Effects of UV intensity and water turbidity on microbial indicator inactivation

ISSN 1001-0742Journal of Enwironmental Seiences Vol. 18, No. 4, pp.650- 653, 2006CN11- -2629/XArticle D: 101-07420604-0650-04CLC number: X703.1; X125Document code: AEffects of UV intensity and water turbidity on microbial indicatorinactivationLIU Wen-jun", ZHANG Yong-ji(Department of Environmental Science and Engnering, Tsinghua University, Beijing 10084, China. E-mail: wjiliu@tsinghua.edu.cn;zhangyongji@sohu. com)UV disinfection was effective in klling all the selected microbial indicators, the resistance order of the microorganisms was asfllows: MS-2 coliphage > Bacillus subilis > E. coli > Staphylococcus aureus and Candida albicans. UV intensity had influence on theinactivation of all the microorganisms, high UV disinfection eficency was obtained with higher UV intensity. Turbidity had impact onthe bacteria inactivation rate, but there was no evidence that turbidity had any negative contribution to MS-2 coliphage. Under thesame UV dosage, higher UV intensity could overcome the negative influence of turbidity on UV performance, enhanced microorg-anism inactivation effect in turbidity water.Keywords: UV disinfection; intensity; exposure time; microbial indicatorinfluencing UV performance, it may decrease the UVIntroductiontransmitance of the water and afect dose delivery, orDisinfection of drinking water with chlorine hasshield microorganisms from UV light, thus altering thebeen used for more than one hundred years for its lowcharacteristics of the dose response curve. UVcost and effective in killing water born pathogens,intensity and turbidity may have different effects onhowever, the production of trihalomethanes and thUV performance, however, few studies have evaluatedsurvival of chlorine-resistant microorganisms such asthe effects of the two factors influencing UVvirus, cryptosporidium and giardia oocysts areperformance together. In this study， differentobserved under ordinary condition of chlorinationmicrobial indicators were selected for its dose(Singer, 1999; Rodriguez and Drtofrd, 2000; Krasnerresponse to UV irradiation, the influence of irradiateet al., 1989; Alexander et al, 2002; Drescher et al.,intensity and turbidity on the inactivation efficiency2001). Ozone is known to be an effective disinfectantwas examined.for its capability of inactivation chlorine-resistant1 Materials and methodsmicroorganisms, but it will disappear rapidly throughautodecomposition to oxygen, another is that1.1 Low pressure UV irradiation system and ra-hazardous products such as aldehydes may bediometryproduced by the reaction of ozone and organicThe collimated beam apparatus was used for UVmaterials (Driedger et al, 2001; Sohn et al, 2004;disinfection experiment. A 40-W low pressureFacile et al, 2000). Ultraviolet (UV) irradiation is onemercury vapor germicidal lamps emitting mono-of the most practical disinfection methods in waterchromatic UV radiation at 253.7 nm was used in the .treatment because it can inactivate bacteria, viruses,experiment, it was directed through a circular openingbacterial spores and oocysts of protozoa (Frederick,to provide incident radiation perpendicular to the2000; Zhang, 2004; Sommer et al, 1996a). Thesurface of the test suspensions. UV irradiance wasefficiency of UV disinfection in water depends onmeasured with a radiometer and a UV detectormany factors, such as UV dose delivered to the(Beijing Normal University, UV-B). The measuredmicroorganisms, lamp envelope, ageing of lamp,incident irradiance at the surface of the test liquid wasconcentration of suspended solids and the thickness ofcorrected for non homogeneity of irradiation acrossthe fluid (Sommer et al, 1997; Emerick, 2000). UVthe surface area of the Petri dish to provide thedose is defined as the products of UV intensity andaverage incident iradiance. The average iradiance inexposure time as chemical disinfection concentrationthe mixed suspension was determined mathematicallyand time, it was thought that the same dose mayfrom an integration of the Beer-Lambert Law over theproduce the same ffect at different UV intensity, busample depth (effet al., 2003).some research showed that the same dose produced1.2 Turbidity water preparationdifferent