Evaluating
TOC analytical results
Tests indicate particulate fraction of total organic
carbon in a natural water is more accurately
measured by the combustion method
than by the ultraviolet–persulfate
oxidation method.
Issam Najm,
Joseph Marcinko,
and Joan Oppenheimer
T
otal organic carbon (TOC) is commonly used
as the primary surrogate for measuring the concentration of natural organic matter (NOM) in drinking
water. Several methods are available for measuring
the TOC concentration in water. The two most common are the ultraviolet
(UV)–persulfate oxidation
The Disinfectants/Disinfection By-products (D/DBP) Rule includes
method and the combustotal organic carbon (TOC) as a regulatory compliance parameter
tion method.1
with the idea that TOC concentration is a direct indicator of the
Both methods use the
potential for DBP formation upon chlorination. A comprehensive
principle of completely
study was conducted to evaluate the ability of the two most
oxidizing the organic carcommon methods—ultraviolet (UV)–persulfate oxidation and
bon in NOM to carbon
catalytic combustion—to measure the particulate fraction of the
dioxide (CO2) and meaTOC in water and determine whether this fraction contributes to
suring the amount of CO2
DBP formation. Results showed that particulate TOC fraction in a
produced. The quantified
natural water was more accurately measured by the combustion
CO 2 level is then conmethod. Therefore, the method used by a water utility to evaluate
verted to a TOC concenTOC removal through a water treatment plant can significantly
tration in the original
affect the chemical dosages required for regulatory compliance
water sample on the basis
and treatment cost. Furthermore, chlorination testing results
of a predetermined stansuggest that the DBP formation reactions may not be affected by
dard organic carbon conparticulate TOC, leading the authors to propose that dissolved
centration. The only sigorganic carbon rather than TOC is a more appropriate indicator
of DBP formation potential in water treatment.
For executive summary,
see page 158.
84
VOLUME 92, ISSUE 8
© 2000 American Water Works Association, Journal AWWA August 2000
JOURNAL AWWA
FIGURE 1
Molecular structure of potassium hydrogen phthalate (A) and proposed structure of natural humic
substance (fulvic acid) (B)12
A
B
O
OH
O
HO
O
H
OH
O
C
H
C
C
O
H
OH
C
O C
C
O O
OH
O
OH
C
OH
O C
OH O
C
O C
C
OH
OH
O
C
OH
OH
O
O
O
C
– +
O K
O
O
HO
H
OH
O
OH
H
C
C
OH
OH
C O
C
HO
O C O
H
OH
O
HO
H
O
C
C
O C
OH
O
O
C
OH
OH
C O
C O
OH
OH
O
H
OH
OH
OH
OH
nificant difference between the two methods is the 1, part A). In addition, the standard solution is premeans by which the organic carbon is oxidized to
pared in particulate-free water. However, natural
CO2. The UV–persulfate method relies on the comwater and KHP solution differ in two primary respects.
bined oxidation strengths of the UV light, oxygen,
First, natural humic substances have very comand persulfate to convert the organic carbon into
plex and varying molecular structures (Figure 1,
CO2, whereas the combustion method relies on cat- part B),12 which may have substantially different
alytic combustion of the organic carbon to CO2.
oxidation potential compared with that of KHP. SecThe TOC values obtained using different oxida- ond, natural water may include a substantial contion processes have been compared in numerous centration of particulate organic matter. Differences
studies, many of them performed by the marine
in the extent of oxidation of the particulate organic
chemistry community.2–5 However, these studies were
matter will result in differences in the measured
primarily conducted using particulate-free or filtered
TOC concentration in the water. This is primarily
water. In addition, the high chloride concentration in problematic for raw water and not necessarily for
seawater can interfere with the efficiency of photo- settled or filtered water.
chemical wet oxidation methods by competing for
The Information Collection Rule (ICR) and the
the persulfate ion.6
enhanced coagulation requirements of the Stage 1
Other researchers have compared TOC analytical Disinfectants/Disinfection By-products (D/DBP)
methods using freshwater.7,8 Their findings suggest Rule are the first to require public water utilities
that the UV–persulfate oxidation method measures
lower organic carbon concentrations than the highhe greater the particulate organic content
temperature combustion
method. It is not clear,
of the water, the greater the difference
however, whether these
in the total organic carbon concentrations
differences were due to the
dissolved or particulate
reported by the two analytical methods.
fraction of NOM.
