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近年来,纳米材料在化妆品、电子、医疗保健、食品和环境修复等领域得到了广泛的应用[1-2],氧化锌纳米颗粒(ZnO-NPs)是备受关注的金属纳米氧化物之一[3-4],其中污水排放是纳米材料释放的主要途径[5]。另一方面,抗生素作为一种新型污染物在医院和家庭等环境中大量的使用,不可避免的被释放到水体环境中,尤其是在污水处理厂的污泥中进行富集[6-7]。而四环素(TC)是用于畜牧业生产和人类治疗中使用量最大的一类抗生素[8-9],但其50%~80%未经代谢和吸收就通过粪便和尿液排出[10],大量残留的TC对人体健康和微生物带来了严重威胁[11]。
胞外聚合物(EPS)是指直接覆盖在微生物表面或填充在微生物聚集体之间的高分子聚合物[12],EPS能形成保护层和营养吸收层抵抗有害的外界环境,还能在有机物较低时为微生物提供重要的碳源和能源[13-14]。其中,蛋白质和多糖约占EPS总量的70%~80%,是其主要成分[13, 15-16]。已有研究[17]表明,有毒物质在废水中的存在会导致微生物分泌EPS的成分和含量的不同,以此来抵御有毒物质的侵害。在活性污泥污水处理过程中,ZnO-NPs和TC作为痕量污染物可能影响EPS的成分和含量,从而进一步影响活性污泥性能。李维等[18]发现投加的ZnO-NPs其大部分会团聚在活性污泥表面上,致使EPS的产量和性质发生改变,低浓度ZnO-NPs对活性污泥EPS产量影响不大,高浓度(50 mg·L-1) ZnO-NPs使EPS中的蛋白质和多糖含量总体呈先上升后下降的趋势,并且会导致细胞发生凹陷。李娟英等[19]发现受抗生素类污染物影响的活性污泥EPS中蛋白质和多糖含量增加,且蛋白质的增加会导致污泥疏水性增强,导致絮凝性能恶化和SVI值下降。宋超[20]发现EPS中的蛋白质是与TC作用的主要成分,且蛋白质含量约是多糖的2倍,并用光谱学和能谱学发现TC中的羟基官能团发生变化最为明显,其可能会影响四环素的活性。
目前,在ZnO-NPs或TC对活性污泥EPS的研究中,主要集中于关于ZnO-NPs或TC对污泥EPS的单一影响的研究,关于二者共存的系统对EPS的影响研究鲜有报道。因此,本研究考察了二者通过浓度梯度递增的方式对EPS中蛋白质和多糖含量的影响,以此为ZnO-NPs和TC共存下对活性污泥EPS的影响机制提供理论依据。
SBR中纳米氧化锌和四环素复合投加系统对污泥胞外聚合物的影响
Effect of combined addition of ZnO nanoparticles and tetracycline on extracellular polymeric substances of sludge in SBR system
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摘要: 为研究氧化锌纳米颗粒(ZnO-NPs)和四环素(TC)对SBR系统内活性污泥胞外聚合物(EPS)特性的响应变化,在模拟室外光照条件下,考察了递增浓度ZnO-NPs和TC单独或复合投加方式下对EPS中蛋白质和多糖的影响。结果表明:ZnO-NPs、TC和复合投加系统中EPS的蛋白质含量均明显高于多糖,在各系统中,低浓度的投加量对蛋白质和多糖的含量改变无明显影响;随着浓度的递增和反应周期的延长,相比于空白组,ZnO-NPs系统中的蛋白质和多糖含量分别下降了33.58%和64.75%;TC和复合投加系统中蛋白质含量分别升高了57.86%、68.58%,多糖含量分别下降了43.60%和40.38%,且2个系统蛋白质和多糖含量变化趋势相似,因此,判断复合投加系统可能受TC影响较大。FT-IR分析显示,ZnO-NPs、TC和复合投加系统主要对EPS中蛋白质和多糖中的—OH、—NH2、C=O、C—OH及C—O产生影响。3D-EEM分析表明,EPS中蛋白质基团受到主要影响。该研究可为纳米颗粒和抗生素共存情况下对污泥EPS的影响提供依据。Abstract: In this study, the effects of zinc oxide nanoparticles (ZnO-NPs) and tetracycline (TC) on the property variation of extracellular polymer substance (EPS) in activated sludge of SBR system were determined. Under the simulated outdoor illumination conditions, the effects of gradually increasing concentrations of ZnO-NPs or TC alone and their combined system on protein and polysaccharide in EPS were investigated. Results showed that the protein content of EPS in ZnO-NPs, TC or their combined system were significantly higher than the polysaccharide content, while low doses of these additives had no significant effect on the variations of protein and polysaccharide contents. With the increase of additives contents and the extension of the reaction cycle, compared with the control system, the protein and polysaccharide contents in the ZnO-NPs system decreased by 33.58% and 64.75%, respectively. In the TC or combined system, the protein content increased by 57.86% and 68.58%, while the polysaccharide content decreased by 43.60% and 40.38%, respectively. The similar change trends of protein and polysaccharide content in TC and combined systems could imply that the combined system may be more susceptible to TC. FT-IR analysis showed that ZnO-NPs, TC and combined system mainly affected the —OH、—NH2、C=O、C—OH and C—O in the proteins and polysaccharides of EPS, and 3D-EEM indicated that the three systems mainly affected the protein function groups of EPS. This study can provide research basis for the effect of nanoparticles and antibiotics coexistence on sludge EPS.
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Key words:
- ZnO nanoparticles /
- tetracycline /
- extracellular polymeric substance /
- SBR /
- combined addition
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表 1 各反应器ZnO-NPs和TC投加方式
Table 1. ZnO-NPs and TC addition ways in each reactor
mg·L-1 空白组浓度 ZnO-NPs系统浓度 TC系统浓度 复合投加系统浓度(ZnO-NPs+TC) 0 0.1 5 0.1+5 0 5 15 5+15 0 15 25 15+25 0 25 50 25+50 -
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