摘要
卫生填埋是目前国内外垃圾处理的主要方式。在垃圾填埋过程中会产生一种难处理的高浓度有机废水，其特点是水质水量波动大、成份复杂，有毒有害物质含量高，经常规处理后的渗滤液残留COD一般为500mg／L左右。在我国目前尚没有一种成熟的典型处理工艺，大量已建成的采用常规工艺的渗滤液处理工程基本都达不到《生活垃圾填埋污染控制标准》(GB16889-1997)中的一级排放标准，更未建立渗滤液中微量有毒有害物质的排放标准，常规的COD等有机物监测指标也不能对它们实施有效的监测。但随着分析手段及人们对环保意识的提高，垃圾渗滤液中的这些有毒有害物质如环境内分泌干扰物(EEDs)对人体的危害已越来越受到健康组织的重视。这类污染物质即使含量极其微小(ng／L)，一旦它们进入机体，将对生物体产生严重的后果，如生殖器官、内分泌系统、神经系统、免疫系统异常，产生致癌、致畸、致突变等生物效应，因此环境内分泌干扰物的研究受到了国内外学者的高度重视。垃圾渗滤液作为一个重要的点污染源其控制和治理已经成为当前环境保护领域内的一项重大研究课题。
渗滤液中溶解有机质(DOM)是渗滤液中有机物的主要成分，也是残余COD的主要来源，同时对有机、无机化合物在自然界的迁移、转化和归宿等有非常重要的影响。显然溶解有机质的以上行为都与其结构密切关系，因而充分了解这些物质的组成特征具有非常的意义。
本论文以武汉市两个填埋场(记为R-填埋场和J-填埋场)和宜昌黄家湾填埋场(记为H-填埋场)为研究对象，其中R-填埋场的填埋龄约为5年，J-填埋场已封场两年，H-填埋场为5-10年，对渗滤液中的溶解有机质和有机物污染状况调查基础上，选择以内分泌干扰物(双酚A(BPA)、雌二醇(E_2)、雌酮(E_1)、邻苯二甲酸酯类(PAEs))为代表性有机污染物，围绕DOM对EEDs在固／液两相分布的影响规律和原理，研究了DOM对EEDs的吸附机制和对光降解过程的影响，主要成果如下：
(1)系统地对渗滤液这种复杂多相体系中的溶解有机质进行了表征。本工作集成超滤、树脂分离、色谱柱、高速离心、冷冻干燥、真空干燥和旋转蒸发等手段分离提取垃圾渗滤液中DOM，将DOM分为分子量不同的3个组分(1-4：1-0.45μm；1-6：0.45μm-1000 Da；1-5：＜1000 Da)，分为极性相异的5类(HoA：疏水酸性；HoN／B：疏水中／碱性；HiA：亲水酸性；HiN／B：亲水中性／碱性；pc：亲水性)，并对每一组分水样进行定性定量分析如常规分析(如COD、pH、氨氮、浊度、硬度等)、紫外-可见光光谱(uV-Vis)、荧光光谱(FL)、凝胶色谱(GPC)、液相色谱(HPLC)、全谱直读等离子体原子发射光谱(ICP-AES)、离子色谱(IC)、总有机碳(TOC)，对提取的固样进行元素分析、傅立叶变换红外光谱((FTIR)，质子核磁共振(~1H NMR)、在线裂解与气质联用(Py-GC-MS)等研究。结果表明渗滤液中溶解有机质是由一系列不同分子量、不同化学特性的大分子组成，并且这些特性随填埋场的年龄、填埋组分及填埋场所处的气候条件有关。其中以小分子量的(＜1000Da)的含氮有机物为主，J-填埋场的有机物具有较高的芳香性特征(如较大的分子量，较高的比紫外吸收(SUV_(254))，较高的H／C，较高的芳香组分等)对有机物的环境行为影响更强。被树脂吸附的疏中／碱(HoN／B)和亲中／碱(HiN／B)组分主要为脂肪或芳香胺类化合物，而被碱洗脱的疏水酸(HoA)、亲水酸(HiA)是溶解有机质中主要的小分子化合物(＜1000Da)，荧光光谱等证实了类富量酸(like-fulvic)这类较难降解的发色团有机物是渗滤液的主要成分。在R-填埋场，溶解有机质含有比文献高的H／C、N／C值表明了填埋场内较为活跃的微生物环境。在线热解气质联用更证实了溶解性有机质含有糖类、脂肪、蛋白质及木质素等大分子有机物及其降解产物，这些大分子有机物由一系列小分子化合物通过不同的键合作用形成。
(2)全面地调查了渗滤液中有机污染状况并确立了一套适合测定内分泌干扰物的方法。垃圾渗滤液中有机污染组分含量痕量且性质差异较大，没有一套高精度的普适方法。本文通过对渗滤液预分离，采用固相萃取、液液萃取、树脂抽提、层析净化分离分组等手段对渗滤液有机物进行了全面的调查，全方位地了解到我国垃圾渗滤液中有机污染成分与国外有很大的不同。不仅包括来自自然植物或疏水废物组分的降解产物，更让人注意的是大多数合成化合物大量出现在我国的垃圾渗滤液中，如表面活性剂、增塑剂、医药品、杀虫剂、激素类、石油类等。在此基础上，建立了一套同时测定双酚A、雌二醇、雌酮、固醇类和邻苯二甲酸酯类的方法。