Mechanisms for degradation and transformation of β-blocker atenolol via electrocoagulation, electro-Fenton, and electro-Fenton-like processes

Abstract

This study investigated the mechanism of atenolol degradation and transformation through ˙OH-based electro-Fenton (EF), SO₄˙⁻-based EF-like, and electrocoagulation (EC) processes. EF and EF-like processes were performed using a sacrificial Fe anode in the presence of hydrogen peroxide (H₂O₂) and peroxomonosulfate (PMS) or peroxodisulfate (PS), respectively. The influence of atenolol concentration, current density, initial solution pH (pH_i), and electrolyte and its concentration on atenolol degradation was investigated, and the EF and EF-like processes enhanced the degradation efficiency as compared to EC alone. The ˙OH-based EF process achieved greater degradation efficiency than the EF-like and EC processes, consistently yielding 90–98% degradation, even over a broad pH range (pH_i 3–11). In contrast, the SO₄˙⁻-based EF-like process achieved better mineralization (TOC reduction) efficiency than the EF and EC processes. Among the tested electrolyte media (Cl⁻, CO₃²⁻, HCO₃⁻ SO₄²⁻, and NO₃⁻), Cl⁻-assisted electrochemical processes displayed superior atenolol degradation, while NO₃⁻ ions adversely affected the degradation and mineralization processes. Identification of atenolol degradation and transformation products by LC-MS analysis established four major pathways for atenolol degradation. These pathways proceeded via radical attack on the sensitive isopropyl group, aromatic benzene ring, and terminal acetamide sites. This study also supports the role of H₂O₂, PMS, PS and co-existing inorganic anions which considerably decides the formation of free reactive radicals and oxidative species, which may trigger diverse mechanisms of degradation.