Inactivation of Escherichia coli by Photochemical Reaction of Ferrioxalate at Slightly Acidic and Near-Neutral pHs

Fenton chemistry, which is known to play an effective role in degrading toxic chemicals, is difficult to apply to disinfection in water treatment, since its reaction is effective only at the acidic pH of 3. The presence of oxalate ions and UV-visible light, which is known as a photoferrioxalate system, allows the Fe(III) to be dissolved at slightly acidic and near-neutral pHs and maintains the catalytic reaction of iron. This study indicates that the main oxidizing species in the photoferrioxalate system responsible for microorganism inactivation is OH radical. Escherichia coli was used as an indicator microorganism. The CT value (OH radical concentration × contact time; used to indicate the effect of the combination of the concentration of the disinfectant and the contact time on inactivation) for a 2-log inactivation of E. coli was approximately 1.5 × 10⁻⁵ mg/liter/min, which is approximately 2,700 times lower than that of ozone as estimated by the delayed Chick-Watson model. Since the light emitted by the black light blue lamp is similar to sunlight in the specific wavelength range of 300 to 420 nm, the photoferrioxalate system, which can have a dual function, treating water for both organic pollutants and microorganisms simultaneously, shows promise for the treatment of water or wastewater in remote or rural sites. However, the photoferrioxalate disinfection system is slower in inactivating microorganisms than conventional disinfectants are.     

银与光所产生的协同效应的微生物灭活机理及其家电产品中的应用

研究发现在使用紫外线(UV-A, 395 nm)进行照射时, 银溶液对微生物的灭活作用得到增强, 特别是对真核微生物的灭活作用得到显著增强。为解明这种银与光所产生的协同效应的微生物灭活机理, 使用电子自旋共振仪(Electron spin resonance, ESR)对溶液进行检测, 并采用扫描电子显微镜(SEM)以及测定线粒体酶活性等方法, 从微生物形态学及生理学特性方面对真核微生物细胞进行分析, 推测出了其作用机理。分析认为, 在光照下氧化银(Ag2O)被激活并与水分子发生反应产生羟基自由基(·OH)。羟基自由基破坏真核微生物的细胞壁, 失活其细胞内线粒体酶活性, 从而引起真核微生物细胞死灭。在实验中, 作为原核微生物的代表使用金黄色葡萄球菌(Staphylococcus aureus), 作为真核微生物的代表使用了白色念珠菌(Candida albicans)和须癣毛癣菌(Trichophyton Mentagrophytes), 并对各种类进行了检测对比。本文还阐述了把这项微生物增殖抑制技术具体应用于洗衣机的具体结果, 并进行了讨论。     

银与光所产生的协同效应的微生物灭活机理及其家电产品中的应用

研究发现在使用紫外线(UV-A, 395 nm)进行照射时, 银溶液对微生物的灭活作用得到增强, 特别是对真核微生物的灭活作用得到显著增强。为解明这种银与光所产生的协同效应的微生物灭活机理, 使用电子自旋共振仪(Electron spin resonance, ESR)对溶液进行检测, 并采用扫描电子显微镜(SEM)以及测定线粒体酶活性等方法, 从微生物形态学及生理学特性方面对真核微生物细胞进行分析, 推测出了其作用机理。分析认为, 在光照下氧化银(Ag2O)被激活并与水分子发生反应产生羟基自由基(·OH)。羟基自由基破坏真核微生物的细胞壁, 失活其细胞内线粒体酶活性, 从而引起真核微生物细胞死灭。在实验中, 作为原核微生物的代表使用金黄色葡萄球菌(Staphylococcus aureus), 作为真核微生物的代表使用了白色念珠菌(Candida albicans)和须癣毛癣菌(Trichophyton Mentagrophytes), 并对各种类进行了检测对比。本文还阐述了把这项微生物增殖抑制技术具体应用于洗衣机的具体结果, 并进行了讨论。     

Disinfection of water containing natural organic matter by using ozone-initiated radical reactions

