COMPARISON OF NATURAL ORGANIC MATTER (NOM) REMOVAL PROCESSES ON DISINFECTION BYPRODUCT (DBP) FORMATION DURING DRINKING WATER TREATMENT.

Transcription

1 COMPARISON OF NATURAL ORGANIC MATTER (NOM) REMOVAL PROCESSES ON DISINFECTION BYPRODUCT (DBP) FORMATION DURING DRINKING WATER TREATMENT A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science John Ryan Less May, 2011

2 COMPARISON OF NATURAL ORGANIC MATTER (NOM) REMOVAL PROCESSES ON DISINFECTION BYPRODUCT (DBP) FORMATION DURING DRINKING WATER TREATMENT John Ryan Less Thesis Approved: Accepted: Advisor Dr. Stephen Duirk Dean of the College Dr. George K. Haritos Faculty Reader Dr. Christopher Miller Dean of the Graduate School Dr. George R. Newkome Faculty Reader Dr. Lan Zhang Date Department Chair Dr. Wieslaw Binienda ii

3 ABSTRACT Natural aquatic organic matter (NOM) reacts with chlorinated disinfectants used to treat public drinking water supplies resulting in the formation of toxic and carcinogenic disinfection byproducts (DBPs). Therefore, treatment processes that reduce the concentration of NOM prior to drinking water disinfection have been found to reduce the formation of these unwanted DBPs. Conventional enhanced coagulation was compared with a novel anion exchange resins for reducing DBP precursors located in the negatively charged fraction of the NOM matrix. Three anion exchange resins (AERs) were compared (IRA-910, IRA-958, and MIEX) to determine which resin would not only remove NOM but DBP precursors as well. All the AERs were found to be highly proficient at NOM reduction specifically the moieties that absorb UV light at 254 nm and 272 nm over 75 minutes of contact time; however, MIEX removed NOM at a faster rate than the Amberlite resins. Results show that ph had no significant effect on the removal of chromophores and fluorophores (i.e. EEM base pairs A and C) when treated with MIEX or enhanced coagulation. Coagulation was effective at removing 30-45% NOM for Akron and Barberton source waters based on peak intensity excitation-emission pairs taken from the EEM (excitationemission matrix). Peak intensity in the T region of the EEM for the Barberton source iii

4 water, which correlates to positively charged soluble microbial, was found to be relatively resilient to each NOM removal process. DBP formation was determined as a function of ph for the different NOM removal processes. MIEX resulted in significant reduction in DBP concentrations for both source waters when compared to DBP formation in the chlorinated raw source waters. MIEX out performed both coagulants reducing the formation of DBPs in both source waters. At an elevated chlorine concentration in the raw samples, as ph increases from 6.5 to 8, chloroform formation increases, TCAA concentrations decrease and dichloroacetic acid (DCAA) is not affected. The two coagulants both reduced DBP formation; however, alum appeared to reduce DBP concentrations more significantly than ACH at ph 8.2. iv

5 ACKNOWLEDGEMENTS I would like to thank my committee members: Dr. Lan Zhang, and Dr. Christopher Miller. Your guidance throughout this experience is greatly appreciated. I would also like to thank Andrew Skeriotis, Daniel Leslie, Danyang Wu, Elizabeth Crafton, and Nancy Sanchez for all of their help and guidance. I would like to thank my family and friends for their support. Finally, I would like to express my sincere gratitude to my advisor, Dr. Stephen Duirk for his help throughout this process. Without his encouragement and guidance as my advisor and my friend I would not have accomplished all that I have. v

6 TABLE OF CONTENTS Page INTRODUCTION Perspective Research Objectives Research Approach... 4 LITERATURE REVIEW Chlorination, DBP formation, and NOM Characterization Conventional Technologies Processes for NOM removal Anion Exchange for NOM Removal Spectroscopic Techniques used to Determine NOM Removal EXPERIMENTAL PROCEDURES Materials Methods and Procedures Anion exchange resin (AER) preparation and experiments Coagulation Experiments Chlorine Experiments DBP Analysis vi

7 3.2.5 Fluorescence and UV Spectroscopy Ion Analysis RESULTS AND DISCUSSION Kinetic Removal of NOM with selected AERs Comparison of NOM Removal Processes MIEX removal of NOM as a function of ph MIEX and Enhanced Coagulation Treatment Processes for NOM Removal DBP Formation DBP Formation after Coagulation/MIEX Treatment During Simulated Drinking Water Treatment Conditions DBP Formation after Coagulation/MIEX Treatment at Elevated Chlorine Concentrations SUMMARY AND RECOMMENDATIONS Summary Recommendations BIBLIOGRAPHY Appendix A 64 vii

8 LIST OF TABLES Table Page 3.1 NOM and source water characteristics for the Akron/Barberton raw waters Anion exchange resin structural characteristics and capacities Spectral Characteristics of Akron/Barberton prior to Chlorination Spectral characteristics of Akron/Barberton prior to Chlorination Average DBP concentrations for treated Akron/Barberton water after 24 hours in the presence of aqueous chlorine Average DBP concentrations for treated Akron/Barberton water after 24 hours in the presence of aqueous chlorine DBP- Carbon ratio in final DBP formation for ph DBP- Carbon ratio in final DBP formation for ph viii

