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以气溶胶形式存在于空气中的致病微生物极易引起传染病扩散和传播。如近两年新型冠状病毒肺炎 (COVID-19) 疫情的暴发与流行对人类健康产生了严重威胁。经研究发现,气溶胶传播或是COVID-19的主要传播途径之一[1-2]。因此,微生物气溶胶污染与控制已成为研究热点。微生物气溶胶是由微生物依附于气溶胶粒子形成,可通过不同机制对人体健康产生不利影响,如引发呼吸系统疾病、引起传染病传播、增加患癌风险等[3]。而传统的微生物气溶胶净化方法存在一定局限性,如化学消毒剂法易产生残留和二次污染[4];过滤吸附法无法实现微生物灭活,被截留的微生物可以长期存活和繁殖,有一定安全隐患[5]。低温等离子体因其灭活效率高且可实现动态消毒,发展成为新兴的广谱杀菌方法。
低温等离子体是电子、离子、自由基等粒子组成的混合体。与热等离子体不同,低温等离子体中能量主要用来加热电子,整个体系温度较低,故其使用范围更广[6]。低温等离子体的产生方式有电晕放电、辉光放电、介质阻挡放电等。电晕放电是在曲率半径很小的电极上施加直流、交流或脉冲高压产生局部放电[7],放电区域小,仅在放电极周围,是一种低电流密度的非均匀放电[8]。辉光放电与电晕放电放电过程类似,但放电强度有所不同。辉光放电充满整个放电空间,是一种低气压下稳定的自持放电[9]。介质阻挡放电将绝缘介质置于放电空间内,放电形式为微放电。相比之下,介质阻挡放电放电更均匀,可在常压下进行。因此,本研究拟选用介质阻挡放电产生低温等离子体。
低温等离子体中起杀菌作用的有紫外线、带电粒子及活性物种[10-11]。波长260 nm左右的紫外线通过损伤细菌DNA抑制细菌的繁殖能力[11]。积累在细胞膜表面的带电粒子导致细胞膜内外产生跨膜电势,通过电穿孔作用导致细胞死亡。而活性物种由于具有强氧化性被认为是起主导作用的杀菌成分[12-13]。王英等[14]发现,经低温等离子体处理后,苹果汁中的耐高渗酵母菌数量可减少6.82 log,灭活效果显著。LIN等[15]通过低温等离子体实现了鸡蛋壳上沙门氏菌有效灭活,同时鸡蛋的营养品质和感官特性不受影响。低温等离子体还可快速且有效地灭活物体表面存留的SARS-CoV-2[16]。
然而,有关低温等离子体灭活微生物气溶胶的研究较少。微生物气溶胶与物体表面微生物的灭活差异很大。灭菌对象为物体表面时,反应装置多为低温等离子体射流,放电区与射流形成区在空间上有所分离[17]。通过低温等离子体喷射将活性物种等有效杀菌成分直接作用于物体表面,不受限于物体形状。灭菌对象为微生物气溶胶时的反应装置多为传统间隙式。微生物气溶胶与放电生成的低温等离子体在同一空间内混合接触,低温等离子体中的活性物质、带电粒子、紫外线等充分作用于微生物气溶胶导致其失去活性。因此,有必要对低温等离子体灭活微生物气溶胶的灭活效果及影响因素进行研究。
本研究在搭建低温等离子体灭活微生物气溶胶实验台的基础上,选取安全且典型的实验微生物,研究了不同工作电压、流速和相对湿度对微生物气溶胶灭活效果的影响。采用电压电流波形图、李萨如图、发射光谱图和电子顺磁共振表征并分析低温等离子体的放电特性和成分特征,通过对比低温等离子体放电前后微生物气溶胶的可培养性、细胞膜完整性、蛋白质质量浓度及总有机碳水平的差异评估系统的灭活效果,再以杀菌率为评价指标,得到不同影响因素的对灭活效果的影响规律,以期为低温等离子体灭活微生物气溶胶的应用提供参考。
低温等离子体灭活微生物气溶胶的效果及影响因素
Inactivation effect of non-thermal plasma on bioaerosol and its influencing factors
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摘要: 微生物气溶胶相关的突发性疫情时有发生,故研发新型高效的微生物气溶胶灭活技术已引起广泛关注。采用低温等离子体灭活枯草芽孢杆菌气溶胶,对低温等离子体电学特性和光学特性进行测定诊断,并测定活性氧。从细菌可培养性、细胞膜完整性、蛋白质泄露及细胞矿化4个方面分析评估灭活效果,并以杀菌率为指标,研究了外加电压、流速及相对湿度对灭活效果的影响。结果表明,低温等离子体可实现枯草芽孢杆菌气溶胶灭活,灭活效果显著。随着外加电压的增加,灭活效率呈上升趋势。在外加电压为10~13 kV时,对应灭活效率为48%~83%。灭活效率与流速成反比,随着流速的增加,灭活效率减小。流速为11~14 L·min−1时,灭活效率为80%~47%。在不同相对湿度条件下,灭活效率呈先上升后下降的趋势。在RH=40%时,灭活效率达到最大值,为86%。这表明低电压、高流速和高相对湿度不利于微生物气溶胶灭活。本研究结果可为低温等离子体灭活微生物气溶胶技术的应用提供参考。Abstract: Sudden outbreaks related to bioaerosols occur from time to time, so the development of new and efficient bioaerosols inactivation technology has attracted extensive attention.The purpose of this study was to inactivate the Bacillus subtilis aerosol using non-thermal plasma technology. The electrical and optical characteristics of the non-thermal plasma are measured and diagnosed, and reactive oxygen species are also measured.The inactivation effect is analyzed from the four aspects of bacterial cultivability, cell membrane integrity, protein leakage and cell mineralization.Using the sterilization rate as an indicator, the influence of the applied voltage, flow rate and relative humidity on the inactivation effect is studied. The results show that non-thermal plasma can inactivate the Bacillus subtilis aerosol significantly. The inactivation efficiency increases with the increase of applied voltage. When the applied voltage is 10~13 kV, the inactivation efficiency is 48%~83%. As the velocity of flow increases, the inactivation efficiency decreases. When the flow rate is 11~14 L·min−1, the inactivation efficiency is 80%~47%.Under different relative humidity conditions, the inactivation efficiency increased first and then decreased, and reached the maximum value of 86% when RH=40%.Therefore, it can be concluded that low voltage, high flow rate and high relative humidity are not conducive to bioaerosol inactivation.
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Key words:
- bioaerosol inactivation /
- non-thermal plasma /
- inactivation effect /
- influencing factors
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