A Review on Pulsed Light Technologies in Water Treatment

A REVIEW ON PULSED LIGHT TECHNOLOGIES IN WATER TREATMENT Rajat Nag (15202684), Michelle Savian (15203989) and Mayukh Bhattacharjee (15202910) School of Biosystems and Food Engineering, University College Dublin, Belfield, Dublin 4, Ireland. Abstract Pulsed light technology consists of successive repetitions of short duration (325 ms) high power flashes emitted by xenon lamps. These flash lamps radiate a broadband emission light (approx. 200 to 1000 nm), with a considerable amount of this light being in the shortwave UV spectrum. PL technology´s main use in water treatment has been in the inactivation of pathogens (Bohrerova et al., 2008). The presence of parasitic species such as Cryptosporidium and Giardia in water supplies causes gastrointestinal illness such as diarrhoea, vomiting, and cramps. The EPA Maximum Contaminant Level Goal (MCLG) for these parasites are zero. Hence water disinfection has been a common practice without any country limitations. Chlorination cannot prevent Cryptosporidium and Giardia, whereas UV treatment has proven effective at causing cell death in numerous microbial species. However, it does have its limitations, such as depth of- water penetration, presence of contaminants and the repair mechanisms organisms possess to fix UV damage. New methods of delivering UV light to the treatment area – such as pulsed UV (PUV) – have been developed which may eliminate these issues. Consequently, the aim of this study was to review if a PUV system provides a suitable means of disinfecting water, with particular emphasis on parasite species. Introduction Cryptosporidiosis is a diarrheal disease caused by the parasite Cryptosporidium which resides in the intestines of humans and animals and is passed in the stool of the infected host. The parasite is protected by an outer shell that allows it to survive outside the body for extended lengths of time in extreme temperatures and also makes it very resistant to chlorine-based disinfectants. At present, there are 26 known species of Cryptosporidium which can infect a wide range of animals and humans. Of the 26 species, 20 are known to have the capability to infect humans (Ryan et al., 2014). Giardia lamblia is a flagellated protozoan parasite which causes the highly infectious disease state known as ‘giardiasis’ in host individuals. This problematic parasite is frequently associated with gastrointestinal infection in both developed and developing countries: routes of transmission include the consumption of contaminated food and water, person-to-person and often animal-to-person transmission via the faecal oral route. As with parasites such as Cryptosporidium, the removal of Giardia from water supplies has proven problematic due to its resistance to current water-disinfection methods and the low number of cysts required for infection to occur. The previous experiments allow standardization of setups between different research centres and might also be the basis for further optimization works of PL. According to Roberts and Hope (2003), the ability of UV light to inactivate cellular microorganisms and viruses is well known, however such systems have only found limited practical application in the pharmaceutical industry. There has been no study prior to Vimont et al. (2015) and Uslu et al. (2015) on pulsed UV disinfection for wastewater-treatment systems. Therefore, the research reported in this paper was undertaken to evaluate the efficacy of pulsed UV treatment for decontamination of synthetic municipal wastewater effluents (SMWEs) and real municipal wastewater effluents (RMWEs), by determining inactivation profiles of E. coli and B. The aim of the present work was to review pulsed light technology for inactivation of parasites in sewage treatment effluent and drinking water, including its limitations and potential advantages. Materials and Methods Pulsed light (PL) technology consists of discharges of high power electrical pulses in a rare gas (e.g. xenon or krypton) flash lamp to produce intense light pulses. Even though the peak power of each pulse is high, the total pulse energy, compared to that obtained by continuous radiation, is relatively low because of its short duration (Dunn et al., 1995). The duration of each pulse generally ranges between 50 and 3000 micro seconds. Contrary to low or high pressure mercury lamps, where light is mainly emitted at wavelengths close to 254 nm and 365 nm respectively, the pulsed light technology provides a broadband emission light (approx. 