【作者】 乔瑞平；

【导师】 庄源益；

【作者基本信息】 南开大学 ， 环境科学， 2005， 博士

【摘要】 微囊藻毒素是水体富营养化藻类中产生的一类肝脏毒素,是潜在的肿瘤促进剂,而且具有化学稳定性,不能被常规饮用水处理工艺有效地脱除。高级氧化技术是以羟基自由基（·OH）为主要氧化剂的水处理技术,在适当的条件下,可以将污染物矿化为水、二氧化碳和无机盐。高级氧化技术为微污染水中微囊藻毒素的降解指明了方向。为了研究微囊藻毒素的降解技术,首先优化了从实验室培养的铜绿微囊藻中提取微囊藻毒素的程序,并建立了固相萃取和高效液相色谱（SPE-HPLC）富集和分析微囊藻毒素的方法。本文以广泛存在的微囊藻毒素MC-LR、MC-RR 为研究目标,采用了均相高级氧化技术如UV/H2O2光氧化和Fenton 试剂氧化、非均相高级氧化技术如UV/TiO2-Fe3+光催化氧化、常规混凝与Fenton 试剂氧化联用技术以及高锰酸钾氧化技术等,研究了微囊藻毒素的降解行为。研究结果表明,UV/H2O2光氧化能有效地降解微囊藻毒素,·OH 氧化和UV光分解是微囊藻毒素降解的直接原因;藻毒素的降解经历了异构化、·OH 对共轭二烯和肽键的亲电加成、ADDA 和肽环断裂、有机中间体的进一步降解等过程,降解过程能近似用准一级动力学方程描述;根据UV 光分解、H₂O-2 和·OH 氧化微囊藻毒素的原理和稳态近似法,建立了UV/H₂O₂ 光氧化降解藻毒素的动力学模型,能很好地解释溶液中H₂O₂、HO-2 、CO-3 、HCO-3 等对藻毒素降解的影响;对比实验表明UV 光分解对藻毒素有一定的降解作用,而H2O2氧化藻毒素的效率很低。UV/H₂O₂ 光氧化体系中,UV 和H-2O₂ 氧化去除藻毒素具有协同作用,H₂O₂ 在UV 照射下产生的·OH 对藻毒素有很强的氧化能力;UV/H₂O₂ 光氧化过程中溶液pH 值的变化,说明藻毒素并不是直接被矿化为CO2、H₂O 和其它无机小分子物质,而是经历了一系列中间产物,由大分子逐渐变为小分子物质;藻毒素的降解效率与其起始浓度、pH 值、H₂O₂浓度、光照强度及反应时间等有关。藻毒素起始浓度的增加会显著减小其降解速率。在中性和弱碱性条件下,藻毒素的降解速率较快。在较低的H₂O₂浓度范围(0～1 mmol·L^{-1_</sup>内,H₂O₂浓度的增加可以显著地提高藻毒素的降解速率,MC-LR、MC-RR 降解的总表观速率常数kobs与H₂O₂ 浓度的关系可分别表示为: k_obs = 0.0378C_H2O20.2115（MC-LR） 、k_obs = 0.0512C₍H₂O₂₀.1467（MC-RR）。H₂O₂ 浓度较高时,会明显抑制藻毒素的降解。光照强度的增大能促进藻毒素的降解,但是二者之间并没有直接的正比关系。最佳实验条件下,起始浓度为0.20 mg/L 的MC-LR 和0.72mg/L 的MC-RR 溶液的去除效率分别可以达到80.8%和94.8%。Fenton 试剂也能有效地氧化微囊藻毒素,但氧化机理与UV/H₂O₂ 光氧化有所差异。反应初始阶段,大部分微囊藻毒素得到降解,降解过程与准一级动力学有很好的相关性,然后进入一个相对缓和的氧化过程;藻毒素的降解效率与}更多还原

