Optimization of electrocatalytic H2O2 production at pilot plant scale for solar-assisted water treatment

Abstract

This manuscript summarizes the successful start-up and operation of a hybrid eco-engineered water treatmentsystem, at pilot scale. The pilot unit, with 100L capacity, has been devised for the efficient electrocatalyticproduction of H2O2at an air-diffusion cathode, triggering the formation of%OH from Fenton's reaction withadded Fe2+catalyst. These radicals, in combination with those formed at a powerful boron-doped diamond(BDD) anode in an undivided cell, are used to degrade a mixture of model pesticides. The capability of the plantto produce H2O2on site was initially optimized using an experimental design based on central composite design(CCD) coupled with response surface methodology (RSM). This aimed to evaluate the effect of key processparameters like current density (j) and solution pH. The influence of electrolyte concentration as well as liquidand air flow rates on H2O2electrogeneration and current efficiency at optimizedjand pH was also assessed. Thebest operation conditions resulted in H2O2mass production rate of 64.9mgmin−1, 89.3% of current efficiencyand 0.4kWh m-3of energy consumption at short electrolysis time. Performance tests at optimum conditions werecarried out with 75L of a mixture of pesticides (pyrimethanil and methomyl) as a first step towards the elim-ination of organic contaminants by solar photoelectro-Fenton (SPEF) process. The combined action of homo-geneous (%OH) and heterogeneous (BDD(%OH)) catalysis along with photocatalysis (UV photons collected at asolar CPC photoreactor) allowed the removal of more than 50% of both pesticides in 5min, confirming the fastregeneration of Fe2+catalyst through cathodic reduction and photo-Fenton reaction.