Photoelectro-Fenton as post-treatment for electrocoagulated benzophenone-3-loaded synthetic and urban wastewater

Abstract

The removal of benzophenone-3 (BP-3), a ubiquitous pollutant in municipal wastewater treatment facilities, was optimal by means of a sequential electrocoagulation (EC)/UVA photoelectro-Fenton (PEF) treatment. Overall mineralization was attained upon combination of EC (Fe/Fe cell, 15 mA cm−2, 20 min) with PEF (boron-doped diamond/air-diffusion cell, 33.3 mA cm−2, 720 min), being superior to EC/electro-Fenton (EF) and requiring shorter time than single PEF. In EC, an Al/Al cell yielded the largest removal of BP-3 in a simulated matrix at pH 11.0 due to precipitation of its neutral form caused by a substantial pH drop, with optimum current density of 15 mA cm−2. EC of BP-3-loaded urban wastewater at natural pH was quite effective also with a Fe/Fe cell, being preferred since it provided the required metal catalyst for subsequent treatment. Among the electrochemical advanced oxidation processes tested, PEF was superior to electrochemical oxidation with electrogenerated H2O2 (EO-H2O2) and EF, especially when using the boron-doped diamond instead of a RuO2-based anode, due to the oxidation of generated active chlorine and hydroxyl radicals, along with the photolytic action of UVA irradiation. GC-MS revealed the formation of 14 cyclic products in PEF treatment, two of them being also formed during EC.