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Ecotoxicology and Human Environmental Health

Does GAC with Chlorination Produce Safer Drinking Water? From DBPs and TOX to Calculated Toxicity Amy A. Cuthbertson, Susana Y. Kimura, Hannah K. Liberatore, R. Scott Summers, Detlef R. U. Knappe, Benjamin D. Stanford, J. Clark Maness, Riley E. Mulhern, Meric Selbes, and Susan D. Richardson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b00023 • Publication Date (Web): 30 Apr 2019 Downloaded from http://pubs.acs.org on May 1, 2019

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Environmental Science & Technology

Does GAC with Chlorination Produce Safer Drinking Water? From DBPs and TOX to Calculated Toxicity Amy A. Cuthbertson1, Susana Y. Kimura1,2, Hannah K. Liberatore1, R. Scott Summers3, Detlef R. U. Knappe4, Benjamin D. Stanford5, J. Clark Maness4, Riley E. Mulhern3, Meric Selbes6, and Susan D. Richardson1,* 1Department

of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208; 2Department of Chemistry, University of Calgary, 2500 University Dr. NW Calgary, Alberta, Canada T2N 1N4; 3Department of Civil, Environmental and Architectural Engineering, University of Colorado, Boulder, CO 80309-0428; 4North Carolina State University, Department of Civil, Construction, and Environmental Engineering, Campus Box 7908, Raleigh, NC 276957908;; 5Hazen and Sawyer, 143 S. Union Blvd., Suite 200, Lakewood, CO 80228; 6Hazen and Sawyer, 4035 Ridge Top Road, Suite 400, Fairfax, VA 22030

*Corresponding author; Address: Department of Chemistry and Biochemistry, University of South Carolina, 631 Sumter Street, Columbia, SC 29208; Tel: 803-777-6932; Fax: 803-777-9521; E-mail: [email protected]

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Abstract 20

Granular activated carbon (GAC) adsorption is well-established for controlling regulated

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disinfection by-products (DBPs), but its effectiveness for unregulated DBPs and DBP-associated

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toxicity is unclear. In this study, GAC treatment was evaluated at three full-scale chlorination

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drinking water treatment plants over different GAC service lives for controlling 61 unregulated

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DBPs, 9 regulated DBPs, and speciated total organic halogen (total organic chlorine, bromine,

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and iodine). Plants represented a range of impacts, including algal, agricultural, and industrial

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wastewater. This study represents the most extensive full-scale study of its kind and seeks to

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address the question of whether GAC can make drinking water safer from a DBP perspective.

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Overall, GAC was effective for removing DBP precursors and reducing DBP formation and total

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organic halogen, even after >22,000 bed volumes of treated water. GAC also effectively

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removed preformed DBPs at plants using pre-chlorination, including highly toxic iodoacetic

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acids and haloacetonitriles. However, 7 DBPs (mostly brominated and nitrogenous) increased in

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formation after GAC treatment. In one plant, an increase in tribromonitromethane had significant

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impacts on calculated cytotoxicity, which only had 7-17% reduction following GAC. While

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these DBPs are highly toxic, the total calculated cytotoxicity and genotoxicity for the GAC

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treated waters for the other two plants was reduced 32-79% (across young-middle-old GAC).

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Overall, calculated toxicity was reduced post-GAC, with pre-oxidation allowing further

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reductions.

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Introduction

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Drinking water disinfection is vital for prevention of waterborne illness. Since its introduction in

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the U.S. in the early 1900s, disinfection is reported to have contributed significantly to an

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estimated 29-year increase in life expectancy.1 An unintended consequence of disinfection is the

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formation of disinfection by-products (DBPs), which have been associated with adverse health

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effects, including bladder cancer, colon cancer, miscarriage, and birth defects.2-10 In the U.S.,

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regulations are enforced for four trihalomethanes (THMs), five haloacetic acids (HAAs),


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bromate, and chlorite under the Stage 2 Disinfectants and DBP Rule.11 Several recent studies

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indicate that while THMs and HAAs are the dominant DBPs formed upon chlorination, they are

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not necessarily drivers of toxicity associated with DBP formation.12-14

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DBPs are formed by the reaction of disinfectants with natural organic matter (NOM), bromide,

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and iodide.6, 15 Many NOM fractions can react to form THMs and HAAs, while phenolic NOM

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structures have been shown to form haloacetaldehydes (Table S1, Supporting Information

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[SI]).16 Free and combined amino acids, aldehydes, and aromatic NOM have been shown to form

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haloacetamides and haloacetonitriles.17-19 The presence of inorganic nitrogen, such as ammonia,

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nitrite and nitrate, can play a role in the formation of nitrogenous DBPs (N-DBPs),20 which are

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generally more toxic than DBPs without nitrogen,21-24 yet no N-DBPs are currently regulated.

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Extensive studies have shown that iodo-DBPs, which are also not regulated, are typically more

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toxic than brominated DBPs (Br-DBPs), which are much more toxic than chlorinated

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analogues.25-28 Table S1 summarizes precursors associated with each DBP class measured in this

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study.

