Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Disinfection.

Monroe L. Weber-Shirk School of Civil and

Environmental Engineering

Disinfection

Overview

Disinfection Options Chlorine Ozone Irradiation with Ultraviolet

light Iodine Silver

Disinfection mechanisms Chicks law CT

Problems with Disinfection Disinfection-by-products Tastes and odors Real pathogens Getting the right dose

Chlorine sources Chlorine Chemistry

Metals Water Ammonia Organics

The case for Chlorine It kills stuff Residual Recontamination Regrowth

Chlorine free Some European cities

The Case for Chlorine

It kills stuff ( ) Residual

It’s the law… But is it a good idea?Chlorine is the only available disinfectant that provides

a residual

RecontaminationDoes a chlorine residual provide protection against

recontamination?How much chlorine would be required?

RegrowthVery few pathogens multiply in drinking water

Revenge

Chlorine Based Disinfectants

ContaminantMRDLG1

(mg/L)2

MRDL1

(mg/L)2

Potential Health Effects from Ingestion of Water

Sources of Contaminant in Drinking Water

Chloramines (as Cl

2)

MRDLG=41

MRDL=4.01

Eye/nose irritation; stomach discomfort, anemia

Water additive used to control microbes

Chlorine (as Cl

2)MRDLG=41

MRDL=4.01

Eye/nose irritation; stomach discomfort

Water additive used to control microbes

Chlorine dioxide (as ClO

2)

MRDLG=0.81

MRDL=0.81

Anemia; infants & young children: nervous system effects

Water additive used to control microbes

Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

Chlorine

First large-scale chlorination was in 1908 at the Boonton Reservoir of the Jersey City Water Works in the United States

Widely used in the US Typical dosage (1-5 mg/L)

variable, based on the chlorine demandgoal of 0.2 mg/L residual

Trihalomethanes (EPA primary standard is 80 mg/L)1

Chlorine concentration is measured as Cl2 even when in the form of HOCl or OCl-

Chlorine oxidizes organic matter

1) http://water.epa.gov/lawsregs/rulesregs/sdwa/mdbp/mdbp.cfm#trihalomethanes

Chlorine: The Rules

Minimum free chlorine residual in a water distribution system should be 0.2 mg/L.1

For all systems using surface water or groundwater under the influence of surface water for supply, a detectable disinfectant residual must be maintained within the distribution system in at least 95% of the samples collected (or heterotrophic bacteria counts must be less than or equal to 500 cfu/ml as an equivalent) and at least 0.2 mg/L concentration of residual disinfectant (free or combined) entering the distribution system must be maintained.2

1) http://10statesstandards.com/waterstandards.html#4.3.3 2) http://www.epa.gov/ogwdw/disinfection/tcr/pdfs/issuepaper_effectiveness.pdf

Chorine isn’t always required

The European Union does not require disinfection. Of the 15 original European Union member states, only Spain and Portugal require disinfection in distribution systems.1 

1) http://www.epa.gov/ogwdw/disinfection/tcr/pdfs/issuepaper_effectiveness.pdf

Life without Chlorine

Amsterdam stopped chlorinating in 1983Chlorine chemistry council continues to

lobby hard with scare tactics to discourage considering alternativesFalse reports that cholera epidemic in Peru was

caused by stopping chlorination

http://www.americanchemistry.com

Why is a Residual Required? Why is Chlorine the only option?

Inactivating microorganisms in the distribution system Treatment breakthrough Leaking pipes, valves, and joint seals Cross-connection and backflow Finished water storage vessels Improper treatment of equipment or materials before and during

main repair Intentional introduction of contaminants into distribution system

Indicating distribution system contamination (If residual chlorine is monitored continuously it might be possible to detect an increase in contamination from a decrease in chlorine.)

Controlling biofilm growth

Protection against recontamination?

