Applied Science, Faculty of
Civil Engineering, Department of
DSpace
UBCV
Borah, Archita
Master of Applied Science - MASc
University of British Columbia
Biological Ion Exchange (BIEX) offers effective removal of dissolved organic carbon (DOC) from surface waters without the need for frequent regeneration, making it suitable for small and remote communities. Traditional work hours, night routines, and system maintenances can impose conditions in small and remote communities, where inflow of water to be treated is highly variable, and possibly intermittent. The present study investigated the impact of periods of no inflow on DOC removal by BIEX systems. Various operating conditions were applied to the BIEX systems, to investigate if the extent of the potential impacts of periods of no inflow were influenced by the duration and/or frequencies of these periods. Effluent recirculation within the BIEX systems were also considered as a means to mitigate the extent of the potential impacts of periods of no inflow. The results of the present study indicated that three phases with distinct treatment mechanisms occurred in the BIEX systems: primary IEX, secondary IEX, and stunted secondary IEX (i.e., biodegradation). Considering these three phases of treatment, in general, operation of BIEX systems with periods of no inflow impacted DOC removal. The extent of the potential impacts of no inflow on DOC removal was also affected by the duration and/or frequency of the periods of no inflow. DOC removal in BIEX systems operated with a daily and short (~3h) period of no inflow and a weekly and long (~2d) period of no inflow were similar to continuous operations. However, a daily and long (~8h) period of no inflow resulted in a lower DOC removal than continuous operations. Also, in general, extent of the potential impacts of operation with periods of no inflow on DOC removal could not be mitigated by effluent recirculation within the BIEX systems. Overall, the study offered insight into operation of BIEX systems with periods of no inflow and the impact of the duration and/or frequency of periods of no inflow as well as effluent recirculation on the DOC removal performance. The results of the present study concluded BIEX systems can maintain water quality even under periods of no inflow.
Impact of periods of no inflow on dissolved organic carbon (DOC) removal by Biological Ion Exchange (BIEX) systems by Archita Borah B.Eng, Gauhati University, 2016 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) March 2022 © Archita Borah, 2022 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, a thesis entitled: Impact of periods of no inflow on dissolved organic carbon (DOC) removal by Biological Ion Exchange (BIEX) systems submitted by Archita Borah in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering Examining Committee: Dr. Pierre Bérubé, Professor, Environmental Systems Engineering, Department of Civil Engineering Supervisor Dr. Madjid Mohseni, Professor, Department of Chemical and Biological Engineering and Scientific Director, RES’EAU Centre for Mobilizing Innovation Supervisory Committee Member iii Abstract Biological Ion Exchange (BIEX) offers effective removal of dissolved organic carbon (DOC) from surface waters without the need for frequent regeneration, making it suitable for small and remote communities. Traditional work hours, night routines, and system maintenances can impose conditions in small and remote communities, where inflow of water to be treated is highly variable, and possibly intermittent. The present study investigated the impact of periods of no inflow on DOC removal by BIEX systems. Various operating conditions were applied to the BIEX systems, to investigate if the extent of the potential impacts of periods of no inflow were influenced by the duration and/or frequencies of these periods. Effluent recirculation within the BIEX systems were also considered as a means to mitigate the extent of the potential impacts of periods of no inflow. The results of the present study indicated that three phases with distinct treatment mechanisms occurred in the BIEX systems: primary IEX, secondary IEX, and stunted secondary IEX (i.e., biodegradation). Considering these three phases of treatment, in general, operation of BIEX systems with periods of no inflow impacted DOC removal. The extent of the potential impacts of no inflow on DOC removal was also affected by the duration and/or frequency of the periods of no inflow. DOC removal in BIEX systems operated with a daily and short (~3h) period of no inflow and a weekly and long (~2d) period of no inflow were similar to continuous operations. However, a daily and long (~8h) period of no inflow resulted in a lower DOC removal than continuous operations. Also, in general, extent of the potential impacts of operation with periods of no inflow on DOC removal could not be mitigated by effluent recirculation within the BIEX systems. iv Overall, the study offered insight into operation of BIEX systems with periods of no inflow and the impact of the duration and/or frequency of periods of no inflow as well as effluent recirculation on the DOC removal performance. The results of the present study concluded BIEX systems can maintain water quality even under periods of no inflow. v Lay Summary Biological Ion Exchange (BIEX) systems can effectively treat water without the need for frequent regeneration, making this approach suitable for small and remote communities. BIEX systems must be designed to operate under intermittent flow caused by variable water demand in such communities. The present study investigated the impact of periods of no inflow on water treatment with BIEX systems, in terms of organic matter removal. The results suggested that operation of BIEX systems with periods of no inflow impacted organic matter removal. Operations of BIEX systems with a daily and short (~3h) period of no inflow as well as a weekly and long (~2d) period of no inflow were similar to continuous operation. However, a daily and long (~8h) period had a negative impact on the DOC removal by BIEX systems. Generally, the extent of potential impacts of periods of no inflow was not mitigated by effluent recirculation. vi Preface This dissertation is an original, unpublished, and independent work by the author, Archita Borah. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables .............................................................................................................................. xiii List of Figures ............................................................................................................................. xiv List of Equations ........................................................................................................................ xvi Acknowledgements ................................................................................................................... xvii Chapter 1: Introduction ................................................................................................................1 1.1 Overview ......................................................................................................................... 1 Chapter 2: Literature Review .......................................................................................................3 2.1 Natural Organic Matter (NOM) ...................................................................................... 3 2.1.1 Source and characteristics ........................................................................................... 3 2.1.2 Technologies available for DOC removal .................................................................. 4 2.2 Biological Ion Exchange (BIEX) .................................................................................... 4 2.2.1 Primary Ion Exchange (Primary IEX) ........................................................................ 5 2.2.2 Secondary Ion Exchange (Secondary IEX) ................................................................ 5 2.2.3 Biological Processes ................................................................................................... 6 2.2.4 Summary of literature review on BIEX ...................................................................... 7 2.3 Water treatment in small and remote communities ...................................................... 10 2.3.1 Water treatment with periods of limited to no inflow ............................................... 11 2.4 Knowledge Gap ............................................................................................................ 13 viii Chapter 3: Research Objectives and Hypotheses .....................................................................14 Chapter 4: Materials and Methods ............................................................................................15 4.1 Materials ....................................................................................................................... 15 4.1.1 Feed water ................................................................................................................. 15 4.1.2 BIEX System Setup .................................................................................................. 16 4.1.3 Operations of the BIEX systems ............................................................................... 19 4.1.4 Sampling procedure .................................................................................................. 19 4.2 Analytical Methods ....................................................................................................... 20 4.3 Data Analysis and Interpretation .................................................................................. 23 4.3.1 Mass Balance Analysis ............................................................................................. 23 4.3.1.1 Resin regeneration ............................................................................................ 24 4.3.2 Statistical Analysis .................................................................................................... 25 4.4 Quality Assurance and Quality Control (QA/QC) ........................................................ 26 4.4.1 Analytical methods ................................................................................................... 26 4.4.2 Data Analysis ............................................................................................................ 26 Chapter 5: Results and Discussion .............................................................................................28 5.1 Overall performance of BIEX systems ......................................................................... 28 5.1.1 Organics removal ...................................................................................................... 28 5.1.1.1 DOC removal .................................................................................................... 28 5.1.1.2 UV absorbance and specific UV absorbance in the effluents ........................... 32 5.2 Performance during phases of treatment ....................................................................... 35 5.2.1 Phase 1: Primary IEX................................................................................................ 36 5.2.1.1 Inorganics release and/or removal and organics removal during Phase 1 ........ 38 ix 5.2.1.1.1 Chloride release during Phase 1 .................................................................. 38 5.2.1.1.2 Sulphate removal during Phase 1 ................................................................ 41 5.2.1.1.3 DOC removal during Phase 1 ..................................................................... 46 5.2.2 Phase 2: Secondary IEX............................................................................................ 49 5.2.2.1 Inorganics release and/or removal and organics removal during Phase 2 ........ 51 5.2.2.1.1 Chloride release during Phase 2 .................................................................. 51 5.2.2.1.2 Sulphate release during Phase 2 .................................................................. 52 5.2.2.1.3 DOC removal during Phase 2 ..................................................................... 54 5.2.3 Phase 3: Stunted Secondary IEX .............................................................................. 57 5.2.3.1 Inorganics release and/or removal and organics removal during Phase 3 ........ 59 5.2.3.1.1 Chloride release during Phase 3 .................................................................. 59 5.2.3.1.2 Sulphate release during Phase 3 .................................................................. 60 5.2.3.1.3 DOC removal during Phase 3 ..................................................................... 62 5.3 Summary of rates of DOC removal .............................................................................. 63 5.4 Estimate of overall DOC removal pathways ................................................................ 65 5.4.1 DOC removal pathways defined by organic carbon mass balance ........................... 65 5.4.2 Patterns observed in DOC removal pathways .......................................................... 67 5.5 Other significant findings ............................................................................................. 67 5.5.1 Change in different phases of treatment in response to feed water changes ............ 67 5.5.2 Patterns in organics removal and inorganics release and/or removal ....................... 69 5.5.2.1 Patterns in organics removal ............................................................................. 69 5.5.2.2 Patterns in inorganics release and/or removal .................................................. 70 5.5.2.2.1 Patterns in chloride release .......................................................................... 70 x 5.5.2.2.2 Patterns in sulphate removal and/or release ................................................ 71 Chapter 6: Conclusion .................................................................................................................72 6.1 Conclusion .................................................................................................................... 72 6.1.1 Objective 1 ................................................................................................................ 72 6.1.2 Objective 2 ................................................................................................................ 72 6.1.3 Objective 3 ................................................................................................................ 73 6.2 Engineering implications of the present study .............................................................. 73 References .....................................................................................................................................75 Appendices ....................................................................................................................................83 Appendix A BIEX systems’ Experimental setup...................................................................... 83 A.1 Experimental Setup ................................................................................................... 83 A.2 Jericho Pond water characteristics ............................................................................ 84 A.3 Preparation of Purolite® A860 resins ....................................................................... 84 A.4 Operation of BIEX systems ...................................................................................... 85 A.5 Effluent volume corrections ...................................................................................... 86 Appendix B Estimation of IEX capacity .................................................................................. 89 Appendix C Normalization of cumulative bed volumes........................................................... 91 Appendix D Raw concentration data ........................................................................................ 92 D.1 Effluent DOC concentration data .............................................................................. 92 D.2 Percent DOC removal data ....................................................................................... 92 D.3 Effluent UV absorbance and specific absorbance data ............................................. 93 D.4 Effluent Chloride concentration data ........................................................................ 95 D.5 Effluent Sulphate concentration data ........................................................................ 96 xi Appendix E Summary of rates of removal and/or release in different phases of treatment ..... 99 E.1 Chloride release during Phase 1 ................................................................................ 99 E.2 Sulphate removal during Phase 1 ............................................................................ 100 E.3 DOC removal during Phase 1 ................................................................................. 