AEPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development EPA-600/D-82-255 August 1982
ENVIRONMENTAL
RESEARCH BRIEF
Survey of Private Sector Provision of Operation and
Maintenance Services to Publicly Owned Treatment Works
Don C. Niehus, Gregory A. Brown, and Jamet M. Jouthoofd
Municipal Environmental Research Laboratory, USEPA
Cincinnati, OH 45268
Abstract
The objective of this research was to determine whether
aqueous chlorine and chlorine dioxide react with activated
carbon, or with compounds absorbed on activated carbon,
to produce compounds that would not form in the absence
of activated carbon. The experimental conditions were
either typical of those found in drinking water treatment
plants, or they permitted conclusions to be made about the
nature of the reaction under water treatment plant
conditions.
Free chlorine is rapidly reduced to chloride by activated
carbon Extraction of carbon after reaction showed that
compounds such as toluene, benzaldehyde, and benzoic
acid were formed, but they were not found in the column
effluent under water treatment plant conditions. Reaction
with an amount of chlorine far exceeding that experienced
m drinking water treatment leads to the formation of
chloroform and other compounds, as well as a high
molecular weight, chlorinated, darkcolored product all of
which are eluted from the column.
Hypochlorous acid (HOCI) reacted with adsorbed humic
substances to produce chloroform and other compounds,
but the amount of chloroform formed per unit mass of HOCI
reacted was less than that found when the reaction took
place in the absence of carbon. Apparently the carbon
destroys much of the HOCI that otherwise would have
reacted with the humic substances. HOCI also reacted with
adsorbed phenolic acids including vanillic acid, syringic
acid, and p-hydroxybenzoic acid that are structural
breakdown products of humic substances to produce a
variety of polyphenols and quinones that were not formed'
in the absence of carbon.
Chlorine dioxide (CIO2) also rapidly reacts with virgin
carbon. When small amounts react such as would be
expected in drinking water treatment plants, it appeared
that all of the ClOa was converted to CT. Some evidence
was found that chlorate (ClOa) was also formed when
greater amounts reacted. No extractable oxidation products
were, however, identified on the carbon surface.
The CIO2 reaction with hydrocarbons such as ethylbenzene,
indan, tetralin, diphenylmethane, and fluorene at pH 3.5
gave oxidized derivatives such as ketones and (sometimes)
alcohols. In the presence of activated carbon, monochloro
and/or dichloro derivatives were produced under some
conditions in addition to the oxygenated compounds
observed in the absence of carbon.
Byproducts of CI02 reactions in water by chlorite (CIOJ) and
ClOs. Virgin carbon readily reacts with ClOi, although its
capacity for reaction was sharply reduced after 80 to 90 mg
ClOa/g carbon had reacted. The reaction between ClOSand
adsorbed vanillic acid produced many unique organic
products, whereas no reaction took place in the absence of
carbon. ClO-j is inert on the carbon surface, however, and
does not react except for a small amount of uptake by ion
exchange.
This Research Brief was developed by the principal
investigators and EPA's Municipal Environmental Research
Laboratory, Cincinnati, OH, to announce key findings of the
research project that is fully documented in the reports and
publications listed on the end.
Introduction
Activated carbon, both powdered and granular, is
frequently contacted by both organic compounds and
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residual chlorine when it is used in water treatment.
Carbon is an effective adsorbent of trace organic
substances and is also a very effective reductant of free and
combined chlorine. Although much work has been devoted
to these separate roles of carbon, little attention has been
given to studying the combined effects of chlorination and
adsorption. For example, chlorine may react with activated
carbon or with organic compounds adsorbed on carbon to
produce compounds not normally found in aqueous
chlorination reactions. It has been shown by others that
activated carbon can promote many kinds of reactions
including redox processes, peroxide decomposition,
substitution, racemization, and cis-trans isomerization.
Carbon will also possibly participate in the reactions of
organic compounds with chlorine.
Chlorination, as normally practiced in water and
wastewater treatment, results in the formation of
trihalomethanes and other chlorinated organic compounds
that may be undesirable from the viewpoint of water
pollution control and human health. Accordingly,
alternatives to chlorine for the disinfection of water and
wastewater are being sought; CIO2 is one disinfectant that
has received considerable attention as an alternative
disinfectant to chlorine. It is currently used at many water
treatment plants to oxidize taste- and odor-causing
compounds, and if it were to be substituted for chlorine as a
predisinfectant, the likelihood of it contacting activated
carbon and compounds adsorbed on carbon will be much
increased. Thus, it is important that the reactions that will
take place when this contact occurs also be identified.
