Study On Fenton Like System Promoted By Organic Acid Complexation With Iron Ion For Treatment Of Organic Wastewater

As one of the classic advanced oxidation technologies（AOPs）,Fenton oxidation method catalyzes the decomposition of H₂O₂ to produce hydroxyl radical（·OH）.·OH is highly oxidizable,the organic pollutants which are difficult to be degraded by traditional biological,physical and chemical methods can be oxidized and degraded non-selectively.Although the conditions of Fenton reaction are mild,the equipment is simple and the operation is convenient.However,its effective pH range is narrow;H₂O₂ is prone to disproportionation,which leads to low utilization rate,and it is not convenient for storage and transportation.The Fe³⁺produced is easy to precipitate,increasing the treatment cost.In order to solve the above problems,the homogeneous Fenton method has been gradually emerged in recent years.The addition of complexing agents（tartaric acid,protocatechuic acid,gallic acid）can significantly expand the effective pH range of the reaction,promote the Fe³⁺/Fe²⁺cycle,and reduce the generation of iron sludge.Persulfate（PDS）and calcium peroxide（CaO₂）can be used as stable oxidants to effectively replace H₂O₂.PDS is used as the source of SO₄.^-,CaO₂ can release H₂O₂ slowly.Therefore,the homogeneous Fenton oxidation method has a good application prospect.Based on this,the specific research contents of this paper are as follows:（1）CaO₂ was used as the solid source of H₂O₂ and tartaric acid（TA）was used as the complexing agent to construct CaO₂/Fe²⁺/TA system.By exploring the effects of various parameters on the degradation efficiency of organic pollutants,the reaction conditions of the system were optimized:the optimal dosage ratio of CaO₂/Fe²⁺/TA was 1/0.5/1 mmol L^-1,and the optimal pH range was 3-9.The CaO₂/Fe²⁺/TA system can achieve a decolorization rate of 94.82%and a mineralization rate of 30%for methylene blue（MB）within 300 s,and a removal rate of 99.61%and a mineralization rate of 17%for sulmethoxazole（SMX）within 600 s.The presence of·OH,superoxide anion(O₂^·-)and monoline oxygen（¹O₂）was confirmed by free radical masking assay and electron paramagnetism detection（EPR）.The degradation products of MB and SMX were determined by high performance liquid chromatography-mass spectrometry（HPLC-MS）,and the biotoxicity of SMX degradation intermediates was analyzed.Finally,the influence of common anions(SO₄^2-,Cl^-,NO₃^-,HCO₃^-)on the removal efficiency was evaluated.（2）Procatechuic acid（PCA）was introduced as the complexing agent and PDS as the oxidant to construct the PDS/Fe²⁺/PCA system.PCA can form a complex with Fe³⁺to prevent the precipitation of Fe³⁺and realize the efficient cycle of Fe³⁺/Fe²⁺.By studying the effects of various reaction parameters on the performance of the system,the optimal conditions were obtained as follows:[PDS]₀=1 mmol L^-1,[Fe²⁺]₀=30μmol L^-1,[PCA]₀=30μmol L^-1,and the optimal initial pH was 3-7.PDS/Fe²⁺/PCA system can effectively degrade of methyl orange（MO）,MB,rhodamine B（Rh B）,tetracycline（THC）and metronidazole（MTZ）.Free radical masking experiments and EPR confirmed the existence of SO₄.^-,·OH and ¹O₂ active oxygen species.The influence of common anions（Cl^-,NO₃^-,HCO₃^-）on the removal efficiency was evaluated.（3）Gallic acid（GA）was used as the complexing agent and PDS was used as the oxidant to construct PDS/Fe²⁺/GA system.The effect of the system degrade MTZ was studied,the optimal dosage of GA and Fe²⁺was explored,when the mole ratio of GA and Fe²⁺was 1:1,the degradation rate of MTZ was 83%.The degradation included a rapid stage and a slow stage,and the initial rapid degradation stage was controlled by the reaction between PDS and Fe²⁺,and the slow degradation stage was depended on the control of the regeneration of Fe²⁺.Free radical masking experiments and EPR confirmed the existence of three active oxygen species,such as SO₄.^-,·OH and ¹O₂.The degradation products of MTZ were detected by HPLC-MS,and the degradation pathway of MTZ was suggested.The biotoxicity of MTZ degradation intermediates was simulated.Finally,the effects of common anions(SO₄^2-,Cl^-,NO₃^-)and humic acid（HA）on the system performance were evaluated.