101 E.4 Rate of release and/or removal during Phase 2 ....................................................... 102 E.5 Rate of release and/or removal during Phase 3 ....................................................... 102 Appendix F Anion loading in the BIEX systems, defined by phases of treatment ................ 103 Appendix G Ion exchange during Phase 1 and Phase 2 .......................................................... 108 G.1 Phase 1: Ion exchange ............................................................................................. 108 G.2 Phase 2: Ion exchange ............................................................................................. 112 Appendix H Summary of statistical analysis results in different phases of treatment............ 114 H.1 Phase 1: Chloride release ........................................................................................ 114 H.2 Phase 1: Sulphate removal ...................................................................................... 115 H.3 Phase 1: DOC removal............................................................................................ 117 H.4 Phase 2: Chloride release ........................................................................................ 118 H.5 Phase 2: Sulphate release ........................................................................................ 120 H.6 Phase 2: DOC removal............................................................................................ 122 H.7 Phase 3: Chloride release ........................................................................................ 123 H.8 Phase 3: Sulphate release ........................................................................................ 124 H.9 Phase 3: DOC removal............................................................................................ 124 H.10 Comparing Rates of DOC removal in Phase 2 and Phase 3 ................................... 126 Appendix I Results of organic mass balance .......................................................................... 127 I.1 Organic mass balance based on normalized cumulative DOC removed ................ 127 xii I.2 Organic mass balance based on resin regeneration ................................................. 127 Appendix J Time-series results ............................................................................................... 129 xiii List of Tables Table 1 Summary of results and key conclusions ........................................................................... 7 Table 2 Normalization multipliers for the BIEX systems considered for analysis....................... 27 Table 3 Summary of normalized cumulative BVs corresponding to end of Phase 1 ................... 37 Table 4 Exchange ratios in Phase 1 for the different operating conditions investigated .............. 49 Table 5 Summary of normalized cumulative BVs corresponding to Phase 2 .............................. 50 Table 6 Exchange ratios in Phase 2 for the different operating conditions investigated .............. 56 Table 7 Summary of normalized cumulative BVs corresponding to start and end of Phase 3 ..... 58 xiv List of Figures Figure 1 A schematic of a bench-scale BIEX system ................................................................... 16 Figure 2 Bench-scale BIEX systems............................................................................................. 18 Figure 3 A summary of the cumulative composite sample collection schedule ........................... 20 Figure 4 Normalized weekly effluent composite DOC concentrations of the BIEX systems ...... 29 Figure 5 Normalized cumulative DOC removed in the BIEX systems over a 23-week study period ............................................................................................................................................ 31 Figure 6 Normalized weekly effluent composite UV absorbance of the BIEX systems .............. 33 Figure 7 Normalized weekly effluent composite specific UV absorbance of the BIEX systems 34 Figure 8 Typical rates of DOC removal, chloride release, and sulphate removal and/or release, as observed in System C.................................................................................................................... 36 Figure 9 Normalized weekly effluent composite chloride concentrations in the BIEX systems . 39 Figure 10 Rates of chloride release in Phase 1 ............................................................................. 41 Figure 11 Normalized weekly effluent composite sulphate concentrations in the BIEX systems....................................................................................................................................................... 42 Figure 12 Rates of sulphate removal in Phase 1 ........................................................................... 43 Figure 13 Normalized cumulative sulphate removed to chloride released during Phase 1, as observed in System C.................................................................................................................... 44 Figure 14 Percent overloading of sulphate at the end of Phase 1 ................................................. 45 xv Figure 15 Rates of DOC removal in Phase 1 ................................................................................ 47 Figure 16 Normalized cumulative DOC removed to normalized cumulative chloride released during Phase 1, as observed in System C ..................................................................................... 48 Figure 17 Rate of chloride release in Phase 2 ............................................................................... 52 Figure 18 Rates of sulphate release during Phase 2 in the BIEX systems .................................... 53 Figure 19 Rates of DOC removal in Phase 2 ................................................................................ 55 Figure 20 Typical normalized cumulative DOC removed to normalized cumulative sulphate released during Phase 2, observed in System C ............................................................................ 56 Figure 21 Rates of chloride release in Phase 3 ............................................................................. 60 Figure 22 Rates of sulphate release in Phase 3 ............................................................................. 61 Figure 23 Rates of DOC removal in Phase 3 ................................................................................ 63 Figure 24 Summary of rates of DOC removal in Phase 1, 2, and 3.............................................. 64 Figure 25 Normalized cumulative DOC removed in the BIEX systems during Phase 1, Phase 2, and Phase 3 and the DOC recovered from the BIEX resins by regeneration ............................... 66 xvi List of Equations Equation 1 ..................................................................................................................................... 22 Equation 2 ..................................................................................................................................... 23 Equation 3 ..................................................................................................................................... 24 Equation 4 ..................................................................................................................................... 27 xvii Acknowledgements This dissertation is a product of the support and guidance of several individuals. First and foremost, I would like to express my gratitude to my supervisor, Dr. Pierre Bérubé, for his guidance and support. He has been the best mentor and instilled in me a sense of discipline and curiosity towards research. Pierre encouraged me to be insightful and allowed me a safe space to perform to the best of my abilities and beyond. I would like to thank the Filtration Technology Group for their continued support on our trips to Jericho Pond, filtering water, and making sure the work produced is accurate and of the highest quality. I would also like to thank Otman, Felix, and Claudia for sharing their advice, assistance, and wealth of expertise in the laboratory. Their help has been insurmountable in ensuring the data collection and analysis is reliable. Special thanks to Dr. Madjid Mohseni, Dr. Benoit Barbeau, Karl Zimmerman, and the BIEX research group at UBC and Jacinthe Mailly at Ecole Polytechnic, Montreal for their guidance, expertise, and analytical support on my samples and results. To my parents Runumoni and Puspendra; my sister and brother in-law: Ankita and Abhinav, and my nephew: Anvik; Moni, and Bunny – Thank you. Your moral support emboldened me to take a flight to Canada and pursue graduate studies at UBC. To my friends and partner, I could not have been able to do this without you. Lastly, I think it is important to acknowledge that this dissertation was completed during a global pandemic. My gratitude goes to Dr. Bonnie Henry and healthcare workers for allowing a safe return to the laboratory after a four-month lockdown. xviii To women in engineering. 1 Chapter 1: Introduction 1.1 Overview Natural organic matter (NOM), commonly quantified as dissolved organic carbon (DOC), is ubiquitous in commonly used surface water sources like rivers, lakes etc. (Matilainen and Sillanpaa, 2010). DOC can impact the aesthetics of water by inducing colour or odour to surface water. DOC can also induce a greater chemical demand on water treatment processes, cause bacterial growth in water distribution channels, and react with disinfecting agents, like chlorine, to form disinfection by-products. Several innovative technologies like coagulation, flocculation, nanofiltration, and ion exchange currently exist that can effectively remove DOC from surface waters. Ion Exchange (IEX) is a favourable technological solution for DOC but requires frequent regeneration using highly concentrated brine solutions. The complexity and cost associated with the safe handling and disposal of the spent brine solutions can be substantial. The operation of IEX in biological mode, known as Biological Ion Exchange (BIEX), significantly reduces the required regeneration frequency (Winter et al., 2018). In BIEX columns, DOC can be exchanged with the chloride counterions (i.e., primary IEX) and subsequently, with the sulphate counterions that were previously retained during primary IEX (i.e., secondary IEX) (Liu et al., 2021). In addition to primary and secondary IEX, DOC can also be continuously removed due to biological processes (biosorption, biodegradation, bioregeneration) (Liu et al., 2021). In small and remote communities, water demand in households, which is mostly associated with domestic uses, can be intermittent. Combined with a lack of water demand buffering capacity, common in small communities, periods of intermittent water demand generate conditions where the inflow of water to be treated may also be intermittent. Therefore, 2 water treatment systems in small and remote communities must be able to operate efficiently under periods of intermittent inflow i.e., with periods of no inflow. Previous studies have suggested that periods of periods of no inflow can impact water treatment processes in biofiltration systems (Niquette et al., 1998; Peter-Varbanets et al., 2012; Mckie et al., 2019). However, the impact of periods of no inflow on DOC removal with BIEX systems is unknown. The present study assessed the performance of BIEX systems with periods of no inflow, in terms of DOC removal. 3 Chapter 2: Literature Review 2.1 Natural Organic Matter (NOM) 2.1.1 Source and characteristics Natural organic matter (NOM) is an overarching term representing a complex matrix of organic compounds like humic substances, polysaccharides, amino sugars, proteins, peptides, lipids, small hydrophilic acids, and others that are commonly present in raw drinking water sources (Sillanpää, 2015; Karanfil et al., 1999). While NOM does not directly impact human health, the presence and characteristics of NOM can affect the efficacy of drinking water treatment processes, and consequently the safety of drinking water (Health Canada, 2019). NOM can affect the aesthetic quality of water like taste, odour, or colour (Thurman, 1985). Chemical disinfectants like chlorine can react with different fractions of NOM to form disinfection by-products (DBPs) like trihalomethanes (THMs) and haloacetic acids (HAAs) (Stevens et al., 1976; Rook, 1974). Although THMs and HAAs have been linked to cancers and reproductive issues in animals, there is currently not enough evidence linking THMs or HAAs to any health concerns in humans (Health Canada, 2006; Health Canada, 2008). NOM can also encourage bacterial growth and biofilm development in the drinking water distribution systems. Disinfectants like chlorine can also react with NOM to increase the formation of biodegradable organic carbon (BDOC) that can further promote bacterial growth and development in distribution systems (Camper, 2014; Croft, 2012). NOM is commonly quantified using summative parameters like total organic carbon (TOC), dissolved organic carbon (DOC), and UV absorbance (Sillanpää, 2015; Thurman, 1985). In most source waters, most of the NOM is present in dissolved forms (Government of Canada, 4 2019). For this reason, the discussion which follows focuses on the DOC content, as a surrogate of NOM, in the raw drinking water sources. 2.1.2 Technologies available for DOC removal Current physical and chemical technologies available for DOC removal include coagulation, sedimentation, membrane filtration, activated carbon, biofiltration, and IEX processes (Sillanpää, 2015; Matilainen et al., 2010). The applicability of these technologies in water treatment systems for small and remote communities depends on their cost and complexity of operation and maintenance. Technologies that are robust with low production of residuals and are simple to operate are typically better suited for small and remote communities. Although physical and chemical DOC removal systems like coagulation, membrane filtration (e.g., nanofiltration), and sorption-based processes (e.g., activated carbon and ion exchange) can effectively remove DOC, their complexity and/or cost of operations make them unsuitable for use in small and remote communities (Amini et al., 2018). Biological DOC removal systems, like biofiltration, are relatively simple to operate. However, they cannot effectively remove DOC from raw water (Basu et al., 2015). Biological Ion Exchange (BIEX), which combines IEX and biofiltration, has emerged as an effective, yet simple approach, for DOC removal (Amini et al., 2018). 2.2 Biological Ion Exchange (BIEX) The possibility of operating IEX resins for a long period of time with reduced need for regeneration led to the development of Biological Ion Exchange (BIEX) (Winter et al., 2018; Schulz et al., 2017). The mechanisms of DOC removal in BIEX systems are not yet fully known. Several studies have reported that the long-term DOC removal achieved in BIEX systems could 5 potentially be attributed to primary IEX, followed by secondary IEX and potentially biodegradation, in parallel with primary and/or secondary IEX. 2.2.1 Primary Ion Exchange (Primary IEX) In BIEX systems, DOC is initially removed by the exchange of DOC with resin bound counter ions such as chloride (Amini et al., 2018). In addition to DOC, other material present in the raw water, such as sulphate, may also be exchanged with the chloride (Liu et al., 2021). Chloride is continuously released from the BIEX systems while DOC and other material, is exchanged. The initial exchange of DOC and other material with resin bound chloride is defined as primary ion exchange (Liu et al., 2021). Eventually, the resin-bound chloride originally present in the BIEX systems is exhausted (typically within days or weeks of operation), and the chloride release from the BIEX resins progressively declines (Amini et al., 2018). At this point of operations, the BIEX systems are deemed to have reached primary IEX exhaustion (Amini et al., 2018). 2.2.2 Secondary Ion Exchange (Secondary IEX) Once primary ion exchange capacity is exhausted, BIEX systems can operate beyond the exchange capacity of the original resin-bound counter ions (e.g., chloride). The BIEX systems can take advantage of a subsequent exchange of DOC with previously retained ions such as sulphate (Zimmerman et al., 2021). Sulphate is continuously released from the BIEX systems, while DOC is exchanged. The subsequent exchange of DOC with previously exchanged ions, such as sulphate, is defined as secondary ion exchange (Liu et al., 2021). Previous studies have reported that the beginning of secondary IEX coincides with the end of primary IEX (i.e., primary IEX exhaustion), and that all resin bound chloride ions are 6 released prior to the start of release of the previously exchanged sulphate ions (Edgar and Boyer, 2021; Zimmerman et al., 2021). Zimmerman et al., (2021) reported a higher sulphate uptake than expected based on milliequivalents, compared to chloride release, for feed waters with a relatively high sulphate concentration. They defined the greater cumulative uptake of sulphate, compared to the cumulative release of chloride, as “overloading”. Some studies have also reported a lower DOC removal in high sulphate feed waters compared to low sulphate feed waters (Zimmerman et al., 2021). For high sulphate feed waters, the relationship between the DOC ions removed and the sulphate ions released (i.e., Exchange ratio) can be non-linear, as the release of sulphate ions exceed the removal of DOC ions from the feed waters ((Edgar and Boyer, 2021; Zimmerman et al., 2021). While the mechanisms governing sulphate overloading is unknown, this phenomenon has been reported only in high sulphate feed waters. Eventually (i.e., during secondary IEX) the excess sulphate is completely released, and the loading of sulphate returns towards resin capacity (Zimmerman et al., 2021). 