Integrating ZVI-dehalogenation into an electrolytic soil-washing cell

Combination into a single electrochemical reactor of soil washing, ZVI dehalogenation and anodic oxidation can be used to degrade directly the clopyralid contained in spiked soil. Treatment is efficient, achieving the complete removal of chlorinated organics as well as the complete mineralization of the liquid waste produced. However, this combined process does not seem to improve the efficiency with respect to a system operated without addition of iron. Results show that the dechlorinated intermediates formed are less reactive than the parent pollutants, being particularly important the formation of oxalic acid, because its combination with iron (II) helps to explain the decrease in the overall rate of mineralization. This negative impact on the efficiency of the electrochemical process is not completely undesirable, because the toxicity of the waste decreases importantly in the very early stages with the use of iron, opening the possibility of a combination with biological treatments. Again, the accumulation of oxalate intermediates helps to explain this conclusion. Results point out the important effect of the size of iron particles used on the treatment and the complexity of the mechanisms that develop in the cell, which are explained in terms of the different parameters monitored.