United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-094 Sept. 1984
Project Summary
Effect of Particulates on
Disinfection of Enteroviruses in
Water by Chloramines
Pasquale V. Scarpino
The inactivation kinetics of
chloramines (monochloramine and di-
chloramine) on an enterovirus, polio-
virus 1 (Mahoney), and on an enteric
indicator of fecal pollution, Escherichia
col/11229, were examined in laboratory
bench-scale studies using the kinetic
(stirred beaker) apparatus. The disinfect-
ing ability of chloramines in the pres-
ence of viral aggregates and organic
particulates was compared with viral in-
activation in pure buffer systems with
unassociated viruses and without added
particulates. In addition, comparisons of
chloramines, hypochlorous acid, and
hypochlorite ion were made in a variety
of test situations involving, for example,
(1) several types of particulates (entero-
virus-associated animal cells, solids-
associated primary effluents, and fecal
suspensions), (2) aggregated and unas-
sociated single viruses, (3) different
temperatures of reactivity, (4) different
pH's, and (5) different disinfectant com-
binations.
Aggregated poliovirus was more re-
sistant to both monochloramine and di-
chloramine than were the unassociated
viruses. Almost doubling the mono-
chloramine dose from 12 to 22 mg/L at
5 C and pH 9 did not double the rate of
virus disinfection. Dichloramine inac-
tivated poliovirus 1 less effectively than
did monochloramine. Monochloramine
formed at pH 9 and then adjusted to pH
7 gave a stable solution of mostly
monochloramine. Viral disinfection
rates then examined at both pH 7 and 9
were similar, but monochloramine killed
the test bacterium E. coli 10 times more
rapidly at pH 7 than at pH 9. Forming
monochloramine was about 1.2 times
more effective as a disinfectant than
newly made, preformed monochlora-
mine at 5 C and pH 9.
Poliovirus 1 survivors that had been
exposed eight times to monochloramine
at 15 C and pH 9 were 2.3 times more
resistant to monochloramine than both
the initially used, unexposed virus and
those viruses exposed fewer than eight
times to monochloramine.
Human epidermoid carcinoma (HEp-2)
and Buffalo Green Monkey (BGM) cells
were used to study the effects of cell-
associated turbidity on the disinfection
process. The object was to mimic the
natural state of viruses as they are
freshly discharged in feces. The rate of
disinfection was influenced by both the
disinfectant used and the cell-induced
turbidity of the system. Both of the cell-
associated viruses were more suscepti-
ble to hypochlorous acid than to mono-
chloramine. Increasing the turbidity
increased the resistance of the cell-
associated viruses to monochloramine.
Total coliforms in fecal suspensions
disinfected with hypochlorous acid
showed an initial rapid die-away of
greater than 99.9% during the first
minute of interaction, followed by a pro-
tracted period of survival. The turbidity
of primary effluents also gave protection
to naturally occurring coliforms disin-
fected with monochloramine.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented In a
separate report of the same title (see
Project Report ordering information at
back).
-------
Introduction
Background
Knowledge about virus inactivation in
water is assuming greater importance as
streams, rivers, and lakes that serve as drink-
ing water sources for many cities become
more and more contaminated with sewage.
Enteric viruses infective for man are the most
important viral agents known to be present
in water and wastewater, and more than 100
different types may be present in human
feces. Enteric viruses include the entero-
viruses (primarily polioviruses, coxsackie-
viruses, and echoviruses), hepatitis type A,
Norwalk type agents, rotaviruses, reoviruses,
adenoviruses, and parvoviruses. Since en-
teric viruses are found in the feces of infected
persons and are readily isolated from urban
sewage, they may enter water supplies and
present health hazards to humans. Virolo-
gists in several countries have reported the
presence of enteroviruses in drinking water
samples obtained from public water supply
systems that use conventional treatment
methods of filtration followed by disinfec-
tion. These studies all involve water that is
bacteriologically safe and contains a chlorine
residual considered to be virucidal. The
passage of viruses through a water treatment
plant's treatment train could be due to an
enhanced viral resistance to chlorine, the
presence of natural paniculate matter, the
association of the viruses with the alum used
for flocculation, or virus association with
organic matter.
