Improving biodegradability of soil washing effluents using anodic oxidation

In this work, a combination of electrochemical and biological technologies is proposed to remove clopyralid from Soil Washing Effluents (SWE). Firstly, soil washing was carried out to extract clopyralid from soil. After that, four different anodes-Ir-MMO, Ru-MMO, pSi-BDD and Carbon Felt (CF)-were evaluated in order to increase the biodegradability of the SWE. CF was selected because was the only one able to transform the pesticide to a more biodegradable compounds without completely mineralizing it. Finally, biological oxidation tests were performed to determine the aerobic biodegradability of the SWE generated. From the obtained results, it was observed that at the beginning of the electrolysis the toxicity slightly increased and the biodegradability decreases. However, for electric current charges over 2.5 A·h dm−3 the toxicity drastically decreased, showing an EC50 of 143 mg L−1, and the BOD5/COD ratio increased from 0.02 to 0.23.