OZONE, CHLORINE DIOXIDE,
AND CHLORAMINES AS
ALTERNATIVES TO CHLORINE
FOR DISINFECTION OF
DRINKING WATER
STATE-OF-THE-ART
WATER SUPPLY RESEARCH
OFFICE OF RESEARCH AND DEVELOPMENT
U,S, ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
NOVEMBER 1977
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OZONE, CHLORINE DIOXIDE,
AND CHLORAMINES AS
ALTERNATIVES TO CHLORINE
FOR DISINFECTION OF
DRINKING WATER
State-of-the-Art
Water Supply Research
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
November 1977
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TABLE OF CONTENTS
Page
INTRODUCTION 1
GENERATION AND USAGE OF ALTERNATE DISINFECTANTS 3
Ozone 3
Generation 3
Usage 4
Chlorine Dioxide 6
Generation in Aqueous Solution 6
Usage 7
Chlorine Dioxide Use in the Unted States 8
Chlorine Dioxide Use in Canada 8 .
Chlorine Dioxide Use in Europe 8
Chloramines, Combined Chlorine, or Chloramination 9
Generation 9
Usage 9
Summary 10
MICROBIOLOGICAL ASPECTS OF DISINFECTION 11
Comparative Disinfection Efficiency 12
Chemical Basis for Disinfectant Activity 14
Comparative Resistance of Microorganisms 15
Protective Effects of Particulate Matter 19
Influence of Water Quality 20
Stability During Water Distribution 20
Summary 20
MEASUREMENT OF DISINFECTANT RESIDUALS 24
Free Chlorine ' 25
Ozone 25
Chlorine Dioxide 25
Chloramines 26
Free Chlorine with Chloramines 26
Chlorine with Chlorine Dioxide 27
Ozone with Chlorine 27
Complex Combinations 27
Summary 29
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TABLE OF CONTENTS
(Continued)
BY-PRODUCTS AND END PRODUCTS OF DISINFECTION 30
Chemistry 30
Free Chlorine 30
Ozone 33
Chlorine Dioxide 34
Chloramines 43
Health Effects 44
Chlorine 44
Toxicology 44
Epidemiology 47
Ozone 48
Chlorine Dioxide 50
Toxicity 50
Hemolytic Anemia 51
Chloramines 55
Comparative Studies 56
Summary 57
COST OF DISINFECTION 58
General Considerations 58
Basis of Cost Estimates 59
Chlorine 59
Ozone 61
Chlorine Dioxide 63
Chloramines 64
Summary 66
DISCUSSION 68
SUMMARY 73
ACKNOWLEDGMENTS 73
REFERENCES 74
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OZONE, CHLORINE DIOXIDE AND CHLORAMINES AS ALTERNATIVES
TO CHLORINE FOR DISINFECTION OF DRINKING WATER
State-of-the-Art
Compiled by James M. Symons, Chief, Physical and Chemical Contaminants
Removal Branch (P&CCRB), Water Supply Research Division (WSRD), Municipal
Environmental Research Laboratory (MERL)
Written by:
J. Keith Carswell, Research Engineer, P&CCRB, WSRD, MERL
Robert M. Clark, Systems Analyst, P&CCRB, WSRD, MERL
. Paul Dorsey, Research Assistant, P&CCRB, WSRD, MERL
Edwin E. Geldreich, Chief, Microbiological Treatment Branch (MTB), WSRD, MERL
W. Paul Heffernan, Research Pharmacologist, Laboratory Studies Division,
Health Effects Research Laboratory (HERL)
John C. Hoff, Research Virologist, MTB, WSRD, MERL
0. Thomas Love, Jr., Research Engineer, P&CCRB, WSRD, MERL
Leland J. McCabe, Research Epidemiologist, Field Studies Division, HERL
Alan A. Stevens, Research Chemist, P&CCRB, WSRD, MERL
All in the Office of Research and Development, U.S. Environmental Protection
Agency, Cincinnati, Ohio
INTRODUCTION
Although free chlorine is a good disinfectant, the problems of the formation
of halogenated organics, particularly chloroform and related trihalomethanes,
during its use have caused the entire subject of drinking water disinfection
to be reviewed. Three other disinfectants are used by various water utilities
throughout the world; ozone, chlorine dioxide, and chloramines. If any
disinfectant or combination of disinfectants is to replace free chlorine as
the most commonly used disinfectant, several criteria must be met, as follows:
It must be easily generated and be in widespread use;
It must be a good biocide;
It must provide an easily measured residual;
It must produce fewer undesirable by-products than does free chlorine; and
It must be cost effective.
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The water supply research program, in support of a possible Agency
regulation of trihalomethane concentrations, is currently evaluating the
disinfectants ozone, chlorine dioxide, and chloramines as free chlorine
alternatives with respect to these characteristics. This document will
be a progress report on this evaluation. The report will be organized
by sections, covering the individual criterion noted above. Each section
will contain a summary review of the literature and a summary of research
findings to date (Fall 1977) based on in-house and extramural projects.
Because research is continuing in most areas, many of the studies discussed
are unfinished and will be presented as progress reports. Detailed
papers will be published in the technical literature on these studies as
they are completed. In total, however, this report will summarize the
Agency's knowledge on the subject of disinfectant alternatives at this
writing.
Although this paper focuses on the possibility of changing disinfectants
as a solution to the disinfection by-product problem, by-product formation
is as much a result of the organic content of the water being disinfected as
it is the result of chlorine being used. Therefore, another, and possibly
preferable, option, which is beyond the scope of this paper, would be to
reduce concentrations of disinfectant by-products by chlorinating water that
had been treated, possibly with granular adsorbants, to remove the natural
organic materials with which chlorine reacts. This would hsrve the additional
benefit of reducing the concentration of synthetic organics in finished
waters as well as limiting the biological nutrients being carried into
distribution systems.
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GENERATION AND USAGE OF ALTERNATE DISINFECTANTS
Based on a review of the literature and a research grant sponsored
by the Water Supply Research Division (WSRD) the following information
is presented to demonstrate that the three alternate disinfectants
considered in this paper meet the first criterion of suitability as a
replacement for chlorination, that generation technology exists and that
their use is sufficiently widespread that they should be considered
"common practice."
OZONE
Generation
Lawrence and Cappelli in their recent review article list three
methods used for ozone generation:
a. silent electric discharge in air or oxygen
b. electrolysis of water
c. ultraviolet radiation of air or oxygen
Of these three, only (a) is used commercially because of its higher
generation efficiency (maximum of 5-6 weight percent ozone).
In the usual generation process, low pressure, clean dry air (or
oxygen) is passed between large area electrodes separated by an air gap
and a dielectric (usually glass) across which an alternating potential
of 15,000 volts (or greater) is maintained. In this type of ozone
generator, the production efficiency depends on the rate of gas flow,
the applied voltage and the cooling water (or air) temperature.
2
Mignot has reviewed in detail the numerous methods used for contacting
ozone with the liquid to be treated. These methods include:
a. Liquid dispersion in an atmosphere of ozonized air.
b. Fine orifice injection of ozonized air at the bottom of a co-
or countercurrent contact chamber, with or without contact
media and/or performated septa.
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c. An injector operating on the total flow of water to be treated
to aspirate low pressure ozonized air into a contact chamber
and create mixing turbulence.
d. Similar to (c), with the injector operating on a portion of
the total water flow
e. Over-ozonation of a portion of the water to be treated with
mixing with the remaining non-ozonated portion
f. Porous media injection of ozonated air into a single or multiple
(series) contact chamber with co- or counter-current flow
g. Injection of ozonized air by porous diffusers in a pressurized
contact chamber with recovery of the residual ozonized air for
re-injection at the chamber entrance (the Torricelli system).
h. Turbine diffusion of ozonized air without recirculation of the water
to be treated.
i. Same as (h), with recirculation of the water to be treated
Selection of an appropriate method of contacting is a very important
aspect in the design of an ozone treatment system.
Usage
Lawrence and Cappelli have listed a number of common uses of ozone
in drinking water treatment. They include:
a. Disinfection
b. Precipitation of iron and manganese
c. Destruction of sulfites
d. Destruction of many surfactants
e. Removal of turbidity
f. Oxidation of taste, odor and color producing compounds
g. Oxidation of other organic compounds
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Hill , in reviewing the development of water and wastewater ozonation,
lists several facts on the early use of ozone for drinking water treatment:
a. First permanent ozone installation — 1893 at Oudshoon, Holland
(Rhine River)
b. Other early ozone installations — 1901 at Wiesbaden, Germany;
1902 at Paderborn, Germany; 1906 at Nice, France
c. By 1916 there were 49 water treatment plants (26 in France)
using ozone
d. By 1940, there were 119 plants, with 90 in France and 14 in Italy.
The International Ozone Institute has summarized what was then (1976)
4
known of the use of ozone for drinking water treatment in the United States.
This information includes:
a. Two water treatment plants are using ozone in operation.
Whiting, Indiana began using ozone in 1941 for taste and odor
control. Strasburg, Pennsylvania has been using ozone since
1973 for disinfection.
b. Monroe and Bay City, Michigan have ozonation facilities under
construction.
c. New York City, Boston, Washington D.C., Louisville, and the State
of Vermont have conducted research and/or pilot plant studies
on ozonation in drinking water treatment.
d. Haverhill, Massachusetts and Laconia, New Hampshire have conducted
pilot plant studies.
e. Vineland, New Jersey has received State approval to conduct a
pilot-scale demonstration project
f. Boca Raton, Florida is considering an ozonation study.
In 1976, the WSRD funded a Research Grant titled: "Status of
Ozonation and Chlorine Dioxide Technologies for Treatment of Municipal
Water Supplies." This project is a fact finding, state-of-the art
survey of municipal water treatment practices involving the use of ozone
and chlorine dioxide in the United States and selected foreign countries.
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Thus far this study has developed some preliminary information on
the use of ozone in other countries. Nineteen water treatment plants
(18 in Quebec, 1 in the Northwest Territory) have been identified in
Canada.
In Europe, Asia and Africa, a total of 1034 water treatment plants
using ozone have been identified through a search of the literature and
through contact with the manufacturers of ozone generation equipment.
The vast majority of these plants are in France (577) , with West Germany
(247) and Switzerland (135) each having substantial numbers. Nineteen
other countries have so far been identified as having at least one ozone
facility.
CHLORINE DIOXIDE
Generation in Aqueous Solution
Chlorine dioxide, like ozone, is usually generated and used on
site, although products referred to as "stabilized" chlorine dioxide are
available on the Market. Chlorine dioxide is usually generated in
aqueous solution for water treatment, as gaseous chlorine dioxide generation
is not well suited to this application. White notes that chlorine
dioxide would not be available for use in water or wastewater treatment,
if it were not for the availability of solid sodium chlorite. This
chemical was first made availble in commercial quantities by Matheson
(now Olin-Matheson) in 1940.
Two methods are commonly used to generate chlorine dioxide for
water treatment:
a. From chlorine and sodium chlorite
C12 + H20 —> HOC1 + HC1 Eq.(l)
HOC1 + HC1 + 2NaCK>2 —> 2C102 + NaCl + H20 Eq. (2)
This method is commonly used where a gas chlorinator is available.
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b. From sodium hypochlorite and sodium chlorite
NaOCl + HC1 — > NaCl + HOC1 Eq.(3)
HC1 + HOC1 + 2NaC102 — > 2C102 + 2NaCl + H20 Eq.(4)
In either method, the addition of a mineral acid can be used to
control the reaction stoichiometry, and thus eliminate an excess of
either free chlorine (prevent trihalomethane formation) or chlorite
(toxicity problems) .
In the case where a gas chlorinator is used, the chlorinator effluent
must be at pH 3.5 or lower, and contain at least 500 mg/£ chlorine, if
Q
complete reaction of the sodium chlorite is to be effected. To achieve
this condition, the usual practice is to set the chlorine-technical
sodium chlorite ratio at 1:1 to provide excess chlorine. If excess
chlorine is not desired, the chlorine- technical sodium chlorite ratio is
set at the theoretical 1:3 ratio and acid is added to maintain the pH at
3.5 or lower.
Although not as common in practice, chlorine dioxide can also be
generated from sodium chlorite and acid. The following equation illustrates
9
this, using sulfuric acid as the acid.
10 NaC102 + 5H2S04 — > 8 C102 + 5 Na2S04 + 2HC1 + 4 H20 Eq.(5)
This reaction has the advantage of producing "chlorine-free" chlorine dioxide
easily.
Usage
White reports the first known use of chlorine dioxide as a water
treatment process in the United States occurred at Niagara Falls, New
York in 1944. Chlorine dioxide was used to control phenolic tastes and
odors from industrial wastes as well as tastes and odors from algae and
decayed vegetation. The 1963 Inventory of Municipal Water Supplies
showed that only 8 of 11,590 water treatment plants in the Inventory
used chlorine dioxide.
