Degradation mechanism and toxicity assessment of clofibric acid by Fe ²⁺ /PS process in saline pharmaceutical wastewater

A considerable effort has been made to exploring the oxidation of clofibric acid (CA) in advanced oxidation processes (AOPs). However, few studies are available on degradation mechanism and toxicity assessment of CA in saline pharmaceutical wastewater. Here the effect of chlorine on the degradation kinetics of CA by Fe²⁺/ persulfate (PS) process were studied. Oxidation efficiency, mineralisation, intermediate by-products, reactive oxygen species (ROS) and toxicity assessment were examined. Notably, a high removal efficiency (70.91%) but low mineralisation (20.99%) of CA were observed at pH 3.0 during the Fe²⁺/PS system. Furthermore, we found Cl^- exerted a beneficial impact on CA degradation. However, the degree of CA mineralisation was relatively minor. Under high salinity (100 mM) condition, the primary reactive species within the Fe²⁺/PS system were <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>SO</mml:mi></mml:mrow><mml:mn>4</mml:mn><mml:mrow><mml:mrow><mml:mo>⋅</mml:mo></mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math>, OH^·, Cl₂/HClO, and Fe(IV). Several undesirable chlorinated by-products were formed. A reasonable degradation pathway was proposed. According to the ecological structure-activity relationship (ECOSAR) programme, some transformation products exhibited higher toxicity levels than CA itself in both acute and chronic toxicity assessment, especially in high-salinity environments. These findings elucidate an increased challenges and ecological risk for CA oxidation by Fe²⁺/PS treatment in saline pharmaceutical wastewater.