200 to1100 nm) with a considerable amount of light in the short-wave UV spectrum. About 20% of the emitted light corresponds to the UV-C, 8% to the UV-B and 12% to the UV-A region (Wekhof, 2000). Furthermore, the UV irradiance of flash lamps are about three or four orders of magnitude higher than standard mercury lamps (Schaefer et al., 2007). Apart from this, the pulsed light technology overcomes the disadvantages of the presence of mercury in traditional UV processes which is of environmental concern. There is a numbers of traces have been found regarding pesticides in Baranda et al. (2012). To evaluate the presence and evolution over time of this herbicide, as well as the formation of derivatives, a liquid chromatography-mass spectrometry (electro spray ionization) ion trap operating in positive mode was used. The degradation process followed first-order kinetics. Fluences of about1.8e2.3 J/cm2 induced a 50% reduction of atrazine concentration independently of its initial concentration in the range 1e1000 mg/L. Remaining concentrations of atrazine, below the current legal limit for pesticides, and were achieved in a short period of time. While atrazine was degraded, no chlorinated photoproducts were formed and ten de-halogenated derivatives were detected. Pulsed light treatments were performed using an SBSXeMatic- 2L-A device (SteriBeam Systems GmbH, Kehl, Germany). For the emission of a single light pulse, the electric power is stored in an energy storage capacitor and later quickly released to a xenon lamp, which then emits a high intensity light pulse of 325 ms duration. The emitted light spectrum includes wavelengths from 200 to 1000 nm, with a considerable amount of light (approximately 40%) in the UV range. Woodling and Moraru (2005) investigated the effect of container material (stainless steel) surfaces in PUV technology. Four types of stainless-steel surfaces were inoculated with Listeria innocua and treated with up to 12 pulses of light. The PL treatments were performed using a RS-3000C SteriPulse System (Xenon Corp., Woburn, Mass., U.S.A.). The system consists of a controller unit and a treatment chamber that houses a Xenon flash lamp capable of delivering a radiant energy of 1.27 J/cm2 at 0.76 in (1.93 cm) from the quartz face of the lamp housing. Each inoculated and dried coupon was centered individually on an adjustable stainless-steel shelf in the PL unit at 2 in (5.08 cm) beneath the Xenon lamp and treated with 1 to 12 pulses. All PL experiments were performed at least in triplicate. Pure Bright® unit was run at the manufacturer's recommended flow rate of 15.14 l/min (4 gal/min) as described in Huffman et al. (2000). Each microbial challenge consisted of 75.7 l of influent water containing 105 CFU/ml of Klebsiella, 104 PFU/ml of polio and rotavirus and 104 oocysts/ml of Cryptosporidium. Influent and effluent samples were collected and assayed using standard methods for the detection of viable bacteria (membrane filtration) and viruses (cell culture).The PureBright system (PurePulse Technologies, Inc., San Diego, CA) was evaluated using a modification of the EPA Guide Standard and Protocol. Roberts and Hope (2003) did a similar experiment with viruses. The inactivation of a range of viruses using varying doses of high intensity broad spectrum white light was investigated using a small-scale laboratory system. A number of resistant non-enveloped viruses were included as such agents have proven particularly difficult to remove or inactivate in therapeutic biological products. In order to investigate the effect of the presence of protein on virus inactivation, studies were conducted in both the absence and presence of foetal-calf serum (FCS). A range of enveloped virus type 1(HSV-1) and non-enveloped viruses, i.e encephalomyocarditis (EMC), polio virus type1, hepatitis A(HAV), bovine parvovirus(BPV) and canine parvovirus(CPV) were used. Viruses were diluted in phosphate buffered saline (PBS). The protein concentration of the serum containing solutions was determined by the Biorad-dye-binding method using BSA as a standard. Samples to be treated were placed in small plastic sample dishes. The intensity was adjusted by varying the distance of the sample from the lamp. The total fluence received by each sample was calculated by multiplying the fluence per flash by the number of flashes. Virus ineffectivity before and after treatment was determined by plaque assay on BHK-21 cells, vero cells and BSC cells. Virus titre was calculated from sample dilution, assay volume and plaque number. Where viruses were undetectable, the titre was calculated using 1 plaque. Vimont and Jean (2015) and Uslu et al. (2015) did research on the application of pulse light in waste water. Vimount (2015) worked with viruses whereas Uslu (2015) mentioned the