Most viruses in the natural environment
are associated with solids and do not occur
in a free state. The association of viruses
with solids does not necessarily mean virus
inactivation. In fact, clay solids do not ap-
pear to have any deleterious effect on the
viruses. Concern exists that particulates (tur-
bidity) in drinking water may interfere with
disinfection. Thus, turbidity in drinking water
may alter the virus minimal infectious dose
by protecting the viruses. This possibility
resulted in the National Interim Primary
Drinking Water Regulations (NIPDR), which
allow a maximum contaminant level of 1
Nephelometric Turbidity Unit (NTU), or up
to 5 NTU if that level does not interfere with
achieving and maintaining disinfection.
Studies suggest the occurrence of an
evolutionary or adaptive alteration that in-
creases the resistance of the virus popula-
tion after repeated sublethal exposures to
free chlorine. Virus inactivation in water ap-
pears to be favored by acid conditions.
Objectives
Because chloramine (combined chlorine)
is commonly used in place of chlorine to
disinfect waters with high levels of trihalo-
methane precursors (organics), more precise
data are needed on the efficiency of chlora-
mine disinfection alone and in the presence
of particulate matter (turbidity) in drinking
water. The main objective of this study was,
therefore, to investigate the effects of par-
ticulates in water on the disinfection of
enteroviruses by chloramines. The complete
study objectives are outlined below:
1. To determine the effect of turbid water
on the disinfection of test microbes (primarily
poliovirus 1 and the reference bacterium E.
co//) using combined available chlorine (the
chloramines). These results were then com-
pared with those of free chlorine (hypo-
chlorous acid and hypochlorite ion). The
relationship of particulate material to
disinfection efficiency was then examined.
Particulates included human fecal solids,
sewage-primary effluent solids, and animal-
cell-associated poliovirus 1.
2. The disinfection ability of chloramines
(both monochloramine and dichloramine)
was studied at various chloramine concen-
trations, temperatures, contact times, and
pH values; at various concentrations and
types of particulates; and with single versus
aggregated preparations of test virions.
Comparisons were also made of disinfection
efficiencies for monochloramine used as a
preformed dose and as forming doses. Also
studied were the virus inactivation with dou-
ble monochloramine doses and the addition
of multiple doses of poliovirus 1 during the
progress of the experiment.
3. To select a monochloramine-resistant
poliovirus 1 mutant.
Methods
All of the disinfection studies were per-
formed using the kinetic apparatus. The
poliovirus 1 (Mahoney strain) stocks used in
these studies were prepared as either ag-
gregates or singles. Enterovirus-associated
animal cells were prepared to simulate natu-
rally found cell-associated viruses that can
be excreted from the intestinal tract of
humans. Two cell lines were used — human
epidermoid carcinoma (HEp-2) and Buffalo
Green Monkey (BGM) cells. Primary effluent
from a municipal sewage treatment plant and
human feces were used to prepare solids-
associated, naturally occurring coliforms.
Animal viruses were titered by the plaque
technique in BGM continuous cell lines. £.
co// survivors were recovered and
enumerated with surface-inoculated tryp-
ticase soy agar plates, whereas primary
effluent studies used the most probable
number multiple-tube fermentation method
through the confirmed test.
Results and Discussion
Monochloramine and
Dichloramine Disinfection of
Poliovirus 1 Singles and
Aggregates
A number of studies have implicated ag-
gregates in the viral inocula as the cause of
aberrations in survival curves when viruses
are exposed to destructive chemical and
physical agents such as disinfectants. This
study showed aggregated poliovirus 1 to be
1.7 times more resistant to the disinfectant
than the singles preparation (Figure 1).
Similar results were found in the dichlora-
mine studies. The disinfectant apparently
penetrates slowly into the aggregated viral
mass, thus enabling some viruses to survive
and develop in the tissue culture recovery
system.
Effects of Temperature On
Inactivation of Poliovirus 1
Singles by Monochloramine and
Dichloramine
Since chemical disinfection is a rate pro-
cess, the chemical reaction rate increases
with increasing temperatures. The empirical
rule of thumb is that the rate of the reaction
increases by a factor of 2 to 3 for each
10-degree rise in temperature. The tempera-
ture coefficient for a 10-degree change (Q10)
when destroying virus by free chlorine has
been observed to increase the rate of virus
inactivation by a factor of 2 to 3 (200 to 300
times). Studies for 99% inactivation of
poliovirus 1 singles by monochloramine at
pH 9 and temperatures of 5, 15, and 25 C
yielded an average Q10 value of 2.75,
whereas at the 90% level, the average value
was 1.95. The 90% inactivation kinetics of
poliovirus 1 singles by dichloramine at 5 and
15 C yielded a Q10 of 2.5, which was within
the 2 to 3 factor increase noted earlier.