Whenever CI02 is used, CIOJ and ClOa are also formed.
Thus, the reactions of these species were also examined.
The experiments used in this research were designed so
that the results could be used to show what products would
likely form at drinking water treatment plants. Given that
potentially harmful compounds formed on carbon can
escape to the product water, it will be most important to
prevent contact between these disinfectants and carbon
during drinking water purification. It was not possible to
study all aspects of the problem during this research
project, but the results obtained do show that compounds
formed when carbon is present do not form in aqueous
solution when carbon is absent.
Free Chlorine-Activated Carbon Reaction
Free chlorine solutions prepared by bubbling chlorine gas
into distilled, deionized, and purged water was reacted with
activated carbon that had been baked at 175°C for 1 week to
remove volatile compounds. Application of a 10 mg/L, pH
5.6 to 6, free chlorine solution to a column of granular
activated carbon (GAC) until 0.1 g chlorine as CI2/g GAC
had reacted showed no volatile compounds in the column
effluent atconcentrationsgreaterthan were inthe influent.
Extraction of the carbon showed that toluene, benzalde-
hyde, benzoic acid, 2-methoxyfluorene, and benzalace-
tophenone were formed, but they were not found in the
column effluent. A greater extent of reaction at pH 7 to 8,1.3
to 4.5 g as CI2/g GAC, led to the appearance of a dark-
colored compound in the effluent and up to 50 /t/g/L
chloroform in the column effluent.
A chlorine solution of approximately 500 mg/L as CI2 was
reacted with carbon, and the colored product thus produced
was concentrated and separated for analysis. The H, N, and
S composition was similar to that of the virgin carbon, but
the C content was much lower and the 0 and Cl contents
much higher than virgin carbon. The molecular weight of
the product was very great (100,000 to 300,000 MW as
determined by ultrafiltration), and it was shown to be
nonmutagenic to several Salmonella and E. coif test
systems. This product is not expected to be formed under
drinking water treatment conditions, and its presence in
drinking water has never been reported (6).
Batch reactions at a very high dosage of free chlorine {2.5 g
as CI2/g of carbon) produced several chlorinated organic
compounds, including chloroform, trichloroethane, and
several chlorinated aromatics. Nonchlorinated aromatic
compounds, such as benzene and toluene, also were
produced. The production of chlorinated organic compounds
was mostly favored at high pH, and benzene and toluene
were produced in neutral and basic solution that had black
color. The increases in concentrations of various organic
compounds were quite marked; for example, chloroform
was present at 2.7 mg/L in a pH 11.5 batch reaction (6).
For all column runs at lower (50 mg HOCI as CI2 or less/L)
chlorine dosage, no volatile organic compounds were
observed in the effluent before 2 g as CI2/g of carbon had
been achieved. After this ratio, chloroform levels in the
effluent were as large as 50/jg/L. Soxhlet extraction of the
carbon from a column receiving 10 mg chlorine/L until
0.11 g of CI2/g of carbon had reacted indicated several
nonchlorinated aromatics that were not present in the
influent. Halogenated compounds were not produced and
desorbed since the total organic halogen (TOX) of the
effluent remained below a measurable concentration
throughout the column run (6).
Determination of TOX profiles in carbon columns receiving
chlorine solutions initially were hampered by interference
of the ClOs ion in the TOX test (1). Subsequent experiments
showed the ClOs interference could be eliminated if the
sample to be combusted was first nitrate washed (2,4,5). A
review of the development of the TOX test is given in
reference 5. The TOX profiles that resulted when 10 mg
HOCI asCI2/L, at pH4.8, were applied showed that the TOX
buildup at the inlet was high but that the TOX did not
penetrate deeply into the column. However, when
hypochlonte ion (OCL~) at pH 8.2 to 8.5 was applied, TOX
on the carbon developed much further into the bed. It was
also found that more TOX was produced from OCI~ than
from HOCI (7.0 vs. 2.8 mg as Cl/g as CI2 reacted) (5).