【Abstract】 The increase of population and the consequent intensification of agricultural andindustrial activities have led to the enhancement of eutrophication in superficialfreshwater bodies, and then it has led to cyanobacteria blooms more frequentworldwide. Microcystins are mainly produced by freshwater cyanobacteria such asMicrocystis, Oscillatoria, Nostoc, Aphanizomenon and Anabaena. Microcystinsdisplay hepatotoxic behaviour and cause tumor promotion. Furthermore, theirchemical characteristic is so stable that the conventional water treatment processeshave only limited efficiency in removing soluble microcystins. The advancedoxidation processes （AOPs）, which involve the production of reactive oxidativespecies, especially the hydroxyl radicals （·OH）, are capable of mineralizing organiccontaminants into H2O, CO2 and other inorganics. AOPs provide promising treatmentoptions for microcystins-containing water.To meet the need of further research, microcystins were extracted firstly from theMicrocystis aeruginosa cultured in laboratory. The accumulation, separation andpurification procedures of microcystins were optimized, and then the solid phaseextraction and high performance liquid chromatography （SPE-HPLC） analyticalmethod was developed for analysis of microcystins. Experiments were carried out toinvestigate the degradation behaviours of microcystins using some AOPs includingthe homogeneous and heterogeneous oxidative techniques and other practicaltechniques. The main conclusions are as follows:The UV/H2O2 photooxidation was effective in removing microcystins in water,and UV photolysis and ·OH were responsible for the degradation of microcystins. Themajor destruction pathway of microcystin included the isomerization of microcystin,electrophilic addition of ·OH on the conjugated diene structure of ADDA moiety andpeptide bond, cleavage of dihyroxylated ADDA and the peptide bond, and furtheroxidation of the intermediates. The degradation process accorded approximativelywith the pseudo-first-order kinetics. Considering the contributions of individual UVphotolysis, H2O2 and ·OH oxidation in the combined homogeneous system, asimplified kinetic model for the degradation of microcystins was developed using thepseudo-first-order equation and steady-state approximation. This kinetic modelprovided better understanding for the effects of H₂O₂、HO₂ 、CO₃ and HCO₃ on thedegradation of microcystins. The control experiments showed that H2O2 was difficultto oxidize microcystins while UV direct photolysis could decompose microcystinspartially. However, the UV/H2O2 system could significantly enhance the degradationefficiency due to the synergetic effect between UV radiation and H2O2 oxidation.The ·OH generated from the decomposition of H2O2 under the UV irradiation wasresponsible for the synergetic effects. The variation of pH in the process indicated theformation of organic acids, which showed that microcystins were not mineralized toH2O, CO2 and other inorganics directly but converted to some intermediates firstly,then partial mineralization was achieved. The degradation efficiencies of microcystinsdepended on the following factors: A lower initial microcystin concentration led to afaster and more efficient degradation; The neutral and weak alkaline solutions weremore appropriate to carry out degradation reaction; In a lower H2O2 concentrationrange, the degradation of microcystins improved significantly with increasing H2O2concentration. Under the experimental conditions, the relationships between theobserved rate constants and H2O2 concentrations could be described as follows:kobs = 0.0378CH2O20.2115（MC-LR）, kobs = 0.0512CH2O20.1467 （MC-RR）. On the other hand, thedegradation of microcystins retarded obviously while H2O2 increased to a largerconcentration. It was attributed to the ions and radicals could scavenge ·OH in thesolution; Increasing UV light intensity could enhance but was not directlyproportional to the degradation rate of microcystins. Under the optimal conditions, thedegradation efficiencies of MC-LR and MC-RR could reach 80.8% and 94.8%,respectively. Fenton reagent oxidation was also effective in removing microcystins. In all cases,most of microcystins degradation occurred during the initial 10 min of reaction.Microcystins transformation was characterized by pseudo-first order kinetics duringthis brief initial phase, while the subsequent phase exhibited a sharp drop indegradation rate. This behavior suggested a mechanism where Fenton reagentproduced an initial surge of ·OH that resembling a “pulse”injection as opposed to the“continuous”injection observed in the UV/H2O2 system. There existed an optimalFe2+ dosage, and a higher addition resulted in brown turbidity that hindered theabsorption of the UV light required for photolysis and caused the recombinationof ·OH. In this case, Fe2+ reacted with ·OH as a scavenger. After reacting for 30 min,the degradation efficiencies of MC-LR and MC-RR could up to 92.4% and 95.8%under the experimental conditions, respectively. In the presence of UV radiation, theoxidation potential of Fenton and Fenton-like reagent could be enhanced vigorouslyand followed the sequence of UV/Fe2+/H2O2 ≈UV/Fe3+/H2O2 > Fe2+/H2O2 >Fe3+/H2O2. The effect of UV light attributed to the direct ·OH formation andregeneration of Fe2+ from the photolysis of the Fe（III） complex in solution. The effectof ferric chloride flocculation on soluble microcystins was negligible. However, itcould remove most organic materials that would be favourable for the degradation ofmicrocystins by Fenton and Fenton-like reagent oxidation. The experiments performed in the heterogeneous photocatalytic processesexhibited best degradation results of microcystins and followed the order:UV/TiO2-Fe3+/H2O2>UV/TiO2-Fe3+>UV/TiO2. The doping of Fe3+ greatly improvedthe photocatalytic reactivity of TiO2, and H2O2 appeared to significantly enhance thedegradation of microcystins due to the higher generation rate of ·OH. The experimentsresults showed that the degradation of microcystins on TiO2-Fe3+ was in accordancewith Langmiur-Hinshelwood （L-H） kinetic model well. Under the experimentalconditions, the apparent reaction rate constants of MC-LR and MC-RR were 0.2435and 0.4102 mg·L?1·min?1, and the corresponding Langmiur adsorption equilibriumconstants KA were 2.6301 and 0.7606 mg?1·L, respectively. The degradationefficiencies of microcystins mainly depended on the TiO2-Fe3+ dosage and UV lightintensity. Increasing the addition amount of TiO2-Fe3+ would increase both the surfacearea of catalyst available for adsorption and the Fe（III） complex. However, there更多还原