CHLORINE DECAY AND DISINFECTION BY-PRODUCT FORMATION OF
DISSOLVED ORGANIC CARBON FRACTIONS WITH GOETHITE
A Thesis
Presented to
The Graduate Faculty of The University of Akron
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
Chris Wannamaker
May, 2008
CHLORINE DECAY AND DISINFECTION BY-PRODUCT FORMATION OF
DISSOLVED ORGANIC CARBON FRACTIONS WITH GOETHITE
Christopher Wannamaker
Thesis
Approved:
Accepted:
________________________________
Advisor
Dr. William B. Arbuckle
________________________________
Department Chair
Dr. Wieslaw Binienda
________________________________
Co-Advisor
Dr. Christopher Miller
________________________________
Dean of the College
Dr. George K. Haritos
________________________________
Faculty Reader
Dr. Daren Zywicki
________________________________
Dean of the Graduate School
Dr. George R. NewKome
________________________________
Date
ii
ABSTRACT
Water from the raw water intake at Barberton, Ohio water treatment plant was
collected on two separate dates and fractionated into operationally defined dissolved
organic carbon (DOC) fractions following Pu’s (2005) procedure which stemmed from
Leenheer (1981). Six solutions were prepared at a DOC of approximately 3.0 mg/L for
subsequent testing: (1) Hydrophobic neutral (2) Hydrophobic acid (3) Hydrophilic neutral
(4) Hydrophilic acid (5) Raw water and (6) a mixture of the four fractions (comprised of
25% each fraction by DOC mass). Chlorination of the six solutions in the presence of
increasing concentrations of goethite, an iron oxide, quantified the reactivity compared to
a control test (without goethite).
The four operationally defined DOC fractions represented more than 92% of the
dissolved organic carbon (DOC) present in the raw water for both sample days. The four
fractions were studied for their adsorptive nature with goethite, chlorine consumption,
and HAA5 and THM4 formation with goethite. As expected, unaltered raw water
exhibited the greatest DOC adsorption, increase in chlorine consumption and DBP
increases with goethite. The raw water tested demonstrated that the only DBPs that
potentially change with the addition of goethite were chloroform, TCAA and DCAA.
While chloroform increased for all fractions except HPIN, change in TCAA and DCAA
production caused by goethite was insignificant for all four fractions. The HPOA
fraction was the most susceptible to the effect of goethite as HPOA had the greatest
iii
increase due to the presence of goethite. Though HPIA was similar to HPOA in TTHM
production with goethite, HPIN had the least amount of change in TTHM with goethite.
The TTHM increases brought about by goethite were not dependent on the amount of
DOC mass that adsorbed to goethite or the increase in chlorine consumption caused by
adsorption. Instead, it was the type of DOC fraction, suggesting that the different DOC
fractions contain different conglomerations of NOM moieties which change in reactivity
to chlorine in as little time as a couple months.
iv
TABLE OF CONTENTS
Page
LIST OF TABLES........................................................................................................... viii
LIST OF FIGURES .............................................................................................................x
I. INTRODUCTION ........................................................................................................ 1
1.1
Perspective .................................................................................................. 1
1.2
Research Objectives.................................................................................... 2
1.3
Research Approach ..................................................................................... 3
II. LITERATURE REVIEW ............................................................................................. 4
2.1
Overview..................................................................................................... 4
2.2
Dissolved Organic Carbon Characterization .............................................. 4
2.3
DOC Adsorption to Iron Oxide................................................................... 6
2.4
Chlorine Demand of DOC .......................................................................... 9
2.5
DBP Formation of DOC Fractions ........................................................... 12
2.6
DBP Formation of DOC with Goethite .................................................... 15
2.7
Carbon Functional Groups of Fractions.................................................... 17
III. EXPERIMENTAL PROCEDURES........................................................................... 21
3.1
Reagents and Glassware ........................................................................... 21
3.2
Total Organic Carbon (TOC) Analysis..................................................... 22
3.3
Disinfect By-product (DBP) ..................................................................... 22
v
3.4
Internal Standards ..................................................................................... 24
3.5
Ultra Violet Absorbance ........................................................................... 24
3.6
Goethite..................................................................................................... 24
3.7
Free Chlorine Analysis ............................................................................. 25
3.8
Resin Cleaning .......................................................................................... 25
3.9
Fractionation ............................................................................................. 27
3.10
Evaporating Apparatus.............................................................................. 30
IV. RESULTS AND DISCUSSION ................................................................................. 32
4.1
Water Sample Fractionation ..................................................................... 32
4.2
DOC Fraction Adsorption to Goethite...................................................... 42
4.3
Chlorine Demand ...................................................................................... 56
4.4
DBP Formation of Aqueous Solutions ..................................................... 69
4.5
4.4.1
DBP Formation ........................................................................... 70
4.4.2
TTHM Formation........................................................................ 71
4.4.3
HAA5 Formation ........................................................................ 75
DBP Formation with Goethite .................................................................. 84
4.5.1
DBP Formation with 1 g/L Goethite........................................... 85
4.5.2
DBP Formation with 6 g/L Goethite........................................... 88
4.5.3
DBP Formation for 1-6 g/L Goethite.......................................... 95
V. SUMMARY AND RECOMMENDATIONS........................................................... 103
5.1
Summary ................................................................................................. 103
5.2
Recommendations................................................................................... 107
BIBLIOGRAPHY........................................................................................................... 109
vi
APPENDIX..................................................................................................................... 116
vii
LIST OF TABLES
Table
Page
2.1
Six Fractions of NOM and Their Corresponding Definitions .............................. 20
4.1
Sample Identification. ........................................................................................... 33
4.2
Fractionation Results from 20 Liters of 1-30-07 Water........................................ 36
4.3
Fractionation Results from 20 Liters of 3-28-07 Water........................................ 36
4.4
DOC Characteristics Throughout Sequential Fractionation Procedure. ............... 40
4.5
DOC Fraction Characteristics After Fractionation. .............................................. 41
4.6
Water Characteristics. ........................................................................................... 44
4.7
Solution Concentrations after Adsorption. ........................................................... 46
4.8
Percent DOC Adsorbed......................................................................................... 50
4.9
Maximum Percent DOC Adsorbed....................................................................... 55
4.10
Chlorine Demands. ............................................................................................... 63
4.11
Chlorine Percent Increases from 1 – 6 g/L Goethite............................................. 67
4.12
DBP Production (ppb)........................................................................................... 77
viii
4.13
DBP Production per DOC Mass (ug/mgC)........................................................... 78
4.14
DBP Production per Chlorine Consumed (ug/mgCl2). ......................................... 78
4.15
DBP Production per DOC Mass (ug/mgC) of Hydrophobic Versus
Hydrophilic and Acid Versus Neutral Fractions. .......................................... 83
4.16
DBP Production per Chlorine Consumed (ug/mgCl2) of Hydrophobic
Versus Hydrophilic and Acid Versus Neutral Fractions. .............................. 83
4.17
Percent DBP Increase at 1 g/L Goethite. .............................................................. 87
4.18
Solution Characteristics at 1 g/L Goethite. ........................................................... 87
4.19
Percent DBP Increase at 6 g/L Goethite. .............................................................. 91
4.20
Solution Characteristics at 6 g/L Goethite. ........................................................... 91
4.21
TTHM Increase from 1 – 6 g/L Goethite.............................................................. 98
4.22
HAA5 Increase from 1 – 6 g/L Goethite. ............................................................. 98
4.23
Chloroform Increase from 1 – 6 g/L Goethite. ..................................................... 99
4.24
TCAA Increase from 1 – 6 g/L Goethite. ............................................................. 99
4.25
DCAA Increase from 1 – 6 g/L Goethite............................................................ 100
ix
LIST OF FIGURES
Figure
Page
3.1
The sequence of five columns of resin used to separate raw water into six
operationally defined fractions. Columns one through three contain
XAD-8, followed by column number four containing AG-MP-50
cation exchange resin, followed by column number five containing
WA-10 anion exchange resin. Underlying fractions are removed
from the corresponding column of resin by using the subsequent
chemical......................................................................................................... 30
3.2
A systematic diagram of the concentrating apparatus used for the
hydrophilic neutral (HPIN) fraction. ............................................................. 31
4.1
Percent DOC adsorbed for 1 and 2 g/L goethite of 1-30-07 solutions. ................ 51
4.2
Percent DOC adsorbed for 1 and 2 g/L goethite of 3-28-07 solutions. ................ 52
4.3
Percent DOC adsorbed of 1-30-07 solutions. ....................................................... 53
4.4
Percent DOC adsorbed of 3-28-07 solutions. ....................................................... 54
4.5
Chlorine consumption versus SUVA254................................................................ 64
4.6
Chlorine consumed of increasing goethite concentrations. .................................. 65
4.7
Chlorine consumed of increasing goethite concentrations. .................................. 66
4.8
Aqueous chlorine demand versus goethite chlorine demand................................ 68
4.9
TTHM versus SUVA regression........................................................................... 79
x
4.10
HAA5 versus SUVA regression. .......................................................................... 80
4.11
TTHM comparison between aqueous and goethite at 1 and 6 g/L. ...................... 92
4.12
Chloroform comparison between aqueous and goethite at 1 and 6 g/L................ 93
4.13
HAA5 comparison between aqueous and goethite at 1 and 6 g/L........................ 94
4.14
Brominated and non-brominated DBPs of 1-30-07 solutions............................. 101
4.15
Brominated and non-brominated DBPs of 3-28-07 solutions............................. 102
xi
CHAPTER I
INTRODUCTION
1.1
Perspective
The organic content of surface waters is comprised of a complex mixture of
aromatic and aliphatic hydrocarbons structures with attached carbon functional groups,
making the study of their affect on water quality hard to pin point (Leenheer and Croue
2003). However, a technique developed by Leenheer (1981) separates dissolved organic
carbon (DOC) operationally into six subclasses called fractions known as hydrophobic –
acid, –base and –neutral and hydrophilic – acid, –base and –neutral (HPOA, HPOB,
HPON, HPIA, HPIB, and HPIN, respectively). This has been an accepted separation
process for years. With this technique, the separated DOC fractions can be studied for
reactivity with chlorine and disinfection byproduct (DBP) formation.
Goethite (α-FeOOH) and magnetite (Fe3O4) are reported as the main iron oxides
at the water-surface interface inside corroded cast iron distribution pipes (Benjamin et al
1996, Sarin et al. 2001). An American Water Works Association survey conducted in
1996 determined 30 percent of United States water mains are comprised of unlined
cast/ductile iron or steel (AWWA 1998). Inside of these iron pipes, complex reactions
take place between chlorine, iron oxide, and natural organic matter (NOM) to form
(DBPs) (Bower 2003). Though the mechanisms between the oxide and water interface
are difficult to study and understand, experiments using goethite have shown chloroform
1
production and chlorine demand increases (Hassan et al 2006). In addition, certain DOC
fractions have a higher affinity to goethite than other fractions (Kaiser 2003), which is
why chunks of pipe deposit maintain a significant chlorine demand and DBP formation
potential after removal from a pipe (Valentine et al 2000). This implies that the
adsorption of DOC fractions is related to their nature of carbon which is related to the
ability to change in reactivity in the presence of goethite. Testing affinity, chlorine
demand, and DBP formation of DOC fractions in the presence of increasing goethite
concentrations will simulate a water distribution system. This thesis will quantify the
amount of goethite it takes to significantly affect water quality using four major DOC
fractions (HPON, HPOA, HPIN, and HPIA).
1.2
Research Objectives
The overall objective is to evaluate adsorption isotherms of four major DOC
fractions from raw water using goethite while assessing the impact of chlorine demand
and DBP formation caused by goethite. Specific objectives include:
1. To evaluate how well four DOC fractions adsorb to goethite at a beginning pH of
8.0 ± 0.1.
2. To assess the impact that goethite has on raw water and DOC fractions in a
modified DBP formation potential test. Measurements of THM4, HAA5, and
chlorine consumed at increasing goethite concentrations will define which DOC
fractions have the greatest and least susceptibility to goethite.
3. To explain the relation between the percent DOC adsorbed of four DOC fractions
to goethite with the chlorine demand and DBP formation of each.
2
1.3
Research Approach
Raw water collected from Barberton (Ohio) on 1-30-07 and 3-28-07 was
fractionated into six operationally defined fractions following Leenheer (1981) and Pu
(2005). Four DOC fractions (HPOA, HPON, HPIA, and HPIN) were studied since
insufficient mass of the HPOB and HPIB fractions existed in the raw water, prohibiting
testing. Six solutions were studied (1) HPOA, (2) HPON, (3) HPIA, (4) HPIN (5) the
raw water, (6) and an equal mixture of HPOA, HPON, HPIA, and HPIN (comprised of
25% each fraction by DOC mass). Adsorption isotherms, chlorine consumed, and THM4
and HAA5 formation were analyzed to determine which of these six solutions were most
affected by goethite. Six incrementally increasing concentrations of goethite were used
to simulate increasing goethite exposure as the water’s residence time increases through
corroded iron pipes in a distribution system.
3
CHAPTER II
LITERATURE REVIEW
2.1
Overview
Natural organic matter (NOM) in raw surface water is a complex mixture of
carbon functional groups making its study with goethite and chlorine difficult. This
complex mixture of NOM can be separated into six operationally defined fractions by
using a procedure introduced by Leenheer (1981) and revised by Pu (2005). Studies
involving these fractions have been done for years; however, which fractions are most
detrimental to water qualities, such as chlorine consumption and DBP formation, remains
a debate (Marhaba et al 2001, Kanokkantapong et al 2006b, Croue et al 2000b).
2.2
Dissolved Organic Carbon Characterization
The nature of organic matter in surface waters consists of an agglomeration of
different carbon functional groups (Leenheer et al 2003). These carbon functional groups
are decaying plants and biotic masses transferred by watersheds to near by reservoirs.
Since these carbon functional groups are vast and difficult to study as a whole, techniques
have been developed to separate them. Two of the most common methods for separating
water into sub-classes of carbon (also called fractions) are by either size exclusion (Chow
et al 2005) or adsorptive classification using resins of ionic and non-ionic characteristics
(Leenheer 1981, Thurman et al 1981, Marhaba et al 2000, Pu 2005). Six operationally
4
defined fractions obtained using the adsorptive procedure are hydrophobic and
hydrophilic –acid, –base and –neutral fractions abbreviated as HPOA, HPOB, HPON,
HPIA, HPIB, and HPIN, respectively.
Studies using resin for fractionation of DOC into phobic and philic material
usually follow techniques established by Leenheer (1981) or Thurman et al. (1981). Both
authors use the DAX-8 non-ionic resin because of its ability to partition the hydrophobic
DOC from the hydrophilic. Furthermore, DAX-8 resin has proven itself through multiple
studies because of its high surface area, small affinity to water and stability to not bleed
carbon. Thurman et al. separates water into the hydrophobic fraction, and further into
humics and fulvics; Leenheer systematically separates the hydrophobic fraction into
HPOA, HPOB, and HPON. In addition, Leenheer also partitioned the hydrophilics into
acid, base, and neutral using a cation called AG-MP-50 and an anion exchange resin
called Duolite-A7. It should be noted that these fractions are operationally defined
because of how they adsorb to resins and not by physical structure of molecules.
To avoid confusion in discussion, the Amberlite XAD-8 (Rohm and Haas Co.)
resin was bought by Supelite (Supelco-Sigma-Aldrich Co.) and called DAX-8. Chow
(2006) tested both the XAD-8 (old) and DAX-8 (new) resins to demonstrate their
comparability of DOC separation and influences on DBP production. He concluded the
DAX-8 adsorption efficiency was systematically 4% greater than XAD-8, however, the
DBP production of the effluent from each proved to be statistically the same.
Since Leenheer (1981), others have used his technique and report short-comings
(Marhaba et al 2003, Pu 2005), most of which have been resolved. First, NaOH was used
to replace NH4OH for adjusting pH and for eluting fractions from the resins, this
5
alleviated concerns of chloramines being produced and interfering with the disinfection
by-product formation tests to be conducted later. Secondly, Leenheer suggested using
one column of DAX-8 resin; however, 100% elution of HPON, HPOB, and HPOA is
extremely difficult, hence, contamination of one fraction to the next would occur. In
addition, mass balance checks would contain potential error due to DOC remaining on
the single column between hydrophobic fractions. Marhaba et al (2003) fixed this by
using three separate DAX-8 columns, one for each hydrophobic fraction. In addition,
recommending to remove HPON first, HPOB second and the HPOA third, resulted in
less adjustment of the raw waters’ pH. Third, due to DOC bleeding from the Duolite-A7
resin, a weaker anion-exchange resin, called WA-10, was used and proved to be very
stable and sufficient for the separation of the HPIA fraction without DOC bleeding.
2.3
DOC Adsorption to Iron Oxide
Adsorption of DOC to metal oxides can be influenced by several factors including
pH, molecular weight, and bivalent cations (Tipping 1981, Davis et al 1981, Tipping
1982). In addition, oxide sites that are able to adsorb DOC are also a crucial factor when
evaluating adsorption isotherms. The oxide sites for goethite have been identified as
negative, positive or neutral hydroxyl sites (OH) with pKa values of 6.03 and 8.53
(Stumm 1992). Reasons why particular fractions may or may not adsorb to these
hydroxyl sites may also be explained by carbon functional groups. Studies to determine
which DOC fractions adsorb more readily to iron oxide have concluded that the HPOA
and HPIA fractions adsorbed the most while HPIN was least likely if at all able to adsorb
(Benjamin et al 1993, Korshin et al 1997).
6
Corrosion inside cast iron pipes are layers of iron oxide composed mainly of
goethite (α-FeOOH), magnetite (Fe3O4), and lepidocrocite (γ-FeOOH). Goethite is
suggested to be at the surface due to its dominating production over lepidocrocite under
high pH and slow oxidation from reactions with chlorine and dissolved oxygen (Sarin et
al 2000, Benjamin et al 1996, Cornell et al 1996). Sarin et al (2000) used the Rietveld
method (1969) to conclude that the outermost, shell-like surface layer from six different
pipe deposits of the first 2-5 mm of corrosion was composed of 33-58% goethite, 31-44%
magnetite and 9-20% lepidocrocite by weight. While the outer layers of pipe deposits
contain comparable amounts of magnetite, goethite was decided on simply because it was
easier to produce than magnetite. Goethite is a stable, mostly insoluble, iron oxide
normally found as circular needles or rods estimated to have 0.02 mol sites/mol of Fe
(Benjamin 1993). These sites provide a medium for natural organic matter (NOM) to
adsorb by six generalized mechanisms such as: (1) anion exchange (electrostatic
interaction), (2) ligand exchange-surface complexation, (3) hydrophobic interaction, (4)
entropic effect, (5) hydrogen bonding and (6) cation bridging (Gu et al. 1994). The
occurrence of DOC adsorbing to goethite has been studied for some time in order to
observe and understand which fractions interact the greatest with iron oxides (Hassan et
al. 2006, Tipping 1981, Benjamin et al 1993, Kaiser 2003, Meier 1999, Tipping 1982).
