Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments

Resistance and inactivation kinetics of bacterial strains isolated from the non-chlorinated and chlorinated effluents of a WWTP

The microbiological quality of water from a wastewater treatment plant that uses sodium hypochlorite as a disinfectant was assessed. Mesophilic aerobic bacteria were not removed efficiently. This fact allowed for the isolation of several bacterial strains from the effluents. Molecular identification indicated that the strains were related to Aeromonas hydrophila, Escherichia coli (three strains), Enterobacter cloacae, Kluyvera cryocrescens (three strains), Kluyvera intermedia, Citrobacter freundii (two strains), Bacillus sp. and Enterobacter sp. The first five strains, which were isolated from the non-chlorinated effluent, were used to test resistance to chlorine disinfection using three sets of variables: disinfectant concentration (8, 20 and 30 mg·L(-1)), contact time (0, 15 and 30 min) and water temperature (20, 25 and 30 °C). The results demonstrated that the strains have independent responses to experimental conditions and that the most efficient treatment was an 8 mg·L(-1) dose of disinfectant at a temperature of 20 °C for 30 min. The other eight strains, which were isolated from the chlorinated effluent, were used to analyze inactivation kinetics using the disinfectant at a dose of 15 mg·L(-1) with various retention times (0, 10, 20, 30, 60 and 90 min). The results indicated that during the inactivation process, there was no relationship between removal percentage and retention time and that the strains have no common response to the treatments.

Mechanism of the synergistic inactivation of Escherichia coli by UV-C light at mild temperatures

UV light only penetrates liquid food surfaces to a very short depth, thereby limiting its industrial application in food pasteurization. One promising alternative is the combination of UV light with mild heat (UV-H), which has been demonstrated to produce a synergistic bactericidal effect. The aim of this article is to elucidate the mechanism of synergistic cellular inactivation resulting from the simultaneous application of UV light and heat. The lethality of UV-H treatments remained constant below ∼45°C, while lethality increased exponentially as the temperature increased. The percentage of synergism reached a maximum (40.3%) at 55°C. Neither the flow regimen nor changes in the dose delivered by UV lamps contributed to the observed synergism. UV-H inactivation curves of the parental Escherichia coli strain obtained in a caffeic acid selective recovery medium followed a similar profile to those obtained with uvrA mutant cells in a nonselective medium. Thermal fluidification of membranes and synergistic lethal effects started around 40 to 45°C. Chemical membrane fluidification with benzyl alcohol decreased the UV resistance of the parental strain but not that of the uvrA mutant. These results suggest that the synergistic lethal effect of UV-H treatments is due to the inhibition of DNA excision repair resulting from the membrane fluidification caused by simultaneous heating.

Photodegradation of naproxen and its photoproducts in aqueous solution at 254 nm: a kinetic investigation

The kinetics of photodegradation of the non steroidal anti-inflammatory drug naproxen (+)-S-2-(6-methoxynaphthalen-2-yl)propanoic acid, an emerging organic pollutant, was studied in aqueous solutions under deaerated and aerated conditions. The photolysis experiments were carried out under monochromatic irradiation (λ = 254 nm) at pH = 7.0 and T = 25 °C. Simplified reaction schemes of photodegradation of naproxen are proposed in absence and in presence of oxygen respectively. The schemes take into account the photolysis of naproxen and its photoproducts and the reactions of the measured species with oxygen dissolved in the liquid bulk. According to these schemes, two kinetic models were developed which correlate the experimental data, for runs performed in absence and in presence of oxygen, with a fair accuracy and allowed to estimate the best values for the unknown kinetic parameters. The calculated quantum yield of direct photolysis of naproxen under deaerated media is in good agreement with the one previously reported. Under aerated conditions, the generation of singlet oxygen has also been taken into account. The obtained results, under the adopted conditions, indicated a marked influence of dissolved oxygen on the photodegradation rates of naproxen and the relative distribution of the major reaction intermediates.

Removal of faecal indicator pathogens from waters and wastewaters by photoelectrocatalytic oxidation on TiO(2)/Ti films under simulated solar radiation

PURPOSE

The disinfection efficiency of water and secondary treated wastewater by means of photoelectrocatalytic oxidation (PEC) using reference strains of Enterococcus faecalis and Escherichia coli as faecal indicators was evaluated. Operating parameters such as applied potential (2-10 V), initial bacterial concentration (10(3)-10(7) CFU/mL), treatment time (up to 90 min) and aqueous matrix (pure water and treated effluent) were assessed concerning their impact on disinfection.

METHODS

PEC experiments were carried out using a TiO(2)/Ti film anode and a zirconium cathode in the presence of simulated solar radiation. Bacterial inactivation was monitored by the culture method and real-time SYBR green PCR.

RESULTS

A 6.2 log reduction in E. faecalis population was achieved after 15 min of PEC treatment in water at 10 V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to only about 4.3 log reduction, whilst negligible inactivation was recorded when the respective electrochemical oxidation process was applied (i.e. without radiation). PEC efficiency was generally improved increasing the applied potential and decreasing initial bacterial concentration. Regarding real wastewater, E. coli was more susceptible than E. faecalis during treatment at a potential of 5 V. Wastewater disinfection was affected by its complex composition and the contained mixed bacterial populations, yielding lower inactivation rates compared to water treatment. Screening the results obtained from both applied techniques (culture method and real-time PCR), there was a discrepancy regarding the recorded time periods of total bacterial inactivation, with qPCR revealing longer periods for complete bacterial reduction.

CONCLUSIONS

PEC is superior to PC in terms of E. faecalis inactivation presumably due to a more efficient separation and utilization of the photogenerated charge carriers, and it is mainly affected by the applied potential, initial bacterial concentration and the aqueous matrix.