9 LIST OF FIGURES Figure Page Figure 4.1 Monitoring DOC removal as a function of time in the presence of AERs [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.2 Monitoring UV 254 reduction as a function of time in the presence of AERs [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.3 Monitoring UV 272 reduction as a function of time in the presence of AERs [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.4 Monitoring EEM base pair A reduction as a function of time in the presence of AERs [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.5 Monitoring EEM base pair C reduction as a function of time in the presence of AERs [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.6 Monitoring UV 254 removal as a function of time in the presence of MIEX [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.7 Monitoring UV 272 removal as a function of time in the presence of MIEX [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.8 Monitoring EEM base pair A removal as a function of time in the presence of MIEX. [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure 4.9 Monitoring EEM base pair C removal as a function of time in the presence of MIEX. [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c Figure EEM spectra for (a) Akron Raw, (b) MIEX, (c) ACH, and (d) Alum ([DOC] Raw = 6.43 mg/l, [DOC] MIEX = 1.52 mg/l, [MIEX] Dose = 3.2 g/l, [DOC] ACH = 4.20 mg/l, [ACH] Dose = 10 mg/l, [DOC] Alum = 4.08, [Alum] Dose = 40 mg/l) Figure Fluorescence intensity: (a) Barberton Raw and (b) MIEX treated water ([TOC] Raw = 4.15 mg/l, [TOC] MIEX = 1.51 mg/l, and [MIEX] Dose = 3.2 g/l) ix

10 Figure TCAA formations at ph 6.5 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l- C, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) Figure TCAA formation at ph 8.2 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l- C, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) Figure DCAA formation at ph 6.5 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l- C, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) Figure DCAA formation at ph 8.2 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l- C, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) Figure Chloroform formation at ph 6.5 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l-c, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) Figure Chloroform formation at ph 8.2 for Akron source water as a function of NOM removal process. ([Cl 2 ] T = 10.5 mg/l, [TOC] Raw = 6.43 mg/l-c, [TOC] MIEX =1.52 mg/l-c, [TOC] ACH = 4.20 mg/l-c, [TOC] Alum =4.08 mg/l-c, and Temp.= 25 C) x

11 CHAPTER I INTRODUCTION 1.1 Perspective Chlorination has been a well established method for disinfecting public drinking water supplies in order to minimize outbreaks of waterborne pathogens protecting communities from diseases like cholera and typhoid fever. However, the reaction of aqueous chlorine with natural organic matter (NOM) results in the formation of unwanted disinfection byproducts (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the two most prevalent DBPs classes resulting from chlorination of drinking water supplies (Liang & Singer, 2003). These DBPs and have been found to be carcinogenic, genotoxic, cytotoxic, and hepatotoxic (Muellner et al., 2007; Plewa et al, 2008). Therefore, the drinking water disinfection process must not only maintain the microbial integrity of a community water system but minimize exposure to toxic carcinogens. To minimize human health effects from consuming DBPs formed in chlorinated drinking water, the Disinfectants/Disinfection Byproducts (D/DBP) rule established maximum contaminant levels (MCLs) for these two classes of DBPs (USEPA, 1998 and USEPA, 2006), which is 60µg/L and 80µg/L for the sum of regulated HAAs and THMs respectively. For the HAAs, 60µg/L represents the sum of the 5 regulated HAAs 1

12 including trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), and dibromoacetic acid (DBAA) on a total mass per volume basis. The sum of the concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform are regulated on at a total of 80µg/L. One strategy to reduce the DBP formation is to reduce the concentration of NOM prior to chlorination. Stage 1 of the D/DBP rule defines the amount of NOM to be removed through enhanced coagulation as a function of source water alkalinity (Bell- Ajay et al., 2000). Stage 2 of the D/DBP rule mandates that there must be a minimum disinfectant residual detected throughout the entire drinking water distribution system. Therefore, reducing DBP formation is highly dependent on treatment processes that not only reduce the concentration of NOM but the specific components that contribute to DBP formation (i.e., DBP precursors). Anion exchange resins are an efficient and emerging treatment process for removing NOM from public drinking water supplies. Anion exchange resins are highly complex polymeric surfaces designed for trapping and exchanging ions (Croue et al., 1999; Singer, 2002; Tan et al., 2005). Anion exchange occurs when the resin exchanges the negatively charged exchangeable ion bound to the resin surface with negatively charged NOM components resulting in NOM being absorbed to the resin surface. Some AERS have been found to reduce NOM concentrations by approximately 90% and DBP formation by 70% (Boyer & Singer, 2005 and Wert et al, 2005). 2

13 Fluorescence spectroscopy is a technique used to characterize NOM based on composition of the organic matrix. NOM fluorescence occurs when an electron in the NOM structure absorbs energy from light which excites an electron and promotes it into an unoccupied orbital. The energy difference between the ground state and the exited singlet state determines the wavelengths at which light will be emitted as the electron returns to the ground state (Stedmon et al., 2003). NOM profiling has been achieved through the use of fluorescence excitation-emission matrices (EEM), which captures the fluorescence spectra across a wide range of excitation and emission wavelengths (Christensen et al., 2005). NOM can then be characterized by peak intensity excitationemission pairs taken from the EEM (Marhaba and Kochar, 2000). These EEM spectra peaks can represent DBP precursors in source waters. Monitoring the removal of these peaks during the conventional surface water treatment process could indicate the effectiveness of these processes to reduce DBP precursor concentrations prior to chlorination. 1.2 Research Objectives Objective 1: Compare the performance of three strong anion exchange resins (AERs) (MIEX, IRA-910, and IRA-958) for their application in drinking water treatment (i.e. NOM removal). NOM removal was assessed by measuring total organic carbon (DOC), reduction UV absorbance at 254nm (UV 254 ) and 272nm (UV 272 ), and reduction in fluorescence EEM base pair intensities. 3

14 Objective 2: The effect of ph on each NOM removal processes. MIEX and two coagulants (ACH and alum) were used to treat two surface water sources with significantly different fluorescence spectral characteristics. NOM/DBP precursor removal was determined by reduction in spectral characteristics of the NOM remaining. Objective 3: Determine DBP formation as a function of ph for the three NOM removal treatment processes. DBP formation was then evaluated under simulated drinking water treatment conditions in order to determine which NOM removal treatment process was the most effect as ph of the source water was varied from Research Approach A thorough literature review was conducted to understand human health effects and the regulations implemented by U.S. EPA to minimizing exposure to toxic and carcinogenic DBPs. Then, novel and conventional technologies for NOM removal were evaluated in order to determine the correlation to NOM removal and DBP precursor reduction. Source waters with different NOM characteristics were collected during the months of August November and used to examine the impact of AERs and enhanced coagulation on NOM removal. DBP precursor reduction was then evaluated by the kinetic formation of DBPs in the presence of aqueous chlorine. Results will be analyzed for statistical variation of NOM properties, and their correlation to DBP formation. 4

