Water Research 36 (2002) 3834–3848

Probing reactivity of dissolved organic matter for disinfectionby-product formation using XAD-8 resin adsorption and

ultrafiltration fractionation

Mehmet Kitisa, Tanju Karanfila,*, Andrew Wigtonb, James E. Kilduffb

aDepartment of Environmental Engineering and Science, Clemson University, 342 Computer Court, Anderson, SC 29625, USAbDepartment of Environmental and Energy Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180, USA

Received 1 May 2001; received in revised form 1 January 2002

Abstract

The disinfection by-product (DBP) reactivity (yield and speciation upon reaction with chlorine) of dissolved organic

matter (DOM) isolated from two surface waters was investigated. The source waters, each having significantly different

specific ultraviolet absorbance (SUVA254), molecular weight (MW) distribution and polarity, were fractionated using

XAD-8 resin adsorption and ultrafiltration (UF), with good DOM mass balance closures (based on dissolved organic

carbon). It was found that such fractionation preserved both the SUVA and the reactivity of the source waters, as

demonstrated by statistically similar DBP formation and speciation from chlorinated source water and source waters

reconstituted from XAD-8 or UF fractions. In addition, there was no evidence of synergistic effects among DOM

components when reacting with chlorine.

Consistent trends between DBP yields and MW were not found. Hydrophobic fractions of DOM (isolated by XAD-

8) were the most reactive DOM components; however, hydrophilic components also showed appreciable DBP yields,

contributing up to 50% of total DBP formation. In contrast, strong and unique correlations were observed between the

SUVA of individual fractions and their trihalomethane (THM) and haloacetic acid (HAA9) yields, confirming that the

aromaticity of DOM components is more directly related to reactivity than other physicochemical properties. The

finding of a single correlation independent of the fractionation process employed is notable because XAD-8 adsorption

and UF fractionate DOM by significantly different mechanisms. These results confirm that SUVA is a distributed

parameter that reflects DOM heterogeneity. Therefore, the SUVA distribution within natural water represents an

important property that can be used as a reliable predictor of DBP formation. Finally, bromine appears to be more

effectively incorporated into low UV-absorbing (i.e., low SUVA), low MW and hydrophilic DOM fractions. r 2002

Elsevier Science Ltd. All rights reserved.

Keywords: Natural organic matter (NOM); Chlorine; Disinfection by-products (DBPs); Reactivity; XAD-8 resin; Ultrafiltration;

Specific ultraviolet absorbance (SUVA)

1. Introduction

Natural organic matter (NOM), present nearly in all

surface and groundwaters, can undergo a variety of

reactions in natural and engineered environmental

systems. The reactions that occur between NOM and

disinfectants/oxidants (e.g., chlorine) used in drinking

water treatment produce by-products, generally known

as disinfection by-products (DBPs). Some of these DBPs

are classified as suspected carcinogens. The dissolved

and colloidal fractions of NOM (i.e., DOM, those

components passing through a 0.45-mm filter) serve as

*Corresponding author. Tel.: +1-864-656-1005; fax: +1-

864-656-0672.

E-mail address: tkaranf@clemson.edu (T. Karanfil).

0043-1354/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 0 4 3 - 1 3 5 4 ( 0 2 ) 0 0 0 9 4 - 5

major precursors in these reactions. DOM is a hetero-

geneous mixture of various organic molecules originat-

ing from aquagenic (e.g., biota in a water body)

and pedogenic (e.g., soil and terrestrial vegetation)

sources. As a result, its isolation and fractionation into

more homogenous components has been the most

common approach to facilitate the interpretation of

results from DOM characterization and reactivity

studies. A number of methods, ranging from sorption

by synthetic resins to separation (based on size) by

membranes, have been developed for DOM isolation

and/or fractionation [1–8].

Resin adsorption chromatography (RAC), employing

various synthetic resins, has been used to isolate and

fractionate DOM from natural waters with varying

degrees of success [1,5,6,9,10,11]. This chromatographic

separation method concentrates and isolates DOM

components into operationally defined fractions depend-

ing on their affinities to different resins and their back-

elution efficiencies. DOM fractions obtained by RAC

were found to exhibit a wide range of DBP formation

upon reaction with chlorine [10,12,13–17]. In general,

the humic fractions (i.e., ‘‘hydrophobic acids’’ isolated

by adsorption to XAD-8, a neutral methylmethacrylate

resin) have been found to contribute significantly to

DBP formation. However, hydrophilic fractions (i.e.,

those not retained on XAD-8 resin) have also been

shown to produce appreciable amounts of DBPs in some

waters [10,14–16,18].

Ultrafiltration (UF) has been used to fractionate

DOM into different molecular weight (MW) fractions

[2,3,7,8,19,20]. UF is a pressure-driven membrane

process in which dissolved solutes are separated accord-

ing to their molecular sizes. UF membranes are typically

characterized by molecular weight cut-off (MWC)

values established by the manufacturers, who calibrate

membranes by measuring membrane rejection of macro-

molecules having known molecular weights. However,

these macromolecules often have structural character-

istics significantly different than DOM. As a result, it is

not possible to directly relate the molecular weight of

DOM fractions to manufacturer-specified MWC values.

