Combining bioadsorption and photoelectrochemical oxidation for the treatment of soil-washing effluents polluted with herbicide 2,4-D

BACKGROUND: The aim of this work is to evaluate the effectiveness of complete treatment of soil spiked with 2,4-D, consisting of soil washing, followed by bioadsorption with activated sludge and electrochemical and photoelectrochemical oxidation of resulting wastewater using BDD anodes combined with UV light irradiation. RESULTS: Results show that 2,4-D is very efficiently removed from synthetic soil by soil-washing without the use of surfactants. The effluent can be treated by bioadsorption with fresh activated sludge coming from a municipal wastewater treatment plant and the maximum adsorption capacity is 0.012 mg 2,4-D mg(-1) biomass. Despite the low contact time between the biomass and the soil-washing effluent, results fit well to a Langmuir isotherm. CONCLUSIONS: Photoelectrolysis with diamond anodes is more efficient than single electrolysis and the influence of potential radicalary oxidants produced on the anode surface from sulfate and chloride and activated by UV light can explain the better results. Both electrolysis and photoelectrolysis can lead to the complete mineralization of 2,4-D, regardless of the biomass/herbicide ratio applied in the previous bioadsorption process. (C) 2016 Society of Chemical Industry