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城市垃圾填埋处理过程中会产生大量垃圾渗滤液,其成分复杂且含有较多的难降解污染物,同时随着填埋时间的延长,其有机物的性质也会随之改变,很难获取准确信息,给渗滤液的处理带来了困难。溶解性有机物(dissolved organic matter,DOM)是渗滤液的主要成分之一,占总有机碳(total organic carbon,TOC)的80%以上[1]。现有研究[2-3]表明,垃圾渗滤液中的DOM主要包含腐殖酸、富里酸和亲水性有机物这3种成分,DOM中溶解态有机碳(dissolved organic carbon,DOC)通常在800~20 000 mg∙L−1,其中腐殖质在成熟渗滤液中的比例可超过70%[4]。随着填埋时间的延长,DOM的组成也会发生显著变化,通常表现为腐殖质类有机物含量有所增加[5-6]。
为获取渗滤液更多的有机物信息,通常使用光谱法、树脂分离或凝胶色谱分离法结合TOC或光谱进行分析。HUO等[7]采用XAD-8和阳离子交换树脂分离DOM,对各种组分的特性进行了比较,发现随着填埋时间增加,腐殖酸的比例可增加到45%左右,因此,腐殖质类物质通常会成为表征的首要目标物。基于有机物中的多种不同荧光基团[8-9],通过三维荧光可将类腐殖质分子分为类富里酸和类腐殖酸2大类有机物,同时还可分辨类蛋白有机物[10-14]。AFTAB等[13]采用三维荧光分析渗滤液有机物,发现有机物的主要成分是类腐殖质有机物,约占62%,其余多为类蛋白有机物。席北斗等[14]采用三维荧光和紫外可见光谱研究了不同年限垃圾渗滤液中DOM的组成变化,发现年轻垃圾渗滤液中类蛋白有机物是DOM的主要部分,随着填埋时间增加,类腐殖质有机物逐渐增多。在现有色谱分析基础上,有研究者将液相色谱分离法(size-exclusion chromatography,LC)和不同检测器结合,对有机物进行表征,如可将LC与二维荧光检测器[13]、有机碳检测器[15]等组合成为实时检测系统。此系统可将DOM分成不同组分,并可对组分的表征参数进行实时分析,如此可获得同一组分不同表征方式之间的差异,进而获取更多的有机物信息。
渗滤液中有机物通常难以生物降解,因此,氧化预处理工艺对渗滤液有机物去除具有重要意义。臭氧氧化可改变渗滤液中难降解有机物的分子结构,将大分子疏水有机物分解为亲水性小分子,主要包括醇类、有机酸或其他高生物利用度的化合物,改善生物降解性。因此,将臭氧氧化与有机物组分或结构联合分析,对渗滤液的处理具有重要意义。本研究采集不同龄渗滤液,利用液相色谱-有机碳-有机氮-紫外吸收(size-exclusion chromatography-organic carbon detection-organic nitrogen detection-ultraviolet visible detection,LC-OCD-OND-UVD),并结合树脂分离、三维荧光和紫外可见光谱对渗滤液有机物进行了表征和分析,研究了不同年限垃圾渗滤液中DOM的有机物组成特征及臭氧氧化对有机物组分的影响,研究结果可为垃圾渗滤液中的处理提供参考。
垃圾渗滤液有机物特征及臭氧对其结构的影响
Characteristics of organic matter in landfill leachate and the effect of ozonation on its structure
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摘要: 为分析不同填埋龄的垃圾渗滤液中有机物的组分特征及臭氧氧化对其结构的影响,选取成熟和年轻的垃圾渗滤液,利用液相色谱-有机碳-有机氮-紫外吸收(LC-OCD-OND-UVD)、紫外可见光谱、三维荧光光谱和树脂分离技术表征了不同填埋龄垃圾渗滤液中有机物的组分特征。结果表明:在2种垃圾渗滤液有机物中,主要组分为以类富里酸为代表的憎水性腐殖质类和亲水的中性小分子有机化合物,且其组分比例随着填埋龄增加可分别提高至60%和28%。年轻渗滤液中的高含量生物多聚物组分(BP)是其最显著特征。臭氧氧化可快速分解BP并最终生成类腐殖质的分解产物,但TOC去除率<10%。对于含量低于4%的腐殖质类小分子酸,因其含氮杂环结构成为最难矿化的有机物,故较低臭氧投加量无法将其氧化分解。LC-OCD-OND-UVD结合其他表征方法印证分析是获取有机物信息的有效手段,可为深入了解有机物的氧化分解过程提供参考。Abstract: The mature and young landfill leachates were selected to analyze the characteristics of organic matters and the effect of ozonation on its structure. The size-exclusion with organic carbon detection, organic nitrogen detection and ultraviolet visible detection (LC-OCD-OND-UVD), UV-vis spectrum, three-dimensional fluorescence spectrum and resin separation technology were used to investigate the characteristics of the organic matters in different landfill leachate. The results showed that the hydrophobic humics represented by fulvic-like substances and the hydrophilic low molecular neutral organics were the main components of the organic matters in two types of landfill leachate. The proportions of the components increased to 60% and 28% with the increase of landfill age, respectively. The significant characteristic of the organic matter in the young leachate was the high content (28%) of biopolymer (BP) component. Most of the BP could be decomposed by ozonation and some of humic-like organic matter was generated simultaneously. However, only low removal rates (<10%) of the total organic carbon (TOC) occurred. The small molecular weight humics-like acid (LMWA) with heterocyclic structure containing nitrogen was the most difficult to be mineralized, thus it cannot be decomposed at low ozone dosage. The combination of LC-OCD-OND-UVD with other methods is an effective strategy for the characterization of the complicated organic components in landfill leachate. This provides a new perspective for the further understanding of ozonation process of organic matter.
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Key words:
- landfill leachate /
- dissolved organic matter /
- humics /
- organic component /
- ozonation
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表 1 垃圾渗滤液主要水质指标
Table 1. Characteristics of the landfill leachates
渗滤液 COD/
(mg∙L−1)TOC/
(mg∙L−1)UV254/
cm−1B/C 色度 SUVA/
(L∙(mg∙m)−1)SS/
(mg∙L−1)pH 电导率/
(mS∙cm−1)渗滤液1 1 030 258 5.55 0.29 1 000 2.26 97 8.44 13.51 渗滤液2 6 925 2 211 29.5 0.24 8 000 1.57 167 8.26 48.11 -
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