Improving photolytic treatments with electrochemical technology

Photochemical reaction is an Advanced Oxidation Process that have been extensively applied to wastewater treatment. New design of reactors, improvement of the hydrodynamics and light irradiation has led to good results. However, for many aromatics and recalcitrant compounds this technology is not efficient to achieve complete degradation at short time and cost-effective. In this way, couple another technology to this system could be a good alternative to improve the efficiency. Electrochemical Oxidation (EO) appears as a robust technology that uses efficient materials like conductive diamond electrodes to generate power oxidants species through direct or mediated oxidation. In this work, the enhanced degradation of 2,4-D an important chlorinated phenoxy herbicide by couple photochemical reactions and electrochemical oxidation was evaluated when the photoreactor acts primarily in relation to electrolytic treatment. For this, the influence of current density on the process efficiency was evaluated at natural pH conditions using sulphate media as electrolyte. Results show that there is a clear negative effect when EO is coupled to photolysis at low current density. However, at higher current the effect becomes positive (there is a synergism between the processes). In terms of energy, electrolysis worse the performance of photolysis when this non electrochemical process is the primary and photolysis enhances electrolysis when this later treatment acts as the primary treatment. In this way, photoelectrochemical process can be very promising with a rather advantageous cost/benefit ratio. Regarding to intermediates, couple EO to Photochemical process improve considerately the oxidation of these compounds, once very low or zero concentration of intermediates was detected after 1 h of treatment, especially at higher current density applied. Results are explained in terms of the generation of free radicals from the photoactivation of electrogenerated oxidants near the anode and in the bulk, improving the process performance.