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污泥是污水生物处理过程中产生的副产物,富集了污水中大量的有机物、氮磷营养盐以及重金属等污染物;厌氧消化是实现污泥稳定化、无害化的主要技术之一,也是实现污泥中有机质降解转化产甲烷进而能源回收利用的主要途径[1-3]。水解阶段是限制污泥厌氧消化产甲烷效率的限速步骤[2-3],因此,污泥预处理是强化污泥厌氧消化产甲烷的主要技术措施。例如,180 ℃下高温热水解76 min可使污泥产甲烷量提升1.6倍[3]。然而,长时间的 (30 min) 高温热水解 (150~170 ℃,0.6~0.8 MPa) 预处理释放的溶解性有机物 (dissolved organic matter,DOM) 含有大量难降解组分。一方面,致使消化污泥脱水滤液的处理难度大[4];另一方面,一些如腐殖酸[5]等难降解有机物,对厌氧消化微生物代谢活性产生抑制影响。
不同于热水解、碱、超声波等常规的预处理技术,蒸汽爆破预处理技术避免了热水解预处理的长时间高温高压作用,从而可能降低难降解有机物的生成。已有研究表明[6-7],污泥经过蒸汽爆破预处理后,厌氧消化产甲烷性能得到大幅提升。其主要原因在于,预处理后污泥细胞结构被破坏,释放大量溶解性有机物,如蛋白质、多糖、核酸 (DNA) 、脂肪等;同时,可能导致了释放的DOM组分可生物降解性发生改变,但蒸汽爆破预处理对污泥DOM分子组成特征的影响及其与厌氧消化产甲烷的关系,目前尚不清楚。以紫外可见光分光光谱、荧光光谱、红外光谱等的光谱分析方法只能宏观表征DOM组成特征[8],难以从分子水平上揭示DOM组成特征及其与厌氧消化的关系。傅里叶变换离子回旋共振质谱 (Fourier Transform Ion Cyclotron Resonance Mass Spectrometry,FT-ICR MS) 具有超高的分辨率 (>200 000) 、质量精确度 (误差<0.000 001) 和灵敏度,可以使DOM中复杂的有机物分子质谱峰的完全分离,从而在分子水平上解析DOM组成特征[8-9]。近年来,FT-ICR MS除了被广泛应用于分析水环境中天然有机物的分子组成特征,也在污泥堆肥[10]、污泥水热处理产生滤液的厌氧消化[9]等的DOM分子组成以及可生物降解有机物特征识别等方面得到应用。
本研究在三维荧光光谱 (3D-EEM) 分析的基础上,拟利用FT-ICR MS深入分析污泥经蒸汽爆破预处理和厌氧消化过程中DOM的分子组成,识别难降解或可降解有机物分子特征,揭示其与厌氧消化产甲烷关系,以期为污泥预处理过程中可生物降解和难降解有机物的生成和控制提供参考。
基于FT-ICR MS的蒸汽爆破预处理强化污泥厌氧消化的有机物分子解析
Molecular analysis of organic compounds in anaerobic digestion of sludge enhanced by steam explosion pretreatment based on FT-ICR MS
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摘要: 污泥预处理后有机物的释放和组成变化会直接影响厌氧消化产甲烷效率,傅里叶变换离子回旋共振质谱 (FT-ICR MS) 可以深入解析溶解性有机物 (DOM) 分子组成的变化。通过蒸汽爆破技术对污泥进行预处理,考察不同预处理条件对污泥溶解性有机物分子组成及厌氧消化的影响。研究结果表明,蒸汽爆破预处理明显提升了污泥中溶解性有机物的浓度 (最高可提升2.69倍) ,而高压短时间的预处理更为明显地提升了污泥累积甲烷产量。基于三维荧光光谱 (3D-EEM) ,预处理后污泥不同DOM组分的荧光区域积分标准体积占比发生变化,但不同实验组在厌氧消化过程中荧光区域积分标准体积占比差异并不明显。基于FT-ICR MS的分子水平分析发现,蒸汽爆破预处理后污泥DOM中可生物降解的脂肪族/蛋白质类和脂质类有机物相对占比 (质谱峰相对强度) 分别增加了3.30%和9.29%,难降解的木质素/CRAM类有机物占比下降了10.53%,DOM分子的双键当量 (DBEw) 、氧含量 (O/Cw) 和芳香度 (AImodw) 降低。此外,预处理增多了低O/C (0.1~0.4) 的可生物降解组分以及与微生物代谢活性有关的含硫DOM分子数量,这可能是厌氧消化产甲烷提升的原因之一。本研究结果可为识别污泥预处理过程中可生物降解和难降解有机物组分及其分子特征提供参考。Abstract: The release and composition change of organic matter after sludge pretreatment will directly affect the efficiency of anaerobic digestion and methanogenesis. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) can deeply analyze the change of molecular composition of dissolved organic matter (DOM). The sludge was pretreated by steam explosion technology, and the effects of different pretreatment conditions on the molecular composition of dissolved organic matter and anaerobic digestion of sludge were investigated. The results showed that steam explosion pretreatment significantly increased the concentration of dissolved organic matter in sludge (2.69 times at most), while high-pressure short-time pretreatment significantly increased the cumulative methane production of sludge. Based on three-dimensional fluorescence spectroscopy (3D-EEM), the proportion of integrated standard volume of fluorescence region of different DOM components of pretreated sludge changed, but the proportion of integrated standard volume of fluorescence region in different experimental groups during anaerobic digestion was not significantly different. The molecular level analysis based on FT-ICR MS showed that the relative proportion of biodegradable Aliphatic/protein and Lipid organics (relative intensity of mass spectrum peak) in sludge DOM after steam explosion pretreatment increased by 3.30% and 9.29% respectively, the proportion of refractory Lignin/CRAM organics decreased by 10.53%, and the double bond equivalent (DBEw), oxygen content (O/Cw) and aromaticity (AImodw) of DOM molecules decreased. In addition, pretreatment increased the biodegradable components with low O/C (0.1~0.4) and the number of sulfur-containing DOM molecules related to microbial metabolic activity, which might be one of the reasons for the increase of methane production in anaerobic digestion. The results of this study can provide a reference for identifying the biodegradable and refractory organic components and their molecular characteristics in the sludge pretreatment process.
