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土壤有机质(SOM)作为土壤的一个重要组成部分,它控制着进入土壤环境中有机污染物的去向及其迁移转化[1-2],而不同来源及形成年代的土壤有机质常表现出化学组成和物理结构的差异[3],因而对土壤中有机污染物的影响各异[4-6]。活性污泥是源于市政污水处理的一种絮凝物,我国每年产生的污泥量可达6000万吨左右,其有机质含量通常介于6.5%—48%,且生物源组分占到其总量的70%以上[7];泥炭土广泛分布于我国云贵高原及东北部地区,其有机质含量可达10%—60%,且具有含水率高、密度小和孔隙比大等特点[8]。活性污泥主要靠微生物活动降解污水中的有机质,而泥炭土则是依靠大量的生物质堆积腐熟,两者的有机质构成就有所差异。
近年来的研究表明,土壤有机质组分一直处在动态更替中,分子组成的异质性成为土壤有机质的普遍特征[4]。13C核磁共振、红外荧光等传统技术手段往往不能精确地区分土壤有机质组分差异。而生物标志物分子鉴别技术为探索土壤有机质异质性提供了新的途径[9]。分子生物标志物在环境中能够很好的保留其母源有机质的碳骨架分子信息,因此,采用分子生物标志物表征土壤有机质组成时,可利用一些特征参数指示有机组分的来源与降解程度[10]。而去除与土壤有机质结合的活性矿物时,一部分生物标志物被释放,可能使这些特征参数更准确地用于指示其来源[11-12]。
本研究以主要是微生物来源的活性污泥和植物性来源的滇池泥炭土两种材料为研究对象,分别进行水处理和酸处理,进而实验观察对憎水性有机污染物菲(PHE)和离子型有机污染物双酚A(BPA)的吸附特征,采用分子生物标志物技术结合元素分析和比表面积测定,探讨不同来源有机质分子组成的差异和活性矿物对于游离态脂和木质素酚类的保护机制,期望更好地理解有机污染物与SOM组分的非均质相互作用。
活性污泥和泥炭土有机质分子组成差异及其对有机污染物的吸附影响
The difference in molecular composition of organic matter between biosolids and peat and their effects on the adsorption of organic contaminants
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摘要: 土壤有机质(SOM)是控制土壤环境中有机污染物迁移转化的关键组分,不同来源土壤有机质的组成、矿物保护机制及其对有机污染物的吸附差异还不够明确。本研究采用分子生物标志物技术结合元素组成及比表面积分析表征酸处理前后的活性污泥和滇池底泥的有机质变化,进一步考察其对菲(PHE)和双酚A(BPA)的吸附特征。结果表明,活性污泥中可提取游离态脂组分和木质素酚类组分要低于泥炭土,但降解程度要远高于泥炭土。活性矿物去除后,泥炭土中游离态脂含量明显增加,而活性污泥的游离态脂含量稍有减少,这可能是因为活性污泥游离态脂主要以短链脂肪碳为主,在酸处理过程中容易导致流失。而糖类的显著增加证明了易分解有机碳组分在土壤中被稳定保存。活性污泥和泥炭土中的木质素酚类的含量随着酸处理显著减少,这表明与活性矿物结合的木质素酚类具有更高的氧化程度,导致其溶解性增强。此外,游离态脂降解程度在去除活性矿物后呈降低趋势,而木质素酚类的降解程度却呈增大趋势,这说明活性矿物选择性保护降解程度低的游离态脂和降解程度高的木质素酚类。对于菲的吸附,两种土壤在去除活性矿物后因为极性组分的流失,吸附能力均有所提升,但对于双酚A的吸附,活性污泥由于在酸处理后木质素酚类和游离态脂的减少暴露出更多的吸附位点,而呈现出了吸附能力升高的趋势,泥炭土则因其被丰富的有机质包裹,在去除活性矿物后没太大变化。本研究为揭示不同源SOM与有机污染物之间的相互作用具有重要意义。Abstract: Soil organic matter (SOM) is a key component for controlling the migration and transformation of organic contaminants in the soil environment. The molecular composition of SOM from different sources, mineral protection mechanisms and their differences in the adsorption of organic contaminants remain unclear. In this study, molecular biomarker technology combined with elemental analysis and specific surface area was used to characterize the organic matter composition in biosolids and Dianchi peat before and after acid treatment, and further investigated its adsorption characteristics for phenanthrene (PHE) and bisphenol A (BPA). The results showed that the amounts of extractable free lipids and lignin derived phenols are lower in the biosolids than in the peat, but the degradation degree of biosolids were much higher than that of peat. After reactive minerals were removed, the free lipids content in the peat increased significantly, while the free lipids in the biosolids decreased slightly. This may be attributed to the fact that the free lipids in the biosolids, mainly including short-chain fatty carbons, were dissolved during the acid treatment. In addition, a large number of sugars were released and detected. This result proved that the easily degraded organic matters are well-preserved in the soil. The contents of lignin derived phenols in biosolids and peat decreased significantly after acid treatment, which indicated that the lignin derived phenols associated with reactive minerals have a higher oxidation degree. In addition, the degradation of free lipids showed a decreasing trend after the removal of reactive minerals, while the degradation of lignin phenols showed an increasing trend. This result suggested that reactive minerals selectively protected free lipids with a low degree of degradation and lignin phenols with a high degree of degradation. For the adsorption of PHE, the adsorption capacity of the two soils were improved due to the loss of polar components after the removal of reactive minerals. For the adsorption of BPA, the biosolids showed an increasing trend of adsorption capacity because of the reduction of lignin derived phenols and free lipids after acid treatment to expose more adsorption sites. But the adsorption of peat soil for BPA had no changed after the removal of reactive minerals, probably because adsorption sites were wrapped in rich organic matter. This work is of great significance for revealing the interaction mechanism between SOM and organic contaminants.
