Biodegradability improvement and toxicity reduction of soil washing effluents polluted with atrazine by means of electrochemical pre-treatment: Influence of the anode material.

This work focuses on the partial anodic electro-oxidation of atrazine-polluted soil washing effluents (SWE) in order to reduce its toxicity and to improve its biodegradability. Concretely it has been evaluated the influence of the anodic material used. It is hypothesized that such partial oxidation step could be considered as a pre-treatment for a subsequent biological treatment. At first, atrazine was extracted from a polluted soil by means of a surfactant-aided soil-washing process. Then, four different anodic materials were studied in partial electro-oxidation pre-treatment batch experiments at different electric charges applied: Boron Doped Diamond (BDD), Carbon Felt (CF), and Mixed Metal Oxides Anodes with Iridium and Ruthenium. Atrazine, TOC, surfactant and sulphate species concentrations, as well as changes in toxicity and biodegradability, were monitored during electrochemical experiments, showing important differences in their evolution during the treatment. It was observed that BDD was the most powerful anodic material to completely degrade atrazine. The other materials achieve an atrazine degradation rate about 75%. Regarding mineralization of the organics in SWE, BDD overtakes clearly the rest of anodes tested. CF obtains good atrazine removal but low mineralization results. All the anodes tested slightly reduced the ecotoxicity of the water effluents. About the biodegradability, only the effluent obtained after the pre-treatment with BDD presented a high biodegradability. In this sense, it must be highlighted the mineralization obtained during the BDD pre-treatment was very strong. These results globally indicate that it is necessary to find a compromise between reaching efficient atrazine removal and biodegradability improvement, while also simultaneously avoiding strong mineralization. Additional efforts should be made to find the most adequate working conditions.

Selection of anodic material for the combined electrochemical-biological treatment of lindane polluted soil washing effluents.

This paper focuses on the removal of lindane from soil washing effluents (SWEs) using combined electrochemical -biological processes. In particular, it has been evaluated the influence of the anodic material used in the electrolysis of the SWE on the biodegradability and toxicity of the effluents. Four anode materials were tested: Boron Doped Diamond (BDD), Carbon Felt (CF), and Mixed Metal Oxides Anodes with iridium and ruthenium (MMO-Ir and MMO-Ru). These materials were tested at different current densities and electric current charges applied. Lindane, TOC, sulphate, and chlorine species concentrations were monitored during electrochemical experiments, showing important differences in their evolution during the treatment. In spite of reaching a good removal of lindane with all the materials tested, results showed that Boron Doped Diamond working at 15 mA cm-2 achieved the best biodegradability results in the electrolyzed effluents, because the ratio BOD5/COD increased from 0.2 to 0.5, followed by Carbon Felt anode. Regarding toxicity, Carbon Felt decreased toxicity by 80%. Opposite to what it was expected, MMO anodes did not achieve biodegradability improvement and they only showed reduction in toxicity at high electrical charges.