Removal Of Endocrine Disrupting Chemicals In Water By Catalyzing Hydrogen Peroxide And Persulfate

Advanced oxidation processes based on persulfate and H₂O₂are becoming one of the leading means for the removal of refractory organics in water,due to their higher efficiency,shorter processing cycle and wider application range.In this dissertation,several highly efficient heterogeneous catalysts were developed to to active persulfate and hydrogen peroxide for the production of reactive oxygen species(ROS),five advanced oxidation systems were constructed to degrade the endocrine disrupting chemicals in water.The degradation performances were studied and compared,the ROS species were identified with radical quenchers,the catalytic mechanism was elucidated,the reaction conditions were optimized.The surface morphology,physical structure,chemical composition as well as the stability of the catalysts were analyzed based on the results of characterization including XRD,SEM,TEM,XPS,XRF,et al.The research findings of this dissertation supplement the theory systems of heterogeneous advanced oxidation technology and reactive oxygen species,providing more available choices for the efficient removal of organic contaminants in water.The main research contents and conclusions are as follows:(1)Steel slag was firstly employed as a solid alkalinity to activate K₂S₂O₈for reactive oxygen species to remove bisphenol A in water.The results indicate that about 72%of bisphenol A can be effectively removed within 60 minutes under the adopted condition([K₂S₂O₈]₀=3 g/L,[Steel Slag]=3 g/L,T=25?).Radical scavenger studies confirmed that all of theO₂^·-,SO₄^·-and^·OHcontributed to the bisphenol A degradation with the contribution of 68.97%,9.52%and 21.51%,respectively.The gradual decrease of Ca O and Fe O in steel slag composition during the reaction were observed.A redox mechanism was then proposed that both of the alkali activation and Fe O catalysis were responsible for the radicals production.(2)Fe₃O₄nanoparticle supported on coal fly ash was prepared by co-precipitation method,and proved to be capable of heterogeneously catalyzing both K₂S₂O₈and H₂O₂for reactive oxygen species and degrading bisphenol A in water.The two systems were compared systematically.Under the optimized condition,systems with K₂S₂O₈and H₂O₂can remove 76.9%and 90.1%of the bisphenol A after 60 minutes,meanwhile,35.93%and23.86%of TOC were removed after 120 minutes.Radical scavenger studies demonstrated that the primary radical species in two systems wereSO₄^·-/^·OHand^·OH,respectively,thus leading to the different bisphenol A degradation pathways and by-products.According to the results of characterization,the Fe₃O₄nano-particles on the catalyst presented good dispersibility and stability before and after the reaction.The oxidant efficiency in system with H₂O₂was obviously higher,while the system with K₂S₂O₈has a stronger buffer capacity toward solution p H and temperature variations.Meanwhile,the latter one was less influenced by the real water matrix due to the lower university ofSO₄^·-toward organics.(3)H₂O₂and K₂S₂O₈were combined as a binary oxidants system in order to get a better oxidation efficiency.The binary oxidants were heterogeneously catalyzed by the magnetic coal fly ash.With the oxidants ratio of 90/10 and solution p H<6.5,bisphenol A can be totally degraded within 60 minutes,meanwhile,the mutual effects among the three coexisting radicals(O ₂^·-,SO₄^·-,^·OH)can be least.Radical scavenger studies showed that the types,existing ratios and mutual transformation of reactive oxygen species can be affected by solution p H,catalyst surface properties as well as the oxidants ratio,thus influencing the degradation efficiency of bisphenol A.(4)A magnetic sepiolite composite was prepared by co-precipitation method and firstly applied to catalyze H₂O₂for reactive oxygen species to remove bisphenol A in water,which can be completely degraded at p H 6.0 within 30 minutes after the addition of H₂O₂(1000mg.L^-1).The results of activity tests and characterization showed that the bisphenol A was degraded through a combined processes of adsorption and oxidation.Based on the clay feature of sepiolite support,the powder composite was extruded into a small cylindrical sample and loaded in a fixed-bed reactor,which was operated under continuous-flow condition and room temperature.After treating 30 L of bisphenol A,the catalyst remained activity with removal efficiency above 80%and good structural stability.According to the results of XPS,the Fe²⁺/Fe³⁺ratio inside Fe₃O₄varied from 1:2.01 to 1:3.42 after the continuous operation,demonstrating that the active Fe²⁺had turned in to Fe³⁺irrevocably,which might be one of the main reasons of catalyst activity decrease.(5)Above mentioned five heterogeneous catalytic systems were further applied to treat three other EDCs with different structures including amoxicillin,atrazine and dibutyl phthalate.Based on the results of reactivity tests,all the five heterogeneous advanced oxidation systems exhibited general applicability in degrading different EDCs.However,removal efficiencies toward different EDCs varied a lot due to the different reactive oxygen species in each systems.