Proponents of maintaining a disinfectant residual point to situations where residuals were not maintained and preventable waterborne disease outbreaks occurred. Haas (1999) argues that both a 1993 Salmonella outbreak caused by animal waste introduced to a distribution system reservoir and a 1989 E. coli O157:H7 outbreak could have been forestalled if distribution system chlorination had been in effect. Both of these outbreaks were due to bacterial pathogens that are sensitive to chlorine and could have been at least partially inactivated.1

1) http://www.epa.gov/ogwdw/disinfection/tcr/pdfs/issuepaper_effectiveness.pdf

Chlorine Demand vs. Total Organic Carbon

y = 0.51x - 0.16R² = 0.93

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5

Chl

orin

e D

eman

d (m

g/L

)

Total Organic Carbon (mg/L)0.5 mg chlorinemg carbon

Samples were incubated in the dark for 1 h at 10°C.

Chlorine Protection against Recontamination?

How much sewage would residual chlorine at 0.2 to - 0.5 mg/L protect you from?

y = 0.51x - 0.16R² = 0.93

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5

Chl

orin

e D

eman

d (m

g/L

)

Total Organic Carbon (mg/L)

How much organic matter could be treated by residual Cl2?

Take a town of 5000 people Flow rate per person is about 3 mL/s* Average flow rate is 15 L/s Assume storage tank is half full when

contamination event occurs Small town storage tanks typically provides 1/3

day of storage – 432,000 L Assume 0.2 mg/L Cl2 residual – 0.4 mg/L C

173 gm of organic carbon* Based on consumption in Tamara, Honduras.

Effect of Chlorination on Inactivating Selected Bacteria

Bacteria Cl2 (mg/l)

Time(min)

Ct Factor (mg-min/l)

Reduction(%) Ct for pC* of1

Reference

Campylobacter jejuni 0.1 5 0.5 99.99 0.125 Blaser et al, 1986

Escherichia coli 0.2 3 5 99.99 1.25 Ram and Malley, 1984

Legionella pneumophila 0.25 60-90 18.75 99 9.4 Kuchta et al, 1985

Mycobacterium chelonei 0.7 60 42 99.95 13 Carson et al, 1978

Mycobacterium fortuitum

1.0 30 30 99.4 13.5 Pelletier and DuMoulin, 1987

Mycobacterium intracellulare

0.15 60 9 70 17.2 Pelletier and DuMoulin, 1987

Pasteurella tularensis 0.5-1.0 5 3.75 99.6-100 1.6 Baumann and Ludwig, 1962

Salmonella typhi 0.5 6 3 99 1.5 Korol et al, 1995

Shigella dysenteriae 0.05 10 0.5 99.6-100 0.2 Baumann and Ludwig, 1962

Staphylococcus aureus 0.8 0.5 0.4 100 -- Bolton et al, 1988

Vibrio cholerae(smooth strain)

1.0 < 1 < 1 100 -- Rice et al, 1993

Vibrio cholerae (rugose strain)

2.0 30 60 99.999 12 Rice et al, 1993

Yersinia enterocolitica 1.0 30 30 92 27 Paz et al, 1993

Effect of Chlorination on Inactivating Selected Viruses

Viruses Cl2 (mg/l)

Time (min)

Ct factor(mg-min/l)

Reduction (%)

Ct for pC* of1

Reference

Adenovirus 0.2 40-50 sec 0.15 99.8 0.06 Clarke et al, 1956

Coxsackie 0.16-0.18

3.8 0.06 99.6 0.025 Clarke and Kabler, 1954

Hepatitis A 0.42 1 0.42 99.99 0.105 Grabow et al, 1983

Norwalk 0.5-1.0 30 22.5 -- -- Keswick et al, 1985

Parvovirus 0.2 3.2 0.64 99 0.32 Churn et al, 1984

Poliovirus 0.5-1.0 30 22.5 100 -- Keswick et al, 1985

Rotavirus 0.5-1.0 30 22.5 100 -- Keswick et al, 1985

Effect of Chlorination on Inactivating Selected Protozoa

Protozoa Cl2

(mg/l) Time (min)

Ct Factor(mg-min/l)

Reduction

(%) Ct for

pC* of1 Reference

Cryptosporidium parvum

80 90 7200* 90 7200 Korich et al, 1990

Entamoeba histolytica

1.0 50 50 100 -- Snow, 1956

Giardia lamblia -- -- 68-389 99.9 30 AWWA, 1999

Naegleria fowleri 0.5-1.0 60 45 99.99 11 de Jonckheere and van de Voorde, 1976

How many pathogens does it take to make you sick?

https://confluence.cornell.edu/display/cee4540/Bad+Bugs

Inactivation of Shielded Pathogens

Many of the studies measuring inactivation of pathogens by disinfectants were conducted using dispersed pathogens

What happens if the pathogens are embedded in an organic particle?