The depuration dynamics of oysters (Crassostrea gigas) artificially contaminated with hepatitis A virus and human adenovirus

Within the country of Brazil, Santa Catarina is a major shellfish producer. Detection of viral contamination is an important step to ensure production quality and consumer safety during this process. In this study, we used a depuration system and ultraviolet (UV) disinfection to eliminate viral pathogens from artificially infected oysters and analysed the results. Specifically, the oysters were contaminated with hepatitis A virus (HAV) or human adenovirus type 5 (HAdV5). After viral infection, the oysters were placed into a depuration tank and harvested after 48, 72 and 96 h. After sampling, various oyster tissues were dissected and homogenised and the viruses were eluted with alkaline conditions and precipitated with polyethylene glycol. The oyster samples were evaluated by cell culture methods, as well as polymerase chain reaction (PCR) and quantitative-PCR. Moreover, at the end of the depuration period, the disinfected seawater was collected and analysed by PCR. The molecular assays showed that the HAdV5 genome was present in all of the depuration time samples, while the HAV genome was undetectable after 72 h of depuration. However, viral viability tests (integrated cell culture-PCR and immunofluorescence assay) indicated that both viruses were inactivated with 96 h of seawater recirculation. In conclusion, after 96 h of UV treatment, the depuration system studied in this work purified oysters that were artificially contaminated with HAdV5 and HAV.

Depuration of Oysters (Crassostrea gigas) contaminated with Vibrio parahaemolyticus and Vibrio vulnificus with UV light and chlorinated seawater

The efficacy of depuration using UV light and chlorinated seawater for decontaminating Vibrio parahaemolyticus and Vibrio vulnificus from oysters was investigated. Oysters were contaminated with a five-strain cocktail of V. parahaemolyticus or V. vulnificus to levels of 10(4) to 10(5) CFU ml(-1) for bioaccumulation. The depuration was conducted in a closed system in which 350 liters of seawater was recirculated at a rate of 7 liters/min for 48 h at room temperature. Counts of V. parahaemolyticus or V. vulnificus were determined at 0, 6, 18, 24, and 48 h. Three treatments were conducted: T1, control treatment; T2, UV treatment; and T3, UV plus chlorine treatment. After 48 h of depuration of V. parahaemolyticus, T3 reduced the count by 3.1 log most probable number (MPN) g(-1) and T2 reduced the count by 2.4 log MPN g(-1), while T1 reduced the count by only 2.0 log MPN g(-1). After 48 h of depuration of V. vulnificus, T2 and T3 were efficient, reducing the counts by 2.5 and 2.4 log MPN g(-1), respectively, while T1 reduced the count by only 1.4 log MPN g(-1). The UV light plus chlorine treatment was more efficient for controlling V. parahaemolyticus in oysters. Both UV light and UV light plus chlorine were efficient for V. vulnificus. The present study is the first report showing the efficacy of depuration systems for decontaminating V. parahaemolyticus and V. vulnificus in oysters cultivated on the Brazilian coast. This study provides information on processes that can contribute to controlling and preventing such microorganisms in oysters and could be used for effective postharvest treatment by restaurants and small producers of oysters on the coast of Brazil.

Evolution of phytoplankton cultures after ultraviolet light treatment

Introducing invasive species in new environments through ballast water is a specific problem of contamination and has recently become one of the main concerns of Maritime Organizations. Ultraviolet-C radiation (UV-C) is a technological alternative to prevent this maritime pollution. This study addresses the effect of UV-C on different phytoplankton cultures and also the ability to recover following exposure to damage. A UV-C low-pressure lamp irradiates the cultures. The distance from the source and the thickness of the layer prevent part of the energy from reaching the culture and the disinfective process is diminished. Some cultures such as Chlorella autotrophica and Chaetoceros calcitrans can easily recover from UV-C damage. However, Phaeocystis globosa does not have this ability. C. calcitrans forms cysts and exhibits two different behaviours depending on the dose applied.

Impact of virus aggregation on inactivation by peracetic acid and implications for other disinfectants

Viruses in wastewater and natural environments are often present as aggregates. The disinfectant dose required for their inactivation, however, is typically determined with dispersed viruses. This study investigates how aggregation affects virus inactivation by chemical disinfectants. Bacteriophage MS2 was aggregated by lowering the solution pH, and aggregates were inactivated by peracetic acid (PAA). Aggregates were redispersed before enumeration to obtain the residual number of individual infectious viruses. In contrast to enumerating whole aggregates, this approach allowed an assessment of disinfection efficiency which remains applicable even if the aggregates disperse in post-treatment environments. Inactivation kinetics were determined as a function of aggregate size (dispersed, 0.55 and 0.90 μm radius) and PAA concentration (5-103 mg/L). Aggregation reduced the apparent inactivation rate constants 2-6 fold. The larger the aggregate and the higher the PAA concentration, the more pronounced the inhibitory effect of aggregation on disinfection. A reaction-diffusion based model was developed to interpret the experimental results, and to predict inactivation rates for additional aggregate sizes and disinfectants. The model showed that the inhibitory effect of aggregation arises from consumption of the disinfectant within the aggregate, but that diffusion of the disinfectant into the aggregates is not a rate-limiting factor. Aggregation therefore has a large inhibitory effect if highly reactive disinfectants are used, whereas inactivation by mild disinfectants is less affected. Our results suggest that mild disinfectants should be used for the treatment of water containing viral aggregates.

Synergism effects for Escherichia coli inactivation applying the combined ozone and chlorine disinfection method

Water disinfection assays were carried out using ozone and chlorine in non-sequential steps--the individual method--and in sequential steps--the combined ozone/chlorine method. Escherichia coli strain ATCC 11229 was used as the indicator microorganism. For the assays using the individual method, the applied dosages of ozone were 2.0, 3.0 and 5.0 mg/L, and 2.0 and 5.0 mg/L of chlorine were used. For the assays applying the combined method, the dosages (dosage combination) were, in mg/L: 2.0 O3 + 2.0 Cl, 3.0 O3 + 2.0 Cl2, 5.0 O3 + 2.0 Cl2 and 2.0 O3 + 5.0 Cl2. The applied contact times were 5, 10, 15 and 20 minutes for the individual method as well as for the combined method. For all used dosages and contact times, E. coli inactivation was superior to the inactivation obtained in the individual method, indicating the occurrence of synergism for E. coli inactivation in the combined method.