Effects of pH on Inactivation of
Poliovirus 1 Singles and E. coli
by Monochloramine
Most finished drinking waters in the
United States are maintained below pH 9 —
usually between 7 and 9. At pH 9 and above,
the chloramine that is formed when hypo-
chlorous acid reacts with ammonia is
predominantly monochloramine. Thus many
research studies are done at pH 9 or above.
However, pH values lower than 9 can be en-
countered in drinking water treatment. To
determine the disinfectant quality of a still
predominantly monochloramine system at a
pH below 9, monochloramine levels were
first preformed at pH 9, and the pH was im-
mediately adjusted to 7. Initial concentrations
-------
of monochloramine were stable at this lat-
ter pH for more than 4 hr. The change in pH
had no apparent effect on the disinfection
of the poliovirus 1 singles, but it increased
the rate of monochloramine disinfection of
E co//about 10 times (Figure 2). The effect
of pH on transport mechanisms across the
bacterial cell membrane may have influenced
the greater monochloramine destructive ef-
fect at pH 7. Earlier work has demonstrated
that Entamoeba histolytica cysts take up
more chlorine and have lower survival rates
at low pH. Other research using the sur-
rogate animal virus, bacteriophage f2 (in-
stead of an animal virus like poliovirus 1)
produced greater virus inactivation at lower
pH. The fact that the present study did not
produce a similar effect points up the need
for caution when using a surrogate animal
virus. These studies should be continued
using other animal viruses to determine
whether inactivation by monochloramine is
greater at pH 7 than at pH 9.
Disinfection ofE. coli Using
Preformed and Forming
Monochloramines
Chloramine research studies usually use
preformed monochloramines as the disinfec-
tant. For many years, ammonia (NH3) has
been combined with chlorine (CI2) to form
chloramines for the treatment of drinking
water. Ammonia is still deliberately added to
some chlorinated public water supplies to
provide a combined available chlorine
residual (i.e., chloramines). Monochloramine
is the principal chloramine that is en-
countered in drinking water treatment, but
in recent years, chloramines have not been
recommended as a primary disinfectant be-
cause of their perceived low germicidal effi-
ciency. Another concern is whether forming
monochloramines are better disinfectants
than preformed monochloramines. Thus the
present study attempts to cast more light
upon the real-world situation in which
monochloramines are formed during the pro-
cess of disinfection and are not added in the
preformed state.
The disinfection efficiencies of preformed
monochloramine (NH2CI) and forming
monochloramine (free chlorine and NH3)
against the test bacterium £ coli were com-
pared along with reference to the disinfec-
tion ability of free chlorine alone. The
forming monochloramine (Figure 3) was
about 1.2 times more effective than the
preformed monochloramine. Split-second
exposure of the E coli inoculum to the
hypochlorite-hypochlorous acid mixture that
existed at pH 9 in the forming monochlora-
mine study may have been responsible for
the initial faster kill of the test bacteria.
10
i
Poliovirus 1 "Singles"
Poliovirus 1 Aggregates
J I 1 I I I I I
J I I I I I I I
10
100
Minutes
1000
Figure 1.
Concentration-time relationship for 99% activation of poliovirus 1 singles and
aggregates by monochloramine at pH 9 and 15 C.
100
NH2CL Level
(mg/L)
• Poliovirus 1
A Poliovirus 1
&E. coli
0 E. coli
8.5
8.7
2.0
2.2
PH
7.0
9.0
7.0
9.0
10
1.0
0.1
.01
100
Preformed NH2CI
1.0
.01
A 1.92 mg/L NH2CI, Preformed
• 1.86 mg/L NH2CI. Forming
A 0.5 mg/L (HOCL + OCI-)
60 120 180 240 300
Minutes
Figure 2. The inactivation of poliovirus 1
singles and Escherichia coli at 5
C by monochloramine at pH 9
and 7 (preformed at pH 9).
10 20 30 40 50 60 70
Minutes
Figure 3. Disinfection of E. col i / 7 223 at 5
C and pH 9 by forming and
preformed monochloramines
compared with a 0.5-mg/L
mixture of hypochlorous acid
(HOCIj and hypochlorite ion
roc/-/
-------
The disinfection rates for the forming and
preformed monochloramines were the same
after the first 15 min of the study; the ob-
served differences in the positioning of the
lines can be attributed to the differences in
bacterial numbers after the first 3 min of the
study. Although the original bacterial inocula
were similar, there was a greater initial kill
of the bacteria in the forming monochlora-
mine study than in the preformed mono-
chloramine. After the first 3 min of the
forming monochloramine experiment, the
ability of the newly formed monochloramine
to kill the remaining bacteria was the same
as that encountered in the preformed study,
but there was more bacteria to disinfect in
the preformed study. The brief' initial ex-
posure of the bacteria in the inoculum to the
free chlorine present before the mono-
chloramine was completely formed appears
to account for the differences between the
two monochloramine survival curves.