microorganisms Escherichia coli (K12) and Bacillus subtilis [American Type Culture Collection (ATCC) 6633] as model vegetative and spore-forming microorganisms present in wastewater. E. coli was obtained from the Penn State Food Science Culture Collection (University Park, Pennsylvania) and B. subtilis was obtained from the American Type Culture Collection (Manassas,Virginia). Pulsed UV-light treatment was carried out with a laboratory scale, batch pulsed UV-light sterilization system (SteriPulse-XL 3000, Xenon Corporation, Woburn, Massachusetts). The system generated 5.6 J=cm2 per pulse on the strobe surface at an input voltage of 3,800 V, with 3 pulses and 360-μs duration per pulse. The pulsed UV system uses a xenon lamp, which delivers broadband light ranging from UV to infrared (100– 1,100 nm). A blower is used to cool down the strobe, but cooling air does not reach the treatment chamber due to the quartz window below the strobe. The distance between the center axis of the UV lamp and the quartz window was 5.8 cm. Volumes of 15, 30, and 45 mL in SMWE were treated under pulsed UV light for 5, 10, and 15 seconds for E. coli, and 5, 10, 15, and 25 seconds for B. subtilis according to the surface response design. The samples were placed inside the sterilization chamber in sterile aluminum dishes with vertical walls (7-cm diameter × 1.6-cm depth) at three sample distances from the quartz window, as follows: (1) 8 cm, (2) 11 cm, and (3) 13 cm. Area of application PL technology has been used for the elimination of microbiological hazards in foods and food-related items and its main use in water has been the inactivation of pathogens. However, chemical pollutants that absorb UV light could also be considered, due to the characteristics of the technology (broadband emission light with high UV content). Table 1 shows the area of main focus of the researchers over the last ten years. However there is a lot of research work being done on the same topic. Table 1: The list of application area of Pulse Light Technology and reference works Area of interest Degradation of the herbicide atrazine in water Surface properties of containers, particularly topography, influence the microbicidal effect of PL. A novel point-of-use device that utilizes pulsed white light to evaluate Microbial Water Purifiers. How atrazine may be photo degraded by PL technology The different amounts of light received by L. innocua cells when treated with direct or reflected light could explain the aforementioned results. Pathogen removal from waste water Name of the literature Baranda et al. (2012) Woodling and Moraru (2005) Huffman et al. (2000) Baranda et al. (2014) Lasagabaster and Martínez de Marañón (2013) Vimont and Jean (2015) Uslu et al. (2015) Findings Previously published UV inactivation studies by Chang et al. (1985 cited Huffman et al., 2000) have reported that 3.0 mJ/cm2 will achieve a 3 log10 inactivation of E. coli, while an in- activation of 3 log 10 of viruses (polio or rota) required an increased dosage of approximately 21± 29 mJ/cm2, researched by Chang et al., 1985 and Harris et al., 1987(cited Huffman et al., 2000). MS-2 bacteriophage was shown to be significantly more resistant than other viruses to UV disinfection, requiring 64±93 mJ/cm2, reported by Sobsey, 1989 and Wie-denmann et al., 1993 (cited Huffman et al., 2000) for a 4 log10 inactivation. A more recent study has reported, Clancy at al. (1998, cited Huffman et al., 2000) that a dose of 1900 mJ/cm2 from a pulsed UV source (broad spectrum) was required to provide a 2 log10 inactivation of Cryptosporidium parvum as determined by vital dye staining. The same study found that low pressure mercury systems required a dose of 4380 mJ/cm2 for a >4.0 log10 inactivation of Cryptosporidium as determined by animal infectivity. Meanwhile a 3.9 log10 inactivation of Cryptosporidium at a dose of 19 mJ/cm2 and a >4.5 log inactivation at 66 mJ/cm2 were achieved, by Bukkari et al. (1999 cited Huffman et al, 2000), using a medium pressure mercury system. The new proposed decontamination technology was evaluated for its degradation effectiveness as well as for the generation of photoproducts, Baranda et al. (2014). The degradation process followed firstorder kinetics for all studied compounds except for parathion. Fluences about 4.65 J/cm2 induced a 50% reduction of simazine, atrazine,phosmet, azinphos ethyl and pirimiphos-ethyl, regardless of whether these compounds were PL treated separately or mixed in an aqueous solution. A higher fluence (9.81 J/cm2) was needed to induce a 50% reduction of chlorpyrifos-ethyl, it being more difficult to degrade in the presence of other pesticides in the same solution. Roberts