15 CHAPTER II LITERATURE REVIEW 2.1 Chlorination, DBP formation, and NOM Characterization Aqueous chlorine has been used in the United States to disinfect drinking water preventing outbreaks of waterborne pathogens for over 100 years. Chlorine, either as gas or concentrated aqueous hypochlorite solution, is the predominant choice for primary and secondary disinfection for 90% of drinking water systems in the US (AWWA, 2000). However, aqueous chlorine has been found to react with natural organic matter (NOM) and other anthropogenic chemicals not removed through conventional drinking water treatment (i.e., coagulation, flocculation, sedimentation, and filtration) (Bell-Ajy et al., 2000). Public health concerns exist due to the formation of disinfection byproducts (DBPs), particularly trihalomethanes (THM) and haloacetic acids (HAA), which are the two most prevalent DBPs classes resulting from chlorination (Liang & Singer, 2003). THMs and HAAs are carcinogenic, genotoxic, cytotoxic, and hepatotoxic (Muellner et al., 2007; Plewa et al, 2008). Toxicological studies have shown that exposure to THMs and HAAs can elicit reproductive and developmental effects in laboratory animals as well as human health effects such as blood and kidney damage (USEPA, 2006). Based on the potential for human health effects from consuming DBPs formed in chlorinated drinking 5

16 water, the Disinfectants/Disinfection Byproducts (D/DBP) rule established the maximum contaminant levels (MCLs) for a few classes of these byproducts in finished drinking water and determined specific NOM removal requirements through enhanced coagulation (USEPA, 1998; USEPA, 2006). The MCLs for HAAs and THMs are 60µg/L and 80µg/L respectively. For HAAs, 60µg/l represents the sum of the 5 regulated HAAs including trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), and dibromoacetic acid (DBAA) on a total mass per volume basis. The sum of the concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform are regulated on at 80µg/l for THMs. NOM removal prior to chlorination is one strategy to reduce the DBP formation. Stage 1 of the D/DBP rule established guidelines for the amount of NOM to be removed through enhanced coagulation as a function of source water alkalinity (Bell-Ajay et al., 2000). Stage 2 of the D/DBP rule mandated that there must be a minimum disinfectant residual detected throughout the entire drinking water distribution system. Therefore, reducing DBP formation is highly dependent on treatment processes to reduce the concentration of NOM but also the components that specifically result in DBP formation (i.e., DBP precursors). However, NOM is a complex mixture of soluble organic components that are operationally divided into two fractions: hydrophobic and hydrophilic (Marhaba & Yong Pu, 2003). Hydrophobic fractions primarily consist of humic and fulvic acids (Kanokkantapong et al., 2006). Humic acid is described as being soluble in dilute alkaline media and will precipitate upon acidification; whereas fulvic 6

17 acid will remain in the solution at ph 2 (Steelink, 1977). The hydrophilic fraction is composed of low molecular weight carbohydrates, proteins, and amino acids (Marhaba & Yong Pu, 2003). Each fraction can act as a precursor to DBP formation in the presence of chlorine, though hydrophobic fraction contains higher concentrations of DBP precursors (Leenheer & Croué, 2003). 2.2 Conventional Treatment Processes for NOM removal Conventional technologies used to remove NOM during drinking water treatment include enhanced coagulation, membranes and activated carbon. Of these processes, coagulation is the most widely used in water treatment. Enhanced coagulation is defined as an excess amount of coagulant added to not only reduce turbidity but to reduce the concentration of NOM (Singer, 2002). Negatively charged NOM creates a coagulant demand for positively charged aluminum (Al 3+ ) species resulting in a stoichiometric relationship between the alum dose and the raw water concentration and composition NOM that is ph dependent (Edzwald & Tobiason, 1999). Due to the negatively charged carboxylic acids groups within the hydrophobic NOM fraction, NOM and turbidity are removed during enhanced coagulation (Bell-Ajay et al., 2000; AWWA, 2000). Lowering the ph to reach optimal NOM removal with aluminum based coagulants may not always be cost effective, so alternative treatment processes may need to be evaluated (AWWA, 2000). Activated carbon, in either powder (PAC) or granulated (GAC) forms, has been used to remove NOM by adsorption to the carbon surface reducing the presence of DBP 7

18 precursors in the finished water prior to chlorination (Kim & Kang, 2008). PAC is widely used to reduce the concentration of trace organics in drinking water. Activated carbon processes are very costly do to the amount of PAC required for NOM removal or the operation and maintenance of up flow GAC contactors or sand filter caps. Since NOM is comprised of a wide range of molecular weights and functional groups, membranes are an alternative method for NOM removal (Chang et al., 2009). Membrane filtration consists of four different types of pressure driven processes: reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). RO has been used for the removal of anions and cations from fresh water, which can be very costly due to the power required to generate pressures of 150-1,200 psi. NF is used for removing NOM, color, DBP precursors and hardness. NF has emerged as a reliable treatment process for NOM removal and water softening because the membranes operate at the lower pressures (75-150psi) (Jacangelo et al., 1995). UF membranes cover a wider range of particle sizes and can provide NOM removal at high pressures or liquid-solid separation at lower pressures (Jacangelo et al, 1995). MF primarily deals with particulate and microbial removal due to the membrane pore size approximately 0.1 µm. Membranes can substantially reduce NOM concentrations but require conventional surface water pretreatment (coagulation, flocculation, and sedimentation) to reduce constituents that can foul the membranes like hydrophobic NOM and divalent cations such as calcium and magnesium (Chang et al., 2009). 8