In addition, DOM concentration, ionic strength, and pH

affect molecular configuration [21], and thus the

rejection of DOM components by a single UF mem-

brane. Therefore, as in the RAC method, DOM

fractions obtained from UF depend on operational

conditions. A wide range of DBP formation upon

chlorination has been reported for various MW

fractions obtained by UF [2,3,16,19,22]. While no

significant trend between DOM MW and DBP forma-

tion is evident from these studies, MW fractionso5 kDa

generally exhibited higher reactivity. We hypothesize

that the lack of a clear trend is due to fact that chemical

composition of DOM components is a more important

predictor of DBP formation than size.

DOM fractions obtained from RAC or UF can be

characterized using various techniques including ele-

mental analysis, pyrolysis GC/MS, 13C-NMR, and IR/

FTIR. Although these techniques provide important

information about the structural characteristics of DOM

components, they demand large DOM masses for

analysis and are not feasible for practical treatment

operations. On the other hand, a simple surrogate

parameter, specific ultraviolet absorbance (SUVA),

provides rapid information about DOM aromaticity,

an important property related to DOM reactivity.

SUVA is defined as the UV absorbance, specified at a

wavelength generally between 254 and 280 nm, normal-

ized by DOC. SUVA has often correlated well with DBP

formation [12,17,23–26], and as a result, its use by

practitioners and researchers has increased in recent

years.

2. Motivation and objectives

During isolation and fractionation processes, the

original water composition may change as a result of

concentration changes, exposure to acids, bases and/or

solvents, and adsorption by surfaces. Questions have

been raised about whether these changes chemically alter

the structure and/or reactivity of DOM components

[27–29]. In addition, reports in the literature suggest the

possibility that reactivity is not conserved upon fractio-

nation, and that synergistic effects may be important.

For example, based on greater trihalomethane (THM)

formation by NOM fractions (humic, non-humic, and

low-molecular weight) as compared to whole water,

Owen et al. [14] cite the possibility of synergistic effects

in chlorine substitution or oxidation. In contrast, Chang

et al. [30] found that the THM formation potential

(THMFP) for various organic fractions, prepared by

resin adsorption and reacted with sodium hypochlorite,

recovered only 57% of the THMFP concentration

produced by the raw water. While many studies have

examined the reactivity of NOM fractions, studies

specifically designed to examine whether fractionation

changes DOM reactivity are lacking. Therefore, the first

objective of this research was to evaluate the reactivity

(DBP formation and speciation) of fractions generated

by resin adsorption or UF as compared to both the

unfractionated source water, and source water recon-

stituted from fractions. A systematic approach was

taken to assure good mass balance closure, to verify that

potentially reactive fractions were not lost during

fractionation. Potentially confounding influences (in-

cluding the oxidant to carbon ratio, and bromine

concentration) were also carefully controlled. This study

focuses on one resin, XAD-8, because it is the resin most

commonly employed in fractionation studies.

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3835

The second objective was to compare the DBP

reactivity of different DOM components obtained from

XAD-8 and UF fractionation, and to evaluate whether

reactivity correlates more strongly with the SUVA of

individual fractions, or with other physicochemical

properties (polarity and size). Previous work has

documented strong correlations between the DBP

formation (both THM and haloacetic acids (HAA9))

and the SUVA of DOM remaining in solution after

carbon adsorption and alum coagulation [31]. However,

in those experiments, the DOM removed from solution

was not recovered, and its reactivity could not be

measured. In contrast, the XAD-8 and UF fractionation

techniques used in the present research allow (near)

complete recovery of all DOM fractions. This will allow

a rigorous test of SUVA as a robust parameter for

correlating DOM reactivity.

3. Materials and methods

3.1. Source waters

Two surface waters with significantly different SUVA,

DOC, and physicochemical characteristics were selected

for this study (Table 1). A high-SUVA water was

obtained from the influent of the Myrtle Beach (MB)

drinking water treatment plant in South Carolina, which

uses the Intercoastal Waterway as its source. A low-

SUVA water was collected from the Tomhannock (TM)

reservoir, the water supply for the city of Troy, New

York. DOM was isolated and concentrated from each

source water using a reverse osmosis (RO) system, as

described elsewhere [32]. Isolating and concentrating

DOM provides several advantages over direct use of

source waters, including: (1) reduced storage require-

ments; (2) providing a consistent supply of DOM for the

duration of the study; (3) providing sufficient mass of

DOM to investigate concentration effects; and (4)

providing sufficient starting mass of DOM such that

after fractionation by either resin adsorption or ultra-

filtration, individual fractions would have a high enough

concentration to allow further study. Mass balance

calculations and subsequent reactivity experiments

showed that over 95% of the DOM was recovered from

each source, with no impact on its DBP reactivity as a

result of RO isolation [32].