In a study by Hassan et al. (2006), two goethite concentrations of 1 and 5 g/L
were pre-selected to evaluate how much goethite would be sufficient to alter reaction
mechanisms in raw water batch experiments. As it turned out, the 5 g/L goethite
demonstrated a non-significant change in DOC adsorbed in comparison to the 1 g/L, as
determined by fluorescence using relative percent absorbance. He concluded that there
7
were sufficient hydroxyl sites present in 1g/L of goethite to adsorb the DOC. The batch
tests he conducted had a DOC concentration of 5.50 and 6.00 mg/L. Using fluorescence
and relative absorption he determined that raw water of any DOC concentration is limited
by the number of DOC reactive sites able to adsorb and not by the goethite concentration.
Kaiser (2003) produced Langmuir models of HPOA and hydrophilic organic matter using
DOC concentrations ranging from 24 to 960 mg/L as C. He concluded that goethite has
an adsorption capacity for HPOA and hydrophilic material of between 52.9 – 59.9 and
10.2 – 23.3 milligram of carbon per gram of goethite, respectively. In addition to the
Langmuir models, Kaiser conducted carbon nuclear magnetic resonance (C-NMR)
analysis and the results supported his conclusions of why the HPOA adsorbed
significantly more than the hydrophilic material. Kaiser (2003) concluded, after
performing adsorption isotherms of HPOA and hydrophilic matter, that the aromatic
carbon functional groups were the reason for greater adsorption.
Other reports have also shown that hydrophobic factions rich in carboxylic and
aromatic carbon functional groups will adsorb much stronger to iron oxides than the
corresponding hydrophilic fractions that contain phenolic functional groups rich in O,Nalkyl C (Kaiser 2003, Benjamin et al 1993, Gu et al. 1995). This is in agreement to how
the iron oxide hydroxyl sites are positioned and freely accepting of COO- functional
groups as seen below.
8
≡Fe-OH
≡Fe-O
R-COO--
C-R+OH≡Fe-OH
≡Fe-OH--O
Benjamin et al. calculated that 8.86 mg DOC was adsorbed per gram of iron oxide, which
suggests that the iron is limited by the number of hydroxyl sites when excess DOC is
available. This would imply that the carbon functional sites able to adsorb to goethite
would limit the adsorptive nature of waters when limited to goethite (Edwards et al
1996). In addition, adsorption time would seem important; however, findings have
demonstrated that contact time needed for full adsorption to occur is quite small (Tipping
et al 1981, Benjamin et al 1993)
Tipping et al (1981) mixed goethite at approximately 0.1 g/L with humic fraction
and found its concentration became constant after 16 hours, meaning that equilibrium had
been reached in this time. Benjamin et al (1993) used an empty bed contact time (EBCT)
for an iron oxide coated sand (IOCS) column of approximately 10 minutes after
examining an optimized curve of TOC removal versus contact time. An equilibrium
period of 24 hours was selected for this study to ensure complete adsorption equilibrium
had taken place.
2.4
Chlorine Demand of DOC
Chlorine consumption in distribution systems can be caused by a number of
factors such as reactions with organic and inorganic chemicals, biofilms attached to the
distribution pipe walls, the corrosion process, and mass transport between the bulk flow
9
and pipe wall (Vasconcelos et al 1997). These factors have led researchers to model
chlorine decay rates of both the bulk flow and at the water-deposit surface (Rossman et al
2001, Vasconcelos et al 1997, Kiene et al 1998). Hassan (2005) conducted a control test
on the chlorine consumption of buffered deionized (DI) water with no DOC in the
presence of 1 and 5 g/L of goethite. He concluded that neither goethite concentration had
any chlorine demand in the absence of DOC. The goethite he used did not contain any
major mass of Fe(II) that could reduce free chlorine, thus implying that without adsorbed
NOM, biofilm, or any other contaminants contributed by water, chlorine consumption
will not occur. Some researchers believe that chlorine decay is further influenced by pH,
temperature, chlorine dosage, dissolved oxygen, organic carbon concentrations, and
UV254 (Rodriguez et al 2002, Dugan et al 1995, Koechling 1998, Valentine et al 2000,
Tuovinen et al 1984).
Different carbon functional groups can also influence chlorine decay; for
example, aromatic phenolic activated carbon groups have been well correlated chlorine
consumption (Reckhow et al 1990). In addition, hydrophobic acids (HPOA) have been
identified as containing significantly higher aromatic carbon than hydrophilic matter
(Kaiser 2003) and therefore would be expected to consume more chlorine per mass of
DOC. Kaiser (2003) also concluded that the HPOA adsorb much stronger to iron oxide
than hydrophilic matter. Though Benjamin et al (1993) concluded that the hydrophilic
acid (HPIA) fraction adsorbed as strongly as the HPOA fraction, they both agreed on
HPOA’s ability to absorb to iron oxide. In agreement, Valentine et al (2000) extracted
DOC from pipe deposit material taken from distribution systems and, depending on the
extraction method, obtained readings in the range of 0.2 – 12 mg C/g of deposit. They
10
further attempted to exhaust the chlorine demand of the pipe deposit, revealing the
mixture of DOC and iron oxide had a chlorine demand >20mg Cl2/g of deposit.
However, all deposits contained 27 – 40% iron by weight while 30 – 60% of the iron was
ferrous, implying a probable source for chlorine demand.
Hassan et al. (2006) used synthetic goethite at 0 (control), 1, and 5 g/L to test
reactivity changes of two different water sources, at varying chlorine dosages and a fixed
pH at 8.0. They concluded that chlorine decay was always higher in the presence of
goethite, though decay did increase proportionally with increasing goethite
concentrations. Rossman et al (2001) tested water under similar conditions by comparing
water only (no deposits) chlorine decay to an 88 foot pipe loop system maintained in a
laboratory. The pipe used had been in service for many years and showed signs of
considerable corrosion and tubercle formation. While the bottle tests containing no
deposit material or iron oxide, and the loop system were chlorinated at similar
concentrations (4.0 and 3.9 mgCl2/L, respectively), the loop system demonstrated a much
higher decay rate. To better illustrate this difference, they subtracted the bottle’s chlorine
decay rate (Kb) from the decay rate of the loop system which produced a chlorine decay
rate strictly contributed by the wall of the pipe (Kw). This Kw decay rate was up to an
order of magnitude larger than Kb. The evidence of increased chlorine decay in the
presence of pipe deposits is apparent and should be strongly considered when conducting
bulk chlorine decay rates for a water treatment plant in the laboratory.
11
2.5
DBP Formation of DOC Fractions
Natural organic matter (NOM) constitutes the major component of total organic
carbon (TOC) in most water. NOM has been identified as the main precursor to the
formation of trihalomethanes (THM) and haloacetic acids (HAA) (Rook 1974, Stevens et
al 1976, Christman et al 1983). Unless stated otherwise, the THM formation potential
(THMFP) reported consists of the sum of chloroform, bromodichloromethane,
chlorodibromomethane and bromoform denoted as THM4 or TTHM. Likewise, HAA
formation potential (HAAFP) is the sum of monochloroacetic (MCAA),
monobromoacetic (MBAA), dichloroacetic (DCAA), trichloroacetic (TCAA),
dibromoacetic (DBAA) denoted as HAA5. The THMFP and HAAFP of different
materials can be reported in many ways, such as ugTHM/mgDOC or simply the mass of
THMs or HAAs produced per volume that the experiments were conducted with units of
ug/L. Distinction of methods used for reporting formation potentials will be made clear
throughout the following sections.
One of the most common methods for separating DBP precursors from raw water
is by fractionation into hydrophobic and hydrophilic mater (Marhaba et al 2000, Liang et
al 2003). Furthermore, separation of the hydrophobic and hydrophilic DOC matter into
acid, base, and neutrals can aid researchers in finding which fraction is the largest DBP
producer. While much research has already concluded which fractions are most potent in
producing DBPs, there remains a disagreement as to which one does in fact produce more
DBPs (Marhaba et al 2001, Kanokkantapong et al 2006b, Croue et al 2000b, and Chang
et al 2001). While some researchers only fractionate the HPOA and leave the rest
together, others use the Amberlite XAD-4 (Rohm and Haas) and further separate what are
12
called transphilics, creating three separate solutions (Liang et al 2003). Though this
thesis does not use this fractionation procedure, the HPOA obtained from this procedure
can be useful in DBP discussion.
Chang et al. (2001) fractionated water into HPOA, HPOB, HPON and hydrophilic
material and chlorinated each fraction at approximately 45 mg/L as Cl2 so that more than
3 mg/L as Cl2 remained after a 7 day chlorination period. He found that all hydrophobic
fractions produced approximately twice the THMs and HAAs than the hydrophilic
material while HPOA produced the largest THM and HAA per DOC of any other
fraction. On the other hand, Marhaba et al (2001) fractionated raw surface water into six
fractions, and chlorinated with the same procedure as Chang et al (2001). They
concluded that HPIA contributed 69% of the waters THMFP ability while HPON
contributed 18%. The HAAFP contributors were determined to be the HPON at 56% and
HPOA at 26% of the raw waters full formation ability. The other fractions did not
produce more 6% of the raw waters formation potential for either THMs of HAAs.
Though Marhaba et al agree with Chang et al about the hydrophobic matter having the
largest HAAFP, they disagree with which fraction has the largest THMFP.
Kanokkantapong et al (2006b) and Panyapinyopol et al (2005a) fractionated
Bangkok, Thailand main water supply and conducted 7-day DBPFP tests similar to
Chang et al (2001). Both authors used two different terms to describe DBPFP for each of
the six fractions that they called either “total DBPFP” or “specific DBPFP.” The total
formation potential was the mass of the DBPs produced from each fraction individually
normalized to the total DOC mass of the beginning raw water. Specific formation
potential was the mass of the DBPs produced from each fraction normalized to the DOC
13
mass of the respective fraction. They concluded that HPOB and HPIB had the highest
specific THMFP and HAAFP of all fractions. The HPON fraction exhibited the second
largest specific THMFP, while HPIA, HPIN, and HPOA fractions were similar though
the HPOA was the lowest. Specific HAAFP test revealed that HPIA was the lowest
while HPIN was the highest next to HPOB and HPIB.
Though ugTHM4/mgDOC and ugHAA5/mgDOC are most commonly used to
report formation potentials (FPs), chloroform, TCAA and DCAA FPs (ug/mgDOC) are
also useful, as these three species usually comprise the major components of THM4 and
HAA5. Croue et al (2000b) separated a surface water from the South Platte River into
HPOA, HPON, HPIA and HPIN fractions while further chlorinating them at a DOC
concentration between 4 and 7 with a (Cl2)dose / DOC ratio of 4 mg/mg at a pH of 8.0.
They concluded that the HPOA held the highest chloroform FP at 46 ugCHCl3/mgC,
HPIA held the second highest at 35, while HPON and HPIN were comparable at 29 and
28 ugCHCl3/mgC, respectively. Although HPOA and HPIA also held the highest
TCAAFP at 28 and 24 ugTCAA/mgC, HPIN had the highest DCAAFP at 19
ugDCAA/mgC, though HPIA was second at 16 ugDCAA/mgC.
DOC fractions have been tested for DBPFP by many researchers, and overall
there does not seem to be a trend in their reactivity to producing DBPs. However, many
would still argue that hydrophobic fractions do have a higher tendency to produce THMs
because of higher SUVA values typically linked to this fraction (Kanokkantapong et al
(2006b), Panyapinyopol et al (2005a, Croue et al 2000b). The UV254 parameter of water
has been used for many years to correlate its value to THM formation potential in water
(Edzwald et al 1985). In addition, higher UV254 absorbance has been said to be caused by
14
aromatic moieties in water (Christman et al 1983, Chin et al 1994, and Croue et al 2000),
and hydrophobic fractions have been known to contain considerably greater amounts of
phenolic and aromatic carbon structures (Kaiser 2003, Croue 2004). Kim et al (2005)
found that the hydrophobic fractions, while high in phenolic content, were the main
precursor for THMs. In contrast, the HAAs were produced primarily from the
hydrophilic fraction which was higher in carboxylic carbon. He studied how the different
treatment processes through a water treatment plant changed the hydrophobicity of the
water. Starting and progressing from the raw water to pre-chlorinated, settled, and finally
the filtered water, he saw the phenolic content was readily removed (38.7%) more than
the carboxylic content (approx. 4%). Also, the hydrophobic fraction was removed more
readily (20.8%) than the hydrophilic fraction (4.6%). In conjunction, he saw the
THMFP/DOC of the hydrophobic fraction decrease throughout the treatment plant from
85.6 to 42.3 ug/mg. Also, the HAAFP/DBP of the hydrophilic fraction decreased from
33.7 to 24.1 ug/mg (Kim et al. 2005). Kim et al (2005) further concluded that chemical
and structural characteristics such as aromaticity and functionality influence the amount
and species of DBPs formed.
2.6
DBP Formation of DOC with Goethite
The reactions that take place inside a distribution system are indisputably
complex, but the formation of HAAs and THMs in the presence of iron oxides (e.g.
goethite) is more complex. Many report THMs increasing in the presence of goethite as
reaction time with chlorine increases, however, the fate of HAAs seems to vary
throughout distribution systems (Hassan et al 2006, Bower 2003, Golden 2005, Rossman
15
et al 2001). The occurrence of THMs increasing as travel time through a distribution
system has been known and evaluated for many years (Baribeau et al 2004, Rodriguez et
al 2004, Rossman et al 2001). The disappearance of HAAs, specifically DCAA, in a
distribution system is said to be biodegradation from contact with biofilm (Williams et al
1996).
One of the major concerns of distribution systems is the iron oxide on pipe walls
acting as a sponge for NOM until available chlorine comes in contact with it producing
DBPs. While the HPOA and HPIA are believed to adsorb strongest to iron oxide coated
sand (Benjamin et al 1993), the HPOA fraction has been evaluated and concluded as
containing mainly phenolic and carboxylic aromatic carbon groups (-COOH). The
aromatic carbon were most susceptible to absorb to iron oxides (Kaiser 2003) and
produce DBPs; therefore HPOA and HPIA would be expected to increase DBP
production with increased goethite concentrations.
Tipping et al (1982) describes the adsorption of organic matter to goethite in
terms of electrophoresis which is able to demonstrate that goethite becomes negatively
charged due to the adsorption of humic substances. They further explain that humic
substances contain carbon functional groups that are both able and unable to adsorb,
leaving the non-adsorbed molecule repulsed away from the oxide surface. This visual
picture of adsorbed NOM molecules extending away from iron oxide sites into the bulk
solution leads researchers to a conclusion about why distribution systems demand up to
ten times the amount of chlorine than identical water in aqueous tests. However, not only
do distribution systems consume more chlorine, but they produce more THMs than the
control aqueous systems (Rossman et al 2001).
16
2.7
Carbon Functional Groups of Fractions
Explanations to why DOC fractions adsorb to goethite and react differently with
chlorine, producing different levels and species of HAA’s and THM’s, should not be
without the discussion of carbon functional groups. Engineers have a decent idea of how
to remove sufficient carbon in water treatment plants by coagulation and settling so that
regulations are met. However, there is a lack of knowledge as to which carbon
components should be removed to reduce chlorine consumption and DBP precursors for
distribution. In addition, pipe deposits formed on the inside of ductile iron pipes are
selective for certain carbon functional groups in DOC. This is problematic since pipe
deposits with adsorbed DOC can be a major chlorine consumer and THM producer
(Rossman et al 2001, Hassan et al 2006, Bower 2003, Valentine et al 2000). One of the
approaches to quantifying DBP precursors is to study the carbon content of hydrophobic
and hydrophilic fractions using either carbon nuclear magnetic resonance (C-NMR),
Fourier transform infrared (FTIR), gas chromatograph mass spectrometer (GC-MS), and
even an high pressure liquid chromatogram (HPLC) analysis. Kanokkantapong et al.
(2006) comprised a list of the major carbon functional groups and concluded the
fractions’ differences based on C-NMR and FTIR analysis (Table 2.1).
Thorough investigations of carbon functional groups can provide explanations to
many phenomena that occur during water treatment and distribution. Answers to why
chlorine is consumed higher with waters with higher SUVA254, and why certain DOC
fractions adsorb better to iron oxides can help be explained by discussion of carbon
functional groups. The ultraviolet (UV) spectra at a specific absorbance at 254 nm has
been correlated (R2 = 0.83) with aromatic carbon (Croue et al 2000c). In addition,
17
oxygen atoms within hydroxyl groups locally donate electrons to the carbon atoms they
are attached to, thus increasing the electron richness of the aromatic molecules (Croue et
al 2000b). This is the reason waters with high SUVA values tend to consume more free
chlorine which oxidizes molecules thus reducing the free chlorine (HOCl or OCl-).
Hanna et al (1991) concluded using C-NMR analysis that methoxyl, phenolic, and
ketonic structural groups were more reactive to chlorine than alkyl or carboxyl while
carbohydrates were least reactive.
Croue (2004) showed the aliphatic carbon content to decrease from water as the
DOC became more hydrophilic. On the other hand, the ketone and aromatic carbon
increased as the hydrophobic content increased. In contrast, as the hydrophilic content
increases, so does the aliphatic C-O and carboxyl content. He further believes that higher
hydrophobic content implies higher molecular weight meaning higher aromatic content.
On the other hand, higher hydrophilic content implies higher nitrogeneous structures and
oxygenated functional groups.
Kaiser (2003) conducted a thorough investigation of hydrophobic and hydrophilic
organic matter and the carbon content using carbon nuclear magnetic resonance (C NMR)
analysis. His hydrophobic material was similar to Leenheer’s (1981) HPOA, while the
hydrophilic content contained the acid, base and neutral materials. He concluded that the
hydrophobic content contained more phenolic and aromatic carbon as opposed to the
hydrophilic material which contained higher levels of oxygen-nitrogen substituted
aliphatic carbon (O,N-alkyl C) which was suggested to be due to carbohydrates. Further
in his study he produced Langmuir isotherms of the hydrophobic acid and hydrophilic
18
organic matter with goethite as the absorbent. From this test, he confirmed hydrophilic
matter always showed less sorption than hydrophobic acids (Kaiser 2003).
19
Table 2.1
Six Fractions of NOM and Their Corresponding Definitions
(Kanokkantaong et al 2006)
Fraction
Symbol
Definition
Hydrophobic Acid
HPOA
Aliphatic carboxylic acids of five to nine
carbons, one and two-ring aromatic
carboxylic acids, aromatic acids, one and
two-ring phenols, and tannins
Hydrophobic Neutral
HPON
Hydrocarbon; aliphatic alcohols, alkyl
alcohols, ethers, ketones, and aldehydes,
aliphatic carboxylic acids and aliphatic
amines with more than five carbons, aromatic
carboxylic acids with more than nine carbons,
and aromatic amines of three rings or greater
Hydrophobic Base
HPOB
Proteins, one and two-ring aromatic amines
except for pyridine, and high molecular
weight alkyl
Hydrophilic Acid
HPIA
Aliphatic acids of less than five carbons,
hydroxyl acids, sugars, low molecular weight
alkyl monocarboxylic and dicarboxylic acids
Hydrophilic Neutral
HPIN
Aliphatic amides, alcohols, aldehydes, esters,
ketones with less than five carbons, and
polysaccharides
Hydrophilic Base
HPIB
Aliphatic amines with less than nine carbons,
amino acids, pyridines, purines, pyrimidines,
and low molecular weight alkyl amines
20
CHAPTER III
EXPERIMENTAL PROCEDURES
The methods, materials, reagents and analytical procedures used to obtain all data
are presented in this chapter. All water samples were analyzed at the University of
Akron, Ohio. Six solutions are evaluated: (1) Raw water (2) Hydrophobic neutral
(HPON) (3) Hydrophobic acid (HPOA) (4) Hydrophilic neutral (HPIN) (5) Hydrophilic
acid (HPIA) and (6) A mixture of the four fractions (MIX) (each fraction at 0.75 mg/L as
TOC). All six solutions were diluted to a total organic carbon concentration of 3 mg/L
with a starting pH of 8.0. Goethite concentrations varied from 0-6 g/L in increments of 1
g/L for each of the six solutions. Samples were buffered to a 10-5M concentration of
sodium bicarbonate, a lower concentration than recommended in order to prevent
interference with NOM adsorption to goethite. In addition, all samples were tumbled for
24 hours, allowing NOM and goethite to stabilize prior to measurements for DOC
adsorption and an additional 48 hours for chlorination.
