Appropriate Treatment for Controlling Risk of Legionella in Recycling Greywater in Cooling Towers Group Members Dipti Kamath Dhamodharan K Abhinav Garg Mentors Prof Charles ID: 933033
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Slide1
OSI Delhi Summer 2014Case Study
Appropriate Treatment for Controlling Risk of Legionella in RecyclingGreywater in Cooling Towers
Group Members: Dipti KamathDhamodharan KAbhinav Garg
Mentors:
Prof. Charles
N Haas
Prof. James
Gomes
Slide2Legionella
Gram Negative bacteriaMain pathogenic strain: Legionella
PneumophilaOptimum conditions for growth:DO : 0-10mg/lTemp: 0-70 °CpH: 5-8.5
Slide3Hazard Identification
Legionella bacteria cause a collection of infections sub-clinical Pontiac feversevere form of pneumoniaLegionnaires diseaseExposure pathway: inhalation aloneThe bacteria grow best in warm water, like the kind found inHot tubsCooling towersHot water tanksLarge plumbing systemsDecorative fountains
Legionellosis
Slide4Year
CityVenue
source1976Philadelphia, Pennsylvania1976 Philadelphia Legionnaires' disease outbreakAir conditioning1979Ballarat, Australia
psychiatric hospital
shower water system
1985
Wollongong,
Australia
social club building
small cooling tower
1986
Adelaide, Australiacommunitysmall cooling tower at hospital1987Wollongong, Australiashopping centresmall cooling tower at a shop1989Sydney, Australiabowling clubsmall cooling tower1989Burnie, Tasmaniacommunitysmall cooling tower at hospital1992Sydney, Australiashopping centresmall cooling tower1995Sydney, Australiashopping centresmall cooling tower at hospital2000Melbourne, AustraliaMelbourne AquariumCooling tower2005Toronto, CanadaSeven Oaks Home for the AgedCooling tower
Outbreaks
Slide5Exposure Assessment
PROBLEM STATEMENT
Apartment building houses 400 personsGreywater produced used as cooling waterCentralized ACLegionella present in greywater2 cases for GW:
treatment provided
treatment not provided
Slide6Cooling Towers
Natural draft
Mechanical draftInduced draft Forced draft
Drift formation and Emission through the Exhaust fan at the top of cooling towers are the carriers of legionella
Slide7The Process
Slide8Assumptions
High Income Group Water demand (39,960 ± 23,920 l/day
)Grey water (Production) (48.32 ± 0.35%)
AC Capacity (400
tonnes
) *
Cooling Water requirement (60,560 ± 30,280 l/day
) *
(Taking external temperature into consideration)
If grey water produced is less than requirement, more water is added
Slide9Legionella Concentration in Cooling Water
Assumptions…Referred Various papers/Reports
Lognormal Distribution *Conc. in Greywater (20,05,66,667 ± 48,96,20,476.2 CFU/l)
Legionella
Pneumophila
:
92% of total
Legionella sp
. *
Conc. in extra water
(98,261 ± 12,16,30 CFU/l) Biofilm considered with incorporation a growth factor (=2); no specific time duration considered *
Slide10Mixing ratioAssumed as 1:10 *
Assumptions…
Cooling Tower DetailsDrift varies from 0 – 1% Depends on drift eliminatorsExhaust velocity = 10 m/sExhaust fan diameter = 2.64 m
Legionella
Exposure
Exposure time
Assumed to be 0.5 ± 23
hours *
Inhalation
Rate dependent on body weight, age
Slide11Dose Response
Agent strainRoute
Dose unitsResponseBest fit modelOptimized parameter(s)LD50/ID50 Philadelphia 1inhalationCFUinfectionexponential
k = 5.99E-02
1.16E+01
Source: Muller et al. (1983)
Recommended Model : Exponential Model
Slide12Risk Characterization
CaseConditionRisk1No treatment of greywater1±4.6 %
2.Drift eliminators ( drift reduced to 0.01%)0.08±0.3%3.1Treatment of greywater with chemical treatment(~80% reduction of legionella)0.48 ± 3.8%3.2Treatment of greywater with chemical treatment and disinfection(~95% reduction of legionella)0.19 ± 2.4%3.3Treatment of greywater with chemical treatment(80% redn) + drift eliminator
0.005±0.05 %
3.4
Treatment of
greywater
with chemical treatment, disinfection a
