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苯甲酸是常见的难降解工业废水组分之一,也是苯系物及木质纤维素类废弃物厌氧代谢过程中的重要中间产物。芳香族化合物需要经苯甲酸和苯甲酰辅酶A通过β氧化,形成乙酸、H2和CO2[1-3]。在厌氧产甲烷的过程中,苯甲酸降解为乙酸的反应是与产甲烷菌利用乙酸和氢气的互营产甲烷反应相结合而进行的。有学者发现,厌氧微生物互营降解苯甲酸与有机酸的产甲烷过程中存在种间直接电子传递(direct interspecies electron transfer,DIET)过程[4-5]。LOVELY等[6-7]最早发现了种间直接电子传递的机制,即厌氧沉积物中的微生物在进行有机质氧化的过程中会释放电子到胞外,以Fe(Ⅲ)为电子受体,并可产生超细粒磁铁矿。纳米Fe3O4(nanoparticles,Fe3O4 NPs)是一种性能稳定、无毒、导电性强、制备简单且生物相容性较好的磁性材料[8]。添加Fe3O4 NPs等可促进废水、废弃物产甲烷的过程[8-10]。目前,关于这类导电材料用于强化有机酸互营产甲烷菌群的DIET过程的研究较多。已确认能进行DIET的微生物主要有地杆菌(Geobacter)和希瓦氏菌(Shewanella)[10]。通常,Geobacter被认为是厌氧消化体系能发生DIET的标志微生物,但Geobacter的存在并不是发生DIET的必要条件。这是由于导电物质可富集某些具有胞外电子转移能力的微生物,实现厌氧消化体系主要电子转移方式的改变[11]。有研究表明,Desulfuromonas、Pseudomonas等电活性微生物可能也具有进行DIET的能力[12-13]。因此,需要进一步探究地杆菌以外微生物的DIET能力及作用机制,并优化导电材料强化厌氧消化产甲烷的工艺,以促进有机废水和废弃物的资源化处理。
研究苯甲酸的微生物降解过程,对于提高芳香族类污染物的降解效率有重要意义。关于铁氧化物对苯甲酸降解影响的研究表明,铁基材料可促进苯甲酸的降解。例如,ZHUANG等[14]以水稻土为接种物,发现纳米磁铁矿(1.93 g·L−1)和赤铁矿(2 g·L−1)使苯甲酸的降解率分别提高了53%和25%,促进了芽孢杆菌Bacillaceae与产甲烷菌Methanobacterium之间的直接电子传递。AROMOKEYE等[15]以海洋沉积物的富集培养物为实验对象,研究了磁铁矿和纤铁矿对苯甲酸降解的影响后发现:添加磁铁矿(6.96 g·L−1)或赤铁矿(4.8 g·L−1)可加速苯甲酸的降解和促进甲烷生成,使苯甲酸降解速率提高22.55%;而纤铁矿抑制了苯甲酸降解和甲烷生成,使苯甲酸降解速率降低45.10%~56.37%;添加磁铁矿的体系中苯甲酸厌氧降解菌Sporotomaculum作为主要微生物(占细菌的53%~62%),而添加纤铁矿的体系中主要微生物为脱硫肠状菌Desulfotomaculum(占细菌的20%~37%)。马金莲[16]以底泥沉积物为接种物,发现添加Fe3O4 NPs(1.55 g·L−1)和Fe2O3(1.6 g·L−1)可提升硫酸盐还原条件下的苯甲酸降解速率。YAN等[17]以中温苯酚与葡萄糖人工合成废水厌氧处理污泥为接种物,通过批次实验发现:纳米磁铁矿提高了苯酚的厌氧降解速度,增强了苯酚厌氧降解菌Syntrophorhabdus和苯甲酸厌氧降解菌Syntrophus的富集及互营代谢过程。
苯甲酸厌氧降解菌作为互营微生物,其生长十分缓慢,难以分离培养[18]。文献报道过的这类降解菌有8种,主要分布在厚壁菌门(Firmicutes)和变形菌门(Proteobacteria)[18-19]。Sporotomaculum syntrophicum(后简称S. syntrophicum)是厚壁菌门的一种可产生孢子的细菌,具有苯甲酸降解速度快、耐受性强的特性,当其与产甲烷菌共培养时可将苯甲酸转化为甲烷[20]。本研究以S. syntrophicum与产甲烷菌Methanospirillum hungatei(后简称M. hungatei)的共培养体系为研究对象,研究添加纳米Fe3O4和Fe2O3对苯甲酸厌氧降解过程的影响,以期为铁基纳米材料强化苯甲酸污染物的去除提供参考。
铁基纳米材料对苯甲酸降解菌Sporotomaculum syntrophicum与产甲烷菌Methanospirillum hungatei的厌氧互营体系降解苯甲酸的影响
Effect of iron -based nanomaterials on anaerobic benzoate degradation by syntrophic co-culture of Sporotomaculum syntrophicum and Methanospirillum hungatei