3.2. XAD-8 resin and ultrafiltration fractionation of

DOM

DOM concentrates were applied to a pre-cleaned

XAD-8 resin (Supelite DAX-8, Supelco, St. Louis, MO)

column at pH 2 to fractionate the organic matter. The

fraction adsorbed by the resin and subsequently back-

eluted from the column using a pH 11 solution is

designated hydrophobic (HPO), while the fractions

collected from the effluent of the column are designated

hydrophilic (HPL). HPL samples were collected as a

function of elution volume, representing a wide range of

column distribution coefficients ðk0Þ: This was done to

investigate the effect of k0 on the SUVA and DBP

reactivity of the HPL fractions and to calculate mass

balances. After elution or recovery, the pH of each

collected fraction was immediately adjusted to the

source water value. Both HPO and HPL fractions were

stored as aqueous solutions in amber bottles at 41C until

use.

A hollow-fiber, cross-flow ultrafiltration system was

used to obtain apparent MW fractions (A/G Technol-

ogy Corporation, Needham, MA). All system tubing

was peroxide-cured silicone (Cole Parmer) chosen for

low organic leachables and acid/base stability. Process

solution was delivered by a peristaltic pump from a 5-L

reservoir into the membrane element; permeate flow was

collected, while the retentate flow was recycled back to

the reservoir. Feed solution was recirculated through the

system at a rate of 4L/min, providing high cross-flow

and shear rates of about 8000 s�1 to minimize accumula-

tion of organic matter at the membrane surface.

Membrane elements were cleaned by recirculating a

0.1N NaOH solution at a cross flow rate of 4L/min for

a minimum of 1 h, followed by a clean water rinse. Six

membranes (1, 3, 5, 10, 30 and 100 kDa) were used to

obtain up to seven fractions; membranes with MWC

larger than 5 kDa were not used with the TM water

because only 11% of the total DOC was in this large

MW fraction. The HPO fraction of the TM water was

further separated into four size fractions to investigate

the size distribution and DBP reactivity within HPO

components. All UF fractions were stored as aqueous

solutions in amber bottles at 41C until use.

Transport of organic molecules across UF membranes

is influenced by many factors related to solution

Table 1

Compositional characteristics of the natural source watersa

Parameter Unit Myrtle Beach

(MB)

Tomhannock

(TM)

DOC mg C/L 20.2 3.3

UV254 Abs. cm�1 0.939 0.069

SUVA254 L/mg Cm 4.65 2.09

Total

alkalinity

mg CaCO3/L 44 39

Total

hardness

mg CaCO3/L 26 54

pH — 7.2 7.0

Bromide mg/L 43 o25b

aValues reported are the average of triplicate measurements.bMinimum reporting level was 25 mg/L.

M. Kitis et al. / Water Research 36 (2002) 3834–38483836

chemistry, membrane properties, and solute/membrane

interactions, which together control membrane rejection

during analysis. To control variability in macromolecule

separation results among different DOM samples,

solution chemistry was adjusted to an ionic strength of

0.01M (as NaCl) and pH 7 for all samples and buffer

solutions prior to ultrafiltration. To achieve a high

degree of separation, and maintain a sufficiently high

permeate concentration to allow further experimenta-

tion, the following cascade-type fractionation protocol

was used (Fig. 1).

The first step was to concentrate the whole DOM

solution on the 1 kDa membrane. Starting with the

lowest MWC membrane maximized the concentration

of the lowest MW fraction by avoiding continual

dilution of the permeate stream as fractionation

proceeds. In addition, as will be described further, this

approach provides opportunities to subsequently im-

prove the separation of various MW fractions, narrow-

ing their MW distribution. Initial concentrations and

concentration factors varied somewhat, but in all

experiments, the system concentration was kept below

100mg/L, to minimize accumulation at the membrane

surface [33]. Concentrated retentate was then diafiltered

with solute-free buffer solution. Diafiltration increased

the separation of the o1 kDa components, but also

diluted the filtrate. The concentration of the o1 kDa

filtrate was allowed to decrease to about 3mg/L, after

which the process was stopped, yielding the o1 kDa

fraction. The o1 kDa components remaining in the

retentate were removed subsequently. Next, the reten-

tate was diluted back to its original volume, and was first

concentrated and then diafiltered on the next larger

MWC (3 kDa). The permeate in this step yielded a dilute

solution of the 1–3 kDa fraction, which was then

concentrated again on the 1 kDa membrane to reduce

its volume, increase its concentration, and remove

remaining o1 kDa components, thereby serving to

‘‘clean’’ the 1–3 kDa fraction. The DOM retained by

the 3 kDa membrane was then diluted and applied to the

next larger MWC, and the process was repeated. The

permeate from membranes having MWC’s >1kDa

were concentrated on lower MWC membranes, serving

to improve recovery and provide narrower MW

P

Buffer

P

Buffer

P

Buffer

P

Buffer

5k Damembrane

P

Buffer

Fractionation step Cleaning step

11

2233

4455

Whole NOM

>1kDa

<1 kDa fraction

1-3 kDa <1 kDa fraction

1-3 kDa fraction

>3 kDa 1-3 kDa fraction3-5 kDa

3-5 kDa fraction >5 kDa(To subsequent membranes)

3k Damembrane

1k Damembrane

3k Damembrane

1k Da membrane

Fig. 1. Schematic depiction of the ultrafiltration protocol employed. Feed solutions are in bold. Feed solutions are retentates when

applied to the next higher molecular weight cut-off (MWC), and permeates when applied to the next lower MWC for concentration

and cleanup. Final fractions are boxed. Supplemental fractions produced from cleanup steps are in italic, and are indicated by dashed

lines.