3.1
Reagents and Glassware
All chemicals used in this study were reagent grade. Barnstead NANOpure water
(Barnstead, Dubuque, Iowa) model number D2716 with an additional type 1 organic free
system model number D3806 was used for all dilutions and rinsing. All glassware used
to conduct disinfection by-product formation potential (DBPFP) tests were EP Scientific
21
Environmental Boston Round Bottles, capped using a polypropylene cap with PTFE
liners. Prior to use, each bottle was washed using powder Alconox (Alconox inc., White
Plains NY) then submerged in an acid bath at a pH of 2 acidified with hydrochloric acid
for 24 hours. The bottles were rinsed three times with deionized (DI) water and placed in
a chlorine bath for an additional 24 hours. Rinsed again with deionized water, the bottles
were placed in an oven at 100 degrees Celsius for 24 hours. Following the oven, they
were allowed to cool, capped and stored at room temperature.
3.2
Total Organic Carbon (TOC) Analysis
A Shimadzu TOC-5000 Analyzer was used for all carbon analysis by a non-
purgeable organic carbon (NPOC) method. Samples were acidified to a pH between 2
and 3 with 1.0 N hydrochloric acid then purged for a minimum of four minutes with
hydrocarbon free air. Calibrations were performed using 2.1254 grams of Potassium
Phthalate Monobasic added to one liter of DI water, yielding a 1000 mg of NPOC per
liter solution. Standards for a calibration curve were set at 1, 3, 5, and 7 ppm as NPOC
using the 1000 mg of NPOC per liter solution. Each sample was repeated three times of
which had to reach a coefficient of variance of < 2% by area or a standard deviation of
area < 200.
3.3
Disinfect By-product (DBP)
All analysis of DBP’s consisted of four trihalomethanes (chloroform,
bromodichloromethane, chlorodibromomethane, and bromoform) and five haloacetic
acids (HAA5) (monochloroacetic (MCAA), monobromoacetic (MBAA), dichloroacetic
(DCAA), trichloroacetic (TCAA), dibromoacetic (DBAA)). EPA methods 551.1 and
22
552.2 were followed for all THM and HAA5 analysis, respectively. A Shimadzu GC17A (Kyoto, Japan) equipped with an electron capture detector (ECD) was used for both
THM and HAA analysis. A J&W Scientific (Folsom, CA) model DB-1 column was used
for THM analysis with the following GC settings:
1. Injection temperature was 225º C
2. ECD temperature was 300º C.
3. Column temperature program was 35º C held for 9 minutes, then a 1º C per
minute increase to 40º C which was maintained for 3 minutes, and finally a 6º C
per minute increase until a temperature of 150º C was reached, which was held for
1 minute.
4. The injection was splitless with a set time for 0.3 minutes at which time it turns to
split with a split flow ratio set to 20. This split after 0.3 minutes is to ensure no
build up of compounds in the injection port between samples occurs.
5. Current was set to 0.1 with the range set to 1.0.
6. Flow was set to 101 milliliters per minute.
A Phenomenex (Torrance, CA) column, model ZB-1701, was used for HAA analysis
with the following GC settings:
1. Injection temperature is 225º C
2. ECD temperature is 260º C
3. The column program was 35º C held for 4 minutes, when temperature was
increased at a rate of 14º C per minute to a final 200º C and held for zero minutes
4. The injection was split at a ratio of 1:20
5. Current was set to 0.5 with the range set to 1.0
23
6. Flow was set to 127 milliliters per minute
7. A flow program was set to hold 127 milliliters per minute for 4 minutes at which
time flow increased at a rate of 7 milliliters per minute to a flow of 200 milliliters
per minute and held for zero minutes. The flow program was to ensure sufficient
flow through the column as it was heated which causes a decrease in pressure.
3.4
Internal Standards
Bromofluorobenzene and 1,2,3-trichloropropane were used for THM and HAA
internal standards, respectively. Internal Standards were used because of the variation in
sensitivity of the ECD detector between samples. Concentrations of the internal
standards inside the 1.5 mL vials to be analyzed for DBPs were made to be 1000 and 100
ppb for the THM and HAA analysis, respectively.
3.5
Ultra Violet Absorbance
A Shimadzu UV 1601 dual beam spectrophotometer was used for all UV254
measurements in a 1 x 1 cm quartz cell.
3.6
Goethite
Goethite (α-FeOOH) was made according to Schwertmann and Cornwell (2000).
The procedure consists of adding 100 milliliters of 1.0M ferric nitrate nonahydrate to a
two liter polyethylene flask followed by 180 milliliters of 5.0M potassium hydroxide and
filling with deionized water. The flask is then capped and heated at 70˚C for 60 hours.
Next, the two liters of solution were centrifuged at 2000 rpm’s to remove the goethite
from the hydroxide-water solution. The goethite was rinsed three times with clean
24
deionized water to remove the excess hydroxide. Afterwards, the goethite was scrapped
into a mortar and thoroughly dried. Using a pestle and mortar, the goethite was crushed
until able to pass through a number 80 U.S. Standard sieve. X-ray diffraction analysis
was performed using a Phillips XRG 3100 X-Ray generator equipped with a
diffractometer controller and compiled using PC-APD software from Phillips to ensure it
was primarily goethite. Tests were performed by Tom Quick in The University of
Akron’s geology department who confirmed the samples were ~100% goethite.
3.7
Free Chlorine Analysis
Free chlorine was measured using a modified version of the DPD colorimetric
method according to Standards Methods for the Examination of Water and Wastewater
(APHA et al., 1995).
3.8
Resin Cleaning
The DAX-8 macroporous methylmethacrylate copolymer was received from
Supelco and added directly to a 0.1 N NaOH solution, which was changed every 24 hours
for five consecutive days. Afterwards, the NaOH solution was rinsed from the resin with
copious amounts of deionized water until the conductivity was <10µs. Next, a four day
Soxhlet extraction cleaning process of methanol, diethyl-ether, acetonitrile, and
methanol, each for 24 hours, was executed to remove all possible contaminants from the
manufacture. Resin was stored in methanol until used for the first time. After using for
NOM fractionation, the resin was cleaned in a 1.5 liter beaker filled with DI water. With
a large stir bar vigorously stirring, sufficient 10 N NaOH was added to raise the pH to
between ten and eleven, stirred for ten minutes, followed by sufficient 18 N sulfuric acid
25
to lower the pH to approximately two, and stirred for another 10 minutes. The extreme
pH changes removes all adsorbed DOC which had not been removed, via elution, during
the fractionation procedure. The water was decanted and the resin rinsed approximately
three times with clean deionized water where it was stored until the next use.
Resin used for HPON, HPOB, or HPOA where kept separated from each other to
eliminate cross contamination between fractions. Once the column was packed with the
appropriate resin, it was rinsed with approximately 10 bed volumes of deionized water.
The resin then received a second sequential rinsing, first with three bed volumes of 0.1 N
NaOH, 10 bed volumes of deionized water, three bed volumes of 0.1 N sulfuric acid, then
enough deionized water until the effluent was <0.2 ppm of TOC and conductivity <10 µs.
AG-MP-50 (Bio-Rad) cation exchange resin is first cleaned by Soxhlet extraction
with methanol for 24 hours. The resin was packed in the column with at least one third
of space at the top to allow for resin expansion and was rinsed with deionized water.
Once the effluent had reached a TOC of <0.2 ppm and a conductivity <10 µs, the resin
was hydrogen saturated by passing four bed volumes of 2 N HCl through at a rate less
than 30 bed volumes per hour. Finally, the resin was rinsed with deionized water until
the effluent had reached a TOC of <0.2 ppm and conductivity was <10 µs.
WA-10 anionic exchange resin was placed in the column and rinsed with DI
water until the effluent was <0.2 ppm of TOC and conductivity <10 µs. To prepare for
fractionation, 1.0 N NaOH was pumped through the column until the pH of the effluent
was as high as the 1.0 N NaOH being pumped in (approximately 12). Afterwards,
deionized water was pumped through the column until the effluent was <0.2 ppm of TOC
and conductivity was <10 µs.
26
3.9
Fractionation
The fractionation procedure followed Leenheer (1981) with modifications by Pu
(2005). Fractionation of hydrophobics was done with three separate columns of DAX-8.
The DAX-8 resin was not packed with glass wool to prevent disturbing of the top portion
of the bed only because it seemed redundant. NaOH was substituted for NH4OH for
concerns of chloramines being produced and interfering with the disinfection by-product
formation tests to later be conducted. For background and explanations of the
fractionation procedure used, see the literature review section on Dissolved Organic
Carbon Characterization. The procedure used was as follows:
HPON
1. Raw water was filtered through a 0.45 micron nylon filter.
2. Water’s pH adjusted to 7.0 ± 0.1 using either NaOH or H2SO4.
3. Pump the water at a rate between 8 and 12 bed volumes (BV) per hour through
the DAX-8 resin column one, as seen in figure 3.1.
4. Once the water has finished, pump one BV of deionized water through the resin
doing so in a fashion where no air pockets form inside the column of resin.
5. Immediately following DI water, the flow direction is reversed, with two BVs of
methanol pumped at a rate of less than four BVs per hour.
6. Furthermore, the resin was removed and placed in amber glassware and shaken
periodically for 24 hours in a 2:1 methanol to resin ratio.
7. Once all methanol was evaporated at 40º C, 200 mL of DI water was added and
stirred at approximately 100 rpm with a stir bar, and heated for an additional 24
hours at 70º C to remove any volatile organics.
27
HPOB
1. Water without HPON fraction was pH adjusted to 10 ± 0.1 with 10 N NaOH.
2. Follow steps 3 and 4 from HPON procedure using DAX-8 column number 2, see
figure 3.1.
3. Immediately following DI water, the flow direction is reversed and 0.25 BV of
0.1 N H2SO4 followed by 1.5 BV of 0.01 N H2SO4 are pumped at a rate of less
than four BV per hour.
4. Finally, flip column, finish collecting the HPOB fraction, and neutralize solution
to a pH of seven.
HPOA
1. Water without HPON and HPOB fractions was pH adjusted to 2 ± 0.1 with 36 N
H2SO4.
2. Follow steps 3 and 4 from HPON procedure using DAX-8 column number 3, see
figure 3.1.
3. Immediately following DI water, the flow direction is reversed and 0.25 BV of
0.1 N NaOH followed by 1.5 BV of 0.01 N NaOH are pumped at a rate of less
than four BV per hour.
4. Finally, flip column, finish collecting the HPOA fraction, and neutralize solution
to a pH of seven.
HPIB
1. Water now containing only hydrophilics remains at a pH of 2 ± 0.1.
2. Water is pumped at 5 BV per hour through the AG-MP-50 which is column
number four in figure 3.1.
28
3. The resin is rinsed with one BV of DI water followed by eluting the HPIB
fraction with 1.0 N NaOH at a rate of 2 BV per hour in the forward direction.
4. Neutralize eluent to a pH of seven.
HPIA
1. Water pH remains at 2 ± 0.1.
2. Sample water is pumped at 8 BV per hour through the WA-10 resin which is
column number five in figure 3.1.
3. Rinse WA-10 resin with 1 bed volume of DI water.
4. HPIA is forward eluted with 2.0 N NaOH at less than 12 BV per hour.
5. Neutralize eluent to a pH of seven.
HPIN
1. The only fraction remaining in solution at this point is HPIN, and the pH exiting
the WA-10 resin should be approximately 9.5 ± 0.5.
29
NaOH or
NaOH
H2SO4
H2SO4
pH 7
pH 10
pH 2
pH 2
pH 2
1
2
3
4
5
pH ~ 8-9
Eluted:
HPON
HPOB
HPOA
HPIB
HPIA
HPIN
Using:
Methanol
H2SO4
NaOH
NaOH
NaOH
Remaining
Figure 3.1
The sequence of five columns of resin used to separate raw water into six
operationally defined fractions. Columns one through three contain XAD8, followed by column number four containing AG-MP-50 cation
exchange resin, followed by column number five containing WA-10 anion
exchange resin. Underlying fractions are removed from the corresponding
column of resin by using the subsequent chemical.
3.10
Evaporating Apparatus
The HPIN fraction was less than the desired concentration and therefore had to be
concentrated. A water reducing system was designed so clean air passed over slightly
30
heated (approx 70ºC) HPIN fraction in a water solution. An aquarium aerator was placed
inside a container with the aerating hose protruding through the lid, hot glued closed and
made air tight. A second hole was made in the lid and a hose placed so to pull suction.
This suction hose was wedged into a predrilled plastic cap, which screwed onto a 500 mL
amber bottle. A second hole in this cap had another hose leading to a glass column
containing pre-washed and dried activated carbon. The column was packed with glass
wool on both ends to further reduce the possibility of carbon dust from entering the HPIN
solution. This was an alternative to a rotary evaporator.
Open to
Atmosphere
GAC
Glass Wool
Air Flow
Air Tight
Seal
HPIN
Plastic Lid
Air Outflow
Plastic
Container
Air Tight
Seal
Air
Intake
Aerator Pump
Figure 3.2
A systematic diagram of the concentrating apparatus used for the
hydrophilic neutral (HPIN) fraction.
31
Heater
CHAPTER IV
RESULTS AND DISCUSSION
4.1
Water Sample Fractionation
A water’s dissolved organic carbon (DOC) characteristics play a major role in
adsorption to pipe deposits (e.g. iron oxides), chlorine decay, and disinfection by-product
formation (Benjamin et al 1993, Krasner et al 1996). The separation of DOC into six
operationally defined fractions known as hydrophobic and hydrophilic –acid, –base and –
neutral (HPOA, HPOB, HPON, HPIA, HPIB, and HPIN respectively) are prepared so
that studies can reveal which fractions are most problematic in terms of chlorine demand
and DBP production. Though the six fractions are operationally defined, their carbon
structure characteristics are distinctly different according to C-NMR and FTIR analysis
(Kaiser 2003, Krasner et al 1996, Kanokkantapong et al 2006). The carbon functional
groups observed in the six fractions justify the different ways they respond to pipe
deposits, chlorine and hence DBP production.
Six dissolved organic carbon (DOC) fractions were separated from two different
water samples (1-30-07 and 3-28-07) that came from a surface water treatment plant
influent (Barberton, OH). Water samples were fractionated into operationally defined
DOC fractions stemming from Leenheer (1981) as later refined by Pu (2005). Although
six fractions were separated from the raw water sample, only four fractions were used in
experiments. This was done since the hydrophobic acid (HPOA), hydrophobic neutral
32
(HPON), hydrophilic acid (HPIA), and the hydrophilic neutral (HPIN) fractions
accounted for 92 and 96% of the mass in 1-30-07 and 3-28-07 water samples,
respectively. Two additional solutions were tested: the original raw water from which the
fractions were derived and an equal mixture of the four fractions (comprised of 25% each
fraction by DOC mass). Sample labels created for the six solutions from each day are
listed in Table 4.1.
Table 4.1
Sample Identification.
ID
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
Sample
Filtered raw water
Hydrophobic Acid Fraction
Hydrophilic Acid Fraction
Hydrophobic Neutral Fraction
Hydrophilic Neutral Fraction
An equal mixture of HPOA, HPIA, HPON, and HPIN
MIX-1
each fraction at 0.75 mg/L DOC in solution
Raw-2
Filtered raw water
HPOA-2
Hydrophobic Acid Fraction
HPIA-2
Hydrophilic Acid Fraction
HPON-2
Hydrophobic Neutral Fraction
HPIN-2
Hydrophilic Neutral Fraction
An equal mixture of HPOA, HPIA, HPON, and HPIN
MIX-2
each fraction at 0.75 mg/L DOC in solution
Note: 1- Indicates water samples collected on 1-30-07
2- Indicates water samples collected on 3-28-07
33
Both water samples were fractionated following the same procedure, however, the
fractions’ percentages in the raw water varied. Percentages of the HPON, HPOB and
HPIA fractions increased 8, 2.5 and 8%, respectively, from 1-30-07 to 3-28-07 water
samples. The HPIB and HPIN fractions decreased 6.5 and 11%, respectively, while
HPOA remained the same at ~32% (Table 4.2 and 4.3). Kanokkantapong et al. (2006)
experienced similar fraction variations in three summer waters fractionated between June
and August, 2003. They experienced variations in fraction percentages greater than 3%
with the HPON (6%), HPOB (5%), HPIA (9%), and HPIN (15%) fractions. This
variation in fraction composition is expected, since the nature of water will change with
the seasons.
HPON, HPOB, HPOA, HPIB, and HPIA fractions recovered from the DAX-8,
AG-MP-50 and WA-10 resins are low, with the exception of 3-28-07 HPIA, where 39%
excess DOC was recovered from the WA-10 resin (Table 4.2 and 4.3). Approximately
40% of the HPON mass was lost through the elution process, probably due to insufficient
agitation of the DAX-8 and methanol as they were periodically shaken, not continuously
mixed. Interestingly, HPIA demonstrated 39% (3.9 mg DOC) of excess mass recovered
during the 1-30-07 water fractionation while 33% (4.62 mg as C) of HPIA’s DOC mass
was lost for 3-28-07 recovery. It should be noted that the accuracy of the TOC
measurement was 0.2 mg/L as NPOC and if TOC values before or after fractionation had
been off by this amount, it could account for this 33% loss. On the other hand, only 68% (1.33-2.0 mg as C) of the HPOA DOC mass was lost, demonstrating the best
recoveries of all fractions (Table 4.2 and 4.3). The overall percent recovery (excluding
HPIN mass in calculation) for resin extracted fractions was 88 and 76% for 1-30-07 and
34
3-28-07 water samples, respectively. Though 12 and 24% losses seem large, Croue et al
(2000a) reported losses of 20 and 32% after fractionating water into six operationally
defined fractions from two separate water sources. An objective for Leenheer (1981) was
to devise a fractionation procedure where greater than 90% of the total DOC mass could
be recovered. Though 100% recovery is preferred, it is difficult to achieve, though
percentages of 90-109% have been reported (Kanokkantapong et al. 2006, Marhaba et al
2000, Kitis et al 2002). Marhaba et al (2003) quoted Leenheer et al (2000) about the
fractionation procedure as saying “recovery of representative portions…is suitable for
various spectral characterization and reactivity studies” not “necessarily defined as 100%
recovery of the DOM.”