Ozone is widely used to disinfect drinking water and wastewater due to its strong biocidal oxidizing properties. Recently, it was reported that hydroxyl radicals ((.)OH), resulting from ozone decomposition, play a significant role in microbial inactivation when Bacillus subtilis endospores were used as the test microorganisms in pH controlled distilled water. However, it is not yet known how natural organic matter (NOM), which is ubiquitous in sources of drinking water, affects this process of disinfection by ozone-initiated radical reactions. Two types of water matrix were considered for this study. One is water containing humic acid, which is commercially available. The other is water from the Han River. This study reported that hydroxyl radicals, initiated by the ozone chain reaction, were significantly effective at B. subtilis endospore inactivation in water containing NOM, as well as in pH-controlled distilled water. The type of NOM and the pH have a considerable effect on the percentage of disinfection by hydroxyl radicals, which ranged from 20 to 50%. In addition, the theoretical T value of hydroxyl radicals for 2-log B. subtilis removal was estimated to be about 2.4 x 10(4) times smaller than that of ozone, assuming that there is no synergistic activity between ozone and hydroxyl radicals.     

Different inactivation behaviors of MS-2 phage and Escherichia coli in TiO2 photocatalytic disinfection

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO(2) photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (.OH), which is generated on the surface of UV-illuminated TiO(2), plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H(2)O(2) and O(2).(-), etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe(2+), were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O(2).(-) and H(2)O(2), according to the present results.     

Visible light inactivation of bacteria and fungi by modified titanium dioxide.

Visible light induced photocatalytic inactivation of bacteria (Escherichia coli, Staphylococcus aureus, Enterococcus faecalis) and fungi (Candida albicans, Aspergillus niger) was tested. Carbon-doped titanium dioxide and TiO2 modified with platinum(IV) chloride complexes were used as suspension or immobilised at the surface of plastic plates. A biocidal effect was observed under visible light irradiation in the case of E. coli in the presence of both photocatalysts. The platinum(IV) modified titania exhibited a higher inactivation effect, also in the absence of light. The mechanism of visible light induced photoinactivation is briefly discussed. The observed detrimental effect of photocatalysts on various microorganism groups decreases in the order: E. coli > S. aureus approximately E. faecalis>C. albicans approximately A. niger. This sequence results most probably from differences in cell wall or cell membrane structures in these microorganisms and is not related to the ability of catalase production.     

Disinfection of microorganisms by use of electrochemically regenerated periodate

A new method for disinfection of microorganisms by electrochemically regenerated periodate was developed. Oxidation of iodate to periodate was observed at 1.25 V versus a silver/silver chloride electrode in a cyclic voltammogram of potassium iodate. When 1.25 V was applied in 1.0 mM potassium iodate, approximately 4-log inactivation of Escherichia coli was observed in 30 min.     

Disinfection of Water Containing Natural Organic Matter by Using Ozone-Initiated Radical Reactions

Ozone is widely used to disinfect drinking water and wastewater due to its strong biocidal oxidizing properties. Recently, it was reported that hydroxyl radicals (^·OH), resulting from ozone decomposition, play a significant role in microbial inactivation when Bacillus subtilis endospores were used as the test microorganisms in pH controlled distilled water. However, it is not yet known how natural organic matter (NOM), which is ubiquitous in sources of drinking water, affects this process of disinfection by ozone-initiated radical reactions. Two types of water matrix were considered for this study. One is water containing humic acid, which is commercially available. The other is water from the Han River. This study reported that hydroxyl radicals, initiated by the ozone chain reaction, were significantly effective at B. subtilis endospore inactivation in water containing NOM, as well as in pH-controlled distilled water. The type of NOM and the pH have a considerable effect on the percentage of disinfection by hydroxyl radicals, which ranged from 20 to 50%. In addition, the theoretical T value of hydroxyl radicals for 2-log B. subtilis removal was estimated to be about 2.4 × 10⁴ times smaller than that of ozone, assuming that there is no synergistic activity between ozone and hydroxyl radicals.     

