紫外线强度及剂量对大肠杆菌光复活的影响

以水中大肠杆菌为研究对象,考察了不同紫外线强度及剂量对大肠杆菌的灭活效果以及对其光复活的影响.结果表明:大肠杆菌的灭活率随着紫外线剂量的增加而增加,而相同剂量下高强度的紫外线对大肠杆菌的灭活效果要好于低强度的,且高紫外线强度有利于控制大肠杆菌的光复活程度.当紫外线强度为0.153 mW/cm2、紫外线剂量为60 mJ/cm2时,其对大肠杆菌的灭活率高达5个对数级.高剂量紫外线照射下大肠杆菌发生光复活的能力明显弱于低剂量下的,紫外线剂量为120 mJ/cm2时的大肠杆菌光复活率较5 mJ/cm2时的低了3个对数级.     

紫外线剂量对大肠杆菌光复活的影响

为探究紫外线剂量对大肠杆菌光复活现象的影响,通过调节紫外线强度和紫外线辐射时间控制紫外线剂量的大小,研究了不同紫外线剂量条件下大肠杆菌光复活的程度。结果表明,较高紫外线剂量辐射下大肠杆菌的光复活程度显著低于较低紫外线剂量辐射下,紫外线剂量为92. 28 m J/cm2时的大肠杆菌光复活率比26. 88 m J/cm2时小2. 72个对数数量级。当紫外线辐射时间不变时,紫外线强度越强,大肠杆菌光复活率越小。同一强度下,紫外线辐射时间越长,大肠杆菌光复活率越小。经较高紫外线剂量辐射后的大肠杆菌,发生光复活现象的时间显著滞后于较低紫外线剂量。     

紫外线消毒应对小规模供水单元突发性微生物污染研究及工程实例

结合B市M单位自备井微生物污染事件及应对过程,以小规模供水单元突发性微生物污染为背景,将紫外线消毒作为应对手段,考察了紫外强度、紫外线穿透率对紫外线消毒效果的影响,并研究了大肠杆菌可见光复活.结果表明:较大剂量时,紫外强度对消毒效果的影响会减弱甚至不产生影响;在相同紫外强度条件下,紫外线穿透率对紫外线消毒效果的影响显著...     

紫外消毒出水的微生物光复活及其控制技术

污水厂出水经紫外线（UV）消毒后在排放过程中会出现微生物的复活现象，为此考察了采用UV-氯和UV-过氧乙酸（PAA）控制光复活的效果。经研究发现：在UV照射剂量为5．4mJ／cm^2、投氯量为2．5mg／L、反应时间为10min和UV照射剂量为5．4mJ／cm^2、过氧乙酸投量为10mg／L、反应时间为10min的条件下，对大肠菌群的灭活率均可达4个对数级以上，并能控制光复活现象。从消毒稳定性、经济适用性、安全毒副性等方面考虑，可采用UV—PAA作为污水厂出水消毒及抑制光复活的技术。     

浊度对紫外灭活大肠杆菌和MS-2噬茵体的影响

以大肠杆菌和MS-2噬菌体为细菌和病毒的替代指标，考察了浊度及颗粒物分布对紫外线灭活大肠杆菌和MS-2噬菌体的影响。结果表明，紫外线对大肠杆菌的灭活率高于对MS-2噬菌体的灭活率，当紫外线剂量为10mJ／cm^2时，对大肠杆菌的灭活率为4．66个对数级，而对MS-2的灭活率仅为0．45个对数级；浊度对紫外线灭活大肠杆菌的效果有一定的影响，当浊度〈4NTU时对灭活效果的影响较小，而当浊度〉4NTU时，会对灭活效果产生明显的影响；颗粒物对紫外线灭活大肠杆菌的影响与其粒径有关，粒径〉5μm的颗粒物对消毒效果的影响较为明显，而粒径〈5μm的颗粒对紫外线消毒效果的影响较小。综合不同粒径颗粒物对消毒效果的影响可以认为，就试验水样而言，浊度对紫外线消毒效果的影响主要是由粒径〉5μm的颗粒造成的；而浊度及颗粒物的粒径分布对紫外线灭活MS-2噬菌体的效果没有显著影响。     

