Solar-powered CDEO for the treatment of wastewater polluted with the herbicide 2,4-D

• Electro-oxidation powered by PV panels is efficient and environmentally friendly.
• Current intensity and voltage change with solar power irradiated.
• Changing oxidation conditions are caused by fluctuation in solar irradiation.
• The way of powering the electrolysis influences on the concentration of intermediates.
• Hydroquinone, benzoquinone and chlorophenols are the main intermediates.

In this work, the remediation of wastewater polluted with 2,4-D via conductive-diamond electrochemical oxidation using solar energy as a direct electrical power source has been investigated. The changes in operating conditions during the solar test are clearly related to the day–night cycle, with a maximum solar irradiation intensity of 450 W m−2 at noon and an average daily charge supplied of 22.5 A h m−2 d−1. A solar irradiation intensity greater than 100 W m−2 is necessary to produce current, and values over 200 A m−2 are required for efficient solar-powered processes. Despite fluctuations in the intensity supplied to the electrochemical cell, electrolysis with diamond electrodes can attain complete depletion of 2,4-D and its mineralization, although the changing operating conditions applied during the electrolysis powered by solar energy favor the accumulation of many intermediates. In contrast, only very low concentrations of two intermediates were detected during electrolysis powered galvanostatically with a power supply at 3.0 A, indicating that the intensity highly influences the oxidation rate involved in the electrolysis.