New water disinfection system using UVA light-emitting diodes

AIM: To evaluate the ability of high-energy ultraviolet A (UVA) light-emitting diode (LED) to inactivate bacteria in water and investigate the inactivating mechanism of UVA irradiation. METHODS AND RESULTS: We developed a new disinfection device equipped with high-energy UVA-LED. Inactivation of bacteria was determined by colony-forming assay. Vibrio parahaemolyticus, enteropathogenic Escherichia coli, Staphylococcus aureus and Escherichia coli DH5alpha were reduced by greater than 5-log(10) stages within 75 min at 315 J cm(-2) of UVA. Salmonella enteritidis was reduced greater than 4-log(10) stages within 160 min at 672 J cm(-2) of UVA. The formation of 8-hydroxy-2'-deoxyguanosine in UVA-LED irradiated bacteria was 2.6-fold higher than that of UVC-irradiated bacteria at the same inactivation level. Addition of mannitol, a scavenger of hydroxyl radicals (OH(*)), or catalase, an enzyme scavenging hydrogen peroxide (H(2)O(2)) to bacterial suspensions significantly suppressed disinfection effect of UVA-LED. CONCLUSION: This disinfection system has enough ability to inactivate bacteria and OH(*) and H(2)O(2) participates in the disinfection mechanism of UVA irradiation. SIGNIFICANCE AND IMPACT OF THE STUDY: We newly developed UVA irradiation system and found that UVA alone was able to disinfect the water efficiently. This will become a useful disinfection system.     

Evaluation of photoreactivation of Escherichia coli and Enterococci after UV disinfection of municipal wastewater

Because chlorine disinfection is not permitted in the province of Quebec, wastewater disinfection by ultraviolet (UV) light has been used for years in wastewater treatment plants. Thermotolerant coliforms discharge criteria are set for each plant and are adjusted by a factor of 1 log to compensate for photoreactivation in UV-disinfected effluents. The current study evaluated levels of Escherichia coli and enterococci photoreactivation from disinfected wastewater under varying temperature, visible light, and type of UV lamps. Escherichia coli photoreactivation increased significantly after exposure to 5600 lx compared with 1600 lx of visible light. This increase was significantly higher in warm water (25 degrees C) than cold water (4 degrees C). The level of photoreactivation of E. coli was also higher after wastewater disinfection by low-pressure UV lamps as opposed to medium-pressure UV lamps. Enterococci, however, were not photoreactivated under any test conditions. This result suggests that enterococci could be a better indicator than thermotolerant coliforms or E. coli. The use of enterococci would also eliminate the requirement to set different discharge criteria based on disinfection type (UV or chemical) and would also provide a better assessment of treatment efficiency for more resistant microorganisms.     

UV inactivation of pathogenic and indicator microorganisms

Survival was measured as a function of the dose of germicidal UV light for the bacteria Escherichia coli, Salmonella typhi, Shigella sonnei, Streptococcus faecalis, Staphylococcus aureus, and Bacillus subtilis spores, the enteric viruses poliovirus type 1 and simian rotavirus SA11, the cysts of the protozoan Acanthamoeba castellanii, as well as for total coliforms and standard plate count microorganisms from secondary effluent. The doses of UV light necessary for a 99.9% inactivation of the cultured vegetative bacteria, total coliforms, and standard plate count microorganisms were comparable. However, the viruses, the bacterial spores, and the amoebic cysts required about 3 to 4 times, 9 times, and 15 times, respectively, the dose required for E. coli. These ratios covered a narrower relative dose range than that previously reported for chlorine disinfection of E. coli, viruses, spores, and cysts.     

UV inactivation of pathogenic and indicator microorganisms.

Survival was measured as a function of the dose of germicidal UV light for the bacteria Escherichia coli, Salmonella typhi, Shigella sonnei, Streptococcus faecalis, Staphylococcus aureus, and Bacillus subtilis spores, the enteric viruses poliovirus type 1 and simian rotavirus SA11, the cysts of the protozoan Acanthamoeba castellanii, as well as for total coliforms and standard plate count microorganisms from secondary effluent. The doses of UV light necessary for a 99.9% inactivation of the cultured vegetative bacteria, total coliforms, and standard plate count microorganisms were comparable. However, the viruses, the bacterial spores, and the amoebic cysts required about 3 to 4 times, 9 times, and 15 times, respectively, the dose required for E. coli. These ratios covered a narrower relative dose range than that previously reported for chlorine disinfection of E. coli, viruses, spores, and cysts.     

Radiation inactivation of rabbit muscle aldolase.

