microbial risk from_the_philadelphia_water_supply (2)
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Microbial Risk from the Philadelphia Water Supply
Anne WolffQiuyan Yuan
Yu-Min SuJian Yang
Outline
• Introduction•Hazard ID• Exposure assessment•Dose response•Risk assessment•Risk management
Problem
•Cryptosporidium presents in surface water, it cause Cryptosporideosis. •What is the risk of Cryptosporideosis
caused by drinking water in Philadelphia?
Objective• Develop a QMRA model to estimate risk of Crypto
from the Philadelphia public water supply.• Use this model to assess what level of removal of
crypto would correspond to the observed risk• Provide some insight into the plausibility of the
claim advanced by these studies that US drinking water is associated with measureable risk of gastrointestinal illness.
Cryptosporidium• First described by Ernest Tyzzer in 1907• Protozoan parasite infecting the
intestinal tract of vertebrates• Currently 26 known species infecting
humans, other mammals, birds, reptiles, fish
• C. parvum and C. hominis are the primary species that infect humans
Carey, C.M., et al, 2003 severntrentservices.com
Cryptosporidiosis
• Gastrointestinal disease caused by Cryptosporidium
• Most common symptom is watery diarrhea but other clinical symptom may include: stomach cramps, nausea, vomiting, fever, dehydration
• Clinical symptoms appear 2 to 10 days after infection and last 1 to 2 weeks.
• Immune compromised, children and the elderly are most vulnerable to infection
• Infection is by fecal-oral route
Cryptosporidium in Drinking Water Supplies
• Cryptosporidium has become a significant pathogen in drinking water outbreaks since the 1980’s• Oocysts are resistant to being killed by the
standard chlorine disinfection • Cryptosporidium pathogens enters water
through the infected feces of animals and humans
Lifecycle and Infection Route
Cryptospiridiosis Statistics from Philadelphia Department of Public Health
Turbidity
• Turbidity is a measure of water clarity • Suspended particles include soil, algae, plankton,
microbes ranging in size from 0.004 -1.0 mm• Microbes in drinking water supply may escape
disinfection by attaching or being hidden by particles• Relationship to Cryptosporidium
Turbidity is used as an indicator for the presence of Cryptosporidium
log10 removal Cryptosporidium oocysts = 0.996 log10 removal turbidity + 0.494 (R2 = 0.71)
• Source: LeChevallier and Norton, 1991.
Framework
Hazard ID
CoagulationGravity Settling
Filtration
Nanofiltration
Daily ingestion
Recovery of method
Children
Adults
Fraction reach to GI
CryptoConcentration
Different treatment
Different population
Risk assessment
Treatment
Adults Children
Exposure assessment
Dose response
K for adult K for children
Parameters• Concentration of Crypto in surface water:
• Recovery efficiency by detection method: 32.3%
Treatment Plant Location
LARGER DATABASEMaximum
cysts per 100 L90th percentile
per 100 LAverage
cysts per 100 L
CRYPTOSPORIDIUMBaxter 100 70 32Queen Lane 1200 200 96Belmont 250 50 43
Parameter
•Water consumption: • Adult ingestion: 2 L/day• Children ingestion: 1 L/day
• The fraction of Crypto that will reach the receptor, assumption: 10%
Parameters• Drinking water treatment method
• log10 removal Cryptosporidium oocysts = 0.996 log10 removal turbidity + 0.494 (R2 = 0.71)
Turbidity log Removal
Crypto log Removal
Crypto removal rate(%)
Coagulation Gravity Settling
Filtration1.6 - 4.0 0.96 -1.87 89.09 - 98.67
Nanofiltration 2.36-2.69 1.35-1.48 95.53 - 96.71
Dose response model
• P(d)=1-exp(-k*dose) Exponential Model
k
Adult 0.0572
Children 0.1 (Assumption)
Crypto in the surface water
Risk assessment
• Risk goal (EPA 1 in 10,000 annual infection risk)• Assumptions (conservative)• Risk assessed at the first downstream
customer• Every crypto measured/reported in raw water
is infectious
Risk assessment
Scenario 1- present
treatmentAdults Children
Scenario 2- present
treatmentAdults Children
5% 2.73E-05 2.56E-05 5% 1.14E-04 1.15E-0450% 4.25E-03 3.09E-03 50% 3.39E-02 2.60E-0295% 2.08E-02 2.56E-02 95% 1.57E-01 1.21E-01Scenario 1-
Nano-filtration
Adults ChildrenScenario 2-
Nano-filtration
Adults Children
5% 2.26E-05 2.21E-05 5% 9.78E-05 1.05E-0450% 2.76E-03 1.96E-03 50% 2.32E-02 1.72E-0295% 1.37E-02 8.06E-03 95% 1.16E-01 8.27E-02
• Scenario 1: Annual average condition• Scenario 2: Spike in turbidity
Risks from literature
The annual risk of contracting Cryptosporidiosis in the United States may range from:• 4 in 1,000 to 1 in 100,000. (Haas, 1994)• 1 in 1,000 to 1 in 100,000 (Haas, 1994; Perz et
al., 1998).• 1 in 10,000 annual risk of infection is 0.003/100L
(95% confidence interval 0.0018 -0.0064/100L) (Haas, 1994).