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Information is still being gathered on the WSRD extra-mural project
and a final report is not due until early in 1978. Some information on
the use of chlorine dioxide is available, however. It should be considered
preliminary in nature at this writing (Fall 1977).
Chlorine Dioxide Use in the United States
103 facilities have been identified as using or have used
chlorine dioxide
27 - Georgia
24 - Ohio
18 - Pennsylvania
8 - Michigan
Many of the treatment facilities in Georgia and Pennsylvania are
thought to be small ground water systems with well-head chlorine dioxide
disinfection prior to distribution. Most of the United States facilities
are using chlorine dioxide for taste and odor control (phenols), for
iron and manganese oxidation or for final disinfection.
Chlorine Dioxide Use in Canada
Ten facilities have been identified as using chlorine dioxide. All
are in the Province of Ontario and all use chlorine dioxide for taste
and odor control. Three of these plants are said to have "severe" taste
and odor problems.
Chlorine Dioxide Use in Europe
In Europe, chlorine dioxide is used in several thousand water
treatment facilities, most of them of very small size. Countries where
extensive use is known include: West Germany, Switzerland, France, and
to a lesser extent, Belgium. Italy and The Netherlands also are known
to have a small number of chlorine dioxide facilities. At most locations,
chlorine dioxide is used for final disinfection prior to distribution.
The principal reason for its extensive use ir that it does noi: Impart a chlorinous
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taste to the water. When completed, the final report from the WSRD
research grant will provide more extensive information on the use of
both ozone and chlorine dioxide in drinking water treatment.
CHLORAMINES, COMBINED CHLORINE, OR CHLORAMINATION
Generation
Combining ammonia with chlorine to form chloramines has been variously
called the chloramine process, chloramination and combined residual
chlorination. The usual goal in this water treatment process is to form
monochloramine according to the reaction:
HOC1 + NH —> NH Cl + H70 (monochloramine) Eq.(6)
J £, £,
Reaction conditions to optimize production of monochloramine include:
a. A pH range of 7 to 8.
b. A chlorine-to-ammonia ratio of 5:1 (by weight), or less. The
natural free ammonia content of the water, if any, should be
included in determining this ratio. The preferred ratio,
according to White , is 3:1 (by weight), although widely
varying ratios are found in practice.
At higher chlorine-to-ammonia ratios, or at lower pH values, other
cahloramine species will form according to the reactions:
NH2C1 + HOC1 —> NHC12 + H20 (dichloramine) Eq. (7)
NH2C1 + HOC1 —> NCI + H20 (trichloramine, or nitrogen trichloride) Eq.(8)
The production of these latter species is related to the familiar
chlorination "breakpoint" phenomenon. Their presence may contribute to
taste and odor problems in the finished water.
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Ammonia may be added to the water before or after the addition of
chlorine. In the former case, pre-ammoniation can prevent the formation
of tastes and odors resulting from the reaction of chlorine with phenols
or other substances. In the latter, post-ammoniation permits a free
chlorine residual to exist within the treatment plant, followed by the
establishment of a lasting chloramine residual in the distribution
system. The ammonia-chlorine process finds its widest use in this application,
according to White .
Usage
One of the first small scale and subsequently full scale practical
applications of combined chlorine as a disinfectant in water treatment
was in Ottawa, Ontario (Canada). Joseph Race, chemist and bacteriologist
for the City of Ottawa experimented with the material as a disinfectant
during the winter of 1915-1916 because "the price of bleach advanced to
extraordinary heights." About the same time the City of Denver, Colorado
(USA) was successfully applying a combination of chlorine and ammonia to
12
control nuisance organisms in their distribution system. By 1918,
chloramines were being used in the Catskill system of the water supply
for New York City because in previous use chlorine had disasterous
13 7
effects on trout. White further reports that chloramines were most
popular between 1929 to 1939 at which time their popularity decreased because
of the discovery of breakpoint chlorination along with the inability to
purchase ammonia during World War II.
The 1963 Inventory of Municipal Water Supplies shows only 308 of
the 11,590 water treatment plants in the Inventory using an ammonia-
chlorine process. The current unpublished inventory lists about 40,000
water supplies, however no differentiation on the type of disinfectant
used is recorded.
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SUMMARY
These three disinfectants are judged to be sufficiently common in
practice to be seriously considered as alternates to chlorination. Other
disinfectants such as silver, iodine, pH, heat, ionizing radiation, permanganate,
ultra-violet radiation, bromine chloride, ferrate, and so forth are recognized to
exist but will not be discussed in this paper as their use for treating
drinking water is minimal at the present time (Fall 1977).
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MICROBIOLOGICAL ASPECTS OF DISINFECTION
The primary reason for the use of disinfectants in potable water
treatment is to kill or inactivate pathogenic microorganisms that may be
present. The material presented in this section describes the relative
merits of chlorine, ozone, chlorine dioxide and chloramines as disinfectants
from the microbiological standpoint, the second basic criterion of an
acceptable disinfectant.
COMPARATIVE DISINFECTION EFFICIENCY
In considering the relative merits of the various chemicals used
for disinfection of potable water that are reviewed in this paper, the
major factor used to compare the different agents is their disinfection
efficiency. This may be expressed in terms of relative disinfection
concentrations needed to attain the same disinfection rate or relative
disinfection rates produced by the same concentration of disinfecting
agent. Because of the lack of standardization of methods by which
disinfection research has been conducted, the variation in resistance
shown by different isolates of the same microorganism species and variation
in resistance between species, only generalized statements about the
comparative efficiency of disinfectants can be made. In this context
the disinfecting agents under consideration may be ranked as follows in
order of decreasing efficiency .
C102 (>) HOC1 (>) OCr(>) NHC12 (» NH2C1 Eq. (9)
ozone (>) chlorine dioxide (>) hypochlorous acid (>) hypochlorite ion (>)
dichloramine (>) monochloramine
This order is derived from the results of numerous disinfection investigations
and provides a general overview of the comparative efficiency of various
disinfectants for inactivation of microorganisms.
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A further complicating factor, particularly with attempts to rank
the free chlorine and combined chlorine disinfectants, results from
changes in chemical species that occurs with changing pH, temperature,
and concentration. For instance, at pH 9.5 - 10 the usual pH for investigation
of OC1 disinfection, HOC1 is present in low concentrations and because
of its high relative germicidal efficiency compared to OC1, some of the
inactivation measured may be caused by the HOC1 rather than OC1 .
Similarly, in the case of chloramines, an equilibrium state exists as
follows:
<—
NH + HOC1—> NH Cl + H2 NHC12 + H20 Eq. (10)
Thus, a low concentration of HOC1 may be present and may contribute
to chloramine disinfection activity observed. This equilibrium is
further influenced by temperature, pH, the presence of other chemical species,
and disinfectant concentrations present. Because of the effect of increasing
temperature on the rate at which chemical reactions occur, the overall
effect of increasing temperature is one of increasing disinfection
rates, although the effect may not be the same for different disinfectant
species. For instance, the relative effective ratio of OC1 to HOC1 for
destruction of Endamoeba histolytica cysts was found to be 1 to 150 at
3°C and 1 to 300 at 23°C. That is, HOC1 was 300 times as effective as
OC1~ at 23°C , but only 150 times as effective as OC1~ at 3°C.
14
Although such effects usually are slight, Scarpino et al. in
discussing some unusual disinfection results, speculated that a borate
buffer system used in one of their studies may have had a major effect
on the HOC1—>OC1 equilibrium, may have suppressed ionization, or may have
resulted in the formation of previously undescribed viricidal forms.
Using this buffer system, their resultc indicated that OCT was seven
times as effective as HOC1 against poliovirus t>pe
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In the same buffer system, HOC1 was 50 times as effective as OC1 in
inactivating Escherichia coli. Because no further investigations of
this phenomenon have been published, the reason for these findings is
unknown.
Rather than the linear ranking of Equation (9) shown above, division
of these disinfectants into two groups based on their disinfection
efficiency is probably a better approach. One group, consisting of
those agents that are considered very powerful disinfectants, includes
ozone, chlorine dioxide, and HOC1. The other group, consisting of
weaker disinfectants includes OC1 , monochloramine and dichloramine.
CHEMICAL BASIS FOR DISINFECTANT ACTIVITY
Chemical disinfectant activity is dependent on contact between the
disinfecting agent and the microorganism surface followed by reaction
with the surface and/or penetration of and reaction with vital internal
constituents resulting in death or inactivation of the microorganism.
In the case of the disinfectants under consideration the reactions that
take place are oxidative in nature. Thus, oxidation potential is an
important factor with regard to disinfecting capabilities. Not all
chemicals having a high oxidation potential are good disinfectants,
however. For example, Morris pointed out that gaseous oxygen, 0_ has
a higher oxidation potential than many effective disinfectants. The
statement of Peleg "...substances that do not possess a high oxidation
potential will not be germicidally active. Conversely, chemical species
that have high oxidation potential may [or may not] possess germicidal
potential", reiterates this point. Therefore, chemicals with a high
oxidation potential cannot be assumed a_ priori to be good disinfectants.
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Another factor involved in disinfectant activity relates to the
chemical dissociation of the disinfecting agent and the presence of a
charge on the germicidally active portion of the molecule. An ion such
as OC1 is a relatively poor disinfectant because the presence of the
negative electrical charge prevents its approach to and diffusion through
cell membranes of microorganisms. All three of the very effective
germicides, ozone, chlorine dioxide, and HOC1 have high oxidation potentials
and also are undissociated. The germicidally reactive ozone chemical
species is not known, but it may be the OH (hydroxy radical) or the HO-
(hydroperoxyl radical). Other species such as 0_ (ozonide radical),
0- (superoxide radical), and 0 (oxide radical) have been demonstrated,
but their role in germicidal activity is not known . Most experimental
results indicate that the disinfection efficiency of ozone varies with
pH and that it is somewhat more efficient at a lower pH (6.0) than at a
higher pH (10.0). This is probably because of the greater stability of
ozone in water at lower pH's.
COMPARATIVE RESISTANCE OF MICROORGANISMS
Based on the results of many previous studies, the inherent resistance
of different kinds of microorganisms also may be ranked. As in the
case of comparative ranking of disinfectants, the figures are not precise,
but do provide a general impression of relative resistance. The rankings
in order of decreasing resistance are as follows:
protozoan cysts > enteroviruses > enteric bacteria Eq. (11)
In a currently funded WSRD research grant at the University of
Illinois involving an intensive examination of the chlorine resistance
of 6 different enteroviruses, their resistance to HOC1 (pH 6.0) was
found to vary by a factor of five in the time required for a four log
reduction.
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The time required for a four log reduction of these same viruses using OC1
(pH 10.0) ranged from 10 to 150 times that required for equivalent
18
reduction by HOC1. These results indicate that changing the pH had
different effects on the chlorine resistance of different viruses.
Further indication of this phenomenon is shown in chlorine dioxide
disinfection studies. In contrast to chlorine, chlorine dioxide does
not react with water to hydrolyze, although it does disproportionate to
CIO (chlorite), and CIO ^(chlorate). The chlorine dioxide molecule
19
remains in the same form over a pH range of at least 4 to 8.4. The
rate at which E. coli is inactivated by chlorine dioxide increases,
19
however, as the pH increases within this range. A similar effect with
20
polio virus was shown by Cronier et al. They showed that chlorine
dioxide inactivated poliovirus 1 over three times as last at pH 9.0 as
at pH 7.0. Thus, both E. coli and poliovirus 1 are much more sensitive
21
to chlorine dioxide at a slightly alkaline pH. Moffa et al. in
studying the disinfection of storm water, found a diphasic inactivation
curve when using chlorine dioxide. Although chlorite and chlorate
concentrations were not measured, they attributed the second slower
phase of inactivation to the disappearance of chlorine dioxide and the
appearance of chlorite. They concluded therefore that chlorite had "—
weak bactericidal and viricidal properties—."
Differences in disinfection resistance between different isolates
22
of the same virus type have also been shown. Kelly et al. showed that
the time required for a three log reduction of several different poliovirus
1 isolates varied from 3 to 6 minutes during exposure to 0.2 to 0.3 mg/Jl
23
of free chlorine. Recent studies by Bates et al. indicate that progeny
of poliovirus 1 repeatedly cycled through chlorine disinfection are
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somewhat more resistant to chlorine than the original parent stock
virus. The resistant progeny required about 2.5 times the length of
exposure required by the parent stock for inactivation to the same
level.
The existence of extremely resistant polio 1 viruses has also been
r\ I
reported recently . At free chlorine levels of about 0.5 mg/£ and pH 7.1,
these isolates showed a decline of about one log in 2 minutes with little,
if any, further decrease in titer after 30 minutes exposure. Thus,
these viruses apparently show a complete resistance to chlorine for
upwards of 30 minutes, rather than merely a difference in time required
for complete destruction. Isolates of these resistant viruses have been
obtained and further experiments are in progress in the laboratories of
Dr. Engelbrecht of the University of Illinois and Dr. Sharp of the
University of North Carolina, both funded by WSRD research grants.