HOCI-Adsorbed Compound Reactions
Adsorption of humic acid on GAC followed by application of
free chlorine resulted intheformationof chloroform, which
then appeared in the GAC column effluent. However,
reaction of chlorine under the same conditions except that
carbon was not present resulted in much more chloroform
per unit weight chlorine reacted. The free chlorine reacts
with GAC as well as adsorbed humic substances; thus,
much more chlorine was required to form a given amount of
chloroform (7).
The compounds formed on the carbon surface were
extracted, identified, and compared with the compounds
formed in aqueous solution in the absence of carbon. The
compounds in the aqueous solution were adsorbed on
XAD-2 and then eluted. Many compounds werefoundtobe
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formed both in aqueous solution and on the carbon Some
dihydroxybenzene molecules and chlorinated dihydroxy-
benzene molecules were found only on the carbon,
indicating that the carbon surface was affecting the
reaction (7).
The influence of the carbon surface on chlorine organic
compound reactions at pH 6 was further examined using
three phenolic acids: p-hydroxybenzoic acid, vanillic acid,
and synngic acid compounds that are structural
breakdown products of humic acid and constitutents of
natural water. Results showed a variety of polyphenols and
qumones that were produced only on the carbon surface by
decarboxylation of the aromatic ring, hydroxylation of the
aromatic ring, demethylation of methoxy substituents,
oxidation to quinones, and chlorine substitution reactions.
The aqueous solution was extracted with both XAD-2 and
carbon to ensure that these compounds were not present. A
generalized reaction scheme for the vanillic acid HOCI
reaction on the carbon surface was proposed (3,8).The
dihydroxybenzenes and chlorinated dihydroxybenzenes
recovered from the carbon on which HOCI had reacted with
humic substances probably resulted from similar reactions.
(3,8)
Adsorption of Chlorinated Organic Compounds
Humic andf ulvic acid solutions were chlorinated to produce
solutions with a wide variety of chlorinated organic
compounds The solutions were then applied to columns of
GAC to determine the usefulness of adsorbed TOX as a
measure of adsorption efficiency and remaining capacity
and to determine the relative adsorbability of chloroform
and the rest of the organohalogen compounds (2,4). The
adsorbed TOX profiles, determined by removing carbon
samples at different column depths and measuring the TOX
of these samples, were very sharp and sensitive to the
amount of TOX applied. The applied TOX was more
efficiently adsorbed than total organic carbon (TOC), but
TOX broke through faster than the chloroform. Comparison
of the TOX profiles with those obtained at Jefferson Parish
from full-scale GAC filters showed that the latter were not
as sharp but that adsorbed TOX would still be a useful
measurement to control GAC filters (4).
CIO2-Activated Carbon Reactions
Chlorine-free CIO2 was prepared by purging CIO2 from a
solution of NaCIO2 and potassium persulfate (K2S2Oa) and
collecting it in chilled, deionized, distilled water. Batch
experiments at pH 3.5 using ClOs concentrations up to
400 mg/L did not result in formation of volatile compounds
(as shown by a purge-and-trap procedure). The TOX of the
solution in contact with the carbon was also near the
detection limit. At these high CIO2 concentrations, much
(22% to 37%) of the CI02 was converted to ClOi, with the
rest apparently being reduced to Cl~. Column tests with
more dilute solutions (3.8 mg/L) again showed no
production of volatile compounds, further, the only
inorganic product with Cl was Cl~ There were low
concentrations of TOX on the GAC after the reaction was
stopped, but it was far less than that observed for free
chlorine for an equivalent extent of reaction. Soxhlet
extract ion of the carbon indicated three organic compounds
that were not present in the influent, but none of them were
halogenated compounds (9)
CIO2 Adsorbed Compound Reactions
The hydrocarbons used for reaction studies were
ethylbenzene, indan, tetralin, diphenylmethane, and
fluorene. Chlorine dioxide was shown to react rapidly with
these compounds in dilute (ca. 0.6 mg/L, 5 x 10~6 M)
aqueous solution at pH 3.5. Hydrocarbons with benzylic
hydrogen atoms reacted, probably by radical pathways, to
give oxidized derivatives such as ketones and (sometimes)
alcohols at the benzylic positions. In the presence of
activated carbon, monochloro and/or dichloro derivatives
were produced under some conditions m addition to the
oxygenated compounds observed in the absence of the
carbon. Tests using the appropriate blanks showed that
these compounds were not produced from the CIO2-
activated carbon reaction Typical results are shown in
Table 1 for ethylbenzene and tetralin. Similar data are
available for the other compounds, and the reaction with
indan was also evaluated at pH 5.3 and 7.0.