19 2.3 Anion Exchange for NOM Removal Anion exchange resins are efficient and emerging alternative technology for removing NOM. Anion exchange resins are complex polymeric surfaces designed for trapping and exchanging ions that are bounded to a bead like structure (Croue et al., 1999; Singer, 2002; Tan et al., 2005). Anion exchange occurs when a resin exchanges its negatively charged exchangeable ion with negatively charged NOM functional groups, causing the NOM to absorb to the resin surface. Waters containing low molecular weight humic substances, soluble microbial products and proteins can be difficult to remove by coagulation (Edswald, 1993; Bolto et al., 2004); therefore, anion exchange resins (AERs) have been used for the selective removal of these DBP precursors. AERs are capable of removing high and low molecular weight (MW) organic components while coagulation/flocculation mostly removes high molecular weight NOM components. Humbert et al. (2008) examined the potential of AERs for NOM removal and found that AERs are able to remove 75% of NOM after approximately 30 minutes of contact time. MIEX is a strongly base anion exchange resin used to remove NOM from raw water sources using chloride as the exchangeable anion. Ion exchange resins usually have an exchange capacity value >1.0. Due to its innovative yet proprietary formation, MIEX s capacity is usually significantly less than other commercially available anion exchange resins. However, the smaller size, 180µm, and magnetic iron bead structure allows for selective removal of NOM and promotes bead aggregation increasing it settling characteristics when compared to other AERs (Singer et al., 2007). MIEX resin (Orica Watercare, Watkins, CO) has been successfully used to remove NOM and 9

20 bromide from a wide range of source waters with significantly different characteristics (Hsu & Singer, 2010; Mergen et al., 2008; Tan & Kilduff, 2007; Drikas et al, 2009; Singer & Bilyk, 2002). When MIEX was applied to waters containing higher concentrations of bicarbonate, bromide, and chloride; NOM and bromide were effectively removed although bromide removal was found to be a function of water hardness (Hsu & Singer, 2010). Pre-treatment with MIEX has shown to reduce DBP formation potential of HAAs (HAAFP) and THMs (THMFP) by up to 70% (Boyer & Singer, 2005). Based on the chemical makeup of the raw water, pre-treatment with MIEX can remove up to 90% of DOC (Wert et al, 2005). MIEX has high selectivity for NOM with high specific ultra-violet absorbance, SUVA, which has been found to be a reliable estimation of source water aromaticity (Boyer et al, 2008; Hsu & Singer, 2010). MIEX has faster kinetic removal of NOM compared to other AERs (Humbert et al., 2005). 2.4 Spectroscopic Techniques used to Determine NOM Removal Spectroscopic techniques have been used to characterize the reaction of aqueous chlorine with NOM. Initially, differential UV spectroscopy at λ = 272 nm, has been used to characterize the reaction of aqueous chlorine with NOM (Korshin et. al., 1997). Correlations were later developed to describe the formation of THMs and HAAs due to changes in adsorption at 272 nm, which was used as a surrogate for NOM structural changes due to reaction with aqueous chlorine (Korshin et. al., 2002). However, UV spectroscopy provides a featureless spectra proving difficult to ascertain specific information about structural changes in NOM due to reaction with aqueous chlorine. 10

21 Fluorescence spectroscopy is an optical technique used to characterize NOM based on concentration and composition. NOM fluorescence occurs when an electron in the NOM structure absorbs energy from light which excites an electron and promotes it into an unoccupied orbital (Stedmon et al., 2003). After the energy is relaxed, the electron eases to its ground state emitting light. The difference in the initial state and the excited state determines the range of light wavelengths emitted, which are generally lower in energy than the excitation wavelength (Hudson et al., 2007). NOM profiling has been achieved through the use of fluorescence excitation-emission matrices (EEM), which captures the fluorescence spectra across a wide range of excitation and emission wavelengths (Christensen et al., 2005). Coble (1996) characterized humic-like and protein-like organics in freshwater, coastal, and marine environments by observing the location of peak intensities within the matrix. Due to the complexity of the EEM spectra, NOM has been characterized by peak intensity excitation-emission pairs taken from the EEM (Marhaba and Kochar, 2000). The EEM spectra for most freshwaters used as drinking water sources can be characterized through three main fluorescence intensities, peak A (humic and fulvic-like), peak C (humic and fulvic- like) and peak T (protein-like). The A and C peaks are evaluated because the humic/fulvic- like material are primarily responsible for the formation of DBPs during chlorination (Coble, 1996). The intensities of peaks A, C, and T have been successfully used to monitor DOC removal (Gone et al., 2009). Fluorescence peaks A, C generally decrease throughout water treatment procedures like enhanced coagulation, while peak T (i.e., protein-like peak) is less affected by conventional surface water treatment processes. 11

22 Specific components within the EEM spectra have been correlated with both DBP formation and chlorine consumption. Johnstone and Miller (2009) used regional analysis of fluorescence EEMs before and after chlorination to predict chlorinated DBP formation through parallel factor analysis (PARAFAC). PARAFAC is a statistical model that decomposes data into tri-linear components, which is well suited to describe three dimensional EEM spectra (Stedmon et al., 2003). Combined with multifactor regression analysis, the three components determined from PARAFAC modeling and chlorine consumption were found to correlate to chloroform, TCAA, and DCAA formation. Using the PARAFAC component model to analyze fluorescence spectra could be an effective tool to predict DBP formation and identify DBP precursors in the EEM spectra. 12