As fractions are sequentially removed through the fractionation procedure, SUVA
values of the remaining water reveal characteristics of the removed fractions. For
instance, the HPON fraction contributed 15% DOC and only 7% UV254 absorbance in the
1-30-07 raw water (Table 4.4 and 4.5); while in the 3-28-07 raw water contributed 24%
DOC and 28% UV254 absorbance. Interestingly, HPON-1 and HPON-2 solutions both
had the lowest SUVA values when diluted to ~3.0 mg/L as NPOC (Table 4.6). The
higher SUVA values for HPON-2 suggest that HPON-2 contained more aromatic
moieties than HPON-1. As expected, the SUVA value decreased after HPOA removal
for both days due to significant amounts of UV254 removal, most likely because of its
high aromatic content per DOC mass (Benjamin et al 1993, Kaiser 2003). HPOA
contributed the most DOC and UV254 absorbance for both
35
Table 4.2
Fractionation Results from 20 Liters of 1-30-07 Water.
HPON HPOB HPOA
HPIB
HPIA
HPIN
Total
Mass Removed
from Raw (mg)
10.8
0.20
23.6
5.4
10.0
21.4
71.4
Percent in Raw
Water (%)
15%
0.3%
33%
7.6%
14%
30%
100%
Mass Recovered
from Resin (mg)
6.4
0.16
21.6
1.8
13.9
21.4
65.2
Percent
Recovered from
59%
81%
92%
33%
139% 100.0%
Resin (%)
Note: Mass removed is based on before and after resin adsorption TOC measurements.
Table 4.3
Fractionation Results from 20 Liters of 3-28-07 Water.
HPON HPOB HPOA
HPIB
HPIA
HPIN
Total
Mass Removed
from Raw (mg)
15.6
2.0
21.2
0.4
14.2
12.2
65.6
Percent in Raw
Water (%)
24%
3%
32%
0.6%
22%
19%
100%
Mass Recovered
from Resin (mg)
9.8
1.41
19.9
0.0
9.56
12.2
52.8
Percent
Recovered from
63%
70%
94%
0%
67%
100%
Resin (%)
Note: Mass removed is based on before and after resin adsorption TOC measurements.
36
days at 33 and 32% DOC, and 40 and 41% UV254 absorbance for 1-30-07 and 3-28-07
waters, respectively. On the other hand, the HPIA fraction contributed 14% DOC and
9% UV254 for 1-30-07 raw water, changing slightly in 3-28-07 raw water to 22% DOC
and only 3% UV254. This is not surprising since HPIA has been known to have very low
UV254 absorbance (Kanokkantapong et al 2006a). The HPIN surprisingly contributed
nearly 25% UV254 absorbance of the raw water for both days though low UV254
absorbance has been reported for hydrophilic matter (Kaiser 2003).
The major components of most surface water are the HPOA, HPIA, HPON and
HPIN fractions with percent DOC of total waters ranging from 11-59%, 5-53%, 0.9-17%
and 0.2-19%, respectively (Marhaba 2000, Benjamin 1993, Kanokkantapong et al. 2006).
The HPON and HPIN fractions did exhibit slightly more DOC mass than excepted;
however, raw surface water DOC is difficult to study throughout varying locations and
climates. Due to HPOA’s abundance in most raw surface waters, others have
fractionated only the HPOA fraction and called it the hydrophobic content of their water
samples (Singer et al 2003).
The SUVA values of the prepared NOM solutions (Table 4.1) can be compared to
the amount of UV254 they contributed to the raw water (Tables 4.4). The exception is the
HPIA fraction which contributed 9 and 3% of the UV254 absorbance in 1-30-07 and 3-2807 raw waters, though both HPIA solutions had the second largest SUVA values amongst
the fractions (Table 4.6). This seems abnormal, since HPIA contributed little to the
SUVA in the raw water; however, Li et al (2006) observed nearly 100% removal of
UV254 from raw water passed through an IOCS column which removed primarily the
HPOA and HPIA fractions. Therefore it would appear that HPOA and HPIA could
37
contribute a large portion of SUVA since HPOA-1 and HPOA-2 contained the largest
SUVA values (Table 4.6). Though it is reasonable that HPIN-1 and HPIN-2 had lower
SUVA values, HPON-2 should have had a higher SUVA than HPIN-2 based on other
studies (Croue et al 2000b, Kanokkantapong et al 2006a). The HPON fraction for 3-2807 raw water contributed 28% of the UV254 absorbance while the HPIN contributed 23%
(Table 4.5). In contrast, the HPIN-2 prepared solution had a SUVA value of 2.0 while
HPON-2 was 1.4 L m-1mg-1 (Table 4.6). These results could be related to the
suppression and destruction of NOM molecules during the fractionation procedure, where
the HPIA fraction had the greatest ionic strength (Table 4.6), possibly explaining the
significant increase in SUVA. Overall, the acid fraction solutions produced the highest
SUVA values while the neutral solutions had the smallest, regardless of how the fraction
contributed UV254 to the raw water (Table 4.6).
In summary, raw waters from both sample days contained four fractions that
accounted for more than 92% of the total DOC mass, these fractions are HPOA, HPIA,
HPON, and HPIN. While the DOC fraction composition in the raw waters was expected,
insufficient mass of the HPOB and HPIB prohibited their testing (Marhaba 2000,
Benjamin 1993, Kanokkantapong et al. 2006). As NOM fractions were sequentially
removed from the raw water, their DOC mass and UV254 contributions to the raw water
were revealed. Comparisons of UV254 of the fractions as they were removed from the
raw water and after they were prepared for testing differed for the HPIA fraction. It
contributed 9 and 3% of 1-30-07 and 3-28-07 raw water UV254 during sequential
fractionation, respectively. However, of the four prepared NOM solutions, HPIA-1 and
HPIA-2 each had the second largest UV254 values (Table 4.6). On the other hand, HPON
38
from 3-28-07 raw water contributed 28% of the UV254, though HPON-2 had the lowest
UV254 among the four prepared fractions. In regards to variations in UV254 between
sample days, HPON in the 1-30-07 raw water exhibited significantly less UV254 (7%)
than the 3-28-07 raw water (28%). In addition, HPOB demonstrated similar but opposite
results in UV254 contributions in the raw water. This is interesting since HPON was
removed before HPOB in the fractionation procedure, yet they appeared to share UV254
moieties and perhaps HPON and HPOB have like moieties.
39
Table 4.4
DOC Characteristics Throughout Sequential Fractionation Procedure.
Fraction
1/30/2007
Raw Water
HPON
HPOB
HPOA
HPIB
HPIA
3/28/2007
Raw Water
HPON
HPOB
HPOA
HPIB
HPIA
DOC
UV254
SUVA
(mg/L)
(cm-1)
(L m-1 mg-1)
3.57
3.03
3.02
1.84
1.57
1.07
0.096
0.089
0.069
0.031
0.029
0.020
2.69
2.94
2.28
1.68
1.85
1.87
3.28
2.5
2.4
1.34
1.32
0.61
0.106
0.076
0.075
0.032
0.027
0.024
3.23
3.04
3.13
2.39
2.05
3.93
40
Table 4.5
DOC Fraction Characteristics After Fractionation.
Fraction
1/30/2007
Raw Water*
HPON
HPOB
HPOA
HPIB
HPIA
HPIN
DOC
UV254
Percent
DOC of
Raw Water
Percent
UV254 of
Raw Water
(mg/L)
(cm-1)
(%)
(%)
3.57
0.54
0.01
1.18
0.27
0.50
-
0.096
0.007
0.020
0.038
0.002
0.009
-
15
0.3
33
7.6
14
30
7
21
40
2
9
21
3/28/2007
Raw Water*
3.28
0.106
HPON
0.78
0.030
24
28
HPOB
0.10
0.001
3.0
1
HPOA
1.06
0.043
32
41
HPIB
0.02
0.005
0.6
5
HPIA
0.71
0.003
22
3
HPIN
19
23
Note: Percent DOC and UV254 of raw water of each fraction calculated as (fraction) /
(raw water)
41
4.2
DOC Fraction Adsorption to Goethite
The adsorption of DOC to goethite will alter reaction pathways causing greater
susceptibility of DOC to react with chlorine and in most cases causing greater DBP
formation (Bower 2003). Goethite offers hydroxyl sites where carboxylic and aromatic
carbon functional groups are adsorbed and/or rearranged in molecular structure (Boyce et
al 1983, Benjamin et al 1993). The following discussion focuses on the adsorption of the
DOC from raw water and NOM fractions to goethite.
Six increasing concentrations of goethite (1-6 g/L) were used to mimic water’s
contact with corroded pipes, which increases with increasing residence time in a
distribution system. A control was tested for each solution and did not contain any
goethite, it is referred to as the aqueous test. The aqueous test provided the beginning
DOC concentration and UV254 measurements for comparison to the goethite tests. The
beginning pH of all solutions were adjusted to 8.0 ± 0.1 by using NaOH or H2SO4 with a
4.0 x 10-5 M concentration of NaHCO3 added to stabilize the pH throughout the
experiment processes. This low concentration of sodium bicarbonate was used to
minimize the interference of DOC adsorbing to goethite. However, pH measurements
after adsorption were between 8.5 and 9.3 due to goethite’s two pKa’s of 6.05 and 8.53
(Stumm 1992), indicating that there was not sufficient NaHCO3.
Goethite was added after solutions were prepared to an approximate DOC
concentration of 3.0 mg/L, adjusted to a pH = 8.0 ± 0.1; conductivity and UV254 were
measured (Table 4.6). A DOC concentration of 3.0 mg/L was used since both raw waters
contained NPOC of 3.57 and 3.28 mg/L. Therefore, solutions were diluted with
deionized, organic free water instead of concentrating to a higher DOC level. Since some
42
solutions contained slightly more/less DOC than 3.0 mg/L, the exact DOC measurements
of the aqueous tests were recorded as the beginning DOC concentration after tumbling
for 24 hours alongside the goethite samples (Table 4.6). This was done so that aqueous
tests and the goethite tests were analyzed at the same time so that any decreases would
indicate adsorption. Conductivities varied considerably since different chemicals and
molarities of these chemicals were used to remove each fraction from its respective resin
(see Methods and Materials). In addition, sodium hydroxide and sulfuric acid were used
for raising and lowering the pH of samples. The SO4-2 would have affected adsorption at
lower pH’s (Tipping et al 1982), even though concentrations did not reach above 3.0
mM; however, a beginning pH of 8.0 ± 0.1 was used for all solutions, therefore
adsorption interference from SO4-2 was accepted as non-significant. Tipping et al (1982)
showed by electrophoresis analysis that neither NaCl at concentrations of 0.01 M nor
SO4-2 at a pH of 8.0 would affect electrophoretic mobility of goethite. In addition,
Tipping points out that even humics have less of an ability to adsorb to goethite at higher
pH’s. This is why Benjamin et al (1993) acidified his influent water to a pH of 3.8 before
pumping through an iron oxide coated sand column for optimum removal of DOC.
A beginning pH of 8.0 ± 0.1 was selected based on the desire to understand the
behavior of these solutions in a distribution system, unlike Benjamin et al’s (1993) of 3.8
which would not be used in a water distribution system. Chlorination occurred after
adsorption, which occurs simultaneously in a distribution system. However, the
evaluation of how adsorbed DOC produced DBPs in the presence of chlorine was more
desired than chlorine affecting DOC adsorption. Adsorption is expected to occur mostly
in the HPOA and HPIA fractions (Benjamin et al 1993) which likely contain aromatic
43
content indicated by the specific ultraviolet absorbance (SUVA) at 254 nm wavelength
(Li et al 2006).
Table 4.6
Water Characteristics.
Beginning DOC
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
(mg/L)
3.10
3.23
3.03
3.04
2.83
2.80
Conductivity
(µS/cm)
477
1056
15,200
125
1284
5,200
UV254
-1
(cm )
0.096
0.092
0.055
0.036
0.037
0.054
Raw-2
3.09
469
0.106
HPOA-2
3.04
250
0.106
HPIA-2
3.09
9,980
0.098
HPON-2
3.13
355
0.044
HPIN-2
3.04
1577
0.061
MIX-2
2.74
3,050
0.071
Note: Characteristics of the water are used for all subsequent tests.
SUVA
(L m-1 mg-1)
3.1
2.8
1.8
1.2
1.3
1.9
3.4
3.5
3.2
1.4
2.0
2.6
Goethite concentrations ranging from 1-6 g/L were selected based on previous
tests indicating comparable adsorption of DOC at 1 and 5 g/L goethite, although chlorine
demand and DBP production increased between these two concentrations (Hassan et al
2006). Iron oxide creates a reaction pathway with NOM which allows for more chlorine
consumption and greater DBP production of raw waters (Hassan 2005, Bower 2003).
DOC adsorption to goethite increases as goethite concentrations increase in raw surface
waters. However, this occurs until sites on the DOC, such as carboxyl acid and aromatic
phenolic groups (Kaiser 2003) are all adsorbed (Hassan et al 2006) (Table 4.7). A
possible reason why certain DOC fractions did not adsorb as well as expected may have
44
been due to suppression or destruction of DOC sites caused by the extreme pH changes
and double layer compression encountered throughout the fractionation procedure
(Benjamin et al 1993). In this study, the raw water COOH and OH functional groups
were not suppressed since the raw water was unaltered for the adsorption tests. Hence,
much greater adsorption was observed in Raw-1 and Raw-2. In addition, Raw-1 and
Raw-2 had an alkalinity of 85 and 66 mg/L as CaCO3, respectively, while the fractions
estimated alkalinities were 5-8 mg/L as CaCO3 due to the added HCO3-. An observation
about Raw-1 and Raw-2 is 75 and 67% of the total carbon adsorbed by 6 g/L had already
adsorbed at 1 g/L goethite, respectively (Table 4.7). At 2 g/L goethite, Raw-1 and Raw-2
adsorption increased to 94 and 87% of the total carbon adsorbed by 6 g/L, respectively.
This implies that 2 g/L of goethite supplies sufficient hydroxyl sites to adsorb
approximately 90% of the carbon capable of adsorbing.
This observation supports Hassan et al. (2006) who also observed that
insignificant adsorption differences existed between the 1 and 5 g/L goethite. They
implied that raw water is limited by how many NOM carbon sites are actually able to
adsorb to iron oxides, not by the hydroxyl sites on the oxide. In addition, the fate of
individual NOM fraction adsorption will vary depending on the presence and
concentration of goethite (Hassan et al 2006). Benjamin et al (1993) studied how well
iron oxide coated sand (IOCS) would remove natural organic matter (NOM) from a raw
water influent of a water treatment facility. Using optimized adsorption isotherms, he
concluded that increased contact time, the presence of calcium up to 150 mg/L as Ca,
influent DOC concentration, nor the vertical flow velocity increased the kinetics of
adsorption of DOC fractions entering the IOCS column.
45
Table 4.7
Solution Concentrations after Adsorption.
Goethite (g/L)
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
0
3.10
3.23
3.03
3.04
2.83
2.80
1
2.05
2.88
2.68
2.60
2.61
2.74
2
1.78
2.85
2.70
2.68
2.60
2.64
3
1.86
3.04
2.65
2.30
2.62
2.46
4
1.82
3.05
2.46
2.66
2.60
2.50
5
1.70
2.86
2.61
1.90
2.63
2.43
6
1.70
2.87
2.58
2.02
2.65
2.63
Raw-2
3.09
2.23
1.98
HPOA-2
3.04
2.87
2.57
HPIA-2
3.09
2.64
2.33
HPON-2
3.13
2.77
2.49
HPIN-2
3.04
2.76
2.83
MIX-2
2.74
2.51
2.60
Note: DOC in mg/L after 24-hour adsorption.
1.92
2.62
2.23
3.00
2.90
2.50
1.93
2.54
2.13
2.68
2.89
2.58
1.77
2.45
2.19
2.98
3.03
2.45
1.81
2.57
2.11
3.13
3.02
2.46
Goethite adsorption tests revealed that the HPIN fraction adsorbed less than any
other fraction (Table 4.9). In an insightful test conducted by Korshin et al. (1997), six
operationally defined fractions were examined in the influent and effluent of an ironoxide-coated sand (IOCS) column. They found the hydrophobic and hydrophilic acid
fractions contributed greater than 90% of the organic content in the elution solution. The
regenerating solution was a NaOH eluent used to restore the hydroxyl sites once the DOC
concentration in the effluent of the IOCS column resembled the influent. They concluded
that five DOC fractions adsorbed to the IOCS while HPIN did not show significant
adsorption. They also believe that both of the acid fractions outcompete other carbon
functional groups, even causing previously sorbed fractions such as HPIN to be released
back into solution. With C NMR data, fractions enriched with aromatic and carboxylic
carbon adsorbed more when compared to the influent (Korshin et al 1997).
46
It appears the percent adsorbed would continue to increase as the goethite
concentration surpassed the 2 g/L goethite concentration for the 3-28-07 sample (Figure
4.2). However, the increase in percent adsorbed past 2 g/L goethite was insignificant
with the exception of HPIA-2 which increased an additional 7% and the HPON-2 which
decreased by 20% (Figure 4.4). The HPIN fraction demonstrated consistent adsorption
with values of 0 – 9% for both sample days. Adsorption tests of 1-30-07 solutions
exhibited an insignificant increase past the 2 g/L goethite with the exception of HPON-1
which increased 20% (Figure 4.3). The increase in adsorption for HPON-1 was
interestingly the opposite of HPON-2 which decreased in percent adsorbed past 2 g/L
goethite. Overall, increased goethite concentrations did not result in an increase in DOC
adsorption except of Raw-1 and Raw-2 (Figure 4.3 and 4.4). While Raw-1 and Raw-2
adsorption increased as goethite concentrations increased, these solutions were nonfractionated and resisted pH change from the addition of goethite better than the other
solutions. The other solutions were prepared with deionized water, and contained very
little alkalinity or buffer intensity making them more susceptible to an increase in pH
caused by goethite.
Li et al (2006) correlated SUVA with NOM adsorption to iron oxide coated sand
(IOCS) and concluded that the IOCS selectively removed molecules enriched in activated
aromatic moieties. NOM with higher UV254 absorbance indicates higher aromaticity and
molecular weights of molecules (Croue et al 2000, Kitis et al 2002, Li et al 2006). Raw-1
and Raw-2 had the greatest DOC adsorption of any solution with SUVA values at 3.1 and
3.4 (L m-1 mg-1), respectively (Figures 4.1 and 4.2). While HPOA-1, HPOA-2, and
HPIA-2 had distinctly higher SUVA values than the other fraction solutions, only HPOA47
2 and HPIA-2 demonstrated significant adsorption. On the other hand HPON-1 and
HPON-2 had the lowest SUVA values, yet their adsorption was among the highest of the
fractions. This means that SUVA is not a reliable parameter for predicting DOC
adsorption.