Sequential Addition of
Poliovirus 1 to Determine the
Extent of Monochloramine
Disinfecting Efficiency
Survival curves in these studies often
show retardant die-away and inactivation
patterns. Although the disinfectant level was
never depleted during the course of the ex-
perimentation, the question arose as to
whether changes had nevertheless occurred
in the disinfectant's efficiency to account for
retardant curves. Thus a second inoculum
of poliovirus 1 was added 2 hr after the first
virus administration to determine whether
the inactivation rate of this subsequent virus
inoculum would mimic the first portion of the
curve. The rapid initial inactivation rate reap-
peared, indicating that the disinfection effi-
ciency of the original monochloramine had
not been affected or altered and that this
monochloramine was still capable of inac-
tivating the additional inoculum.
Effect of Increasing
Concentrations of
Monochloramines on the
Inactivation of Poliovirus
1 Singles
During this research, it was noted that in-
creasing the monochloramine concentration
did not proportionally increase the rate of in-
activation of poliovirus 1 singles. Though 12
mg/L of monochloramine was about four
times more effective at the 99% inactivation
point than the lower concentration of 5.4
mg/L, 22 mg/L was as effective as 12 mg/L.
This result is contrary to that of some re-
searchers who used E. coli as the test
organism and consistent with results of other
investigators who used viruses.
Effect of Chloride Ions on
Monochloramine Disinfection of
Poliovirus 1 Singles and
E. coli
Poliovirus 1 has been found to be inac-
tivated more rapidly by chlorine in the form
of hypochlorite ion (OCI') at pH 10 than by
hypochlorous acid (HOCI) at pH 6. The
borate buffer system (containing KCI) is
believed to have an influence on the
hypochlorite ion and hypochlorous acid
virucidal relationships. Since 0.2 N HCI was
used in this study to prepare preformed
monochloramine at pH 9, the effect of the
chloride ion on the disinfection process was
investigated. The addition of 0.2 N HCI made
the 0.05 M borate buffer system (without
KCI) about 0.02 M with respect to chloride
ions. In a similar study with £ coli at 5 C,
3.2 mg/L monochloramine was formed at
pH 7, 0.02 M chloride ions were added as
the sodium salt, and disinfection was com-
pared with that at the same level of
monochloramine at pH 7, but without the
added chloride ions. No effect of the added
chloride ions was observed. Thus the ob-
served difference in disinfection at pH 9 and
pH 7 for E. coli (Figure 2) was due to the pH
change to 7 and not to the addition of chlo-
ride ions when the 0.2 N HCI was added to
the buffer system.
Selection for Monochloramine-
Resistant Poliovirus 1
Studies have suggested that viruses
become resistant to free chlorine after
repeated sublethal exposures. Thus a test
was undertaken to determine whether suc-
cessive exposures of virus to monochlora-
mine would have the same effect. Two
procedures were used to prepare virus
singles (aggregates could increase virus
resistance). Polioviruses prepared by both
procedures were exposed separately under
the same test conditions for similar time
periods. After exposure to monochloramine,
the more resistant plaques representing sur-
vivors were isolated, regrown, and re-
exposed to monochloramine. Eight repetitive
monochloramine exposure cycles were per-
formed for viruses prepared by both pro-
cedures. The viruses prepared by one
method developed no resistance to mono-
chloramine, whereas those prepared by the
other method gradually did. The poliovirus
prepared by the latter method and exposed
eight times were 2.3 times more resistant to
monochloramine than either unexposed
poliovirus or virus exposed seven times to
monochloramine (Figure 4).
200
, Initial Singles Poliovirus
exposed to 9.15 mg/L NH2C/
Poliovirus 1 Singles
survivors of 7 exposures
now exposed to 10.5mg/L NH,CI
• Poliovirus 1 Singles
survivors of 8 exposures now
exposed to 8.95 mg/L NH2CI
,0/L.
7234
Hours
Figure 4. Inactivation of prepared polio-
virus at pH 9 and 15 C before
and after repeated exposure to
monochloramine.
