Evaluation Technique for Water Treatment Plant in terms of NOM Size, Structure,
and Functionality (SSF Technique) as well as HAAFP/Reactivity
Sangyoup Lee1, Jaeweon Cho1, Seonha Chae2, In S. Kim1
1
2
Dept. of Environmental Sci. and Eng., K-JIST, Kwangju 500-712, Korea,
Water Supply & Sewerage Research Team, Water Resources Research Institute, Korea Water Resources
Corporation, Taejon, Korea
Abstract
In this study, a tool was suggested to help water treatment plants evaluate either conventional or
advanced treatment processes with respect to the removal of natural organic matter (NOM). This tool,
called size/structure/functionality (SSF), is a technique that requires the characterization of NOM size
distribution, structure, and charge density (functionality). Characterizing the NOM size distribution for
each process demonstrated that the NOM removals by granular activated carbon (GAC) adsorption and
sand filtration were mainly controlled by molecular diffusion and size exclusion, respectively. The
formation potential (FP) of haloacetic acids (HAA) and its reactivity (= HAAFP/dissolved organic carbon
(DOC)) were related to the NOM characteristics, as determined by the SSF for each process. Hydrophilic
NOM exhibited the highest HAAFP reactivity, and it was preferentially removed by the GAC adsorption
process compared to transphilic and hydrophobic NOM. However, tribromoacetic acids (TBAA) and
trichloroacetic acids (TCAA) still remained at a high concentration after the GAC adsorption process.
Functionality analysis with carboxylic/phenolic acidities measurements revealed that conventional
(coagulation/sedimentation/filtration) and advanced (ozonation/GAC adsorption) processes did not use
the charge interaction mechanism efficiently for NOM removal.
Key words- SSF evaluation, natural organic matter, haloacetic acids, NOM molecular size, NOM structure,
NOM functionality
Introduction
A conventional water treatment plant in Korea was evaluated using NOM size/structure/functionality
(SSF) analyses because conventionally treated water exhibited fairly high HAAFP and its reactivity.
Meanwhile, the formation potential of trihalomethanes (THMs) was very low for the same source water.
A pilot test with ozonation and GAC adsorption processes was performed and evaluated using the SSF
technique. It is anticipated that the SSF techniques may be used for both the evaluation of conventional
treatment and the determination of advanced treatment alternatives in terms of NOM removal and
HAAFP minimization.
Materials and Methods
Water source used
The drinking water source from Suksung Reservoir and samples from each process of conventional
actual plant and advanced pilot plant were taken to the laboratory. All samples were pre-filtered with a
0.45 m filter and stored in a refrigerator at a temperature of 5C. The NOM characteristics of the source
water and treated waters are shown in Table 1.
Table 1 NOM characteristics of the source water used
Molecular Weight (daltons)
Source
DOC
(mg/L)
UVA254
(cm-1)
SUVA
(Lmg-1m-1)
pH
Suksung
Reservoir
3.40
0.079
2.3
7.1
Br(g/L)
49.0
Conductivity
(S/cm)
328
Number-avg.
Weight-avg.
1,815
2,352
NOM size analysis
The NOM size distribution was measured using a high performance size exclusion chromatograph
(HPSEC) with a proteinanous silica column (Waters) and a HPLC (Waters 510)/autosampler (Waters 717
plus). Polystyrene sulfonates with 1800, 4600, 8000, and 18000 daltons were used for a calibration
standard equation between the MW size and retention time, and a 4 mM phosphate buffer solution with
added NaCl (for a 0.1 M ionic strength) was used as an eluent solution (Chin et al., 1994).
NOM structure (hydrophobic, transphilic, and hydrophilic) analysis
Pre-filtered water samples were processed through XAD-8 followed by XAD-4 resins to isolate the
hydrophobic (XAD-8 adsorbable), transphilic (XAD-4 adsorbable), and hydrophilic (neither XAD-8 nor
XAD-4 adsorbable) NOM fractions. The adsorbed hydrophobic and hydrophilic (transphilic) acids were
eluted using a 0.1 N NaOH solution.