23 CHAPTER III EXPERIMENTAL PROCEDURES 3.1 Materials Chlorination experiments were conducted with commercial 10-15% sodium hypochlorite (NaOCl) purchased from Sigma Aldrich (St. Louis, Missouri). Aqueous stock solutions and experiments utilized laboratory-prepared deionized water (18.2 MΩcm -1 ) from a Barstead ROPure/DiamondPure system (Barnestead-Thermolyne Corp., Dubuque, IA). All water samples, prior to analysis, were 0.45 µm filtered with membrane filters purchased from Millipore (Billerica, MA), which was prerinsed with deionized water. The ph for each experiment was adjusted with either 1 N H 2 SO 4 or NaOH and measured using a Thermo Scientific Orion 5 star meter with a ROSS ultra combination ph electrode probe. All other organic and inorganic chemicals were certified ACS reagent grade. The glassware used in this study was soaked in a concentrated free chlorine solution for 24 hours, and rinsed multiple times with deionized water and dried prior to use. All chlorination experiments were conducted at constant temperature (25± 1 C). Source waters used in the experiments were collected from the Akron and Barberton water treatment plant intake prior to conventional surface water treatment. Akron and Barberton were chosen in this study due to their different water 13

24 characteristics. Akron is more humic and fulvic like while Barberton is more microbial. The Akron/Barberton source water characteristics are shown in Table

25 Table 3.1 NOM and Source Water Characteristics Fluorescence Base Pairs (RU) ph TOC (mg/l) UV254 UV272 A C T SUVA (L/mg) Akron Barberton Alkalinity (mg CaCO3/L) Chloride (mg/l) Sulfate (mg/l) Fluoride (mg/l) Nitrate (mg/l) Sodium (mg/l) Potassium (mg/l) Hardness (mg CACO3/L) Akron Barberton

26 3.2 Methods and Procedures In order to compare the three commercial resins as well as the two coagulants the following experiments were ran Anion exchange resin (AER) preparation and experiments MIEX anion exchange resin (Orica Water Care, Watkins, CO) arrived in a sodium chloride brine solution. Amberlite IRA-910 and IRA-958 (Rohm and Haas, Philadelphia, PA) were purchased from Sigma Aldrich. Before use the Amberlite resins were first rinsed with 6 liters of deionized water. Approximately 50 g of the Amberlite resins were added to 200 ml of methanol and shaken for 30 minutes, collected from the methanol with Whatman GF/C glass filter, and repeated until three full methanol rinses were achieved. Storage solution for the Amberlite IRA-910 was 7.5% NaOH solution and the Amberlite IRA-958 was stored in 20% NaCl and 2% NaOH solution, and MIEX was stored in the 5%NaCl solution it arrived in. Prior to use, each resin was filtered with a 0.45µm membrane filter using a Fisher Scientific Maxima C vacuum pump, rinsed with 5L of deionized water, and then dried under vacuum. The characteristics of the three strong anionic resins used are listed in Table 2. 16

27 Table 3.2 Anion exchange resin structural characteristics and capacities AER Type Structure Size (µm) Capacity (meq/ml) Water Content (%) MIEX (OricaWatercare) MP Acrylic IRA-910 (Rohm & Haas) MP Styrene 510 > IRA-958 (Rohm & Haas) MP Acrylic 630 >

28 The efficacy of the three selected AERs was evaluated with batch experiments performed on 1.5 L rough filtered (20-25µm pore size) source water under constant stirring at 150 rpms with a Phipps and Bird stirrer (Richmond, VA) in the presence of 3.2 g/l of AER. Samples of treated water (20 ml) were taken at five different contact times (15, 30, 45, 60, and 75 minutes) and UV 254, 272, TOC, and fluorescence peaks A, C, and T were monitored as a function of time. Additional MIEX experiments were conducted over the ph for both source waters. The ph of 1 L of source water was adjusted to ph 6.5 and 7.5 using 1 N sulfuric acid, 1 L adjusted to ph 9.0 using 1 N sodium hydroxide and 1 L was kept at its native ph ( 8, see Table 3.1). Then each ph adjusted source water was stirred for approximately 1 hour at 150 rpms, as previously described. After settling, the water was then filtered through pre-rinsed 0.45 µm filters. All the experiments were performed in duplicate Coagulation Experiments The two coagulants were used to compare their NOM removal capacity compared to anion exchange. Aluminum chloro hydrate (ACH) and aluminum sulfate (Alum) were chosen due to their wide-spread use in the water treatment industry. Previous doseresponse jar tests found the optimal doses of ACH and Alum were 10mg/l and 40 mg/l respectively for effective NOM removal. The coagulants were first rapid mixed using a Phipps and Bird stirrer at 100 rpms for 1 minute, then 30 rpms for 30 minutes to promote flocculation, and allowed to settle for 1 hour. 18

29 3.2.3 Chlorine Experiments Chlorination experiments were performed on raw, anion exchange (i.e., MIEX), and coagulant treated source waters over the ph range of Initially, 500-mL of either treated or native source water was dosed with aqueous chlorine under rapid mix conditions achieving an initial aqueous chlorine concentration of 3.55 mg/l-cl 2. After chlorination, the 500mL of treated water was transferred to four 120 ml chlorine demand-free amber bottles. The chlorinated samples were stored in the dark and incubated at 25±1 C. After 24 hours, chlorine residuals were quenched with sodium sulfite at 20% stoichiometric excess of the initial aqueous chlorine concentration prior to analysis for DBPs, ph, fluorescence, and UV 254 and UV 272 measurements. The amber bottles were used in their entirety and ph was monitored to ensure it did not vary by more that ±0.2 of their original ph over the time course of the experiment. Additional chlorination experiments were performed at a chlorine concentration of 10.5 mg/l to clearly define the effect each treatment process on DBP formation. After 1, 4, 12, and 24 hours, bottles were quenched and 100 ml samples were analyzed for DBPs, ph, fluorescence, and UV 254 and UV 272 were also monitored. Chlorine residuals were measured at 1 and 24 hours DBP Analysis Samples for DBP analysis were extracted immediately after quenching to avoid potential artifacts due to sample storage. These samples were first acidified with concentrated sulfuric acid to ph < 0.5, then 30 g of dried sulfate was added to each 19