Biofilm control in water by a UV-based advanced oxidation process

An ultraviolet (UV)-based advanced oxidation process (AOP), with hydrogen peroxide and medium-pressure (MP) UV light (H(2)O(2)/UV), was used as a pretreatment strategy for biofilm control in water. Suspended Pseudomonas aeruginosa cells were exposed to UV-based AOP treatment, and the adherent biofilm formed by the surviving cells was monitored. Control experiments using H(2)O(2) or MP UV irradiation alone could inhibit biofilm formation for only short periods of time (<24 h) post-treatment. In a H(2)O(2)/filtered-UV (>295 nm) system, an additive effect on biofilm control was shown vs filtered-UV irradiation alone, probably due to activity of the added hydroxyl radical (OH•). In a H(2)O(2)/full-UV (ie full UV spectrum, not filtered) system, this result was not obtained, possibly due to the germicidal UV photons overwhelming the AOP system. Generally, however, H(2)O(2)/UV prevented biofilm formation for longer periods (days) only when maintained with residual H(2)O(2). The ratio of surviving bacterial concentration post-treatment to residual H(2)O(2) concentration played an important role in biofilm prevention and bacterial regrowth. H(2)O(2) treatments alone resulted in poorer biofilm control compared to UV-based AOP treatments maintained with similar levels of residual H(2)O(2), indicating a possible advantage of AOP.

Photocatalytic inactivation of spores of Bacillus anthracis using titania nanomaterials

Studies on photocatalytic inactivation of spores of Bacillus anthracis have been carried out using nanosized titania materials and UVA light or sun light. Results demonstrated pseudo first order behaviour of spore inactivation kinetics. The value of kinetic rate constant increased from 0.4h(-1) to 1.4h(-1) indicating photocatalysis facilitated by addition of nanosized titania. Nanosized titania exhibited superior inactivation kinetics on par with large sized titania. The value of kinetic rate constant increased from 0.02 h(-1) to 0.26 h(-1) on reduction of size from 1000 nm to 16 nm depicting the enhanced rate of inactivation of Bacillus anthracis Sterne spores on the decrease of particle size.

Inactivation of MS2 coliphage in Fenton and Fenton-like systems: role of transition metals, hydrogen peroxide and sunlight

The inactivation of coliphage MS2 by iron- and copper-catalyzed Fenton systems was studied to assess the importance of this process for virus inactivation in natural systems and during water treatment by advanced oxidation processes. The influence of H(2)O(2) (3-50 microM) and metal (1-10 microM) concentrations, HO(*) production, and sunlight on inactivation was investigated. Inactivation was first order with respect to H(2)O(2), but the dependence on the metal concentration was more complex. In the Cu/H(2)O(2) system, the inactivation rate constant k(obs) increased with added Cu up to 2.5 microM, and then leveled off. This was consistent with Cu saturation of the solution, indicating that only soluble Cu contributed to inactivation. In contrast, inactivation in the Fe/H(2)O(2) system was governed by colloidal iron. Irradiation by sunlight only affected the Fe/H(2)O(2) system, leading to a 5.5-fold increase in k(obs) (up to 3.1 min(-1)). HO(*) production, measured by electron spin resonance, could not account for the observed inactivation in the Fe/H(2)O(2) system. Other oxidants, such as ferryl species, must therefore play a role. Experiments using bulk oxidant scavengers revealed that inactivation occurred by a caged mechanism involving oxidant production by metals located in close proximity to the virus. Overall, our results show that the Fenton/photo-Fenton process may serve as an efficient technology for virus disinfection.

Inactivation of MS2 coliphage by Fenton's reagent

Fenton's reagent (i.e., Fe[II]/H2O2) is known to generate strong oxidants capable of oxidizing a broad spectrum of organic compounds in aqueous solution. This study demonstrates the successful inactivation of MS2 coliphage (MS2) by the oxidants produced from Fenton's reagent. The inactivation process of MS2 by Fenton's reagent was found to proceed in two distinct stages. The first stage inactivation, which took place rapidly within 1 min reaction time, was mainly achieved by the reaction of Fe(II) with H2O2 (i.e., the Fenton reaction). The second stage, which occurred by the catalytic reactions of Fe(III) with H2O2, exhibited much slower inactivation than the first stage. The rate of MS2 inactivation increased as pH decreased from 8.0 to 6.0. The addition of oxalate and humic acids significantly inhibited the MS2 inactivation, whereas 1,10-phenanthroline and bipyridine resulted in a gradual and steady inactivation of MS2. These observations on the effects of pH and iron-chelating agents indicate that oxidants formed on the surface or inside MS2 are responsible for the inactivation.

Synergistic effects of ethanol and UV radiation to reduce levels of selected foodborne pathogenic bacteria

The purpose of this study was to determine whether combined treatments would produce synergistic disinfection effects on food products during food processing compared with single treatments. We investigated the bactericidal effects of a commercial chemical disinfectant (ethanol) and of UV radiation on Bacillus cereus F4810/72, Cronobacter sakazakii KCTC 2949, Staphylococcus aureus ATCC 35556, Escherichia coli ATCC 10536, and Salmonella enterica Typhimurium NO/NA in vitro. Various concentrations of ethanol (10, 30, 40, and 50%) were tested with various exposure doses of UV radiation (6, 96, 216, 360, and 504 mWs/cm(2)) with a UV lamp. The combined ethanol-UV treatments resulted in greater reductions in bacterial counts than did either treatment alone. The synergistic effect values for B. cereus, C. sakazakii, S. aureus, S. enterica Typhimurium NO/NA, and E. coli were 0.40 to 1.52, 0.52 to 1.74, 0.20 to 2.32, 0.07 to 1.14, and 0.02 to 1.75 log CFU/ml, respectively. The results of this study suggest that a significant synergistic benefit results from combining ethanol and UV treatments against foodborne pathogens in vitro.

Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water

The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40mJcm(-2) for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66mJcm(-2).

Polyhexamethylene biguanide exposure leads to viral aggregation

AIMS

This study reports the activity of two biguanides against MS2 bacteriophage used as a surrogate virus for nonenveloped mammalian viruses and provides an explanation as to their apparent limited efficacy.

METHODS AND RESULTS

When tested in a standard suspension test, two polyhexamethylene biguanides (PHMB), VANTOCIL TG and COSMOCIL CQ, reduced the viability of MS2 by only 1-2 log(10) PFU ml(-1). Exposure time up to 30 min did not affect the activity of the biguanides, although both PHMB were shown to strongly interact with MS2 proteins.

CONCLUSIONS

Inactivation kinetics and change in virus hydrophobicity suggested that PHMB induces the formation of viral aggregates. This hypothesis was supported using dynamic light scattering that showed an increase in viral aggregates sizes (up to 500 nm) in a concentration-dependent manner.

SIGNIFICANCE AND IMPACT OF THE STUDY

It has been reported that viral aggregation is responsible for virus survival to the biocide exposure. Here, this might be the case, because the virucidal activity of the biguanides was modest and viral aggregation important. The formation of viral aggregates during virus exposure to PHMB was unlikely to overestimate the virucidal potential of the biguanides.

Optimization and evaluation of a decontamination step with peroxyacetic acid for fresh-cut produce

Since several disadvantages are associated with the use of sodium hypochlorite as a decontamination agent, the attention for alternative agents such as peroxyacetic acid (PAA) is increasing. In this study the effectiveness of PAA to remove the native microflora was tested in four types of fresh-cut vegetables: grated carrots, fresh-cut white cabbage, iceberg lettuce and leek. Furthermore, the influence of varying PAA concentrations (0, 25, 80, 150 and 250 ppm) and varying contact times (1, 5 and 10 min) was described by means of a linear model. The efficiency of PAA to remove the native flora was highly dependent on the type of fresh-cut produce: the highest microbial reductions were obtained for carrots (0.5-3.5 log cfu/g) and white cabbage (0.5-3.5 log cfu/g) followed by iceberg lettuce (0.4-2.4 log cfu/g). The obtained efficiency was the lowest for fresh-cut leek (0.4-1.4 log cfu/g). Furthermore, all the treated samples, regardless of the type of vegetable and the contact time and concentration of the PAA treatment, were acceptable for consumption.

Ultraviolet light-emitting diodes in water disinfection

BACKGROUND, AIM, AND SCOPE

The novel system of ultraviolet light-emitting diodes (UV LEDs) was studied in water disinfection. Conventional UV lamps, like mercury vapor lamp, consume much energy and are considered to be problem waste after use. UV LEDs are energy efficient and free of toxicants. This study showed the suitability of LEDs in disinfection and provided information of the effect of two emitted wavelengths and different test mediums to Escherichia coli destruction.

MATERIALS AND METHODS

Common laboratory strain of E. coli (K12) was used and the effects of two emitted wavelengths (269 and 276 nm) were investigated with two photolytic batch reactors both including ten LEDs. The effects of test medium were examined with ultrapure water, nutrient and water, and nutrient and water with humic acids.

RESULTS

Efficiency of reactors was almost the same even though the one emitting higher wavelength had doubled optical power compared to the other. Therefore, the effect of wavelength was evident and the radiation emitted at 269 nm was more powerful. Also, the impact of background was studied and noticed to have only slight deteriorating effect. In the 5-min experiment, the bacterial reduction of three to four log colony-forming units (CFU) per cubic centimeter was achieved, in all cases.

DISCUSSION

When turbidity of the test medium was greater, part of the UV radiation was spent on the absorption and reactions with extra substances on liquid. Humic acids can also coat the bacteria reducing the sensitivity of the cells to UV light. The lower wavelength was distinctly more efficient when the optical power is considered, even though the difference of wavelengths was small. The reason presumably is the greater absorption of DNA causing more efficient bacterial breakage.

CONCLUSIONS

UV LEDs were efficient in E. coli destruction, even if LEDs were considered to have rather low optical power. The effect of wavelengths was noticeable but the test medium did not have much impact.

RECOMMENDATIONS AND PERSPECTIVES

This study found UV LEDs to be an optimal method for bacterial disinfection. The emitted wavelength was found to be an essential factor when using LEDs; thus, care should be taken in selecting the proper LED for maximum disinfection.

Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes

The decomposition of two haloacetic acids (HAAs), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), from water was studied by means of single oxidants: ozone, UV radiation; and by the advanced oxidation processes (AOPs) constituted by combinations of O(3)/UV radiation, H(2)O(2)/UV radiation, O(3)/H(2)O(2), O(3)/H(2)O(2)/UV radiation. The concentrations of HAAs were analyzed at specified time intervals to elucidate the decomposition of HAAs. Single O(3) or UV did not result in perceptible decomposition of HAAs within the applied reaction time. O(3)/UV showed to be more suitable for the decomposition of DCAA and TCAA in water among the six methods of oxidation. Decomposition of DCAA was easier than TCAA by AOPs. For O(3)/UV in the semi-continuous mode, the effective utilization rate of ozone for HAA decomposition decreased with ozone addition. The kinetics of HAAs decomposition by O(3)/UV and the influence of coexistent humic acids and HCO(3)(-) on the decomposition process were investigated. The decomposition of the HAAs by the O(3)/UV accorded with the pseudo-first-order mode under the constant initial dissolved O(3) concentration and fixed UV radiation. The pseudo-first-order rate constant for the decomposition of DCAA was more than four times that for TCAA. Humic acids can cause the H(2)O(2) accumulation and the decrease in rate constants of HAAs decomposition in the O(3)/UV process. The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2mgTOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO(3)(-) concentration of 1.0mmol/L.

