1. The document analyzes the risk of Legionella bacteria growth in the cooling towers of an apartment building that uses recycled greywater for cooling. It finds that treating the greywater can significantly reduce risk, with over 95% reduction when combining chemical treatment, disinfection and drift eliminators in the cooling towers. 2. Monte Carlo analysis showed that exposure duration and Legionella concentration in greywater were the primary factors influencing risk variability. Treating greywater and adding drift eliminators to reduce aerosol emissions reduced the risk the most, with a risk of 0.002-0.005% compared to 1% without any treatment. 3. Limitations included lack of local data on greywater production

1. OSI Delhi Summer 2014
Case Study
Appropriate Treatment for Controlling
Risk of Legionella in Recycling
Greywater in Cooling Towers
Group Members:
Dipti Kamath
Dhamodharan K
Abhinav Garg
Mentors:
Prof. Charles N
Haas
Prof. James Gomes

2. 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

3. 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

4. Year City Venue source
1976
Philadelphia,
Pennsylvania
1976 Philadelphia
Legionnaires' disease
outbreak
Air 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

5. 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

6. 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

7. The Process
Production - Grey water
Transportation –
Cooling tower
storage
Cooling –
Sprayed onto
pipes (cooling
water)
Drifting –
Mist comes out
with exhaust

8. 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

9. 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 *

10. – 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

11. 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

12. 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%
3.2
Treatment 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%

13. Risk
0
0.5
1
1
2
3.1
3.2
3.3
3.4
Risk
Cases
Risk Characterization
Excel file

14. 1
0.08
0.48 0.19 0.005 0.002
-6
-4
-2
0
2
4
6
8
1 2 3.1 3.2 3.3 3.4
Risk
Cases
Risk Characterization

15. Monte Carlo analysis
Contribution of individual parameters to variance was found as
follows:
Sensitivity graphs
Parameters
Cases
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

16. Monte Carlo analysis for Case 1

17. 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

18. 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

19. 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

20. Conclusion
Treatment measures considered and compared
A generalized framework was made
Risk assessed for the said problem
Monte Carlo analysis

21. • Birks, R., Colbourne, J., S. Hills, Hobson, R., 2004. Microbiological water quality in a large in-building, waterrecycling facility. Water
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• 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
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• 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