30 sample and initially mixed by hand prior to being spiked with 1.0 µg/l of 1, 2 dibromopropane (internal standard). Finally, 3-mL of Methyl tert-butyl Ether (MtBE) was added for DBP extraction. Samples were mixed for 30 minutes with a Burrell wrist action shaker (Pittsburgh, PA). The organic phase was then removed and transferred to amber vials. For THM analysis, 0.5 ml of the organic phase from each sample was transferred into the 2.0mL amber vials for analysis. Diazomethane was used to derivatize the neutral HAA species to either corresponding methyl esters. To the inner tube of the diazomethane generator, 367mg of diazold and 1.0mL of carbitol were added. The outer generator tube contained 3mL of MtBE. Using a glass body syringe, 1.5mL of 37% KOH was added slowly and diazomethane was generated for approximately 30 minutes. Then 0.25mL of diazomethane was added to 0.5 ml of the sample extract and mixed together in 2.0 ml vials. Derivatization was allowed to proceed for 30 minutes prior to quenching excess diazomethane with silica gel. The four regulated THMs and all nine HAAs were quantified from extracted standards over the calibration range of ppb. HAA and THM analysis was performed with an Agilent 7980A gas chromatograph/mass spectrometer (GC/MS) (Santa Clara, CA) operated in constant pressure mode. A 30 meter, 250µm diameter Restek RTX-5ms column with a film thickness of 0.5µm was used for the analysis. The THM temperature initially started at 35 C and was held for 5 minutes before ramping at 20 C/minute until 250 C. The HAA method had an initial temperature of 35 C and held for 5 minutes, and then ramped in three steps: 1) 5 C/ minute to 7 5 C that held for 15 minutes, 2) 5 C/ minute to 100 C that held for 5 minutes, 3). 5 C/ minute to 135 C and held for 5 minutes. 20

31 3.2.5 Fluorescence and UV Spectroscopy Fluorescence and UV spectroscopy was used to obtain the spectral characteristics for the source waters as well as to monitor spectral changes as a function of treatment process. Prior to obtaining the fluorescence spectra, the sample was first acidified with sulfuric acid to lower the ph to and the ionic strength was adjusted with 0.1M KCl. The fluorescence spectra for both the raw and treated samples were obtained with a Hitachi F-7000 fluorescence spectrophotometer (Schaumburg, IL). From the fluorescence spectra, three peaks (A, C, T) were selected to best describe the source water Table 3.1. The three peaks values are provided in Raman Units (RU). A Shimadzu UV-1601 spectrophotometer (Columbia, MD) was used to obtain the UV absorbance of samples containing NOM at 254 nm and 272 nm Ion Analysis Ion analysis was performed using a Dionex ICS-3000 ion chromatograph (IC) (Sunnyvalle, CA). The IC was calibrated for anions: Fluoride, nitrite, bromide and arsenate are from 0-100µM; iodate from 0-40 µm; nitrate and phosphate from µm; sulfate and chloride from µm. The IC is calibrated for cations: sodium, potassium, magnesium, calcium from µm and ammonia for µm. Anion analysis was performed with an AS20 column with an AG20 guard and a potassium hydroxide eluent gradient of 5mM for 0-5 minutes, 5mM-30mM for 5-15 minutes, 30-55mM for minutes. Cation analysis was performed with a CS12A column with a CG12A guard under isocratic conditions with 20 mm Methanesulfonic acid eluent. The 21

32 IC flow rate, for both the cations and anions, was 1mL/min, under constant temperature 30 C, and a 10mL injection volume. 22

33 CHAPTER IV RESULTS AND DISCUSSION This chapter was divided into three sections to discuss the experimental results. The first section presents experimental results of NOM removal by anion exchange resins (AERs). Section two compares the effect of magnetic ion exchange (MIEX) resin and other removal NOM removal strategies as a function of ph. The final section compares DBP formation upon chlorination of the treated source water (i.e., enhanced coagulation or MIEX) over the ph range and at different initial chlorine concentrations. 4.1 Kinetic Removal of NOM with select AERs AERs have shown to be a treatment option to remove NOM components that conventional treatment processes do not. However, very little is known about the kinetic rate of NOM removal in the presence of different AERs. Therefore, three AERs commonly used in drinking water treatment, MIEX, IRA-910, and IRA-958, were examined for their capacity to remove NOM as monitored by TOC and UV absorbance at λ 254 and λ 272 as a function of time (Figures ). An AER resin dose of 3.2 g/l was chosen based on the suggested manufacture MIEX resin dose of 5ml/L, which was used for all three resins. The three resins were found to be effective at removing NOM; however, MIEX removed NOM at faster rate than the other Amberlite resins. At an initial NOM concentration of 6.43 mg/l, MIEX reduced the NOM concentration 23

34 approximately 68% within 15 minutes of contact time to 2.04 mg/l while the residual NOM concentrations in the presence of IRA-910 and IRA-958 resins were 3.66 and 3.46 mg/l respectively (Figure 4.1). IRA-910 and IRA-958 removed approximately 60% of the NOM initially present, while MIEX removed 77% of the NOM after 75 minute contact time as measured by TOC. While MIEX appeared to remove NOM more rapidly, all AERs were found to be highly proficient at NOM removal, specifically the moieties that absorb UV light at 254 and 272 nm over 75 minutes of contact time (Figures 4.2 and 4.3). When monitoring NOM removal with UV spectroscopy, the IRA-910 and IRA-958 resins removed approximately 80% of UV 254 and UV 272 absorbing moieties, while MIEX removed 91% of NOM components initially present that absorb UV light. This appears to indicate that the AERs prefer sorption of aromatic moieties; however, MIEX was found to remove more NOM and the components that absorb UV light as a function of time. Fluorescence spectroscopy was also used to monitor the reduction of specific components within NOM-EEM spectra in the presence of the AERs as a function of time. The fluorescence spectra showed that EEM base pairs designated A and C sharply decrease with increasing contact times in the presence of all three AERs. MIEX showed a slightly higher removal after 75 minutes resulting in a reduction of 71% and 75% for peaks A and C respectively, while the IRA-910 and IRA-958 had a reduction of EEM base pairs A and C of 67-68% and 72-73% respectively. 24

