Study On The Degradation Of Carbamazepine In An Ultrasound-enhanced FeS/PDS System

As a new class of emerging pollutants,pharmaceutical and personal care products（PPCPs）are posing an enormous threat to the environment.Carbamazepine,a typical PPCPs pollutant,is expected to consume up to 1,014 tons per year on a global scale,and its residues in the environment poses great risks to various organisms as well as humans.In this paper,carbamazepine（CBZ）used as the target pollutants was degreaded by the oxidant of persulfate（PDS）activated by ferrous sulfide（FeS）.On this basis,ultrasound was introduced to the system to enhance the treatment efficiency and then the system mechanism was analyzed.Firstly,the basic FeS/PDS system was studied.The effects of dosages of FeS and PDS,initial pH,and CBZ concention on the degradation of CBZ were investigated.In the process,the changes of CBZ concentration,dissolved iron and PDS consumption rate were mainly focused.The results showed that FeS can effectively activate PDS to degrade CBZ and the reaction process was consistent with the pseudo first-order reaction kinetics.Increasing the dosage of FeS and PDS was beneficial to the reaction,but the excessive dosage could not greatly increase the degradation rate.CBZ was basically degraded at the initial pH of 3.0-7.0,and the final pH was generally reduced to the same level（2.9-3.1）.The degradation efficiency was not obvious when the initial pH was greater than 9.0.When the initial concentrations of CBZ increased,the degradation rate reduced,and more oxidant was needed to maintain the reaction.Secondly,the Ultrasound was introduced into the basic FeS/PDS system to establish a novel US/FeS/PDS system to improve overall removal efficiency.By comparing the performance of US,US/PDS,US/FeS,FeS/PDS and US/FeS/PDS systems on CBZ,the enhancement effect of ultrasound was confirmed.Different environmental factors including the dosages of FeS and PDS,initial pH,temperature and three kinds of anions were investigated.The results showed that the increase of FeS and PDS concentrations in a certain range was beneficial to the degradation of CBZ.The improvement of excessive dosage was very limited and also uneconomical.The initial pH showed a significant effect on the novel system,the degradation efficiency was better under acidic conditions,while alkaline condition would inhibit the reaction.High temperature was beneficial to the reaction,and the activation energy required for the system was only 35.58 kJ/mol.Cl^-,HCO₃^-and NO₃^-all showed inhibitory effects on the system.With the concentrations of three anions increasing,the inhibition effects became more obvious,and the inhibition of HCO₃^-was the strongest.In order to explore the reaction mechanism of CBZ degradation by the US/FeS/PDS system,the FeS solids before and after the reaction were characterized by X-ray diffraction and X-ray photoelectron spectroscopy.It was found that the FeS material used in this experiment was Troilite-2H,and some FeS₂ impurities existed on the surface.The structure of FeS was relatively stable,and the internal crystal structure did not change significantly before and after the reaction.However,about 5%Fe²⁺was oxidized to Fe³⁺,and 7%S^2-was converted into other forms,which suggested that S^2-was likely to participate in the iron ion cycle.It was confirmed by free radical trapping experiments and EPR identification experiments that SO₄^·-and HO·were the main radical forms.The contribution rate of HO·remained basically unchanged,while the contribution ratio of SO₄^·-was increasing during the reaction.The SO₄^·-ratio reached 50.5%at the end of reaction.The degradation products during the reaction process were detected by LC-APCI-MS,and 12 intermediate products were obtained and three possible degradation pathways of CBZ were deduced.