在三个填埋场中R-填埋场有机物含量最高，但J-填埋场含有较多难降解的大分子有机物，热解气质联用较好地分析了其来源及演化过程。我国的垃圾渗滤液中BPA和DEHP高达127.66和232.5μg／L，并且这些浓度不仅与填埋场年龄及填埋组分有关，而且随采样季节也发生很大的变化。BPA与溶解有机碳有一定的正相关性，主要存在于真溶液中，而DEHP主要存在于渗滤液的胶体中，因此可以通过吸附絮凝的方式得到较好的去除。一些常规的垃圾渗滤液处理工艺也被调查，发现它们很难同时处理一些难降解的有机物，因而更深的处理工艺被要求如光催化氧化。此外，20多种固醇类化合物首次在国内垃圾填埋场渗滤液中检出，其中高含量的污染标志物(粪甾醇)的检出很好地指示了渗滤液的污染特征，不同的污染指标指数指示了不同填埋场的微生物活动现状，并强调垃圾填埋场即使封场，其污染对水体仍是一个长期的威胁点源。
(3)研究了渗滤液中DOM与EEDs的吸附机制，探讨了利用吸附沉淀去除EEDs的可能性。环境内分泌干扰物在环境中一般较难降解、化学性质稳定半衰期较长，同时这些有机物常常毒性较强，不利于微生物的生长，常规的生物处理方法较难达到满意的去除效果。在实验室的吸附实验中，通过液相色谱(HPLC)、傅立叶变换红外光谱((FTIR)，质子核磁共振(~1H NMR)、顺磁共振(ESR)等技术分析发现渗滤液DOM与BPA，E_2和E_1的吸附是氢键、离子键和电荷转移等多重机制协同作用的结果，因而它们的吸附等温线不是简单的线性吸附，更符合佛罗里德方程，得出了垃圾渗滤液中DOM与BPA，E_2和E_1的结合常数。在此基础上探讨了利用溶解有机质作为络合吸附剂，絮凝沉淀同时去除EEDs的可能性。此过程包括两个阶段：DOM与有机物络合阶段；絮凝阶段。结果表明PAEs(如DEHP、DnOP)能很好地被絮凝去除。并提出了强疏水性有机物(K_(ow)＞4.5)能有效地利用这种方法去除。
(4)提出了光催化氧化处理内分泌干扰物的新工艺。光催化氧化是一种刚刚兴起的新型现代水处理技术，具有工艺简单、能耗低、易操作、无二次污染等特点，尤其对一些特殊的污染物比其他氧化法有更显著的效果。实验中探索了渗滤液中不同分子量、不同分子结构、不同渗滤液水质对内分泌干扰物光催化氧化降解有很人影响，J-填埋场DOM因有较高的芳香性对光降解影响较大。在研究二者相互作用的机理中，发现DOM对光解的影响具有双重的作用，一方面作为光敏剂对EEDs在太阳光辐射条件下起促进作用，另一方面由于与EEDs竞争吸收或光淬灭在紫外光催化氧化过程中起阻碍作用，提出了EEDs光降解的途径，在此基础上建立了光降解多变量模型，提出了一套光催化氧化同时降解垃圾渗滤液溶解有机质和内分泌干扰物的新工艺，其理论和方法可指导和应用于高浓度难降解有机废水的处理领域，为处理目前众多难降解有机物提供新的思路，具有重要的理论和实践意义。
本论文创新点：
●集成超滤、树脂、色谱柱、高速离心、冷冻干燥、真空干燥和旋转蒸发等手段分离提取垃圾渗滤液中DOM，综合利用各种表征手段(如元素分析，FTIR，UV，NMR，Py-GC／Ms，GPC，HPLC，GC-MS，FL等)全面系统地研究了垃圾渗滤液中所提取DOM的组成与分子结构特征。
●建立了一套测定垃圾渗滤液中EEDs的方法，全面调查了三个垃圾渗滤液中有机污染物的污染状况，20多种固醇类化合物首次在国内垃圾填埋场渗滤液中检出。
●以内分泌干扰物E_2，E_1，BPA和PAEs为代表，研究了垃圾渗滤液DOM中不同组分对其吸附、光解行为的影响。
Leachate pollutant from MSW landfills has been a major environmental concern.The purpose of this research was to characterize the chemical/physical and orgnic/inorganic composition of leachates from three landfills in China,labeled as R-landfill (the landfill of about 5 landfill ages in Wuhan),J-landfill (closed landfill in Wuhan) and H-landfill (located in Yichang with 5-10 ages) and understand the interaction mechanisms between dissolved organic matter (DOM) and environmental endocrine disruptors (EEDs).