Assuming that SUVA is linear in terms of DOC concentration versus UV254, then
estimations of MIX solutions’ SUVA values using fraction solutions’ SUVA can be
made. If an average of the SUVA values of the four fractions are added together
0.25*(HPOA+HPON+HPIA+HPIN)), then mathematically MIX-1 and MIX-2 would
have SUVA values of 1.8 and 2.5 L m-1mg-1, respectively. This is comparable to actual
values of MIX-1 and MIX-2 which were 1.9 and 2.6 L m-1mg-1, respectively. This style
of analysis indicates that aromaticity was conserved through the mixing of fractions since
MIX-1 and MIX-2 SUVA values resembled Raw-1 and Raw-2, respectively. Although
SUVA was maintained after mixing of fractions, adsorbing sites were not since only 13
and 11% of MIX-1 and MIX-2 adsorbed to goethite, respectively (Table 4.9). After
mixing of DOC fractions, adsorption was significantly lower than expected, suggesting
that mixing subdued DOC sites. If 25% of the maximum mass adsorbed of the four
individual fractions are summed and then normalized to the beginning mass of both MIX
solutions, 21 and 23% DOC would have adsorbed of MIX-1 and MIX-2, respectively.
These percentages represent the predicted maximum adsorbed for the MIX solutions
which are distinctly higher than the actual percent adsorbed of 13 and 11% for MIX-1
and MIX-2, respectively (Table 4.9). This signifies that slightly more than 20% DOC
from both MIX solutions would have adsorbed had the NOM sites not been destroyed or
suppressed through the mixing of DOC fractions.
48
In summary, Raw-1 and Raw-2 had 45 and 43%, respectively, of the total DOC
adsorbing to the goethite hydroxyl sites, which was expected (Hassan et al 2006). Due to
the HPOA composition described by others as containing mostly carboxylic acids,
phenolic, and aromatic carbon functional groups (Kaiser 2003), HPOA was expected to
have the greatest adsorption capability amongst the fraction solutions. However, both
HPOA solutions lacked the expected adsorption potential, both adsorbing less than the
HPIA fraction (Table 4.9). The HPIA solutions were expected to adsorb as strong as the
HPOA solutions (Benjamin et al 1993) in spite of its presumed composition of more
aliphatic and less aromatic carbon functional groups (Kanokkantapong et al 2006a).
HPIA and HPON fractions adsorbed the most, while the HPIN fraction adsorbed the
least. The DOC in the MIX solutions was expected to adsorb better than what was
observed based on individual fraction performance. While all fractions are found in the
Raw water, and DOC adsorption was greater than 40% for both raw waters, the DOC
sites were unaltered by fractionation. Reasons why Raw water had greater adsorption
than the MIX solutions are vast and not fully known. However, after individual fractions
performed reasonably well with adsorption, mixing them together significantly decreased
DOC sites able to adsorb. This suggests that when NOM fractions are not competing for
goethite hydroxyl sites, as when they are mixed together, additional DOC sites are a
available for adsorbing.
49
Table 4.8
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
Percent DOC Adsorbed.
1
34
11
12
14
7.8
2.1
2
43
12
11
12
8.1
5.7
3
40
5.9
13
24
7.4
12
4
41
5.6
19
13
8.1
11
5
45
11
14
38
7.1
13
6
45
11
15
34
6.4
6.1
Raw-2
28
36
38
38
43
41
HPOA-2
5.6
15
14
16
19
15
HPIA-2
15
25
28
31
29
32
HPON-2
12
20
4.2
14
4.8
0.0
HPIN-2
9.2
6.9
4.6
4.9
0.3
0.7
MIX-2
8.4
5.1
8.8
5.8
11
10
Note: Percents based on aqueous solution DOC concentrations. [(AQ-GOE)/AQ*100]
50
4.0
1 g/L
2 g/L
SUVA
DOC Adsorbed (%)
40
3.5
3.0
30
2.5
20
2.0
10
1.5
0
1.0
Raw-1
Figure 4.1
SUVA (L m-1 mg-1)
50
HPOA-1 HPIA-1 HPON-1 HPIN-1
MIX-1
Percent DOC adsorbed for 1 and 2 g/L goethite of 1-30-07 solutions.
51
4.0
3.5
3.0
30
-1
DOC Adsorbed (%)
40
-1
1 g/L
2 g/L
SUVA
SUVA (L m mg )
50
2.5
20
2.0
10
1.5
0
1.0
Raw-2
Figure 4.2
HPOA-2 HPIA-2 HPON-2 HPIN-2
MIX-2
Percent DOC adsorbed for 1 and 2 g/L goethite of 3-28-07 solutions.
52
Raw-1
HPOA-1
50
HPIN-1
MIX-1
HPON-1
HPIA-1
DOC Adsorbed (%)
40
30
20
10
0
1
2
3
4
Goethite (g/L)
Figure 4.3
Percent DOC adsorbed of 1-30-07 solutions.
53
5
6
Raw-2
HPOA-2
50
HPIN-2
MIX-2
HPON-2
HPIA-2
DOC Adsorbed (%)
40
30
20
10
0
1
2
3
4
Goethite (g/L)
Figure 4.4
Percent DOC adsorbed of 3-28-07 solutions.
54
5
6
Table 4.9
Maximum Percent DOC Adsorbed.
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
Mass Adsorbed
Max Absorbed
SUVA
(mg)
0.178
0.048
0.072
0.145
0.029
0.047
(%)
45
12
19
38
8
13
(L m-1 mg-1)
3.1
2.8
1.8
1.2
1.3
1.9
43
19
32
20
9
11
3.4
3.5
3.2
1.4
2.0
2.6
Raw-2
0.168
HPOA-2
0.075
HPIA-2
0.124
HPON-2
0.081
HPIN-2
0.036
MIX-2
0.037
Note: The SUVA reported is before adsorption.
55
4.3
Chlorine Demand
One of the most insightful parameters for characterizing water is chlorine
demand, which indicates how reactive NOM components are in water (Table 4.10).
When coupled with disinfection by-product (DBP) formation, chlorine demand can be a
sign of the efficiency of chlorine to produce DBPs. DBPs are always formed when
chlorine oxidizes NOM; however, most of the DBPs formed are not part of the regulated
HAA5 or THM4. Therefore, the chlorine demand is as crucial of information as the DBP
production. The chlorine demands of the four fractions in aqueous solution were
significantly different and varied with increasing concentrations of goethite. With the
exception of the HPIN fraction and HPOA-1, chlorine consumption increased in the
presence of goethite (Table 4.11). Studies of chlorine decay in distribution systems have
shown that wall decay rates caused by iron oxides are up to an order of magnitude larger
than bulk water rates (Rossman et al 2006).
One of the most understudied parameters of operationally defined fractions is
their chlorine demand. Most authors strictly study the disinfection by-product formation
potential (DBPFP) of the six fractions while maintaining the chlorine residual above a
certain value, usually 3-5 mg/L as Cl2 (Kanokkantapong et al 2006c). Dosing DOC with
extremely high concentrations of chlorine and reacting 7 days is widely accepted as the
proper method to finding the full DBPFP of water. However, the long reaction time and
greater kinetic rates expected from a high chlorine dose can mislead researchers when
trying to understand how water responds through a treatment and distribution process.
Though an initial chlorine dose of 9.0 mg/L is still large, it better simulates actual
56
treatment conditions along with the shorter reaction time of 48 hours instead of the
alternative 7-day DBPFP test.
The aqueous only (no goethite) chlorine demands of the four DOC fractions were
different (Table 4.10). While the Raw solution’s had large chlorine demands, some
fractions had larger, specifically the HPIN-1, HPIN-2 and HPIA-2 solutions. HPIN-1
and HPIN-2 solutions had the largest demands (1.9 and 2.7 mgCl2/mgC) while their
SUVA values were amongst the lowest (1.3 and 2.0 L m-1 mg-1). This agrees with Croue
et al (2000b) who discovered that out of the HPOA, HPON, HPIA, and HPIN fractions,
the HPIN had the highest chlorine demand (1.0 mgCl2/mgC) while also the lowest SUVA
value (0.5 L m-1 mg-1). This data was gathered with a 4 to 7 mg/L as Cl2, using a ratio of
4 mgCl2 to 1 mg DOC with a contact time of 3 days. If the chlorine demand is divided
by SUVA, a quick comparison can be made about how chlorine reactivity correlates to
SUVA (Table 4.10). The HPIN fraction from Croue et al had a Cl2 demand per SUVA of
2.0, while HPIN-1 and HPIN-2 have values of 1.46 and 1.35, respectively. These ratios
are significantly higher than any other solutions treated for both days.
While the HPIN solutions had the highest chlorine demand for both days, the
HPOA-1, HPIA-1 and HPON-1 solutions exhibited similar Cl2 demands to each other
with values between 1.0 and 1.3 mgCl2/mgC. The HPOA-2 and HPON-2 were again
similar to each other at 1.3 and 0.9 mgCl2/mgC, though the HPIA-2 was much higher at
2.2 mgCl2/mgC. In addition, the HPIA-2 and HPIN-2 chlorine demands were much
larger than their HPIA-1 and HPIN-1 counterparts. Chlorine demands for the HPOA
solutions for both days were identical, while the HPON-2 solution slightly decreased
compared to HPON-1. HPIA-2 and HPIN-2 chlorine demands increased 120 and 42%,
57
respectively, compared to HPIA-1 and HPIN-1. This was interesting since Raw-2
chlorine demand increased approximately 40% compared to Raw-1. Since only the
HPIA-2 and HPIN-2 exhibited an increase over their Raw-1 counterparts, they should
account for the 40% increase in Cl2 demand exhibited by Raw-2 versus Raw-1. The
SUVA values also increased for these two hydrophilic fractions. This would suggest that
the higher aromatic content caused this significant increase; however HPOA-2 SUVA
increased while its chlorine demand remained the same as HPOA-1. SUVA was not a
good indicator for chlorine demand, resulting in an R-squared value of 0.12, though the
slope was positive indicating that higher SUVA produced higher chlorine demands.
(Figure 4.5).
In regards to DOC fraction composition in the Raw waters, Raw-2 contained
larger amounts HPIA (8%), which could explain the increase in chlorine demand,
however, Raw-2 decreased in HPIN (11%) compared to Raw-1. HPIA-2 appeared to be
the most unusual since it only contributed 3% of Raw-2’s UV254 absorbance (Table 4.5)
and yet demonstrated a SUVA of 3.2 (L m-1 mg-1) which was the second highest out of
the four fraction solutions (Table 4.10). In addition, DOC adsorption was the greatest for
HPIA-2 at 32% for 3-28-07 fraction solutions (Table 4.9). It is worth noting that the four
NOM fractions maintained identical SUVA rankings amongst themselves from 1-30-07
to 3-28-07 solutions; however, all four fractions increased in SUVA for 3-28-07 water.
The SUVA ranking from highest to lowest was HPOA, HPIA, HPIN and HPON. The
rankings of DOC adsorbed were not as consistent as the rankings for SUVA, except that
HPIN always adsorbed the least.
58
One of the reasons to evaluate how DOC adsorption and SUVA effects chlorine
demand is because of previous conclusions (Hassan et al 2006, Li et al 2000). The
increase in percent DOC adsorbed with HPOA-2 and HPIA-2 was 7% and 13%,
respectively, when compared to their counterparts HPOA-1 and HPIA-1. Also, HPIA-2
increased the most in SUVA among the other fractions. In return, chlorine demands
significantly increased for HPOA-2, though HPIA-2 was the same as HPIA-1. This
indicates that chlorine demand is not directly correlated to the SUVA, but rather the DOC
fraction. DOC adsorption decreased for HPON-2 by 18% compared to HPON-1, while
its chlorine demand and SUVA values were similar. The HPON solutions did not show
large chlorine demands, though percent DOC adsorbed was amongst the highest with the
lowest SUVA values. Therefore, HPON would disprove the assumptions that greater
SUVA increases DOC adsorption, though adsorption increasing chlorine consumption
would still be viable. Lastly, the HPIN solutions had the greatest chlorine demand but
lowest percent DOC adsorbed with nearly the lowest SUVA values. While HPIN had the
greatest chlorine demand, less chlorine was used in the presence of goethite compared to
HPIN aqueous tests.
One reason to evaluate a MIX solution containing the four major fractions was to
determine if it behaved the same as raw water from which they originated.
Panyapinyopol et al (2005b) mixed all six fractions back to their individual DOC
concentrations in the raw water. They determined that the raw water had a chlorine
demand of 9 mg/L while the mixed fractions had only a 6 mg/L. Furthermore, they
chlorinated the six individual fractions at their original DOC concentrations and
discovered that the summation of the six individual chlorine demands equated to 7.3
59
mg/L used. The chlorine demand of MIX-1 and MIX-2 were slightly greater than Raw-1
and Raw-2, respectively. Hypothetically, if the four individual fractions each contributed
25% of the MIX solutions’ chlorine demand, then MIX-1 and MIX-2 would have
expected chlorine demands of 1.3 and 1.8 mgCl2/mgC, with the actual values being 1.7
and 2.3, respectively. These data suggest that more chlorine reactive sites are contained
in Raw-2 than in Raw-1, thus reactivity carried through the fractionating procedure with
minimal destruction.
According to Hassan et al (2006), the agglomeration of DOC molecules that have
adsorbed to goethite become rearranged from the effects of the goethite so that DOC
molecules may attach to hydroxyl sites. Essentially, DOC is a complex mixture of
different carbon functional groups. This complex mixture contains carbon groups which
would prefer to bond more than other functional groups (e.g. those present in HPOA and
HPIA) to the hydroxyl sites on the goethite. When these functional groups are
surrounded by other non-bonding carbon moieties, the goethite acts as a magnet and
repositions the agglomeration of carbon moieties until the bonding of a carbon group
occurs. This repositioning of molecules to allow for adsorption may expose additional
functional groups and allow for greater oxidation. This is possibly why greater DOC
adsorption occurred in non-fractionated raw water, since the conglomerations of NOM
molecules are tightly bonded and not broken apart as they would be after fractionating.
Chlorine decay rates in distribution systems have been extensively studied and the
results indicate that the iron oxides present in the pipes increase the chlorine consumption
(Rossman et al 2001, Bower 2003). As goethite concentrations increased for Raw-1 and
Raw-2 the chlorine consumption increased up to 41 and 21% compared to the aqueous,
60
respectively (Figure 4.6 and 4.7). Raw-1 and Raw-2 increases in chlorine consumption
agree with other studies (Hassan 2005, Bower 2003, Rossman et al 2001). However, the
DOC fraction’s chlorine consumption varied with goethite exposure. The HPOA fraction
contains greater amounts of aromatic carbon functional groups causing more adsorption
(Benjamin et al 1993) and would be expected to decay more chlorine with increased
goethite concentrations due to its large SUVA value. However, HPOA-1 and HPOA-2
aqueous chlorine demands were identical even though the chlorine consumed by 6 g/L
goethite in HPOA-2 was 33% greater than HPOA-1 (Table 4.11).
The other fraction proven to adsorb to goethite readily (Benjamin et al 1993) is
the HPIA fraction. HPIA-1 chlorine consumption behaved the same as HPOA-1,
showing less chlorine consumed than the aqueous at 3 g/L goethite and then reaching
approximately the same chlorine consumed as the aqueous by 6 g/L goethite. Just as
HPOA-2, HPIA-2 increased steadily from 1-6 g/L goethite consuming up to 13% more
chlorine by 6 g/L compared to the HPIA-2 aqueous solution. In contrast to the HPOA
and HPIA fractions, chlorine consumption for HPON-1 and HPON-2 consistently
increased up to 27 and 20%, respectively, by 6 g/L goethite compared to the aqueous.
Neither the HPIN-1 nor the HPIN-2 had an increase in chlorine demand in the presence
of goethite (Table 4.11). All in all, goethite proved to increase chlorine demand through
the increasing goethite concentrations (Figure 4.8).
In conclusion, the DOC adsorption for HPOA-1 and HPOA-2 were similar,
though chlorine consumption in HPOA-2 was 33% more consumption than HPOA-1
through increasing goethite exposure. On the other hand, chlorine consumption for
HPIA-1 and HPIA-2 was similar even though DOC adsorption increased significantly for
61
HPIA-2. The HPON solutions exhibited similar chlorine consumption and DOC
adsorption throughout increasing goethite exposure. Aqueous chlorine demand was
greatest in the HPIN fraction, though this fraction demonstrated the least susceptibility to
DOC adsorption and increase in chlorine demand in the presence of goethite. In addition,
the four fraction solutions maintained identical SUVA rankings amongst themselves from
1-30-07 to 3-28-07 solutions; however, all four fractions increased in SUVA for 3-28-07
water. The SUVA ranking from highest to lowest was HPOA, HPIA, HPIN and HPON.
While SUVA increased the greatest in HPIA-2 by 78% compared to HPIA-1, DOC
adsorption also increased in HPIA-2 while chlorine demands with goethite were similar.
In contrast, SUVA increased 25% in HPOA-2 compared to HPOA-1, and though DOC
adsorption was similar, the chlorine demand increased by 33% throughout increasing
goethite exposure. Likewise, the SUVA for HPIN-2 increased 53% compared to HPIN1, though neither the DOC adsorption nor chlorine consumption changed in the presence
of goethite. Lastly, the SUVA increase in HPON-2 was only 16%, as both HPON
solutions exhibited similar DOC adsorption and chlorine consumption throughout
goethite exposure. These data suggest that neither DOC adsorption nor SUVA values can
predict chlorine consumption in the presence of goethite. Instead, operational DOC
fractions have their own unique responses to goethite.
62
Table 4.10
Chlorine Demands.
Chlorine
Beginning
Demand
DOC
SUVA
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
(mgCl2/mgC)
1.5
1.3
1.0
1.1
1.9
1.7
(mg/L)
3.10
3.23
3.03
3.04
2.83
2.80
-1
(L m mg )
3.1
2.8
1.8
1.2
1.3
1.9
SUVA
0.49
0.46
0.58
0.91
1.46
0.87
Raw-2
HPOA-2
HPIA-2
HPON-2
HPIN-2
MIX-2
2.1
1.3
2.2
0.9
2.7
2.3
3.09
3.04
3.09
3.13
3.04
2.74
3.4
3.5
3.2
1.4
2.0
2.6
0.62
0.37
0.71
0.64
1.35
0.88
63
Cl2 Demand /
-1
0.14
HPIN-2
Cl2 Consumed (uM)
0.12
HPIA-2
0.10
MIX-2
0.08
HPIN-1
0.06
HPON-1
0.04
Raw-2
MIX-1
Raw-1
HPOA-1
HPIA-1
HPOA-2
HPON-2
0.02
r ² = 0.12
0.00
1.0
1.5
2.0
2.5
3.0
-1
-1
SUVA (L m mg )
Figure 4.5
Chlorine consumption versus SUVA254.
64
3.5
4.0
Raw-1
HPOA-1
3.0
HPIN-1
MIX-1
HPON-1
HPIA-1
Cl2 Consumed (mg/mgDOC)
2.5
2.0
1.5
1.0
0.5
0.0
0
1
2
3
4
5
Goethite (g/L)
Figure 4.6
Chlorine consumed of increasing goethite concentrations.
