OSI Delhi Summer 2014Case Study

Appropriate Treatment for Controlling Risk of Legionella in

RecyclingGreywater in Cooling Towers

Group Members: Dipti Kamath

Dhamodharan KAbhinav Garg

Mentors: Prof. Charles N

HaasProf. James

Gomes

Legionella

• Gram Negative bacteria• Main pathogenic strain: Legionella Pneumophila• Optimum conditions for growth:

– DO : 0-10mg/l– Temp: 0-70 °C– pH: 5-8.5

Hazard Identification

• Legionella bacteria cause a collection of infections – sub-clinical Pontiac fever– severe form of pneumonia

• Legionnaires disease

• Exposure pathway: inhalation alone• The bacteria grow best in warm water, like the kind

found in• Hot tubs• Cooling towers• Hot water tanks• Large plumbing systems• Decorative fountains

Legionellosis

Year City Venue source

1976 Philadelphia, Pennsylvania

1976 Philadelphia Legionnaires' disease

outbreakAir conditioning

1979 Ballarat, Australia psychiatric hospital shower water system

1985 Wollongong, Australia social club building small cooling tower

1986 Adelaide, Australia community small cooling tower at hospital

1987 Wollongong, Australia shopping centre small cooling tower at a shop

1989 Sydney, Australia bowling club small cooling tower

1989 Burnie, Tasmania community small cooling tower at hospital

1992 Sydney, Australia shopping centre small cooling tower

1995 Sydney, Australia shopping centre small cooling tower at hospital

2000 Melbourne, Australia Melbourne Aquarium Cooling tower

2005 Toronto, Canada Seven Oaks Home for the Aged Cooling tower

Outbreaks

Exposure Assessment

PROBLEM STATEMENT

• Apartment building houses 400 persons• Greywater produced used as cooling water• Centralized AC• Legionella present in greywater

2 cases for GW: – treatment provided– treatment not provided

Cooling Towers

• Natural draft

• Mechanical draft

Induced draft  Forced draft

Drift formation and Emission through the Exhaust fan at the top of cooling towers

are the carriers of legionella

The Process

Production - Grey water

Transportation – Cooling tower storage

Cooling – Sprayed onto pipes (cooling water)

Drifting – Mist comes out with exhaust

Assumptions

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

Legionella 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 *

– Mixing ratio• Assumed as 1:10 *

Assumptions…

– Cooling Tower Details• Drift varies from 0 – 1%

– Depends on drift eliminators• Exhaust velocity = 10 m/s• Exhaust fan diameter = 2.64 m

Legionella Exposure

– Exposure time• Assumed to be 0.5 ± 23 hours *

– Inhalation• Rate dependent on body weight, age

Dose Response

Agent strain Route Dose units Response Best fit model Optimized

parameter(s) LD50/ID50

Philadelphia 1 inhalation CFU infection exponential k = 5.99E-02 1.16E+01

Source: Muller et al. (1983)

Recommended Model : Exponential Model

Risk Characterization

Case Condition Risk

1 No treatment of greywater 1±4.6 %

2. Drift eliminators ( drift reduced to 0.01%) 0.08±0.3%

3.1 Treatment 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%

3.3 Treatment of greywater with chemical treatment(80% redn) + drift eliminator 0.005±0.05 %

3.4 Treatment of greywater with chemical treatment, disinfection and drift eliminator 0.002±0.027%

1 2 3.1 3.2 3.3 3.4

00.10.20.30.40.50.60.70.80.9

1

Cases

Risk

Risk Characterization

Excel file

1 2 3.1 3.2 3.3 3.40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1 1

0.08

0.48

0.19

0.005 0.002Cases

Risk

Risk Characterization

Monte Carlo analysis

Contribution of individual parameters to variance was found as follows:

Sensitivity graphs

ParametersCases

1 2 3.1 3.2 3.3 3.4

Exposure duration (%) 73.9 8.3 74.7 74.7 81.8 79.6

Concentration of Legionella in GW (CFU/L/Day)

15.4 76.5 17 17 15.8 16.9

Drift (%) 6.3 4.6 4.6

Water Demand (l/Day) 4.2 14.8 3.6 3.6 2.3 3.6

Greywater (%) 0.1 0.0 0.0 0.0 0.0 0.0

Cooling water requirements 0.0 0.0 0.0 0.0 0.0 0.1

Concentration of Legionella 0.1 0.4 0.0 0.0 0.0 0.0

Monte Carlo analysis for Case 1

Risk 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 – Thermal– UV

– Ionization– Ozonation

• Cost-benefit analysis can be done to find the best option

Not considered due to high costs; only used in DW

Risk Communication

Stake Holders

Exposure due to Recreational Activity– Like Garden Area

Might cause spread of disease to Kids and Elders(More Vulnerable to infections)

Exposure in Balconies

Limitations of Work

• Large data gaps found– Greywater production– Mixing ratio values– Legionella concentration w.r.t Indian scenario– Growth factor– Exposure time- survey– Treatment studies

Conclusion

Treatment measures considered and compared

A generalized framework was made

Risk assessed for the said problem

Monte Carlo analysis

• Birks, 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.htm

References