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3837

fractions. In applying this protocol (to all but the 1 kDa

membrane), the diafiltration volume was selected to

achieve high removal of components (>90%) small

enough to pass a particular membrane. This was done

by determining the average rejection for a retentate

mixture and modeling the mass throughput as described

previously [7,33]. In some cases, the system was operated

in the diafiltration mode using the excess sample volume

as the diafiltration solution, as described by Cai [20].

DOC concentrations were measured using a high-

temperature combustion TOC analyzer (TOC-5000,

Shimadzu, Kyoto, Japan). Mass balance calculations

were performed to determine the DOM recoveries (as

%DOC) after each fractionation experiment. Recovery

was calculated as the total DOM mass recovered in

individual fractions divided by the total DOM mass

applied. These calculations also quantified the contribu-

tion of each fraction (as %DOC) to the total mass of

DOM in the source water. SUVA was used to

characterize the DOM in all fractions. UV absorbance

was measured by a spectrophotometer (DU 640, Beck-

man, Fullerton, CA). Bromide concentration was

determined using an ion chromatography system

(ED40 electrochemical detector; GP50 gradient pump;

AS50 autosampler; AS9-HC column, Dionex, Sunny-

vale, CA) according to USEPA Method 300 [34].

3.3. DBP reactivity experiments

DBP yield and speciation from reaction of DOM in

each source water with chlorine was examined in three

sets of experiments. The first set evaluated the formation

of DBPs upon chlorination of the original source water

sample. The second set of experiments evaluated the

formation of DBPs upon chlorination of individual

DOM fractions. Finally, the third set evaluated the

formation of DBPs upon chlorination of source water

reconstituted from individual fractions to examine

whether the reactivity of source water DOM changed

as a result of isolation and fractionation techniques.

A target DOC of 3mg/L was selected for all DBP

formation experiments, a value close to that of the TM

source water, and representative of typical DOC values

in drinking water sources in the United States [35]. All

the XAD-8 and UF fractions, and original source water

samples were diluted to 3mg/L DOC using distilled and

deionized water (DDW). Source waters were reconsti-

tuted from XAD-8 or UF fractions by combining them

in proportion to their mass contributions to the source

water DOM. After dilution or reconstitution, bromide

was spiked into MB samples, if necessary, to achieve a

bromide level equivalent to that of the original source

water (i.e., 43 mg/L). No bromide spike was necessary for

TM samples because bromide concentrations were

below the detection limit (o25mg/L). DOC and bromide

concentrations of all samples were measured again after

dilution, reconstitution and/or spiking for verification.

Generally, the differences between the target and

measured concentrations were o10%.

After adjusting DOC and bromide levels, all samples

were buffered at pH 870.3 with 0.01M phosphate, and

UV absorbance at 254, 272 and 280 nm was measured.

Then, all the samples were chlorinated employing the

uniform formation condition protocol (UFC) [36]. After

a 24-h incubation period, residual free chlorine was

measured following Standard Method 4500-Cl F [37]

and was quenched with sodium sulfite prior to analysis

for DBPs. DBP formation was quantified in terms of

THM, haloacetonitriles (HANs), haloketones (HKs),

chloral hydrate (CHY), and chloropicrin (CP) according

to USEPA method 551.1 [38], and HAA9 according to

Standard Method 6251 B [37] with some modifications.

More detailed information about the experimental

protocols and the analytical techniques used in this

study can be found elsewhere [26]. For both waters

tested, the extent of THM and HAA9 formations was

significantly higher than those of other DBPs (i.e.,

HANs, HKs, CHY, and CP), thus, only the THM and

HAA9 results are discussed in this paper.

4. Results and discussion

4.1. Fractionation of DOM

DOM recovered in UF and XAD-8 fractions ranged

between 89.9% and 109.1% (as DOC), indicating

minimal organic matter losses (Table 2). The positive

errors in the recovery were attributed to analytical

errors, including the very low-level DOC measurements

required for some fractions. Fig. 2A shows the apparent

MW distribution of source water DOM as measured by

UF. For both waters, the o1 kDa fraction was

Table 2

DOM recoveries during UF and XAD-8 fractionation

Source water Fractionation type Recoverya

MB UF 99.6b

XAD-8 105.6c

TM UF 109.1b

XAD-8 89.9c

UF for HPO Fraction 105.5b

aRecovery as % DOC.bMultiple runs with each water were not conducted.

However, the aggregate standard deviation of 5 separate runs

with 3 waters was 4.7.cMultiple runs with each water were not conducted.

However, the aggregate standard deviation of 11 separate runs

with 3 waters was 3.5.

M. Kitis et al. / Water Research 36 (2002) 3834–38483838

dominant, contributing almost half of the total DOC.

The MW distribution of DOM in the MB water was

broader than the TM water �26% of the DOC was in

the MB >5kDa fraction, as compared to 11% for the

TM water. These trends were confirmed by molecular

weight distributions measured using size exclusion

chromatography (data not shown).