ClOa and ClOs Reactions with Activated Carbon
and ClOi Reaction with Adsorbed Compounds
CI02 was reduced to Cl~ by activated carbon. One virgin
carbon was tested, and it had a capacity for reaction of
about 80 to 90 mg CI02/g GAC before the reaction rate was
sharply reduced. The effect of adsorbedorganiccompounds,
and reactivation, on this reaction remains to be determined
(5,10).
A small amount of ClOs was taken up by carbon, probably by
ion exchange, but no oxidation-reduction reaction took
place
The reaction between ClOjj and adsorbed vanillic acid
yielded several reaction products identifiable by GC/MS,
but no products were found in the absence of carbon. The
carbon seemed to promote hydroxylation, decarboxylation,
ring cleavage and CO2 addition reactions. The products
formed are listed in Table 2.
Conclusions
Several disinfectant and disinfectant byproducts were
found to react readily with activated carbon Hypochlorous
acid, HOCI, and hypochlorite ion, OCT, reacted to produce
some organic byproducts, but none of these byproducts
were found in the column effluent when chlorine dose and
times of reaction conditions were found m the column
effluent when chlorine dose and times of reaction
conditions were used that are typical of drinking water
treatment plants. Chlorine dioxide, CIO2, and chlorite,
CIO;>, also readily reacted with one virgin carbon, but few
organic byproducts were formed from these reactions
Chlorate, ClOs, did not react
The reaction of HOCI, CIO2, and CIOJ with adsorbed organic
compounds resulted in the formation of organic products
that were not found m the absence of activated carbon.
Most of the concentration of these species appears to react
with the activated carbon itself, but sufficient amounts
react, with adsorbed compounds to form organic products
that can be measured HOCI reacted with adsorbed humic
substances and a variety of adsorbed phenolic compounds
to produce several polyphenols and quinones that were not
formed in the absence of carbon. Adsorbed hydrocarbons
reacted with CI02 to form halogenated compounds and
CI02 reacted with adsorbed vanillic acid to produce more
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Table 1. Chlorine Dioxide-Hydrocarbon Reactions at pH 3.5
Compound Mol Wt.
Aqueous Soln"
Carbon Extract"
ETHYLBENZENE
1. ethylbenzene0
2. acetophenone
3. a-methylbenzyl alcohol
4. methyl-2-(or 3-) chlorobenzoate
5. a-phenylethyletherd
TETRALIN
1 . c/s-decaline
2. trans-deca\\ne
3. tetralin0
4. naphthalene6
5. 1,2-dihydronaphthalene
6. /3-o-hydroxyphenylpropionic acid
1 '. a-tetralone
8. a-tetralol
9. a-naphthoquinone
10. hydroxy-1-tetralone or
hydroxycoumarm
1 1. a-tetralone monochloro derivative
12. a-tetralol monochloro derivative
13. tetralin dichloro derivative
14. /3-o-carboxyphenylpropionic acid
methyl ester
106 + +
1 20 +f +'
122 +
170 +
226 +
138 + +
138 + +
132 + +
128 + +
1 30 trace
166 ?
146 +' +'
148 + +
158 +f
162 +
180 +
182, +
trace
222 +
XAD-2 extracts of aqueous solutions reacted for 2.9 mm, 1 hr, and 2 days.
DSoxhiet extraction of 2 g of carbon receiving a reaction mixture of chlorine dioxide and hydrocarbon reacted for 2.9 min.
cStarting material.
dFrom CIO2-GAC reaction.
6 Impurity
' Major product.
9 Reaction product of impurity.
oxygenated compounds that were not formed in the
absence of carbon.
Addtional studies are needed to characterize the types of
reactions that occur between disinfectants and compounds
adsorbed on activated carbon, and to determine whether
those products that are formed can be displaced into the
product water in significant concentration. When such data
are available, it will be possible to make an informed
decision about whether selected disinfectants should be
permitted to contact activated carbon when certain species
of adsorbed compounds are likely to be present.