Hydrogen peroxide vapor: a novel method for the environmental control of lactococcal bacteriophages

Bacteriophage contamination can be problematic, especially in industrial settings. We examined the in vitro efficacy of hydrogen peroxide vapor (HPV) for the inactivation of two lactococcal bacteriophages dried onto stainless steel discs. A more than 6-log reduction was achieved on both bacteriophages compared with unexposed controls by 50 min of HPV exposure in an isolator. HPV might be useful for the environmental control of bacteriophages.

Comparison of low- and medium-pressure ultraviolet lamps: Photoreactivation of Escherichia coli and total coliforms in secondary effluents of municipal wastewater treatment plants

It has been reported that Medium-Pressure (MP) ultraviolet (UV) lamps have an advantage over low-pressure (LP) lamps for water disinfection in terms of the photoreactivation of pure cultured bacteria. However, few studies have investigated the behavior of microorganisms in wastewater. Hence, in this study, the degree of photoreactivation, after UV exposure using both LP and MP lamps, in municipal wastewater samples was examined under a variety of conditions. Pure cultured Escherichia coli was also used to provide a comparison with previous studies. E. coli was found to undergo photoreactivation after both LP and MP exposure. The Colony Forming Ability (CFA) ratios were 0.60 and 0.32, and the percentage of photoreactivation was 50% and 20%, respectively, for LP and MP lamps with a germicidal UV dose of 5 mJ/cm2. However, the advantage of the MP lamp was diminished for larger UV doses, since no photoreactivation was detected when the UV dose was 15 mJ/cm2 for either LP or MP lamps. The microorganisms present in wastewater showed similar results to those of E. coli, however, no significant difference was found between the use of either a LP or a MP lamp. Also, when a UV dose of 40 mJ/cm2 was applied, the percentage photoreactivation was less than 1%, no matter which type of lamp was used. From this work, it is concluded that the selection of the type of UV lamp for wastewater treatment plants, as regards photoreactivation of total coliforms, is not critical as long as the applied germicidal UV dose is greater than 40 mJ/cm2.

Efficiency of KrCl excilamp (222 nm) for inactivation of bacteria in suspension

AIMS

To examine the killing efficiency of UV KrCl excilamp against gram-positive and gram-negative bacteria.

METHODS AND RESULTS

Vegetative cells of Bacillus cereus, Bacillus subtilis, Escherichia coli O157:H7, Staphylococcus aureus and Streptococcus pyogenes at initial populations from 10(2) to 10(7) colony-forming units (CFU) ml(-1) were treated by KrCl excilamp in sterile Ringer's solution with and without H(2)O(2). The number of viable cells was determined using spread plating techniques and nutrient agar method with subsequent incubation at 28 degrees C or 37 degrees C for 24 h. At estimated populations of 10(2)-10(5) CFU ml(-1) E. coli O157:H7 and Staph. aureus were the most sensitive and showed 100% disinfection within 15 s (29.2 mJ cm(-2)). Bacillus subtilis was more sensitive to UV treatment than B. cereus. The UV/H(2)O(2) inactivation rate coefficients within this population range were two times higher than those observed for UV treatment alone. No effect of H(2)O(2) was observed at 10(7) CFU ml(-1) for Bacillus sp. and Strep. pyogenes.

CONCLUSIONS

The narrow-band UV radiation at 222 nm was effective in the rapid disinfection of bacteria in aqueous suspensions.

SIGNIFICANCE AND IMPACT OF THE STUDY

KrCl excilamps represent UV sources which can be applied for disinfection of drinking water in advanced oxidation processes.

Evaluating slurry broadcasting and injection to ley for phosphorus losses and fecal microorganisms in surface runoff

The recent growth in the size of dairy cattle farms and the concentration of farms into smaller areas in Finland may increase local water pollution due to increased manure production and slurry application to grass. Therefore, a field study was conducted to monitor losses of total phosphorus (TP), dissolved reactive phosphorus (DRP), and fecal microorganisms in surface runoff from a perennial ley. Cattle slurry was added once a year in June 1996-1997 (Study I) and biannually in June and October 1998-2000 (Study II). The slurry was surface broadcast or injected into the clay soil. The field had a slope of 0.9 to 1.7%. Mineral fertilizer was applied on control plots. Biannual slurry broadcasting increased DRP (p < 0.001) and TP losses (p < 0.001) and numbers of fecal microorganisms in surface runoff waters. The highest losses of TP (2.7 kg ha(-1) yr(-1)) and DRP (2.2 kg ha(-1) yr(-1)) and the highest numbers of fecal coliforms (880 colony-forming units [CFU] per 100 mL) and somatic coliphages (2700 plaque-forming units [PFU] per 100 mL) were measured after broadcasting slurry to wet soil followed by rainfall in fall 1998. Injection reduced the TP and DRP losses in surface runoff by 79 and 86%, respectively, compared with broadcasting (17 Oct. 1998-27 Oct. 1999). Corresponding numbers for fecal coliforms were 350 CFU (100 mL)(-1) and for somatic coliphages were 110 PFU (100 mL)(-1) in surface runoff after injection in October 1998. Slurry injection should be favored when spreading slurry amendments to grassland to avoid losses of P and fecal microorganisms in runoff to surface waters.

Antibacterial behavior of silver-modified clinoptilolite-heulandite rich tuff on coliform microorganisms from wastewater in a column system

