Chloride-Enhanced Fe(II)/PMS/H2O2 System for Degradation of PBTC and Simultaneous Recovery of Iron Phosphate
Phosphonate wastewater, characterized by stable C–P bonds, poses significant environmental risks due to its resistance to degradation and potential to contribute to eutrophication. This study developed a chloride-enhanced Fe(II)/PMS/H2O2 system for the oxidative degradation of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and simultaneous recovery of phosphorus as iron phosphate (FePO4). Under optimal conditions (0.1 mmol/L PBTC, 1.0 mmol/L Fe(II), 0.5 mmol/L PMS, 0.5 mmol/L H2O2, 10 mmol/L NaCl, initial pH 3.0, 60 min), total phosphorus (TP) removal reached 100%, with phosphorus nearly completely recovered as FePO4 precipitate. Increasing NaCl concentration and temperature enhanced TP removal, while pH significantly influenced removal efficiency and product speciation; acidic conditions (pH < 4.3) favored FePO4 precipitation. Coexisting Ca2+ and Mg2+ had negligible effects, whereas HCO3− and humic acid (HA) inhibited TP removal in a concentration-dependent manner. Radical quenching and electron spin resonance (ESR) analyses identified hydroxyl radicals (•OH), ferryl ion (Fe(IV)=O), sulfate radicals (SO4•−), and chlorine radicals (Cl•) as primary reactive species, with •OH playing a dominant role. Chloride introduction promoted the generation of multiple reactive species, and Cl• and its derivative Cl2•− directly attacked the C–P bond and phosphonate group, facilitating phosphorus release as PO43− and subsequent FePO4 formation. The system's feasibility was validated using actual industrial circulating cooling water. This study provides a novel approach for phosphonate wastewater treatment and phosphorus recovery.