Studies on the efficiency
of oxidation of pure compounds in solution have to monitor for TOC concentrations in raw and
demonstrated that numerous chemicals are recalci- treated water. With this requirement, these two
trant to various oxidation processes.4,9–11 The standard rules have brought to the forefront the need for an
organic compound used to calibrate all TOC analyz- accurate and reliable measurement of TOC coners is potassium hydrogen phthalate (KHP),1 which
centration in natural water. Both the UV–persulhas a relatively simple molecular structure (Figure
fate oxidation method and the combustion method
T
AUGUST 2000
© 2000 American Water Works Association, Journal AWWA August 2000
I. NAJM ET AL
85
FIGURE 2
The samples contained
turbidity concentrations of 8,
16, and 18 ntu, respectively.
(The 8-ntu turbidity samples
were two distinct samples
that contained identical turbidity concentrations.) Results suggest that the higher
the turbidity of the sample,
the greater the difference
between the TOC concentration measured by the two
methods. Figure 2 indicates
that the UV–persulfate method underestimates the TOC
concentration in the water
samples with relatively high
levels of turbidity.
The authors set out to
evaluate three possible explanations for this behavior:
(1) Because the two TOC
analyzers use different purging times for removing the
inorganic carbon from the
water before analysis, the TOC
analyzer using the combustion
method may not be purging
as much of the inorganic carbon as the UV–persulfate
method.
(2) Inorganic solids present in the water may be
interfering with the UV–persulfate method’s ability to oxidize the soluble organic carbon into CO2.
(3) The UV–persulfate
method is not capable of oxidizing the particulate organic
matter to the extent achieved
by the combustion method.
Effect of natural water turbidity on total organic carbon (TOC)
analytical results
Ultraviolet–persulfate method
Combustion method
TOC Concentration—mg/L
8
6
4
2
0
8
8
16
18
Turbidity—ntu
FIGURE 3
Example standard curve for the ultraviolet–persulfate method
for total organic carbon (TOC) analysis
Adjusted Instrument TOC Reading—mg/L
12
y = 0.9985x + 0.0512
2
R = 0.9998
(10; 9.99)
10
8
6
(4; 4.15)
4
2
(1; 1.06)
Analytical methods
(0.4; 0.43)
0
0
2
4
5
8
TOC Standard—mg/L
are approved for TOC analysis under the ICR. This
article evaluates the two methods and compares
their ability to measure particulate organic carbon
present in natural water.
Statement of problem
Figure 2 shows TOC concentrations of three natural water samples analyzed using the UV–persulfate method and the combustion method. Analyses
were performed in six replicates. Error bars shown in
Figure 2 represent the standard deviation range for
each analysis.
86
VOLUME 92, ISSUE 8
TOC analyses. TOC
analyses were conducted
using the UV–persulfate
method and the combustion
method. The following sections briefly describe the procedures used to prepare
samples for each analysis.
UV–persulfate method. A TOC analyzer* was used
to analyze 10-mL samples by the UV–persulfate
method. The samples and all standards were first
dosed with 1 mL of 20 percent phosphoric acid and
then purged with commercial air† for 2.5 min before
analysis. The instrument was calibrated with American Chemical Society (ACS)-grade KHP.‡ Four standard concentrations of 0.4, 1.0, 4.0, and 10 mg/L
and one blank laboratory water were used to calibrate the instrument every day. An example cali10
12
© 2000 American Water Works Association, Journal AWWA August 2000
JOURNAL AWWA
TOC Concentration—mg/L
Adjusted Area Count
bration curve is shown in FigFIGURE 4 Example standard curve for the combustion method for total organic
ure 3. The value of the TOC
carbon (TOC) analysis
reading of each standard was
adjusted by subtracting the
50,000
instrument reading of the
blank water sample. For the
45,000
standard curve shown in Figy = 4265.7x + 290.55
(10; 42,621)
2
R = 0.9992
ure 3, for example, the instru40,000
ment reading for the 1.0-mg/L
35,000
standard was 1.12 mg/L. The
blank laboratory water was
30,000
0.059 mg/L. Therefore, the
instrument reading of 1.06
25,000
mg/L reported in Figure 3 for
20,000
the 1.0-mg/L standard was
(4; 18,173)
calculated by subtracting
15,000
0.059 mg/L from the 1.12mg/L reading. This applies to
10,000
all other standards.