Fig. 2B shows the distribution of hydrophobic and

hydrophilic components as measured by XAD-8 frac-

tionation. The HPO fraction was dominant in the MB

water (66%), whereas the opposite was true for the TM

water (64% HPL). The apparent MW distribution in the

HPO fraction of TM water was also characterized by

UF. A MW distribution similar to that of the source

water was found [26]; the smallest MW fraction

(o1 kDa) comprised 65% of the total HPO DOC, while

only 15% of the DOC was in the >5kDa fraction. This

result could be explained by the rather narrow MW

distribution of the DOM in TM source water.

The MB water exhibited significantly higher SUVA

values than the TM water for each size fraction

examined (Fig. 3A). In addition, for each water the

relationship between SUVA and size was different. For

the MB water, SUVA increased with increasing MW,

indicating a good correlation between the size and

aromatic character of DOM components. This is

consistent with similar reports in the literature (e.g.,

[39]). In addition, relatively large SUVA254 values (i.e.,

>4) were found for all MW fractions >1kDa,

suggesting that aromatic moieties are present in

significant quantities in all size fractions of MB DOM.

In contrast, no clear trend was apparent between MW

and SUVA of TM DOM fractions. The 1–3 kDa

fraction had the largest SUVA, while the largest MW

fraction (>5kDa) had the lowest SUVA value. The

latter suggests the presence of aliphatic, and low

aromaticity components with little UV-absorbance.

Candidate compounds include high MW proteins or

carbohydrates [40,41]. The presence of such compounds

would be consistent with an algogenic source, although

our data is not sufficient to confirm such an inter-

pretation.

Myrtle Beach Tomhannock

Myrtle Beach Tomhannock

<1 kDa44%

1-3 kDa14%

3-5 kDa16%

5-10 kDa10%

30-100 kDa8%

>100 kDa 6%

10-30 kDa2%

<1 kDa51%

1-3 kDa35%

3-5 kDa3% >5 kDa

11%

HPO66%

HPL34%

HPO36%

HPL64%

A

B

Fig. 2. The relative occurrence (as %DOC) of different UF (A) and XAD-8 (B) fractions in MB and TM waters.

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3839

XAD-8 fractions also exhibited a wide range of

SUVA values (Fig. 3B). For both waters, the HPO

fraction had a significantly higher SUVA value than the

HPL fraction and the original source water. This was

expected based on previous research showing that HPO

fractions isolated by XAD-8 resins have higher aromatic

content than the HPL fractions [6,12,17]. It was found

that as the column distribution coefficient ðk0Þ increased,

the SUVA of the HPL fractions increased. The column

distribution coefficient is directly proportional to the

volume of water processed through the resin bed.

Therefore, as k0 increases, available adsorption sites on

the resins are occupied, resulting in the breakthrough of

higher UV-absorbing DOM components. This result

emphasizes the fact that XAD-8 column fractions are

operationally defined, and that selection of k0 is

0

2

4

6

8

SourceWater

HPO (0-20) (20-34) (34-80) (80-107) (0-59) (59-108)

SU

VA

254

(L/m

g D

OC

-m)

MB

TM

0

2

4

6

8

SourceWater

<1 kDa 1-3 kDa 3-5 kDa >5 kDa 5-10kDa

10-30kDa

30-100kDa

>100kDa

SU

VA

254

(L/m

g D

OC

-m)

MB

TM

A

B

Fig. 3. SUVA254 values of UF (A) and XAD-8 (B) fractions in MB and TM waters. In part B, numbers in parenthesis represent the k0

range of HPL fractions. Error bars indicate the 95% confidence intervals.

M. Kitis et al. / Water Research 36 (2002) 3834–38483840

important in designing fractionation experiments and

for comparing results between studies. As observed for

the source water, no clear trend was apparent between

MW and the SUVA of UF fractions prepared from the

TM HPO fraction.

The differences in the MW and HPO/HPL distribu-

tions of the two surface waters examined in this research

suggest that the sources of DOM in these waters are

quite different. Pedogenic humic substances and/or

DOM originating from terrestrial vegetation generally

contain more aromatic moieties and lignin, larger MW

components and more intense color per C atom; in

contrast, aquagenic humics generally contain more

aliphatic moieties and more carboxylic functional

groups [41,42]. Taken as a whole, the evidence suggests

that MB water exhibits a significant pedogenic DOM

signature. Factors contributing to this conclusion

include (1) relatively high SUVA254 values (e.g., >4);

(2) high MW components; (3) hydrophobic character-

istics; and, (4) a watershed that contains many forests

and wetland areas. In contrast, the hydrophilic, low

SUVA and low MW properties of the TM DOM are

consistent with a more aquagenic signature.

4.2. The impact of UF and XAD-8 fractionation on the

SUVA and DBP reactivity of source water DOM

To investigate the impact of UF and XAD-8

fractionation, the SUVA and DBP reactivity of source

water DOM was compared to reactivity of source waters

reconstituted from the XAD-8 or UF fractions. Frac-

tions were mixed in proportion to their mass contribu-

tions to the source water DOM. For both TM and MB

waters, it was found that the SUVA values (at 254, 272

and 280 nm wavelengths) of the reconstituted source

waters were statistically similar (within the 95%

confidence intervals) to the unfractionated source water

[26]. This result confirms that XAD-8 and UF fractiona-

tion did not modify the spectroscopic characteristics of

the original DOM. Because UV absorbance is a function

of both the concentration of UV-absorbing components

and their structural configuration, we conclude that no

irreversible modifications to the DOM molecular

structure occurred from exposure to strong acids and

bases, from interactions with resin materials during

RAC and/or with membrane materials during UF, or

from aggregation resulting from increases in concentra-

tion. Similarly, no statistically significant impact of UF

fractionation on the SUVA of the TMHPO fraction was

observed.