65
6
Raw-2
HPOA-2
3.0
HPIN-2
MIX-2
HPON-2
HPIA-2
Cl2 Consumed (mg/mgDOC)
2.5
2.0
1.5
1.0
0.5
0.0
0
1
2
3
4
5
Goethite (g/L)
Figure 4.7
Chlorine consumed of increasing goethite concentrations.
66
6
Table 4.11
Chlorine Percent Increases from 1 – 6 g/L Goethite.
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
1
17
-8
-7
2
2
0
2
16
-19
-1
12
5
-4
3
23
-14
-3
12
-9
2
4
34
-14
5
15
-9
13
5
38
-5
14
19
-8
6
6
42
1
8
28
-7
9
Raw-2
10
15
19
23
27
28
HPOA-2
13
19
22
25
30
33
HPIA-2
3
9
8
10
13
13
HPON-2
4
0
11
6
20
20
HPIN-2
-6
-7
-5
-6
-6
-17
MIX-2
-2
3
1
5
9
13
Note: 1) Positive values represent an increase in chlorine consumption compared to
aqueous and vise versa.
67
Aqueous Cl2 Consumed per mg DOC (uM/mgDOC)
350
300
250
200
150
100
50
50
100
150
200
250
300
Goethite Cl2 Consumed per mg DOC (uM/mgDOC)
Figure 4.8
Aqueous chlorine demand versus goethite chlorine demand.
68
350
4.4
DBP Formation of Aqueous Solutions
The quantity of disinfection by-products (DBPs) formed during chlorination of
DOC can vary depending on the amount of NOM in solution. Correlations of higher
SUVA waters producing higher THMs, specifically chloroform, have been reported,
suggesting that fractions containing aromatic carbon moieties would exhibit higher
THMs (Chow et al 2005). The reactivity and potency of DOC to form DBPs by
examining ugDBP/mgDOC produced is also a critical aspect revered by researchers to be
the reason for fractionating raw water into fractions (Kanokkantapong et al 2006a,
Kanokkantapong et al 2006b, Kitis et al 2002). Certain DOC fractions have been
reported as having a higher formation potential for different species of DBPs such as
chloroform, trichloroacetic acid (TCAA), and dichloroacetic acid (DCAA) (Croue et al
2000b). Though these three species of DBPs are usually the major components of total
DBPs found in treated water, total brominated and non-brominated DBP species can also
be insightful. The reason for testing DOC fractions and their reactivity to chlorine
producing DBPs is so these fractions may be targeted for removal through treatment
facilities, thus reducing DBPs that reach consumers.
A method used for evaluating DBP production is to divide the weight of DBPs
produced by the weight of DOC present during chlorination (ugDBP/mgC). While the
target DOC concentration of each solution was 3.0 mg/L, slight variances between
solutions can be misleading when examining the DBP formation potentials using strictly
ppb. An additional approach to determine reactivity of DOC fractions is to examine DBP
production that is normalized to the amount of free chlorine consumed (ugDBP/mgCl2).
69
This simplistic approach allows for magnification of DBP production that came about
with either more or less chlorine demand. To further examine which species of DBPs are
favorably formed from individual fractions, the three main species (chloroform, TCAA,
and DCAA) of DBPs were examined closely using these normalized methods. Standard
deviations for chloroform, TCAA, and DCAA were 5, 1 and 3 ppb, respectively. This
means that a change in chloroform more than 5 ppb between samples was considered a
measurable change. All solutions reported herein were tested at the same chlorine dosage
(9.0 mg/L), starting pH (8.0 ± 0.1), temperature (20ºC), reaction time (48-hour), and
DOC concentrations (~3.0 mg/L). Therefore, discussion of each solutions’ (Table 4.1)
DBP formation is easier with respect to the kinetics of chlorine consumption producing
DBPs.
4.4.1 DBP Formation
Preliminary studies of raw waters and the preliminary fractions indicated that raw
water containing all six DOC fractions would produce the largest quantity of DBPs. This
was confirmed by Raw-1 and Raw-2 producing 241 and 283 ppb, which are the largest
quantities of DBPs produced of any of the solutions (Table 4.12). Among the NOM
fractions, HPON-1 and HPON-2 stood apart as producing significantly less DBPs with
values of 106 and 124 ppb, respectively. HPOA and HPIA solutions produced similar
amounts of DBPs for both days, while HPIN-1 and HPIN-2 fractions produced the most
DBPs of all the NOM fractions, with values of 200 and 248 ppb, respectively.
The conclusions about the DBPs (ppb) produced compared to when they were
normalized by the DOC mass are identical. Interestingly, when the solutions were
70
normalized to the amount of chlorine they consumed, different conclusions are made
about their ability to produce DBPs. Raw-1 and Raw-2 are no longer the largest
producers of DBPs when normalized with chlorine consumption. Instead, DBP
formation (ug/mgCl2) in HPIA-1 was greater then Raw-1 while HPOA-2 and HPON-2
had greater formation than Raw-2 (Table 4.14). Analysis based on chlorine consumption
reveals that HPIA-1, HPOA-2 and HPON-2 contain NOM sites that were easier to
oxidize and form DBPs than even the Raw water.
4.4.2 TTHM Formation
While more HAA5 (ppb) was formed than TTHM (ppb) in 1-30-07 solutions, the
opposite was true for 3-28-07 solutions. THM (ppb) formation was greatest in the
HPOA, HPIA, and HPIN solutions for both days, while with the HPON significantly less
THM was produced (Table 4.12). This was the same conclusion when normalized by
their DOC mass (Table 4.13). This agrees with Panyapinyopol et al (2005a) who
concluded that HPON was the least problematic in forming THMs. Also, they concluded
that HPON was relatively inactive to chlorine reactions. However, HPOA-2 and HPON2 had the largest TTHM (ug/mgCl2) formation. Though HPIA-1 was similar to HPOA-1
with values of 22 and 19 ug/mgCl2, respectively, these values were significantly less than
the HPOA-2 and HPON-2 THM values, both at ~33 ug/mgCl2. These increased TTHM
(ug/mgCl2) values for HPOA-2 and HPON-2, compared to their counterparts HPOA-1
and HPON-1, were unusual since the typical level of TTHM (ug/mgCl2) was
approximately 19 ± 3 for 1-30-07 water, but was 33 ± 1 for 3-28-07 water (Table 4.14).
71
This may have been caused by an increase in available TTHM sites in Raw-2 and that
these TTHM sites are mainly contained in the hydrophobic fractions.
Raw-1 and Raw-2 produced nearly the greatest yields of chloroform with values
of 82 and 110 ppb, (Table 4.12) and yields per carbon of 27 and 36 ug/mgC, respectively
(Table 4.13). The only solution to produce more chloroform than a Raw solution was
HPOA-2 at 126 ppb, 42 ug/mgC. Both HPOA solutions exhibited greater yields of
chloroform than any other fraction (Table 4.13). The large production of chloroform
from HPOA and Raw solutions was expected because of their large SUVA254 values
ranging from 2.8 to 3.5 L m-1 mg-1 which were the largest SUVA values. The production
of chloroform from the HPOA fraction (ug/mgC) was followed by the HPIA, HPON, and
HPIN fractions, which all demonstrated similar values to each other. One exception was
HPIN-2 producing only 21 ugCHCl3/mgC, which was significantly less than all other 328-07 solutions. However, this was accompanied by all 3-28-07 solutions significantly
increasing in chloroform production in comparison to 1-30-07 solutions. The 34%
chloroform increase in Raw-2 was consistent with HPOA-2, HPIA-2 and HPON-2
chloroform production increasing between 65 – 74%, compared to 1-30-07 solutions.
The HPIN-2 also increased in chloroform production, though this was only a 16%
increase. In conclusion, the HPOA solutions exhibited the greatest chloroform formation
potential amongst the fractions while the HPIN solutions were the least.
The concept that chloroform precursors are limited by reactive sites available to
react with chlorine to produce chloroform was difficult to conclude with MIX solution
results. Each MIX solution contained 25% mass of the HPOA, HPIA, HPON and HPIN
fractions. With this, a simple calculation can be made to represent a theoretical value.
72
Assuming that the four fractions each produced 25% of their individual formation
potentials when mixed together, MIX-1 and MIX-2 would have theoretically formed 17
and 26 ugCHCl3/mgC, respectively. The actual chloroform values for MIX-1 and MIX-2
were 22 and 27 ugCHCL3/mgC, respectively (Table 4.13). While MIX-2 is consistent
with this theory, MIX-1 produced more chloroform than expected. Panyapinyopol et al
(2005b) tested a mixture of all six DOC fractions and found that less chlorine was
consumed than the raw water at an identical DOC concentration. Also, less TTHMs were
produced than the sum of the six DOC fractions individually. While chlorine to carbon
ratios are kept constant throughout any DBP test performed on DOC fractions such as
these by Panyapinyopol et al (2005b), individual fractions still produced more. This
would suggest that mixed fractions do prohibit each other from producing greater
concentrations of DBPs.
When examining the chloroform produced per chlorine consumed, Raw-1 and
Raw-2 had nearly identical values of 17 and 18 ugCHCl3/mgCl2, respectively (Table
4.14). Producing the least, HPIN-1 and HPIN-2 had values of 9 and 8 ugCHCl3/mgCl2.
HPIN was expected to produce the least amount of chloroform because of its estimated
low aromatic content (Kitis 2002, Panyapinyopol et al 2005a). Not only did HPIN
produce the least amount of chloroform (ppb), but HPIN also consumed the most
chlorine, making its values even lower. On the other hand, HPOA was expected to have
a higher aromatic content and thus produce more chloroform. While HPOA-1 produced
~40% (22 ppb) more chloroform than HPIA-1 and HPON-1, all three produced very
similar chloroform amounts per chlorine consumed. This shows that while HPOA-1 had
more chloroform precursors, HPIA-1 and HPON-1 produced equivalent chloroform per
73
chlorine consumed. While there were insignificant differences in chloroform formation
(ugCHCl3/mgCl2) for 1-30-07 solutions other than HPIN-1, the 3-28-07 solutions showed
significant increases. HPOA-2 and HPON-2 nearly doubled the chloroform produced
with values of 32 and 31 ug/mgCl2, respectively (Table 4.14). This suggests that
chloroform precursors are contained in the HPOA and HPON fractions, and perhaps the
increase in HPON DOC mass in Raw-2 increased its chloroform production.
One of the lesser but still significant contributors to TTHM was
bromodichloromethane (BDCM). Though this compound was only 15 and 20 ppb for
Raw-1 and Raw-2, respectively, these values doubled in HPIN-1 and HPIN-2. The HPIA
solutions also showed BDCM formation potential, with values the same as the
corresponding Raw solutions. Interestingly, neither of the hydrophobic solutions from
either day showed any signs of large BDCM formation potential with values barely above
2 ppb (Table 4.12). This may have been due to larger bromide concentrations in HPIA
and HPIN, though Panyapinyopol et al (2005a) reports that the majority of bromide was
removed in the HPIA fraction. They also report that HPIN had no BDCM formation
while HPIA produced more than any other fraction aside from HPOB and HPIB.
Nonetheless, bromide had to be present in order to produce BDCM, and free chlorine
(OCl-) in the presence of Br- is converted to OBr- with ease. A higher level of Br- in the
HPIN solutions caused the greater chlorine demand and greater brominated compounds
(Ates et al 2007). Though the Br- should have been removed with the HPIA, anion
exchange, it apparently was not since the brominated DBPs must have Br- in order to
form. Since the WA-10 anionic resin used was specifically for organic removal, the resin
may have allowed the Br- ion to pass through with little to no Br- adsorption. Greater
74
brominated DBPs were observed in the HPIN fraction than any of the fractions,
suggesting that this fraction contained a greater Br- concentration.
Though SUVA was not necessarily a good indicator for chlorine decay, SUVA
was a very good indicator for THM production. The correlation between TTHM
formation and SUVA has an R-squared value of 0.57 (Figure 4.9). Trihalomethanes
(THMs) have been correlated with specific ultraviolet absorbance (SUVA) at 254 nm.
Chow (2006) correlated the TTHMFP and SUVA and found the relationship to be R2 =
0.38. This suggests that more aromatic DOC fractions would lead to more TTHM
production, as was observed in the HPOA and HPON fractions. Though HPOA had
considerable TTHM production, HPIA and HPIN fractions were comparable to HPOA
(Table 4.12).
4.4.3 HAA5 Formation
Raw-1 and Raw-2 have the greatest HAA5 formation potential at 46 and 49
ug/mgC, respectively (Table 4.13) among the solutions. Even when normalized to the
chlorine consumed, the Raw solutions exhibited significantly higher HAA5 values than
the other fraction solutions. The one exception to this was HPIA-1 at 82
(ugHAA5/mgCl2)/mgC, while Raw-1 produced 77 (ugHAA5/mgCl2)/mgC. Though
Raw-1 produced 43 ppb more of HAA5 than HPIA-1, less chlorine was used by HPIA-1,
indicating that HAA precursors were more readily available than any other solution. The
lowest formation of HAA5 came from HPON-1 and HPON-2 with values of 18 and 11
ug/mgC, respectively. Even when the HPON solutions were normalized to the chlorine
consumed, they exhibited the lowest formation. This agrees with Croue et al (2000b)
75
who concluded that among the HPOA, HPIA, HPON and HPIN fractions, the HPON
produced the least amount of HAAs. This HAA from Croue et al. was the summation of
TCAA and DCAA only. They also reported HPON as having the least reactivity with
chlorine to produce HAAs at 33 ugHAA/mgCl2. However, HPON was comparable to
the HPIN fraction at 34 ugHAA/mgCl2 (Croue et al 2000b). This was similar for the
HPON-2 and HPIN-2 with values of 12 and 14 ugHAA/mgCl2, respectively (Table 4.14).
The TCAA formation from all the solutions showed less mass production than
chloroform and DCAA. While TCAA was not formed in large quantities, there were
large variations between the fractions. The Raw solutions produced significantly more
TCAA than any other solution. The HPOA and HPIA fractions produced the next largest
amount of TCAA. The HPIN fractions were significantly lower than HPOA and HPIA,
with the HPON demonstrating the least ability to produce TCAA when normalized to the
mass of DOC (Table 4.13). Though DCAA was more consistent and produced greater
amounts than TCAA, DCAA was nearly identical for all fraction solutions. Ranging
between 5.2 and 16 ugDCAA/mgC, the fraction solutions never produced more DCAA
than the Raw solution. However, when normalized to the chlorine consumed, the HPOA1 and HPIA-1 demonstrated comparable efficiency to produce DCAA to Raw-1. Croue
et al (2000) found that more TCAA was formed in the HPOA and HPIA with nearly
identical values of 24 – 28 ug/mgC than the HPON and HPIN fractions with values
between 15 – 16 ug/mgC.
Kanokkantapong et al (2006a) conducted chlorination tests on mixed fractions
and at varying concentrations and concluded that less HAAs were formed when fractions
were mixed together than individually. This was different than MIX-1 and MIX-2 when
76
compared to the individual fraction formation potentials. Assuming that the four
fractions each produced 25% of their individual formation potentials when mixed
together, MIX-1 and MIX-2 would have theoretically formed 30 and 26 ugHAA5/mgC,
with actual values of 24 and 32 ugHAA5/mgC, respectively (Table 4.13).
Table 4.12
DBP Production (ppb).
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
TTHM
98
79
72
52
86
87
HAA5
143
94
100
54
114
66
DBP
241
173
172
106
200
153
CHCl3
82
77
55
50
51
70
BDCM
15
2.2
14
1.7
27
16
TCAA
54
40
29
10
19
16
DCAA
52
40
36
27
39
25
Raw-2
HPOA-2
HPIA-2
HPON-2
HPIN-2
MIX-2
132
128
121
90
136
110
151
75
101
34
112
88
283
203
222
124
248
198
110
126
93
89
65
85
20
2.2
25
1.2
52
22
51
18
23
4.3
13
22
70
37
49
16
31
41
77
Table 4.13
DBP Production per DOC Mass (ug/mgC).
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
TTHM
32
24
24
17
30
31
HAA5
46
29
33
18
40
24
DBP
78
53
57
35
71
55
CHCl3
27
24
18
16
18
25
BDCM
4.8
0.7
4.7
0.6
10
5.5
TCAA
18
12
10
3.3
6.7
5.7
DCAA
17
12
12
9.0
14
9.0
Raw-2
HPOA-2
HPIA-2
HPON-2
HPIN-2
MIX-2
43
42
39
29
45
40
49
25
33
11
37
32
91
67
72
39
81
72
36
42
30
28
21
31
6.5
0.7
7.9
0.4
17
8.1
16
6.1
7.5
1.4
4.4
8.0
23
12
16
5.2
10
15
Table 4.14
DBP Production per Chlorine Consumed (ug/mgCl2).
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
TTHM
21
19
22
16
16
19
HAA5
31
22
32
16
21
14
DBP
51
41
54
32
37
33
CHCl3
18
18
17
15
9
15
BDCM
7
5
7
4
5
4
TCAA
12
9
9
3
3
3
DCAA
11
10
11
8
7
5
Raw-2
HPOA-2
HPIA-2
HPON-2
HPIN-2
MIX-2
20
33
18
32
17
18
23
19
15
12
14
14
43
52
32
44
30
32
17
32
13
31
8
14
5
7
4
6
4
4
8
5
3
2
2
4
11
9
7
6
4
7
78
1.2
HPOA-2
Raw-2
1.0
HPIN-2
MIX-2
TTHM (uM)
0.8
HPIA-2
HPON-2
Raw-1
MIX-1
0.6
HPIN-1
0.4
HPOA-1
HPIA-1
HPON-1
0.2
r² = 0.57
0.0
1.0
1.5
2.0
2.5
SUVA (L m-1 mg-1)
Figure 4.9
TTHM versus SUVA regression.
79
3.0
3.5
4.0
1.2
1.0
HPIN-1
Raw-1
HPIA-1
0.8
HAA5 (uM)
Raw-2
HPIN-2
0.6
HPIA-2
MIX-2
HPOA-1
MIX-1
HPOA-2
HPON-1
0.4
HPON-2
0.2
r ² = 0.17
0.0
1.0
1.5
2.0
2.5
SUVA (L m-1 mg-1)
Figure 4.10
HAA5 versus SUVA regression.
80
3.0
3.5
4.0
In comparing hydrophobic and hydrophilic DOC fractions, DBP production was
significantly greater in the hydrophilic fractions (Table 4.15). Also, the hydrophilic
fractions had greater TTHM and HAA5 formation potentials; however, the hydrophobic
fractions had greater chloroform production. The hydrophobic carbon was also more
efficient in producing chloroform when interpreted on a chlorine consumed basis, though
hydrophilic carbon consistently produced more DCAA (Table 4.15). Interestingly, when
the hydrophilic and hydrophobic carbon were normalized to the chlorine consumed, the
hydrophilic was more effective in producing HAA5 for 1-30-07 fractions (Table 4.16).
However, the 3-28-07 hydrophilic carbon efficiency to produce HAA5 was very similar
to the hydrophobic carbon. Hydrophobic carbon for 3-28-07 solutions were very
effective in producing TTHMs (ug/mgCl2). This indicated that precursors may transform
and change by the season and even by the month. Pu (2005) tested THM formation
potential of raw water in December and August of 2003. Changes in THM formation
(ugTHM/mgC) from August to December 2003 of the HPOA (-108), HPIA (8), HPON (21), and HPIN (-59) fractions would be considered substantially different (Pu 2005).