Aggregation or clumping of viruses has long been considered to be a
factor involved in increased viral resistance to disinfectants. Until
recently, however, no evidence of this has been available. Through a
series of WSRD research grants at the University of North Carolina,
evidence of this phenomenon and information on the factors involved in
25-29
virus aggregation and deaggregation have been obtained. Although
the effects are complex and appear to be different with different viruses,
some general information has been developed from these studies as follows:
1. Although differences in halogen resistance of up to 300 fold
between aggregated and dispersed viruses have been shown, the
differences thus far shown are merely differences in rates of
inactivation. No evidence of complete resistance to inactivation
because of aggregation has been found.
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2. pH and metallic cations are important determinants with regard
to aggregation. Aggregation does not appear to be related to
virus isoelectric point characteristics.
3. Induced aggregates of some viruses are quite stable although
those of other viruses can be dispersed easily. Natural virus
aggregates appear to be more stable than induced aggregates.
Of the most resistant forms of microorganisms of concern, protozoan
cysts, only Endamoeba histolytica has been extensively studied with
regard to disinfection. Most of this research has been conducted using
30
chlorine in various forms. Newton and Jones showed that ozone was a
more effective cysticidal agent than chlorine. Although chlorine dioxide
would be assumed to be an effective cysticidal agent, research findings
on this point could not be found. The resistance of E. histolytica cysts
to chlorine is such that White states, "The best protection against
this disease (amebiasis) is removal of the organisms from water supplies
by filtraiton. They are large enough to be trapped by sand filters, and
require high doses of free residual chlorine (10 ppm) and long contact
time (one hour or more) to effect disinfection." According to Palin ,
the range of free residual chlorine recommended by the National Research
Council for insuring cyst destruction within a 30 minute contact time
ranged from 2 mg/£ to 70 mg/£ depending on the pH and temperature of the
water being treated. Despite this and the lack of universal filtration
of water supplies originating from source waters that may contain E.
histolytica cysts, waterborne outbreaks of amebiasis are rare in the
United States.
Outbreaks of giardiasis, a disease caused by Giardia lamblia, a
protozoan that also forms cysts, have, however, been occurring with
increasing frequency in recent years. In contrast to E. histolytica, a
method for determining viability of G. lamblia cysts has not yet been
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developed. Although they are assumed to be highly resistant to disinfection,
little is known about the resistance of these cysts to various disinfectants.
A WSRD funded research grant at the University of Oregon Medical School
in Portland on development of methods for determining viability is in
progress and current results indicate that a method for determining
cyst viability in vitro will soon be available for use in disinfection
32
studies on this microorganism.
PROTECTIVE EFFECTS OF PARTICULATE MATTER
As indicated previously, for disinfection to be effective, contact
must occur between the disinfectant and the microorganisms to be inactivated
or killed. Because source waters may contain a variety of inorganic and
organic particulates, some of which may originate as fecal wastes, and
because of the tendency of microorganisms, particularly viruses, to
adsorb to various kinds of particles, removal of particulate matter,
usually measured by light scattering, has been considered very important
during water tratment. Although the major reason for removal of particulate
matter (turbidity) has been the concern about its interference with
disinfection, little direct evidence of such interference was available
until recently.
Previously laboratory studies had established that enteric bacteria
and enteroviruses ingested by aquatic nematodes found in some water
33
supplies were protected against very high doses of chlorine . In
another instance, persistence of coliforms in a water supply system
containing a substantial level of residual chlorine was attributed to
ingestion and survival of the coliforms in small crustaceans present in
34
the water . More recent studies indicate that virus adsorbed onto
surfaces of particles such as clay remain exposed to the disinfectant
•5 |- o f
and disinfection rates are affected only slightly, if at all. ' Further,
viruses precipitated with aluminum phosphate, or flocculated with calcium
-------
- 20 -
carbonate or alum or either unprotected or are protected to only a minor
Q X O Q
degree. Viruses associated with cell debris, however, are well
protected from inactivation, showing survival for up to 50 minutes at
37
HOC1 concentrations of 1.5 - 2.0 mg/Jl . Protection of coliforms associated
with primary sewage effluent solids .for at least 60 minutes at HOC1
38
concentrations of 0.5 mg/S, also has been shown
All of these studies have been conducted using free chlorine as
the disinfectant. Similar studies sponsored by WSRD research grants are
in progress at the Unversity of Cincinnati using chlorine dioxide and
at the University of Maine using ozone and studies using chloramines are
planned. Based on the comparative disinfection efficiency of various
disinfectants, one might speculate that the same order of efficiency
would be maintained in inactivating microorganisms associated with
particulate matter. The efficiency of ozone, in particular, is difficult
to predict because of its extremely reactive nature and consequent rapid
disappearance after addition to water.
INFLUENCE OF WATER QUALITY
The organic content of water influences the disinfectant demand of
water. Waters with lower organic content require the application of
lower doses of disinfectant to achieve good disinfection. Figures 1 and
2 show that the lower organic content of the effluent from granular
activated carbon beds resulted in a reduced requirement for disinfectant,
either ozone or chlorine dioxide, when compared to a typical filter
effluent. This has important implications when considering the problem
of by-products discussed later in this paper.
STABILITY DURING WATER DISTRIBUTION
In addition to their disinfection efficiency as defined above,
another important consideration is the stability of these agents over a
period of time and their ability to remain as residual disinfectants
-------
- 21 -
cc
O
X
00
H
<
_l
E
O
O
UJ
<
o.
a
oc
o
z
H
co
DUAL MEDIA EFFLUENT, pH=7.3
FILTRATION/ADSORPTION
GRANULAR ACTIVATED CARBON EFFLUENT
pH=7.9
GAC AGE: 8 WEEKS IN SERVICE
OZONE CONTACT TIME=6 MIN.
0.1
0.2 0.3 0.4
APPLIED OZONE, mg/L
0.6
Fig. 1. POST DISINFECTION WITH OZONE
-------
- 22 -
IWUUU
1
1000(
CO
tr
i <
CIO 2 CONTACT TIME = 30 min.
pH = 7.0 - 8.1
, TEMPERATURE = 22 - 26°C
\
\
\
\
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\
^ \
\ \
* JL.
\ \
\ \
A \ *
« \\ \ \
"* \V
< \ vW^DUAL MEDIA EFFLUENT
•^ I * »
^ I \ \\ _^ss^^ FILTRATION/ADSORPTION
^_ & \ \ i ^-^-^=j"-— ^
Z T .L-— =====¥*==::=^^^ GRANULAR ACTIVATED
§ 100 tlr^ \v CARBON EFFLUENT
0
LU
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z
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1
\ \ \\ GAC AGE: 24 WEEKS IN
\ \ \\ SERVICE
\ \ ^
' , \\
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\ \ *
- \\
\ \
\
\ \ \^ NONE DETECTED AT
\ \ ^^^\ 0.2 mg/l CIO 2 DOSE
i '. ^ * \
\ \ — ' ^
\ ' \
; \ N
\ v
\ \ \
\ ^ i *, i i
0.1 0.2 0.3 0.4 0.5
APPLIED CHLORINE DIOXIDE, mg/l
Fig. 2. POST DISINFECTION WITH CHLORINE DIOXIDE
-------
- 23 -
to prevent growth of microorganisms in storage and distribution systems
after initial disinfection during water treatment. Although the major
concern regarding the regrowth of microorganisms is related more to
harmful effects on the distribution system and aesthetic effects such as
taste, odor and appearance rather than to potential health hazards,
regrowth is not a trivial problem. Further, the maintenance of a biocidal
residual to the consumers tap not only keeps the system clean and protects
against some cross-connection contamination, but also its sudden disappearance
is a rapid indication of distribution system problems. On the other
hand, the application of chlorine can depress the pH and aggravate corrosion
problems in some instances.
The level of cross connection protection attained by maintenance of
a disinfectant residual has been the subject of much conjecture. A WSRD
funded research grant in progress at the Johns Hopkins University is
39
providing some information on this. The results of batch studies in
which E. coli, polio 1 and f2 bacteriophage mixed with sewage were added
in proportions of up to 5 percent by volume to water containing various
levels and types of chlorine residual indicated that both free and
combined chlorine residual at equivalent concentrations eventually gave
comparable degrees-of inactivation of E. coli. A free residual at pH 6,
however, provided inactivation in 2 minutes whereas an equivalent concentration
of combined residual required two hours to inactivate E. coli. Neither
free residual nor combined residual at pH 8 consistently inactivated
polio virus or f2 bacteriophage to the lower sensitivity limit of the test.
The distribution system problems associated with the use of combined
clorine residual or no residual have been documented in several instances. ' '
In these cases the use of combined chlorine is characterized by an
initial satisfactory phase in which chloramine residuals are easily
-------
- 24 -
maintained throughout the system and bacterial counts are very low. Over
a period of years, however, problems may develop, including increased bacterial
counts, dropoff of chloramine residuals, increased taste and odor complaints, and
reduced main carrying capacity. Conversion of the system to free chlorine residual
results initially in an increase of taste and odor problems resulting from sloughing
off of accumulated organic material and problems in maintaining a free chlorine
residual. Following this phase, a free chlorine residual is established throughout
40
the system, bacterial counts are lower and taste and odor complaints decline.
Of the disinfectants under consideration, a residual level can be maintained with
all except ozone, which, because of its high reactivity, disappears very rapidly.
SUMMARY
In considering the overall biocidal or germicidal advantages and disadvantages
of these disinfecting agents as alternatives to free chlorine, which is currently
advocated, from a microbiological point of view chlorine dioxide would be best.
It is highly efficient, is most effective in the pH range in which water
treatment is practiced, and can be maintained as a residual disinfectant in
distribution systems. Chloramines have disadvantages with respect to their
much lower disinfection efficiency, possible failure to completely inactivate
pathogens present, their ineffectiveness in providing a barrier to cross
connection contamination, and their failure to prevent regrowth in distribution
systems in some cases. Ozone, although extremely efficient as a disinfectant,
cannot be maintained as a residual in distribution systems. In the future, the
effectiveness of these three alternate disinfectants and the influence of
particulates and mixing intensity on disinfection will continue to be studied
in both in-house and extramural bench-, and pilot- and field scale projects
sponsored by WSRD.
-------
- 25 -
MEASUREMENT OF DISINFECTANT RESIDUALS
In order to properly control the use of a disinfectant, the residual
concentration of the disinfectant must be easily measurable, and where
distribution system protection is needed, this residual must be maintained
and monitored, the third criterion of an acceptable alternate to chlorine.
FREE CHLORINE
For measurement of free chlorine residuals (HOC1+OC1~+C12) the 14th
42
edition of Standard Methods lists and describes in detail eight methods
of residual analysis: Two iodometric methods, Phenylarsine oxide —
Amperometric Titration, Stabilized Neutral Orthotolidine (SNORT), DPD
Ferrous Titrimetric, DPD Colorimetric, Leuco Crystal Violet, and Syringaldazine
(FACTS). The relative usefulness of each method plus known possible
interferences in the analyses are described in the reference. Each
method is based on the oxidizing capacity of aqueous chlorine and measures
in some quantitative way the oxidation products of the reaction of the
chlorine residual with the method reagent materials.
OZONE
Because all of the alternate disinfectants under consideration are
also oxidizing agents (ozone, chlorine dioxide, chloramines) some version
of most of the above methods is applicable to the analysis of each of the
42
alternates as well. Indeed, Standard Methods lists an iodide—iodine
titrimetric method as the quantitative approach to ozone residual measurement
where concentrations are over one mg/£. An amperometrically determined
43
end point extends the lower range of this analysis.
-------
- 26 -
CHLORINE DIOXIDE
lodimetry, a modified orthotolidine, and amperometric titration are
42 44
recommended for chlorine dioxide measurements . Recently, Miltner
45 46 47 48
reviewed the work of Palin ' , Adams, et al. and Hong and Rapson
and ultimately applied the DPD titrimetric procedure to the measurement
of aqueous chlorine dioxide during his work describing the prevention of
49
formation of trihalomethanes by use of this alternate disinfectant.
CHLORAMINES
42
Amperometric titration is considered a standard of comparison for
free or chloramine residuals, although some of the other chlorine methods
such as the DPD methods are also applicable to the determination of
chloramines.
COMBINATION OF DISINFECTANTS
Thus, the measurement of chlorine and alternate disinfectant residuals
per se is not a particularly difficult analytical task where considerations
are given to the interferences and limitations described in each of the
methods referenced. The measurement of individual disinfectants is only
slightly more complicated when disinfectants are used in combination
with one another. Commonly encountered examples of this are chloramines
in the presence of chlorine (chlorine used with ammonia or where ammonia
or organic amines are already present when chlorine is applied), chlorine
in the presence of chlorine dioxide (chlorine dioxide is often produced
by the action of excess chlorine on chlorite), and chlorine in the
presence of ozone. Even these three examples have relatively straightforward
analytical solutions:
42
Free Chlorine with Chloramines
Free chlorine (HOC1, Cl- or OC1~) is measured by either of the DPD
methods or by amperometric titration followed by sequential measurement
of iodine liberated by the reaction of the respective mono- and dichloramine
with added iodide under specified pH conditions.