NOM functionality (charge density) analysis
Using a micro titrator (Metroh, CH-910), the carboxylic and phenolic acidities were measured for
XAD-isolated hydrophobic and hydrophilic acids. The pH of a titration sample was lowered to 3.0 and
carbonate in the sample was sparged out with nitrogen gas for at least ten minutes prior to actual titration.
A NaOH solution of 0.05 N was used to increase the pH of the sample, and the amount of NaOH
consumed to increase pH 3-8 and 8-12 corresponds to carboxylic and phenolic acidities, respectively.
HAA measurement
The source and treated samples were chlorinated using a concentrated HOCl solution with a chlorine
concentration based on 3[DOC concentration] + 7.5[NH4+ concentration]. The chlorinated samples
were incubated at a temperature of 20C for 72 hours, and the HAAFP was extracted using the Modified
EPA 552 micro-extraction method with a diazo methane addition. The HAA was measured using a GC
(HP 5890 Series II Plus) with an autosampler (HP 6890 Series).
Results and Discussion
NOM size
A comparison of the MW distributions of the source and treated water samples is shown in Fig. 1(a),
and the NOM fractional rejections (FR) (Cho et al., 1999) calculated from the MW distribution for each
process are represented in Fig. 1(b). NOM with larger sizes exhibited higher FR than NOM with smaller
sizes for conventional treatment, but the larger NOM molecules (around 1500 daltons) exhibited even less
removal than the smaller NOM molecules (between 1000 and 1100 daltons) for the ozonation/GAC
adsorption processes. Through these results, it can be concluded that (1) size exclusion (or steric
hindrance) was a major mechanism for NOM removal by conventional treatment (including alum
coagulation, sedimentation, and sand filtration), and (2) the diffusion transport of small size molecules
was a dominant mechanism for NOM removal by ozonation followed by GAC adsorption processes.
Fig. 1.
(a) NOM MW distribution comparison of source, conventionally treated (alum coagulation,
sedimentation, and sand filtration), ozonated, and GAC treated water samples; (b) Fractional NOM
rejections by conventional treatment and ozonation/GAC adsorption.
The FRs of three NOM fractions provided by conventional treatment and ozonation/GAC adsorption are
shown in Figs. 2 (a)-(c). Through these results, it can be determined which size ranges of NOM molecules
were removed preferentially by a certain treatment alternative compared to other sizes of NOM molecules.
For example, the smaller molecules of hydrophobic NOM were preferentially removed by O 3/GAC
adsorption, which is in agreement with the results of Kilduff et al. (1996).
(a)
1
Fractional rejection
Ozonation/GAC
Conventional
0.8
0.6
0.4
0.2
0
500
750
1000
1250
1500
Relative MW (daltons)
1750
2000
Conventional
Ozonation/GAC
(c)
1
Fractional rejection
Conventional
0.8
0.6
0.4
Ozonation/GAC
0.2
0
500
750
1000
1250
1500
1750
2000
Relative MW (daltons)
Fig. 2.
Fractional NOM rejections by conventional treatment and ozonation/GAC adsorption for (a)
hydrophobic NOM, (b) transphilic NOM, and (c) hydrophilic NOM.
NOM structure
Figs. 3 and 4 represent the NOM fractions for the source and treated samples by each process as well
as the removal of each NOM fraction by each process, respectively. It was shown that the hydrophilic
NOM fraction was preferentially removed by both the conventional and advanced treatment processes.
F ra c tio n (% )
50
40
30
20
10
hydrophobic
0
Fig. 3.
transphilic
conventional
ozonated
hydrophilic
GAC
R e m o v a l p e rc e n ta g e (% )
source
NOM structure informaion for source and treated waters.
60
50
40
30
20
10
0
conventionally treated
total NOM
hydrophobic
Ozonation/GAC
transphilic
Fig. 4. Removal percentage of each NOM fraction by each process.
hydrophilic
NOM functionality
For the conventionally treated samples, the acidities of both hydrophobic and hydrophilic acids were
higher compared to the source water, representing that conventional treatment options did not use charge
interaction mechanism for NOM removal efficiently (see Table 2). However, the hydrophobic acidity was
less for the GAC treated sample due to the preferential removal of charged hydrophobic NOM during the
process.
