oxidation favored acidic pH conditions and a large portion of Mn2+ ions were released from MnO2. With the electro-MnO2 process using RuO2/TiO2 coated titanium mesh as both anode and cathode, glyphosate removal was significantly promoted and most of the released Mn2+ ions were oxidatively reverted to MnO2, which in turn enhanced the removal of glyphosate. Solution pH exerted an insignificant effect on glyphosate removal in the electro-MnO2 process. Major reaction intermediates including sarcosine, glycine, and PO43- were indentified in the initial phase of the MnO2 oxidation and electro-MnO2 processes. Glycine was further decomposed to glycolic acid and NH3-N in the MnO2 oxidation process; in contrast, glycine was oxidized into oxamic acid, glycolic acid and N-contained intermediates, and N-contained intermediates could be finally oxidized into acetic acid, NH3-N and NO3--N in the electro-MnO2 process.