Degradation Efficiency And Mechanism Of Deltamethrin In Water By Ferrous Ion Activated Bisulfite

Deltamethrin is a typical pyrethroid pesticide,which has made a great contribution to the development of agriculture in the world.However,with the extensive use of deltamethrin in agricultural production,its accumulation in the environment is increasingly significant,which has a certain harm to human,nature and ecological environment.The conventional treatment methods of deltamethrin are photodegradation and biodegradation,but these methods have some disadvantages,such as poor degradation efficiency and long degradation cycle.As a new advanced oxidation technology,sulfur autoxidation system has the advantages of good effect and low cost.In this paper,deltamethrin was used as a representative pollutant of pyrethroid pesticides to activate[Fe（Ⅲ）/HSO₃^-],and study its degradation effect and influencing factors,reveal the mechanism of deltamethrin degradation,explore the application effect of the system in actual water,and carry out engineering applicability evaluation and cost analysis.The results show that Fe（Ⅲ）/HSO₃^-can effectively degrade deltamethrin,and when the substrate concentration is 30μg/L,through the analysis of cost and engineering applicability,the optimal reaction conditions of this system are as follows:initial pH=4,Fe（Ⅲ）dosage of 100 mM,HSO₃^-dosage of 1 Mm.Under this condition,the degradation rate is about 69.5%.With the increase of substrate concentration,the degradation effect of deltamethrin decreased gradually,and the degradation amount increased.When Fe（Ⅲ）concentration increased from 60μM to 100μM,the degradation rate of deltamethrin increased,and the degradation effect decreased with increasing Fe（Ⅲ）concentration.When the concentration of HSO₃^-is increased from 0.25 mM to1.5 mM,the degradation rate is increased,and the degradation effect is decreased if the concentration continues to increase.When pH increased from 3 to 7,the degradation rate of deltamethrin decreased gradually.Dissolved oxygen is a necessary factor in the reaction process,and the degradation rate of deltamethrin can be reduced by up to 22%in the absence of oxygen.Light can promote the degradation of deltamethrin in the reaction system.Both bicarbonate and natural organic matter can inhibit the degradation of deltamethrin by this system.Through quenching experiments,this study verified that the free radicals in the reaction process were HO^·and SO₄^·-,and HO^·played a major role.The HO^·free radicals in the reaction process were verified by EPR experiment.Based on density functional theory,we found that the bond breaking reaction between C16 and O21 in deltamethrin was easy to occur,and the product generated by the bond breaking was measured by GC-MS,thus confirming the degradation path.The results showed that the degradation rates of deltamethrin in the effluent of the secondary sedimentation tank of a wastewater treatment plant and the water supply of a waterworks in Wuhan were 46.3%and 62.0%respectively,and the degradation effect of deltamethrin in the two actual water samples decreased to a certain extent;Due to HSO₃^-can reduce the active bromine intermediate to bromine ion,there is almost no bromate in the Fe（Ⅲ）/HSO₃^-system in the presence of bromine ion.This study provides a new technology for the treatment of pyrethroids in water,which can effectively remove pyrethroids in water,ensure the safety of sewage treatment plant effluent and urban water supply,and has certain engineering practicability.