Effective degradation of phenacetin in wastewater by (photo)electro-Fenton processes: Investigation of variables, acute toxicity, and intermediates

Abstract

Electro-Fenton (EF) and solar photoelectro-Fenton (SPEF) processes were employed at different scales to degrade phenacetin (PNT), the first synthetic analgesic. EF experiments were conducted at lab scale, whereas SPEF experiments were performed in an 8 L pre-pilot plant using an electrochemical filter-press cell. Under optimal conditions (25 mg L−1 PNT, 25.3 mg L−1 Fe2+, and current density of 59.5 mA cm−2), EF resulted in degradation and mineralization degrees of 83.9% and 45.2% at 14 and 230 min, respectively. Similarly, PNT was spiked into real wastewater from a municipal secondary treatment plant, resulting in degradation of 68.0% and mineralization of 39.4%, with an energy consumption of 7.0 kWh g−1. The optimal conditions of SPEF (16.8 mg L−1 Fe2+ and current density of 45.9 mA cm−2) led to degradation and mineralization degrees of 55.9% and 37.1% at 36 and 181 min, respectively, with a low energy consumption of 0.142 kWh g−1. Both processes effectively detoxified the solutions, as demonstrated by tests with Artemia salina and Lactuca sativa. Three distinct degradation pathways were proposed based on the identification of eleven reaction intermediates formed upon •OH attack. In conclusion, the low energy cost of the SPEF process underscores its potential for pharmaceutical degradation in wastewater.