Fecal contamination potentially contains pathogens embedded in protective organic matter

Cell Associated virus was inside fetal rhesus kidney derived cells

0 10 20 30 40 50 60 70 80 90 1000

0.51

1.52

2.53

3.54

dispersedcell associatedmodel2nd model

Time (min)

pC*

0.36 mg/L average free Cl2 at pH 6

86

ClC t to get pC* of 4 is (86 min)*(0.36 mg/L)=31 (min mg/L)

What do you conclude?

Conclusions from Virus in Kidney Cells

The rate of virus deactivation dropped significantly when the virus particles were inside kidney cells

The deactivation of embedded virus particles can not be described by a single first order reaction (________________)

What is controlling the rate of virus deactivation?

Chicks Law is violated

Scales of the Embedded Virus

1000 nm

LocationDeactivation

rate

Dispersed Very fast

Inside cell with disrupted cell

wallSlow

Inside intact cell Very slow

Virus particles are about 20 nm

HOCl are about 0.2 nm

1 mm

Mass Transport and Chlorine Protection

Chlorine must diffuse through cell contents to reach virus

Organic material inside the cell reacts with chlorine before it gets to the virus

Scale this up to a Fecal Aggregate

Turbid water could easily have organic particles that are 10 or even 100 mm in diameter

The amount of organic matter in a small particle and the slow diffusion would provide long term protection for embedded pathogens

10 mm

Chlorine saves lives…

If you accept the “Chlorine eliminated Typhoid Myth”

Then you will likely recommend chlorination as the first line of defense in the Global South-

But in small systems (in the Global South)Chlorine dose is generally not controlled based on a

target residual doseSurface water may currently be untreated and hence

have high turbidity that correlates with high chlorine demand that contains pathogens embedded in organic particles

Getting the Right Dose:WHO on Chlorination

Chlorine compounds usually destroy pathogens after 30 minutes of contact time, and free residual chlorine (0.2–0.5 mg per liter of treated water) can be maintained in the water supply to provide ongoing disinfection.

Several chlorine compounds, such as sodium hypochlorite and calcium hypochlorite, can be used domestically, but the active chlorine concentrations of such sources can be different and this should be taken into account when calculating the amount of chlorine to add to the water.

The amount of chlorine that will be needed to kill the pathogens will be affected by the quality of the untreated water and by the strength of the chlorine compound used.

If the water is excessively turbid, it should be filtered or allowed to settle before chlorinating it (___________________________)Remove particles first!

exposed

Chlorine Demand vs. Turbidity

Disclaimer – There is no solid connection between chlorine demand and turbidity

But – organic matter is often associated with particulate matter

If using the standard dose of 2 mg/L, then no residual above 15 NTU!

0

0.5

1

1.5

2

0 5 10 15Chl

orin

e Dem

and

(mg/

L)

Turbidity (NTU)

Based on 6 watersheds in

western Oregon

Turbidity and Chlorine

Chlorine test showing no residual after exposure to turbid tap water (left)

Chlorine Sources

On Site Production (electrolysis) Chlorine gas (Cl2) Liquid Bleach (NaOCl) Calcium hypochlorite (1 mg Ca(OCl)2 is

equivalent to 0.65 mg of Cl2)

Bleach Concentration in terms of sodium hypochlorite (NaOCL)

Bleach concentration in terms of Available Chlorine (As Cl2)

Additional Information (estimated)

Wt. % Trade % Grams per liter Wt. %Trade

%Grams per

liter

Density of the solution(lb/U.S. gal)

Specific gravity of the solution

5 5.4 53.9 4.8 5.1 51.4 9.0 1.08

10 11.6 115.8 9.5 11.0 110.4 9.7 1.16

15 18.6 185.7 14.3 17.7 177.0 10.3 1.24

How much Clorox should you add to a 5 gallon bucket or a 1L bottle?