The water disinfecting behavior of silver-modified clinoptilolite-heulandite rich tuff (ZSAg) as an antibacterial agent against coliform microorganisms from water in a continuous mode was investigated. Silver recovery from the disinfected effluents by the sodium-modified clinoptilolite-heulandite rich tuff (ZSNa) was also considered. Escherichia coli (ATCC 8739) and total coliform microorganisms, as indicators of microbiological contamination of water, were chosen to achieve the disinfection of synthetic wastewater or municipal wastewater. Ammonium (NH(4)(+)) and chloride (Cl(-)) ions were added to the synthetic wastewater as an interfering chemical species on the disinfection processes. The antibacterial activity of the ZSAg as a bactericide was measured by the coliform concentration as evaluated by the APHA method. The amount of silver in the disinfected effluents was determined using atomic absorption spectroscopy. The inactivation of the ZSAg was calculated from the breakthrough curves based on the model reported by Gupta et al. It was found that when the silver concentration in the effluent is less than 0.6 microg/mL, the bacterial survival percentage increased and the volume of disinfected water diminished. The total silver amounts found in the effluent at the end of the disinfection processes varied depending on the water treated (synthetic or municipal wastewater). The presence of NH(4)(+) ions in synthetic wastewater influent notably improved the disinfected water volume (zero NVC/100mL), in comparison to the disinfection of the same influent without NH(4)(+) ions. A contrary water disinfection behavior was observed in the presence of Cl(-) ions. The silver recovery does not depend on the mass of the sodium zeolitic bed according with the wastewater to be treated (synthetic or municipal wastewater) and the presence of NH(4)(+) or Cl(-) ions in the influent also influenced the silver recovery from wastewater. The ZSNa did not have antibacterial activity. Therefore the amount of bactericide agent (silver-modified natural zeolite), coliform microorganisms from water (E. coli or consort of coliform microorganisms) as well as the water quality (synthetic wastewater or municipal wastewater) influenced both the disinfection process and the silver recovery in a column system.

Efficient disinfection of Escherichia coli in water by silver loaded alumina

The catalytic inactivation of Escherichia coli (E. coli) in water by silver loaded alumina as catalyst was investigated. Ag/Al(2)O(3) and AgCl/Al(2)O(3) catalysts exhibited high bactericidal activity at room temperature in water with no need for any light or electrical power input. Dissolved oxygen which can be catalyzed to reactive oxygen species (ROS) was found to be essential for the strong bactericidal activities of the catalysts. Decomposition of the cell wall leading to leakage of the intracellular component and the complete lysis of the whole cell were directly observed by transmission electron microscopy (TEM). The resultant change in cell permeability was confirmed by potassium ion leakage. The different morphological changes between E. coli cells treated with the catalysts and Ag(+) were also observed. The formation of ROS involved in the bactericidal process by AgCl/Al(2)O(3) was confirmed by addition of catalase and ()OH scavenger. Higher temperature and pH value were found to have positive effect on the bactericidal activity of AgCl/Al(2)O(3). All these results indicated that the bactericidal effect of the catalyst was a synergic action of ROS and Ag(+), not an additive one. A possible mechanism is proposed.

Inactivation of MS2 F(+) coliphage on lettuce by a combination of UV light and hydrogen peroxide

The efficacy of a produce decontamination method based on a combination of UV light (254 nm) and hydrogen peroxide (H2O2) to inactivate the MS2 F(+) coliphage inoculated onto iceberg lettuce was evaluated. Lettuce inoculated with 6.57 log PFU of MS2 was reduced by 0.5 to 1.0 log unit when illuminated with UV light alone for 20 to 60 s (12.64 to 18.96 mJ/cm2). In contrast, a 3-log reduction in MS2 was achieved with 2% (vol/vol) H2O2 spray delivered at 50 degrees C. No significant increase in log count reduction (LCR) was observed when H2O2 and UV light were applied simultaneously. However, H2O2 sprayed onto lettuce samples for 10 s, followed by a further 20-s UV illumination, resulted in an LCR of 4.12 that compares with the 1.67 obtained with 200 ppm of calcium hypochlorite wash. No further increase in MS2 inactivation was achieved by the use of either longer H2O2 spray or UV illumination times. The extent of MS2 reduction was significantly (P < 0.05) decreased when the H2O2 spray was delivered at 10 or 25 degrees C compared with 50 degrees C. In the course of aerobic storage at 4 degrees C, lettuce treated with UV light and H2O2 (10 or 25 degrees C) developed discoloration (polyphenol accumulation) within 6 days. In contrast, lettuce treated with UV light and H2O2 at 50 degrees C developed less discoloration within this time period and was comparable to untreated controls. This study demonstrated that the combination of UV light and H2O2 represents an alternative to hypochlorite-based washes to reduce the carriage of viruses on fresh produce.

Sequential UV- and chlorine-based disinfection to mitigate Escherichia coli in drinking water biofilms

This study was designed to examine the potential downstream benefits of sequential disinfection to control the persistence of Escherichia coli under conditions relevant to drinking water distribution systems. Eight annular reactors (four polycarbonate and four cast iron) were setup in parallel to address various factors that could influence biofilm growth in distribution systems. Eight reactors were treated with chlorine, chlorine dioxide and monochloramine alone or in combination with UV to examine the effects on Escherichia coli growth and persistence in both the effluent and biofilm. In general, UV-treated systems in combination with chlorine or chlorine dioxide and monochloramine achieved greater log reductions in both effluent and biofilm than systems treated with chlorine-based disinfectants alone. However, during UV-low chlorine disinfection, E. coli was found to persist at low levels, suggesting that the UV treatment had instigated an adaptive mutation. During UV-chlorine-dioxide treatment, the E. coli that was initially below the detection limit reappeared during a low level of disinfection (0.2 mg/L) in the cast iron systems. Chloramine was shown to be effective in disinfecting suspended E. coli in the effluent but was unable to reduce biofilm counts to below the detection limit. Issues such as repair mechanism of E. coli and nitrification could help explain some of these aberrations. Improved understanding of the ability of chlorine-based disinfectant in combination with UV to provide sufficient disinfection will ultimately effect in improved management and safety of drinking water.

Inactivation of human pathogens and spoilage bacteria on the surface and internalized within fresh produce by using a combination of ultraviolet light and hydrogen peroxide

AIMS

To evaluate the efficacy of ultraviolet (UV) light (254 nm) combined with hydrogen peroxide (H(2)O(2)) to inactivate bacteria on and within fresh produce.