Table 2
NOM acidities for source and treated samples by each process
Hydrophobic acid (meq/gC)
Sample
Source
Conventionally treated
Ozonated
GAC treated
Hydrophilic acid (meq/gC)
-COOH
-OH
-COOH
-OH
5.9
11.6
9.3
7.2
15.9
14.9
13.4
5.9
4.5
10.3
13.9
13.6
12.1
18.0
15.6
29.5
HAA formation potential and reactivity
Conventional treatments (alum coagulation/sedimentation/sand filtration) exhibited virtually no
HAAFP removal, while the ozonation/GAC process exhibited a fairly high HAAFP removal (see Fig. 5).
However, the TCAA and TBAA still remained at a high concentration, even after O3/GAC treatment (see
Table 3) (recall that the final regulation for HAA is 30g/L). Hydrophilic NOM exhibited the highest
R e m o v a l p e rc e n ta g e (% )
HAA reactivity compared to the hydrophobic and transphilic NOM fractions (see Table 4).
100
HAAFP6
80
60
40
Concentrations of raw water:
HAAFP6 = 144.2 ug/L
HAAFP9 = 209.6 ug/L
20
0
Fig. 5.
HAAFP9
conventional
ozonated
HAAFP for source and treated samples by each process.
GAC
Table 3
HAAFP9 (TCAA, TBAA, and other 6 HAAs) for source and treated samples
HAAFP
Source (g/L)
Conventionally treated (g/L)
GAC treated (g/L)
TCAA
73.6
73.6
25.5
TBAA
53.5
44.0
29.3
Total HAA-TCAA-TBAA
82.5
77.8
16.7
Total HAA
209.6
195.4
71.5
Table 4
HAA reactivity of each NOM fraction for source and treated waters
Water
Raw (g/mg)
Hydrophobic (g/mg)
Transphilic (g/mg)
Hydrophilic (g/mg)
HAA6
HAA9
HAA6
HAA9
HAA6
HAA9
HAA6
HAA9
Source
15.2
22.1
28.3
32.3
14.5
24.3
61.5
89.3
Filtered
19.8
27.5
16.2
25.7
14.9
26.9
94.8
131.8
Ozonated
28.1
38.8
13.9
29.1
17.4
30.7
72.3
99.6
GAC
8.7
17.6
12.8
23.4
8.0
30.9
38.8
78.0
Conclusions
-
The SSF technique was successfully introduced as a tool to evaluate water treatment processes along
with NOM rejection and HAAFP.
-
Conventional treatment alternatives appeared to be controlled mainly by the size exclusion
mechanism (no charge interactions) for NOM removal, and exhibited almost no HAAFP removal.
-
Ozonation followed by the GAC adsorption process was controlled by a diffusion transport
mechanism for NOM removal (based on NOM size analysis), and exhibited fairly high HAAFP
removal. However, TCAA and TBAA remained at high concentrations compared to the other six
HAAs, even after the O3/GAC process.
-
Hydrophilic NOM exhibited the highest HAA reactivity (HAAFP/DOC; g/mg C) compared to the
hydrophobic and transphilic NOM fractions.
-
Hydrophilic NOM can be removed preferentially by both the conventional and advanced treatment
(O3/GAC) options.
-
The charge interaction for NOM removal was not used effectively by conventional treatment
processes based on NOM functionality analysis, and it was used for the removal of hydrophobic acids
by GAC adsorption.
Acknowledgments
This work was supported in part by the Korea Science and Engineering Foundation (KOSEF) through the
Advanced Environmental Monitoring Research Center (ADEMRC) at Kwangju Institute of Science and
Technology (K-JIST).
References
Chin, Y., Aiken, G., and O'Loughlin, E. (1994) Molecular weight, polydiversivity, and spectroscopic
properties of aquatic humic substances. Environ. Sci. Technol. 28, 1853 –1858.
Cho, J., Amy, G. and Pellegrino, J. (1999) Membrane filtration of natural organic matter: Initial
comparison of rejection and flux decline characteristics with ultrafiltration and nanofiltration membranes.
Wat. Res. 33, 2517-2526.
Kilduff, J.E., Karanfil T., and Weber W.J. (1996) Competitive interactions among components of humic
acids in granular activated carbon adsorption systems: effects of solution chemistry. Environ. Sci. Technol.
30, 1344-1351.