Pulse radiolysis and steady-state X-radiolysis have been used to investigate the radiation inactivation of aldolase from rabbit muscle. Both eaq-and OH readily react with aldolase, and contribute to inactivation. The radical anions (CNS)2-and (Br)2-react with aldolase at neutral pH. The progressive addition of alkali results in an increase in the second-order rate constants, with an apparent pK approximately 10 +/- 0-3, and with the formation of an unstable intermediate, lambdamax approximately 400 nm resembling a phenoxyl radical. Steady-state radiolysis in the presence of (CNS)2-and (Br)2- at alkaline pH results in increased aldolase inactivation, with a pK of enzyme inactivation similar to that observed for reaction of the radical anions. We propose that a reaction of the radical anoins with tyrosine residues accounts for the resultant inactivation.     

Repair of damage in double-stranded phi X174 (RF) DNA due to radiation-induced water radicals

Experiments in which the yields of radiation-induced OH and H radicals were varied, showed that both types of water radicals inactivate phi X174 RF DNA to about the same extent as measured by transfection of the (irradiated) DNA to E. coli wild-type spheroplasts. On the other hand, using spheroplasts prepared from E. coli strains, deficient in one of the proteins involved in excision DNA repair (uvrA- or uvrC-) or in post-replication repair (recA-), clear differences between damage originating from OH or H radical attack were found. Part of the radiation damage due to H radicals appeared to be repairable by an uvrA-gene-dependent repair mechanism, whereas this repair pathway does not play an important role in the case of OH radical damage. The reverse applies to uvrC-gene-dependent repair, which only affects OH radical damage (obtained under anoxic conditions), but has no influence on damage due to H radicals. Irradiation of double-stranded phi X174 (RF) DNA in the presence of oxygen however, yields damage--due to OH radicals only--which appeared not to be sensitive to either uvrC- or uvrA-gene-dependent repair. Furthermore, post-replication repair (recA) has only very little effect on the amount of inactivation by H or OH radicals, when irradiation is carried out under anoxic conditions. We did not find significant inactivation due to hydrated electrons, whether the biological activity was determined by use of wild-type spheroplasts or of strains deficient in excision or post-replication repair proteins.     

Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO2 Photocatalytic Disinfection

Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO₂ photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (·OH), which is generated on the surface of UV-illuminated TiO₂, plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H₂O₂ and O₂·⁻, etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe²⁺, were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O₂·⁻ and H₂O₂, according to the present results.     

Inactivation of Viruses and Bacteria by Ozone, With and Without Sonication

Selected organisms with public health significance were placed in a reaction chamber for treatment by ozonation, by ozonation and sonication, by sonication, or by sonication during oxygenation. Vesicular stomatitis virus, encephalomyocarditis virus, GDVII virus, Staphylococcus aureus, Pseudomonas fluorescens, Salmonella typhimurium, enteropathogenic Escherichia coli, Vibrio cholerae, and Shigella flexneri were inactivated by treatment with ozone. When microorganisms were suspended in phosphate-buffered saline, they were inactivated rapidly by treatment with ozone. However, microorganisms suspended in secondary effluent from a wastewater treatment plant required longer contact times with ozone for complete inactivation. Simultaneous treatments by ozonation and sonication reduced the contact time for complete inactivation of microorganisms in secondary effluent. Treatment by sonication alone or sonication and oxygenation did not inactivate microorganisms. Therefore, the simultaneous treatment of microorganisms in secondary effluent with ozone and sonication resulted in a synergistic effect.     

Measurement of OH radical CT for inactivating Cryptosporidium parvum using photo/ferrioxalate and photo/TiO2 systems

Aim: This study investigates the inactivation of Cryptosporidium parvum using the OH radical and reports the OH radical CT (OH radical concentration × contact time) values for C. parvum inactivation. Methods and Results: Although a wealth of information has demonstrated the efficacy of the microbial inactivation activity of the OH radical, no studies have performed a quantitative estimation of the OH radical for C. parvum inactivation. The CT value of the OH radical required for 2 log C. parvum inactivation was measured with two OH radical‐generating systems, photo/ferrioxalate and photo/TiO₂. The OH radical was approx. 10⁴–10⁷‐fold more effective for microbial inactivation than other popular chemical disinfectants such as ozone, chlorine dioxide and free chlorine. Conclusions: The OH radical appears to be suitable for microbial inactivation with a calculated CT value required for 2 log C. parvum inactivation of 9·3 × 10^?5 mg min l^?1. Significance and Impact of the Study: This study is the first report of an investigation on the role of the OH radical in the photo/ferrioxalate and photo/TiO₂ systems and on the OH radical CT required for C. parvum inactivation.     