Combustion method. A
5,000
(1; 4,763)
TOC analyzer§ was used to
(0.4; 1,687)
0
analyze 40-mL samples by
0
2
4
6
8
10
12
the combustion method. The
TOC Standard—mg/L
samples were first acidified
with three drops of concentrated hydrochloric acid and
then purged with commerFIGURE 5 Effect of inorganic dissolved carbon on total organic carbon (TOC)
cial air** for 6 min before
analytical results
analysis. The instrument was
calibrated with ACS-grade
Combustion method
Ultraviolet–persulfate method
KHP.†† Four standard con1.0
centrations of 0.4, 1.0, 4.0,
and 10 mg/L and one blank
laboratory water were used
0.8
to calibrate the instrument
every day. An example calibration curve is shown in
0.6
Figure 4. The area count of
each standard was adjusted
by subtracting the area count
of the blank water sample.
0.4
For the standard curve
shown in Figure 4, for example, the area count for the
0.2
1.0-mg/L standard was
6,031. The area count for the
blank laboratory water was
0
1,268. Therefore, the area
0
50
100
200
count of 4,763 reported in
Alkalinity—mg/L as CaCO3
Figure 4 for the 1.0-mg/L
standard was calculated by
subtracting the 1,268 blank
Experimental approach
area count from the 6,031 area count. This applies
The authors conducted a series of tests to deterto all other standards.
Other water quality parameters. Turbidity was mine which, if any, of the three potential factors outdetermined with a bench-top turbidimeter§§ using
*Dohrmann DC-180, Rosemount Analytical Inc., Santa Clara, Calif.
method 2140A as described in Standard Methods.1
†Ultra Zero, Oxygen Service Co., Orange, Calif.
Trihalomethanes (THMs) were determined using
‡Fisher Scientific, Fair Lawn, N.J.
§Shimadzu TOC-500, Shimadzu Corp., Columbia, Md.
USEPA method 551.13 The sum of five haloacetic
**Ultra Zero, Oxygen Service Co., Orange, Calif.
acids (HAA5) were determined using method 6251B
††Fisher Scientific, Fair Lawn, N.J.
1
as described in Standard Methods.
§§Model 2100P, Hach Co., Loveland, Colo.
AUGUST 2000
© 2000 American Water Works Association, Journal AWWA August 2000
I. NAJM ET AL
87
FIGURE 6
Effect of inorganic particulate matter on total organic carbon (TOC)
analytical results
Ultraviolet–persulfate method
Combustion method
5
TOC Concentration—mg/L
4
3
was filtered out using 0.45µm filter paper and then
added to a small volume of
organic-free water. This final
suspension was used to spike
a natural water sample with
particulate organic matter to
obtain various levels of turbidity. The resulting samples
were analyzed in triplicate
using both TOC analyzers.
Discussion
2
1
0
0
5
20
Kaolinite Dosage—mg/L
Results of test 1: effect
of inorganic dissolved carbon. Results of the inorganic
interference testing are shown
in Figure 5. Analyses were
conducted in triplicate (except
for the 0-mg/L point, which
was done in six replicates).
50
The bars shown in Figure 5
depict the standard deviations.
The replicates for the 100mg/L alkalinity sample analyzed by the combustion
method were all equal at 0.5 mg/L and therefore had
a standard deviation of zero. Those results with no
error bars also had a standard deviation of zero.
The data show that alkalinity levels as high as 200
mg/L as CaCO3 did not appear to affect the TOC concentrations measured by each analytical method. This
suggests that each method was equally capable of
purging all the inorganic carbon from the water before
the sample was analyzed for organic carbon concen-
lined earlier was responsible for the difference in TOC
concentrations reported by the two methods.
Test 1: effect of dissolved inorganic carbon. In
this test, a deionized organic-free water sample* was
spiked with four levels of ACS-grade sodium bicarbonate† to create alkalinity values of 0, 50, 100, and
200 mg/L as calcium carbonate (CaCO3). Samples
were then analyzed in triplicate for TOC concentration using both analytical methods. The blank sample (with 0 mg/L as CaCO3
added) was analyzed in six
replicates.
Test 2: inter ference
he combustion method reported
from particulate inorganic
matter. Powdered kaolinite
a corresponding increase in total organic
clay‡ was used to represent
inorganic solids. Natural
carbon concentration with increasing
water samples were first filparticulate organic matter concentration,
tered through 0.45-µm filter
paper§ and then spiked with
whereas the ultraviolet–persulfate method
four doses of kaolinite clay
did not report any noticeable increase.
