Electro-Fenton and solar photoelectro-Fenton treatments of the pharmaceutical ranitidine in pre-pilot flow plant scale

Here, 2.5 L of solutions of the pharmaceutical ranitidine (RNTD) at pH 3.0 have been comparatively degraded by electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) processes using a pre-pilot flow plant with a Pt/air-diffusion cell. RNTD was oxidized by hydroxyl radicals coming from water oxidation at the Pt anode and Fenton's reaction between added Fe2+ and H2O2 generated at the air-diffusion cathode. In SPEF, the cell was coupled to a flat solar photoreactor to irradiate the solution with sunlight. The potent combined action of hydroxyl radicals and photolysis by sunlight explains the higher oxidation ability of SPEF compared to EF, attaining 80% mineralization as maximal. The optimum Fe2+ content as catalyst was 0.50 mM. The effect of current density and drug concentration on the degradation rate of RNTD, mineralization current efficiency and energy consumption for EF and SPEF was examined. The RNTD decay always followed a pseudo-first-order kinetics, having a greater oxidation rate for SPEF by the additional generation of hydroxyl radicals induced by photolysis of Fe(III) species. Malic, pyruvic, acetic, oxalic, oxamic and formic acids were detected as final carboxylic acids. The three latter acids were the main components of the final treated solution in EF because their Fe(III) complexes were not destroyed by generated hydroxyl radicals. The quick photolysis of such Fe(III)-carboxylate species by sunlight explains the greater oxidation power of SPEF. The initial S atom of RNTD was released as sulfate ion, whereas its initial N atoms were converted into ammonium ion along with a smaller proportion of nitrate ion.