Stock 51400mg

L

Dose 2mg

L

20LDose

Stock 0.78mL

Stock 51400mg

L

Dose 2mg

L

1LDose

Stock 39L

Calcium hypochlorite

Relatively inexpensive Easy to transport (high equivalent moles of

Cl2 per unit mass)

Less dangerous than chlorine gas High calcium concentration results in

insoluble calcium carbonate from exposure to the atmospheric CO2 or dissolved carbonates.

Clogs tubing and float valves (submerged orifice works better to avoid contact with atmospheric CO2)

Chlorine Reactions

Cl2 + H2O H+ + HOCl + Cl-

HOCl H+ + OCl-

The sum of HOCl and OCl- is called the ____ ______ _______free chlorine residual

+1 -2 +10Charges -1

Hypochlorous acid Hypochlorite ion

Chlorine and pH

HOCl is the more effective disinfectant

Therefore chlorine disinfection is more effective at ________ pH

Dissociation constant is 10-7.5

HOCl and OCl- are in equilibrium at pH 7.5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

5 6 7 8 9 10

Frac

tion

of F

ree

Chl

orin

e

pH

HOCl OCl-

low

HOCl H+ + OCl-

pk

0.85

-52.69*

0.2828 0.933contact Cl

T

t CpC

pH

Chick’s Law

The death of microorganisms is first order with respect to time

Thus, the remaining number of viable microorganisms, N, decreases with time, t, according to:

where k is an empirical constant descriptive of the microorganism, pH and disinfectant used.

Integrating with respect to time, and replacing limits (N = No at t = 0) yields:

dNkN

dt

0ktN N e

0

lnN

ktN

1

*ln 10

pC kt

k is expected to be highly correlated with concentration

*pC Ct

EPA Pathogen Inactivation Requirements

SDWA requires 99.9% inactivation for Giardia and 99.99% inactivation of viruses

Giardia is more difficult to kill with chlorine than viruses and thus Giardia inactivation determines the CT

Concentration x Time

Safe Drinking Water Act

EPA Credits for Giardia Inactivation

Treatment type Credit

Conventional Filtration 99.7%

Direct Filtration* 99%

Disinfection f(time, conc., pH, Temp.)

* No sedimentation tanks

EPA Disinfection CT Credits

Contact time (min)

chlorine pH 6.5pH 7.5

(mg/L) 2°C 10°C 2°C10°C

0.5 300 178 430 254

1 159 94 228 134

To get credit for 99.9% inactivation of Giardia:

Inactivation is a function of _______, __________________, and ___________.

concentrationtimepH temperature

Where did these numbers (to 3 significant digits) come from?

CT equation for Giardia

CCl = Free Cl2 Residual [mg/L] tcontact = Time required [min] pH = pH of water T = Temperature, degrees C pC* = -[Log(fraction

remaining)]

-52.69 0.150.2828 0.933 *TCl contact ClC t pH C pC

-52.69 0.850.2828 0.933 *Tcontact Clt pH C pC

0.85

-52.69*

0.2828 0.933contact Cl

T

t CpC

pH

Note: These equations are NOT dimensionally correct!

Chicks Law!

Disinfection Byproducts

Contaminant MCLG1

(mg/L)2

MCL (mg/L)2

Potential Health Effects from Ingestion of Water

Sources of Contaminant in Drinking Water

Bromate zero 0.010 Increased risk of cancer Byproduct of drinking water disinfection (plants that use

ozone)

Chlorite 0.8 1.0 Anemia; infants & young children: nervous system effects

Byproduct of drinking water disinfection (plants that use

chlorine dioxide)

Haloacetic acids (HAA5)

n/a6 0.060 Increased risk of cancer Byproduct of drinking water disinfection

Total Trihalomethanes (TTHMs)

none7

----------n/a6

0.10----------0.080

Liver, kidney or central nervous system problems; increased risk of cancer

Byproduct of drinking water disinfection

What happens to residual chlorine when you drink it?

Dark side of chlorine

Bladder cancer in the US in 2011 - New cases: 69,250 - Deaths: 14,990 (http://www.cancer.gov/cancertopics/types/bladder)

15% attributable to exposure to chlorination by-products (http://www.ncbi.nlm.nih.gov/pubmed/8932920)

1/139,000 people may die from bladder cancer from exposure to chlorination by-products

1

149900.15

312640961

139044

Tastes and Odors: Taste Thresholds

Complaints of the chlorine taste should not be discounted Chlorine taste may prevent some consumers from using

treated water Need to convince consumers that

the chemical taste is healthy???