2.2.3 Biological Processes In addition to ion exchange, biological processes also contribute to the removal of DOC in BIEX systems and can be expected to occur in parallel with primary and secondary IEX (Amini et al., 2018). When disinfectants are not used during operations, microbial communities establish themselves to develop a biofilm on the IEX resins (Zearley and Summers, 2012). These biofilms can biologically degrade organic material. The biodegradation of DOC present on the resin could also free up more sites for ion exchange, enabling future DOC removal (Amini et al., 2018). A carbon mass balance of BIEX systems suggests that approximately 31% of the total DOC removal by BIEX is due to biodegradation, while the remainder (i.e., 69%) is due to ion 7 exchange (Amini et al., 2018). Once secondary IEX capacity is exhausted, the DOC removal in the BIEX systems is expected to only be due to biodegradation. The extent of biodegradation in a BIEX system also depends on the raw water characteristics (organic material) and the microbial communities colonizing the media (Liu et al., 2022). 2.2.4 Summary of literature review on BIEX Table 1 summarizes the studies that have investigated DOC removal mechanisms in BIEX systems. Table 1 Summary of results and key conclusions Reference Objectives and key conclusions Schulz et al., 2017 Objective: To assess the performance of IEX systems with and without biological activity in terms of NOM removal. Study conditions: Purolite A860 resins, Jericho Pond (JP) feed water, 30 mins empty bed contact time (EBCT) Key conclusions: • Promotion of biological activity in IEX biofilters enhances NOM removal, with up to 60-62% DOC removal. Winter et al., 2018 Objective: To investigate the impact of different loading approaches and microbial activity on NOM removal efficiency and capacity of IEX resins. Study conditions: Purolite A860 resins, Jericho Pond (JP) and Suwanee River (SRNOM) feed water, 30 mins EBCT Key conclusions: • BIEX columns consistently removed organic material from the feed water and operated beyond the resin capacity exhaustion (as traditionally defined as primary ion exchange). • In the absence of regeneration, an established microbial community on the resins contributes to DOC removal, enabling greater removal of organic material (as traditionally defined as biological contribution to DOC removal in BIEX systems). 8 Amini et al., 2018 Objective: To investigate the impact of long-term operation of IEX resins without any regeneration. Study conditions: Purolite A860 resins, Des Prairies River feed water, 30 mins EBCT Key conclusions: • BIEX systems achieved up to 62% DOC removal. • Primary ion exchange as well as secondary ion exchange mechanism (i.e., displacement of sulphate by NOM), and biological processes (i.e., biodegradation) contributed to DOC removal in the BIEX systems. Ion exchange mechanism can occur simultaneously with bioregeneration in the BIEX systems. • Organic carbon mass balance indicated that biodegradation contributed to 31% of DOC removal while ion exchange contributed to the rest (i.e., 69%) of the DOC removal in the BIEX systems. Liu et al., 2020 Objective: To investigate the potential of BIEX filters for long term NOM removal Study conditions: Purolite A860 resins, Mille-Iles River feed water, 10.8 mins EBCT Key conclusions: • BIEX achieved 29-36% DOC removal, similar to GAC or BAC filters. • Primary IEX, secondary IEX, and biological processes contributed to long term DOC removal in the BIEX systems. After ion exchange exhaustion, some DOC was released in the BIEX filters as sulphate replaced the fraction of NOM that had a lower affinity than sulphate. • Organic mass balance indicated that biodegradation contributed to 21-33% of DOC removal while ion exchange contributed to the rest of the DOC removal in the BIEX systems. 9 Edgar and Boyer, 2021 Objective: To understand the mechanism of continuous DOC removal in regenerated and non-regenerated IEX (i.e., BIEX) columns. Study conditions: Purolite A860 resins, Tempe Town Lake feed water, 30 mins EBCT Key conclusions: • BIEX columns achieved a consistent 50% DOC removal. • Despite biofilm growth on the IEX resins, secondary IEX contributed to continued DOC removal; DOC with higher affinity for the IEX resins was exchanged for adsorbed sulphate in the resins during secondary IEX. • The relationship between anion uptake and release in high sulphate waters ranged between 0.2-0.6. Zimmerman et al., 2021 Objective: To investigate the role of sulphate on DOC removal by BIEX systems Study conditions: Purolite A860 resins, Spanish Banks Creek feed water, 20 mins EBCT Key conclusions: • Average DOC removal for the high sulphate inlet water was 48±5%. • During primary IEX, sulphate and DOC were exchanged for resin-bound chloride, while in secondary IEX, DOC was exchanged for sulphate. • The relationship between anion uptake and release in high sulphate waters was 0.57. • The contribution of biological processes to DOC removal was likely lower than that reported by Amini et al., (2018). Liu et al., 2021 Objective: To assess the impact of temperature and empty bed contact time (EBCT) on NOM removal. Study conditions: Purolite A860 resins, Jericho Pond (JP) feed water, 30 mins EBCT Key conclusions: • BIEX systems achieved an organic carbon removal of approximately 73 ± 6%. • Higher temperature and EBCT can improve DOC removal in BIEX systems and are key important operating conditions to be considered for NOM removing biofilters. Liu et al., 2022 Objective: To evaluate the performance of BIEX resins for removal of organic micropollutants and thereby validate the occurrence of biodegradation Study conditions: Harvested Purolite A860 resins from a pilot plant at the Pont-Viau 10 drinking water treatment plant (Laval, Canada) that were fed with untreated feed water from Des Prairies River (Laval, Canada) for 5 months. Key conclusions: • Biodegradation on the BIEX resins simultaneously depend on the characteristics of organic material in the source waters and the microbial communities colonizing the media. • Even if the BIEX resins were exhausted with respect chloride and/or sulphate, it could be hypothesized that a fraction of NOM sorbed on the resins can be exchanged for organics with higher affinities for resins. 2.3 Water treatment in small and remote communities BIEX is a simple and effective NOM removal technology with low chemical usage, low effluent waste discharge, and high performance (Amini et al., 2018). Therefore, BIEX is suitable for water treatment in small and remote communities. However, none of the studies to date have assessed the impact of intermittent inflow on BIEX treatment systems. Water demand in small and remote communities is typically intermittent, with periods of limited or no demand for water. Periods of intermittent demand may occur in the afternoons due to traditional work hours and daily nighttime routines. More extended periods of intermittent demand may occur during some months of the year due to seasonal activities (i.e., for work or holidays) (Government of Newfoundland and Labrador, 2011; Canada Energy Regulator, 2018). The period of intermittent demand translates to periods of intermittent inflow to the water treatment systems for many small and remote communities. 11 2.3.1 Water treatment with periods of limited to no inflow A few studies have investigated the impact of intermittent inflow on the effectiveness of biofiltration. Niquette et al., (1998) investigated the impact of no inflow for periods of 6 to 24 hours/day on the performance of an exhausted biologically active carbon (BAC) filter. They monitored the DOC concentrations of the effluent from the BAC filter after restart following a filter shutdown. Niquette et al., (1998) reported that the effluent of the BAC filters immediately after restart had a relatively high DOC concentration, potentially because of the composition of the stagnant water of the BAC filter bed. They observed that the period over which the high effluent DOC concentrations occurred was relatively short (~10 mins). Niquette et al., (1998) concluded that BAC filters can withstand less than 24-hour periods of no inflow without any impact on DOC removal performance after filter restart. Niquette et al., (1998) also monitored the DOC concentration in the stagnant substrate in the BAC filter. They reported that after 24 hours of no inflow to the BAC filters, the DOC concentration of the stagnant water below the surface of the BAC filters increased to as high as 6 mg/L C. They speculated that the increase in the DOC concentration of the stagnant water during the period of no inflow reflected potential biofilm detachment and decay. Measurement of dissolved oxygen revealed that anaerobic conditions developed during the periods of no inflow, which caused some of the biofilm to detach and decay, and this decay released DOC. These results offered some insight into the response of BAC filter beds to periods of limited or no inflow. 12 Niquette et al., (1998) also reported that prolonged periods of no inflow to biofilters (>24hours) and no hydraulic backwash can impact DOC removal performance. However, these impacts can be managed by the addition of a biofilter backwash following a period of no inflow. Liu (2001) investigated the impact of biofilter shutdown on the performance of anthracite biofilters. They monitored the removal of biodegradable organic matter (BOM) before and after a 24-hour period of no inflow to the biofilters. Liu (2001) reported that there were no unfavourable influences of the periods of no inflow on the effluent quality from the biofilters. These results indicated that regular shut down of biofilters did not impact the removal of BOM. McKie et al., (2019) compared the performance of pilot scale activated carbon biofilters operated with a continuous inflow with those operated with daily periods of no inflow (~12±4h). The treated water quality in terms of DOC concentration from the effluent of the biofilters immediately after filter restart was monitored. McKie et al., (2019) reported that the biofilters operated with periods of no inflow achieved similar water quality to biofilters operated with continuous flow. On average, biofilters operated with periods of no inflow removed more DOC than biofilters operated with continuous inflow with the same EBCT. These results indicated that periods of no inflow had a beneficial impact on the DOC removal performance of biofilters. During operation of a BIEX system with continuous inflow, a concentration gradient of DOC can develop between the bulk liquid and the surface of a BIEX resin (Dezfoolian, 2019). With periods of no inflow, this concentration gradient can be expected to increase due to biodegradation (Niquette et al., 1998). An increase in the concentration gradient may, in turn, potentially impact biological activity in the biofilters. By recycling the effluent from a BIEX system, as influent, a lower concentration gradient may be maintained between the bulk liquid and the surface of a BIEX resin, during periods of no inflow. 13 2.4 Knowledge Gap Previous studies have established the suitability of BIEX for NOM removal in small and remote communities. However, there is currently no knowledge regarding the impact of no inflow, or effluent recirculation during periods of no inflow, on the performance of BIEX systems. The present study aims to address this knowledge gap. 14 Chapter 3: Research Objectives and Hypotheses The key research objective of the present study was to investigate the impact of periods of no inflow on DOC removal performance with BIEX systems. To meet the key research objective, the present study considered the following hypotheses: 1. Operation with periods of no inflow of the water to be treated impacts DOC removal of BIEX systems. 2. The extent of the potential impacts of operation with periods of no inflow on DOC removal is affected by the duration and/or the frequency of the periods of no inflow. 3. The extent of the potential impacts of operation with periods of no inflow on DOC removal can be mitigated by effluent recirculation. 15 Chapter 4: Materials and Methods 4.1 Materials 4.1.1 Feed water In the present study, the influent to the BIEX systems, hereby referred to as feed water, was a mixture of pond water and dechlorinated tap water. Pond water was collected in two occasions (Batch 1 in July 2020 and Batch 2 in Nov 2020) from Jericho Pond (JP) (Vancouver, BC). At the time of collection, pond water was filtered through a 1 mm screen to remove large suspended materials. In the lab, pond water was first filtered with a 5μm cartridge filter (GE Smart Water RO Set GXRM10G) and subsequently with a 1.5μm glass fiber filter (VWR, Grade 691). The filtered pond water was stored in the dark at 4℃ until use. There were three different types of feed water used in the present study. Prior to use, the filtered pond water was diluted with tap water to achieve a DOC concentration of approximately 5mg/L. Feed water from Batch 1 was collected in July 2020 and had a design DOC concentration of ~5mg/L, a low sulphate concentration of 2.18mg/L, and was used for 11 days from September 16 to Sep 28, 2020. Feed water from Batch 1 (A), also collected at the same time as Batch 1, was similar to that for Batch 1, but was augmented with sodium sulphate to attain a design sulphate concentration of ~50 mg/L. Feed water from Batch 1 (A) was used for 69 days from Sep 28, 2020, to December 7, 2020. Feed water from Batch 2 (A), collected in November 2020, was augmented with sodium sulphate to attain a design sulphate concentration of ~50 mg/L. Feed water from Batch 2 (A) was used for 71 days from December 7, 2020, to February 17, 2021. Throughout the present study, the actual DOC and sulphate concentration of the feed water fluctuated between 4 - 7 mg/L and 37-50 mg/L, respectively. 16 Other parameters like chloride and UV absorbance of the pond waters from Batch 1 and Batch 2 were also measured. A summary of the raw pond water characteristics is presented in Table A1 (Appendix A2). 4.1.2 BIEX System Setup Figure 1 illustrates a schematic of a bench-scale setup of a BIEX system used in the present study. A detailed schematic of the bench-scale BIEX systems is presented in Appendix A1. Figure 1 A schematic of a bench-scale BIEX system 17 Seven BIEX systems, operated in parallel, were used in the present study. Each of the BIEX systems were operated with two distinct types of experimental conditions: either with continuous inflow or with periods of no inflow. For operations with periods of no inflow, conditions with and without effluent recirculation were considered. Each of the BIEX systems consisted of the following components: a feed water tank, a feed pump, a BIEX column, an effluent collection system, a recirculation system for BIEX systems operated with effluent recirculation, and an overflow system for BIEX systems operated without effluent recirculation. The feed water tank was a 19L (5 gallon) PYREX® solution carboy. Every Monday, the feed water tank was refilled with fresh batches of feed water at room temperature. Feed water (prepared as per Section 4.1.1) from the feed tank was conveyed to the BIEX column with a feed pump at EBCT of 30 minutes. A Masterflex® L/S pump motor (1-100 rpm) and pump head were used for feed water pumping. The BIEX columns consisted of cylindrical plexiglass tanks (height = 50cm, ID = 0.948cm) which contained Purolite®A860 resins with a resin volume of 14.117mL. Purolite®A860 resins are microporous polyacrylic strong base ammonium resins with quaternary ammonium functional groups and have an exchange capacity of 0.8 Eq/L (Purolite, 2020). The preparation of the Purolite®A860 resins, before use in the present study, is detailed in Appendix A3. The BIEX columns were operated in downflow mode, with at least two inches of water maintained on top of the resin bed. The bottom of all the BIEX columns were closed with a 2cm mesh of quartz wool (Leco) to prevent any loss of resin with the effluents. The effluent collection system consisted of the effluent tanks (2L volumetric cylinders, Nalgene) and a mini refrigerator (Insignia). The effluent from the BIEX systems were collected 18 in the effluent tanks that were located inside the refrigerator, at a temperature of approximately 2℃. The recirculation and overflow systems consisted of appropriate tubing, timers, solenoid valves, and ball valves (See Figure 1 and 2). The recirculation system recirculated the effluent from the effluent tanks (located in the refrigerator) to the BIEX systems operated with effluent recirculation. The overflow system enabled the redirection of the overflow from the inflow line back to the feed water tank, in the BIEX systems operated without effluent recirculation. The feed tank, the BIEX columns, and effluent tanks were covered with aluminium foil to minimize potential effects of exposure to light (e.g., to minimize algae growth). The process tubing from the feed tank to the BIEX were replaced approximately every 8 weeks to minimize potential foreign biological growth that could occur outside of the BIEX columns. An image of the bench-scale BIEX systems is presented in Figure 2. Figure 2 Bench-scale BIEX systems 19 4.1.3 Operations of the BIEX systems The BIEX systems used in the present study were operated for 23 weeks (153 days) (Sep 17, 2020, to Feb 16, 2021). The BIEX systems were operated either with periods of no inflow or with continuous inflow. For operations with no inflow, conditions with and without effluent recirculation were considered during the period of no inflow to the BIEX systems. Hydraulic backwash was not performed on the BIEX systems in the present study. In the present study, the periods of no inflow to the BIEX systems were daily (3 hours and 8 hours: to simulate daytime and nighttime periods of no inflow, respectively) and weekly (48 hours or 2 days): to simulate weekend or holiday periods or system maintenance periods of no inflow). Out of the seven BIEX systems, 1 system was operated with continuous inflow, referred to as System C. Three BIEX systems were operated with periods of no inflow of 3h, 8h, and 48h and with effluent recirculation; they were referred to as System 3h (R), System 8h (R), and System 2d (R) respectively. Three BIEX systems were operated with periods of no inflow of 3h, 8h, and 48h and without effluent recirculation; they were referred to as System 3h, System 8h, and System 2d respectively. A summary of the operating conditions of the BIEX systems is presented in Table A2 (Appendix A4). 