METHODS AND RESULTS

The produce was steep inoculated in bacterial cell suspension followed by vacuum infiltration. The inoculated samples were sprayed with H(2)O(2) under constant UV illumination. The log count reduction (LCR) of Salmonella on and within lettuce was dependent on the H(2)O(2) concentration, temperature and treatment time with UV intensity being less significant. By using the optimized parameters (1.5% H(2)O(2) at 50 degrees C, UV dose of 37.8 mJ cm(-2)), the surface Salmonella were reduced by 4.12 +/- 0.45 and internal counts by 2.84 +/- 0.34 log CFU, which was significantly higher compared with H(2)O(2) or UV alone. Higher LCR of Escherichia coli O157:H7, Pectobacterium carotovora, Pseudomonas fluorescens and Salmonella were achieved on leafy vegetables compared with produce, such as cauliflower. In all cases, the surface LCR were significantly higher compared with the samples treated with 200 ppm hypochlorite. UV-H(2)O(2)-treated lettuce did not develop brown discolouration during storage but growth of residual survivors occurred with samples held at 25 degrees C.

CONCLUSIONS

UV-H(2)O(2) reduce the bacterial populations on and within fresh produce without affecting the shelf-life stability.

SIGNIFICANCE OF THE STUDY

UV-H(2)O(2) represent an alternative to hypochlorite washes to decontaminate fresh produce.

Bactericidal activity of a Ce-promoted Ag/AlPO4 catalyst using molecular oxygen in water

The catalytic inactivation of Escherichia coli in water by a cerium (Ce)-promoted silver-loaded aluminum phosphate (Ag/ AlPO4) catalyst using molecular oxygen was investigated. With optimum Ce content, the Ag(Ce)/AlPO4 catalyst exhibited strong bactericidal activity. The process of decomposition of the cell wall and cell membrane was directly observed by TEM. The different morphological changes of E. coli cells treated with the Ag(Ce)/AlPO4 catalyst and those treated with Ag+ suggested that the Ag+ eluted from the catalyst surface did not play an important role during the bactericidal process. Results of DMPO spin-trapping measurements by electron spin resonance (ESR) indicated the formation of the reactive oxygen species (ROS) *OH and *O2-, which caused the considerable bactericidal activity. The formation of H2O2 acted as an important intermediate; this was confirmed by addition of catalase as the scavenger. A possible catalytic oxidation bactericidal mechanism using molecular oxygen was proposed for the Ag(Ce)/AlPO4 catalyst.

Synergistic effect of sequential or combined use of ozone and UV radiation for the disinfection of Bacillus subtilis spores

This study was performed to evaluate the inactivation efficiency or synergy of combined ozone and UV processes (combined ozone/UV process) or sequential processes (ozone-UV, UV-ozone) compared with individual unit processes and to investigate the specific roles of ozone, UV and the hydroxyl radical, which is formed as an intermediate in the combined ozone/UV process. The Bacillus subtilis spore, which has often been used as a surrogate microorganism for Cryptosporidium parvum oocysts, was used as a target microorganism. Compared to individual unit processes with ozone or UV, the inactivation of B. subtilis spores by the combined ozone/UV process was enhanced under identical conditions. To investigate the specific roles of ozone and UV in the combined ozone/UV process, sequential ozone-UV and UV-ozone processes were tested for degrees of inactivation. Additionally, the experiment was performed in the presence and absence of tert-butyl alcohol, which acted as a hydroxyl radical scavenger to assess the role of inactivation by the hydroxyl radical in the combined ozone/UV process. Among the five candidate processes, the greatest synergistic effect was observed in the combined ozone/UV process. From the comparison of five candidate processes, the hydroxyl radical and ozone were each determined to significantly enhance the overall inactivation efficiency in the combined ozone/UV process.

Faecal indicator organism concentrations in sewage and treated effluents

The importance of faecal indicator organism (FIO) fluxes within drainage basins is increasing as the European Union (EU) Water Framework Directive and the United States Clean Water Act place requirements on regulators to manage point and diffuse sources of microbial pollution causing non-compliance (EU) or impairment (US) of receiving waters. Central to this management task is knowledge of the likely FIO concentrations in raw sewage and treated effluents, but few empirical data have been published in the peer-reviewed literature. Accordingly, this paper presents results for 1933 samples from 162 different sewage discharge sites in the UK and Jersey, which encompass 12 types of sewage-related discharge, representative of untreated sewage and primary-, secondary- and tertiary-treated effluents. Geometric means (GMs) and 95% confidence intervals (CIs) have been used to characterise base- and high-flow FIO concentrations. The data sets and sub-sets are mostly quite large (n 40) and may therefore be applied with some confidence to comparable discharge sites in similar geographical regions. Very marked, statistically significant reductions in GM FIO concentrations result from secondary and tertiary treatment, and there are statistically significant differences between some secondary and some tertiary treatments. Flow conditions are also shown to be important: untreated sewage and effluent from primary treatment plant have lower concentrations at high flow, due to dilution within combined sewerage systems, whereas some treated effluents (e.g. from activated sludge plant) have higher concentrations at high flow because of the shorter residence time within the plant. Under base-flow conditions, secondary treatments result in estimated GM FIO reductions of 95.22-99.29% (cf. primary-treated effluent). Corresponding figures for tertiary treatment plants (cf. secondary-treated effluent) are 93.24-96.59% for reedbed/grass plots and 99.71-99.92% for UV disinfection. Results suggest that secondary and tertiary treatment plants are less effective under high-flow conditions, but further high-flow sampling is required to confirm this.

The inactivation and removal of airborne Bacillus atrophaeus endospores from air circulation systems using UVC and HEPA filters

AIMS

To (i) evaluate the UV radiation in the 'C' band/high efficient particulate air (UVC/HEPA) instrument's potential to inactivate spores of Bacillus atrophaeus and selected Bacillus species and (ii) test whether a titanium dioxide coating inside the cylindrical HEPA filter improves the system's efficacy.

METHODS AND RESULTS

Known amounts of dried spore preparations of B. atrophaeus, Bacillus cereus, Bacillus megaterium, Bacillus stearothermophilus and Bacillus thuringiensis were exposed to the UVC lamp within a cylindrical HEPA filter for different time lengths (30 min to 48 h) and with different air flow speeds (0-235 l s(-1)). The log(10) reduction (range 5-16 logs) of colony forming units for spores exposed to the UVC compared with the unexposed spores was significant (P < 0.0001). The addition of a titanium dioxide (TiO(2)) veneer to the interior surface of the HEPA filter significantly increased the inactivation of spores (P < 0.0001).