0.0001

0.001

0.01

0.1

1

Tast

e th

resh

old

(mg/

L)

Conclusions

Chlorine can inactivate many types of pathogens with inactivation efficiency a function of pathogen type, embedded protection, contact time, pH, dose…

Chlorination cannot replace particle removal for surface waters

If you can see cloudiness in a glass of water it is too dirty for chlorine!

Chlorine cannot make water contaminated with feces safe to drink

Efforts to prevent contamination of treated water all the way to the consumer’s mouth are very important!

Confusions

The importance of chlorine residual is unclear and there is evidence of negative health effects

Chlorine dosages should be kept as low as possible and it isn’t clear what the optimal target should be

Invitation to an Open House: Monday 12-3 HLS 150

ENGRI 1131 students have built 8 miniature computer controlled drinking water treatment plants.

You are invited to stop by during the open house in Hollister 150 and see what first year engineers can do to make clean drinking water!

Options post CEE 4540

CEE 4550 (full for spring 2012)Help us build/test/implement ram pumpsReduce the cost of AguaClara facilitiesBuild a demonstration plant that fits on a table

top and that is a working model of all AguaClara processes from dose control to SRSF

Consider a Master of Engineering Degree

Take graduate level courses to gain a deeper understanding of environmental engineering

Take elective courses to broaden your skillsWork with a team on a design project (could

be AguaClara or any of a number of projects offered by other faculty)

Quiz?

What have you learned in CEE 4540 that will be most important to you in 5 years?

The Case for a Residual

Disinfect any recontamination Prevent bacteria growth in the treated water

Do pathogens grow in water? “The real reason for maintaining residuals during

treatment and distribution is to control microbiological growths when the water is biologically unstable.”

Control those non-pathogenic slime-forming organisms

“Current practice in North America tries to kill all microorganisms whenever possible”

Protection Against Recontamination

In order to be effective the following requirements must be metThe amount of chlorine demand must not

exceed the residualThe pathogens must be dispersed (not

associated with other particles)This is unlikely if the contamination is faecal

The pathogens must be susceptible to chlorine

Remember intermittent water supplies…

Growth of Bacteria in Water Distribution Systems

Consumption of dissolved oxygen Increased heterotrophic plate counts or coliform

countsThis does not imply a health risk

Decreased hydraulic capacity of the pipes Formation of taste/odor compounds

Geosmin, mercaptans, amines, tryptophans, sulfates

Increased rates of pipe corrosion (for metal pipes)

I don’t have any evidence that this biological growth has a significant public health impact

extra

Pathogen Growth in Distribution Systems (CDC)

Biofilms are coatings of organic and inorganic materials in pipes that can harbor, protect, and allow the proliferation of several bacterial pathogens, including Legionella and Mycobacterium avium complex (MAC).

Mycobacterium avium complex, MAC, is an opportunistic bacterial pathogen, is resistant to water disinfection (much more so than Giardia cysts), and grows in pipe biofilms

We need more data here! Is this a real public health threat?This is inconsistent with the purported (but apparently inconsequential) beneficial role of biofilms in SSF

extra

WHO on Regrowth

There is no evidence to implicate the occurrence of most microorganisms from biofilms (excepting, for example, Legionella, which can colonize water systems in buildings) with adverse health effects in the general population through drinking water, with the possible exception of severely immunocompromised people

Water temperatures and nutrient concentrations are not generally elevated enough within the distribution system to support the growth of E. coli (or enteric pathogenic bacteria) in biofilms.

Thus, the presence of E. coli should be considered as evidence of recent faecal contamination.

http://www.who.int/water_sanitation_health/dwq/en/gdwq3_4.pdf

WHO on Regrowth (2)

Viruses and the resting stages of parasites (cysts, oocysts, ova) are unable to multiply in water.

Relatively high amounts of biodegradable organic carbon, together with warm temperatures and low residual concentrations of chlorine, can permit growth of Legionella, V. cholerae, Naegleria fowleri, Acanthamoeba and nuisance organisms in some surface waters and during water distribution

http://www.who.int/water_sanitation_health/dwq/en/gdwq3_7.pdf

Where is the original research for these conclusions?

