Electrochemical disinfection of groundwater for civil use - An example of an effective endogenous advanced oxidation process.

Lab-scale experiments using real groundwater were carried out using the CabECO® reactor system in order to evaluate its suitability for producing safe water, acceptable for civil purposes. Trials were carried out in discontinuous and in continuous mode, analyzing the influence of electrical and hydraulic process parameters on the quality of treated water. The use of highly boron-doped diamond electrodes in the reactor allowed the electrosynthesis of considerable amounts of ozone. Because of the relatively high amount of chloride in the groundwater samples, a mixture of HOCl/ClO- was also synthesized. Somewhat unexpectedly, the increase in the current density in the explored range 100-1000 A m-2 was accompanied by an increase in the faradaic yield of the electrosynthesis of oxidants, which was more pronounced for ozone than for free chlorine. As reported in literature, the main radical intermediate in the relevant reactions is OH, which can lead to different oxidation products, namely ozone and HOCl/ClO-. The electrolytic treatment also caused a decrease in the concentration of minor components, including NH4+ and Br-. Other byproducts were ClO3- and ClO4-, although their concentration levels were low. Moreover, due to alkali formation at the cathode surface, the precipitation of calcium and magnesium carbonates was also observed. In addition, the experimental investigation showed that even Pseudomonas aeruginosa and Legionella could be completely removed in the treated stream, due to the unique capacity of the reactor to synthesize biocidal agents like ozone, HOCl/ClO-, and chloramines. These effects were particularly evident during batch experiments.