and Hope (2003) found the inactivation of CPV, a virus known to be highly resistant to many physical-chemical inactivation methods, was relatively susceptible to inactivation using PureBrith treatment. . Inactivation was evaluated in several different types of solutions and was tested over a wide range of total fluences. CPV was even more resistant to inactivation in the complete cell culture medium required for effective virus inactivation. This inhibition of virus inactivation was presumably caused by light absorption by the phenol red in the medium. Due to this effect, cell-culture medium was not evaluated further. Inactivation ranged from 3.1 to 3.8 log (0.25 J/cm²) or 3.2 to 4.1 log (1.0 J/cm²) in the absence or presence of protein, respectively. Susceptibility to inactivation was thus very similar in this highly related group of viruses. The results depicted in Uslu et al. (2015) showed that pulsed UV light is highly effective in reducing the viable microorganism concentration in municipal wastewater effluent by the complete inactivation of E. coli and B. subtilis after 15 s of treatment time. B. subtilis had higher resistance than E. coli to inactivation by pulsed UV-light treatment because complete inactivation was achieved after a 25-s pulsed UV treatment(Fig. 1) whereas Vimont and Jean (2015) suggested that pulsed light would be effective for decontaminating effluent from primary sewage treatment. Because of the speed with which it acts, this technology offers several advantages over continuous UV treatment. It could be used to deal with contamination issues, including contamination of shellfish by municipal sewage released into marine product growing areas and contamination of vegetables by irrigation. Fig. 1: Survival-time profiles of E. coli and B. subtilis spores in real wastewater, and total bacterial counts in raw wastewater pulsed UV treatment, at 8 cm. Reference: Uslu et al. (2015) According to Lasagabaster and Martínez de Marañón (2013), the effect of few process parameters, such as the pulse energy, the number of light pulses or the treatment time, have been evaluated in water or buffer systems (Gashemi et al. 2003; Lee et al. 2008). The impact of other PL process parameters affecting the exposure of microorganisms to light (such as the pulse fluence, total fluence, etc.) should be evaluated in order to optimize water disinfection effectiveness by PL. L. innocua inactivation increased with the number of pulses, particularly when the pulse energy was set at 300 J. Inactivation efficiency also rose when increasing the pulse energy from 300 J to 600 J, requiring fewer pulses to cause the same reduction in L. innocua counts. The inactivation curve obtained applying pulses of 300 J was typically sigmoidal. A PL antimicrobial effect has been mainly attributed to DNA damage caused by its high content in UV wavelengths. Differences in the UV light emission spectrum (e.g., proportion of light emitted in the UV-C, UVB and UV-A ranges) amongst the PL devices used in the different studies could explain the presence/absence of a shoulder. Moreover, the lack of efficient cooling systems during PL treatments could also contribute to the absence of this shoulder, since a photo-thermal antimicrobial effect has also been suggested after intense PL treatments. Opportunities and further research The development of this alternative is timely, because the incidence of norovirus illness remains unacceptably high, and its prevention constitutes a superior approach compared to the costs and consequences of treating infections, Vimont and Jean (2015). There is still a need to validate the efficacy of pulsed UV technology for flow-through continuous pulsed UV-light treatment as a future study, Uslu et al. (2015). In contrast Baranda et al. (2014) suggests PL as an environmental friendly water treatment because PL technology (xenon flash lamp) is a mercury free system. However, further studies should be developed to improve the PL efficiency to degrade the most resistant compounds such as methyl-parathion, and evaluate the impact of water characteristics on the efficiency of PL treatment. It is perfectly possible that heating effects at the cell level during the very short duration of the treatment might have been significant and therefore contributed to their death. This hypothesis has yet to be verified and warrants further investigation. To date, there have been few published studies documenting the efficiency of POU devices to remove or inactivate pathogenic micro-organisms using the EPA's (Environmental Protection Agency) GS&P (Guide Standard and Protocol). Conclusion The pulsed light degradation process of atrazine is