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Key words:
- steam explosion /
- sludge /
- anaerobic digestion /
- dissolved organic matter /
- FT-ICR MS
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表 1 接种污泥、脱水污泥基本特征
Table 1. Characteristics of inoculum sludge and dewatered sludge
污泥类型 SCOD/ (mg·L−1) 溶解性蛋白质/(mg·L−1) 溶解性多糖/(mg·L−1) 氨氮/(mg·L−1) 磷酸盐/(mg·L−1) TS/% VS/% 含水率/% 接种污泥 5 020 1 217.08 690.10 2 140 15.2 7.18 2.59 92.82 脱水污泥 7 140 1 644.12 797.12 423 16.8 17.21 10.22 82.79 表 2 不同实验组产甲烷的 Gomptz 模型方程拟合结果
Table 2. Gomptz model equation fitting results of methanogenesis in different experimental groups
处理组 P/ (mL·g−1) Rm/[mL·(d·g)−1] λ/d R2 对照组 200.85 0.81 0.501 0.995 0.6 MPa-8 min 220.87 0.84 0.933 0.998 0.6 MPa-10 min 233.56 0.93 0.739 0.997 0.8 MPa-3 min 236.01 0.95 0.584 0.998 0.8 MPa-5 min 237.86 0.91 0.605 0.998 表 3 基于 FT-ICR MS 的污泥 DOM 分子组成信息
Table 3. Molecular Composition of Sludge DOM Based on FT-ICR MS
类型 分子
总数量CHO
分子数量CHON
分子数量CHONS
分子数量CHOS
分子数量m/zw DBEw AImodw O/Cw H/Cw 对照组 (厌氧消化初始) 3 437 575 (16.73%) 1 732 (50.39%) 355 (10.33%) 755 (22.55%) 336.35 6.853 0.150 0.427 1.329 0.8 MPa-3min
(厌氧消化初始)3 263 528 (16.18%) 1 765 (54.09%) 280 (8.58%) 690 (21.15%) 331.22 6.338 0.139 0.350 1.415 对照组 (厌氧消化结束) 2 117 358 (16.18%) 1 199 (56.64%) 197 (9.31%) 363 (17.15%) 333.52 6.505 0.144 0.355 1.398 0.8 MPa-3min
(厌氧消化结束)3 543 666 (18.80%) 1 861 (52.53%) 358 (10.10%) 658 (18.57%) 336.41 6.799 0.164 0.387 1.357 可生物降解有机物
(对照组)1 891 346 (18.30%) 737 (38.97%) 555 (29.35%) 253 (13.38%) 250.47 5.489 0.217 0.467 1.287 可生物降解有机物
(0.8 MPa-3min)884 138 (15.61%) 342 (38.69%) 289 (32.69%) 115 (13.01%) 295.10 6.333 -0.015 0.363 1.363 难生物降解有机物
(对照组)1 546 229 (14.81%) 995 (64.36%) 220 (14.23%) 102 (6.60%) 254.34 5.291 0.240 0.438 1.349 难生物降解有机物
(0.8MPa-3min)2 379 390 (16.39%) 1423 (59.82%) 401 (16.86%) 165 (6.94%) 234.75 5.158 0.248 0.415 1.330 新生成的难降解微生物
代谢产物 (对照组)571 129 (22.59%) 204 (35.73%) 143 (25.04%) 95 (16.64%) 362.52 6.783 0.309 0.384 1.423 新生成的难降解微生物
代谢产物(0.8MPa-3min)1 164 276 (23.71%) 438 (37.63%) 257 (22.08%) 193 (16.58%) 293.57 6.011 0.349 0.442 1.323 注:括号内的百分比数值代表相对应的CHO、CHON、CHONS、CHOS分子式数量占分子总数量的占比;m/zw、DBEw、AImodw、O/Cw、H/Cw中的w代表加权平均。 -
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