Leachate DOM was characterized by fractioned using Ultrafiltrate (UF) and XAD resin and analyzed qualitatively and quantitatively using combining analysis methods such as UV, fluorescence,GPC,HPLC,FTIR spectroscopy,element analysis,1HNMR and Pyrolysis-gas chromatography/mass spectrometry (Py/GC-MS).The results showed that the compositions of DOM were correlated to landfill age,waste content in landfill and rainfall in landfill region. Fulvic acid in DOM,refractory organic matter,dominated in all samples.High H/C and N/C in leachate DOM (especial in R-landfill) indicated the dominant biochemical process.In older J-landfill had relative lower amount of carbohydrates and proteins by Py/GC-MS analysis,andconcentrated high aromaticity structure of DOM may be the main reason why the residue COD isdifficult to be removed.
A comprehensive determination of the composition of the organic pollutants was obtained byGC/MS analysis.The wider variety of organic substances were identified and attributed to naturalor xenobiotic waste components.Apart from plant material-derived compounds and degradationproducts of peptides,carbohydrates and lignin,numerous xenobiotic substances were identifiedand attributed to the groups of pharmaceuticals,estrogenic compounds (nature and synthesis),plasticizers,pesticides or chlorinated aromatics.BPA,E1,E2 and six Phthalates as targetscompounds were detected in three raw leachates and their treatment samples.The concentrationsof BPA and DEHP were usually high during the whole process up to 127.66 and 232.5μg/L andthe concentrations of them were lower in September because of rainfall dilution effect.The leachates from H-landfill contained relatively lower concentrations of BPA compared with R andJ-leachates.A slight positive correlation was found between BPA concentrations and DOC andthe major portion of the BPA in leachates was found in real dissolved fractions while DEHP infraction 0.45μm-1000Da.Nine classes of organic matters were used to discriminate substancesaffected by degradation processes and persistent compounds.The result suggested that aconventional treatment processes such as biological treatment,coagulation,sedimentation,sandfiltration,and activated carbon adsorption were not suitable to eliminate the potential estrogenictoxicity completely.Therefore,advanced treatment process should be adopted such asUV/catalysis.
DOM plays a significant role on the fate and transformation of organic pollutants.Sorption anddegradation of targets EEDs including BPA,E2,E1 and the mixture of six PAEs (DMP,DEP,DBP,BBP,DEHP and DnOP) have been investigated in the laboratory.The adsorption isotherm ofBPA, E2 and E1 by DOM fits Freundlich model well.Both the unreacted DOM and their EEDsinteraction products were analyzed by FTIR,1HNMR and ESR.The results suggest that multiplebinding mechanisms may occur simultaneously in the adsorption process with the formation ofionic bonds,hydrogen bonds and charge-transfer bonds.
Finally the removal or degradation of EEDs was discussed,a simple technique to removePAEs was proposed,which has a potential to remove organic micropollutants associated withDOM.BPA,E2 and E1 can be removed or degradated by photocatalysis oxidation under sunlightand UV with TiOz irradiation.The direct and indirect photolysis of BPA,E2,and E1 wasinvestigated in the absence and presence of DOM from three landfills.EEDs degradation bydirect photolysis under sunlit irradiation was significantly slower than that in the presence ofDOM.However,distinguishing differences in indirect EEDs photolysis with DOM from directphotolysis were observed primarily due to competitive light absorption and the quenching ofEEDs*.The influence of DOM on the photolysis of EEDs is small as compared with that ofDOM structure.J1-3 increased more carbon normalized rate constant than the other twoinvestigated.The products formed during degradation were detected using UV-Vis spectroscopy,FT-IR,HPLC and GC/MS.The pathway of BPA degradation by TiO_2 photocatalysis wasproposed and the estrogenic activity of E_2 degradation products was discussed.The estrogenicactivity of E_2 should be almost lost concurrently with the initiation of the photocatalyticdegradation.Therefore,TiO_2 photocatalysis could be applied to water treatment to effectivelyremove natural and synthetic estrogens without producing biologically active intermediaryZproducts.
引文
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