results. Sommer et al. (1996a, b) found thatThe synthetic waters had various levels ofUV disinfection did not obey intensity and exposureinor中国煤化工was chosen as thetime rule, higher UV intensity would produce highertendency to swellinactivation effects. Turbidity is another factorYHCNMHGbelievedtobetheFoundation item: The Outstanding Doctoral Dissertation Foundation by China Ministry of Education (No. 200243); *Coresponding authorNo.4Effects ofUV intensity and water turtbidity on microbial indicator inactivation651representative of many natural water turbidity2.1 UV irradiation on microorganism inactiva-particles and a potential worst particle for shielding.tionDifferent amount of kaolin clay was seeded to steriledThe dose response curve for UV irradiation onwater, turbidity was measured with a HANNAdifferent microorganisms at a UV intensity of 0.10turbidity meter, before each use, the turbidity metermW/cm2 was evaluated (Fig.1). MS-2 coliphage andwas calibrated according to the manufacturer'sBacillus subtilis were more resistant than otherinstructions.microorganisms, only 2.4 and 3.1 lg(NJN) reduction1.3 Test organismswas achieved respectively at a UV dose of 40 mJ/cm2,E. coli 1.3373, Bacillus subtilis (ATCC 9372),and MS-2 was more UV resistant than BacillusStaphylococcus aureus (ATCC 6538), Candidasubtilis. Staphylococcus aureus and Candida albicansalbicans (ATCC 10231) were obtained from Micro-were susceptible to UV irradiation and had nearly thebiology School of Chinese Academy of Sciences,same response to UV irradiation, nearly 4.6 ofMS-2 coliphage 15597-B, and its host strain E. colilg(N/N) reduction was achieved at a UV dose of 10(ATCC 15597) was provided by Canadian GAPmJ/cm?. E. coli was more resistant than the other two,Microorganism Company. The growth media and the4 lg(N/!N) reduction was achieve at a UV dose of 10incubation conditions for counting are listed in TablemJ/cm2. In UV disinfection system, a UV dose of 401. Each culture was centrifuged at 6000 r/min for 10mJ/cm2 was applied usually, so it was effectively inmin and the pellet produced was washed 2 times withcontrolling all the microorganisms.sterile distilled water. The washed pellets wereresuspended in 500 ml steriled water (or kaolin clayturbidity water) and diluted to give a viable cell countof approximately 107 cells/ml.Staphylococcus aureusTable 1 Enumeration media and incubation time fo+ Candida albicansmicrobial indicators, MS-2 colip hage甘Bacillus subtilisIncubationMicroorganismEnumeration mediumtime, h5100150E. coliFuchsine sodium sulfte broth24UV dose, mJ/cm2Bacillus subtilis'Nutrient brothFig.1 ffcts of UV rradiation on microbial indicators inactivationUV intensity: 0.10 mW/cm2Staphylococcus aureus Nutrient brothCandida albicans22.2 UV intensity on microorganisms inactivationDifferent microorganisms responded to threeMS-2 coliphage"Tryptone yeast extract brothlevels of UV intensity (0.18, 0.10 and 0.008 mW/cm2)Notes: * Bacilus subtilis were determined after pretreatment for 10 minare listed in Table 2. All the selected microor-in a water bath at 80C; ** MS-2 coliphage was grown in the host strainganisms represented the same tendency to UVE. coli (ATCC 15597)intensity changing, and higher lg(NJ/N) reduction was1.4 Ultraviolet disinfection processachieved at a higher intensity than that of lowerForty millimeter experimental sample was putintensity, such as at a dose of 5 mJ/cm2， theinto 90 mm diameter Petri dish and exposed to UVdifferences in lg(NJN) reduction of E. coli, Staphy-light using the collimated beam apparatus. Dose waslococcus aureus ，Candida albicans between the highestcalculated as that the average incident intensity times(0.18 mW/cm2) intensity and the lowest intensity(0.08exposure time and was regulated by controlling themW/cm?) was 0.54, 1.04 and 0.9, Bac ilus subtilis andexposure time and UV intensity. Three levels of UVMS-2 coliphage followed the same tendency. Thaintensity were selected: 0.18, 0.10 and 0.008 mW/cm?.meant higher UV intensity was necessary for waterReduction of test microorganisms was expressed asdisinfection practice and which was consistent withlg(NJ/N), where N。 