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摘要: 为探究铁基纳米材料在苯甲酸厌氧互营代谢过程中的作用,以厚壁菌门的厌氧互营苯甲酸降解菌Sporotomaculum syntrophicum与产甲烷菌Methanospirillum hungatei的共培养体系为研究对象,考察投加铁基纳米颗粒四氧化三铁(Fe3O4 NPs)和三氧化二铁(Fe2O3 NPs)对苯甲酸厌氧降解转化甲烷的影响。结果表明:10~500 mg·L−1的Fe3O4纳米颗粒对苯甲酸降解速率及产甲烷量没有显著影响;而高浓度的Fe3O4纳米颗粒对苯甲酸降解及产甲烷速率产生了明显的抑制作用,当添加Fe3O4纳米颗粒的质量浓度为600、800、1 000 mg·L−1时,第15天的产甲烷量分别减少了24.29%、44.13%和61.54%。低浓度和高浓度的Fe2O3纳米颗粒对苯甲酸的降解及甲烷的产生均无影响。质量浓度为10~1 000 mg·L−1 的Fe3O4 NPs和Fe2O3 NPs均不能促进S. syntrophicum与M. hungatei共培养体系的种间电子传递过程。本研究结果可为导电材料强化厌氧纯菌降解苯甲酸,以及利用导电材料强化苯甲酸废水及木质纤维素类固体废弃物的处理提供参考。Abstract: To unveil the role of iron-based nanomaterials in syntrophic anaerobic degradation of benzoate, ferric oxide nanoparticles Fe3O4 NPs and Fe2O3 NPs were added to the syntrophic co-culture of Sporotomaculum syntrophicum (belonging to Firmicutes) and Methanospirillum hungatei and their effects were investigated. The results showed that adding Fe3O4 NPs at low concentration (10~500 mg·L-1) did not significantly impact the benzoate degradation rate and methane production. However, high dosage of Fe3O4 NPs revealed serious inhibition. At Fe3O4 NPs dosages of 600, 800 and 1 000 mg·L-1, the methane production was reduced by 24.29%, 44.13% and 61.54%, respectively on day 15. Neither low nor high dosages of Fe2O3 NPs (10~1 000 mg·L-1) influenced benzoate degradation and methane production or was able to promote the interspecies electron transfer in S. syntrophicum and M. hungatei co-culture. This study can provide a reference for enhancing anaerobic degradation of benzoate with pure culture, as well as for treating benzoate wastewater and lignocellulosic solid wastes with conductive materials.
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表 1 导电材料对苯酚和苯甲酸厌氧降解的影响
Table 1. Effect of conductive materials on anaerobic phenol and benzoate degradation
反应体系 芳香族
化合物
的种类芳香族化合
物的浓度/
(mmol·L−1)互营厌氧菌 产甲烷菌 导电材料
种类导电材料的
质量浓度/
(g·L−1)对底物降解率的影响 苯酚废水厌氧
处理污泥[17]苯酚 10.64 Syntrophorhabdus,
SyntrophusMethanosaeta 纳米磁铁矿 5.44 提高100% 水稻土[14] 苯甲酸 8.6 Bacillaceae, Peptococcaceae Methanobacterium 赤铁矿 2 提高25% 纳米磁铁矿 1.93 提高53% 苯甲酸驯化
体系[15]苯甲酸 5 Sporotomaculum Methanobacterium 磁铁矿 6.96 提高约22.55% Desulfotomaculum Methanosarcina, Methanoculleus, Methanosaeta 纤铁矿 4.8 降低45.10%~56.37% 互营共培养体系 苯甲酸 5 S. syntrophicum Methanosarcina, Methanoculleus, Methanosaeta Fe3O4 NPs 0.01~1 0.01~0.5 g·L−1无影响;1 g·L−1,抑制61% Fe2O3 NPs 0.01~1 无影响 注:互营共培养体系指的本研究的结果。 -
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