Concomitant abatement of ciprofloxacin, sulfamethoxazole and cefadroxil in synthetic wastewater using hybrid photoelectrochemical ozonation driven on TiO2 containing C, N and P species

Abstract

Ciprofloxacin (CIP), sulfamethoxazole (SMX) and cefadroxil (CFX) are herein degraded in synthetic wastewater (SWW) composed of 20 mg L−1 of each pharmaceutical compound, Na2SO4, MgSO4 and biodegradable organic matter. Photoelectrocatalytic ozonation (PECO) is used to generate multiple routes of oxidizing agents (i.e. ●OH), attacking the recalcitrant pollutants, and compared against individual oxidation processes: ozonation (O3), photolysis (PH) and photoelectrocatalysis (PEC). A TiO2 electrode with N, P and C incorporated in its structure (CNP-TiNST) is synthesized throughout two subsequent anodization methods: a first electrolyte made up of ethylene glycol and ethylenediamine as C and N sources, and a second electrolyte containing phosphoric acid to introduce P. The synthesized electrode presents a significant absorption in the visible light region, according to the Diffuse Reflectance Spectroscopy (DRS) analysis, obtaining two band gaps with values of 1.62 and 2.79 eV, which are considerably reduced in the pristine TiO2 phase. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) evaluations indicate the formation of mostly anatase phase and heterogeneous short nanostructures, respectively. XPS study reveals Ti-O, Ti-C and Ti-N bonds, confirming its successful incorporation into the photoanode. A photo-current density of 0.35 mA cm−2 is reached by the photoelectrode under Xe lamp irradiation while applying 1 V of potential vs Ag/AgCl. Contaminant removals in all systems are monitored by UV-Vis spectroscopy, High-Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC). The highest degree of contaminant removal in SWW occurs with the PECO process (80% according to HPLC analysis), decreasing TOC by 43% in SWW; and 98% TOC removal of these pollutants in distilled water, after 240 min of treatment. A germination toxicity test is performed on Lettuce Sativa, where 100% germination is achieved in the seeds grown in the treated SWW using PECO.