and N are the concentrations ofSommer et al. (1996a, b) who found that U\organisms being able to reproduce before and afterdisinfection did not obey intensity and exposure timeirradiation respectively. Control samples without UVruleirradiation were also performed in triplicate and wereThe relationship between UV intensity and doseprocessed as the above. To avoid the phenomenon ofrequired to achieve 2 lg(N/N) reduction of microbialphotoreactivation of microorganisms, assayed andindicators is shown in Table 3. The dose required wasincubated immediately after exposure to UVlarger at lower IJV intensitv compared with that ofirradiation. Repeated experiments were performedhigh中国煤化Iicroorganisms. Thatsuch that replicates were available for mostmeaCNMHGenergy to destroymeasurement point.protcuo oulur UvILIUaulu a nowerUV intensity,2 Resultshigher UV intensity was more important than a longer652LIU Wen-jun et al.Vol.18Table 2 Etects of UV intensity on microbial indicators reductionUV intensity, mW/cm2MicroorganismUV dose, mJ/cm?0.180.100.008Time, slg (N/M)Time,slg (N/N)lg(NJN)E. coli2.542.133751.56283.37503.23625.71564.981004.6612504.5Staphylococcus aureus2.312.11751.553.87.42.835.135.114.51Candida albicans2.41302.211.633.813.32.911(4.934.77Bacillus subtilis2(121.6001.225000.714(243.413.15000.236(374.554.33310000MS-2 coliphage1.511.10.562.842.41.874.113.723.31exposure time for the disinfection system. So when amore than 4 NTU. When turbidity was lower than 4UV disinfection system was designed, higher UVNTU, there was nearly no influence on microorganismintensity and less iradiate time was needed than at theinactivation efficiency, however turbidity influencedsame dose over a longer period of exposure time. Themore when the turbidity was more than 12 NTU, foreffects might be due to repair enzymes of the cellexample, E. coli inactivation rate was 3.14 lg(NVIN)which was more influenced by high UV intensitywhen turbidity was 0.5 NTU, and 1.46 lg(NVN)(Sommer et al., 1996a, b).reduction at a turbidity of 12 NTU, the differenceTable 3 Relationship between UV intensity and the dosebetween the higher and lower turbidity was 1.68 of lgrequired for 2 of lg(NJN) reduction(NJ!N)，so turbiditywasn important factorUV intensity, mW/cm?2influencing UV disinfection performance.Table 4 Effcts of turbidity on UV disinfection0.1Turbidity, NTUlg(NJ/N)Ig(NJM)0.54E. coli .3.764.23Staphylococcus wureus3.453.734.21lIg(NJN)Ig(NJMN).814.33E coli3.151.46Bacilus subilis28.228.7Suphylococeus aureus3.213.351.6228.532.839.43.333.241.73Bacillus subrilis'.32.372.3 Effects of turbidity on microorganism inac-MS-2 coliphage'2.552.65tivationNotes: Uv dose was 5 mJ/cm, UV intensity was 0.1 mW/cm2 ; *UVTurbidity affected UV disinfection process in twodose was 40 mJ/cm2ways: they might decrease the UV transmitance of thewater and affected dose delivery or shielded2.4 Relation between UV intensity and turbiditymicroorganisms from UV light, thus altered theon microorganism inactivationcharacteristics of the dose response curve (Laurel etFrom above results it can be known that turbidityal., 2004). Three levels of turbidity (0.5, 4.0, and 12influenced the transmittance of the light, thus reducedNTU) were selected in the research as low, middlethe中国煤化工fects (except MS-2and high turbidity and had different effects oncolipHhad influence ondifferent microorganisms (Table 4). MS-2 coliphagemicrCNMHGect,a higher UVwas not influenced by turbidity, however, otherintensity led to a high efficency under the same dose.microorganisms were influenced when turbidity wasHowever there were few study concentrated on theNo.4Effects of UV intensity and water turbidity on microbial indicator inactivation653relations between them and how these two factorsthat MS-2 coliphage and Bacillus subtilis wereworking together. In this work, we listed theremarkably resistant to UV radiation, E. coli,relationship of UV intensity and turbidity on microbialStaphylococcus aureus and Candida albicans were lessindicator inactivation in Table 5. Higher turbidityresistant and had nearly the same dose response curveclearly reduced the inactivation efficiency of UVto UV irradiation. UV irradiation was effective indisinfection, but at the higher UV intensity, thekilling vegetative bacteria, but it required more U\influence of turbidity could be reduced, that meant adose to kill spore forming bacteria and virus. UVhigh UV