-------
- 27 -
Chlorine with Chlorine Dioxide
44
After a thorough investigation of published methods, Miltner selected
the DPD approach as most reliable and convenient for measuring chlorine
dioxide in his work. When DPD is used (either titrimetric or colorimetric)
two separate measurements are necessary to determine chlorine and chlorine
44
dioxide concentrations, and two approaches to this are possible. Malonic
acid can be added to an aliquot of the sample to react with residual
45 46
chlorine prior to a chlorine dioxide measurement ' and then two DPD
measurements, one before and one after malonic acid addition, will yield
total chlorine dioxide-plus-chlorine and chlorine dioxide respectively.
Chlorine is obtained by difference. The other approach is to purge the
chlorine dioxide from solution by gas stripping leaving the chlorine in
48
solution . In this approach the chlorine is measured directly and the
chlorine dioxide determined by difference. In either case the analysis
for these two species in simple combination is relatively uncomplicated.
Ozone with Chlorine
43
According to Dailey and Morrow , phenyl arsine oxide—amperometric
titration of iodine liberated upon the reaction of both chlorine and
ozone with added iodide followed by a similar titration of a second
aliquot previously treated with ammonia will yield the concentrations of
total ozone-plus-chlorine and chlorine alone respecitvely. The ozone
concentration is obtained by difference. This approach depends upon the
reaction of ozone and chlorine with ammonia to form nitrate (unreactive)
and monochloramine (reactive with iodide) respectively.
Complex Combinations
From the above, the conclusion might erroneously be reached that
the problems of disinfectant residual measurement are fairly well solved.
-------
- 28 -
This is not necessarily the case, however. Where multiple disinfectants
are used, where more than two or three active species need to be quantified,
or possibly where certain organic materials are present (see next section),
the number of analytical steps and techniques as well as the calculations
necessary become much greater and the procedure more complex. For
44
example, Miltner attempted to measure free chlorine, chlorine dioxide,
and all expected inorganic reaction products resulting from the action
of these species with the organic materials in the source water. The
goal was to generate a material balance of inorganic chlorine and oxychlorine
species to aid in assessment of toxicological hazard (to be discussed
later) from products (for example, chlorite and chlorate) possibly
resulting from the widespread application of chlorine dioxide as a
disinfectant alternative to chlorine.
Miltner was able to use a combination of five procedures, two
required in triplicate, to construct a material balance of free chlorine,
chlorine dioxide, chlorite, chlorate and chloride in a few simple cases
in rather dilute solutions. Follow up work conducted over a wide concentration
range indicated that many problems with this total analysis still
exist, especially with the measurements of chlorate and the relatively
small contributions of chloride above background by the applied disinfectant.
Additionally, because of the differences in disinfecting power of
each of the free chlorine species, HOC1 and OC1 (see previous section)
distinguishing between them under any given set of treatment conditions
rather than simply measuring the "free residual" might be desirable.
This represents a different problem from that posed by the need to
measure oxychlorine species of different oxidation states. Johnson has
developed a membrane electrode that claims promise, but it has not yet
been generally accepted as a practical tool in the drinking water industry.
-------
SUMMARY
If such differentiation of oxidizing species as in the two examples
cited above are finally deemed to be unnecessary, disinfectant residual
measurements are likely to remain relatively simple when proper consideration
is given to potential interferences. Future work by WSRD will focus on
the possible interferences of organic compounds when measuring chlorine
dioxide residuals.
-------
BY-PRODUCTS AND END PRODUCTS OF DISINFECTION
The occurrence of trihalomethanes in finished drinking water has
been demonstrated to be widespread and a direct result of chlorination
52-54
practices at the water treatment plant. Because of the health
significance of these trihalomethanes (discussed later in this section)
an alternate disinfectant is being sought. The fourth criterion any
alternate must meet is the creation of less undesirable by-products and
end-products than chlorine.
CHEMISTRY
Free Chlorine
Chloroform results from the generalized reaction:
Free Chlorine + "Precursor" —> Chloroform52"56 Eq.(12)
This occurs to some extent in any water treatment plant where
chlorination for disinfection is practiced and natural organic (humic)
material is present to act as precursor. The reaction is not instantaneous
and occurs over a period of a few days until either chlorine or precursor
is exhausted. In the presence of natural bromide, the reaction products
include some mixed-halogen trihalomethane species (bromodichloromethane,
52
dibromochloromethane) and bromoform. This occurs in most chlorinated
54
drinking water , even where bromide concentrations in the source water
are small. Iodine-containing species have also been observed , presumably
because of the presence of natural iodide. Because the chemical reactions
for formation of these bromine- (and iodine-) containing trihalomethanes
CO
are probably mechanistically similar to that for formation of chloroform,
the trihalomethanes, including chloroform, can be discussed as a group.
-------
- 31 -
Because trihalomethane formation is not an instantaneous reaction,
as long as a free chlorine residual is present, trihalomethane concentrations
will increase in the water as it flows through a water treatment plant
(unless removed during treatment) usually reaching some value higher
than that which would be observed if an analysis for trihalomethane
species was performed immediately after sampling at the first point of
chlorination. (A more complete discussion of these concepts has been
59
presented elsewhere. .) Further, the consumer is likely to receive
water with trihalomethane concentrations higher than those leaving the
plant because the reaction proceeds in the distribution system. Additionally,
not only are the concentrations of trihalomethanes time dependent, but
the rate of reaction is dependent on pH, precursor concentration, nature
of precursor(s), temperature, and to tome degree, free chlorine concentration
early in the chlorination process. ' ' Finally, the ratio of chloroform
to other trihalomethanes is highly dependent on the bromide content of
/• o f o
the source water. ' Typical concentrations of trihalomethanes
54
formed range from < 1 yg/£ to a few hundred yg/£.
In addition to the trihalomethanes, numerous other compounds have
been found in chlorinated waters and their presence attributed to the
64
chlorine applied under those circumstances. For example, Rook has
characterized more than twenty by-products of chlorination of Rotterdam
storage reservoir water. Jolly and Glaze have reported the presence
of a large number of carbon-substituted chlorinated compounds in chlorinated
waste waters. Nitrogenous compounds react with chlorine during both
drinking water and wastewater disinfection to yield the nitrogen-substituted
chloramines. Currently, Morris of Harvard University has a WSRD Research
Grant to study the influence of pH and time on the reactions of chlorine with
-------
- 32 -
nitrogenous compounds likely to be found in natural waters. In addition
to the chlorine demand reactions, the production of chloroform in these
reactions is also being determined. Phenols have long caused a problem
with odors in chlorinated waters by forming the highly odorous chlorophenols.
Generally speaking, however, the concentrations of these compounds, if
formed upon chlorination of drinking water, are much lower in finished
drinking water than are the concentrations of the trihalomethanes at
locations where a free chlorine residual is maintained. Individual chlorinated
compounds other than the trihalomethanes are not generally found at
concentrations in finished drinking water higher than found inx the
corresponding source water. Additional confirmation on this is being
sought through a thorough study of the occurrence of halogenated hydrocarbons
in the Passaic River watershed and the rate of change of these (increase
or decrease) concentrations through the water treatment process at
Little Falls, New Jersey. The work is being carried out by J.V. Hunter
at Rutgers, The State University under a WSRD research grant.
/TQ
The recent findings concerning the carcinogenicity of chloroform has
stimulated EPA efforts to aid in reducing human exposure from the drinking
69
water source to these chlorination by-products . Any efforts to reduce
trihalomethane concentrations should be expected to result in a presumably
beneficial decrease in formation of the other chlorinated by-products.
For example, Sontheimer et al. reported an increase in total organic
chlorine concentration, as concentrated by adsorption on ground granular
activated carbon and measured by a pyrolysis technique, of 186 yg/£ after
breakpoint chlorination of Ruhr River water, although the chloroform
concentration only rose 6 yg/£ and the total trihalomethane concentration
only increased 14 pg/£. Insights as to the reduction in organo-chlorine
load obtained as a consequence of control cf f~~"" 1 on"-''li"~r ^ormation may
-------
- 33 -
be gained as a result of understanding the mechanism of chlorination
reactions of humic substances leading to trihalomethane production.
This is currently under detailed review through a WSRD research grant to
R.F. Christman, et al., at the University of North Carolina.
Ozone
In-house research by EPA's Water Supply Research Division has
shown that disinfection level (<5 mg/£) ozone doses, under the conditions
tested, will not:
a. form trihalomethanes (i.e., oxidize chloride to chlorine with
subsequent reaction with trihalomethane precursors)
b. reduce the concentrations of trihalomethanes already formed prior
to ozonation
c. reduce the concentration of trihalomethane precursors as measured
59
by the trihalomethane formation potential
At the present time plans have not been made to attempt to' identify
other by-products from ozonation in-house, although Chian of the University
of Illinois has found that upon ozonation, 2-propanol was converted to
acetone that in turn was oxidized to acetic and oxalic acids. Trace
amounts of formaldehyde and formic acid were also detected in the ozonated
acetone solution. Further ozonation of acetic acid resulted in the
formation of glyoxylic acid that was oxidized readily to oxalic acid.
Extramural research is now being sponsored by the WSRD on ozone oxidation
by-products and end-products. A research grant to Glaze at North Texas
State University is investigating the use of ozone with and without
ultraviolet radiation in drinking water treatment. The removal of
selected compounds (trihalomethane precursors, trihalomethanes, polycyclic
-------
- 34 -
aromatic hydrocarbons (PAH's), polychlorinated biphenyls (PCB's) and
others) and the oxidation/photolysis products formed are being studied
over a 3-year period. At this time (Fall 1977) preliminary results are
not available.
Chlorine Dioxide
49
Some results of work by Miltner in the WSKD laboratory to monitor
trihalomethane production with time after chlorine dioxide, chlorine,
and chlorine dioxide with chlorine were separately applied to pilot
plant settled water are shown in Figure 3. The upper curve represents
the action of chlorine alone; the curve coincident with the abcissa
represents the application of chlorine dioxide alone; and the curve
between these two represents the action of chlorine to form trihalomethanes
in the presence of chlorine dioxide. These curves demonstrate two important
points: (a) chlorine dioxide does not cause the formation of trihalomethanes
and (b) chlorine dioxide plus excess chlorine (as is often the case in
water treatment) results in the formation of lower concentrations of
trihalomethanes than does the same amount of chlorine alone. Therefore,
with consideration only to minimizing trihalomethane formation, chlorine
dioxide is a possible alternative to chlorine as a disinfectant in water
treatment. Although this is the case, consideration must still be given
to other by-products that may be formed by chlorine dioxide treatment.
Considerable evidence exists that chlorine dioxide reacts with
organic material during water treatment and therefore is likely to
produce organic by-products:
-------
F.A. Cl = FREE AVAILABLE CHLORINE
pH = 7.4
T = 24°C
/ 1.5 mg/l F.A.CI
f y
1.3 mg/l CIO2 + 1.5 mg/l F.A.CI
CIO 2 ALONE
10 20 30 40 50 60
CONTACT TIME, HOURS
70
80
FIGURE 3. TRIHALOMETHANE FORMATION BY CIO 2 AND
EXCESS FREE AVAILABLE CHLORINE,
ERC PILOT PLANT SETTLED WATER
(FROM MILTNER, R. J., 1976)O
I
OJ
-------
- 36 -
1. Because chlorine dioxide is a good disinfectant (see earlier
section), some reaction is taking place between the cell components of
the organism and the chlorine dioxide.
2. Even though chlorine dioxide does not react with ammonia most
waters exhibit a chlorine dioxide demand similar to that of chlorine.
3. At applied chlorine dioxide concentrations higher than those
encountered in drinking water treatment, identifiable by-products have
72
been isolated.
4. Chlorine dioxide destroys phenolic compounds when the oxidant
is used for taste and odor control in water supplies.
5. Most importantly, as was shown earlier, the presence of chlorine
dioxide reduces the formation of trihalomethanes by chlorine. This and
49
other evidence obtained by Miltner indicated that chlorine dioxide
reacts with natural humic acid. This is not surprising because chlorine
73
doxide is effective for reducing color in drinking water supplies.
Before an informed decision can be made as to the relative desirability
of free chlorine and chlorine dioxide with regard to the formation of
organic by-products a detailed investigation and identification of the
products formed during disinfection with both chlorine and chlorine
dioxide was considered necessary and was initiated in the WSRD laboratory.
The possible organic by-products arising from the use of chlorine dioxide
as a disinfectant in drinking water was first considered on the basis of
the existing literature,followed by an on-going laboratory study to
determine whether extrapolations from the literature describing work
where concentrations of oxidant and organic material were generally high
were valid.