References
The following papers and reports contain the findings of
this research project in their entirety. The Ph.D. thesis (#3)
is available from University Microfilms, P.O. Box 1346, Ann
Arbor, Ml 48106. The M.S. theses (#1,2,5) are available
from the University of Illinois Library or Vernon L Snoeyink,
Department of Civil Engineering, University of Illinois, 208
North Romine, Urbana, IL 61801 The articles that are in
press or preparation (#8,9,10) are also available from
Vernon L. Snoeyink until they appear in the journals.
1. McHie, W.F., "Total Organic Chlorine (TOCI) Produced
from the Reaction of Aqueous Chlorine with Activated
Carbon," M.S. Thesis, Department of Civil Engineering,
University of Illinois, Urbana, 1980.
2. Qumn, J.E., "Adsorption of Total Organic Halogen
(TOX) by Granular Activated Carbon Adsorbers," M.S.
Thesis, Department of Civil Engineering, University of
Illinois, Urbana, 1980.
3. McCreary, J.J., "The Reaction of Aqueous Free
Chlorine with Organic Compounds Adsorbed on
Granular Activated Carbon," Ph.D. Thesis, Depart-
ment of Civil Engineering, University of Illinois,
Urbana, 1980.
4. Quinn, J.E. and Snoeyink, V.L., "Removal of Total
Organic Halogen by Granular Activated Carbon
Adsorbers," Jour. Amer. Waterworks Assoc. 72 483-
488(1980).
5. Dielmann, L M.J., III, "The Reaction of Aqueous
Hypochlorite, Chlorite and Hypochlorous Acid with
Granular Activated Carbon," M.S. Thesis, Department
of Civil Engineering, University of Illinois, Urbana,
1981.
6. Snoeyink, V L, Clark, R.R., McCreary, J.J., and McHie,
W.F., "Organic Compounds Produced by the Aqueous
Free Chlorine-Activated Carbon Reaction," Environ.
Sci. and Techno/. 15, 188-192(1981).
7. McCreary, J.J. and Snoeyink, V.L., "Reaction of Free
Chlorine with Humic Substances Before and After
Adsorption on Activated Carbon," Environ, Sci. and
Techno/. 15, 193-197(1981).
8. McCreary, J.J., Snoeyink, V.L., and Larson, R.A., "A
Comparison of the Reaction of Aqueous Free Chlorine
with Phenolic Acids in Solution and Adsorbed on
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Table2. Compounds Identified for the Reaction
between Vanillic Acid and Chlorite in the
Presence of Carbon
'eak # Structure
1 l!JI-CH3
qi H
2 H-C-C-C-CH3
1 II 1
Cl 0 Cl
Name
2-Methyl-3-Furancarboxylic
acid methylester
1,1,3(or 1,1,4)-tnchloro
2-butanone
Mol wt
140
174
OH
3
*4
*5
*6
7
8
9
10
11
12
13
IQj (OCH3)2 Dimethoxyhydroxybenzene
O) (OCH3)3 Tnmethoxybenzene
(Q) (OCH3)4 Tetramethoxybenzene
OH
(Q) (OCH3)3 Trimethoxyhydroxybenzene
COOCH3
(Q)_OCH3 Methylated vanillic acid
OCH3
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
154
168
198
184
196
222
220
206
220
234
222
14 r#Sj(COOCH3)2 Dimethoxybenzene dicarboxylic 254
^*S__,,. acid dimethylester
(UCH3)2
15 Unknown 235
16 Unknown 208
"Indicates that the compound has been found in the vanillic acid-free
chlorine-carbon reaction (McCreary, 1980)
Granular Activated Carbon," Environ. Sci. and
Techno/. In press, 1982.
9. Chen, A.S.C., Larson, R.A., and Snoeyink, V.L.,
"Reactions of Chlorine Dioxide with Hydrocarbons:
Effects of Activated Carbon," Environ. Sci. and
Techno/. In press, 1982.
10. Voudrias, E.A., Dielmann, L.M.J., III, Snoeyink, V.L.,
Larson, R.A., McCreary, J.J., and Chen, A.S.C.,
"Reactions of Chlorite with Activated Carbon and with
Vanillic Acid and Indan Adsorbed on Activated
Carbon," In preparation, 1981.
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