Fig. 4 shows a comparison of specific THM and

HAA9 yields (i.e., THM/DOC or HAA9/DOC) of

unfractionated MB source water with those of recon-

stituted source waters (i.e., measured) from XAD-8 or

UF fractions. In addition, since the contribution of

individual fractions to overall DOM mixture is known,

and their DBP yields were measured, the DBP formation

of the source water was calculated as the sum of

contributions from each fraction:

SDBPYcalculated ¼XN

i¼1

xiSDBPYi

" #; ð1Þ

where xi is the fraction of mass contributed by an

individual XAD-8 or UF fraction to the source water

DOC, SDBPYi is the measured specific DBP yield (i.e.,

for THM or HAA9) of the XAD-8 or UF fraction, and

N is the total number of fractions. The calculated DBP

yields of reconstituted source water from XAD-8 or UF

fractions are also shown in Fig. 4.

Examination of the data in Fig. 4 suggests that neither

XAD-8 nor UF fractionation altered reactive sites

within the DOM that were responsible for DBP

formation. The same conclusion was reached for the

TM water (data not shown). Measured DBP yields for

reconstituted source waters were consistent with yields

calculated by summing contributions of individual

fractions, and were statistically comparable (i.e., within

95% confidence intervals) with that of the unfractio-

nated source water. This finding also suggests that the

contribution of each fraction to total DBP formation

appears to be linearly cumulative; no synergistic effect

among the fractions is apparent. The impact of XAD-8

and UF fractionation on the DOM reactivity was also

evaluated in terms of bromine incorporation factors for

THM ðnÞ and HAA9 ðn0Þ: The bromine incorporation

factor was calculated as the total moles of bromine

incorporated divided by total moles of species formed in

a given DBP class. Similar to DBP formation, bromine

incorporation factors for reconstituted source waters

were consistent with those calculated by summing

contributions of individual fractions, and were statisti-

cally comparable with those of unfractionated source

waters [26]. In addition, the relative occurrence of

individual DBP species in the source waters did not

change. These observations together confirm that the

UF and XAD-8 fractionation did not irreversibly

modify the reactivity of DOM components that

contribute to the formation of DBPs.

4.3. The DBP reactivity of UF and XAD-8 fractions

4.3.1. UF fractions

The THM and HAA9 specific yields of individual UF

fractions after chlorination are shown in Fig. 5A. For

MB water, DBP yields generally increased with increas-

ing MW, with the exception of the 3–5 kDa fraction,

which exhibited reactivity higher than the overall trend

would suggest. The general trend with MW suggests that

larger molecular size DOM fractions are more reactive

precursors for DBP formation, which is consistent with

their higher SUVA values. The positive correlation

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3841

between the MW and DBP formation was not observed

for the TM water. The 1–3 kDa fraction produced the

highest THM and HAA9 yields, whereas the largest MW

(>5kDa) fraction, which also had the smallest SUVA

value, produced the smallest yields. For both waters, the

specific yields of HAA9 were higher than those of THM

in all MW fractions and the unfractionated source

waters.

For MB water, bromine incorporation factors for

both THM and HAA9 formation decreased as the MW

of the fractions increased up to 3–5 kDa, above which

they were relatively constant (Fig. 6A). The o1 kDa

fraction, having the smallest SUVA value, had the

largest ðnÞ and ðn0Þ values among all MW fractions and

the source water, an observation consistent with the

literature [13,16]. This suggests that bromine is incorpo-

rated into lower-MW fractions to a greater extent. For

TM water, there was no clear trend between bromine

incorporation factors and MW (Fig. 6A). The largest ðnÞand ðn0Þ values were found in the 3–5 kDa fraction. In

0

10

20

30

40

50

60

70

80

90

Source water MeasuredXAD-8

MeasuredUF

CalculatedXAD-8

CalculatedUF

TH

M/D

OC

(µg

/mg

)

HPO

<1K

1-3K

3-5K

5-10K10-30K

30-100K

>100KHPL

A

0

10

20

30

40

50

60

70

80

90

Source water MeasuredXAD-8

Measured UF

CalculatedXAD-8

CalculatedUF

HA

A9/D

OC

(µg

/mg

)

HPO

<1K

1-3K

3-5K

5-10K

10-30K30-100K

>100K

HPL

B

Fig. 4. Comparison of specific THM (A) and HAA9 (B) yields of source water, and measured and calculated reconstituted source

waters from XAD-8 or UF fractions for MB water. Error bars indicate the 95% confidence intervals.

