Iron-modified coconut shell biochar-activated peroxymonosulfate for acetaminophen degradation and microbial inactivation in sewage

Abstract

Trace levels of pharmaceuticals in sewage pose persistent environmental risks due to limited degradation in conventional wastewater treatment. This study addresses this by employing coconut shell-derived biochar (CBC) and its iron-modified variant (Fe-CBC) as activators of peroxymonosulfate (PMS) to degrade acetaminophen (ACP) in both aqueous and raw sewage matrices at low concentrations. Under optimized conditions (Fe-CBC: 500 mg L⁻¹; PMS: 400 mg L⁻¹), ACP removal exceeded 99% within 30 min, outperforming peroxydisulfate (PS) activation. Enhanced surface chemistry and iron sites in Fe-CBC substantially promoted reactive oxygen species (ROS) generation, particularly superoxide (O₂˙⁻) and singlet oxygen (¹O₂), which were confirmed via scavenging experiments to be dominant in driving ACP breakdown. The system maintained robust performance across a wide pH range (3–10) and demonstrated resilience against common inorganic ion interferents. Liquid chromatography mass spectroscopy (LC-MS) identification of degradation intermediates enabled the proposal of a mechanistic pathway. Importantly, Fe-CBC exhibited excellent regenerability over multiple reuse cycles, retaining high catalytic efficiency. In real sewage, the Fe-CBC/PMS combination significantly outperformed CBC/PMS in ACP removal and delivered strong biocidal effects, complete inhibition of E. coli, and evident structural damage to rotifers and nematodes after 90 min. Altogether, the Fe-CBC/PMS process shows strong promise as an integrated approach for simultaneous removal of trace pharmaceuticals and microbial contaminants from sewage.