MBR出水的紫外线消毒试验研究

考察了紫外线（UV）对MBR出水中微生物的灭活情况，以及光活化和暗修复对细菌灭活效果的影响。结果表明：UV对MBR出水中的微生物具有良好的灭活效果，当UV剂量为16mJ／cm^2时，对细菌的对数灭活率为3-lg；在相同的UV剂量下，不同UV强度对细菌的灭活效果无显著影响；经UV消毒后的细菌在3h内未出现明显的暗修复现象，但在日光灯和太阳光辐射下可发生明显的光活化现象，且不同光源下的光活化速率和达到饱和的时间有所不同。     

紫外线和氯组合方式对大肠杆菌灭活效果的影响研究

系统地比较了紫外线和氯不同的组合方式对大肠杆菌的灭活效果.结果表明,紫外线和氯联合顺序消毒在一定程度上提高了消毒效果,但不同的组合方式以及两者不同的剂量对灭活效果都有影响.紫外线和氯先后作用的消毒效果优于紫外线和氯同时消毒.先氯后紫外线消毒时,加较高浓度的氯且短时间接触即可达到较好的消毒效果;先紫外线后氯消毒时,氯剂量越大则灭活率越高,若氯浓度相同而接触时间不同,则灭活效果差别不大.     

污水厂二级出水中抗生素抗性菌残留及其特性

抗生素滥用引起抗性菌扩散已成为严重的公共卫生安全隐患。以某污水厂二级出水为研究对象,检测青霉素、氨苄青霉素、头孢氨苄、氯霉素、四环素、环丙沙星、庆大霉素、阿奇霉素和利福平等9种抗生素在不同浓度下的抗性菌数量和比例,分析不同剂量紫外线对抗性菌的灭活效果及其复活能力。结果表明,青霉素、氨苄青霉素、头孢氨苄、氯霉素抗性菌的耐受性较强,复活能力较弱;四环素和庆大霉素抗性菌次之;环丙沙星、阿奇霉素和利福平抗性菌的抗性较弱,复活能力较强。随着抗生素浓度的增加,抗性菌数量减少,紫外线消毒剂量与抗性菌复活能力呈负相关。经紫外线常规消毒剂量灭活后储存过程中抗性菌出现复活现象。     

紫外线对自来水中微生物的灭活作用

选取大肠杆菌和枯草芽孢杆菌分别代表自来水中易被灭活和不易被灭活的微生物,研究了紫外线的灭菌效果。结果表明:紫外消毒对大肠杆菌具有良好的灭活作用,当紫外剂量为10 mJ/cm2时,可以达到4.66个对数级的灭活效果;在相同的紫外剂量下,紫外强度对灭活效果也有一定的影响,在紫外强度较高时会取得较好的灭活效果;原水浊度对紫外灭活大肠杆菌有一定的影响,当浊度>4 NTU时会明显降低紫外线的灭菌效果,浊度物质的存在降低了水的透光率,从而使灭活效果降低。氯对枯草芽孢杆菌的灭活效果很差,在CT值为300(mg/L).m in时的灭活率也仅为0.53个对数级,紫外线对枯草芽孢杆菌灭活效果要明显高于氯,紫外剂量为40 mJ/cm2时对枯草芽孢杆菌的灭活率可达3.3个对数级。     

超声预处理强化紫外线消毒效果的研究

采用超声预处理强化紫外线消毒效果,并从分子生物学的角度探讨了其强化机理.结果表明,无论是单独紫外辐照还是超声预处理/紫外辐照,紫外辐照剂量与大肠杆菌灭活率之间均具有良好的线性关系;进行超声灭活时,超声功率、作用时间及菌悬液体积对灭活率均无显著意义(P>0.05),按影响大小排序为:菌悬液体积>超声功率>作用时间;当单独超声处理200 mL大肠杆菌悬液时,超声功率为200 W、作用时间为20 S条件下的灭活率最高(0.22-1g),该条件下继续进行紫外辐照,灭活率最高达到2.75-1g,1 h光复活后灭活率仍高达1.72-1g,超声/紫外协同作用的灭活率大于二者单独作用的灭活率之和,表明该条件下超声预处理起到了强化紫外线消毒的作用;超声处理只能改变细胞的结构,不能破坏其DNA;酶敏感位点数量与大肠杆菌的灭活率具有较强的相关性,相关系数约为0.88.     