(0, 5, 20, and 50 mg/L),
which resulted in turbidity
levels of 0.04, 4, 15, and 40
ntu, respectively. All filter papers were washed with tration. Therefore, the discrepancies in the TOC results
100 mL of laboratory organic-free water to eliminate shown in Figure 2 were not caused by interference of
possible dissolved organic carbon (DOC) leaching. the inorganic dissolved carbon with either method.
Samples were then analyzed in triplicate for TOC
The differing values measured by the two instruconcentration using both analytical methods.
ments are attributable to the difference in the detecTest 3: measurement of particulate organic
matter. A natural water sample was spiked with var*RO Pure LP/Nanopure, Ultrapure Water System, Barnstead/Therious concentrations of particulate organic matter. The
molyne, Dubuque, Iowa
†Mallinckrodt, Paris, Ky.
particulate matter was obtained by dissolving a high
‡Wards Natural Science Establishment, Santa Fe Springs, Calif.
concentration of humic material** into an organic§Micron Separation Inc., Boston, Mass.
free water. Nondissolved particulate organic matter
**Aldrich Chemical Co., Milwaukee, Wis.
T
88
VOLUME 92, ISSUE 8
© 2000 American Water Works Association, Journal AWWA August 2000
JOURNAL AWWA
TOC Concentration—mg/L
tion limits of each instrument.
In other words, the instru- FIGURE 7 Effect of particulate organic matter on total organic carbon (TOC)
analytical results
ment detection limit of the
TOC analyzer used in the
Ultraviolet–persulfate method
Combustion method
UV–persulfate method is
14
approximately 0.05–0.1 mg/L,
whereas the detection limit of
12
the TOC analyzer used in the
combustion method is close
10
to 0.5 mg/L.
Results of test 2: interference from inorganic par8
ticulate matter. These test
results are shown in Figure 6.
6
Triplicate analyses were conducted, and standard devia4
tions for all data were < 0.06
mg/L. Data suggest that the
addition of up to 50 mg/L of
2
inorganic solids did not appear
to increase or decrease the TOC
0
concentration as reported by
0.04
4
8
16
either analytical method.
Turbidity—ntu
Therefore, the presence of inorganic material was not the
cause of the discrepancies in
TOC results shown in Figure 2.
UV–persulfate method. The authors believe it is this
Results of test 3: measurement of particu- difference that explains the discrepancies in TOC concentrations reported by the two analytical methods
late organic matter. These test results are shown
and shown in Figure 2.
in Figure 7. Error bars indicate the standard deviation
among the replicate samples. Results with no error
Results of chlorination testing. Tests 1–3
demonstrated that concentration of particulate organic
bars had a standard deviation of zero. Test results
matter affected TOC analytical results reported by
indicate that the two analytical methods varied in
their ability to oxidize particulate
organic matter to CO2.
With no particulate matter present (turbidity = 0.04 ntu), both
tudies on the efficiency of oxidation
methods reported equal concentrations of TOC (approximately
of pure compounds in solution
3.6 mg/L). As the concentration
have demonstrated that numerous
of particulate organic matter
increased, however, the differchemicals are recalcitrant to various
ences in the TOC results reported
by the two methods increased sigoxidation processes.
nificantly. For example, with the
addition of particulate organic
matter to a turbidity of 16 ntu, the TOC concentration
the UV–persulfate method but not results reported
reported by the UV–persulfate method increased by
by the combustion method. As discussed later in this
only 0.4 mg/L. However, the TOC concentration
article, this difference in TOC measurement by the
reported by the combustion method increased by 9.4
two methods may significantly affect the “apparent”
mg/L. The 9-mg/L difference in TOC concentration ability of a water utility to meet the enhanced coagreported by the two methods is significant.
ulation requirements of the D/DBP Rule.