4.1.4 Sampling procedure For each of the BIEX systems, all the effluent was collected, generating three two- or three-day cumulative samples per week per BIEX system. The volume of each cumulative sample was recorded to precisely monitor the exact flow through each BIEX system and to enable the calculation of weighted weekly composite concentrations from the analysis performed 20 on the two- or three-day cumulative samples. The cumulative samples also enabled a relevant comparison between operation with daily and weekly periods of no inflow. Time-series samples were also collected during the present study, which is discussed in Appendix J. Figure 3 illustrates the cumulative sample collection schedule undertaken in the present study. Figure 3 A summary of the cumulative composite sample collection schedule For System C, cumulative samples were collected at 11 am on Monday, Wednesday, and Friday. For Systems 3h (R), 3h, 8h (R), and 8h, cumulative samples were collected at 10 am on Monday, Wednesday, and Friday. For Systems 2d (R) and 2d, cumulative samples were collected at 9 am on Monday, Wednesday, and Friday. The cumulative samples collected on a Monday were 72-hour samples as they included the effluents over a 72-hour period (Friday-Saturday-Sunday-Monday) and the cumulative samples collected on Wednesday and Friday were 48-hour samples as they included the effluents over a 48-hour period (Monday-Tuesday-Wednesday or Wednesday-Thursday-Friday). 4.2 Analytical Methods All glassware used for the analytical analysis of the samples were meticulously cleaned prior to and after use to minimize any potential contaminations. The glassware, lids, and sampling vials (including polyvials) were washed with a detergent and rinsed at least three times 21 with tap water, distilled water, and deionized water (Millipore Aqua-Q Ultra-Pure Water system). In addition, all non-volumetric glassware and vials were baked in a muffle oven at 450℃ for a minimum of 4 hours. After cleaning and baking, all glassware were stored in a clean and dry environment with aluminum foil covering all openings of the glassware. Dissolved organic carbon (DOC) analyses were performed to monitor the organic matter removal of the BIEX systems throughout the study. Aliquots of cumulative samples (See Section 4.1.4) were collected in 40 mL amber TOC vials and stored in the dark at T < 4℃ until analysis. Prior to DOC analyses, the aliquots were filtered through a 0.45μm membrane disc filter (Supor® PES Membrane Disc Filters, 47 mm dia, No 60173, Pall corporation). The filters were rinsed with 1L of DI water (Millipore Aqua-Q Ultra-Pure Water system) prior to filtration. DOC analyses were performed according to Standard Methods 5310A using the TOC-L CPH/CPN Total Organic Carbon analyser (Shimadzu). The instrument was calibrated with TOC standards (0, 2.5, 5, 10, 15, 25, and 50 mg/L). For the feed water and effluent water analysed in the present study, nearly all (~90%) of the TOC was present as DOC. Chloride and sulphate analyses were performed to monitor the ion exchange mechanisms in the BIEX systems Aliquots of cumulative samples (See Section 4.1.4) were collected in 50 mL vials and stored in the dark at T<4℃ until analysis. Prior to analysis, aliquots were filtered through a 0.45μm membrane disc filter (Supor® PES Membrane Disc Filters, 47 mm dia, No 60173, Pall corporation). The filters were rinsed with 1L of DI water prior to filtration. Chloride and sulphate analyses were performed according to Standard Methods 4110 using the Dionex Ion Chromatograph system (Dionex Aquion, Thermo Fisher). The instrument was calibrated with IC standards (1, 10, 20, 50, and 100 mg/L). Prior to analysis, samples were transferred to 2mL polyvials from Thermo Scientific. 22 UV absorbance analyses were performed to monitor the removal of the aromatic fractions of NOM from the feed water by the BIEX systems. Aliquots of cumulative samples (See Section 4.1.4)were collected in 50 mL vials and stored in the dark at T<4℃ until analysis. Prior to analysis, aliquots were filtered through a 0.45μm membrane disc filter (Supor® PES Membrane Disc Filters, 47 mm dia, No 60173, Pall corporation). The filters were rinsed with 1L of DI water prior to filtration. UV absorbance measurements were performed at 254nm (UV254) with a 1cm pathlength quartz length according to Standard Methods 5910B using a UV 300 UV-Visible spectrometer (Spectronic Unicam). The spectrometer was calibrated to a reading of zero with DI water. Specific absorbance (SUVA) was calculated based on the ratio of UV254 absorbance (cm-1) and DOC measurements (mg/L) using Equation 1. The SUVA values were multiplied by 100 as the measurements were conducted with a 1cm UV cell (Xie, 2004). Equation 1 SUVA = 𝑈𝑉254𝐷𝑂𝐶 * 100 [L/mg.m] The capacity of the BIEX systems was calculated in milliequivalent basis. For DOC, a charge density of 10.2 meq/g C was assumed (Bazri and Mohseni, 2016). For chloride and sulphate, charge densities of 28.21 meq/g Cl- and 20.82 meq/g SO42- respectively were considered (Zimmerman et al., 2021). The resin capacity of the BIEX systems was estimated to be approximately 11.29 meq, based on the manufacturer resin capacity of 0.8 Eq/mL and volume of resins considered in the BIEX columns (See Section 4.1.2) (Purolite, 2017). 23 4.3 Data Analysis and Interpretation 4.3.1 Mass Balance Analysis In order to gain insight into the mechanisms governing the DOC removal by the BIEX systems, the organic materials accumulated in the BIEX systems were extracted by regenerating the resins (See Section 4.3.1.1). The methodology undertaken for the mass balance analysis is similar to that described in previous works (Amini et al., 2018; Dezfoolian, 2019). The total cumulative mass of DOC removed by the BIEX systems throughout the present study was obtained by subtracting the cumulative mass of DOC in the effluent of the BIEX systems from the cumulative mass of DOC in the feed water (See Equation 2). The total cumulative mass of DOC extracted from the BIEX column was defined as that removed by ion exchange; while the difference between the total cumulative mass of DOC removed by the BIEX systems and that removed by the columns was assumed to be removed by biodegradation (See Equation 3). The calculations for the organic mass balance for the cumulative DOC removed (by ion exchange and biodegradation) were performed according to Equation 2 and 3. Equation 2 Total cumulative mass of DOC removed by the BIEX systems (mg) = Total cumulative mass of DOC in feed water (mg) - Total cumulative mass of DOC in effluent from the BIEX systems (mg) 24 Equation 3 Cumulative mass of DOC removed by biodegradation (mg) = Total cumulative mass of DOC removed by the BIEX systems (mg) - Total cumulative mass of DOC extracted from the resin by regeneration (mg) 4.3.1.1 Resin regeneration At the end of the present study, the resins from the BIEX systems were regenerated three times, with successive 10%, 10%, and 15% brine (NaCl) solutions. The key steps of the regeneration procedure were as follows: a) The BIEX systems were backwashed at a flow equivalent to 45 BV/h with 8 BVs of previously generated effluent from each respective column (Winter et al., 2018). The aim of this step was to remove any coarse particles or excess biomass from the filter bed. b) The contents of each of the BIEX systems were then filtered with a 1.5μm coarse filter paper The weight of the BIEX biofilter material was recorded. The BIEX biofilter material were then rinsed with DI water (Millipore Aqua-Q Ultra-Pure Water system). c) The BIEX biofilter material were then transferred to a beaker and soaked in 100mL of 10% brine solution for 12 hours (first regeneration cycle). The solutions in the beakers were mixed at 35 rpm with a magnetic stirrer. At the end of the first regeneration cycle with 10% brine cycle, the solution in the beakers was filtered with a 1.5μm filter paper (VWR, Grade 691). The filtrate was collected in a 40 mL amber vial and stored at 4°C for analysis. d) Step c was repeated for two more regeneration cycles with 10% and 15% brine solutions. DOC concentration of the filtrate from each of the three regeneration cycles was measured. 25 4.3.2 Statistical Analysis The statistical analysis performed in the present study included paired t-tests (Student and Welch), single factor ANOVAs, Tukey’s Honestly significant difference tests, and linear regressions. To test Hypothesis 1, a Welch t-test at 95% confidence interval was performed and all intermittent inflow operating conditions were compared to the continuous inflow operation. If the results of the Welch t-test did not indicate any impact (i.e., none of the intermittent inflow operating conditions were statistically different to continuous inflow operations), Hypotheses 2 and 3 were not tested. If the results of the Welch t-test indicated any impact (i.e., some or all the intermittent inflow operating conditions were not statistically different to continuous inflow operations), Hypotheses 2 and 3 were tested. To test Hypothesis 2, a Tukey’s Honestly significant difference test was performed and the different duration and/or frequencies of the periods of no inflow were compared to each other. To test Hypothesis 3, a Welch t-test at 95% confidence interval was performed and operations with effluent recirculation were compared to those without effluent recirculation. The rates of removal and/or release of the key parameters monitored (DOC, chloride, and sulphate) were calculated by performing linear regressions on the data sets at a 95% confidence interval. The standard error of the regression slopes was also calculated. The paired t-tests and Tukey’s Honestly significant difference test were performed using the Data analysis tool of Microsoft Excel. The linear regressions were performed using the Regression tool of Data Analysis tool in Microsoft Excel. 26 4.4 Quality Assurance and Quality Control (QA/QC) 4.4.1 Analytical methods For DOC measurements, quality control consisted of two DI water samples, one TOC standard (10 or 20 mg/L), one DI water sample, a spiked sample using TOC standard, and one DI water sample at the start and end of each analytical run. For chloride and sulphate measurements, quality control consisted of one DI water sample and 5 anion standards (1, 10, 20, 50, and 100 mg/L) at the beginning of each analytical run. For UV absorbance measurements, the spectrometer was calibrated to generate an absorbance of zero for a sample containing DI water, prior to start of analysis. 4.4.2 Data Analysis For the DOC, chloride, sulphate, and UV absorbance measurements, outliers were identified based on the Inter-Quartile Range test of outlier detection. Based on this approach, 20 out of 439 DOC measurements, 48 out of 498 chloride measurements, 9 out of 481 sulphate measurements, and 16 out of 513 UV absorbance measurements were eliminated from analysis. Additionally, for some days of the experiments, some measurements could not be recorded due to loss of samples. Hence, the values of the missing measurements were obtained by interpolation from the preceding and succeeding measurements, assuming all other factors are constant. Based on this approach, 12 DOC measurements, 15 chloride measurements, and 27 sulphate measurements were interpolated and considered for analysis. Fresh volumes of feed water were prepared weekly, which resulted in slight fluctuations in the feed water characteristics. To account for these slight fluctuations, all the effluent concentrations were normalized to the feed water concentrations. 27 Although all BIEX systems were designed to have similar resin volumes, the actual volume of the resins, the estimated resin capacity (estimated based on resin volume and capacity reported by Purolite (2017)), and the actual resin capacity (based on the total chloride release from the BIEX systems) differed for each of the BIEX systems. In particular, System 3h (R) contained had a larger volume of resins as compared to other BIEX systems, by about 12%, which in turn resulted in a higher resin capacity. To account for these differences and allow for relevant comparisons, the DOC removed, chloride released, and sulphate removed and/or released were normalized to the resin capacity based on the total chloride release from the BIEX systems, as outlined in Equation 4. The normalization multipliers for each BIEX systems are presented in Table 2. Equation 4 Normalization multiplier = 𝐷𝑒𝑠𝑖𝑔𝑛 𝑟𝑒𝑠𝑖𝑛 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 (11.29 𝑚𝑒𝑞)𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑜𝑓 𝑠𝑡𝑒𝑎𝑑𝑦 𝑠𝑡𝑎𝑡𝑒 𝑐ℎ𝑙𝑜𝑟𝑖𝑑𝑒 𝑟𝑒𝑙𝑒𝑎𝑠𝑒 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝐵𝐼𝐸𝑋 𝑠𝑦𝑠𝑡𝑒𝑚𝑠 (𝑚𝑒𝑞) Table 2 Normalization multipliers for the BIEX systems considered for analysis Systems Average steady-state chloride release (meq) Resin Capacity (meq) based on resin volume and reported by Purolite (2017) Normalization multiplier C 11.42 11.29 (for a resin volume of 14.117 mL and a resin capacity of 0.8 eq/mL) 0.95 3h (R) 19.36 0.58 8h (R) 12.60 0.87 2d (R) 11.26 0.96 3h 12.69 0.88 8h 11.37 0.97 2d 10.37 0.89 Similarly, the cumulative bed volumes achieved in the BIEX systems were normalized to the resin volume (See Appendix C). 28 Chapter 5: Results and Discussion 5.1 Overall performance of BIEX systems The overall performance of the BIEX systems, in the present study, were monitored in terms of the organics removal and the inorganics release and/or removal, as indicated in the sections that follow: 5.1.1 Organics removal 5.1.1.1 DOC removal Figure 4 illustrates the normalized weekly composite DOC concentrations of the effluent from the BIEX systems, calculated from the two- and three-day cumulative samples (outlined in Section 4.1.4) with respect to the weeks of operation (a) and normalized cumulative BVs (b). The normalized daily DOC concentrations for each two- and three-day cumulative samples is included in Appendix D1. Additionally, the distinct phases of DOC removal mechanisms (further discussed in Section 5.2) were also highlighted. 