M. Kitis et al. / Water Research 36 (2002) 3834–38483842

general, since both were low-bromide waters, bromi-

nated DBPs formed in small quantities, resulting in the

very small ðnÞ and ðn0Þ values.The contribution of molecular size fractions to overall

reactivity results from the combined effects of individual

fraction reactivity and apparent molecular weight

distribution. To illustrate this, the percent contribution

of each MW fraction to source water specific DBP yield

was calculated. Because no synergistic effect was found

between the UF or XAD-8 fractions during DBP

formation, the following linear combination was used:

%SDBPYi ¼SDBPYiPN

i¼1 xiSDBPYi

h i� 100: ð2Þ

In the TM water, 93% and 91% of the THM and

HAA9 yields, respectively, of the source water were

produced from the fractions with MW o3 kDa. In

Fig. 5. Specific THM and HAA9 yields of UF (A) and XAD-8 (B) fractions in MB and TM waters. In part B, numbers in parenthesis

represent the k0 range of HPL fractions. Error bars indicate the 95% confidence intervals.

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3843

contrast, percentage yields of the low molecular weight

MB fractions were only about half as large. This large

contribution from the low molecular weight TM

components occurs because the low MW fractions are

more reactive (Fig. 5A), and because they dominate the

source water composition (86% by weight). High MW

components (>5kDa) of the TM water contribute only

4% and 5% to the source water’s THM and HAA9

yields, respectively. This compares to 31% and 37% for

the MB water, as a result of an increase in DBP

reactivity with MW for this water, and a significant mass

fraction of larger components (26% by weight).

4.3.2. XAD-8 fractions

The reactivity of XAD-8 fractions for DBP formation

is shown in Fig. 5B. With the exception of THM

produced from the HPO fraction, XAD-8 fractions of

MB water exhibited larger THM and HAA9 yields than

Fig. 6. THM and HAA9 bromine incorporation factors of UF (A) and XAD-8 (B) fractions in MB and TM waters. In part B, numbers

in parenthesis represent the k0 range of HPL fractions. Error bars indicate the 95% confidence intervals.

M. Kitis et al. / Water Research 36 (2002) 3834–38483844

those of TM water. For both waters tested, the HPO

fraction had higher THM and HAA9 yields than the

HPL fractions and the source water. This is consistent

with previous reports in the literature that humic-type

components of DOM, generally captured by XAD-8

resins, are more reactive to DBP formation [12,15,16].

However, HPL fractions also exhibited appreciable

THM and HAA9 yields. As calculated using Eq. (2),

HPL fractions contributed 27% and 50% of the

THM yield for MB and TM water, respectively [26].

Similar contributions to HAA9 yields were observed

for both waters. Since hydrophilic fractions are less

amenable to removal in conventional water treatment

processes, these contributions to total DBP formation

can have significant implications for the ability of

water utilities to comply with more stringent DBP

regulations.

It was found that both THM and HAA9 yields of the

HPL fractions increased with increasing k0 (Fig. 5B), as

more hydrophobic components, having higher SUVA

values, elute from the column. The effect of k0 was more

pronounced in the more hydrophobic MB water. This

emphasizes the importance of k0 when comparing DBP

reactivities between different studies. In terms of the

reactivity of MW fractions of the HPO fraction in TM

water, no clear trend was found between MW and DBP

yields; results were similar to that found for the source

water [26].

For each water tested, HPL fractions produced

greater yields of brominated species (both THM and

HAA9) than the HPO fraction and source water

(Fig. 6B), an observation consistent with the literature

(e.g., [16]). Very small ðnÞ and ðn0Þ values were found

in the HPO fraction of both waters. In fact, no

brominated HAA9 species were detected in the HPO

fraction of TM water. These results suggest that

hydrophilic moieties of DOM are more susceptible to

bromine incorporation.

4.4. The role of SUVA in DBP reactivity

Because the chemical composition of DOM compo-

nents is expected to play a significant role in DBP

reactivity, and SUVA has been shown to correlate well

with DBP formation [12,17,23,31], correlations between

the SUVA and the DBP yields of UF and XAD-8

fractions were examined (Fig. 7A). All the fractions had

the same DOC, bromide and chlorine concentrations;

thus, differences in DBP yields could be directly related

to differences in SUVA. Two important observations

were made from these correlations. First, although the

correlations between the DBP formation and MW were

not consistent for the two waters (Fig. 5A), the trend of

increasing DBP formation with increasing SUVA is

clear (Fig. 7A). In the context of DBP reactivity, the

chemical properties (i.e., aromaticity) of these DOM

mixtures are more important than their physical size.

Second, although two separation processes with sig-

nificantly different mechanisms were used in the DOM

fractionation, strong and single trends (R2 values of

linear fits ranging between 0.85 and 0.92) were observed

between SUVA and both THM and HAA9 yields,

independent of the fractionation process used. This is

consistent with our previous work, which identified

unique correlations between SUVA and the DBP yield

of DOM fractions obtained from a single water using

carbon and XAD-8 batch adsorption, and alum

coagulation [31]. This, consistent with other research,

confirms that SUVA is a distributed parameter; i.e.,

when we measure SUVA for a water sample, it is a

composite value representing contributions from differ-

ent components:

SUVA ¼XN

i¼1

xiSUVAi; ð3Þ

where xi is a mole or mass fraction, and SUVAi is the

SUVA of a single component or a class of components.