fast, inducing more than 99% of the pesticide degradation in a very short period of exposure time (milliseconds).It is a Mercury Free system. The reduction in L. innocua counts increases with total fluence, showing sigmoidal inactivation curves. Total fluence, or amount of photons striking on the sample, is the most relevant process factor affecting microbial inactivation. Therefore, it should be reported when describing the conditions established for PL processing, Lasagabaster and Martínez de Marañón (2013). The results described in Woodling and Moraru (2005) demonstrate that PL can be effective on both smooth and rough surfaces, but also indicate a complex effect of various surface properties on inactivation. Viable Cryptosporidium oocysts were determined using vital dyes, excystation, cell culture and animal infectivity. The PureBright unit was able to achieve a >7 log10 inactivation of Klebsiella, a >4 log10 inactivation of polio and rotavirus and a >4 log10 inactivation of ryptosporidium parvum, using relatively good quality influent water, Huffman et al. (2000). Much work needs to be completed regarding the determination of UV dosage, the endings of this study suggest that the PureBright unit may be an attractive option for treatment of water supplies that may be microbiologically contaminated. The range of listed viruses that could be inactivated by PureBright treatment included several that are known to have a generally higher resistance to at least some physicochemical inactivation methods. HAV has been transmitted by some factor VIII products. Thus this application treatment may have potential application for virus inactivation in therapeutic biological products such as those derived from genetically engineered cells or human plasma, Roberts and Hope (2003). Although new reactors should be designed to treat large volumes of water, obtained experimental data would open up new possibilities to apply this technology (e.g. different groups of pesticides could be degraded in water used for post-harvest processes). Studies show that pulsed light under the specific required conditions allowed by the FDA is effective at inactivating MNV-1, Vermont and Jean (2015). Since the process is rapid, environmentally friendly, and active against a broad range of microorganisms, including bacteria, yeasts, and enteric viruses, its application to the disinfection of drinking water, clear beverages, food contact surfaces, and even biofilms and sewage treatment effluent should be possible, provided that agents that interfere with light transmission, particularly proteins, are taken into account and investigated. References Baranda, A. B., Barranco, A. and de Marañón, I. M. (2012) 'Fast atrazine photodegradation in water by pulsed light technology', Water Research, 46(3), 669-678. Baranda, A. B., Fundazuri, O. and de Maranon, I. M. (2014) 'Photodegradation of several triazidic and organophosphorus pesticides in water by pulsed light technology', JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 286, 29-39. Garvey, M., Hayes, J., Clifford, E. and Rowan, N. (2015) 'Ecotoxicological assessment of pulsed ultraviolet light‐treated water containing microbial species and Cryptosporidium parvum using a microbiotest test battery', Water and Environment Journal, 29(1), 27-35. Huffman, D. E., Slifko, T. R., Salisbury, K. and Rose, J. B. (2000) 'Inactivation of bacteria, virus and Cryptosporidium by a point-of-use device using pulsed broad spectrum white light', Water Research, 34(9), 2491-2498. Lasagabaster, A. and Martínez de Marañón, I. (2013) 'Impact of Process Parameters on Listeria innocua Inactivation Kinetics by Pulsed Light Technology', Food and Bioprocess Technology, 6(7), 1828-1836. Roberts, P. and Hope, A. (2003) 'Virus inactivation by high intensity broad spectrum pulsed light', Journal of Virological Methods, 110(1), 61-65. Sun, B., Kunitomo, S. and Igarashi, C. (2006) 'Characteristics of ultraviolet light and radicals formed by pulsed discharge in water', Journal of Physics D: Applied Physics, 39(17), 3814-3820. Uslu, G., Regan, J. M. and Demirci, A. (2015) 'Efficacy of Pulsed UV-Light Treatment on Wastewater Effluent Disinfection and Suspended Solid Reduction', Journal of Environmental Engineering, 141(6), 4014090-1-10. Vimont, A., Fliss, I. and Jean, J. (2015) 'Efficacy and Mechanisms of Murine Norovirus Inhibition by Pulsed-Light Technology', APPLIED AND ENVIRONMENTAL MICROBIOLOGY, 81(8), 2950-2957. Woodling, S. E. and Moraru, C. I. (2005) 'Influence of Surface Topography on the Effectiveness of Pulsed Light Treatment for the Inactivation of Listeria innocua on Stainless‐steel Surfaces', Journal of Food Science, 70(7), m345-m351.