An examination of the results shows that the comThe D/DBP Rule intended for TOC removal to be
bustion method reported a corresponding increase
an indicator of the removal of DBP precursors. Therein TOC concentration with increasing particulate
fore, the authors conducted a series of tests to deterorganic matter concentration (measured as increas- mine whether particulate organic matter actually
ing turbidity), whereas the UV–persulfate method contributes to THM and HAA5 formation after chlodid not report any noticeable increase in TOC con- rination. If particulate organic matter does not concentration with increasing particulate organic matter
tribute to DBP formation, then the use of TOC as a
concentration. This indicates that particulate TOC is surrogate parameter for DBP precursors is not valid,
detected by the combustion method but not by the and DOC concentration should be substituted for
S
AUGUST 2000
© 2000 American Water Works Association, Journal AWWA August 2000
I. NAJM ET AL
89
FIGURE 8
Filtered sample (dissolved organic carbon)
Unfiltered sample (total organic carbon)
12
TOC—mg/L
10
8
6
4
2
0
THMs—µg/L
40
30
20
10
0
HAA5—µg/L
40
30
20
10
0
0.04
4
8
Turbidity—ntu
TOC as a measurement of only the dissolved portion
of organic matter.
In the chlorination tests, organic-free water was
buffered at pH 8.0 and then spiked with three levels
of particulate organic matter, which resulted in turbidity levels of 4, 8, and 16 ntu. Each spiked water
was split into two batches, with one batch filtered
through a 0.45-µm filter paper. Each batch of water
was then analyzed for TOC concentration using the
combustion method, dosed with various dosages of
chlorine, and incubated in the dark at 20oC for 24
h. At the end of the incubation period, the samples
were analyzed for chlorine residual.
The chlorinated samples containing a chlorine
residual of 0.5 to 1 mg/L were then analyzed for THM
and HAA5 concentrations. The selected chlorinated
samples containing particulate organic matter were
further filtered through 0.45-µm filter paper, and the
filtrate was analyzed for DOC concentration. This
measurement was used to determine whether the
90
DBP concentrations formed
were the result of the reaction
between chlorine and particulate organic matter or
between chlorine and dissolved organic matter that
leached off the particulate
organic matter during the 24h incubation period. Results
of the chlorination tests are
listed in Table 1 and shown in
Figure 8.
As expected, the buffered
organic-free water resulted
in very low THM and HAA5
formation. The concentrations of THMs and HAA5
formed in the unfiltered samples were proportional to the
TOC concentration (as measured by the combustion
method), suggesting that the
THMs and HAA5 concentrations formed resulted from
the reaction between the
added chlorine and the particulate organic matter.
The ratio of THMs to TOC
in these samples was < 5
µg/mg, which is significantly
lower than the common ratio
of approximately 15 to 20
µg/mg. 14,15 However, DOC
concentrations were also
measured in the chlorinated
16
samples after the 24-h incubation period (right-hand column in Table 1). Comparison
of the DOC concentrations at
the end of the 24-h chlorination period and the DOC concentrations in the filtered samples before chlorination suggests that approximately 6–13 percent of the
particulate TOC may have leached into the water
during the 24-h incubation period (i.e., the 16-ntu
sample contained 10.1 mg/L TOC and 0.4 mg/L DOC).
If the DOC concentrations measured after the 24-h
period are used, the ratio of THMs to DOC in the
samples was approximately 20 to 42 µg/mg. Therefore, it is possible that the THMs and HAA5 formed
were not due to the direct reaction between chlorine and the particulate organic matter but rather to
the reaction between chlorine and the dissolved
organic matter that leached off the particulate matter
during the 24-h incubation period.
This conclusion is supported by the observation
that the required simulated distribution system chlorine dosage for the 16-ntu unfiltered sample (which
contained up to 10.1 mg/L TOC) was only 2.5 mg/L.
The authors’ past experience with chlorination of
natural water with similar organic content suggests
Concentrations of total organic carbon (TOC), trihalomethanes
(THMs), and five haloacetic acids (HAA5) formed in filtered
and unfiltered synthetic water samples
VOLUME 92, ISSUE 8
© 2000 American Water Works Association, Journal AWWA August 2000
JOURNAL AWWA
TABLE 1
Experimental conditions and results of chlorination tests*
TOC—mg/L
Sample
Description
Turbidity
ntu
Buffered water
0.04
THMs
µg/L
HAA5
µg/L
24-h
DOC–TOC
mg/L
NA†
0.3
1.0
0.9
1.5
<2
0.3
1.0
1.0
3.4
NA
2.7
0.5
1.2
0.6
14
0.4
0.4
1.0
0.8
4
8
5.2
0.6
2.0
0.6
30
0.4
0.3
1.0
0.8
16
10.1
0.9
2.5
0.4
4
16-ntu spike—filtered
16-ntu spike—unfiltered
24-h Chlorine
Residual
mg/L
0.2
8-ntu spike—filtered
8-ntu spike—unfiltered
Chlorine
Dose
mg/L
0.4
4-ntu spike—filtered
4-ntu spike—unfiltered
Combustion
UV–
Persulfate
7.1
46
14
0.7–2.8
4.6
30
NA
0.8–5.5
6
NA
45
1.1–10
*TOC—total organic carbon; UV—ultraviolet; THMs—trihalomethanes; HAA5—sum of five haloacetic acids; DOC—dissolved organic carbon
†NA—not applicable
that water containing 10 mg/L TOC has a chlorine
demand considerably > 2.5 mg/L. However, DOC
leaching tests in the absence of chlorine were not
conducted to confirm the proposed hypothesis.