29 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure 4 Normalized weekly effluent composite DOC concentrations of the BIEX systems a) With respect to weeks of operation. b) With respect to cumulative normalized BVs; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined in Figure 4(b). The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems, as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. When considered with respect to time, there was substantial spread in normalized weekly composite DOC concentrations for the different BIEX systems. This was expected because the loading rate to each BIEX system differed as a result of the different operating conditions (See Section 4.1.3). When considered with respect to normalized cumulative BVs, a clearer trend emerged in the normalized weekly composite DOC concentrations for the different BIEX systems. This was expected as the normalized cumulative BVs take into consideration the impact of loading rates on the performance of the BIEX systems. To assess the impact of both time and loading rates, in the discussion that follows, the results are considered with respect to time and/or normalized cumulative BVs. 30 With respect to time, for feed water from Batch 1 (Week 1 to 2), the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between approximately 0.2 to 0.4 (See Figure 4 (a)), indicating that approximately 66-78% of the DOC was removed by the BIEX systems. The high DOC removal for feed water from Batch 1 is consistent with similar studies by Amini et al., (2018), Winter et al., (2018), and Schulz et al., (2017). When feed water was switched from Batch 1 to Batch 1(A), there was a general decrease in DOC removal. For feed water from Batch 1(A) (Week 3 to 12), the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between approximately 0.3 to 1 (See Figure 4 (a)), indicating that approximately 23-48% of the DOC was removed by the BIEX systems. When feed water was switched from Batch 1(A) to Batch 2(A), there was a general increase in DOC removal. For feed water from Batch 2(A) (Week 13 to 23), the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between approximately 0.4 to 0.9 (See Figure 4 (a)), indicating that approximately 14-47% of the DOC was removed by the BIEX systems. A summary of the average DOC removals in the BIEX systems, corresponding to feed waters from Batch 1, Batch 1(A), and Batch 2(A) is included in Table D1 (Appendix D2). With respect to normalized cumulative BVs, up to approximately 1260 normalized cumulative BVs, the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between approximately 0.2 to 0.8 (See Figure 4 (b)). Between approximately 1049-3107 normalized cumulative BVs, the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between approximately 0.3 to 0.9 (See Figure 4 (b)). Between 2392-5430 normalized cumulative BVs, the normalized weekly composite DOC concentrations of the effluent from the BIEX systems ranged between 31 approximately 0.4 to 0.9 (See Figure 4 (b)). Further discussion on DOC removal performance of the BIEX systems is presented in Section 5.2. The capacity of IEX based systems to remove material of interest is often assessed in terms of milliequivalents. For this reason, in the discussions that follow, cumulative results are expressed in terms of milliequivalents. Figure 5 illustrates the normalized cumulative DOC removal of the BIEX systems ( in milliequivalents) (See calculation in Section 4.2) as a function of the normalized cumulative BVs. The different ranges of the distinct phases of DOC removal (further discussed in Section 5.2) were also highlighted in Figure 5. Figure 5 Normalized cumulative DOC removed in the BIEX systems over a 23-week study period Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. When assessing the performance of the BIEX systems with respect to the normalized cumulative BVs, overall trends in the normalized cumulative DOC removed (meq) appeared to 32 be similar for all the BIEX systems. A more detailed analysis of the DOC removal performance with respect to the normalized cumulative bed volumes is presented in Section 5.2. Note that, the normalized cumulative DOC removed in System 8h was lower from the other systems. This discrepancy is also further discussed in Section 5.2. 5.1.1.2 UV absorbance and specific UV absorbance in the effluents Figure 6 illustrates the normalized weekly composite UV absorbance values in the effluent from the BIEX systems, calculated from the two- and three-day cumulative samples (outlined in Section 4.1.4) with respect to the weeks of operation (a) and normalized cumulative BVs (b). The normalized daily UV absorbance values for each two- and three-day cumulative samples is included in Appendix D3. Additionally, the distinct phases of DOC removal mechanisms (further discussed in Section 5.2) were also highlighted. 33 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure 6 Normalized weekly effluent composite UV absorbance of the BIEX systems a) With respect to weeks of operation. b) With respect to cumulative normalized BVs; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined in Figure 6(b). The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems, as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. Throughout the study period, the normalized weekly composite UV absorbance ranged between approximately 0.02 to 0.1 for all the BIEX systems (See Figure 6 (a) and (b)), indicating a consistent removal of UV absorbing compounds from the feed water. No distinct trends were observed in the UV absorbance of the BIEX systems in response to the changes in feed water (except for System C). Figure 7 illustrates the normalized weekly composite specific UV absorbance values in the effluent from the BIEX systems, calculated from the two- and three-day cumulative samples (outlined in Section 4.1.4) with respect to the weeks of operation (a) and normalized cumulative 34 BVs (b). The normalized daily specific UV absorbance values for each two- and three-day cumulative samples is included in Appendix D3. Additionally, the distinct phases of DOC removal mechanisms (further discussed in Section 5.2) were also highlighted. a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure 7 Normalized weekly effluent composite specific UV absorbance of the BIEX systems a) With respect to weeks of operation. b) With respect to cumulative normalized BVs; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined in Figure 7(b). The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems, as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. Throughout the study period, the normalized weekly composite specific UV absorbance ranged between approximately 0.1 to 0.3 for all the BIEX systems (See Figure 7 (a) and (b)). The low normalized weekly composite specific UV absorbance values suggested that characteristics of the organic material in the influent and the effluent from the BIEX systems differed, with the effluent containing proportionately less organic matter that could effectively absorb UV254. The 35 results of the present study are consistent with other studies; Winter et al., (2018) also reported that IEX based systems predominantly remove organics that absorb UV254. Although some variability in normalized weekly composite UV absorbance and specific UV absorbance were observed between the different BIEX systems, the extent of the variability was quite small, especially when compared to the variability in the normalized weekly composite DOC concentrations between the different BIEX systems. For this reason, in the discussions that follow, differences in the performance of the BIEX systems based on the removal of NOM, focuses mainly on DOC removal. 5.2 Performance during phases of treatment When considering the normalized cumulative DOC removed, chloride released, and sulphate removed and/or released, three distinct phases of treatment were observed in all the BIEX systems. The performance of the BIEX systems and the mechanisms governing the performance in each distinct phase is discussed in the following sections. Also, in the following sections, the rates of normalized cumulative uptake (removal) or release with respect to the normalized cumulative BVs are referred to as rates of removal or release, corresponding to the slopes of the linear regression model fitted to the relevant data in a phase. Figure 8 illustrates the typical rates of DOC removal, chloride release, and sulphate removal and/or release as a function of the normalized cumulative BVs. For illustrative purposes, the linear regression model fitted to the normalized cumulative DOC removal in Phase 2 with respect to the normalized cumulative BVs is also plotted in Figure 8 below, and the corresponding rate of DOC removal, which is the slope of the linear regression model, is 0.0002 ± 0.00002 meq/BV. 36 Figure 8 Typical rates of DOC removal, chloride release, and sulphate removal and/or release, as observed in System C From left to right, the first vertical line indicates the change of feed from Batch 1 to Batch 1(A) at 522 BVs and the second vertical line indicates the change of feed from Batch 1(A) to Batch 2(A) at 2778 BVs. The normalized cumulative chloride released, and sulphate removed and/or released, as well as resin capacity are plotted in secondary axis. 5.2.1 Phase 1: Primary IEX Phase 1 in the present study was defined as primary ion exchange (See Section 2.2). The dominant mechanism in the BIEX systems during Phase 1 was expected to be ion exchange with DOC and sulphate as counterions to the release of chloride. During this phase, there was a removal of DOC and sulphate, while chloride was released. Eventually, towards the end of Phase 1, the release of chloride approached resin capacity of the BIEX systems and the BIEX systems reached primary IEX exhaustion. Phase 1 corresponds to the period from the beginning of the study to up to approximately 931 to 1260 normalized cumulative BVs (variable depending on the BIEX systems as presented 37 in Table 3). With respect to the feed water, Phase 1 occurred during the time both Batch 1 and Batch 1(A) was used as feedwater. Table 3 summarizes the normalized cumulative BVs corresponding to the end of Phase 1, estimated based on cessation of chloride release and sulphate removal. Note that even after primary IEX exhaustion, some sulphate continued to be removed (See Section 5.2.1.1.2 for more discussion). However, primary IEX exhaustion was defined based on cessation of chloride release only. Table 3 Summary of normalized cumulative BVs corresponding to end of Phase 1 Systems Week of operation Based on chloride release (BVs) Based on sulphate removal (BVs) C 5 1135 1248 3h (R) 8 1258 1308 8h (R) 8 1222 1222 2d (R) 5 1104 1300 3h 7 1262 1382 8h 7 1137 1173 2d 5 931 1049 Based on chloride release Average BVs corresponding to the end of Phase 1 1150 ± 331 Maximum BVs corresponding to the end of Phase 1 1262 Minimum BVs corresponding to the end of Phase 1 931 Although there was some variability, the BVs corresponding to the end of Phase 1 in all the BIEX systems were relatively similar (i.e., within approximately 300 BVs to each other). This was expected because the primary IEX capacity of all the BIEX systems was similar (Liu et al., 2021). 38 5.2.1.1 Inorganics release and/or removal and organics removal during Phase 1 In the following sections, results are presented in terms of normalized weekly composite effluent concentrations, and the rates of release and/or removal. 5.2.1.1.1 Chloride release during Phase 1 Figure 9 illustrates the normalized weekly composite chloride concentrations of the effluent from the BIEX systems, calculated from the two- and three-day cumulative samples (outlined in Section 4.1.4) with respect to the weeks of operation (a) and normalized cumulative BVs (b). The normalized daily chloride concentration for each two- and three-day cumulative samples is included in Appendix D4. Additionally, the distinct phases of DOC removal mechanisms (further discussed in Section 5.2) were also highlighted. 39 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure 9 Normalized weekly effluent composite chloride concentrations in the BIEX systems a) With respect to weeks of operation. b) With respect to cumulative normalized BVs; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined in Figure 9(b). The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems, as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. In Phase 1, initially for feed water from Batch 1, the normalized weekly composite chloride concentrations ranged between approximately 2.9 to 3.9 for all the Systems (See Figure 9 (b)), indicating that chloride was consistently released from the BIEX systems. For the high sulphate feed water from Batch 1 (A), the normalized weekly composite chloride concentrations of the BIEX systems ranged between approximately 2.9 to 1 (See Figure 9 (b)). Eventually after approximately 1200 normalized cumulative BVs (See Table 3), the normalized weekly composite chloride concentrations for all the BIEX systems decreased to approximately 1 (See Figure 9 (b)), indicating that chloride was no longer being released at the same rates as compared 40 to the start of Phase 1, and that the ion exchange capacity of the resins in the BIEX systems was exhausted. In Phase 1, periods of no inflow did not impact the amount of chloride released from the BIEX systems (i.e., Hypothesis 1). Because there was no impact of periods of no inflow on chloride release, the impact of duration of the periods of no inflow (i.e., Hypothesis 2) and the impact of effluent recirculation (i.e., Hypothesis 3) on chloride release were not investigated. Results from hypothesis testing on chloride release (in milliequivalents) in Phase 1 are presented in Appendix H1. Even though two types of feed water were used during Phase 1 (i.e., Batch 1 from Day 0 to Day 11 and Batch 1(A) from Day 12 to end of Phase 1 for all systems (See Table D2 (Appendix D)), the rate of chloride release for the entirety of Phase 1 (i.e., Day 0 to end of Phase 1 (See Table D2 (Appendix D)) was considered for consistency with the analysis performed for Phases 2 and 3, in lieu of considering Phase 1 corresponding to Batch 1 and Batch 1(A) separately. Figure 10 illustrates the rates of chloride release in Phase 1 for the BIEX systems with the different operating conditions investigated. 41 Figure 10 Rates of chloride release in Phase 1 The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of chloride release in Phase 1 ranged between approximately 0.010 to 0.012 meq/BV (See Figure 10). Rates of chloride release for all the BIEX systems during Phase 1 are summarized in Table E1 (Appendix E1). 5.2.1.1.2 Sulphate removal during Phase 1 Figure 11 illustrates the normalized weekly composite sulphate concentrations of the effluent from the BIEX systems, calculated from the two- and three-day cumulative samples (outlined in Section 4.1.4) with respect to the weeks of operation (a) and normalized cumulative BVs (b). The normalized daily sulphate concentration for each two- and three-day cumulative samples is included in Appendix D5. Additionally, the distinct phases of DOC removal mechanisms (further discussed in Section 5.2) were also highlighted. 42 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure 11 Normalized weekly effluent composite sulphate concentrations in the BIEX systems a) With respect to weeks of operation. b) With respect to cumulative normalized BVs; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined in Figure 11(b). The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems, as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. For feed water from Batch 1, the normalized weekly composite sulphate concentrations ranged between approximately 0.25 to 0.6 for all the systems (See Figure 11 (b)). For the high sulphate feed water from Batch 1 (A), the normalized weekly composite sulphate concentrations of the BIEX systems were less than 0.1 (See Figure 11 (b)). The difference between the normalized weekly composite sulphate concentrations for Batch 1 and Batch 1(A) results from the normalization approach, which considered the influent sulphate concentration which was significantly lower for Batch 1 than Batch 1(A). The low normalized weekly composite sulphate concentrations indicated that sulphate was effectively removed by the BIEX systems. Eventually, after approximately 1200 normalized cumulative BVs, the normalized weekly composite 43 sulphate concentrations increased to approximately 1- 1.25 (See Figure 11 (b)), indicating that sulphate was no longer being removed and that the ion exchange capacity of the resins in the BIEX systems was exhausted. In Phase 1, periods of no inflow did not impact the amount of sulphate removed with the BIEX systems (i.e., Hypothesis 1). Because there was no impact of periods of no inflow on sulphate removal, the impact of duration of the periods of no inflow (i.e., Hypothesis 2) and the impact of effluent recirculation (i.e., Hypothesis 3) on sulphate removal were not investigated. Results from hypothesis testing on sulphate removal (in milliequivalents) in Phase 1 are presented in Appendix H2. Figure 12 illustrates the rates of sulphate removal in Phase 1 for the BIEX systems with the different operating conditions investigated. Figure 12 Rates of sulphate removal in Phase 1 Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. 