WHO Recommendations for Chlorine as Sole Treatment

Low turbidity (<30 NTU) and low chlorine demandLow turbidity probably means good quality

groundwater (from a spring or from a well) For effective use; pre-treat turbid water

Pre-treat means using a particle removal technology first

Surface water would generally not meet the NTU requirement

Chlorine requires process control (feedback based on residual chlorine concentration)

http://www.who.int/water_sanitation_health/dwq/0207tab20/en/

Pathogen Poisson Process Probability

Suppose we have an average pathogen concentration of C in our drinking water

Suppose we drink volume VWhat is the probability that we will ingest k

pathogens?Suppose V = 1 L, C = 2/L, what is probability

of ingesting exactly 2 pathogens?

!

k

CVk

CVP e

k 2

220.27

2!kP e

Probability of k Pathogens

What is probability of k < (dose)?Let dose = 15 Find cumulative probability for k=14

00.10.20.30.40.50.60.70.80.91

0

0.02

0.04

0.06

0.08

0.1

0.12

-10 10 30

Cum

ulat

ive

prob

abil

ity

Pro

babi

lity

of

inge

stin

gex

actl

y k

pat

hoge

ns

Number of pathogens

CV=15

45% chance of not getting sick!

Find probability that k>0

!

k

CVk

CVP e

k

00.10.20.30.40.50.60.70.80.91

00.050.1

0.150.2

0.250.3

0.350.4

0 5

Cum

ulat

ive

prob

abil

ity

Pro

babi

lity

of

inge

stin

g ex

actl

y k

pat

hoge

ns

Number of pathogens

CV=1

0

0 0!CV CV

k

CVP e e

0 1 CVkP e

For CV = 1, Pk>0 = 0.63

For CV = 0.001, Pk>0 = 0.001 (converge for small CV)

Effect of Pathogen Dose

What happens if the pathogen dose is 10 rather than 1?

Let’s assume that the concentration of this new pathogen is 10 times as great (CV=0.01)

What is the probability that you ingest 10 or more?

Pathogens with an infectious dose of 1 are potentially quite harmful even at very low concentrations!

Pathogens with an infectious dose>1 are not dangerous at low concentration!

For CV = 0.001, Pk>0 = 0.001

For CV = 0.01, Pk≥10 = 3x10-27

Waterborne Disease Outbreaks in the US (1985)

G. lamblia was the most frequently identified pathogen for the seventh consecutive year, causing three (20%) of 15 waterborne outbreaks.

In each of the outbreaks, as in well-characterized waterborne outbreaks of giardiasis in the past, water chlorination had been maintained at adequate levels to make outbreaks of bacterial diseases unlikely, but the lack of an intact filtering system capable of filtering Giardia cysts, distribution system problems, and mechanical deficiencies allowed drinking water to become a vehicle of giardiasis.

Waterborne Disease Outbreaks (1993)

The majority of outbreaks (68%) during 1991-1992 were classified as AGI of unknown etiology

Water sampling showed the presence of coliforms and/or deficiencies in chlorination for 91% of these outbreaks

24 outbreaks (71%) were associated with contaminated untreated or inadequately treated groundwater

Two outbreaks were associated with treatment deficiencies in water systems using UV light for disinfection

Three protozoal outbreaks during 1991-1992 occurred in systems that were equipped with chlorine disinfection and met EPA coliform standards but were not equipped with filtration

If you believe chlorine is what prevents waterborne disease outbreaks, then you will look for deficiencies in chlorination

Waterborne Disease Outbreaks (1993)

Four of the six surface water systems associated with WBDOs were equipped with filtration. In three of these outbreaks, raw water quality had deteriorated

because of sewage effluents that were not appropriately diluted as a result of low stream flows during dry weather.

During the outbreaks associated with these systems, filtration deficiencies were noted, with elevated turbidity in finished water.

Decreased filtration efficiency combined with deterioration in raw water quality also contributed to the WBDO in Milwaukee (1993).

It appears that chlorination was unable to provide an effective barrier when filtration failed

A fatal waterborne disease epidemic in Walkerton, Ontario

An estimated 2,300 people became seriously ill and seven died from exposure to microbially contaminated drinking water in the town of Walkerton, Ontario, Canada in May 2000

The Walkerton operators were asked to provide a chlorine residual (majority to be free chlorine) of 0.5 mg/L after 15 min.

