Factors hindering the degradation of pharmaceuticals from human urine in an iron-activated persulfate system

•Hydrolyzed urine notably inhibited pharmaceutical removal in the mFe-PS system.•Phosphate, (bi)carbonate and pH hinder pharmaceutical removal in the mFe-PS system.•Phosphate and carbonate radicals decreased pharmaceutical removal efficiencies.•Phosphate radicals preferentially attack the benzene ring of pharmaceuticals.•Carbonate radicals react with pharmaceuticals through hydroxylation preferentially. This study investigated the degradation of clofibric acid (CFA), bezafibrate (BZF), and sulfamethoxazole (SMX) in synthetic human urine using a novel mesoporous iron powder-activated persulfate system (mFe-PS system), and identified the factors limiting their degradation in synthetic human urine. A kinetic model was established to expose the radical production in various reaction conditions, and experiments were conducted to verify the modeling results. In the phosphate-containing mFe-PS system, the 120 min removal efficiency of CFA decreased from 95.1% to 76.6% as the phosphate concentration increased from 0.32 to 6.45 mmol/L, but recovered to 90.5% when phosphate concentration increased to 16.10 mmol/L. Meanwhile, the increased concentration of phosphate from 0.32 to 16.10 mmol/L reduced the BZF degradation efficacy from 91.5% to 79.0%, whereas SMX removal improved from 37.3% to 62.9%. The mFe-PS system containing (bi)carbonate, from 4.20 to 166.70 mmol/L, reduced CFA and BZF removal efficiencies from 100% to 76.8% and 80.4%, respectively, and SMX from 83.5% to 56.7% within a 120-min reaction time. In addition, alkaline conditions (pH ≥ 8.0) inhibited CFA and BZF degradations, while nonacidic pH (pH ≥ 7.0) remarkably inhibited SMX degradation. Results of the kinetic model indicated the formation of phosphate (H2PO4·/HPO4·−) and/or carbonate radicals (CO3·−) could limit pharmaceutical removal. The transformation products (TPs) of the pharmaceuticals revealed more incompletely oxidized TPs occurred in the phosphate- and (bi)carbonate-containing mFe-PS systems, and indicated that H2PO4·/HPO4·− mainly degraded pharmaceuticals via a benzene ring-opening reaction while CO3·− preferentially oxidized pharmaceuticals via a hydroxylation reaction. [Display omitted]