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Key words:
- soil organic matter /
- biomarkers /
- mineral removal /
- organic contaminant
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表 1 元素分析及土壤基础表征
Table 1. Elemental analysis and soil basic characterization
元素分析Elemental analysis SA /(m2·g−1) WL/% CL/% N/% C/% H/% O/% C/H (N+O)/C HW 2.07 14.5 3.96 24.2 0.31 1.37 21.8 — — HA 3.34 21.2 4.70 22.1 0.38 0.91 14.5 55.8 34.9 PW 2.66 42.8 6.35 32.2 0.56 0.62 23.5 — — PA 2.90 47.4 6.38 29.7 0.62 0.52 16.3 36.6 30.7 注:SA为比表面积;质量损失比WL=酸处理损失的土壤质量/酸处理前的土壤质量;碳损失比CL=酸处理损失的碳含量/酸处理前碳的含量.
Note: SA is the surface area; weight loss ratio WL=soil weight lost after acid treatment/soil weight before acid treatment; carbon loss ratio CL=carbon content lost after acid treatment/carbon content before acid treatment.表 2 不同处理活性污泥和泥炭土有机质的生物标志物丰度(mg·g−1土壤)
Table 2. Relative abundance of molecule biomarkers in organic matter of the treated biosolids and peat (mg·g−1 soil)
n-alkanes n-alkanoic acids n-alkanols Carbohydrates FL V S C VSC HW 0.04 2.06 0.16 0.05 2.26 0.20 0.19 0.18 0.58 HA 0.03 1.21 0.07 0.95 1.31 0.02 0.02 0.01 0.06 PW 0.12 1.26 1.15 0.03 2.53 0.64 0.54 0.55 1.72 PA 0.13 2.01 0.98 3.98 3.12 0.28 0.27 0.34 0.88 注:FL,游离态脂;V,愈创木基;S,紫丁香基;C,对羟基肉桂基;VSC,愈创木基+紫丁香基+对羟基肉桂基的总和.
Note: FL, free lipids; V, vanilly units; S, syringyl units; C, cinnamyl units; VSC, the sum of vanilly units + syringyl units + cinnamyl units.表 3 生物标志物的降解参数
Table 3. The degradation parameters of molecular biomarkers
CPIAF CPIALK RLS ACL S/V C/V P/(V+S) 3,5-DHBA/V HW — 0.68 0.04 16.18 0.93 0.90 0.79 0.36 HA 12.09 1.76 0.11 17.08 1.00 0.43 3.11 0.51 PW 17.76 3.55 7.10 25.30 0.85 0.86 0.53 0.16 PA 19.42 5.16 11.30 25.85 0.95 1.21 0.62 0.34 注:CPIAF,脂肪酸的碳优势指数;CPIALK,烷烃的碳优势指数;RLS,长链烷酸(>C20)含量与短链烷酸含量的比值;ACL,烷酸的平均碳链长度;S/V,紫丁香基/愈创木基;C/V,对羟基肉桂基/愈创木基;P/(V+S) ,对羟基苯酚/(愈创木基+紫丁香基);3,5-DHBA/V,3,5-二羟基苯甲酸/愈创木基;HW的CPIAF没有数值是因为HW中长链烷酸含量低于检出限.
Note: CPIAF, carbon preference index of n-alkanoic acids; CPIALK, carbon preference index of n-alkanes; RLS, ratio of long chain carbon alkanoic acids (C>20) to short chain carbon alkanoic acids; ACL, averaged carbon length of alkanoic acids; S/V, ratio of syringyl to vanillyl; C/V, ratio of cinnamyl to vanillyl; P/(V+S), ratio of p-hydroxyphenols (P) to (vanilly + syringyl); 3,5-DHBA/V, ratio of 3,5-Dihydroxybenzoic acid to vanilly; CPIAF of HW has no value because the content of long chain carbon alkanoic acids in HW is below the detection limit.表 4 两种污染物吸附实验的Freundlich参数
Table 4. Freundlich parameters of two contaminants adsorption experiments
土壤
Soiln SE lgKF R2adj Kd/(L·kg−1) Koc/(L·kg−1 C) Ce=0.01Cs Ce=0.04Cs Ce=0.01Cs Ce=0.04Cs PHE HW 1.117 0.08 3.63 0.982 2576 3028 17878 21015 HA 1.036 0.05 3.85 0.993 6100 6408 28747 30198 PW 0.936 0.07 4.45 0.985 37320 34161 87283 79895 PA 0.936 0.08 4.61 0.982 53526 49009 112810 103290 BPA HW 0.942 0.01 1.94 0.999 80 74 556 513 HA 0.960 0.04 2.10 0.988 119 112 560 530 PW 0.793 0.01 2.77 0.998 447 335 1045 784 PA 0.828 0.01 2.74 0.999 435 343 916 722 -
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