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Use of GAC is well-established for controlling THMs and HAAs because it can effectively

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remove NOM fractions that serve as their precursors.13, 29-31 Studies indicate that some N-DBP

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precursors are not as readily removed using GAC.13, 32 GAC columns are biologically active,

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even if the influent contains a disinfectant, as GAC will reduce the disinfectant at the top of the

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GAC column, allowing biomass to grow in the rest of the bed.33 Thus, in addition to adsorption

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of DBP precursors, biodegradation plays a role in GAC treatment.33

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Many drinking water plants use pre-oxidation (e.g., pre-chlorination), which may result in the

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formation of DBPs within the treatment system. We refer to these as “preformed” DBPs; they

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can be removed by GAC, or with additional disinfection, can act as precursor material for the

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formation of other DBPs.17, 18 One potential benefit of pre-oxidation is transformation of NOM

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into intermediate aromatic halogenated DBPs which may be more easily removed by GAC than

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larger precursor molecules.34

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GAC preferentially removes dissolved organic carbon (DOC) over dissolved organic nitrogen

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(DON), and it does not remove bromide.31, 35, 36 Therefore, the DON:DOC and Br-:DOC ratios

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increase across GAC adsorbers, which may result in increased formation of N- and Br-DBPs,

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due to increased competition of HOBr.13, 31, 35, 36 Higher Br-:DOC ratios cause a shift in halogen

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speciation to more brominated THMs, and some brominated THM concentrations can be higher

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after GAC treatment.35, 36 A shift from dichloroacetonitrile to dibromoacetonitrile has also been

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reported in a bench-scale GAC study.13 Shifts in halogen speciation to more cytotoxic and

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genotoxic brominated DBPs must be evaluated for possible adverse health implications.

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Given concerns about potential increased formation of Br- and N-DBPs, it is important to ask:

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Do GAC treated waters have lower associated toxicity than waters not treated with GAC? One

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way to address this is the “TIC-Tox” approach, which multiplies molar concentrations of

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individual DBPs by their corresponding cytotoxicity and genotoxicity index values.14 Other

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previously published studies have used this approach in modeling toxicity of DBP mixtures, 14, 37,

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38

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be used to assess which DBPs are toxicity drivers, regulated or otherwise.

and have shown increases in calculated genotoxicity following GAC.13 This approach can also


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The goal of our study was to assess the effectiveness of full-scale GAC treatment at chlorination

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plants for controlling: (1) human exposure to a wide range of 70 regulated and unregulated

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DBPs, as well as speciated total organic halogen (TOCl, TOBr, TOI), and (2) the calculated

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toxicity associated with these DBPs. Both removal of preformed DBPs and control of DBPs

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under conditions that represent the utilities’ distribution systems; i.e., simulated distribution

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system (SDS) conditions, were assessed. Using each plant’s SDS conditions allows for the study

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of more realistic DBP concentrations, and therefore, exposure to real populations within those

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systems. Water samples were collected at three full-scale chlorination plants in the U.S., with

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DBP control evaluated across GAC service life (e.g., youngest, middle-aged, and oldest GAC).

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At each plant, the same influent water was used across three different aged filters on the same

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type of carbon, allowing for the comparison of filter age with the same DBP composition.

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Because source water quality can impact the types of DBPs that form, plants were carefully

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chosen to represent a wide range of impacts, including algal, agricultural, and industrial

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wastewater impacts. This study was limited to three full-scale chlorine plants due to the

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extensive analysis required. Formation of 70 DBPs, including haloacetonitriles (HANs),

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haloacetamides (HAMs), halonitromethanes (HNMs), haloacetaldehydes (HALs), haloketones

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(HKs), iodinated acetic acids (IAAs), iodinated trihalomethanes (I-THMs), THMs, and HAAs,

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was studied during full-scale pre-chlorination (preformed DBPs) at two plants and in bench-scale

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SDS tests at all three plants. This is the most extensive list of DBPs studied across GAC filter

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lifetimes. TOCl, TOBr, and TOI were also measured and compared to the total measured DBP

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concentrations, with the balance representing unknown DBPs. This is the first study that

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evaluated TOX across GAC lifetimes in full-scale plants. Preformed DBPs were evaluated



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before and after GAC treatment, providing information on their adsorbability and/or

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biodegradability, which is unknown for many emerging DBPs. Cytotoxicity and genotoxicity

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were calculated using the TIC-Tox method across GAC lifetime.14 Most importantly, this study

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seeks to address whether DBP concentrations correlate with calculated toxicity, and which DBPs

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are the driving forces of toxicity across GAC age.