-------
- 37 -
A b.rief review of the pertinent literature was recently presented
74
by Stevens although a much more extensive and complete review is
72
available elsewhere. Briefly, the literature describes chlorinated
and non-chlorinated derivatives including acids, epoxides, quinones,
aldehydes, disulfides, and sulfonic acids, that are products of reactions
carried out under conditions vastly different from those experienced at
water treatment plants.
74
Stevens reviewed only a few reaction types that were suspected to
be important in water treatment practice. Considered as reacting species
were saturated aliphatic hydrocarbons, olefins, amines, and aromatic
compounds. Based on the literature, chlorine dioxide would not be
expected to react with saturated aliphatic hydrocarbons in aqueous
media. Chlorine dioxide was reported to react with olefins to produce a
variety of chlorinated and non-chlorinated products: aldehydes, epoxides,
chlorohydrins, dichloro-derivatives, and chloro- and unsaturated-ketones.
Amines react with chlorine dioxide in a manner very different from that
of chlorine, chlorine dioxide does not produce chloramines. In general,
the respective aldehydes are formed from amines in the order of reactivity:
72
tertiary > secondary > primary
The best known reactions of aqueous chlorine with aromatic compounds
in the water treatment field are those that occur with phenols. Chlorine
reacts rapidly with phenol to form mono-, di-, and tri-chloro derivatives.
These compounds are highly odorous and are slowly decomposed by excess
chlorine. Other phenolics and substituted aromatics can also be chlorinated.
The formation of chlorophenols by chlorine treatment is one of the chief
reasons that chlorine dioxide has been used in drinking water disinfection
applications.
-------
- 38 -
According to the literature, chlorine dioxide usually does not form
odorous compounds with phenol, but through a complex mechanism, forms
the quinones and chloroquinones, and when in excess, oxalic and maleic
72
acids. Chlorine dioxide treatment of phenols can cause chlorine
substitution or ring cleavage or both depending on the phenol reacted
and the conditions of the reaction. The chlorinated products will
generally be of different structure and are either less odorous or are
formed in much lower yield than those formed by chlorination. For
example, vanillin reacts at pH 4 with chlorine dioxide to give the non-
chlorinated g-formymuconic acid monomethyl ester. Veratryl alcohol,
7 ? 76
however, produces 4,5-dichloroveratrole ' when reacted with chlorine
dioxide, which is one of the products expected from chlorination of
veratryl alcohol.
Some of the more detailed investigations of the reactions of chlorine
dioxide with phenols (ring cleavage or ring retention with or without
chlorine substitution) have been accomplished by Glabisz and Paluch at
78
the Polytechnic University, Szczecin, Poland. Glabisz states
that, at least at concentrations of one mg/& and above, the character of
the reaction products of phenols falls into two groups. The first is
the group in which the ring structure is retained and the end products
are quinones. This group is made up of para-dihydric and monohydric
phenols that are not para substituted. The second group is characterized
by those phenols which undergo ring cleavage to give carboxylic acids as
end products. Examples include para alkyl phenols and ortho or meta
dihydric phenols.
-------
- 39 -
In general, monohydric phenols reacting with chlorine dioxide undergo
chlorination along with oxidation, and those of the first group form the
78
chloroquinones, as well as chlorophenols. Glabisz considers this to be
somewhat similar to the reaction of chlorine with these phenols. Although
chlorine dioxide tends to favor oxidation over chlorination, the relative
amount of chlorinated versus oxidized products depends on the relative
amounts of both chlorine dioxide used and phenols present. Excess chlorine
dioxide favors oxidation.
Because of the potential for undesirable by-product formation resulting
from chlorine dioxide disinfection of drinking water, an in-house investigation
was begun at the WSRD Laboratory to determine if by-products of the type
predicted by the literature, where reactions described were carried out at
generally higher concentrations, would prevail in the drinking water
disinfecting conditions. This work is being carried out in two phases:
1. The search of purgeable compound gas chromatographic data (for
example from trihalomethane analyses) for differences between chlorine dioxide
treated- and untreated waters.
2. Development and use of a more elaborate analytical scheme to detect
products of more diverse nature, specifically those expected from reactions
of phenolic compounds.
The semi-quantitative results of the first phase have already been
74
briefly described where C0 through C0 aldehydes were noted to increase in
/ o
concentration after treatment of a natural water with chlorine dioxide.
In that work, no other dramatic differences were observed between treated
and untreated samples with regard to compounds amenable to the purge-and-trap
* u- i • 54,57,79
type of gas chromatographic analysis used.
-------
- 40 -
Phenol was selected as the model compound for the beginning of the
second phase primarily because of the polyphenolic nature of humic
80
materials (see Figure 4) (trihalomethane precursors) that make up a
large fraction of the organic material present in natural waters where
trihalomethane formation is a problem. This work is not yet complete,
but chlorophenols have been produced at high (5/4) molar ratios of
phenol to chlorine dioxide. Lower ratios (5/14, 1/14) do not produce
chlorophenols, but hydroquinone was isolated from all reaction mixtures.
Other organic by-products such as oxalic and maleic acids, and 2,6- and
2,5-dichloro-p-benzoquinone were not immediately identifiable, although
total organic carbon concentration data indicate that the phenol is not
completely converted to carbon dioxide. To date (Fall 1977) no gas
chromatographable compounds in this category have been identified in
chlorine dioxide-treated natural waters, and humic- and fulvic acid
solutions that were not present in the untreated sample (detection
limits estimated to be in the range of 5 - 10 ug/& as phenol) .
Some circumstantial evidence now seems to indicate formation of
poly quinone-like material from phenol as well as from at least one
42
source of aqueous humic material, however. The DPD colorimetric method
was used to determine the chlorine dioxide demand of a highly colored
natural water. An interference equivalent to approximately 0.3 mg/5, of
chlorine dioxide was observed below the point on the demand curve where
residual concentration began to rise as dose increased. A similar effect
was observed after chlorine dioxide treatment of phenol solutions (see
above). The compound p-benzoquinone, a model for possible organic byproducts
of chlorine dioxide reactions and the oxidized form of hydroquinone (see
above) was also found to produce a color with DPD without chlorine dioxide treatment,
so an alternative test was sought for the determination of chlorine
dioxide that might not be subject to quinone interference. The FACTS
-------
COOH
OH
OCH
OH O
OH HO^OH
N
FIGURE 4. A PROPOSED HUMIC STRUCTURE (FROM
CHRISTMAN & GHASSEMI,)^
-------
- 42 -
42
test, using syringaldazine with spectrophotometric measurement at 530 nm
was found to be a suitable replacement for DPD. This reagent did not give a
color with p-benzoquinone. In a chlorine dioxide demand determination on
a second colored water, however, a water similar to but from a different source
than that used previously, the syringaldazine method gave a higher blank (reagents +
water, no chlorine dioxide) reading than the DPD method. Although the curves
compared well when background was subtracted, neither curve showed the 0.3 mg/£
"false positive" seen with the previous sample.
A chlorine dioxide demand test on a second sample of the first highly
colored raw water gave results similar to the first test reported above
and again showed "false positive" concentrations below the "breakpoint"
of the demand curve without the DPD test. Chlorite was found to be major
inorganic product of chlorine dioxide treatment of this water (see Table I) .
TABLE I
Chlorine Dioxide Treatment of a Colored Natural Water
CIO Dose CIO Residual CIO Cone. Contact Time 23 Hour.
mg/K mg/£ mg/x, Hours Chlorine
Demand
mg/£
13.13 1.19 6.33 23 11.94
The presence of chlorite did not cause this apparent chlorine dioxide residual
using the DPD method. The same effect has not been observed on other raw
water sources or treated humic- or fulvic acid solutions. This general
problem requires considerably more work and will be the subject of a future
more detailed report.
-------
- 43 -
Inorganic by-products may also be of concern. As noted above
evidence obtained at the WSRD laboratory indicates that a large portion
of the applied chlorine dioxide remains as chlorite rather than chloride
although accurately determining what percentage of this results from
simple disproportionation in contrast to being a reduction product from
organic reactions (see previous section on measurement of disinfectant
residuals) has not been possible.
Chloramines
54
During the 1975 National Organics Reconnaissance Survey (NORS) 10 of
the 80 utilities sampled disinfected with chloramines. The sum of the
concentrations of the trihalomethanes found, expressed as ETHM, in the
finished water of these supplies ranged from 1 to 81 yg/£ with an average
of 19 yg/£. For comparison, those utilities that were using breakpoint
chlorination had THM concentrations ranging from 1 to 472 yg/£ in the
finished water with an average concnetration of 72 yg/£. A similar
Q I
study conducted in Ontario, Canada on 48 water utilities included 10
that were disinfecting with combined chlorine, but the report does not
contain sufficient details on treatment practices to assess the impact
of combined chlorine on trihalomethanes. Stevens et al. in a laboratory
experiment, applied both free and combined chlorine for varying contact
times to samples of untreated Ohio River water. Figure 5 shows the
ETHM formation in the chlorinated sample reaching 160 yg/£ after 72
hours, yet the companion sample having combined chlorine formed only 16
yg/& ETHM during the experiment.
54
The reason some of the water utilities in the NORS study using
chloramines had relatively high ETHM's is probably because of free
chlorine being used prior to the addition of ammonia. For example, in
the Kansas City Water Works the ETHM concentration at the time of the
54
NORS was 34 yg/£ This is not surprising because free chlorine is
-------
- 44a -
dosed about 5 hours before the ammonia is added. Another example of
82
this effect is shown by Tuepker for the St. Louis County Water Company.
There, like Kansas City, the water is softened and chlorinated with
approximately an eight hour contact time before ammonia is added. In
that situation the chloroform concentration averaged 49 yg/£ over a 5
month sampling period.
83
According to Lambert et al. trihalomethane production begins only
when monochloramine, and presumably dichloramine, is destroyed by free
chlorine. Further, once water is ammoniated and the disinfectant exists
as combined chlorine the trihalomethane reaction essentially stops.
This is shown by the plateau on the combined chlorine curve in Figure 5.
Finally, the trihalomethane levels reaching the consumer should be
similar to the trihalomethane concentrations .leaving the treatment plant
Q O
when combined chlorine is used as the disinfectant. Tuepker has shown
this to be the case where he reported no measurable differences between
the trihalomethane concentrations leaving the treatment plant and those
measured in the distribution system. As noted previously, free chlorine,
on the other hand, continues to react with precursors in the distribution
system and consumers in outlying reaches can receive water with trihalomethanes
considerably higher than the treatment plant effluent concentrations.
The use of combined chlorine during water treatment is currently being
investigated in a WSRD Research Grant to Professor Leland Harms, South
Dakota Schoo,l of Mines and Technology at the Huron, South Dakota Water
84
Treatment Plant and at the Louisville Water Treatment plant as part of
85
the EPA project with the Ohio River Valley Sanitation Commission .
HEALTH EFFECTS
Chlorine
Toxicology
Concern over the occurrence of chloroform and other halogenated
-------
- 44b -
180 -
COMBINED CHLORINE
--
24 48 72
CONTACT TIME, HOURS
FIGURE 5: COMPARISON OF FREE AND COMBINED
CHLORINE ON THE FORMATION OF
TRIHALOMETHANES IN OHIO RIVER
(AFTER STEVENS, ET
-------
- 45 -
hydrocarbons in drinking water, primarily as a result of chlorine
disinfection, has precipitated investigations to evaluate the consequence
of exposure to these compounds on human health.
i
Chloroform has been used medicinally for anestheia, as a cough
suppressant, a carminative, a flavoring agent, and as a local irritant
in liniments. Chronic ingestion of doses of 23-37 mg/K have been reported
to produce some reversible hepatotoxic effects while ingestion of 0.3 to
o/:
0.96 mg/K for 1 to 5 years resulted in no observed hepatotoxicity
Chloroform is rapidly absorbed from the gastrointestinal tract and
other trihalomethanes may be expected to be absorbed and metabolized in
a similar manner. Human exposure to chloroform'may result from its
presence in ambient air, from industrial exposure and in drinking water.
A Threshold Limit Value (TLV) of 10 ppm in air had been established to
87 '
protect workers and long term clinical studies using a cough suppressant
containing chloroform noted some reversible hepatotoxicity when about 2
88
grams of chloroform had been consumed per day for 10 years. A short
term, few animal study with mice gave an indication that chloroform
89
might be carcinogenic in that species.
In mid-1977 the National Institute of Occupational Safety and Health
issued a "Revised Recommended Chloroform Standard" (unnumbered and undated)
reducing the TLV to 2 ppm and its use in drugs, cosmetics and food
90
packaging has been banned by the Food and Drug Administration because
the potential risk associated with its use are greater than its benefits.
89
water.