When comparing acid and neutral fractions, insignificant differences were seen
with the few exceptions. The acid fractions did produce greater levels of chloroform and
TCAA when interpreted on a carbon basis (Table 4.15). When Croue et al (2000)
summed the acids and neutral DOC fraction chloroform (ug/mgC) formation potentials
together, the acids produced 81 while the neutrals had 57 ug/mgC. For TCAA formation
(ug/mgC), the acids they reported formed 52 and the neutrals had 31 ug/mgC, though
both the acid and neutral fractions produced similar DCAA with values between 30 and
31 ug/mgC (Croue et al 2000).
81
In conclusion, HPIN produced the greatest amount of DBP, TTHM, and HAA5
among the DOC fractions on a per mg of carbon basis. HPIN produced more DBPs
overall because of formation of DBP species other than chloroform, TCAA, and DCAA.
DBP, TTHM, and HAA5 production was similar for HPOA and HPIA fractions while the
least was produced in the HPON fraction. HPOA produced the greatest amount of
chloroform where as HPOA and HPIA had the greatest TCAA production, though DCAA
was similar among all fractions except for HPON with the least.
82
Table 4.15
DBP Production per DOC Mass (ug/mgC) of Hydrophobic Versus
Hydrophilic and Acid Versus Neutral Fractions.
1/30/2007
Hydrophobic
Hydrophilic
3/28/2007
Hydrophobic
Hydrophilic
1/30/2007
Acid
Neutral
3/28/2007
Acid
Neutral
Table 4.16
TTHM
HAA5
DBP
CHCl3
TCAA
DCAA
41
54
47
73
88
127
40
36
16
16
21
26
71
84
35
70
106
154
70
51
7
12
17
26
48
47
62
58
110
105
42
34
22
10
24
23
81
73
57
48
139
121
72
50
14
6
28
15
DBP Production per Chlorine Consumed (ug/mgCl2) of Hydrophobic
Versus Hydrophilic and Acid Versus Neutral Fractions.
1/30/2007
Hydrophobic
Hydrophilic
3/28/2007
Hydrophobic
Hydrophilic
1/30/2007
Acid
Neutral
3/28/2007
Acid
Neutral
TTHM
HAA5
DBP
CHCl3
TCAA
DCAA
35
38
39
53
73
91
34
27
13
13
18
18
65
34
31
28
96
62
64
21
6
5
15
11
41
32
54
37
95
69
36
25
19
7
21
16
50
48
34
26
84
74
46
39
8
3
17
9
83
4.5
DBP Formation with Goethite
As treated water flows through a distribution system it reacts with chlorine in the
bulk flow and at the pipe-water interface to produce DBPs (Rossman 2001). DBP levels
at the extremities of distribution systems suggest that THMs continually increase as long
as chlorine is present; however, HAAs fluctuate at the higher residence times (Rodriguez
et al 2005, Williams et al 1996). When NOM adsorbs to goethite, the electrophoresis
from the hydroxyl sites, shear some carbon groups not involved in adsorptive
interactions, outward and into the bulk solution (Tipping et al 1982). This would suggest
that rearrangement of NOM molecules is what causes an increase in chlorine demand and
DBPs. While there was little change in HAA formation, chloroform and TTHMs
changed the most.
Rossman et al (2001) found that DCAA and chloroform were favored in a
simulated distribution system compared to a water only bottle test. Golden (2005)
concluded that chloroform significantly increased in the presence of goethite while
HAA5 did not. However, he pointed out that the decrease in TCAA and increase in
DCAA in the presence of goethite offset the total HAA5, thus appearing to be unchanged.
All of these tests which involve iron oxide and chlorine have greater chloroform
production and less TCAA than DCAA when compared to water-only. One of the main
reasons for an increase in chloroform and decrease in TCAA is the increased pH (Liang
and Singer 2003) associated with the addition of goethite (control tests).
The addition of powdered goethite may have increased fraction pHs to 9.3. The
Raw waters buffering capacity was much greater than the DI water based fractions
because of the naturally occurring carbonates in the Raw solutions. Though the Raw
84
solutions pH increased incrementally with increasing goethite concentrations, increases
were not as substantial. Nonetheless, all the NOM fractions had nearly identical
alkalinities and buffering capacity except for the DOC fraction’s contributions. All
solutions were adjusted to a beginning pH of 8.0 ± 0.1 and chlorinated at 9.0 mg/L. Also,
every solution had goethite added at incrementally increasing concentrations (1-6 g/L),
the goethite-water mixture equilibrated for 24 hours and then after 48-hour chlorine
exposure they were evaluated for THM4 and HAA5.
4.5.1 DBP Formation with 1 g/L Goethite
The exposure of 1 g/L goethite to each solution was to examine goethite’s effect
on the solution when limited hydroxyl sites were available. With only 1 g/L of goethite,
DOC adsorption is believed to be limited by the goethite and not the NOM molecules
(Bower 2003). TTHM production in Raw-1 and Raw-2 showed significant increases
compared to the aqueous test (no goethite), with increases of 25 and 19 ppb, respectively
(Table 4.17). This increase in TTHM was mainly caused by chloroform, which increased
23 and 19 ppb, respectively. The fraction solutions did not show this much of an
increase, except TTHM increased significantly in the HPON-1 and HPOA-2 solutions.
TTHMs increased 41 ppb or 32% in HPOA-2; and HPON-1 had an increase in TTHM of
15 ppb or 30% (Table 4.17). In the HPIN and MIX solutions, TTHM and chloroform
production did not increase any and even decreased.
With DOC adsorption of both Raw solutions significantly greater than any other
solution, they demonstrated the greatest increases in TTHM (Table 4.18). When coupled
with a 17 and 10% increase in chlorine consumed for Raw-1 and Raw-2, respectively, the
85
answer may seem evident. HPON-1 had 14% of DOC mass adsorb to the goethite
surface with a 15 ppb increase in chloroform. While HPON-1 only increased by ~2%
chlorine consumed, HPOA-2 increased by 13%. With HPOA-2 having merely 6% DOC
adsorption, this solution had a 41 ppb increase in chloroform, which was greater than
Raw-2 (Table 17). On the other hand, HPIN-1 and HPIN-2 demonstrated higher DOC
adsorption than HPOA-2, but lower chlorine consumption, while decreasing in TTHM
and chloroform formation (Table 4.18). With limited sites in only 1 g/L of goethite,
conclusions about DOC adsorption and chlorine consumption effecting DBP formation
are difficult.
The increase in HAA5 production for Raw-1 was 36 ppb while Raw-2 only had a
12 ppb increase (Table 4.17). Other than the Raw solutions, HPOA, HPIA, and the HPIN
solutions had consistent HAA5 increases for both days. Though most solutions increased
in TCAA and DCAA formation, changes were insignificant with changes of only a few
ppb. Even with the MIX solutions resembling the Raw in terms of DOC fraction content,
DBP formation in MIX-2 was only close to Raw-2 because of the lack of HAA5
formation in Raw-2. MIX-1 had no change at all in the presence of goethite while Raw-1
had a 36 ppb increase in HAA5 and 25 ppb increase in TTHM (Table 4.17).
86
Table 4.17
Percent DBP Increase at 1 g/L Goethite.
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
Chloroform
23 (28)
9 (12)
6 (10)
15 (30)
-2 (-5)
-2 (-3)
DCAA
20 (39)
2 (6)
1 (4)
1 (2)
-2 (-6)
-1 (-4)
TCAA
23 (42)
2 (5)
8 (27)
5 (48)
9 (46)
5 (31)
TTHM
25 (25)
9 (12)
7 (10)
15 (29)
-3 (-4)
-3 (-3)
HAA5
36 (25)
10 (10)
11 (11)
6 (11)
6 (6)
3 (5)
Raw-2
19 (17)
8 (11)
4 (8)
19 (14)
12 (8)
HPOA-2
41 (32)
2 (6)
5 (25)
41 (32)
6 (8)
HPIA-2
8 (9)
-2 (-4)
5 (21)
11 (9)
4 (4)
HPON-2
8 (9)
2 (11)
4 (87)
8 (9)
6 (17)
HPIN-2
-5 (-8)
-4 (-10)
4 (27)
-9 (-6)
-1 (<1)
MIX-2
3 (3)
-1 (-2)
7 (30)
4 (4)
7 (8)
Note: 1) Values represent an increase compared to the aqueous test [ppb (%)].
2) Positive values represent and increase, while negative represent a decrease.
Table 4.18
Solution Characteristics at 1 g/L Goethite.
DOC
Adsorbed
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
(%)
34
11
12
14
7.8
2.1
Aqueous
SUVA
Chlorine
Demand
(L m-1 mg-1) (mgCl2/mgC)
3.1
1.8
2.8
1.2
1.8
1.0
1.2
1.1
1.3
1.9
1.9
1.7
Chlorine
Demand
Increase
(%)
17
-8
-7
2
2
0
Raw-2
28
3.4
2.3
10
HPOA-2
5.6
3.5
1.4
13
HPIA-2
15
3.2
2.3
3
HPON-2
12
1.4
0.9
4
HPIN-2
9.2
2.0
2.5
-6
MIX-2
8.4
2.6
2.3
-2
Note: 1) Positive values represent and increase, while negative represent a decrease.
87
4.5.2 DBP Formation with 6 g/L Goethite
When discussing DBP formation in the presence of iron oxides whether in
distribution systems or laboratory batch tests, HAAs seem to vary while THMs steadily
increase in the presence of free chlorine (Bower 2003, Rossman et al 2001). While a
goethite concentration of 1 g/L limits NOM molecules to available hydroxyl reactive
sites, the 6 g/L is considered to be in excess. At the 6 g/L goethite concentration, every
NOM molecule that is able to interact with goethite is considered to have interacted and
changed. Whether this change is a physical reconstruction caused by adsorption or
shearing caused by electrophoresis of the NOM moieties, DBP production was changed
by the addition of goethite (γ-FeOOH).
The 6 g/L goethite demonstrated significant increases in DBP production. More
specifically, chloroform production for Raw-1 and Raw-2 increased by 50 and 44%,
respectively, compared to the aqueous test. The fraction solutions that demonstrated the
greatest chloroform increases were the HPOA and HPIA fractions. On the other hand,
chloroform formation in the HPON and HPIN fractions were significantly less among the
other fractions (Table 4.19). While the acid fractions were most influenced by the
goethite to increase chloroform, the hydrophilic fractions showed the greatest HAA5
increase (Table 4.19). Though HPIA-1 had a decrease in HAA5, HPIA-2 had a 24 ppb
increase caused by DCAA and TCAA. Also, HPIN-2 increased in HAA5 by 28 ppb with
only 10 ppb from DCAA and TCAA. This additional 18 ppb (28 – 10 ppb) was mainly
caused by MCAA, which has been reported to be difficult to analyze on a gas
chromatograph (McGuire et al 2002). Nonetheless, HAA5 varied extensively between
the solutions as well as between days making conclusion very difficult. However, it
88
should be noted that HPIA and HPIN consistently had greater MCAA and BDCM
formation than HPOA and HPON.
With excessive sites available to adsorb DOC in 6 g/L goethite, chlorine
consumption and DBP effects were more pronounced. Assuming from Raw solutions
that greater DOC adsorption induces greater chlorine consumption, thus producing
greater DBPs, there is evidence from fraction solutions that this was not the case. As
expected, Raw-1 and Raw-2 had 45 and 41% DOC adsorb followed by 42 and 28% more
chlorine consumed than aqueous tests, respectively (Table 4.20). To address the
assumption that adsorption increases chlorine consumption, attention is brought to HPIA2 with 32% adsorption and only a 13% increase in chlorine consumption. According to
Hassan (2005) the addition of goethite to deionized water and 100 uM of free chlorine,
the goethite proved to not have any significant chlorine demand. Therefore, any increase
in chlorine consumption caused by goethite was due to the DOC present. While there
remained an increase in chlorine consumed, HPOA-2 had only 15% DOC adsorb but a
33% increase in chlorine (Table 4.20). This may suggest that HPOA-2 was more reactive
with chlorine than HPIA-2 even with less adsorption. HPON-2 had virtually zero
adsorption yet chlorine consumption increased 20%.
Raw-1 and Raw-2 had the greatest increase in TTHMs at 43 and 36% and HAA5
at 13 and 11% increases. Raw-1 and Raw-2 DOC adsorption was also the greatest at 45
and 41% while Cl2 consumption was among the highest with 42 and 28% more Cl2
consumed than the aqueous test. The only fraction solution to increase in chlorine
consumption greater than Raw-2 was HPOA-2 at a 33% increase (Table 4.20). With
more chlorine consumed than Raw-2 and 15% DOC adsorption, HPOA-2 produced 18%
89
more TTHM than the aqueous test (Table 4.19). HPOA-1 data conflicted with this with
only 11% DOC adsorption and nearly zero percent increase in Cl2 consumption. The
greater TTHM increase of 29% does not follow the assumption that adsorption increases
Cl2 consumption, thus increasing TTHM. Though both HPOA solutions increased 23
ppb of TTHM, HPOA-2 produced more TTHM in the aqueous test than HPOA-1 solution
(Table 4.11). This would suggest that neither DOC adsorption nor chlorine consumption
interfered with goethite’s effect of producing more TTHMs. Furthermore, HPON-2 had
nearly zero adsorption yet a 20% increase in Cl2 consumption and failed to demonstrate
any increase in TTHM. Aside from adsorption and Cl2 consumption, certain fractions
(i.e. HPOA and HPIA) exhibit increased TTHM and chloroform formation in the
presence of 6 g/L goethite (Table 4.19). Comparing the 1 and 6 g/L goethite TTHM and
chloroform increases, both concentrations demonstrated the ability to cause greater
formation compared to aqueous test (Figures 4.11 and 4.12). While goethite generally
resulted in greater TTHM production, goethite did not increase HAA5 formation (Figure
4.13).
90
Table 4.19
Percent DBP Increase at 6 g/L Goethite.
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
Chloroform
41 (50)
23 (29)
16 (29)
10 (20)
4 (8)
14 (20)
DCAA
28 (53)
4 (10)
1 (2)
-1 (-3)
3 (9)
2 (10)
TCAA
2 (3)
-13 (-32)
-6 (-20)
1 (15)
6 (32)
-2 (-12)
TTHM
42 (43)
23 (29)
17 (24)
10 (19)
8 (9)
16 (18)
HAA5
18 (13)
-3 (-3)
-7 (-7)
1 (1)
16 (14)
-3 (-4)
Raw-2
48 (44)
19 (27)
-3 (-5)
47 (36)
17 (11)
HPOA-2
23 (18)
6 (17)
-1 (-7)
23 (18)
0.4 (1)
HPIA-2
23 (24)
14 (28)
10 (45)
25 (20)
24 (24)
HPON-2
-2 (-2)
5 (33)
4 (82)
-2 (-2)
8 (24)
HPIN-2
3 (4)
6 (22)
4 (31)
3 (2)
28 (27)
MIX-2
15 (18)
7 (18)
-1 (-7)
17 (15)
8 (10)
Note: 1) Values represent an increase compared to the aqueous test [ppb (%)].
2) Positive values represent and increase, while negative represent a decrease.
Table 4.20
Solution Characteristics at 6 g/L Goethite.
DOC
Adsorbed
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
(%)
45
11
15
34
6.4
6.1
Aqueous
SUVA
Chlorine
Demand
(L m-1 mg-1) (mgCl2/mgC)
3.1
2.1
2.8
1.3
1.8
1.1
1.2
1.4
1.3
1.8
1.9
1.8
Chlorine
Demand
Increase
(%)
42
1
8
28
-7
9
Raw-2
41
3.4
2.7
28
HPOA-2
15
3.5
1.7
33
HPIA-2
32
3.2
2.5
13
HPON-2
0.7
1.4
1.1
20
HPIN-2
1.6
2.0
2.3
-17
MIX-2
10
2.6
2.6
13
Note: 1) Percent chlorine increase is calculated using [(Goethite – Aqueous)/Aqueous].
91
1.4
1 g/L Goethite
6 g/L Goethite
THM4 in Aqueous (uM)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
THM4 in Goethite (uM)
Figure 4.11
TTHM comparison between aqueous and goethite at 1 and 6 g/L.
92
160
1 g/L Goethite
6 g/L Goethite
Chloroform in Aqueous (uM)
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
Chloroform in Goethite (uM)
Figure 4.12
Chloroform comparison between aqueous and goethite at 1 and 6 g/L.
93
1.4
1 g/L Goethite
6 g/L Goethite
HAA5 in Aqueous (uM)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
HAA5 in Goethite (uM)
Figure 4.13
HAA5 comparison between aqueous and goethite at 1 and 6 g/L.
94
4.5.3 DBP Formation for 1-6 g/L Goethite
One of the main reasons for testing increasing concentrations of goethite was to
simulate pipe deposits introducing greater levels of iron oxide to water at maximum
retention times. Incrementally increasing concentrations of 1 g/L, starting at 1 g/L and
ending at 6 g/L was decided on after preliminary studies suggested that 1 g/L limited raw
water to the goethite while 5 g/L offered excess goethite sites (Bower 2003, Hassan
2005). These sites were estimated by Bower (2003) to be in the range of credible
concentrations introduced by water distribution system pipe walls. While very little
variation in HAA5 was produced between increasing goethite levels, TTHM showed
significant increases. Golden (2005) concluded with 5 g/L of goethite, DBPs on average
increased 15 ppb when compared to aqueous tests. Specifically, he concluded that
chloroform on average had a 12 ppb increase while DCAA increased and TCAA
decreased (Golden 2005).
When discussing TTHM and HAA5 variations among goethite concentrations,
chloroform, TCAA and DCAA varied the most, no other species showed variation with
goethite concentration variation. For instance, HPIN favored the formation of BDCM
and MCAA over all other solutions (Appendix A). The individual contributions of
fractions to produce brominated and non-brominated DBP species better illustrated
certain fractions ability to produce varying levels of these DBPs. Showing an overall
trend of increased non-brominated DBP species in 6 g/L goethite compared to aqueous
tests, brominated species remained constant (Figure 4.14 and 4.15).
The effect of steadily increasing TTHM with increasing goethite concentrations
was mainly observed in the Raw solutions (Table 4.21). However, HPOA and HPIA
95
solutions also confirmed this phenomenon with TTHM values increasing more than 20
ppb compared to aqueous tests. The HPON and HPIN solutions were the least
susceptible to TTHM increase while HPIN produced significantly less TTHMs than
HPON for both days. For MIX solutions, increases were observed, however, increases
were about a third the increase of Raw solutions. The increases in TTHM were mainly
because of chloroform increases (Table 4.23).