Test results’ significance
for D/DBP Rule compliance
expected to give comparable settled water TOC
results. The higher TOC measured by utility B is
primarily attributable to particulate organic matter; compared with dissolved organic matter, particulate organic matter is more easily removed by
chemical precipitation.
In fact, if utility B adds enough coagulant to
remove particulate TOC only, it will achieve a settled water TOC of 3 mg/L and meet its enhanced
The ability of a TOC analyzer to accurately measure particulate organic carbon significantly affects a
water utility’s ability (and associated costs) to comply with the
enhanced coagulation requirements of the Stage 1 D/DBP Rule.
he ability or inability of a total organic
The percent TOC removal
carbon analyzer to measure particulate
required with enhanced coagulation for a conventional water
organic carbon present in a raw water
treatment plant is dependent on
the TOC concentration in the raw
source can distort results and affect
water received by that plant.
a utility’s regulatory compliance cost.
Obviously, the ability or inability
of a TOC analyzer to measure particulate organic carbon present in
a raw water source can distort TOC results and affect coagulation requirement. Therefore, it is possible that
a utility’s regulatory compliance cost.
utility A will actually require a higher coagulant
Sample scenario. For example, utility A uses a dosage to reduce the apparent TOC concentration
water source that has an alkalinity of 75 mg/L as
from 3 to 2.25 mg/L, compared with the dosage
CaCO3, a DOC concentration of 3 mg/L, and a par- required by utility B to reduce the TOC concentration
ticulate organic carbon concentration of 2 mg/L. Using
from 5 to 3.25 mg/L. Consequently, meeting the
the UV–persulfate method, utility A measures its raw
enhanced coagulation requirements of the D/DBP
water TOC at 3 mg/L and determines that it is
Rule may be more costly to utility A than to utility B
required to remove a minimum of 25 percent of the simply because of the differences in the TOC analyzraw water TOC by enhanced coagulation. Utility B, ers used by the utilities.
which draws from the same water source, uses the
combustion method and measures the TOC concen- Summary and conclusions
tration in the raw water at 5 mg/L. Using this value,
This study evaluated the two analytical methutility B determines that it is required to remove a ods—the UV–persulfate method and the combustion
minimum of 35 percent of the raw water TOC.
method—most commonly used to determine TOC
The target settled water TOC concentration for concentrations in natural water. Study findings
utility A is 0.75 X 3 = 2.25 mg/L, whereas the tar- included the following:
get TOC concentration for utility B is 0.65 X 5 =
• Results suggest that the combustion method is
3.25 mg/L. Because the turbidity of settled water is more capable of detecting particulate or suspended
commonly < 1–2 ntu, the two instruments are
organic matter than the UV–persulfate method.
T
AUGUST 2000
© 2000 American Water Works Association, Journal AWWA August 2000
I. NAJM ET AL
91
• The greater the particulate organic content of
the water, the greater the difference in the TOC
concentrations reported by the two TOC analytical
methods.
• Inorganic dissolved carbon concentrations (up
to an alkalinity of 200 mg/L as CaCO3) as well as
particulate inorganic carbon (up to 50 mg/L) did not
affect the ability of each method to measure the TOC
concentration in a natural water sample.
• The analytical method used to measure the
TOC concentration in a raw water source may have
D
ifferences in the extent
of oxidation of the
particulate organic matter
will result in differences
in the measured TOC
concentration in the water.
a significant effect on a water utility’s ability to meet
the enhanced coagulation requirements of the
D/DBP Rule.