纯培养条件下细菌需氯量和存活性的试验研究

以埃希氏大肠杆菌和粪肠球菌作为研究对象,在纯培养条件下考察了自由氯、氯胺和二氧化氯的投加量以及细菌初始浓度对需氯量的影响.结果表明:灭活率达到99.9％时,两种细菌的需氯量均随初始菌浓度和消毒剂投加量的提高而增大,粪肠球菌的需氯量大于埃希氏大肠杆菌;投加自由氯时两种细菌的需氯量差别最大,其次是二氧化氯,氯胺的差别最小.     

Ultraviolet and ionizing radiation for microorganism inactivation

The impacts of UV irradiation, gamma irradiation, and a combination of both on Escherichia coli inactivation in primary and secondary wastewater effluents were investigated. UV doses of 35 and 62 J/m(2) were required for a 1-log inactivation of E. coli in the primary and secondary wastewater samples, respectively. A gamma dose of 170 Gy (J/kg) was required for a 1-log inactivation of E. coli in both wastewater samples. Variation in gamma radiation dose rates did not have a significant impact on the extent of inactivation at a given total dose. Gamma irradiation of previously UV-irradiated samples indicated that particle-associated microorganisms, which are protected from UV, can be inactivated by ionizing radiation at a rate similar to that for free microorganism inactivation. An estimation of the energy required for disinfection indicated that, in general, the required energy and the energy cost for E. coli inactivation using ionizing radiation are considerably higher than those for UV radiation.     

Pulsed ultra-violet inactivation spectrum of Escherichia coli

Inactivation of Escherichia coli is examined using ultra-violet (UV) radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV content. The flashlamp provides high-energy UV output using a small number of short-duration pulses (30 micros). The flashlamp is used with a monochromator to investigate the wavelength sensitivity of E. coli to inactivation by the pulsed UV light. Using 8 nm wide pulses of UV radiation, the most efficient inactivation is found to occur at around 270 nm and no inactivation is observed above 300 nm. A pyroelectric detector allows the energy dose to be determined at each wavelength, and a peak value for E. coli population reduction of 0.43 log per mJ/cm(2) is measured at 270 nm. The results are compared with the published data available for continuous UV light sources.     

Enhanced inactivation of E. coli and MS-2 phage by silver ions combined with UV-A and visible light irradiation

Silver ions have been widely used as an effective water disinfectant or antimicrobial material for many decades. In addition, the application of silver ions in combination with other biocides, especially UV(254) (UV-C) irradiation, was reported to be effective in enhancing its germicidal activity. However, it is not yet known how UV-A (300-400 nm) or visible light irradiation, which have little or no antimicrobial activities, affect microorganism inactivation by silver ions. This study newly reports that the inactivation efficiencies of Escherichia coli and MS-2 phage by silver ions were significantly enhanced by UV-A or visible light irradiation. UV-A irradiation enhanced the inactivation of E. coli and MS-2 phage by 3.0 and 2.5 log/30 min, respectively, as compared with the simple summated value of individual applications of silver ions and UV-A. A similar trend was observed with visible light irradiation (>400 nm) although the level of enhancement was lessened. The photochemical reaction of silver-cysteine complex was suggested as a possible mechanism for this enhancement. Spectrophotometric and MALDI-TOF mass analyses support the fact that silver ions coupled with light irradiation causes critical cell damage through the complexation of silver ions with thiol (-SH) groups in structural or enzymatic proteins of the microorganisms and their subsequent photochemical destruction.     