Laboratory studies have produced LDc-f. toxicity data following acute
oral exposure to chloroform at levels of 120 to 1350 mg/K in rats, male
91 92
mice and male and female dogs. ' No teratogenicity was determined in an oral
93
exposure study with rats and rabbits. Evidence of the animal
-------
- 46 -
carcinogenicity of chloroform has been confirmed by several studies that
have been extensively reviewed in the Report of the National Academy of
94
Sciences (NAS) titled "Drinking Water and Health." They have found
chloroform capable of producing malignant and metastatic neoplasms in at
least one feeding study in mice and has produced tumors in both rats and
mice in other studies. Utilizing the standard protocol for carcinogenic
testing, a dose response relationship was found for epithelia tumors of
the kidneys and renal pelvis in the rat and hepatocellular carcinomas in
f Q
mice in studies by the National Cancer Institute , and the latency
period for the carcinogenic effect decreased as the dose increased. Another
95
study showed hepatocellular carcinoma in femal rats and one strain of
male mice. These studies established that chloroform is carcinogenic
to the animals under those experimental conditions and therefore, presents
a potential carcinogenic risk to humans.
94
The National Academy's Safe Drinking Water Committee calculated
the upper 95% confidence estimate of risk at 3 x 10 at an average two
liters consumption of water with 20 yg/£ of chloroform for a lifetime.
(one excess case of cancer for every 33,333 persons exposed for a lifetime).
The NAS suggested that strict criteria be applied when limits for chloroform
in drinking water are established. The use of maximum
tolerable dose in the toxicological studies and the mathematical extrapolation
to human population effects have an air of unrealness, but are based on
a philosophy of safety using what data are available.
Before an alternative disinfectant for drinking water can be considered
for use, the potential toxicity of not only the disinfectant itself, but
also the potential toxicity of the by-products, both inorganic and
organic, of the reactions between the disinfectant and water constituents,
must be evaluated. For example, sodium hypochlorite was reported to be
a weak base substitution mutagen in Salmonella typhimurium.
-------
- 47 -
Epidemiology
54
When the first nationwide data were available from NORS on chloroform
concentrations, they were compared with cancer mortality (all sites) in
the cities served by the supplies sampled and a significant correlation
noted. These data have continued to be analyzed in more sophisticated
ways. An association with bladder cancer and the trihalomethanes other
97
than chloroform is the most solid finding.
Data on water quality for carrying out epidemiological studies have
been lacking and other classifications of exposures have had to be used
in order to proceed with an evaluation of the problem. The studies of
98
the Environmental Defense Fund comparing Parishes (counties) were the
99
first to create a public interest. A recent paper used this technique
of comparing mortality of counties served mostly by surface or ground
water in Ohio. A more elaborate study of this type was conducted by
the University of North Carolina for all the counties in the Ohio River
Valley. These studies found that some aspects of cancer death rates
were higher in counties where most of the people used surface water as
compared to counties where most of the people used ground water. The
assumption in these studies was that surface waters are more heavily
contaminated than ground waters or that more chloroform is produced when
surface waters are chlorinated.
Another general classification can be made of drinking water —
chlorinated or not chlorinated. Three studies have used this dichotomy
as a basis for comparison. The Johns Hopkins study covered a small
population for which many variables were controlled and only obtained
102
suggestive results. The University of California at Los Angeles study
demonstrated the extreme mobility of people in that area and was not
definitive. The Columbia University study had a population of adequate
-------
- 48 -
size without excess mobility and uncovered some interesting results. Males
living in the chlorinated drinking water areas of Erie, Rensselaer, and
Schenectady Counties and females living in the chlorinated drinking water
areas of Erie and Schenectady Counties are at a greater risk of gastrointestinal
and urinary tract cancer mortality than are individuals living in non-
chlorinated drinking water areas.
The epidemiological studies are suggestive that the toxicological studies
are reasonable, but may have in this case underestimated the cancer risk. Studies
with more definitive water quality data and a more rigorous design are now
being conducted.
Ozone
Ozone is a powerful oxidant and as such, can be expected to oxidize
many compounds present in surface waters. Whether these oxidation products
are more harmful or less harmful than the reaction products of chlorine is
not known at this time (Fall, 1977). Numerous studies, summarized below,
have been performed to evaluate the potential toxicity of ozonated water and
wastewater, the majority of such studies concerning themselves with the
formation of carcinogenic, mutagenic, and teratogenic substances from the
ozonolysis of organic contaminants.
Comparative toxicity studies of ozonated and chlorinated waters with
a defined chemical composition of organic materials such as pesticides or
detergents indicated chlorine treated water exhibited a higher toxicity
than ozone treated water, but the greater toxicity to the cell cultur system
was speculated to be because of the residual chlorine rather than oxidative
, 104
products.
-------
- 49 -
Cytochrome P-450 reduction, as an indication of liver necrosis, was
evidenced in one strain of mouse subjected to intraperitoneal injections
of the products of ozonation, but was not apparent after injections with
the products of chlorination, however, the results were reversed with a
104
different strain of mouse. In studies conducted to determine if
ozone would decrease the cytotoxicity of a synthetic military hospital
wastewater containing methanol, ethanol, isopropanol, acetone and acetic
acid, ozone produced products were more toxic to test cells than non-
ozonated waste. Reversion of histidine dependent mutant strains of
Salmonella typhimurium by the products of ozonation of organic compounds
bearing various functional groups showed that ethanol and a mixture of
ethanol, acetaldehyde, and hydrogen peroxide were mutagenic and the
ozonation of benzidine resulted in a form that no longer required metabolic
activation for mutagenicity. Positive results were not obtained in
similar bioassays for samples of unconcentrated secondary treated municipal
effluent that were a) untreated, b) chlorinated, c) chlorinated/dechlorinated,
d) chlorobrominated, or e) ozonated.
Another study currently (Fall 1977) being conducted by Dr. Gruener
in progress at the Hebrew University in Jerusalem showed these preliminary
results on reused water. A reverse osmosis concentrate of reused water
was ozonated and then tested in the Salmonella mutagenicity test. The
same water sample was checked before ozonation and found to be negative.
Water ozonated for 15 minutes was mutagenic in the two strains used:
TA100 (base pair substitution) and TA98 (frameshift). No activation by
microsomal fraction was needed to cause mutations in TA100. In the
strain TA98, although an effect existed in the absence of the liver
fraction (about three times the control value), a four-fold
-------
- 50 -
increase in the number of colonies occurred compared to the control without the
liver fraction in the presence of phenobarbital induced liver fractions; the
number of colonies was 9-10 times higher in the presence of methylcholanthrene
induced- and Aroclor 1254 induced liver fractions. Clearly, the toxicity
problems are so complex that it cannot be stated at this time if ozone
is better or worse than chlorine from the point of view of by-product
formation.
Chlorine Dioxide
Although chlorine dioxide possesses many desirable characteristics
as a disinfectant it is, none-the-less, a powerful oxidant capable of
oxidizing and chlorinating many compounds with which it comes in contact.
The properties of the reaction by-products as well as chlorite and
chlorate ion (end products), - the reduction products of chlorine dioxide
oxidation, are being thoroughly evaluated by the Health Effects Research
Laboratory (HERL) both in-house and through extramural research .
Toxicity
Considerable disagreement exists among literature sources concerning
the toxicity of chlorine dioxide and the majority of reports are
concerned with exposure in air, principally from the paper pulp industry,
describing symptoms of local contact irritation and two cases of illness
108
including one fatality from exposure to 19 ppm inside a bleach tank.
The effects, on rats, of chronic administration of chlorine dioxide
109
in drinking water showed no discernable toxic effects at 10 mg/Ji or
less over a two year period although rats consuming 100 mg/£ showed a
higher mortality rate at the end of the two year period. Enger
reported that laboratory workers, consuming one liter of water containing
0.7 mg chlorine dioxide, experienced a feeling of weakness and gastrointestinal
-------
- 51 -
troubles. Musil supposed that the symptoms were caused by: a) the
chlorine dioxide itself, b) the final products from the reaction between
chlorine dioxide and substances in the water, or c) unreacted chlorite
from the generation of the chlorine dioxide.
The toxicity of chlorite ion arising from the reaction of chlorine
dioxide and organic matter or the disproportionation of chlorine dioxide
in water, similarly, is not wall understood. One of the reported advantages
of chlorine dioxide disinfection is the ability'to maintain a residual
112 113
in the distribution system. Conversely, Myhrstad and Samdal found
that the chlorine dioxide dosed was completely converted to chlorite
within 35 minutes in water from a system using microstraining and ozonation
for treatment. The potential for chlorite ion to be present in water
exists and its toxicity must be evaluated.
Studies have determined the LD _ of chlorite ion, for the rat, to
be 140 mg/K 1 and for sodium chlorite, 182 mg/K ; 208 mg/£ and 50.6mg/£
for bluegill and rainbow trout, respectively and for mallard ducks,
100 mg/K. Rats exposed to 8 mg/£ chlorite or less in drinking water
109
had no discernible toxic effects over a two year period.
Hopf proposed that the toxicity of chlorite might be approximately
the same as chlorate and reported symptoms of a "weak furry feeling" on
the tongues of subjects who drank sodium chlorite concentrations of more
than 0.3 mg/£.
Hemolytic Anemia
The propensity of certain chemicals and drugs to induce hemolytic
anemia has been a subject of much interest for almost a century. The
majority of these substances are aromatic compounds containing amino-,
nitro-, or hydroxy groups, although a number of inorganic compounds such
-------
- 52 -
as hydroxylamines, nitrites, chloramines and chlorates are also active.
Such compounds usually cause red cell injury without evidence of specific
toxicity to other cells or tissues. The hemolytic process is characterized
by two distinctive features in the affected red cells; a) the appearance
of brownish or greenish derivatives of hemoglobin, including methemoglobin
and, b) the formation of water-insoluble stainable granules called Heinz
118
Bodies within the red cell.
Methemoglobin is an oxidation product of the normal blood pigment,
hemoglobin, in which the ferrous iron is oxidized to the ferric state
and is unable to combine reversibly with oxygen and carbon dioxide,
causing a shift in the oxygen dissociation curve thereby hindering the
transfer of oxygen from the blood to the tissues. Abnormal amounts of
methemoglobin will result in a functional anemia with cyanosis. Musil
claimed that chlorite ion, as an oxidizing agent, carries the oxidation
of hemoglobin to methemoglobin in vivo. He recommended a concentration
of 0.0 mg chlorite per liter because of the hazard of methemoglobinemia
in nursing babies. He further recommended that prior to the use of
chlorine dioxide, other methods of treatment, such as activated carbon,
should be considered. Based on these observations, the Norwegian Health
Authority has recommended the absence of chlorite in drinking water.
The repeated administration of methemoglobin producing chemicals
may cause hemolytic anemia, the exact mechanism of which is unknown as
the chemicals themselves may not be directly hemolytic. Data dervied
from experiments conducted at HERL indicated that in vitro, chlorite and
chlorine dioxide will oxidize hemoglobin to methemoglobin and, in the
intact human red cell, oxidizes hemoglobin with corresponding increases in
the incidence of spicule cells of the acanthrocyte and stromatocyte
type, morphological abnormalities that are associated with hemolytic
disorders, after certain "threshold" levels are exceeded.
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- 53 -
Continuous monitoring of the methemoglobin formed in cats from a
single oral dose of sodium chlorite resulted in a dose response that
indicated that chlorite was absorbed into the blood within 10 minutes,
reached a methemoglobinemic maximum in 1-1/2 to 2 hours and was reduced
at a rate of 16 percent per hour.
Although methemoglobin formation from a single dose of a compound
does not necessarily indicate toxicity, an increasing degree of in vivo
lysis of red cells was noted at doses above 20 mg/K and cats given 500
mg/£ chlorite in water exhibited a sharp decrease in hemoglobin content
and packed cell volume after 2 weeks exposure, although methemoglobin
was not detected. Similarly, rats given chlorite in water for 30 days
resulted in significant (p<0.05) increases in red cell count at doses of
0.9 to 1.6 mg/K/day; decreases in hemoglobin and packed cell volume at
doses of 11-16 mg/K/day; and decreased hemoglobin, packed cell volumes
and red cell count at doses of 28-50 mg/K/day. Although methemoglobin
was not detected in any of these animals, probably because the "threshold"
level was not exceeded, a single dose of 50 mg/K resulted in excess of
50 percent of the animal's hemoglobin being oxidized to methemoglobin
within 30 minutes.
Exposure of erythrocytes to mild oxidative stress converts hemoglobin
to methemoglobin, a reaction that is reversible because metabolic pathways
for the reduction of methemoglobin is present in normal erythrocytes.