44 The rates of sulphate removal in Phase 1 ranged between approximately 0.009 to 0.012 meq/BV (See Figure 12). Rates of sulphate removal for all the BIEX systems during Phase 2 are summarized in Table E2 (Appendix E2). Figure 13 illustrates typical normalized cumulative sulphate to chloride released in System C during Phase 1. Similar results were obtained for all the BIEX systems, and these results are presented in Appendix G1. Figure 13 Normalized cumulative sulphate removed to chloride released during Phase 1, as observed in System C The release ions are plotted on the x-axis and the uptake ions are plotted on the y-axis. The dotted line indicates a linear model fitted to the data. The straight line indicates x = y. During Phase 1, when feed water from Batch 1 was used, the extent of sulphate removal was lower than the extent of chloride release (See Figure 13). During this period, sulphate was likely not the major counterion to the release of chloride. Other ions present in the feedwaters were likely the major counterions to the release of chloride during this period (Liu et al., 2021). However, during Phase 1 for feed water from Batch 1 (A), the extent of sulphate removal 45 exceeded the extent of chloride release (indicated by the sharp increase in sulphate removal) (See Figure 13). Overall, during Phase 1, sulphate was likely the major counterion to the release of chloride (See Table 4). The mechanism governing the greater removal of sulphate to the release of chloride is not known and was not investigated within the scope of the present study. Other studies have also reported greater rate of sulphate uptake than the rate of chloride release for IEX filters or BIEX systems as discussed in Section 2.2.2 (Boyer and Singer, 2008; Fu and Symons, 1990; and Zimmerman et al., 2021). A table summarizing a ratio of the amount of sulphate removed to the amount of chloride released (i.e., exchange ratio) is further summarized in Table 4 (See Section 5.2.1.1.3). Figure 14 illustrates sulphate “overloading” in the BIEX systems. Figure 14 Percent overloading of sulphate at the end of Phase 1 The negative percent indicates an underloading of sulphate on the IEX resins. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. At the end of Phase 1, for some of the BIEX systems, the normalized cumulative sulphate removed (as milliequivalents) exceeded the normalized cumulative chloride released (as 46 milliequivalents) (See Figure 14). The difference between the normalized cumulative sulphate removed and the resin capacity was defined as sulphate overloading (See Section 2.2.2). A summary of the normalized cumulative sulphate removed (meq) that resulted in sulphate overloading is presented in Table F1 (Appendix F). In general, no clear trends were observed for sulphate overloading in the BIEX systems. However, in general, sulphate overloading was only observed for the BIEX systems operated continuously (i.e., System C) and with daily and short periods of no inflow (~3h) (i.e., System 3h (R) and System 3h). Zimmerman et al., (2021) also observed sulphate overloading when operating a BIEX system continuously (i.e., without periods of no inflow). However, as with the present study, the mechanisms governing sulphate overloading was not investigated. 5.2.1.1.3 DOC removal during Phase 1 In Phase 1, the normalized weekly composite DOC concentrations ranged between approximately 0.2 to 0.3 (See Figure 4 (a) and (b)), indicating a consistent removal of DOC by the BIEX systems. In Phase 1, periods of no inflow did not impact the amount of DOC removed with the BIEX systems (i.e., Hypothesis 1). Because there was no impact of periods of no inflow on DOC removal, the impact of duration of the periods of no inflow (i.e., Hypothesis 2) and the impact of effluent recirculation (i.e., Hypothesis 3) on DOC removal were not investigated. Results from hypothesis testing on DOC removal (in milliequivalents) in Phase 1 are presented in Appendix H3. Figure 15 illustrates the rates of DOC removal in Phase 1 for the BIEX systems with the different operating conditions investigated. 47 Figure 15 Rates of DOC removal in Phase 1 Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rate of DOC removal in Phase 1 ranged between approximately 0.0003 to 0.0006 meq/BV (See Figure 15). When compared to the BIEX system operated with continuous inflow, System 8h had the lowest rate of DOC removal. Rates of DOC removal for all the BIEX systems during Phase 1 are summarized in Table E3 (Appendix E3). Figure 16 illustrates typical normalized cumulative DOC removed to chloride released during Phase 1, as observed in System C. Similar results were obtained for all the BIEX systems, and these results are presented in Appendix G1. 48 Figure 16 Normalized cumulative DOC removed to normalized cumulative chloride released during Phase 1, as observed in System C The release ions are plotted on the x-axis and the uptake ions are plotted on the y-axis. The dotted line indicates a linear model fitted to the data. The straight line indicates x = y. Exchange ratios (i.e., the slope of ions removed to the ions released) offered insight on the amount of DOC and sulphate removed to the amount of chloride released from the BIEX systems. Table 4 summarizes the exchange ratios (presented as slope of the regression line (at a 95% confidence interval) ± standard deviation of the slope of the regression line) in Phase 1 for the different operating conditions investigated. 49 Table 4 Exchange ratios in Phase 1 for the different operating conditions investigated Systems Exchange Ratios in Phase 1 (Normalized cumulative sulphate removed to the normalized cumulative chloride released) (Normalized cumulative DOC removed to the normalized cumulative chloride released) C 1.180 ± 0.296 0.046 ± 0.003 3h (R) 1.229 ± 0.117 0.050 ± 0.003 8h (R) 1.171 ± 0.112 0.045 ± 0.003 2d (R) 0.964 ± 0.182 0.045 ± 0.004 3h 1.192 ± 0.133 0.050 ± 0.002 8h 1.045 ± 0.151 0.030 ± 0.003 2d 1.039 ± 0.228 0.045 ± 0.005 In Phase 1, the exchange ratios for the DOC removal ranged between 0.030 to 0.050 (See Table 4), indicating that the extent of DOC removal was lower than the extent of chloride release from the BIEX systems. The exchange ratios for the sulphate removal ranged between 0.964 to 1.229 (See Table 4), indicating that the extent of sulphate removal was greater than the extent of chloride release from the BIEX systems, and the major counterion to the released chloride was likely sulphate (See Table 4 and recall Section 5.2.1.1.2). In the feed waters from Batch 1, other ions, such as bicarbonates and nitrates (likely present in relatively low concentrations) which were not monitored and likely acted as counterions to the release of chloride (Liu et al., 2021). 5.2.2 Phase 2: Secondary IEX Phase 2 in the present study was defined as secondary ion exchange (See Section 2.2). The dominant mechanism in the BIEX systems during Phase 2 was expected to be ion exchange, with DOC as counterions to the release of sulphate. During Phase 2, there was a removal of DOC, while sulphate, that was previously retained during Phase 1, was released. Note that for 50 some of the BIEX systems, there was some small but statistically significant amount of chloride release, along with sulphate release, from the resins in Phase 2 (See Section 5.2.2.1.1). Phase 2 corresponds to the period from approximately 1049 to 3107 normalized cumulative BVs (variable depending on the BIEX systems as presented in Table 4). With respect to the feed water, Phase 2 occurred during the time Batch 1(A) was used as feedwater. Table 5 summarizes the normalized cumulative BVs corresponding to the duration of Phase 2, estimated based on start of sulphate release. The start of Phase 2 corresponds to the start of release of sulphate, while the end of Phase 2 corresponds to the start of Phase 3 (See Section 5.2.3). Table 5 Summary of normalized cumulative BVs corresponding to Phase 2 Systems Week of operation Start of Phase 2 (BVs) End of Phase 2 (BVs) Start of Phase 2 End of Phase 2 C 6 14 1292 3107 3h (R) 8 13 1308 2335 8h (R) 8 13 1256 2084 2d (R) 6 14 1304 3065 3h 8 14 1507 2870 8h 8 14 1173 2551 2d 6 15 1049 2805 Average BVs corresponding to the start and end of Phase 2 1270 ± 458 2688 ± 1023 Maximum BVs corresponding to the start and end of Phase 2 1507 3107 Minimum BVs corresponding to the start and end of Phase 2 1049 2084 Although there was some variability, the BVs corresponding to the start of Phase 2 were relatively similar (i.e, within approximately 458 BVs to each other). This is expected considering 51 that secondary IEX is expected to begin once primary IEX capacity is exhausted and the primary IEX capacity of all BIEX systems was similar (Liu et al., 2021). The end of Phase 2, defined as the cessation of sulphate release, differed by a greater extent than the start of Phase 2 (based on BVs) (i.e., within approximately 1023 BVs to each other). However, when considering dates (i.e., week of operation), the end of Phase 2 was similar for all the BIEX systems. This suggests that the end of Phase 2 was governed by time of operation rather than the cumulative loading on the BIEX systems. This is further discussed in Section 5.5.1. 5.2.2.1 Inorganics release and/or removal and organics removal during Phase 2 In the following sections, results are discussed in terms of normalized weekly composite effluent concentrations, and the rates of release and/or removal. 5.2.2.1.1 Chloride release during Phase 2 In Phase 2, the normalized weekly composite chloride concentrations ranged between approximately 1 to 1.2 for all the BIEX systems (See Figure 9 (a) and (b)) indicating that chloride was essentially no longer being released. Although for some systems, some chloride continued to be released during Phase 2, the release was at very low concentrations. In Phase 2, periods of no inflow did not impact the amount of chloride release from the BIEX systems (i.e., Hypothesis 1). Because there was no impact of periods of no inflow on chloride release, the impact of duration of the periods of no inflow (i.e., Hypothesis 2) and the impact of effluent recirculation (i.e., Hypothesis 3) on chloride release were not investigated. Results from hypothesis testing on chloride release (in milliequivalents) in Phase 2 are presented in Appendix H4. Figure 17 illustrates the rates of chloride release during Phase 2 for the BIEX systems with the different operating conditions investigated. 52 Figure 17 Rate of chloride release in Phase 2 The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of chloride release in Phase 2 ranged between approximately 0.0003 to 0.0006 meq/BV (See Figure 17). Although greater than zero, the rate of chloride release in Phase 2 was very very low, being approximately two orders of magnitude lower than Phase 1. Rates of chloride release for all the BIEX systems during Phase 2 are summarized in Table E4 (Appendix E4). 5.2.2.1.2 Sulphate release during Phase 2 In Phase 2, the normalized weekly composite sulphate concentrations ranged between approximately 1 to 1.25 for all the BIEX systems (See Figure 11 (a) and (b)), indicating that sulphate was effectively released by the BIEX systems. In Phase 2, periods of no inflow had an impact on the amount of sulphate released from the BIEX systems. Periods of no inflow impacted the sulphate release in BIEX systems operated with a daily and long (~8h) period and a weekly and long (~2d) period of no inflow. There was no impact of periods of no inflow on the sulphate release in BIEX systems operated with a daily 53 and short (~3h) periods of no inflow. The duration and/or frequency of the periods of no inflow also impacted the amount of sulphate released from all the BIEX systems. The extent of the potential impacts of operation with periods of no inflow on sulphate release could be mitigated by effluent recirculation in only the BIEX systems with a daily and short (~3h) period of no inflow. In the BIEX systems operated with a daily and long (~8h) period and a weekly and long (~2d) period of no inflow, there were no potential benefits of effluent recirculation. Results from hypothesis testing on sulphate release (in milliequivalents) in Phase 2 are presented in Appendix H5. Figure 18 illustrates the rates of sulphate release during Phase 2 for the BIEX systems with the different operating conditions investigated. Figure 18 Rates of sulphate release during Phase 2 in the BIEX systems The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System (R) differed from other systems, as explained in Section 4.4.2. The rates of sulphate release during Phase 2 ranged between approximately 0.0003 to 0.0018 meq/BV (See Figure 18). Rates of sulphate removal for all the BIEX systems during Phase 2 are summarized in Table E4 (Appendix E4). 54 5.2.2.1.3 DOC removal during Phase 2 In Phase 2, the normalized weekly composite DOC concentrations ranged between approximately 0.2 to 0.9 (See Figure 4 (a) and (b)), indicating a consistent removal of DOC by the BIEX systems. In Phase 2, periods of no inflow had an impact on the amount of DOC removed with the BIEX systems. Periods of no inflow impacted the DOC removal in almost all the BIEX systems (with the exception of System 3h and System 2d). The duration and/or frequency of the periods of no inflow also impacted the amount of DOC removed with the BIEX systems operated with a daily and long (~8h) period and a weekly and long (~2d) period of no inflow. The extent of the potential impacts of operation with periods of no inflow on DOC removal could not be mitigated by effluent recirculation in any of the BIEX systems. Results from hypothesis testing on DOC removal (in milliequivalents) in Phase 2 are presented in Appendix H6. Figure 19 illustrates the rates of DOC removal during Phase 2 for the BIEX systems with the different operating conditions investigated. 55 Figure 19 Rates of DOC removal in Phase 2 Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of DOC removal in Phase 2 ranged between approximately 0.0002 to 0.0005 meq/BV (See Figure 19) and were approximately one order of magnitude lower than in Phase 1. When compared to the BIEX system operated with continuous inflow, System 8h again had the lowest rate of DOC removal, similar to the pattern in Phase 1. Rates of DOC removal for all the BIEX systems during Phase 2 are summarized in Table E4 (Appendix E4). Figure 20 illustrates typical normalized cumulative DOC removed to the normalized cumulative sulphate released, during Phase 2 corresponding to feed water from Batch 1(A). Results for all BIEX systems are presented in Appendix G2. 56 Figure 20 Typical normalized cumulative DOC removed to normalized cumulative sulphate released during Phase 2, observed in System C The release ions are plotted on the x-axis and the uptake ions are plotted on the y-axis. The dotted line indicates a linear model fitted to the data. The straight line indicates x = y. Table 6 summarizes the exchange ratios in Phase 2 for the different operating conditions investigated. For System 3h (R), System 8h (R), System 3h, and System 8h, the calculation of exchange ratios included the normalized cumulative chloride release and sulphate release. Table 6 Exchange ratios in Phase 2 for the different operating conditions investigated Systems Exchange Ratios in Phase 2 (Normalized cumulative DOC removed to the normalized cumulative sulphate released) C 0.16 ± 0.02 3h (R) 0.20 ± 0.06 8h (R) 0.18 ± 0.08 2d (R) 0.26 ± 0.04 3h 0.15 ± 0.03 8h 0.14 ± 0.02 2d 0.14 ± 0.02 57 In Phase 2, the exchange ratios for the BIEX systems ranged between 0.14 to 0.26 (See Table 6), indicating that the extent of DOC removal was lower than the extent of sulphate release from the BIEX systems. In this phase, the major counterion to the released sulphate was likely DOC. The exchange ratios in the present study were similar to results from other studies for high sulphate waters. Edgar and Boyle (2021) reported an exchange ratio between 0.2 to 0.6, while Zimmerman et al., (2021) reported an exchange ratio of 0.57 in high sulphate waters. 5.2.3 Phase 3: Stunted Secondary IEX Phase 3 in the present study was defined as stunted secondary ion exchange (See Section 2.2). The dominant mechanism in the BIEX systems during Phase 3 was expected to be ion exchange, with DOC as counterions to the release of sulphate until the complete release of previously retained sulphate (Liu et al., 2021 and Zimmerman et al., 2021). However, this did not occur, and neither Liu et al., (2021) or Zimmerman et al., (2021) have reported results consistent to the ones observed in Phase 3 of the present study. Although secondary IEX was “stunted”, DOC removal continued in the BIEX systems. It was hypothesized that the continued DOC removal, in the absence of secondary IEX, was likely due to biological processes like biosorption, biodegradation, and bioregeneration (Liu et al., 2021). Thus, in the absence of any ion exchange, the dominant mechanism in the BIEX systems during Phase 3 was assumed to be biological in nature. Phase 3 corresponds to the period from approximately 2392 to 5430 normalized cumulative BVs (variable depending on the BIEX systems as shown in Table 6). With respect to the feed water, Phase 3 occurred during the time Batch 2(A) was used as feedwater. 