35 7 DOC content (mg/l) IRA 910 IRA 958 MIEX Contact Time (minutes) Figure 4.1 Monitoring DOC removal for Akron as a function of time in the presence of AERs: [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c,. 25

36 0.12 UV Absorbance at 254nm (1/cm) IRA 910 IRA 958 MIEX Contact Time (minutes) Figure 4.2 Monitoring UV 254 reduction for Akron as a function of time in the presence of AERs: [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 26

37 0.10 UV Absorbance at 272nm (1/cm) IRA 910 IRA 958 MIEX Contact Time (minutes) Figure 4.3 Monitoring UV 272 reduction for Akron as a function of time in the presence of AERs: [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 27

38 60 Intensity (RU) IRA 910 IRA 958 MIEX Contact Time (minutes) Figure 4.4 Monitoring EEM base pair A reduction for Akron as a function of time in the presence of AERs: [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 28

39 25 20 IRA 910 IRA 958 MIEX Intensity (RU) Contact Time (minutes) Figure 4.5 Monitoring EEM base pair C reduction for Akron as a function of time in the presence of AERs: [AER] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 29

40 MIEX was found to perform better then the Amberlite anion exchange resins for NOM removal, especially the components with high aromatic character. This could be due to its physical characteristics that differ from the conventional ion exchange resins. The resin particle size is approximately 180µm, which is times smaller than the Amberlite resins. The smaller resin size creates a higher external surface area allowing for quicker NOM sorption kinetics, which resulted in a reduction in 68% NOM concentration within 15 minutes of contact time. This differs from previously published results that show a slightly faster NOM removal rate due to higher AER concentration (Humbert et al., 2005). The magnetic iron oxide that is incorporated into the resin s structure allows it to aggregate faster, which creates larger particles with better settling characteristics than other the AERs. Therefore, MIEX was chosen to perform additional experiments in order to further assess removal of NOM and potential DBP precursors. 4.2 Comparison of NOM Removal Processes MIEX is now compared at a range of phs in order to determine if MIEX is ph dependent. After determining if MIEX is ph dependent, MIEX will be compared to two coagulants for NOM removal MIEX removal of NOM as a function of ph Preliminary jar-tests experiments were conducted to determine of the effect of ph on NOM removal in the presence of MIEX. Figures show the reduction of intensities of UV 254, UV 272 and fluorescent peaks A and C for Akron source water over the ph range of in the presence of MIEX. Results show that ph had no 30

41 significant effect on the removal of chromophores and fluorophores (i.e. EEM base pairs A and C) when treated with MIEX. Chromophore and fluorophore intensities were within 5% regardless of ph throughout 90 minutes of contact time. Monitoring UV 254 and UV 272 reduction over time, 83% of UV absorbing moieties was removed after 90 minutes of contact time with approximately 65% within the first 15 minutes. Fluorescence peaks A and C were reduced by approximately 63% within 15 minutes of contact time with MIEX, and the peak intensities were overall reduced by 80% after 90 minutes of contact time. The ph of the aqueous system appears to have no effect on NOM removal in the presence of MIEX. 31

42 0.14 UV Absorbance at 254nm (1/cm) ph 9.0 ph 8.2 ph 7.5 ph Contact Time (minutes) Figure 4.6 Monitoring UV 254 reduction as a function of time in the presence of MIEX: [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 32

43 0.12 UV Absorbance at 272nm (1/cm) ph 9.0 ph 8.2 ph 7.5 ph Contact Time (minutes) Figure 4.7 Monitoring UV 272 reduction as a function of time in the presence of MIEX: [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 33

44 1.2 Fluorescence Reduction ph 9.0 ph 8.2 ph 7.5 ph Contact Time (minutes) Figure 4.8 Monitoring EEM base pair A reduction as a function of time in the presence of MIEX: [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 34

45 1.2 Fluorescence Reduction ph 9.0 ph 8.2 ph 7.5 ph Contact Time (minutes) Figure 4.9 Monitoring EEM base pair C reduction as a function of time in the presence of MIEX: [MIEX] = 3.2 g/l and [DOC] o = 6.43 mg/l-c. 35

46 4.2.2 MIEX and Enhanced Coagulation Treatment Processes for NOM Removal Akron and Barberton source waters were treated with MIEX, ACH, and alum and were the effectiveness of each process to remove NOM. NOM was evaluated by measuring DOC concentration, UV absorbance at λ 254 and λ 272 and fluorescence EEM base pairs peaks A and C. The initial DOC concentration for Akron source water was 6.43 mg/l, which the residual DOC concentration was observed to decrease after each treatment process. After 60 minutes of contact time, MIEX significantly decreased DOC concentration by 76% to 1.52 mg/l, while treatment with ACH and alum reduced the DOC concentration to 4.2 and 4.08 mg/l respectively (Tables 4.1 and 4.2). However, DOC reduction may not correspond to reduction in DBP precursors, which is generally indicated by reduction in UV-absorbing moieties. MIEX was also observed to significantly reduce the concentration of UV-absorbing moieties by approximately 80% after one hour of contact time. Although the coagulants may not have achieved similar reduction in DOC concentration when compared to MIEX, ACH and alum were able to remove 50% to 63% of UV-absorbing moieties respectively. For the Akron source water, all three NOM removal processes achieved significant reductions in potential DBP precursors as measured by UV 254 and UV 272. The treatment processes were then applied to the Barberton source water. MIEX was able to reduce the DOC from an initial concentration of 4.15 mg/l to 1.51 mg/l. Treatment with ACH and alum reduced DOC to 2.89 and 2.98 mg/l respectively. The 36