Further oxidative stress, probably involving the oxidation of -SH groups
of the globin, causes irreversible damage with the formation of mixed
disulfides between glutathione and the hemoglobin. Additional damage to
the erythrocyte membrane from further exposure to oxidative stress has
120
been postulated to lead to the destruction of the erythorocyte
In the HERL laboratory, the erythrocyte survival rate of cats drinking
100 mg/& chlorite in water (1.6 mg/K/day) was found to be reduced by
-------
- 54 -
23.6 percent and the survival rate in cats drinking 500 mg/£, (5 mg/K/day)
was reduced 27.2 percent, as compared to control drinking chlorinated
tap water, (p<0.05).
121
Conversely, in other experiments conducted by HERL in which an
assessment of the effects of chlorine dioxide in drinking water on the
hematopoietic system of African Green Monkey was made by exposing male
and female monkeys to 20 and 200 mg/£ chlorine dioxide (avg. 1.72 and
8.96 mg/K/day, respectively) for 13 weeks, no statistical deviation from
normal hemoglobin, hematocrit, red cell count, reticulocyte, methemoglobin
or osmotic fragility values occurred. A series of other hematological
parameters, for example, Heinz Bodies, differential count, red cell and
leukocyte morphology were within normal limits and serum bilirubin and
serum enzymes monitored throughout the study showed no abnormalities or
statistically significant trends, indicating a stable homeostatic response.
Animal response data is difficult, at best, to extrapolate to the
human. Species differences exist in the response to methemoglobinizing
agents. The cat, for example, is generally recognized as the species
most susceptible to methemoglobinemia, and is followed by man, dog,
rat , rabbit and monkey in decreasing order of susceptibility to aromatic
122
amine methemoglobin formation. Segments of the human population also
possess variations in methemoglobin susceptibility and sensitivity to
oxidative stress to the hematopoietic system. Hemolytic anemia is
frequently a serious problem among patients undergoing long-term hemodialysis.
123
Newborn infants are all susceptible to drug induced hemolytic anemias caused
by an abnormality that persists for only a week or two. Genetically
altered hemoglobins may confer abnormal sensitivity to nitrites and
other oxidizing agents that cause methemoglobinemia. The abnormal
pigment, hemoglobin H, is unusually sensitive to oxidation. The life span
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- 55 -
of these affected erythrocytes is about 40 days instead of the usual 120
days.
The enzyme deficienty that results in familial idiopathic methemoglobinemia
has been known for a long time. Individuals with this condition are
deficient in the ability to reduce methemoglobin. Studies have shown
that erythrocytes with decreased glucose-6-phosphate dehyrogenase activity,
an enzyme deficiency present in 13 percent of U.S. Black males, are more
124
vulnerable to oxidant induced hemolysis which may begin with precipitation
125
of hemoglobin within the cell. To continue the research in this
area, studies are being initiated to determine, first, if animals deficient
in glucose-6-phosphate dehydrogenase activity are more susceptible to
oxidative stress caused by exposure to chlorite and chlorine dioxide in
water.
In addition to these controlled laboratory studies, HERL is presently
investigating the feasibility of conducting epidemiological studies on
populations exposed to chlorine dioxide in their drinking water. Although
numerous treatment plants use chlorine dioxide for periodic taste and
odor control, few use it consistently or in concentrations exceeding
1-2 mg/£. Appropriate sites are being sought at this time. Also,
a community water supply in Massachusetts utilized chlorine dioxide
exclusively during World War II. A retrospective mortality study in
which the rates and causes of death and the incidence of neonatal jaundice
for this community could be compared with similar areas utilizing conventional
chlorine disinfection is being considered.
Chloramines
Only two reports of combined chlorine toxicity were found in the
literature. Chloramines have been found responsible for two epidemics of
acute hemolytic anemia characterized by Heinz Bodies in dialyzed uremic
-i o/:
patients. The effected patients had undergone dialysis in two hospitals
that had recently adopted a reverse osmosis technique for purifying dialysis
-------
- 56 -
water. Patients in a third hospital, which utilized activated carbon
filtered water, were not affected. Also monochloramine has been shown
to be a weak mutagen when reversion of trpC to trp in B. subtilis was
127
used as an assay.
.Comparative Studies
A clinical trial is being formulated that will assess the human
tolerance to each of the proposed alternate disinfectants, including
chlorine, and some of the end products such as chlorite and chlorate.
These trials will initially be conducted on normal healthy male subjects,
followed by controlled exposure to levels of chemicals comparable to
those used in water treatment practices to individuals possessing some
of the deficiencies that may render them more susceptible to oxidative
stress than the normal human population. The results of these studies
will determine the absorption, distribution, and metabolism of these
agents and provide a thorough assessment of human tolerance and effects,
if any.
The comparative toxicity of by-products from the three proposed
alternative disinfectants and chlorine is being evaluated by HERL in a
project in which organic concentrates in aqueous solution obtained by a
100-fold reverse osmosis concentration technique, from undisinfected
coagulated, settled and dual-media filtered Ohio River water and different
samples of similar dual-media filtered water disinfected with chlorine,
chlorine dioxide, ozone, or chloramine will be tested for cytotoxicity
in both mamallian cells in culture and bacterial cells, bacterial mutagenesis,
rat mortality, carcinogenic initiation/promotion, effects on DNA binding,
and on Xenobiotic metabolic systems. In the first test, the concentrates
from the four disinfectants were negative for bacterial mutagenesis and
rat mortality and only the concentrate from the system disinfected with
chloramines showed any significant bacterial cytotoxicity. At this time
(Fall, 1977) the carcinogenic initiation/promotion studies are just starting.
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- 57 -
SUMMARY
At the present time (Fall 1977) chlorine is known to produce trihalomethanes
and possibly other chlorinated by-products. Ozone, chlorine dioxide, or
chloramines on the other hand, either do not cause trihalomethane formation,
or cause reduced quantities of trihalomethane to be produced. Evidence
is growing, however, that as strong oxidants, both ozone and chlorine
dioxide do produce non-trihalomethane by-products, and inorganic end
products in the case of chlorine dioxide. Chloramines have not yet been
studied in this regard. As yet, however, none of the organic by-products
of ozone or chlorine dioxide have been demonstrated to be formed at
concentration levels comparable to the trihalomethanes. Both in-house
and extramural research is continuing in the area.
Chloroform has been demonstrated to be a carcinogen in some animal
tests and epidemiological studies support the concept of some adverse
effects from chlorination. Similar data are not currently (Fall, 1977)
available for ozone, chlorine dioxide and chloramines. Preliminary
studies both by EPA and others have not shown any definitive dramatic
adverse effects from the three proposed alternates, but the completion
of on-going research is needed to add confidence for the continued use
of these alternatives. One possible result of these studies could be
the recommendation of a maximum acceptable dose for any or all of these
disinfectants.
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- 58 -
COST OF DISINFECTION
If all other factors are equal, drinking water treatment unit processes
should be selected on a minimum cost basis. In the case where the least
expensive unit process has an unacceptable risk, however, a higher cost
process may actually have a more favorable benefit/cost ratio than a minimum
cost process and might be selected. The fifth criterion of a disinfectant
alternate to chlorine should be cost-effectiveness. The costs of the alternate
disinfectants are discussed below.
GENERAL CONSIDERATIONS
The costs in this section are intended for the development of
planning estimates only and not for the preparation of bid documents or
detailed cost estimates. Exact capital and operating costs are highly
variable from location to location within the United States, even for
plants of the same size and design. Variables — such as local costs of
land, materials and labor; state or regional differences in building
codes; and existing facilities suitable for modification — may accentuate
the differences in treatment costs for similar plants to reduce chloroform
and other trihalomethanes in drinking water.
These cost data are presented in such a way as to enable the planner
to make adjustments to the reported costs when local information is
available. For example, operation and maintenance costs can be reduced
if the delivered cost of chemicals is less than the costs upon which the
estimates were based. A cost index is used to provide a baseline for
projecting costs and for estimating escalation because of inflation.
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- 59 -
BASIS OF COST ESTIMATES
Much of the basic information utilized in this report was obtained from
data developed by the Systems and Economic Evaluation Section (SEES) of EPA's
-i o o -I on
Wastewater Research Division. ' For example, computations for chlorine
costs were performed using a computer program developed by SEES, but operational
modifications were assumed in the analysis to reflect conditions unique
to water supply.
Costs reported as Capital Costs include:
a. construction for site preparation,
b. plant construction,
c. legal, fiscal and administrative service,
d. interest during construction, and
e. start-up costs.
Costs reported as Operation and Maintenance Costs include:
a. chemical costs,
b. labor costs, and
c. operation and maintenance costs, such as utilities, annual
replacement of expendable items, etc.
CHLORINE
In this analysis, a number of variables have been evaluated as to
their effect on the cost of chlorination. Baseline or standardized
values for a set of design parameters were assumed and the cost
of chlorination was calculated. The parameters and their associated
"standardized" levels are shown in Table II.
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- 60 -
TABLE II
Design Parametes for the Cost of Chlorination
Design Pa ramet e r (Variable)
Chlorine Dose
Chlorine Contact Time
Construction Cost Index
Cost of Chlorine
Wholesale Price Index
Direct Hourly Wage Rate
Amortization Interest Rate
Amortization Period
Capacity Factor
Level
2 mg/1
20 min.
273.8
300 $/ton
194.6
$5.58/hr
7%
20 yr.
70 percent
Assuming design flow rates of 1, 5, 10, 100 and 150 mgd, at an
operating to design ratio of 0.7 and the design parameter values in
Table II, the unit costs for chlorination are shown in Table III.
TABLE III
Unit Chlorination Costs (j5/1000 gal)*
Design Capacity
Item
1 mgd
5 mgd
10 mgd
100 mgd 150 mgd
Capital Cost 2.19
Operating Cost 1.06
0.88
0.56
0.62
0.46
0.26 0.24
0.32 0.31
Total Cost
3.25
1.44
1.08
0.58
0.55
*0perating costs are calculated on 70% on design capacity.
-------
- 61 -
OZONE
The standardized design parameters listed in Table IV were used as
the basis for analysis. Because of increased biocidal activity the
disinfectant dose of ozone was assumed to be one-half the chlorine dose
used in Table II.
TABLE IV
Design Parameters for Ozonation Costs
Design Parameters (Variables) Level
Ozone dosage 1 mg/£
Ozone contact time 20 min.
Electrical Power Cost $0.03/kw-hr
Construction cost index 273.8
Cost of Oxygen $0.046/lb.
Wholesale Price Index 194.6
Direct Hourly Wage Rate $5.58/hr
Amortization Interest Rate 7%
Amortization Period 20 yr
Capacity Factor 70 percent
Costs based on these parameters have been calculated for ozone generated
from both air and oxygen. These costs are shown in Table V and VI.
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- 62 -
TABLE V
Unit Costs for Disinfection with Ozone - Air (j^/lOOO gal.)
Design Capacity
Item
Capital Cost
Operating Cost
Total Cost
1
2
2
5
mgd
.90
.75
.56
5
1
1
2
mgd
.36
.05
.41
10
1.
0.
1.
mgd
11
77
88
100 mgd
0
0
1
.76
.40
.16
150
0
0
1
.73
.38
.11
mgd
Operating costs are based on 70% of capacity.
TABLE VI
Unit Costs for Disinfecting with Ozone - Oxygen (<£/1000 gal)
Design Capacity
Item
1 mgd 5 mgd 10 mgd 100 mgd
150 mgd
Capital Cost 4.46 1.50 1.08 0.61 0.58
Operating Cost 2.87 1.17 0.88 0.52 0.49
Total Cost 7.33 2.67 1.96 1.13 1.07
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CHLORINE DIOXIDE
In this cost analysis, the dose of chlorine dioxide was assumed to
be half the dosage of chlorine to achieve equivalent disinfection results.
Therefore, 1 mg/£ of chlorine dioxide would achieve disinfection results
equivalent to those achieved by 2 mg/£ of chlorine, see Table II. If
0.5 mg/£ of chlorine is combined with 1.6 mg/£ of technical grade sodium
chlorite, a 1 mg/£ dosage of chlorine dioxide will result. The equation
below shows this relationship (assuming 80 percent pure NaClO^ yields
1.3 mg/£ of reactive material):
2 NaC10
— > C102 + 2 NaCl
Mol.Wt. (181) (71) (135) (117)
1.3 mg/£ 0.5 mg/£ 0.9 mg/£ 0.8 mg/£
Therefore, the chlorine feeding system and contact basins were estimated
for a 0.5 mg/£ dosage of chlorine with the rest of the standardized
values fixed at the levels shown in Table VII.
TABLE VII
Design Parameters for the Cost of Chlorine Dioxide
Design Parameters (Variable) Level
Chlorine Dose 0.5 mg/£
Contact Time 20 min.
Cost of Sodium Chlorite $0.70/lb
Chlorine Cost $300/ton
Construction Cost Index 273.8
Ratio of Sodium Chlorite Concentration to
Chlorine Concentration 3.2
Wholesale Price Index 194.6
Direct Hourly Wage Rate $5.56/hr
Amortization Interest Rate 7%
Amortization Period 20 yrs.