58 Table 7 summarizes the normalized cumulative BVs corresponding to the duration of Phase 3, estimated based on cessation of sulphate release. The end of Phase 3 corresponds to the end of the study (after 23 weeks of operation). Table 7 Summary of normalized cumulative BVs corresponding to start and end of Phase 3 Systems Week of operation Start of Phase 3 (BVs) End of Phase 3 (BVs) Start of Phase 3 End of Phase 3 C 14 23 (End of study) 3182 5430 3h (R) 14 2392 3937 8h (R) 13 2133 3425 2d (R) 15 3155 4863 3h 15 2942 4522 8h 15 2621 3906 2d 15 2903 4416 Average BVs corresponding to the start and end of Phase 3 2761 ± 1049 4357 ± 2005 Maximum BVs corresponding to the start and end of Phase 3 3182 5430 Minimum BVs corresponding to the start and end of Phase 3 2133 3425 The start of Phase 3 differed substantially (based on BVs), ranging from 2133 BV to 3182 BVs. However, based on time, the start of Phase 3 occurred on similar dates (i.e., weeks of operation) for all the BIEX systems. In addition, the start of Phase 3 coincided approximately with the switch of feedwater from Batch 1(A) to Batch 2(A). This suggests that stunted secondary IEX was initiated by the change in feed water. This is further discussed in Section 5.5.1. For some of the BIEX systems (i.e., System 3h (R) and System 8h (R)), the change of Phase 2 to Phase 3 (i.e., cessation of sulphate release) occurred at almost the same time and 59 closest (approximately 3 to 7 days) of feed water change (Day 89 and Day 85 respectively). For the other BIEX systems, the change of Phase 2 to Phase 3 (i.e., cessation of sulphate release) occurred approximately 10 to 15 days of feed water change: Day 92 for System C, Day 95 for System 2d (R), System 3h, and System 8h, and Day 97 for System 2d. 5.2.3.1 Inorganics release and/or removal and organics removal during Phase 3 In the following sections, results are discussed in terms of normalized weekly composite effluent concentrations, and the rates of release and/or removal. 5.2.3.1.1 Chloride release during Phase 3 In Phase 3, the normalized weekly composite chloride concentrations remained at approximately 1 for all the BIEX systems (See Figure 9 (a) and (b), and based on student t-test at 95% confidential interval (See Appendix H7)), indicating that there was no chloride release from the BIEX systems. As there was no chloride release from the BIEX systems, the three hypotheses for the present study were not tested for chloride release in Phase 3. Figure 21 illustrates the rates of chloride release during Phase 3 for the BIEX systems with the different operating conditions investigated. 60 Figure 21 Rates of chloride release in Phase 3 The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of chloride release in Phase 3 ranged between approximately 0.00002 to 0.00006 meq/BV for all the BIEX systems (See Figure 21). The rates of chloride release in Phase 3 were not statistically greater than zero, and were approximately three to four orders of magnitude lower than Phase 1 and approximately one to two orders of magnitude lower than Phase 2. Rates of chloride release for all the BIEX systems during Phase 3 are summarized in Table E5 (Appendix E5). 5.2.3.1.2 Sulphate release during Phase 3 In Phase 3, the normalized weekly composite sulphate concentrations remained at approximately 1 (See Figure 11 (A) and (b), and based on a student t-test at 95% confidential interval (See Appendix H8)), indicating that there was no sulphate release from the BIEX systems. As there was no sulphate release from the BIEX systems, the three hypotheses for the present study were not tested for sulphate release in Phase 3. 61 Figure 22 illustrates the rates of sulphate release during Phase 3 for the BIEX systems with the different operating conditions investigated. Figure 22 Rates of sulphate release in Phase 3 The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of sulphate release in Phase 3 ranged between approximately 0.00005 to 0.0004 meq/BV (See Figure 22). The rate of sulphate release in Phase 3 was very very low, being approximately one to two orders of magnitude lower than Phase 2. Rates of sulphate release for all the BIEX systems during Phase 3 are summarized in Table E5 (Appendix E5). From the rates of chloride and sulphate release in Phase 3, it is evident that there was no ion exchange due to chloride and/or sulphate release in the BIEX systems during this phase. These results indicate that ion exchange was likely not the dominant mechanism of DOC removal in Phase 3. 62 5.2.3.1.3 DOC removal during Phase 3 In Phase 3, the normalized weekly composite DOC concentrations ranged between approximately 0.4 to 0.9 (See Figure 4 (a) and (b)), indicating a consistent removal of DOC by the BIEX systems. In Phase 3, periods of no inflow had an impact on the amount of DOC removed with all the BIEX systems. The extent of the potential impacts of operation with periods of no inflow on DOC removal was also affected by the duration and/or frequency of the periods of no inflow. The extent of the potential impacts of operation with periods of no inflow on DOC removal could be mitigated by effluent recirculation only in the BIEX system operated with a weekly and long (~2d) period of no inflow. In the BIEX systems operated with a daily and short (~3h) period and a daily and long (~8h) period of no inflow, there were no potential benefits of effluent recirculation. Results from hypothesis testing on DOC removal (in milliequivalents) are presented in Appendix H9. Figure 23 illustrates the rates of DOC removal during Phase 3 for the BIEX systems with the different operating conditions investigated. 63 Figure 23 Rates of DOC removal in Phase 3 Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. The rates of DOC removal in Phase 3 ranged between approximately 0.0001 to 0.0005 meq/BV (See Figure 23), and were approximately one order of magnitude lower than Phase 1 and Phase 2. When compared to the BIEX system operated with continuous inflow, System 8h again had the lowest rate of DOC removal, similar to the pattern in Phase 1 and 2. Rates of DOC removal for all the BIEX systems during Phase 3 are summarized in Table E5 (Appendix E5). As discussed in Section 5.2.3.1, there was likely no ion exchange in the BIEX systems during Phase 3. Therefore, exchange ratios were not calculated for the BIEX systems in this phase. 5.3 Summary of rates of DOC removal Figure 24 summarizes the rates of DOC removal in Phase 1, 2, and 3 for all the BIEX systems with the different operating conditions investigated. 64 Figure 24 Summary of rates of DOC removal in Phase 1, 2, and 3 The bar (left to right) indicates the rates of DOC removal in Phase 1, 2, and 3 respectively, for each BIEX system. Error bars in red represent a 95% confidence interval of the slope of the regression line. Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. Overall, the rates of DOC removal were higher during Phase 1 compared to the other phases for all the BIEX systems (See Figure 24), indicating that DOC removal was greatest for the BIEX systems when primary ion exchange was the dominant mechanism of DOC removal. The rates of DOC removal in Phase 2 were generally not statistically different to Phase 3 for all the BIEX systems (based on a student t-test at 95% confidence interval, See Appendix H10). As discussed in Section 5.2.3.1, in the absence of any obvious ion exchange, the dominant mechanism of DOC removal in Phase 3 was likely biological in nature. Hence, if rates of DOC removal in Phase 2 and Phase 3 were not statistically different, it can be inferred that the mechanism of DOC removal in Phase 2 was similar to that in Phase 3, i.e., biological in nature. It is possible that some secondary ion exchange occurred simultaneously with biological processes, in the BIEX systems during Phase 2, but possibly not with DOC. Additionally, other factors may 65 have contributed to the lower DOC removal observed in Phase 2 such as the release of NOM fractions that have a lower affinity to the resin (Liu et al., 2021). This hypothesis was not investigated in the present study. In general, there was a pattern of high DOC removal (for a daily and short (~3h) period), low DOC removal (for a daily and long (~8h) period), and high DOC removal (for a weekly and long (~2d) period) were similar to the pattern observed in the rates of DOC removal in Phase 2 and to some extent, the pattern of rates of DOC removal in Phase 1 and Phase 3. Additionally, in general, operations of BIEX systems with effluent recirculation had a higher DOC removal, which is also similar to patterns observed in rates of DOC removal in some cases during Phases 1, 2, and 3. 5.4 Estimate of overall DOC removal pathways 5.4.1 DOC removal pathways defined by organic carbon mass balance Figure 25 illustrates the normalized cumulative DOC removed in the BIEX systems and DOC recovered from the regeneration (as milliequivalents per normalized cumulative bed volumes) during the different phases of the study. Details on the mass balance used to estimate the normalized cumulative DOC removed and recovered are presented in Appendix I. 66 Figure 25 Normalized cumulative DOC removed in the BIEX systems during Phase 1, Phase 2, and Phase 3 and the DOC recovered from the BIEX resins by regeneration Recall that System 3h (R) differed from other systems, as explained in Section 4.4.2. DOC recovered for System 3h (R) and System 8h was not available (See Appendix I). From Figure 25, during Phase 1, approximately 28 to 50% of DOC was removed by all the BIEX systems, predominantly by ion exchange. During Phase 2 and 3, approximately 19 to 32% and 18 to 49% respectively of remaining DOC was removed by all the BIEX systems, potentially by a combination of some secondary ion exchange and/or biological processes. This aligns well with the previous observation made that rate of DOC removal in all the BIEX systems were higher in Phase 1 compared to Phase 2 and Phase 3 (See Section 5.3). DOC removed by primary and secondary IEX is expected to remain on the resin beads. In all the BIEX systems, the amount of DOC recovered was lower than the amount of DOC removed by ion exchange. Of the cumulative DOC removed, 75 to 92% of DOC was recovered from the resins. This suggests that 8 to 25% of the cumulative DOC removed was not removed 67 by either primary or secondary ion exchange, but rather by biological processes like biosorption, biodegradation and bioregeneration. Overall, the distribution of DOC removed (by ion exchange and biodegradation), estimated based on resin regeneration, is similar to other studies which indicated that up to 31% of DOC removed in a BIEX system may be due to biodegradation (Amini et al., 2018). 5.4.2 Patterns observed in DOC removal pathways In the BIEX system operated with a daily and short period (~3h) of no inflow, the extent of DOC removed by ion exchange was similar to that of continuous operation, while the extent of DOC removed by biodegradation was lower than continuous operation. In the BIEX systems operated with a daily and long period (~8h) period of no inflow, the extent of DOC removed by ion exchange was similar to that of continuous operation (except for System 8h), while the extent of DOC removed by biodegradation was lower than continuous operation. In the BIEX systems operated with a weekly and long period (~2d) period of no inflow, the extent of DOC removed by ion exchange higher than that of continuous operation, while the extent of DOC removed by biodegradation was lower than continuous operation (Except for System 2d). 5.5 Other significant findings In addition to the objectives of the present study, some other significant findings were observed. The following section discusses the findings. 5.5.1 Change in different phases of treatment in response to feed water changes When feed water was changed from Batch 1 to Batch 1(A), there was no impact on the duration of Phase 1. Within approximately 18 to 35 days after the feed water changed from Batch 1 to Batch 1(A), Phase 1 ended in all the BIEX systems. As there were no observable changes in the monitored parameters (DOC, chloride, and sulphate) in the feed water and 68 effluent of the BIEX systems immediately after or close to when feed water was changed, the change of phases (i.e., from Phase 1 to Phase 2) was hypothesized to be completely related to the expected change in DOC removal mechanism (i.e., from primary IEX to secondary IEX) in the BIEX systems, and not necessarily an impact of feed water change. For some of the BIEX systems (i.e., System C, System 2d (R), and System 2d), primary IEX exhaustion occurred on the same day (Day 30), while for other BIEX systems primary IEX exhaustion occurred approximately 17 days later (Day 47) (for System 3h (R) and System 8h (R)) and approximately 10 days later (Day 40) (for System 3h and System 8h). The bed volumes corresponding to primary IEX exhaustion is detailed in Table 3. When feed water was changed from Batch 1(A) to Batch 2(A), there was a swift transition of the BIEX systems from Phase 2 to Phase 3. Within approximately 3 to 15 days after feed water changed from Batch 1(A) to Batch 2(A), the release of sulphate essentially stopped in all the BIEX systems (See Figure 11 and Section 5.2.3.1.2). Liu et al., (2020) had hypothesized that NOM is an assemblage of molecules with variable charges and there were three fractions of NOM based on their resin affinity (i.e., NOM1 with no affinity for the resin, NOM2 with a lower affinity than sulphate, and NOM3 with a higher affinity than sulphate). It can be hypothesized that feed water from Batch 2(A) contained more NOM2 than NOM3, as compared to feed water from Batch 1 and Batch 1(A). Recall that, Batch 2(A) was collected from the same source (Jericho Pond) but at a different time of the year (See Table A1, Appendix A). It is possible that because Batch 2(A) contained mostly NOM2, none of the NOM was actually exchanged with sulphate, causing the sulphate release to become stunted. The abrupt cessation of sulphate release after feed change indicates that secondary IEX is potentially impacted by raw water 69 characteristics and/or the microbial communities’ response to the raw water characteristics. The investigation of this phenomenon is beyond the scope of the present study. 5.5.2 Patterns in organics removal and inorganics release and/or removal During the different phases of treatment, some patterns were observed in the organics removal as well as inorganics release and/or removal for the BIEX systems operated with periods of no inflow. 5.5.2.1 Patterns in organics removal In Phase 1, for BIEX systems operated with effluent recirculation, the DOC removal decreased with an increasing period of no inflow (i.e., Rate of DOC removal in 3h (R) > 8h (R) > 2d (R)). For BIEX systems operated without effluent recirculation, there was a pattern of high rate of DOC removal (for a daily and short (~3h) period), low rate of DOC removal (for a daily and long (~8h) period), and a high rate of DOC removal (for a weekly and long (~2d) period). Additionally, in Phase 1, for BIEX systems operated with a daily period of no inflow, the rate of DOC removal was generally higher for operations with effluent recirculation (i.e., Rate of DOC removal in 3h (R) > 3h, 8h (R) > 8h). (Except for System 2d (R) and 2d). In Phase 2, for BIEX systems operated with and without effluent recirculation, there was a pattern of high rate of DOC removal (for a daily and short (~3h) period), low rate of DOC removal (for a daily and long (~8h) period), and a high rate of DOC removal (for a weekly and long (~2d) period), similar to the pattern observed for rate of sulphate release during Phase 2. Additionally, in Phase 2, the rate of DOC removal was generally higher for operations without effluent recirculation (i.e., Rate of DOC removal in 3h (R) > 3h, 2d (R) > 2d) (Except for System 8h (R) and 8h). 70 In Phase 3, for BIEX systems operated with effluent recirculation, there was a pattern of increasing rate of DOC removal (low to high) as the period of no inflow increased (i.e., Rate of DOC removal in 3h < 8h < 2d). For BIEX systems operated without effluent recirculation, there was a pattern of high rate of DOC removal (for a daily and short (~3h) period), low rate of DOC removal (for a daily and long (~8h) period), and a high rate of DOC removal (for a weekly and long (~2d) period). Additionally, in Phase 3, the rate of DOC removal was generally higher for operations without effluent recirculation (i.e., Rate of DOC removal in 8h (R) > 8h, 2d (R) > 2d) (Except for System 3h (R) and 3h). 5.5.2.2 Patterns in inorganics release and/or removal 5.5.2.2.1 Patterns in chloride release In Phase 1, for BIEX systems operated with effluent recirculation, the chloride release is similar in all the BIEX systems (i.e., Rate of chloride release in 3h ~ 8h ~ 2d). For BIEX systems operated without effluent recirculation, there was a pattern of high rate of chloride release as the period of inflow increased (i.e., Rate of chloride release in 3h < 8h < 2d). In Phase 2, for BIEX systems operated with effluent recirculation, there was a pattern of decreasing rate of chloride release (high to low) as the period of no inflow increased (i.e., Rate of chloride release in 3h > 8h > 2d). For BIEX systems operated without effluent recirculation, there was a pattern of high rate of chloride release (for a daily and short (~3h) period), low rate of chloride release (for a daily and long (~8h) period), and a high rate of chloride release (for a weekly and long (~2d) period). In Phase 3, there was no chloride release from the BIEX systems (See Section 5.2.3.1.1). 71 5.5.2.2.2 Patterns in sulphate removal and/or release In Phase 1, for BIEX systems operated with effluent recirculation, the sulphate removed did not follow any significant pattern. For BIEX systems operated without effluent recirculation, there was a pattern of high rate of sulphate removal (for a daily and short (~3h) period), low rate of sulphate removal (for a daily and long (~8h) period), and a high rate of sulphate removal (for a weekly and long (~2d) period). In Phase 2, for BIEX systems operated with and without effluent recirculation, there was a pattern of high rate of sulphate release (for a daily and short (~3h) period), low rate of sulphate release (for a daily and long (~8h) period) and a high rate of sulphate release (for a weekly and long (~2d) period). In Phase 3, there was no sulphate release from the BIEX systems (See Section 5.2.3.1.2). 