Electro-Fenton Treatment Of Real Pharmaceutical Wastewater Paired With A Bdd Anode: Reaction Mechanisms And Respective Contribution Of Homogeneous And Heterogeneous Center Dot Oh

Even though there is increasing evidence on the benefits of combining electro-Fenton (EF) and anodic oxidation with boron doped diamond anodes (BDD) for the degradation of organic pollutants, the exact contribution of % OH, BDD(center dot OH) and their synergy in the paired EF-BDD process has still not been clearly established, taking into account i) the applied current/potential; ii) the reactivity of the pollutants and their intermediates formed during treatment and; iii) the matrix effect in real wastewater. In this paper, we address the above points by conducting the EF treatment of real pharmaceutical wastewater (COD0 = 1200 mg L-1 and BOD5/COD = 0.14). In-depth data analysis revealed a synergy between homogeneous and heterogeneous BDD(%OH) that accelerated the mineralization of organics, with homogeneous %OH dominating during the first treatment stages, while BDD prevailed in the last stages through electron transfer reactions. EF-BDD achieved the highest mineralization yield (97.1% of TOC removal at 4.17 mA cm(-2) and 0.2 mM of Fe2+), as compared to EF with a dimensionally stable anode (DSA), a material not producing heterogeneous center dot OH. However, EF-DSA proved equally effective at increasing the biodegradability of the effluent with lower operational costs (BOD5/COD = 0.68 at US$ 1.46 m(-3) in 4 h). Hence, we point out the versatility of EF to reach different targets of water quality depending upon the anode materials: EF-DSA to increase the biodegradability of refractory wastewater vs. more powerful (though costlier) EF-BDD for quasi-complete mineralization.