CONCLUSIONS

The UVC/HEPA unit could inactivate spores of B. atrophaeus, B. cereus, B. megaterium, B. stearothermophilus and B. thuringiensis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The UVC/HEPA unit represents an effective method of decontaminating circulating air within an air-duct system as found in a building.

Reduction of photoreactivation with the combined UV/peracetic acid process or by delayed exposure to visible light

Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, phenomenon. It is affected by several factors, including UV fluence, wavelength, light intensity, and exposure time to photoreactivating light. The effect on photoreactivation of a combined peracetic acid (PAA)/UV process has not been investigated. Accordingly, this study compared the degree of photoreactivation, under both sunlight and artificial lights, following UV and combined PAA/UV inactivation of fecal coliforms. Effluent samples from the Montreal Wastewater Treatment Plant (MWTP) (Quebec, Canada) were exposed, for 3 hours, to both low- and high-intensity artificial lights and sunlight. All resulted in similar photoreactivation levels. However, average photoreactivation for UV-treated wastewater samples was 1.2 logs, compared with 0.1 log for the combined PAA/UV treatment. Hence, the use of PAA in combination with UV can significantly reduce the potential for photoreactivation. To simulate the photoreactivation conditions of the MWTP effluent (which passes through a 4-km outfall tunnel with approximately 3 hours detention time), UV-treated samples were kept in the dark for 3 hours before photoreactivating light exposure. After this period, photoreactivation levels were close to zero. Hence, the effects of photoreactivation may be diminished by use of a combined disinfection scheme and/or by delaying exposure of the disinfected wastewater to light.

Depuration dynamics of oysters (Crassostrea gigas) artificially contaminated by Salmonella enterica serovar Typhimurium

The State of Santa Catarina produces the greatest quantity of edible mollusks in Brazil. To guarantee sanitary qualify, mollusk cultures should be monitored for contamination by pathogenic microorganisms. A self-purification or "depuration" system that eliminates Salmonella enterica serovar Typhimurium contamination from oysters has been developed and evaluated. The depuration process occurred within a closed system, in which 1000 L of water was recirculated for 24 h. The water was sterilized with ultraviolet (UV) light, chlorine, or both together. Oysters (Crassostrea gigas) artificially contaminated with S. typhimurium were harvested every 6 h. Samples of oyster tissue were excised and both the presence and numbers of bacteria were determined. Combined UV light and chlorine treatments resulted in total elimination of bacteria within 12 h. Polymerase chain reaction detected bacteria in water exposed to the three treatments. This pioneering study is the first of its kind in Brazil and represents a major contribution to commercial mollusk culture in this country.

A field study evaluation for mitigating biofouling with chlorine dioxide or chlorine integrated with UV disinfection

The drinking water industry is continually seeking innovative disinfection strategies to control biofouling in transmission systems. This research, conducted in collaboration with the East Bay Municipal Utility District (EBMUD) in California, compared the efficacy of chlorine dioxide (ClO2) to free chlorine (Cl2) with and without pre-treatment with low-pressure ultraviolet (UV) light for biofilm control. An additional goal was to determine disinfection by-product (DBP) formation with each disinfection strategy. Annular reactors (ARs) containing polycarbonate coupons were used to simulate EBMUD's 90-mile aqueduct that transports surface water from a source reservoir to treatment facilities. ARs were dosed with chemical disinfectants to achieve a residual of 0.2 mg/L, which is a typical value mid-way in the aqueduct. The experiment matrix included four strategies of disinfection including UV/ClO2, ClO2, UV/Cl2 and Cl2. Two ARs acted as controls and received raw water (RW) or UV-treated water. The data presented show that the UV/ClO2 combination was most effective against suspended and attached heterotrophic (heterotrophic plate count, HPC) bacteria with 3.93 log and 2.05 log reductions, respectively. ClO2 was more effective than Cl2 at removing suspended HPC bacteria and similarly effective in biofilm bacterial removal. UV light alone was not effective in controlling suspended or biofilm bacteria compared to treatment with ClO2 or Cl2. Pre-treatment with UV was more effective overall for removal of HPC bacteria than treating with corresponding chemical disinfectants only; however, it did not lower required chemical dosages. Therefore, no significant differences were observed in DBP concentrations between ARs pre-treated with UV light and ARs not pre-treated. Disinfection with ClO2 produced fewer total trihalomethanes (TTHMs) and haloacetic acids (HAAs) than chlorination but did produce low levels of chlorite. These data indicate that replacing Cl2 with ClO2 would further control microbiological re-growth and minimize TTHM and HAA formation, but may introduce other DBPs.

Efficiency of the UV/H2O2 process for the disinfection of humic surface waters

The efficiency of the UV/H2O2 process for the disinfection of total coliforms and the prevention of bacterial regrowth in humic surface waters were investigated. Inactivation of total coliforms was determined in water samples containing various concentrations ranging from 0-10 mg/L dissolved organic carbon (DOC) of fulvic acid, which were exposed to various doses (68-681 mWs/cm2) of UV radiation in the presence of 0.125 mg/L and 3.000 mg/L of hydrogen peroxide. Disinfection efficiencies of the UV radiation and the UV/H2O2 processes were compared. The results of bacterial inactivation experiments showed that the performances of the UV and the UV/H2O2 (0.125) were comparable whereas the UV/H2O2 (3.000) process showed significant improvement in performance, especially, in highly humic waters. Inactivation coefficient appeared to be almost doubled by the addition of 3.000 mg/L hydrogen peroxide during the treatment of highly humic waters. In contradiction to significant regrowth which occurred in the single UV radiation treatment, residual bacteria following the UV/H2O2 (0.125) and the UV/H2O2 (3.000) treatments were completely inactivated during dark incubation indicating the elimination of possible bacterial regrowth.