Comparing Electrochemical and Fenton-Based Processes for Aquaculture Biocide Degradation

In this work, malachite green was degraded using different advanced oxidation processes (Fenton, photo-Fenton, sono-Fenton and electrochemical process). Malachite green is used as biocide in aquaculture and is usually discarded with the effluents. On higher pollutant concentration, all the Fenton-based reactions achieved excellent absorbance reduction up to 10 min. Classic Fenton was faster after 10 min of reaction and photo-Fenton acting faster before this point. The photocatalytic effect was better on the oxygen demand reduction (COD) with 86.91% against 79.19% of sono-Fenton and 62.72% of Fenton. All four methodologies had excellent absorbance reduction following the order: photo-Fenton (100% up to 30 min) > electrochemical (99.27%) > Fenton (98.11%) > sono-Fenton (73.99%). Despites the slowly initial degradation obtained for electrochemical process, the reaction achieved high capacity after 60 min. Toxicity tests, using Lactuca sativa seeds, indicated a significant reduction in the effluent toxicity following this sequence: sono-Fenton > photo-Fenton > Fenton > electrochemical. The results showed that all processes studied provided high levels of malachite green removal; however, the adequate use of each technique should be conduct with an accurate evaluation of the needed treatment considering the particularity of each method. Such techniques were successfully applied before to remove dye basic blue 99 and the hormone 17-alpha-methyltestosterone and corroborated by Lactuca sativa toxicity assays.