Photoreactivation of Legionella pneumophila after inactivation by low- or medium-pressure ultraviolet lamp

Photoreactivation of Legionella pneumophila after the inactivation by low-pressure (LP) or medium-pressure (MP) UV lamp was investigated in comparison with that of Escherichia coli. An endonuclease sensitive site (ESS) assay was used to determine the number of UV-induced pyrimidine dimers in the genome DNA of L. pneumophila or E. coli, while the survival ratio of each bacterium was also investigated by cultivation methods. L. pneumophila performed photoreactivation with almost complete repair of pyrimidine dimers associated with the quick recovery of survival ratio. A 3 log inactivation of L. pneumophila by LP or MP UV lamp was, respectively, resulted in 0.5 log or 0.4 log inactivation when photoreactivation was completed. Interestingly, L. pneumophila performed equivalent photoreactivation after LP and MP UV lamp exposures while photoreactivation of E. coli was significantly repressed after the inactivation by MP UV lamp. This study indicated that an attention would be required to design and operate a UV disinfection system targeting L. pneumophila. It was further implied that E. coli would not correctly indicate the fate of L. pneumophila in UV disinfection systems when photoreactivation takes place.     

Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions

Escherichia coli and thermotolerant coliforms are of major importance as indicators of fecal contamination of water. Due to its negative surface charge and relatively low die-off or inactivation rate coefficient, E. coli is able to travel long distances underground and is therefore also a useful indicator of fecal contamination of groundwater. In this review, the major processes known to determine the underground transport of E. coli (attachment, straining and inactivation) are evaluated. The single collector contact efficiency (SCCE), eta0, one of two parameters commonly used to assess the importance of attachment, can be quantified for E. coli using classical colloid filtration theory. The sticking efficiency, alpha, the second parameter frequently used in determining attachment, varies widely (from 0.003 to almost 1) and mainly depends on charge differences between the surface of the collector and E. coli. Straining can be quantified from geometrical considerations; it is proposed to employ a so-called straining correction parameter, alpha(str). Sticking efficiencies determined from field experiments were lower than those determined under laboratory conditions. We hypothesize that this is due to preferential flow mechanisms, E. coli population heterogeneity, and/or the presence of organic and inorganic compounds in wastewater possibly affecting bacterial attachment characteristics. Of equal importance is the inactivation or die-off of E. coli that is affected by factors like type of bacterial strain, temperature, predation, antagonism, light, soil type, pH, toxic substances, and dissolved oxygen. Modeling transport of E. coli can be separated into three steps: (1) attachment rate coefficients and straining rate coefficients can be calculated from Darcy flow velocity fields or pore water flow velocity fields, calculated SCCE fields, realistic sticking efficiency values and straining correction parameters, (2) together with the inactivation rate coefficient, total rate coefficient fields can be generated, and (3) used as input for modeling the transport of E. coli in existing contaminant transport codes. Areas of future research are manifold and include the effects of typical wastewater characteristics, including high concentrations of organic compounds, on the transport of E. coli and thermotolerant coliforms, and the upscaling of experiments to represent typical field conditions, possibly including preferential flow mechanisms and the aspect of population heterogeneity of E. coli.     

Kinetics of UV inactivation of wastewater bioflocs

Ultraviolet disinfection is a physical method of disinfecting secondary treated wastewaters. Bioflocs formed during secondary treatment harbor and protect microbes from exposure to ultraviolet (UV) light, and significantly decrease the efficiency of disinfection at high UV doses causing the tailing phenomena. However, the exact mechanism of tailing and the role of biofloc properties and treatment conditions are not widely understood. It is hypothesized that sludge bioflocs are composed of an easily disinfectable loose outer shell, and a physically stronger compact core inside that accounts for the tailing phenomena. Hydrodynamic shear stress was applied to the bioflocs to peel off the looser outer shell to isolate the cores. Biofloc and core samples were fractionated into narrow size distributions by sieving and their UV disinfection kinetics were determined and compared. The results showed that for bioflocs, the tailing level elevates as the biofloc size increases, showing greater resistance to disinfection. However, for the cores larger than 45 μm, it was found that the UV inactivation curves overlap, and show very close to identical inactivation kinetics. Comparing bioflocs and cores of similar size fraction, it was found that in all cases cores were harder to disinfect with UV light, and showed a higher tailing level. This study suggests that physical structure of bioflocs plays a significant role in the UV inactivation kinetics.