Removal of antibiotic rifampicin from aqueous media by advanced electrochemical oxidation: Role of electrode materials, electrolytes and real water matrices

One of the most commonly detected classes of pharmaceutical products in aquatic environments are antibiotics and their effective removal in sewage treatment plants is limited due to their refractory features. In this context, electrochemical technologies could be an alternative to decrease the pollution level and promote the complete elimination of antibiotics in water. For this reason, the electrochemical treatment of a synthetic effluent as well as different real water matrices polluted with antibiotic rifampicin was investigated, using different electrode materials (anodes: boron doped diamond, (BDD), Pt and PbO2; and cathodes: carbon felt (CF), graphite (Gr), stainless steel (SS) and titanium (Ti)). Effects on the variation of applied current density (j) and supporting electrolyte were examined during the degradation of the antibiotic. Comparative studies have clearly showed that the degradation of rifampicin had better results by using BDD and CF as anode and cathode, respectively, where the process efficiency increased when an increase on the j was attained. Complete color removal was achieved at all j applied (chromophore rifampicin group gives a red-orange color for solutions), whereas only at higher j leads to complete organic matter (in terms of chemical oxygen demand (COD)) removal. For a selected cathode, the efficiency of the anode materials follows the trends BDD>PbO2>Pt, whereas that of cathode follows CF>Ti>SS≈Gr for a selected anode material. Using Na2SO4, Na2CO3 or NaCl, the production of strong secondary oxidant species was favored, promoting the oxidation of dissolved organic matter in synthetic effluents. Meanwhile, when the BDD/CF electrochemical cell was employed with different real water matrices, the degradation and mineralization of the drug was independent of this parameter. Oxalic, acetic, fumaric and maleic acids were the final organic byproducts of rifampicin degradation with the release of heteroatom N under NO3‒ and NH4+ forms.