• Based on the chlorination test results, the
authors hypothesize that free chlorine may not react
with particulate organic matter to form THMs and
HAA5 and that all DBP concentrations formed in
samples containing particulate organic matter were
likely attributable to the reaction between chlorine
and the dissolved organic matter that leached off the
particulate organic matter during the chlorine contact
period. Additional testing is needed to confirm this
hypothesis.
• Based on the DBP formation results obtained,
the authors believe that DOC concentration is more
appropriate than TOC concentration as a surrogate for
DBP precursor concentration.
Acknowledgment
The authors thank the Passaic Valley Water Commission, Little Falls, N.J., for providing the water
samples and Montgomery Watson Laboratories,
Pasadena, Calif., for conducting analyses for trihalomethanes and the five haloacetic acids. The
authors also thank Bryan Trussell for assistance in
conducting the experimental portion of the project.
References
1. Standard Methods for the Examination of Water and
Wastewater. APHA, AWWA, and WEF, Washington (19th ed., 1995).
2. GERSHEY, R.M. ET AL. Comparison of Three Oxidation Methods for the Analysis of the Dissolved
Organic Carbon in Seawater. Marine Chemistry,
7:289 (1979).
92
VOLUME 92, ISSUE 8
3. SHARP, J.H. Total Organic Carbon in Seawater—
Comparison of Measurements Using Persulfate
Oxidation and High-temperature Combustion.
Marine Chemistry, 1:211 (1973).
4. SUGIMURA, Y.& SUZUKI, Y. A High-temperature
Catalytic Oxidation Method for the Determination of Nonvolatile Dissolved Organic Carbon in
Seawater by Direct Injection of a Liquid Sample. Marine Chemistry, 24:105 (1988).
5. WANGERSKY, P.J. Dissolved Organic Carbon Methods: A Critical Review. Marine Chemistry, 41:61
(1993).
6. AIKEN, G.R. Chloride Interference in the Analysis of Dissolved Organic Carbon by the Wet Oxidation Method. Envir. Sci. & Technol., 26:12:2435
(1992).
7. KAPLAN, L.A. Comparison of High-temperature
and Persulfate Oxidation Methods for Determination of Dissolved Organic Carbon in Freshwaters. Limnol. Oceanography, 37:5:1119 (1992).
8. KOPRIVNJAK, J.-F. ET AL. Underestimation of Concentrations of Dissolved Organic Carbon in Freshwater. Water Res., 29:1:91 (1995).
9. IMAMURA, S.; AKIHIRO, H.; & KAWABATA, N. Wet
Oxidation of Acetic Acid Catalyzed by Co-bi
Complex Oxides. Ind. Engrg. Chem. Prod. Res. Dev.,
21:570 (1982).
10. MANTZAVINOS, D. ET AL. Partial Wet Oxidation of
p-Coumaric Acid: Oxidation Intermediates. Reaction Pathways and Implications for Wastewater
Treatment. Water Res., 30:12:2969 (1996).
11. OLLIS, D.F.; PELIZZETTI, E.; SERPONE, N. Destruction of Water Contaminants. Envir. Sci. & Technol., 25:9:1523 (1991).
12. SCHNITZER, M. & KHAN, S.U. Humic Substances in the
Environment. Marcel Dekker Inc., New York
(1972).
13. USEPA. Methods for the Determination of
Organic Compounds in Drinking Water.
EPA/600/4-88/039, Washington (1988).
14. NAJM, I.N. ET AL. Evaluating Surrogates for Disinfection By-products. Jour. AWWA, 86:6:98 (June
1994).
15. AWWA. Water Quality and Treatment. (R. Letterman, technical editor). McGraw-Hill, New York
(5th ed., 1999).
About the authors: Issam Najm is
vice-president and manager of the
applied research department at Montgomery Watson, 555 E. Walnut St.,
Pasadena, CA 91101. Najm holds a
BS in civil engineering from the
American University of Beirut,
Lebanon, and MS and PhD degrees
in environmental engineering from the University of Illinois
at Urbana–Champaign. He has 10 years of experience in the
field of water quality and evaluation and optimization of
water treatment processes. Joseph Marcinko is a chemist
and Joan Oppenheimer is principal chemist at the Pasadena
office of Montgomery Watson.
© 2000 American Water Works Association, Journal AWWA August 2000
JOURNAL AWWA