Interestingly, the Raw solutions were the only solutions to show such significant
changes in HAA5; however, these changes were the result of different HAA species
changes. HAA5 increased 39 ppb in Raw-1 with 2 g/L goethite, but steadily decreased to
18 ppb by the 6 g/L goethite (Table 4.22). A similar large increase was also observed in
Raw-2, with an increase of 34 ppb by the 4 g/L goethite, followed by a decrease to 17
ppb with 5 – 6 g/L goethite. This decrease observed in Raw-1 was due to TCAA; while
Raw-2 had insignificant decreases in TCAA (Table 4.24). This would suggest that Raw2 decreases came from DCAA, instead DCAA increased significantly for both Raw-1 and
Raw-2 (Table 4.25). Furthermore, DCAA reached a maximum of 28 and 20 ppb
increases for Raw-1 and Raw-2, respectively (Table 4.25). Fraction solutions failed to
demonstrate any significant changes in terms of TCAA or DCAA, even though MIX
solutions were similar to the Raw in fraction composition. With such subtle changes in
HAA formation in the fractions, it would appear that HAA precursors were
inactivated/destroyed by the fractionation procedure. While fraction solutions seemed to
produce fair increases in TTHM concentrations, they failed to reveal which fraction was
the cause to TCAA decreases and DCAA increases. Suggesting that reactivity is lost
when fractions are separated from naturally occurring water as exists in the Raw
96
solutions. The MIX solutions did contain different percentages of certain DOC fractions
compared to the Raw. However, this was considered insignificant since DBP variations
were not present in any of the fractions as seen in the Raw.
In conclusion, goethite mostly effected the chloroform production while TCAA
and DCAA only demonstrated variations with goethite in the Raw waters. The HPOA
and HPIA fractions had the highest SUVA values for both sample days and exhibited the
greatest increases in TTHM and chloroform in the presence of goethite. Furthermore,
less TTHM was produced in the HPON fraction, while insignificant TTHM increases
were observed for the HPIN fraction even though its SUVA was slightly more than
HPONs. DOC adsorption to goethite did not prove to be the sole explanation as to why
chlorine consumption or DBPs increase in the presence of goethite. Instead, data
suggests that the DOC fraction was the reason for increases in DBP with goethite,
specifically the HPOA and HPIA fractions. For instance, the TTHM formation was
similar for HPIA-1 and HPIA-2; however, DOC adsorption for HPIA-2 doubled
compared to HPIA-1. This increase in DOC adsorption for HPIA-2 may have caused the
chlorine consumption to also double. On the other hand, DOC adsorption was nearly
doubled for HPON-1 compared to HPON-2, though the chlorine consumption and TTHM
formation for the HPON fractions were nearly identical. While the HPIN fraction had a
greater chlorine demand in the aqueous tests, less chlorine was consumed when goethite
was present in HPIN. Nonetheless, TTHMs changed the least for HPIN in comparison to
the other fractions with goethite.
97
Table 4.21
TTHM Increase from 1 – 6 g/L Goethite.
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
1
25
9
7
15
-3
-3
2
30
30
9
13
0
0
3
44
24
6
9
1
-3
4
39
23
17
9
3
6
5
44
31
22
12
0
13
Raw-2
19
31
43
46
49
HPOA-2
41
20
39
28
30
HPIA-2
11
5
6
19
21
HPON-2
8
5
-1
-1
7
HPIN-2
-9
1
0
5
2
MIX-2
4
12
15
18
14
Note: 1) Positive values represent and increase compared to aqueous tests.
Table 4.22
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
6
42
23
17
10
8
16
47
23
25
-2
3
17
HAA5 Increase from 1 – 6 g/L Goethite.
1
36
10
11
6
6
3
2
39
0
-7
1
11
-5
3
28
14
-3
2
18
2
4
24
0
-5
1
16
-2
5
22
-3
-14
0
13
-4
Raw-2
12
19
26
34
17
HPOA-2
6
8
8
6
3
HPIA-2
4
6
6
2
8
HPON-2
6
14
6
21
8
HPIN-2
-1
-1
4
-5
8
MIX-2
7
10
9
-2
9
Note: 1) Positive values represent and increase compared to aqueous tests.
98
6
18
-3
-7
1
16
-3
17
0
24
8
28
8
Table 4.23
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
Chloroform Increase from 1 – 6 g/L Goethite.
1
23
9
6
15
-2
-2
2
29
29
7
13
0
0
3
41
23
6
9
1
-3
4
38
23
15
10
1
5
5
42
31
20
12
0
11
Raw-2
19
31
43
45
50
HPOA-2
41
20
38
28
30
HPIA-2
8
5
6
17
20
HPON-2
8
5
-1
-1
7
HPIN-2
-5
0
0
3
2
MIX-2
3
10
13
16
13
Note: 1) Positive values represent and increase compared to aqueous tests.
Table 4.24
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
6
41
23
16
10
4
14
48
23
23
-2
3
15
TCAA Increase from 1 – 6 g/L Goethite.
1
23
2
8
5
9
5
2
18
-5
-3
2
10
1
3
10
1
-1
2
10
2
4
6
-9
-4
2
9
0
5
3
-11
-7
1
6
-2
Raw-2
4
3
4
3
-1
HPOA-2
5
3
2
1
-1
HPIA-2
5
3
3
0
1
HPON-2
4
6
2
13
4
HPIN-2
4
4
4
2
4
MIX-2
7
6
2
-2
0
Note: 1) Positive values represent and increase compared to aqueous tests.
99
6
2
-13
-6
1
6
-2
-3
-1
10
4
4
-1
Table 4.25
DCAA Increase from 1 – 6 g/L Goethite.
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
1
20
2
1
1
-2
-1
2
25
1
-6
-1
-1
-4
3
26
7
0
-1
1
2
4
28
3
-1
-1
1
2
5
28
3
-3
-2
2
1
6
28
4
1
-1
3
2
Raw-2
8
13
20
24
20
19
HPOA-2
2
7
8
8
7
6
HPIA-2
-2
2
2
2
6
14
HPON-2
2
7
1
8
5
5
HPIN-2
-4
-3
-2
-4
0
6
MIX-2
-1
1
3
-1
6
7
Note: 1) Positive values represent and increase compared to aqueous tests.
100
4
Brominated AQ
Brominated 6g/L
Non-Brominated AQ
Non-Brominated 6g/L
2.5
3
DBP (uM)
2.0
1.5
2
1.0
1
0.5
0.0
0
Raw-1
Figure 4.14
HPOA-1 HPIA-1 HPON-1 HPIN-1
MIX-1
Brominated and non-brominated DBPs of 1-30-07 solutions.
101
SUVA (L m-1 mg-1)
3.0
4
Brominated AQ
Brominated 6g/L
Non-Brominated AQ
Non-Brominated 6g/L
2.5
3
-1
-1
DBP (uM)
2.0
SUVA (L m mg )
3.0
1.5
2
1.0
1
0.5
0.0
0
Raw-2
Figure 4.15
HPOA-2 HPIA-2 HPON-2 HPIN-2
MIX-2
Brominated and non-brominated DBPs of 3-28-07 solutions.
102
CHAPTER V
SUMMARY AND RECOMMENDATIONS
5.1
Summary
Water from the raw water intake at Barberton, Ohio water treatment plant was
collected on two separate dates and fractionated into operationally defined dissolved
organic carbon (DOC) fractions following Pu’s (2005) procedure which stemmed from
Leenheer (1981). Four DOC fractions that contributed more than 94% of the raw waters’
DOC (HPOA, HPIA, HPON, and HPIN) were used to compare disinfection byproduct
(DBP) formation using similar DOC concentrations, chlorine doses, and reaction times.
In addition to these four fractions, the raw water from which the fractions originated
(Raw), and an equal mixture of the four NOM fractions (MIX) were all tested under
similar conditions. These six solutions were additionally exposed to an iron oxide which
is a major component on the walls of cast iron water distribution pipes.
To simulate the effect iron oxide has on water as it travels through water
distribution system piping, goethite was added to each of the aforementioned six
solutions in increments of one gram per liter. Batch tests conducted at six different
concentrations of goethite (1-6 g/L), including one without goethite (aqueous), were used
to determine which NOM fraction was most susceptible to goethite’s effect. The overall
objective was to evaluate adsorption isotherms of four major DOC fractions from raw
water using goethite while assessing the impact of chlorine demand and DBP formation
103
caused by goethite. The three specific objectives are listed below, followed by findings
and suggestions.
The first objective was to evaluate how well four DOC fractions adsorb to
goethite at a beginning pH of 8.0 ± 0.1 while realizing the pH changes with goethite
addition. The pH changes were considered acceptable since all four fraction solutions
contained similar alkalinity. With similar solutions and testing conditions, other than the
type of DOC fraction being tested, HPOA, HPIA, HPON, and HPIN fractions were tested
for adsorption to goethite. While HPOA showed consistent adsorption typically ranging
from 11 – 16% DOC adsorbed; HPIA and HPON fractions DOC adsorbed more than
30%. Demonstrating the least affinity was the HPIN fraction with DOC adsorption less
than 9.2%. The adsorption of DOC fractions to goethite depends on the DOC fraction,
which suggests that carbon functional groups are responsible for adsorption (Benjamin et
al 1993, Kitis et al 2007, Kaiser 2003, Korshin et al 1997)
The second objective was to assess the impact that goethite has on raw water and
DOC fractions in a modified DBP formation potential test. Measurements of THM4,
HAA5, and chlorine consumed at increasing goethite concentrations defined which DOC
fractions had the greatest and least susceptibility to goethite. The four DOC fractions
were ranked by their DBP formation potential, first in aqueous, then at 1 g/L, 6 g/L and
finally evaluated for the trends that occurred throughout 1-6 g/L goethite. The aqueous
ranking revealed that HPIN produced the greatest amount of DBP, TTHM, and HAA5 on
a per mg of carbon basis. HPIN produced more DBPs because of formation of DBP
species other than chloroform, TCAA, and DCAA. TTHM and HAA5 production was
similar for HPOA and HPIA fractions, while the HPON produced the least. The greatest
104
chloroform production occurred with the HPOA fraction; HPOA and HPIA produced the
most TCAA; DCAA production was similar for all fractions except for HPON, which
produced less.
In the presence of goethite, TTHMs increased the most in the HPOA and HPIA
fractions, with up to ~20 ppb more than the aqueous test. Increases in TTHM for HPON
and HPIN fractions were insignificant. Changes in HAA5 were very small in the
fractions for both days; but the TCAA decreased in the Raw-1 sample by 21 ppb when
the goethite changed from 1 to 6 g/L. The only changes observed for HAAs in the NOM
fractions was HPOA-1 with a 13 ppb decrease in TCAA while HPIN-1 increased in
TCAA by approximately 10 ppb. This suggests that DOC fractions that have been
recovered from the Raw water may have less complex NOM moieties. For instance, a
Raw water NOM molecule may contain ten chloroform precursor sites, and without
goethite, free chlorine can only access three of them. However, when goethite is added,
the electrophoresis effect pulls apart the NOM molecule and exposes the other seven
chloroform precursor sites. In return, chlorine consumption increases once additional
precursor sites are able to be oxidized. While this concept remains the same with DOC
fractions, the complex NOM structure could have been compromised during separation
by the resins. This would inhibit the effect of goethite to break up the NOM molecule
and demonstrate changes in chlorine consumption and DBPs (Bower 2003).
Chlorine demand at increasing goethite levels increased the most for HPON-1,
HPON-2 and HPOA-2. The percent chlorine consumed when compared to the aqueous
increased to 28 and 20% more chlorine consumed for HPON-1 and HPON-2,
respectively, while HPOA-2 consumed 33% more. The opposite was true for HPIN
105
fractions, with chlorine consumption actually decreasing with increasing goethite. As for
HPOA and HPIA fractions, chlorine demands varied between the sample days. While
HPOA-1 and HPIA-1 had less chlorine consumed in most of the goethite concentrations,
HPOA-2 and HPIA-2 had chlorine consumption increase steadily to 33 and 13%,
respectively.
The third objective was to explain the relation between the percent DOC adsorbed
for the four DOC fractions onto goethite with the chlorine demand and DBP formation of
each. The chlorine demand for both Raw waters agreed with previous studies involving
goethite (Bower 2003, Hassan 2005, Golden 2005). Chlorine consumed in Raw-1 and
Raw-2 increased the greatest to 41 and 28% more chlorine consumed at 6 g/L goethite
than aqueous, respectively. Goethite mostly effected the chloroform production while
TCAA and DCAA only demonstrated variations with goethite in the Raw waters. The
HPOA and HPIA fractions had the highest SUVA values for both sample days and
exhibited the greatest increases in TTHM and chloroform in the presence of goethite.
Furthermore, less TTHM was produced in the HPON fraction, while insignificant TTHM
increases were observed for the HPIN fraction even though its SUVA was slightly more
than HPONs. DOC adsorption to goethite did not prove to be the sole explanation as to
why chlorine consumption or DBPs increase in the presence of goethite. Instead, data
suggests that the DOC fraction was the reason for increases in DBP with goethite,
specifically the HPOA and HPIA fractions. For instance, the TTHM formation was
similar for HPIA-1 and HPIA-2; however, DOC adsorption for HPIA-2 doubled
compared to HPIA-1. This increase in DOC adsorption for HPIA-2 may have caused the
chlorine consumption to also double. On the other hand, DOC adsorption was nearly
106
doubled for HPON-1 compared to HPON-2, though the chlorine consumption and TTHM
formation for the HPON fractions were nearly identical. While the HPIN fraction had a
greater chlorine demand in the aqueous tests, less chlorine was consumed when goethite
was present in HPIN. Nonetheless, TTHMs changed the least for HPIN in comparison to
the other fractions with goethite. Overall, data demonstrated that increasing goethite
concentrations to NOM solutions steadily increased chloroform production, though this
was oppositely true for HAA5. The HPOA fraction was the most susceptible to the effect
of goethite as HPOA had the greatest increase due to the presence of goethite. Though
HPIA was similar to HPOA in TTHM increases with goethite, HPIN had the least
amount of change in TTHM with goethite.
5.2
Recommendations
1. Experiments should be done starting at smaller goethite concentrations such as 0.1
g/L to better simulate iron oxide exposure to water in a distribution system, which
introduces small amounts of iron oxide as retention times increase.
2. One of the main reasons for testing DOC fractions’ adsorption on goethite,
chlorine demand, and DBP formation potential is to determine which should be
targeted for removal. However, DBP formation tests have never been conducted
after sequential removal of DOC fractions. For instance, raw water that contains
only five DOC fractions, with HPON removed and the others remaining together
for testing. This could be followed by removal of the HPOB fraction, followed by
placing HPON back into solution so that only HPOB was removed.
107
3. While DOC fraction solutions contained nearly the same amount of alkalinity and
buffering capacity, making the comparisons between them possible, a better
buffer should be used to prevent any (<0.2) pH change. This would be preferable
if the buffer did not interfere with DOC adsorption to goethite as phosphate does.
Some examples of buffers which may be appropriate include carbonate and borate
based buffers.
4. The pH changes which occurred in the goethite tests were approximated to be 1.3
pH units. Though this may have been caused by the powdered goethite satisfying
its hydrogen equilibrium, there is a lack of knowledge about pH changes
occurring throughout distribution systems. The pH changes in a distribution
system would be expected to occur in the extremities of a system, caused by the
iron oxide on the pipe walls.
108
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APPENDIX
DBP in Aqueous Tests.
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
TTHM
98
79
72
52
86
87
BDCM
15
2.2
14
1.7
27
16
HAA5
143
94
100
54
114
66
MCAA
20
1
16
4
43
10
DBP
241
173
172
106
200
153
Raw-2
HPOA-2
HPIA-2
HPON-2
HPIN-2
MIX-2
132
128
121
90
136
110
20
2.2
25
1.2
52
22
151
75
101
34
112
88
21
3
21
2
60
18
283
203
222
124
248
198
116
Chlorine increase from 1 – 6 g/L goethite.
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
1
0.80
-0.33
-0.22
0.08
0.09
0.00
2
0.76
-0.81
-0.03
0.40
0.27
-0.17
3
1.09
-0.57
-0.11
0.39
-0.48
0.10
4
1.60
-0.60
0.15
0.48
-0.49
0.60
5
1.80
-0.22
0.44
0.63
-0.46
0.26
Raw-2
0.68
0.98
1.28
1.49
1.77
HPOA-2
0.50
0.75
0.87
0.98
1.17
HPIA-2
0.20
0.59
0.58
0.69
0.88
HPON-2
0.12
0.00
0.32
0.18
0.55
HPIN-2
-0.53
-0.57
-0.41
-0.49
-0.50
MIX-2
-0.10
0.21
0.06
0.29
0.55
Note: 1) Positive values represent and increase compared to aqueous tests.
6
1.96
0.03
0.24
0.90
-0.37
0.42
1.83
1.29
0.90
0.57
-1.37
0.84
DOC percent adsorption from 1 – 6 g/L goethite
Goethite
Raw-1
HPOA-1
HPIA-1
HPON-1
HPIN-1
MIX-1
1
34
11
12
14
7.8
2.1
2
43
12
11
12
8.1
5.7
3
40
5.9
13
24
7.4
12
4
41
5.6
19
13
8.1
11
5
45
11
14
38
7.1
13
6
45
11
15
34
6.4
6.1
Raw-2
28
36
38
38
43
41
HPOA-2
5.6
15
14
16
19
15
HPIA-2
15
25
28
31
29
32
HPON-2
12
20
4.2
14
4.8
0.0
HPIN-2
9.2
6.9
4.6
4.9
0.3
0.7
MIX-2
8.4
5.1
8.8
5.8
11
10
Note: Values represent the percent DOC adsorbed based off of aqueous tests.
117
Raw-1
HPOA-1
1.5
HPON-1
HPIA-1
HPIN-1
MIX-1
Chloroform (uM)
1.2
0.9
0.6
0.3
0.0
0
1
2
3
Goethite (g/L)
Chloroform versus goethite of 1-30-07 solutions.
118
4
5
6
Raw-2
HPOA-2
1.5
HPON-2
HPIA-2
HPIN-2
MIX-2
Chloroform (uM)
1.2
0.9
0.6
0.3
0.0
0
1
2
3
Goethite (g/L)
Chloroform versus goethite of 3-28-07 solutions.
119
4
5
6
Raw-1
HPOA-1
0.5
HPON-1
HPIA-1
HPIN-1
MIX-1
TCAA (uM)
0.4
0.3
0.2
0.1
0.0
0
1
2
3
Goethite (g/L)
TCAA versus goethite of 1-30-07 solutions.
120
4
5
6
Raw-2
HPOA-2
0.5
HPON-2
HPIA-2
HPIN-2
MIX-2
TCAA (uM)
0.4
0.3
0.2
0.1
0.0
0
1
2
3
Goethite (g/L)
TCAA versus goethite of 3-28-07 solutions.
121
4
5
6
Raw-1
HPOA-1
0.8
HPON-1
HPIA-1
HPIN-1
MIX-1
DCAA (uM)
0.6
0.4
0.2
0.0
0
1
2
3
Goethite (g/L)
DCAA versus goethite of 1-30-07 solutions.
122
4
5
6
Raw-2
HPOA-2
0.8
HPIN-2
MIX-2
HPON-2
HPIA-2
DCAA (uM)
0.6
0.4
0.2
0.0
0
1
2
3
Goethite (g/L)
DCAA versus goethite of 3-28-07 solutions.
123
4
5
6
The inside of a cast iron pipe that was in use for longer than 50 years from
Barberton, OH water distribution system.
124