Degradation performance of carbamazepine by ferrous-activated sodium hypochlorite: Mechanism and impacts on the soil system

Abstract

The existence of carbamazepine (CBZ) in soil environment has been continuously reported and efficient elimination techniques are imperative. This study investigated the feasibility and the optimal conditions of CBZ degradation in soil by using Fe2+-activated hypochlorite (NaOCl). The Fe2+/H2O2, Fe2+/persulfate and Fe2+/NaOCl systems were applied to degrade CBZ under different initial soil pH conditions, of which Fe2+/NaOCl system achieved a higher CBZ removal rate over a wider pH range. The results indicated that 94.5% of CBZ could be degraded after 4 h when NaOCl concentration was 75 mmol kg−1 at Fe2+/NaOCl molar ratio of 1:1, and the reaction followed pseudo-first-order model. The CBZ removal efficiency could be improved with the increasing of NaOCl dosage. The reduction of initial CBZ concentration had a dual effect on CBZ removal efficiency at a fixed NaOCl dosage. Raising the temperature could considerably speed up the reaction. The high liquid to soil ratio, excessive humic acid and inorganic anions (Cl−, HCO3−) were not conducive to CBZ removal. Electron Spin Resonance (ESR) confirmed that the Fe2+/NaOCl system yield more hydroxyl radicals (HO) than that of NaOCl alone for CBZ degradation. The transformation pathways were proposed for CBZ degradation based on the identified intermediates. The investigation with soil surface morphology and mineral composition (Fe, Mn, Cu and Zn) showed no significant differences between the original and the treated soil samples, while the soil microbial community was negatively affected.