Improvement of electrochemical oxidation efficiency through combination with adsorption processes

In this work, a three-step process (adsorption-desorption-electrolysis) is evaluated as an interesting approach for the removal of organochlorinated compounds (clopyralid, lindane and perchloroethylene) with different physical properties (solubility and vapor pressure) from low concentrated wastewater. First steps are based on the adsorptive capacity of granular active carbon (GAC) particles to retain organics and on the solvent capacity of methanol to extract them to concentrated solution and regenerate GAC. In the last step of electrolysis with conductive diamond electrodes, the degradation of pesticide is projected, as well as the recovery of methanol. Results show that clopyralid, lindane and PCE are efficiently retained in GAC, although adsorption efficiency depend on pollutant/GAC ratio and physicochemical properties of pollutant. Pretreatment allows the concentration of clopyralid and PCE solutions up to 8 times, but worse results are obtained in case of lindane solutions. Electrolysis of concentrated methanol solution seems to be more efficient than electrolysis of diluted aqueous wastes, mainly in the case of clopyralid. In all cases, electrochemical degradation fits a first order kinetics confirming mixed oxidation mechanisms with diffusion control of the direct processes and mediated oxidation. Results obtained in terms of current efficiency and energy consumption of electrolysis step point out the lower operation cost of concentrated liquid wastes and encourage further works on the development of cost-effective combined processes for the treatment of diluted solutions polluted with polar compounds (such as clopyralid).