Capacity Factor 70 percent
-------
- 64 -
TABLE VIII
Unit Cost of Disinfecting with Chlorine Dioxide (^/lOOO gal.)*
Design Capacity
Item
Capital Cost
Operating Cost
1 mgd
1.90
1.55
5 mgd
0.76
1.18
10 mgd
0.51
1.12
100 mgd
0.22
1.03
150 mgd
0.20
1.02
Total Cost 3.45 1.90 1.63 1.25 1.22
*0perating Costs are based on 70% of design capacity.
CHLORAMINES
The standardized levels for cost estimation are shown in Table IX.
Assuming design flows of 1, 5, 10, 100 and 150 mgd and an operating to design
ratio of 0.7 and the design parameter values shown in Table IX, the unit
costs for chloramines are shown in Table X.
-------
- 65 -
TABLE IX
Design Parameters for Chloramine Costs
Design Parameters (Variable) Level
Chlorine Dose 0.5 mg/£
Contact Time 20 min.
Construction Cost Index 273.8
Cost of Chlorine $300/ton
Cost of Ammonia $200/ton
Ratio of Chlorine to Ammonia Cone. 5.0
Wholesale Price Index 104.6
Direct Hourly Wage Rate $5.58/hour
Amortization Rate 7%
Amortization Period 20 yrs.
Capacity Factor 70 percent
TABLE X
Unit Chloramine Costs (^/lOOO gal.)*
Design Capacity
Item
Capital Cost
Operating Cost
1 mgd
1.70
0.63
5 mgd
0.62
0.25
10 mgd
0.42
0.19
100 mgd 150 mgd
0.17 0.15
0.10 0.10
Total Cost 2.33 0.87 0.61 0.27 0.25
*0perating costs are calculated on 70% of design capacity.
-------
- 66 -
SUMMARY
Unit costs for five disinfection processes have been developed and
are summarized below in Table XI. Costs for chlorination, chlorine dioxide and
ozonation are developed on the assumption of equivalent disinfecting capability.
The costs for chloramines are calculated on the assumption that the values
shown in Table IX yield 3 mg/2, of monochloromine, which is not equivalent in
disinfecting power to the other disinfectants. Therefore to obtain equivalent
biocidal activity chloramines must be used with some other disinfectant,
such as chlorination or in high quality waters where high biocidal activity
is not needed.
TABLE XI
Summary of Unit Costs for Disinfectants (^/lOOO gal.)
Design Capacity
Item 1 mgd
Chlorination
2 mg/£ 3.25
Cost of Ozone - Air
1 mg/£ 5.65
Cost of Ozone - Oxygen
1 mg/£ 7.33
Chlorine Dioxide
1 mg/fi, 3.45
Cost of Chloramine
3 mg/£* 2.33
5 mgd 10 mgd 100 mgd 150 mgd
1.44 1.08 0.58 0.55
2.41 1.88 1.16 1.11
2.67 1.96 1.13 1.07
1.90 1.63 1.25 1.22
0.87 0.61 0.27 0.25
*Not equivalent to the other disinfectants in biocidal activity.
-------
- 67 -
To change from one disinfectant to another represents a minimal investment.
This is illustrated by Table XII. The data in Table XII is derived from
the assumption that a typical family of 4 consumers would use 117 thousand
gallons of water in the home per year (80 gal/capita/day - a generous
figure). Using data from Table XI an annual cost for disinfection per family
is presented in Table XII, based on system size.
TABLE XII
Cost to a Family of Four in Dollars/Year for the Disinfection Unit Process
Design Capacity
Item 1 mgd 5 mgd 10 mgd 100 mgd 150 mgd
Chlorination
Ozonation -
Ozonation -
Air
Oxygen
Chlorine Dioxide
Chloramines*
$3.
$6.
$8.
$4.
$2.
80/yr
61/yr
58/yr
04/yr
73/yr
$1.
$2.
$3.
$2.
$1.
68/yr
82/yr
12/yr
22/yr
02/yr
$1.
$2.
$2.
$1.
$0.
26/yr
20/yr
29 /yr
91/yr
71/yr
$0.
$1.
$1.
$1.
$0.
68/yr
36/yr
32/yr
46/yr
32/yr
$0.
$1.
$1.
$1.
$0.
28/yr
29/yr
25/yr
43/yr
29/yr
*Not equivalent in biocidal activity to the other disinfectants
Therefore the annual cost per family for any disinfectant is small, and
the cost increment for changing disinfectants is minimal.
-------
- 68 -
DISCUSSION
Choosing the optimum or ideal disinfectant is a difficult task as
each of the candidates discussed in this paper has advantages and disadvantages:
See Table XIII. Other disinfectants are currently (Fall 1977) in minor
use and were not discussed in this paper. In this country, historically, the
disinfectant of choice was chlorine. Chorine was inexpensive and very
effective in controlling waterborne disease and although it sometimes
imparted taste and odor to water, it did not produce any obvious effect
on people's health. Subsequent studies showed humans had a high tolerance
130
to chlorine itself. Later chloramines were substituted in some cases
to prevent taste and odor, although some biocidal activity was sacrified.
Outside of the United States the disinfectants ozone and chlorine dioxide
were widely used. Although slightly more expensive, they were effective,
did not impart a taste and odor to treated water, and did not cause any
obvious effects on the health of consumers. In practice, the disinfectant
dosage was often less than with chlorine, which reduced the additional cost.
Currently (Fall 1977) the situation is changing. Improved analytic
techniques for organic chemicals have shown that chlorine produces at least
one carcinogenic by-product, and epidemiological studies indicate some
adverse effect on health may be caused by drinking chlorinated water.
Therefore, the U.S. Environmental Protection Agency is considering establishment
of limits for the concentrations of disinfection by-products, particularly
trihalomethanes. Should such regulations be promugulated, they will cause
changes in drinking water treatment practices in this country.
-------
- 69 -
The concentrations of trihalomethanes can be controlled either by
changing disinfectants such that less trihalomethanes are produced or
by treating the water, for example with granular absorbants, such that chlorine
could still be used, but trihalomethane concentrations would be reduced. Under
these latter circumstances, the benefits of chlorination could be maintained
without the corresponding undesirable organic by-products being produced
and no alternate disinfectant would be required. This approach would have
the additional benefit of removing synthetic organics found in raw water
as well as controlling concentrations of biological nutrients entering
the distribution system. Another treatment approach would be removal of
the trihalomethanes themselves by treatment.
The details of the final regulation, if promulgated, will influence
which of the above choices are available as alternate treatment procedures.
If fairly high concentrations of trihalomethanes are permitted, free chlorine
can continue to be used in many circumstances, possibly followed by
ammonia to form chloramines. If the permissible concentrations of trihalomethanes
are low, either now or in the future, the use of chlorine will be limited
only to waters with low concentrations of precursors, either naturally or
after treatment, and alternate disinfectants or treatment for removal of
trihalomethanes will have more widespread use. Further, if in an attempt to
limit the formation of all disinfection by-products, the regulation were to
contain a total organic carbon concentration or disinfectant demand limit,
chlorine could have a continuing role in disinfection in some instances.
Considering only the disinfectants themselves, their major characteristics
are presented in Table XIII.
-------
- 70 -
TABLE XIII
SUMMARY OF DISINFECTANT CHARACTERISTICS
Chlorine
Use & Widespread in U.S.
Genera- Off-site
tion generation
Ozone
Widespread outside
U.S. On-site
generation
Chlorine Dioxide
Widespread outside
U.S. On-site
generation
Chloramines
Limited use
On-site
generaticn
C
cti
CO
W 4->
4-1 O
O 3
3 T3
T3 O
O S-i
l-l p<
(X I
I -X)
>^ C
pq W
Biocidal
Activity
Affec.ted by pH
HOC1 - third in
activity
OC1 - weak
Measur.
&
Persist.
of
Residual
Health
o10 mgd
a) co § 100 mgd
o 0^150 mgd
Little pH influence
Most active
Eight methods
HOC1 & OC1~
not easily
distinguished
Persists
42
Titration method
Does not persist
42
Chemistry
Trihalomethanes Some, but not yet
other well characterized
chlorinated No trihalomethanes
compounds, some
of which are
odorous
CHC1_ a carcinogen None positive yet,
epidemiology Still under study
supports some
adverse effect
2 mg/JL
mg/£
Air
Oxygen
3.
1.
25
.08
0.58
0.55
,65
,88
,16
1.11
7.
1,
1.
1.
33
96
13
07
Little pH influence
Second in activity
Affected by pH
NHC12 - Fourth in
activity
NH2C1 - Fifth
activity
in
DPD & FACTS
lodimetry, Mod. OT
Amperiometric
titration
CIO & CIO can
be distinguished
Certain by-products
may interfere with DPD
Persists - slowly
changes to C"10~2 & C10~3
Amperometric
titration
DPD
Persists
Some, but not yet
well characterized
No_trihalomethanes
C102 & C10~3 are
end products
None positive yet,
Both by-products
and end-products
under study
1 mg/&
3.45
Unknown
No trihalomethanes
if no chlorine
present
None positive yet,
Studies beginning
3 mg/A*
,63
.25
.22
2.33
0.61
0.27
0.25
oj *Not equivalent in biocidal activity to the other disinfectants.
-------
- 71 -
Because many on-going studies are not complete, the choice of a
disinfectant alternative to chlorine must be made on the basis of incomplete
information, if circumstances dictate that an alternate disinfectant is the
proper approach. Although each of the alternatives have advantages and
disadvantages, at the present time (Fall 1977), four alternatives are worthy
of consideration: 1) chlorine dioxide; 2) ozone plus chlorine dioxide or
chloramines to maintain a residual; 3) chlorine followed shortly by ammonia
to stop the trihalomethane formation reaction; or 4) chlorine dosed at
a concentration less than the chlorine demand followed by chlorine dioxide or
chloramines to maintain a residual. Each of these options would reduce
trihalomethane concentrations, would provide adequate initial disinfection
and would provide a biocide* in the distribution system. Although theoretically
attractive, chloramines are such weak biocides, that any option based on
their use should be evaluated prior to recommendation, something that
has not yet been accomplished for all situations.
Whether required by a regulation or not, another prudent step would
be to limit the dose of any disinfectant, thereby reducing the potential
for the formation of any undesirable by-products and end-products regardless
of the disinfectant used. In a given situation, if the disinfectant
demand is much greater than 1 mg/£, treatment of the water prior to
disinfection to reduce the disinfectant demand, see Figures 1 and 2,
would be generally beneficial. As an extension of this concept, as
noted above, chlorine could continue to be used as the disinfectant if
the water being chlorinated were properly treated with a granular adsorbant
to remove organic matter.
*Currently (Fall 1977) some State regulatory agencies specify a "chlorine"
residual in the distribution system, something that must be taken into consideration
where applicable. Another possible constraint to use of an alternate disinfectant
is Section 141.21(h) of the National Interim Primary Drinking Water Regulations that
discusses the substition of "chlorine" residual measurements for some required
microbiological contaminant samples.
-------
- 72 -
Although controling disinfectant demand is a prudent concept, the problem
of what to use as a raw water disinfectant, where one is needed or mandated,
remains. The control of growths, such as fresh water clams, in raw water
transmission lines, the prevention of slime growths in flocculating and
settling basins or the destruction of ammonia without producing undesirable
by-products and end-products is a practical problem that has yet to be
completely evaluated. Periodic shock chlorination or the use of small doses
of chlorine, ozone or chlorine dioxide may be effective for controlling
microorganism development.
-------
- 73 -
SUMMARY
Providing a wholesome drinking water to the consumer is the primary
goal of all water purveyors. Effective killing or inactivating of pathogenic
organisms through disinfection is the most important process in drinking
water treatment and distribution. Because chlorination has been so effective
in controlling waterborne disease over the past 70 years in this country, any
departure from current practice must be made cautiously to avoid any
deterioration in the microbiological quality of the Nation's drinking water.
All other criteria by which to judge any new treatment proposal is secondary
to the maintenance of a water free of all pathogens.
Several options exist for disinfecting water without by-product
contamination. Treatment of water to remove by-product precursors or
treatment to remove formed by-products are possibilities. This paper has
focused on a third possibility, replacement of chlorine as the disinfectant.
Although all of the on-going research cited in this paper is not complete,
enough is known at this time (Fall 1977) to suggest that "chlorine-free"
or "low-chlorine-concentration" chlorine dioxide either as the primary
disinfectant or in combination with ozone as the primary disinfectant,
preferably used in waters with a disinfectant demand of about 1 mg/& or
less, would be two possible acceptable alternates to chlorine. Although
not the only possible suggestions, these two meet all of the five criteria
established at the beginning of this paper as necessary for any alternative
to chlorine as a disinfectant.
ACKNOWLEDGEMENTS
The authors and the compiler of this paper wish to thank Mr. Gordon G.
Robeck for his helpful suggestions during review and Mrs. Maura M. Lilly for
typing the several drafts and the final paper.
-------
- 74 -
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