nd drift eliminator
0.002±0.027%
Slide13Risk Characterization
Excel file
Slide14Risk Characterization
Slide15Monte Carlo analysis
Contribution of individual parameters to variance was found as follows:Sensitivity graphsParameters
Cases123.13.23.33.4Exposure duration (%)73.9
8.3
74.7
74.7
81.8
79.6
Concentration
of
Legionella
in GW (CFU/L/Day)15.476.5171715.816.9Drift (%)6.34.64.6Water Demand (l/Day)4.214.83.63.62.33.6Greywater (%)0.10.00.00.00.00.0Cooling water requirements 0.00.00.00.00.00.1Concentration of Legionella0.10.40.00.00.00.0
Slide16Monte Carlo analysis for Case 1
Slide17Risk Management
As can be seen from various cases, the best would be use of water treatment along with drift eliminators w.r.t risk
Other options include ThermalUV IonizationOzonation
Cost-benefit analysis can be done to find the best option
Not considered due to high costs; only used in DW
Slide18Risk Communication
Stake Holders
Exposure due to Recreational ActivityLike Garden Area Might cause spread of disease to Kids and Elders(More Vulnerable to infections)Exposure in Balconies
Slide19Limitations of Work
Large data gaps foundGreywater productionMixing ratio valuesLegionella concentration w.r.t Indian scenarioGrowth factorExposure time- surveyTreatment studies
Slide20Conclusion
Treatment measures considered and comparedA generalized framework was made
Risk assessed for the said problemMonte Carlo analysis
Slide21Birks, R., Colbourne, J., S. Hills, Hobson, R., 2004. Microbiological water quality in a large in-building, waterrecycling facility. Water Science and Technology. 50(2), 165–172.Cilloniz, C., Ewig, S.,
Polverino, E., Marcos, M.A., Esquinas, C., Gabarrus, A., Mensa, J., Torres, A., 2011. Microbial aetiology of community-acquired pneumonia and its relation to severity. Thorax 66 (4), 340-346.Craun, G.F., Brunkard, J.M., Yoder, J.S., Roberts, V.A., Carpenter, J., Wade, T., Calderon, R.L., Roberts, J.M., Beach, M.J., Roy, S.L., 2010. Causes of outbreaks associated with drinking water in the United States from 1971 to 2006. Clinical Microbiology Reviews 23 (3), 507-528.Fry, N.K., Warwick, S., Saunders, N.A., and Embley, T.M.(1991) The use of 16S ribosomal RNA analyses to investigate the phylogeny of the family Legionellaceae
. J GenMicrobiol 137: 1215–1222.Lau, H.Y., Ashbolt, N.J., 2009. The role of biofilms and protozoa inLegionella pathogenesis: implications for drinking water.Journal of Applied Microbiology 107 (2), 368-378.Rose, J. B., Gwo-Shinsgu N, Gerba,C . P. And Sinclaian, (1991). A. Microbialquality and persistence of enteric pathogens in graywater from various household sources. Wat. Res.,25,(l ),3 7.Steinert, M., Hentschel, U., Hacker, J., 2002. Legionella pneumophila: an aquatic microbe goes astray. FEMS Microbiology Review 26 (2), 149-162.Varvara, A, M., Georgia, G., Jenny, K., MD, Christos, H., Legionella species colonization in cooling towers: Risk factorsand assessment of control measures. doi:10.1016/j.ajic.2009.04.285.Exhaust velocity of cooling tower fans (2000ft/min) : External Influences onCooling Tower Performance, marley technical report (2012)Fan diameter for approx. 400 tons cooling tower: ( ≈ 2.64 m):http://www.aaronequipment.com/usedequipment/cooling-towers/cooling-towers/bac-3455c-mm-46145001
Ref for body weight of adults (57.7 kg) in
asia:
Walpole
, Sarah C et al;
Prieto
-Merino, David; Edwards, Phil; Cleland, John; Stevens, Gretchen; Roberts, Ian (18 June 2012).
"The weight of nations: an estimation of adult human biomass"
.
BMC Public Health (BMC Public Health 2012, 12:439) 12: 439. doi:10.1186/1471-2458-12-439. PMC 3408371.PMID 22709383.Retrieved 12 July 2012.Ref for body weight of infants in india: http://www.guidetochildcare.org/normal-growth-and-development.htmReferences
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