Solar photoelectro-Fenton flow plant modeling for the degradation of the antibiotic erythromycin in sulfate medium

Highlights: • Use of a 10 dm³ solar plant with a FM01-LC cell and a CPC photoreactor. • Predominant H₂O₂ production at the graphite-felt cathode and photolysis at the CPC. • Close agreement was obtained between theoretical and experimental data. • Four heterocyclic, one aromatic, one tertiary amine and five carboxylic acids detected. • Release of nitrate ions and, to a lesser extent, ammonium ion. - Abstract: A solar photoelectro-Fenton (SPEF) plant containing a filter-press FM01-LC flow reactor in series with a compound parabolic collector (CPC) as photoreactor, operating in batch recirculation mode, was simulated using a parametric model. The degradation of 10 dm³ of solutions of the heterocyclic antibiotic erythromycin (ERY) in 0.050 mol dm⁻³ Na₂SO₄ at pH 3.0 was used for validation. The filter-press reactor contained a platinized titanium plate anode and a graphite-felt cathode that produced H₂O₂ from the reduction of dissolved oxygen (0.24 mmol dm⁻³). Trials were performed under potentiostatic and galvanostatic conditions with predominance of H₂O₂ production, minimizing H₂ evolution reaction. The effect of initial catalyst (Fe²⁺) concentration, current density (j), initial antibiotic concentration as dissolved organic carbon (DOC) and volumetric flow rate on the ERY mineralization was studied. Good agreement between simulations and experimental DOC decays was obtained. Mineralization current efficiencies and specific energy consumptions were also determined. The best performance under galvanostatic conditions was found for 0.225 mmol dm⁻³ ERY (100 mg dm⁻³ DOC), 0.50 mmol dm⁻³ Fe²⁺, volumetric flow rate of 3.0 dm³ min⁻¹ and j_cath = -0.16 mA cm⁻², reaching 69% mineralization with current efficiency of 75% and specific energy consumption of 0.059 kWh (g DOC)⁻¹. Six organic by-products were identified by gas chromatography-mass spectrometry, whereas final short-chain carboxylic acids like formic and oxalic acid were detected by ion-exclusion high-performance liquid chromatography. The initial N atom of ERY was predominantly converted into NO₃⁻ ion, although NH₄⁺ ion was formed as well.