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Materials and Methods Sampling of drinking water treatment plants

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Three full-scale drinking water plants were sampled; for each plant, three GAC service lives

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were evaluated, which was quantified in terms of throughput in bed volumes (BV, i.e. the

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volume of water treated relative to the GAC bed volume) and was different for each plant to

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reflect early, middle, and late stages of GAC operation. Operating characteristics and source

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water quality parameters for each plant and water sample are summarized in Table 1. Total

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organic carbon (TOC), absorbance at 254 nm (UV254), specific ultraviolet absorbance (SUVA),

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bromide, iodide, and total nitrogen (TN) were quantified as surrogates for DBP precursors (Table

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1). All plants used one or more pre-oxidants prior to GAC treatment (chlorine dioxide and

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chlorine in Plant 1, KMnO4 and chlorine in Plant 2, KMnO4 in Plant 3) and relied on chlorine as

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the primary disinfectant post-GAC and as the secondary disinfectant throughout the distribution

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system. Information regarding sampling dates, flow rates, empty bed contact times (EBCT),

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GAC type, and DOC breakthrough is found in Table S2. Due to the real-world nature of this

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study, the activated carbons were slightly different at the different plants studied, but they were

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consistent within each plant, allowing the impact of carbon age and impact of GAC vs. no GAC

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to be evaluated at each plant. Schematic diagrams of each plant are found in Figures S1-S3. All

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plants operated GAC contactors in a staged parallel mode and blended the effluents. GAC 6 ACS Paragon Plus Environment

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influents and effluents at different service times were collected. Plant 3 was sampled on two

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occasions: in the first event, samples were taken after treating 9,200 BV of water; the second

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event occurred after GAC was replaced in two contactors.

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Chlorination of samples

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For each sample, water was analyzed for preformed DBPs, and SDS testing was carried out

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according to protocols set by each plant (Text S1). Chlorine residual concentrations and contact

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times were equivalent to each plant’s longest water age in the distribution system (3-7 days). For

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example, Plant 1 was pH adjusted with borate buffer to 8.0 and spiked with 1.0 to 4.0 mg/L to

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achieve a chlorine residual of approximately 1.0 mg Cl2/L after 24 h of reaction.

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Samples were collected in duplicate in two 1-L bottles, one containing ascorbic acid and one

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ammonium chloride (quenching agents; chlorine to quencher molar ratio of 1:1.3 based on an

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assumed maximum potential residual chlorine concentration of 5 mg/L as Cl2) and adjusted to

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pH 3.5-4 with 1 M H2SO4. Samples were shipped cold overnight and extracted the same day

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received or stored at 4°C and extracted within 2 days. Quantified DBPs were stable over this

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storage time.39-41 Further details are provided in Text S2.

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Chemicals and reagents

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Analytical standards for unregulated DBPs (Table S3) were purchased or custom-synthesized at

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the highest purity available (CanSyn Chem. Corp., Toronto, Ontario; Sigma-Aldrich, St. Louis,

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MO; Aldlab Chemicals, Boston, MA; TCI America, Boston, MA). Organic solvents were of the



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highest purity. Acetonitrile, methyl tert-butyl ether (MTBE), methanol, hexane, and pure water

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were purchased from Sigma-Aldrich (St. Louis, MO) and Fisher Scientific (Pittsburgh, PA).

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Analytical Methods

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Background water quality and regulated DBPs. Water quality parameters (residual chlorine,

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DOC, UV254, SUVA, TN, ammonia, nitrite, nitrate, bromide and iodide) were measured using

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methods described in Table S4. THMs and HAAs were measured using EPA Methods 551.1 and

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552.3, respectively.42, 43

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Unregulated DBPs. Three extraction methods and two derivatization methods were required to

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analyze 57 unregulated DBPs.41 For, HANs, HKs, I-THMs, HNMs, and tri-HALs, a single

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liquid-liquid extraction (LLE) with 100 mL of sample, 2 mL MTBE, and 30 g sodium sulfate

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was conducted for samples quenched with ascorbic acid (Text S3.1). For HAMs, IAAs, and a

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subset of compounds (bromodichloronitromethane, dibromochloronitromethane,

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tribromonitromethane, and tribromoacetonitrile), 100 mL were pH adjusted with H2SO4 to pH

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10 months of GAC service life at Plant 2).

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Impact of GAC on simulated distribution system (SDS) DBPs

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GAC effectively controlled SDS-DBPs at all three chlorination plants (Figure 2 and S6). The

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DBP sum decreased after treatment, with control ranging from 48 to 82% at Plant 1, 58 to 89%

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at Plant 2, and 6 to 67% at Plant 3, decreasing with service time. These combined results

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correlate with TOC removal (Figures S7-S9), and similar correlations were obtained with UV254 14 ACS Paragon Plus Environment

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(Table 1). When accounting for molar concentrations, the total measured SDS Cl-DBPs

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accounted for 15-40% of the TOCl at Plant 1, 51-57% at Plant 2, and 53-100% at Plant 3. The

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total measured SDS Br-DBPs accounted for 45-52% of the TOBr at Plant 1, 73-100% at Plant 2,

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and 38-45% at Plant 3. Total measured I-DBPs only accounted for 3-10% of the TOI at Plant 1,

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0-4% at Plant 2, and

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