Federal Regulation• Crypto is regulated by the federal government as
a primary drinking water contaminant.• Community size based (10,000)• 12 month sampling every 5 years to determine
the removal treatment process.
Risk Management• Treatment (Removal & Inactivation)
• Other mitigations (BWA, research, etc.)• Early warnings (Turbidity, E coli, particle count, etc.)• Multi-barrier, event management, customer education, research;
Conventional Treat
Lime Softening Credit CFE Credit IFE Credit
Bin 3 Treatment
Log Removal 3 3.5 4 4.5 5
C 0.96 0.00096 0.000303579 0.000096 3.03579E-05 0.0000096Inf 0.028 0.028 0.028 0.028 0.028 0.028Consu 1.2 1.2 1.2 1.2 1.2 1.2
DR 0.032256 0.000032256 1.02002E-05 3.2256E-06 1.02002E-06 3.2256E-07
Ann Risk 1.00E+00 1.12E-02 3.56E-03 1.13E-03 3.57E-04 1.13E-04 TEXAS COMMISSION ON ENVIRONMENTAL QUALITY PTR SECTION STAFF GUIDANCE
Vulnerable populations: immunocompromised, children, elderly;For extra stringency suggest installing home water filters with one of the following on label:Reverse osmosis (with or without NSF 53 or NSF 58 labeling)Absolute pore size of 1 micron or smaller (with or without NSF 53 or NSF 58 labeling)Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst removalTested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst reduction
Risk Communication and Management for the Public
Risk Management
• Turbidity removal followed by:• UV• Chlorination• Ozone
References• Carey, C.M., H. Lee, & J.T. Trevors.(2004). Biology, persistence and detection of Cryptosporidium parvum and Cryptosporidium hominis
oocyst. Water Research, 38, 818–862.• Centers for Disease Control. “Parasites: Cryptosporidium”. Retrieved from http://www.cdc.gov/parasites/crypto/index.html• City of Philadelphia Department of Public Health. (2013). Division of Disease Control Annual Report• Efficiency of the activated carbon filtration in the natural organic matter removal• EPA Guidance Manual- Turbidity Provisions. 1999.• EPA, Exposure Factors Handbook Chapter 3—Ingestion of Water and Other Select Liquids. 2011.• EPA, Cryptosporidium: Drinking Water Health Advisory, 2001• Haas, C.N., Crockett, C.S., Rose, J.B., Gerba, C.P., and Fazil, A.M. 1996. Assessing the risk posed by oocysts in drinking water. J. AWWA,
88:9:131-136.• Haas, C.N., Hornberger, J., Ammangandla, U., Heath, M., and Jacangelo, J.G. 1994. A volumetric method for assessing Giardia inactivation.
J. AWWA, 86:2:115-120.• J. Hatt, E. Germain, S. Judd, 2013, Granular activated carbon for removal of organic matter and turbidity from secondary wastewater,
Water Science & Technology, 67(4), 846-853.• M. Jenkins, S. Tiwari, J. Darby, 2011, Bacterial, viral and turbidity removal by intermittent slow sand filtration for household use in
developing countries: Experimental investigation and modeling, Water Science, 45, 6227-6239.• M. LeChevallier, W. Norton, 1992. Examining Relationships Between Particle Counts and Giardia, Cryptosporidium, and Turbidity. J. AWWA.• M. Lechevallier, W. Norton, R. Lee, 1991, Giardia and Cryptosporidium spp. in filtered drinking water supplies, Applied and Environmental
Microbiology, 57 (9), 2617-2621.• M. Sato, A. Galvani, J. Padula, A. Nardocci, M. Lauretto, M. Razzolini, E. Hachich, 2013, Assessing the infection risk of Giardia and
Cryptosporidium in public drinking water delivered by surface water system in Sao Paulo State, Brazil, Science of the Total Environment, 442, 389-396.
• Perz, J.F., Ennever, F.K., and LeBlancq, S.M. 1998. Cryptosporidium in tap water: comparison of predicted risks with observed levels of disease. Am. J. Epidemiol., 147:3:289-301.
• R. Aboytes, G. Di Giovanni, F. Abrams, C. Rheinecker, W. McElory, N. Shaw, M. Lechevallier, 2004, Detection of infectious cryptosporidium in filtered drinking water, J. AWWA.
• S. Xia, J. Nan, R. Liu, G. Li, 2004, Study of drinking water treatment by ultrafiltration of surface water and its application to China, Desalination, 170, 41-47.
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