Disinfection of HEp-2-Cell-
Associated Poliovirus 1
With Monochloramine
Disinfection studies with animal-cell-
associated poliovirus 1 were performed using
two continuous cell lines, HEp-2 and BGM
kidney cells. The cell-associated virus system
approximates the state of viruses as they are
excreted from the body into domestic sew-
age. The viruses are protected by their cell
association (Figure 5). This effect is more
dramatic when the viruses are 99.9%
through 99.99% inactivated.
The effect of organic turbidity on the
disinfection of HEp-2 cell-associated polio-
virus was studied with monochloramine con-
centrations ranging from 4.15 to 21.0 mg/L
at 5 C and pH 7 and 9 (Figure 6). Nearly
doubling the monochloramine dosage (from
12.2 to 21.0 mg/L) at pH 9 in the presence
of almost the same turbidity reduced the
time required for 90% virus inactivation from
50 to 30 min. Increasing the turbidity from
0.8 NTU to 2.0 NTU at monochloramine
levels of 10.35 and 11.3 mg/L, respectively,
and pH 7 significantly decreased disinfection
efficiency. Turbidity caused by the presence
of animal cells interfered with the disinfec-
-------
tion process. The pH change from 9 to 7 had
no apparent effect on the rate of poliovirus
1 inactivation whether or not the virus was
associated with animal cells.
700
^ 70
2
5
k.
3
1.0
10
O 2.2 mg/L; Cell-Assoc. (2.45 NTU)
A 2 28 mg/L. Cell-Assoc. (1.25 NTU)
• 2.98 mg/L. Aggregated
_ ±3,04 mg/L, Aggregated
8 '
HEp-2
Cell-associated
•*— Poliovirus 1
Aggregated
Poliovirus 1
Oil
12345
Minutes
Figure 5. Inactivation of aggregated and
HEp-2 cell-associated poliovirus
1 with hypochlorous acid at pH 6
and 5 C
20
10
l
O
NH-,CI Level Turbidity pH
O
O Poliovirus 1 Singles
J I—I I I I I
i l l I I l l
10
100
Minutes
Figure 6.
Concentration-time relationship for 90% inactivation of poliovirus 1 singles and
HEp-2 cell-associated poliovirus 1 at different turbidity levels and concentrations of
monochloramine at 5 C and pH 7 and 9
Disinfection of BGM
Cell-Associated Poliovirus 1
With Hypochlorous Acid,
Monochloramine, and
Dichloramine
The inactivation of BGM-cell-associated
poliovirus 1 was studied using three disinfec-
tants — hypochlorous acid at 15 C and pH
6.0, monochloramine at 15 C and pH 9, and
dichloramine at 5 C and pH 4.5. All the sur-
vival curves showed extended tailings caused
by the association of the poliovirus 1 to the
cells and to themselves (aggregation) dur-
ing the disinfection process. Disinfection
rates of BGM-cell-associated poliovirus 1 by
monochloramine and hypochlorous acid at
similar turbidities and concentrations were
compared. Whereas only 15 sec was needed
for 90% of the cell-associated viruses to be
inactivated by the hypochlorous acid, 95 min
was required to reach 90% inactivation with
the monochloramine. Even under these dif-
ficult conditions for disinfecting viruses,
hypochlorous acid was about 380 times as
effective as the monochloramine. Figure 7
summarizes the monochloramine concen-
S
O
\
20
10
D
A
a
*
o
Turbidity
(NTU)
0.7
1 0
1.98
20
.65
90
1.6
NH2CI Level
(mg/L)
332
3.16
5.47
6.0
7.0
7.0
1 16
Poliovirus 1 Singles
• •¥•
I
I
70
700
Minutes
Figure 7.
Concentration-time relationship for 90% inactivation of BGM-cell-associated and
unassociated poliovirus 1 by various concentrations of monochloramine at15C and
pH9.
-------
tration-time plot for the 90% inactivation of
BGM-cell-associated and unassociated
viruses. The BGM-cell-associated poliovirus
1 points are represented by bold symbols.
Most of these associated points were above
the poliovirus 1 unassociated singles curve,
indicating that the cell-associated viruses
were being protected from inactivation.
A final study was done comparing the in-
activation of BGM cell-associated polio-
viruses with the survival of unassociated
poliovirus 1 singles using dichloramine as the
disinfectant at 5 C and pH 4.5. No dif-
ferences were observed in the disinfection
rates of the two poliovirus preparations,
though the dichloramine concentrations
were similar (17.0 mg/Lforthe unassociated
versus 17.35 mg/L for the associated polio-
virus). The lack of protection could be due
to rapid penetration of the cell mass by the
dichloramine.