Inactivation of Cryptosporidium parvum oocysts and Clostridium perfringens spores by a mixed-oxidant disinfectant and by free chlorine.

Cryptosporidium parvum oocysts and Clostridium perfringens spores are very resistant to chlorine and other drinking-water disinfectants. Clostridium perfringens spores have been suggested as a surrogate indicator of disinfectant activity against Cryptosporidium parvum and other hardy pathogens in water. In this study, an alternative disinfectant system consisting of an electrochemically produced mixed-oxidant solution (MIOX; LATA Inc.) was evaluated for inactivation of both Cryptosporidium parvum oocysts and Clostridium perfringens spores. The disinfection efficacy of the mixed-oxidant solution was compared to that of free chlorine on the basis of equal weight per volume concentrations of total oxidants. Batch inactivation experiments were done on purified oocysts and spores in buffered, oxidant demand-free water at pH 7 an 25 degrees C by using a disinfectant dose of 5 mg/liter and contact times of up to 24 h. The mixed-oxidant solution was considerably more effective than free chlorine in activating both microorganisms. A 5-mg/liter dose of mixed oxidants produced a > 3-log10-unit (> 99.9%) inactivation of Cryptosporidium parvum oocysts and Clostridium perfringens spores in 4 h. Free chlorine produce no measurable inactivation of Cryptosporidium parvum oocysts by 4 or 24 h, although Clostridium perfringens spores were inactivated by 1.4 log10 units after 4 h. The on-site generation of mixed oxidants may be a practical and cost-effective system of drinking water disinfection protecting against even the most resistant pathogens, including Cryptosporidium oocysts.     

Inactivation of Campylobacter jejuni by chlorine and monochloramine

Campylobacter jejuni and closely related organisms are important bacterial causes of acute diarrheal illness in the United States. Both endemic and epidemic infections have been associated with consuming untreated or improperly treated surface water. We compared susceptibility of three C. jejuni strains and Escherichia coli ATCC 11229 with standard procedures used to disinfect water. Inactivation of bacterial preparations with 0.1 mg of chlorine and 1.0 mg of monochloramine per liter was determined at pH 6 and 8 and at 4 and 25 degrees C. Under virtually every condition tested, each of the three C. jejuni strains was more susceptible than the E. coli control strain, with greater than 99% inactivation after 15 min of contact with 1.0 mg of monochloramine per liter or 5 min of contact with 0.1 mg of free chlorine per liter. Results of experiments in which an antibiotic-containing medium was used suggest that a high proportion of the remaining cells were injured. An animal-passaged C. jejuni strain was as susceptible to chlorine disinfection as were laboratory-passaged strains. These results suggest that disinfection procedures commonly used for treatment of drinking water to remove coliform bacteria are adequate to eliminate C. jejuni and further correlate with the absence of outbreaks associated with properly treated water.     

Inactivation of Campylobacter jejuni by chlorine and monochloramine.

Campylobacter jejuni and closely related organisms are important bacterial causes of acute diarrheal illness in the United States. Both endemic and epidemic infections have been associated with consuming untreated or improperly treated surface water. We compared susceptibility of three C. jejuni strains and Escherichia coli ATCC 11229 with standard procedures used to disinfect water. Inactivation of bacterial preparations with 0.1 mg of chlorine and 1.0 mg of monochloramine per liter was determined at pH 6 and 8 and at 4 and 25 degrees C. Under virtually every condition tested, each of the three C. jejuni strains was more susceptible than the E. coli control strain, with greater than 99% inactivation after 15 min of contact with 1.0 mg of monochloramine per liter or 5 min of contact with 0.1 mg of free chlorine per liter. Results of experiments in which an antibiotic-containing medium was used suggest that a high proportion of the remaining cells were injured. An animal-passaged C. jejuni strain was as susceptible to chlorine disinfection as were laboratory-passaged strains. These results suggest that disinfection procedures commonly used for treatment of drinking water to remove coliform bacteria are adequate to eliminate C. jejuni and further correlate with the absence of outbreaks associated with properly treated water.