The range of SUVAi for different components is a

measure of DOM heterogeneity, one that correlates with

DBP reactivity. The way in which SUVA is distributed

provides more information than a composite value of

SUVA. Therefore, these results provide additional

support for the finding that the SUVA distribution of

DOM components, which reflects the distribution of

unsaturated bonds within DOM, represents an impor-

tant characteristic of natural waters.

SUVA also correlated with both THM and HAA9

bromine incorporation factors of individual fractions,

independent of their MW or hydrophobicity (Fig. 7B).

As the SUVA decreased, both ðnÞ and ðn0Þ values

increased, suggesting that bromine is more effectively

incorporated into lower UV-absorbing DOM fractions.

This suggests that SUVA may also effectively distin-

guish between sites that have preferential affinity for

chlorine substitution, and those that react with bromine.

In addition, as discussed before, lower-MW and

hydrophilic fractions, which had lower SUVA values,

were also found to have larger ðnÞ and ðn0Þ values.

Bromine is a stronger and faster halogenating agent than

chlorine. However, the mechanistic reasoning associated

with the finding that bromine incorporates more into

lower-SUVA (i.e., less aromatic), more hydrophilic, and

lower-MW DOM fractions is not well understood. In

both waters, ðnÞ values were larger than ðn0Þ for each

XAD-8 or UF fraction or source water. In addition, the

slopes of the SUVA-bromine incorporation factor fits in

the tested waters were always larger for THM, suggest-

ing that the relative occurrence of brominated THM

species is larger than that of brominated HAA species

after chlorination of DOM, especially for the lower-

SUVA fractions (Fig. 7B).

M. Kitis et al. / Water Research 36 (2002) 3834–3848 3845

5. Conclusions

The primary conclusions from this work are that (1)

DOM isolation and/or fractionation procedures using

XAD-8 adsorption and UF do not alter either the

SUVA or the reactivity of DOM (in terms of DBP

formation and speciation) as compared to the source

water, at least for the techniques described in this study;

and, (2) although XAD-8 adsorption and UF fraction-

ate DOM with significantly different mechanisms, for

each water tested, strong and unique correlations were

observed between SUVA and both THM and HAA9

yields, independent of the fractionation process em-

ployed. Because there was no consistent trend between

the MW and DBP formation for the UF fractions of the

two waters tested in this study, aromaticity of DOM

components is more important than the size for

predicting DBP formation. These results provide further

0.0

0.1

0.2

0.3

0 1 2 3 4 5 6 7 8

SUVA254 (L /mg DOC-m)

Br

Inco

rp. F

acto

r (n

or

n')

fo

r T

M

0.0

0.1

0.2

0.3

Br

Inco

rp. F

acto

r (n

or

n')

fo

r M

B

TM-n TM-n'

MB-n MB-n'

B

MB-n

MB-n'

TM-n

TM-n'

0

20

40

60

80

100

0 1 2 3 4 5 6 7 8

SUVA254 (L /mg DOC-m)

DB

P Y

ield

s (µ

g/m

g D

OC

) fo

r T

M

0

20

40

60

80

100

120

140

DB

P Y

ield

s (µ

g/m

g D

OC

) fo

r M

B

MB-THM MB-HAA9

TM-THM TM-HAA9

MB-THM

MB-HAA9

TM-THM

TM-HAA9

A

Fig. 7. The role of SUVA of UF and XAD-8 fractions in DBP yields (A) and bromine incorporation factors (B) for MB and TM

waters.

M. Kitis et al. / Water Research 36 (2002) 3834–38483846

support for the finding that SUVA is a distributed

parameter that varies among DOM components, reflects

the degree of DOM heterogeneity, and represents an

important property of natural waters that can be used to

predict DBP formation. Secondary conclusions from

this work include:

* The column distribution coefficient ðk0Þ is an

important parameter in designing fractionation

experiments and must be considered when comparing

results between different studies.* There is no significant synergistic effect between the

DOM components in their reaction with chlorine to

form THM and HAA9.* Hydrophobic components of DOM (isolated by

XAD-8) were the most reactive DOM components

for DBP formation. However, hydrophilic compo-

nents also showed appreciable DBP formation. It

may be difficult to reduce total DBP formation for

waters with large amount of hydrophilic fractions

because they are difficult to remove using conven-

tional water treatment processes.* Bromine appears to be more effectively incorporated

into low UV-absorbing (i.e., low SUVA), low MW

and hydrophilic DOM fractions.

Acknowledgements

This work was supported in part by a Research Grant

(R-828-045-01-0) from the United States Environmental

Protection Agency’s Science to Achieve Results (STAR)

program (Office of Research and Development, Na-

tional Center for Environmental Research and Quality);

however, it has not been subjected to the Agency’s peer

and policy review and therefore does not necessarily

reflect the views of the Agency and no official endorse-

ment should be inferred. Support from the National

Science Foundation for equipment acquisition through

the MRI program (Grant BES-9871241) is gratefully

acknowledged. The financial support of the Turkish

Ministry of Education for the graduate studies of

Mehmet Kitis is appreciated. Partial financial support

for JEK and AW from the Eastman Kodak Company is

acknowledged. The authors thank the administrative

and technical staffs of the Myrtle Beach, SC, and Troy,

NY, drinking water treatment plants.

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