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.

Biological treatment of wastewater polluted with an oxyfluorfen-based commercial herbicide.

Fluoxil-24 is a commercial herbicide based on oxyfluorfen (a hazardous non-soluble organochlorinated compound) and additional compounds used as solvents. The aim of this work is to study the biotreatability of this commercial herbicide in water through batch experiments performed at different temperatures (15, 20, 25 and 30 °C) and initial concentrations (85, 150, 300 and 500 mg L-1 of oxyfluorfen). Activated sludge from an oil refinery wastewater treatment plant was acclimated and used for biodegradation experiments. Two main mechanisms, volatilization and biodegradation, were observed to be responsible of the herbicide removal. Fluoxil-24 removal efficiencies between approximately 40% and 80% were reached after 70 h, depending on the conditions used, and oxyfluorfen was not completely removed. Regarding the influence of the temperature, thermal inhibition problems appeared at 30 °C, and the volatilization rate of solvents increased, causing oxyfluorfen to become unavailable for microorganisms. An increase of herbicide initial concentration did not clearly affect the herbicide removal efficiency, whereas it negatively affected the biological mechanism. The experimental results were fitted to a mathematical model that included both simultaneous mechanisms of volatilization and Monod biodegradation kinetics. The model was able to predict the experimental results, and the calculated model parameters confirmed the effect of the variables under study.

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.