intensity could overcome the negativeintensity would influence the inactivation effect of UVcontribution of turbidity on microorganismsperformance of all the selected microbial indicators.inactivation.Under the same UV dose, higher intensity was moreTable 5 Relation between UV intensity and turbidity onefective in killing microorganisms than lowermicroorganism inactivationintensity, and it required less UV dose at higher UVintensity at the same inactivation rate. TurbidityUV intensit, mW/cm2Turbidity,influenced the effect of UV killing bacteria when itMicroorganismsTtitu 0.180.100.008was over 4 NTU, but higher UV intensity couldlg(NJN)_ lg(NJM) lg(NJN)minimize negative contribution of the turbidity onE. coli0.53.393.142.51microorganisms inactivation.3.213.15122.461.460.87References:Staphylococcus aureus0.3.87Alexander A M, Emest A M, Peter M W et al, 2002. The Efeet ofUV43.663.31light .on the inactivation of Giardia Lamblia and Giardia Muriscysts as determined by animal infectivity assay []. Wat Res, 362.541.621.32(8): 2098- -2108.Candida albicans3.813.332.91Drescher A C, Greene D M, Gadgil A J, 2001. Cryptosporidiuminactivation by low- pressure UV in a water []. J Environ Health,3.883.2464(3):31-35.2.711.731.23Driedger A M Y, Staub E, Pinkernell U et al., 2001. Inactivation ofBacillus subrils'3.412.23Bacillus Subtilis spores and formation of bromate duringozonation[J]. Wat Res, 35(12): 2950- -2960.3.31.84Facile N, Barbeau B, Prevost M et al, 2000. Evaluating bacterial2.532.371.02aerobic spores as a surrogate for Giardia and CryptosporidiumMS-2 coliphage').52.842.551.87Emerick W R, LogeJ F, Ginn T et al, 2000. Modeling the inactivation2.872.411.11of particle associated coliform bacteria [J]. Wat Env Res, 72(4):2.662.60.98Frederick W P, 2000. Regulations in 2000 and beyond[J]. J AWWA, 92Notes: UV dose was 5 mJ/cm; * UV dose was 40 mJ/cm2(3):40-53.JeffK, Asce M, Chen C L et al. 2003. Standardized colimated beamtesting protocol for water/wastewater ultraviolet disinfection[]. J3 DiscussionEnviron Eng, 129(8): 774- 779.Krasner S W, McGuire M J, Jacangelo J G et al, 1989. The occurrenceThree levels of UV intensity and turbidity wereof disinfection by-products in U.S. drinking water [J].J AWWA,selected in our experiments, the experimental data81(8):41-53.illuminated that higher UV intensity for a short timeLaurel P, James MJ R, Mark K et al,, 2004. Efect of low turbidity andalgae on UV disnfection performnance []. J AWWA, 96 (6):was important than the same dose over a longer period128- -137of exposure time for microorganism inactivation. ThisRodriguez M L, Drtofrd J, 2000. Estimation of water utility complianceeffect might be due to that repair enzymes of the cellwith trihalomethane regulations using a modeling approach [0. JWat SRT, 49(2):57- -73.were more influenced by high UV intensity and the1999. Humic substances as precursors for potentiallyDNA could not duplicate again. Turbidity hadharmful disinfection by-products []. Wat Sci Tech, 40 (9): 25-different influences on bacteria and virus, there wasSohn J, Amy G, Cho J et al, 2004. Disinfectant decay and disinfectionlittle influence on MS-2 coliphage, but bacteria wereby-products formation model devclopment: chlorination andinfluenced more when turbidity exceeded 4 NTU. Oneozonation by-products[]. Wat Res, 38(10): 2461- -2478.possible explanation was MS-2 did not associate withSommer R, Cabaj A, Haider T, 1996a. Microbicidal efect of reflectedUV radiation in devices for water disinfection [0]. Wat Sci Tech,the particles, leaving the bacteriophage susceptible to34(7): 173- -177UV disinfection (Laurel et al, 2004). Other bacteriaSommer R, Haider T, Heidenreich A et al, 1996b. Increasedwere shielded by turbidity in the water, so it wereinactivation of Saccharomyces cerevisiae by protraction of UVI Environ Microbiol, 62(6);: i977- 1983.influenced by turbidity in the water. So in actualSomInfluence of lamp inensityoperation, we should decrease water turbidity before it中国煤化I ifecton of water U. Watpassed through UV disinfection unit.4 ConclusionsZhangTYHCNMHGheriseofuvinCina[].Water21,10: 18- -21In this study, UV intensity and water turbidity onUV performance were investigated. Results showed(Received for review September 18, 2005. Accepted January 17, 2006)