Coliform Disinfection Studies
Disinfection studies using coliforms were
divided into two groups: (a) disinfection of
naturally occurring coliforms from fecal
suspensions, and (b) disinfection of fecal col-
iforms associated with primary effluent
solids. The turbidity associated with either
system was found to interfere with disinfec-
tion efficiency.
Conclusions
Virus aggregates are, along with organic
particulates, a major part of the mechanism
for the maintenance of virus infectivity in
water. In these studies, aggregated polio-
virus 1 (at the 99% inactivation point) at 15
C and pH 9 was about 1.7 times more resis-
tant to disinfection by monochloramine than
unassociated virus singles. The singles virus
preparation disinfected by dichloramine at 15
C and pH 4.5 was inactivated (at the 90%
inactivation point) about 8 times as rapidly
as the aggregated virus.
The average temperature coefficient for a
10-degree change (Q10) was 2.75 in mono-
chloramine-temperature reactivity studies
with poliovirus 1 singles at pH 9 and
temperatures of 5, 15, and 25 C. For
dichloramine, a 10-degree change in tem-
perature gave a Q10 of 2.5 for poliovirus 1
singles. Both Q10 values are within the 2 to
3 factor increase used as the rule of thumb
for each 10-degree rise in temperature.
Monochloramine formed at pH 9 and then
adjusted to pH 7 was a better disinfectant
for bacteria but not for the test virus. Lower-
ing the pH from 9 to 7 increased mono-
chloramine disinfection efficiency about 10
times for the bacteria.
Forming monochloramine was about 1.2
times more effective than the preformed
monochloramine for disinfecting E coli. The
faster disinfection rate could be due to the
initial presence of hypochlorous acid before
the monochloramine was completely
formed.
Resistance to monochloramine developed
gradually in single viruses prepared by one
of the two methods used. Poliovirus 1 sur-
vivors exposed eight times to monochlora-
mine and then disinfected with 8.95 mg/L
monochloramine were 2.3 times more resis-
tant to monochloramine than either the virus
never exposed to monochloramine or the
virus previously exposed seven times to
monochloramine.
The presence of HEp-2 and BGM cell-
associated turbidity interfered with the cell-
associated virus by hypochlorous acid and
monochloramine but not by dichloramine.
The solids in human feces and primary ef-
fluents protect naturally occurring coliforms
from disinfection.
Recommendations
A dramatic increase in monochloramine
disinfection efficiency was produced for E.
coli by lowering the pH of monochloramine
from 9 to 7. Since most finished drinking
waters are maintained in the United States
at a pH below 9, the mechanism of action
should be further investigated. In addition,
other animal viruses besides poliovirus
should be studied to determine whether they
are affected by the pH change.
Additional studies are required with dif-
ferent cell lines to determine whether they
have similar viral protective effects during
disinfection.
Studies should be conducted to determine
the cost effectiveness of reducing the tur-
bidity levels from 5 to 1 NTU in drinking
water treatment. A reduced turbidity level of
1 NTU is recommended because of our
studies and those of others on coliforms
associated with primary effluent solids, fecal
solids, and cell-associated viruses.
In future turbidity studies, methods for
determining the organic or inorganic nature
of the particulates must be developed to
ascertain their potential for inhibiting
disinfection.
Methods should be established for stan-
dardizing the apparatus and the methods for
disinfection research and for reporting the
physical state of the test organisms — that
is, viral-associated (aggregates or cell-
associated) or unassociated (singles) pre-
parations.
The usefulness of chloramines, especially
the monochloramines, in field situations
should be more carefully evaluated. Under
certain conditions such as forming situa-
tions, they may be useful.
Dichloramine's ability to penetrate organic
masses such as cells should be more thor-
oughly investigated.
The development of resistant strains of
viruses in nature should be thoroughly
studied. Laboratory studies can only point
out a potential problem; field studies are re-
quired to pinpoint possible health risks that
might exist in the natural environment.
Pasquale Scar pi no is with University of Cincinnati, Cincinnati, OH 45221.
John C. Hoffis the EPA Project Officer (see below).
The complete report, entitled "Effect of Particulates on Disinfection of
Enteroviruses in Water by Chloramines," (Order No. PB 84-190 693; Cost:
$ 11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
*USGPO: 1984-759-102-10681
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United Slates
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
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