47 Table 4.1 DOC concentration and UV spectral characteristics for Akron and Barberton source waters before and after MIEX over the ph range of Percent removals are given in brackets in respect to the initial value. DOC (mg/l) UV 254 (cm -1 ) UV 272 (cm -1 ) Akron Raw Akron MIEX 1.52 (76%) (81%) (79%) Barberton Raw Barberton MIEX 1.51 (63%) (66%) (63%) Table 4.2 DOC concentration and UV spectral characteristics for Akron and Barberton source waters before and after enhanced coagulation over at ph 6.5 and 8.2. Percent removals are given in brackets in respect to the initial value. DOC (mg/l) UV 254 (cm -1 ) UV 272 (cm -1 ) Akron Raw Akron ACH 4.2 (35%) (54%) (50%) Akron Alum 4.08 (37%) (63%) (58%) Barberton Raw Barberton ACH 2.89 (30%) (34%) (24%) Barberton Alum 2.98 (28%) (25%) (13%) 37

48 amount of DOC removed for Barberton is comparable to the amount of UV-absorbing materials removed. MIEX was able to remove 66% while ACH and alum removed 13-34%. The NOM removal process were found to be less effect for the Barberton source water when compared to Akron; however, MIEX significantly reduced the DOC concentration and intensities of UV absorbing moieties with respect to enhanced coagulation. The coagulants were observed to be more effective in removing DOC and UVabsorbing moieties for the Akron source water when compared to the Barberton source water. SUVA is the ratio of the intensity of UV-absorbing moieties at λ 254 to DOC concentration (UV 254 expressed as per meter divided by the concentration of DOC expressed in milligrams per liter). Carbon-13 nuclear magnetic resonance has been used to determine a strong correlation between SUVA 254 and the aromatic carbon content for a large number of NOM fractions (Croué et al., 1999), which has been used as a surrogate for DBP formation potential. The initial SUVA 254 value for Akron was 1.96 L/mg-m and Barberton was 1.13 L/mg-m. After alum treatment for both Akron and Barberton source waters, the SUVA value dropped for Akron to 1.12 L/mg-m while the SUVA for Barberton increased to 1.17 L/mg-m. Similar results were found for MIEX as well as ACH. This suggests that DOC removed by each treatment process for the Barberton source water may not significantly contribute to DBP formation upon chlorination. Previous research has found DBP formation to be dependent on SUVA, with higher SUVA values yielding greater THM and HAA formation potentials in the presence of aqueous chlorine (Liang and Singer, 2003). Therefore, the DBP precursors in the 38

49 Barberton source water are not significantly removed by any of the treatment processes applied here. Fluorescence spectroscopy was also used to monitor the reduction of specific components within in the NOM matrix. The Akron and Barberton source water were characterized by peak intensity excitation-emission pairs taken from the EEM spectra (Marhaba and Kochar, 2000). The locations of the Akron peaks are: peak A is located on excitation λ= 219 nm, emission λ= 404 nm, peak C is located on excitation λ= 304 nm, emission λ=414 nm and peak T is located on excitation λ= 224 nm and excitation λ= 298 nm. The Akron source water has initial peak intensities for A, C and T equal to 53.56, and RU (Figure 4.10). The region where the T peak occurs for the Akron source water was not well defined assumed to be due to relaxation of the A peak, which the fulvic peak is substantial. Peak T is related to microbial activity resulting in low molecular weight compounds containing amine moieties and other soluble protein material, therefore, no protein-like moieties appear to be present in the Akron source water. MIEX reduced peaks A and C for Akron by 86% and 89% respectively. ACH coagulation reduced peak intensities 45% for peak A and 44% for peak C. Alum also reduced peak intensities by 42%for peak A and 47% for peak C. Though all the treatments showed adequate removal of NOM, MIEX was found to significantly reduce humic/fulvic components in the Akron source water. Fluorescence spectroscopy was then used to examine the effectiveness each treatment had on reducing the intensities of the A, C, and T peaks in the EEM spectra of Barberton source water. The locations of the EEM peaks for Barberton are: peak A is 39

50 located on excitation λ= 219 nm and emission λ= 406 nm, peak C is located on excitation λ= 309 nm and emission λ= 416 nm, and peak T is located on excitation λ= 224 nm and excitation λ= 298 nm. The Barberton source water had initial peak intensities for A, C and T equal to 22.82, and RU respectively. MIEX reduced peak intensities for A, C, and T by 74%, 76% and 26% respectively. ACH coagulation reduced peak intensities for A, C, and T by 42%, 43% and 12% respectively. Alum was also found to reduce peak intensities for the Barberton source water with a 36% reduction in peak A, 37% for peak C and 16% for peak T. Overall, reduction in peak intensities A and C were observed to be similar with respect to each treatment process for both source waters; however, the peak intensity T was found to be relatively resilient to each NOM removal process for the Barberton source water. In order to determine which DOC components are effectively removed during coagulation, Gone et al plotted the reduction of fluorescence intensity peaks A, C, and T to DOC removal. Their results showed that Al and Fe salts do not efficiently coagulate nitrogen compounds and proteins found in the T region of the EEM spectra; however, iron and aluminum salts were found to be very effective at reducing peak intensities in the A and C region of the EEM spectra that are mostly associated with humic and fulvic materials. 40

51 (a) (b) (c) (d) Figure EEM spectra for (a) Akron Raw, (b) MIEX, (c) ACH, and (d) Alum ([DOC] Raw = 6.43 mg/l, [DOC] MIEX = 1.52 mg/l, [MIEX] Dose = 3.2 g/l, [DOC] ACH = 4.20 mg/l, [ACH] Dose = 10 mg/l, [DOC] Alum = 4.08, [Alum] Dose = 40 mg/l). 41

52 (a) (b) (c) (d) Figure EEM spectra for: (a) Barberton Raw, (b) MIEX treated water,, (c) ACH, and (d) Alum ([TOC] Raw = 4.15 mg/l, [TOC] MIEX = 1.51 mg/l, and [MIEX] Dose = 3.2 g/l,[doc] ACH = 2.89 mg/l, [ACH] Dose = 10 mg/l, [DOC] Alum = 2.98, [Alum] Dose = 40 mg/l). 42