Radiation-assisted electrochemical processes in semi-pilot scale for the removal of clopyralid from soil washing wastes

This work focuses on the scale-up of irradiated-assisted electrochemical processes with diamond anodes for the removal of clopyralid from washing soil wastes. In particular, it is studied the influence of the ratio electrochemical power/total power in the performance of conductive diamond photoelectrochemical oxidation (CDPEO) and conductive diamond sonoelectrochemical oxidation (CDSEO) at high and low ultrasounds frequencies. The comparison is carried out in terms of mineralization, clopyralid decay, reaction intermediates and inorganic speciation. The CDPEO-7.7 W tests carried out in a single cell and in a stack of cells show that the stack seems to be less efficient in terms of clopyralid removal and mineralization than the single cell. The ratio electrochemical energy/photoelectrochemical energy is more favorable in small devices, where the photolytic energy is not only a complement but a primary treatment. Regarding inorganic speciation, chloro-species show a similar behavior in absence and presence of US or UV irradiation. Opposite, irradiation seems to inhibit the reduction of nitrate to ammonium, independently on the irradiation power used. In terms of energy efficiency, an increase of the radiation power does not entail a high efficiency/energy consumption ratio, and CDPEO-7.7 W and CDSEO-24 kHz-100 W show efficiency/energy consumption ratios 3.7 and 2.3 times higher than that of CDSEO-10 MHz-450 W.