Evidence at the Inquiry revealed that chlorine dosage practice at Well #5 was insufficient to achieve a 0.5 mg/L residual even in the absence of any chlorine demand.

Although the evidence did not allow for an estimate of the chlorine demand at the time Well #5 was contaminated, it was reasonable to assume that the contamination causing this outbreak was accompanied by a chlorine demand sufficient to consume entirely, or almost entirely, the low chlorine dose thereby allowing inadequately disinfected water into the distribution system

Evidence that chlorination that doesn’t produce a residual doesn’t provide protection

Calicivirus - An Emerging Contaminant in Water

Annual estimates among adults in the U.S. reveal approximately 267 million episodes of diarrhea leading to 612,000 hospitalizations and 3,000 deaths

In the last 3 decades it has become increasingly clear that viral agents are responsible for much of this public health burden

Human caliciviruses (HuCVs) have been estimated to cause 95–96% of nonbacterial gastroenteritis outbreaks (Fankhauser et al., 1998; K.Y. Green et al., 2000).

These viruses are considered ubiquitous in nature and stable in the environment, thereby increasing their propensity to spread and cause disease

Calicivirus

Four generaLagovirusVesivirusNorwalk-like viruses (Noroviruses or NLVs)Sapporo-like viruses (Sapoviruses or SLVs)

Single structural protein that makes up the viral capsid

27-40 nm in diameter

Cause disease in humans

Norovirus: Infectious Dose

Human volunteer feeding studies have determined the number of viral particles needed to initiate infection is 10 to 100

The infectious dose may well be the result of mass transfer limitations in the gut i.e. the virus needs to be transported to the villi in the

gastric mucosa and attach to initiate infection

Thus it is likely that 1 viral particle is sufficient to initiate infection

Huffman, D. E., K. L. Nelson, et al. (2003).

Weber-Shirk

Norovirus: Clinical Illness and Diagnosis

The most common symptoms of NLV infections include mild to moderate diarrhea, abdominal cramps, and nausea (Adler and Zickl, 1969; Hedberg and Osterholm, 1993).

Other symptoms may include headache, malaise, chills, cramping, and abdominal pain. Stools typically do not contain blood or mucus.

The onset of illness is generally within 24 to 28 h of exposure with a relatively short duration of illness (12 to 60 h).

Adult infection with NLV can be distinguished from bacterial pathogens such as Salmonella and Shigella due to its characteristic projectile vomiting (Adler and Zickl, 1969; Caul, 1996)

Norovirus: Inactivation

A 1-log reduction in the RTPCR signal of Norwalk virus was observed after treatment with 2 mg/L monochloramine at pH 8 for 3 h

Norwalk virus appears to be fairly resistant to free chlorine and monochloramine

Chlorine Disinfection Mechanisms*

Oxidation of membrane-bound enzymes for transport and oxidative phosphorylation

Oxidation of cytoplasmic enzymes Oxidation of cytoplasmic amino acids to nitrites

and aldehydes Oxidation of nucleotide bases Chlorine substitution onto amino acids DNA mutations DNA lesions

*It is possible that none of these mechanisms have been documented

(more likely)

Ammonia Reactions

Substitution reactions… The combined chlorine maintains its oxidizing potential Total chlorine is combined chlorine plus free chlorine

NH3(aq) + HOCl NH2Cl+ H2O

NH2Cl + HOCl NHCl2+ H2O

-3 -3+1 +1+1

Combined chlorine

extra

Breakpoint Chlorination

Removal of ammonia by chlorination

Oxidizing equivalents of chlorine are consumed

2NH3(aq) + 3HOCl N2+ 3Cl- + 3H2O

-3 +1 0 -1

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Does Chlorine Completely oxidize organic matter?

Oxidation statesCarbon in organic matter (-4)Carbon in carbon dioxide (+4)Chlorine in HOCl (+1)Chloride (-1)

Therefore should take 4 moles of chlorine (Cl2) per mole of organic carbon

23.6 g chlorine/g organic carbon

4HOCl + CH4 CO2 + 2H2O + 4Cl- + 4H+

NO!

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