72 Chapter 6: Conclusion 6.1 Conclusion The overall research objective of the present study was to investigate the impact of periods of no inflow on DOC removal performance with BIEX systems. The following were the key conclusions made in the study: 6.1.1 Objective 1 The present study concluded that, in general, periods of no inflow impacted DOC removal in BIEX systems. The impacts of periods of no inflow on the DOC removal were varied based on the phases of treatment the BIEX systems underwent (primary IEX, secondary IEX, and/or biodegradation). During primary IEX, periods of no inflow did not impact the DOC removal in the BIEX systems. During secondary IEX and/or biodegradation, periods of no inflow had an impact on the DOC removal in the BIEX systems. 6.1.2 Objective 2 The present study concluded that the extent of the impacts of periods of no inflow were affected by the duration and/or frequency of periods of no inflow. • BIEX systems operated with a daily and short (~3h) period of no inflow generally had a similar DOC removal pattern to that for BIEX system with continuous inflow. • BIEX systems operated with a daily and long (~8h) period of no inflow generally had a lower DOC removal pattern than that for BIEX system with continuous inflow. • BIEX systems operated with a weekly and long (~2d) period of no inflow generally had relatively similar DOC removal pattern to that for BIEX system with continuous inflow. 73 The extent of the impacts of periods of no inflow were affected by the duration and/or frequency of periods of no inflow, during secondary ion exchange and/or biodegradation. In general, when comparing the different durations of the periods of no inflow, there was a pattern of high DOC removal (for a daily and short (~3h) period of no inflow), low DOC removal (for a daily and long (~8h) period of no inflow), and a high DOC removal (for a weekly and long (~2d) period of no inflow). 6.1.3 Objective 3 The present study did not produce any consistent evidence that the extent of impacts of periods of no inflow on DOC removal by BIEX systems were mitigated by effluent recirculation. Generally, the amount of DOC removed in BIEX systems operated with effluent recirculation was similar to that removed in BIEX systems without effluent recirculation. For a few of the operating conditions investigated, the DOC removal for the BIEX systems operated with effluent recirculation were greater than those for BIEX systems operated without effluent recirculation. This might suggest that effluent recirculation may benefit BIEX systems in their DOC removal performance, particularly in the case of a daily and long period of no inflow. 6.2 Engineering implications of the present study The operation of BIEX systems for NOM removal, under intermittent inflow conditions, is necessary for ensuring the supply of safe drinking water in small and remote communities. The periods of no inflow to the BIEX systems, in most cases, did not result in significantly negative impacts on the DOC removal. Additionally, in some cases, the BIEX systems with effluent recirculation had a better water quality than BIEX systems without effluent recirculation. The implications of these observations are beneficial for operations of BIEX systems in small and 74 remote communities: as BIEX systems can maintain water quality even under periods of no inflow. This work inspired the following ideas for future research. 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Figure A1 A schematic representation of bench-scale setup of the BIEX systems The experimental setup included: a) 1 BIEX system with a continuous inflow, b) 3 BIEX systems with periods of no inflow and with effluent recirculation and c) 3 BIEX systems with periods of no inflow and without effluent recirculation. For BIEX systems with no inflow, three periods of no inflow (3h, 8h, and 84 2d) considered. The BIEX systems were named as C, 3h (R), 8h (R), 2d (R), 3h, 8h, and 2d, depending on their operation with and without effluent recirculation. A.2 Jericho Pond water characteristics Table A1 presents a summary of the raw Jericho Pond water characteristics. Table A1. Summary of raw pond water characteristics Raw Jericho Pond water batches pH DOC (mg/) Chloride (mg/L) Sulphate (mg/L) UV absorbance (cm-1) SUVA Batch 1 (Collected July 2020) 6.32 12.11 20.19 2.179 0.092 0.759 Batch 2 (Collected Nov 2020) 6.3 10.98 14.56 7.83 0.09 0.819 A.3 Preparation of Purolite® A860 resins To maintain a consistent volume of Purolite®A860 resins in all the BIEX systems, the BIEX columns were filled with 10g of dry Purolite®A860 resins (equivalent to a 20cm layer in the 50cm BIEX columns). Prior to the start of the present study, the virgin dry resins in each BIEX column were rinsed repeatedly with 5 BVs of DI (Millipore) water until any ‘free-floating’ chloride ions from the resin bed were evidently removed. The filtrate from each rinse was monitored with a conductivity meter at 25℃ (Bach-Simpsons Limited). Figure A2 illustrates the conductivity results for the effluent of the BIEX systems after the rinse. 85 Figure A2 Electrical conductivity of rinsed resins filtrate from each column System 3h (R) is indicated by a grey rectangle because it differed from other systems as explained in Section 3.3.2. The measurement of electrical conductivity is good indicator of the presence of chloride ions in a sample (EPA, 2021). As presented in Figure A2, the conductivity of the effluents of all the BIEX systems was highest for 1 BV immediately after the first rinse, which suggested that free floating chloride ions were present on the ion exchange resins. However, after four to five rinses, the effluent of the BIEX systems had a very low or unchanging conductivity which indicated that almost all the free-floating chloride ions were washed off from the resin bed. At this point, the resins were ready for the experimental study. A.4 Operation of BIEX systems Table A1 summarizes the operating conditions for the BIEX systems in the present study. 86 Table A2 Summary of operating conditions investigated in the present study System characteristics BIEX systems Nomenclature C 3h (R) 8h (R) 2d (R) 3h 8h 2d Operating conditions With continuous inflow With periods of no inflow Operating method -do- With effluent recirculation Without effluent recirculation Operating cycles N/A Daily Weekly Daily Weekly Design EBCT 30 mins Length of on/off period N/A 21h/3h 16h/8h 5d/2d 21h/3h 16h/8h 5d/2d Start of Off period N/A 8 AM 3 AM 10 AM (W) 8 AM 3 AM 10 AM (W) On period N/A 11 AM 11 AM 10 AM (F) 11 AM 11 AM 10 AM (F) Inflow On period Feed Feed water Feed water Feed water Feed water Feed water Feed water Off period N/A Effluent Effluent Effluent N/A N/A N/A *N/A: Not applicable, W: Wednesday, F: Friday A.5 Effluent volume corrections The beakers used as effluent tanks at the beginning of the study were found to be not accurate for measuring the volume of the effluent. To correct for the inaccuracy, each of the beakers was calibrated against a Nalgene (1L) volumetric graduated cylinder. Using the trendline equation, the corrected volume of the beakers was calculated. 87 The correction equation is of the form y=mx+x, where y= corrected volume of graduated cylinder (effluent tank), x = measured volume in the beaker (previously used effluent tanks), m = slope of the line, and c= constant. Table A3. Volume corrections for the BIEX systems Calibration Volumes Calibration Graph Correction Equation Beaker Graduated cylinder 0.2 0.2 0.4 0.41 0.6 0.63 0.8 0.82 1 1.1 y=1.105x-.031 Beaker Graduated cylinder 0.1 0.12 0.3 0.28 0.5 0.49 0.7 0.675 0.9 0.87 y=0.9475x+0.0133 Beaker Graduated cylinder 0.2 0.2 0.4 0.41 0.6 0.61 0.8 0.815 1 1.032 y=0.10345x-.0073 88 Beaker Graduated cylinder 0.2 0.19 0.4 0.39 0.6 0.59 0.8 0.8 1 0.94 y=0.955x+0.009 Beaker Graduated cylinder 0.2 0.19 0.4 0.39 0.6 0.59 0.8 0.8 1 0.93 y=0.945x+0.013 Beaker Graduated cylinder 0.2 0.19 0.4 0.4 0.6 0.59 0.8 0.8 1 0.92 y=0.93x+0.022 Beaker Graduated cylinder 0.2 0.19 0.4 0.4 0.6 0.605 0.8 0.8 1 1.105 y=1.115x-0.049 89 Appendix B Estimation of IEX capacity After the procedure described in Section 4.2.5, the ion exchange capacity of the resins from BIEX systems was estimated by titration. The key steps of the estimation procedure were as follows: a) The resins previously soaked in brine were rinsed with 30BV of DI water (Millipore Aqua-Q Ultra-Pure Water system) at a flow equivalent to 2 BV/h. b) The rinsed resins were transferred to a beaker and soaked in 475 mL of NaNO3 (25.6g/L). The soaked resins were agitated at 400 rpm for 30 minutes. The aim of this step was to displace all chloride ions in the resins by nitrate ions. c) The soaked resin solution was then filtered through a 0.45μm filter paper and the filtrate was collected in a volumetric flask. The filtrate was diluted with DI water (Millipore Aqua-Q Ultra-Pure Water system) to make a volume of 500 mL. d) 20mL of diluted filtrate was collected in a volumetric flask and spiked with 1 mL of K2CrO4 (20g/L). e) The spiked filtrate was titrated with 0.1N of AgNO3 until the solution turned orange in colour due to AgCl precipitation. The ion exchange capacity of the resins was calculated as per Equation B4 below (expressed as mEq/mL of resin). Equation B1 Concentration of Cl- ion, [Cl-] = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐴𝑔𝑁𝑂3 (𝑚𝐿)∗𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑜𝑓 𝐴𝑔𝑁𝑂3 (𝑁)𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡𝑖𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑠𝑎𝑚𝑝𝑙𝑒 (𝑚𝐿) * Molar mass of Cl- 90 Equation B2 Volume of Cl- ion exchanged, Cl- (eq) = [𝐶𝑙−]𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐶𝑙− * 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑁𝑎𝑁𝑂3 (𝑚𝐿)1000 Equation B3 Ion Exchange Capacity (mEq/mL) = 𝐶𝑙−(𝑚𝑒𝑞)𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑠𝑖𝑛𝑠 (𝑚𝐿) = 1000∗𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐴𝑔𝑁𝑂3 (𝑚𝐿)∗𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝑜𝑓 𝐴𝑔𝑁𝑂3 (𝑁)∗𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑁𝑎𝑁𝑂3 (𝑚𝐿)1000∗𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡𝑖𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑠𝑎𝑚𝑝𝑙𝑒𝑠 (𝑚𝐿)∗𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑠𝑖𝑛𝑠 (𝑚𝐿) Considering the volumes of titration sample (20mL), resin samples (variable depending on the systems), and NaNO3 (500mL), the final summarized equation for the resin capacity is: Equation B4 Ion Exchange Capacity (mEq/mL) = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝐴𝑔𝑁𝑂3 (𝑚𝐿)∗0.1𝑁∗500 𝑚𝐿 200 𝑚𝐿∗𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑠𝑖𝑛𝑠 (𝑚𝐿) 91 Appendix C Normalization of cumulative bed volumes As outlined in Section 4.3.2, the normalization multipliers for the cumulative bed volumes were obtained by the following equation: Equation C1 Normalization multiplier = 𝐷𝑒𝑠𝑖𝑔𝑛 𝑟𝑒𝑠𝑖𝑛 𝑣𝑜𝑙𝑢𝑚𝑒 (14.117 𝑚𝐿)𝐴𝑐𝑡𝑢𝑎𝑙 𝑟𝑒𝑠𝑖𝑛 𝑣𝑜𝑙𝑢𝑚𝑒 𝑎𝑠 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝑤𝑖𝑡ℎ 𝑡ℎ𝑒 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑜𝑙𝑢𝑚𝑛𝑠 𝑎𝑛𝑑 𝑡ℎ𝑒 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑟𝑒𝑠𝑖𝑛 ℎ𝑒𝑖𝑔ℎ𝑡 Table C1 summarizes the normalization multipliers used to normalize the cumulative bed volumes in the present study. Table C1. Normalization multipliers for cumulative bed volumes of the BIEX systems Systems Resin volume (mL) Design resin volume (mL) Normalization multiplier C 15.88 14.117 0.89 3h (R) 16.51 0.85 8h (R) 15.52 0.91 2d (R) 13.76 1.03 3h 14.82 0.95 8h 13.97 1.01 2d 14.82 0.95 92 Appendix D Raw concentration data D.1 Effluent DOC concentration data Figure D1 illustrates the normalized effluent DOC concentrations of the BIEX systems with respect to the days of operation and normalized bed volumes. a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure D1. Typical normalized effluent DOC concentrations from the BIEX systems. a) With respect to weeks of operation. b) With respect to cumulative normalized bed volumes; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined for this plot. The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System. 3h (R) are indicated by grey rectangle because it differed from other systems as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. D.2 Percent DOC removal data The average percent of DOC removals in the BIEX systems corresponding to feed water from Batch 1, Batch 1(A), and Batch 2(A) is presented in Table D1. 93 Table D1. Average DOC removals (presented as Removal % ± Standard deviation) in the BIEX systems Systems Feed water corresponding to Batch 1 Batch 1(A) Batch 2(A) C 68.55 ± 7.98 23.33 ± 16.29 46.93 ± 9.47 3h (R) 72.71 ± 3.21 48.12 ± 19.62 25.04 ± 12.49 8h (R) 69.24 ± 2.47 40.32 ± 18.89 25.50 ± 14.11 2d (R) 77.96 ± 2.94 45.92 ± 21.27 40.90 ± 10.89 3h 71.55 ± 2.22 45.58 ± 17.24 38.96 ± 11.70 8h 66.34 ± 2.57 30.74 ± 16.70 14.10 ± 10.76 2d 72.89 ± 7.67 41.18 ± 20.90 35.20 ± 10.62 D.3 Effluent UV absorbance and specific absorbance data Figure D2 illustrates the normalized effluent UV absorbance values of the BIEX systems with respect to the days of operation and normalized bed volumes. 94 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure D2. Typical normalized effluent UV absorbance from the BIEX systems. a) With respect to weeks of operation. b) With respect to cumulative normalized bed volumes; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined for this plot. The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. Figure D3 illustrates the normalized effluent SUVA values of the BIEX systems with respect to the days of operation and normalized bed volumes. 95 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure D3. Typical normalized effluent SUVA from the BIEX systems. a) With respect to weeks of operation. b) With respect to cumulative normalized bed volumes; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined for this plot. The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. D.4 Effluent Chloride concentration data Figure D4 illustrates the normalized effluent chloride concentration of the BIEX systems with respect to the days of operation and normalized bed volumes. 96 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure D4. Typical normalized effluent chloride concentrations from the BIEX systems. a) With respect to weeks of operation. b) With respect to cumulative normalized bed volumes; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined for this plot. The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. Primary IEX exhaustion was defined to have occurred when the effluent chloride concentrations became statistically similar to the feed water chloride concentrations (based on a t-test at a 99.99% confidence interval). D.5 Effluent Sulphate concentration data Figure D5 illustrates the normalized effluent sulphate concentration of the BIEX systems with respect to the days of operation and normalized bed volumes. 97 a) b) Batch 1 Batch 1(A) Batch 2(A) Phase 1 (P1) Phase 2 (P2) Phase 3 (P3) Figure D5. Typical normalized effluent sulphate concentrations from the BIEX systems. a) With respect to weeks of operation. b) With respect to cumulative normalized bed volumes; as all BIEX systems had variable loading rates, the timeline of feed water from Batch 1, 1(A), and 2(A) could not be defined for this plot. The data points connected by the black solid line correspond to System C, the operating condition against which all other conditions examined were compared. Data points for System 3h (R) are indicated by grey rectangle because it differed from other systems as explained in Section 4.4.2. Error bars represent standard errors at 95% confidence interval. Secondary IEX exhaustion was defined to have occurred when the effluent sulphate concentrations became statistically similar to the feed water sulphate concentrations (based on a t-test at a 99.99% confidence interval). Table D2 summarizes the days/weeks of operation and bed volumes achieved at the time of primary IEX exhaustion and start of secondary IEX in the BIEX systems with the different operating conditions investigated. 98 Table D2. Days/Weeks of operation corresponding to primary IEX exhaustion and start of secondary IEX Systems End of Primary IEX Start of secondary IEX Days of operation Weeks of operation Days of operation Weeks of operation C 30 5 35 6 3h (R) 47 8 49 8 8h (R) 47 8 47 8 2d (R) 30 5 37 6 3h 40 7 47 8 8h 40 7 42 7 2d 30 5 33 6 99 Appendix E Summary of rates of removal and/or release in different phases of treatment E.1 Chloride release during Phase 1 Figure E1 illustrates the rates of chloride release corresponding to Batch 1 and Batch 1(A) in Phase 1. Figure E1. Rate of chloride release during Phase 1 For Batch 1 (left) and Batch 1(A)(right). The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Table E1 summarizes the rates of chloride release during Phase 1, corresponding to Batch 1 and Batch 1(A) respectively, as well as the final rates considered for analysis in this study. Table E1. Summary of rates of chloride release in Phase 1 Systems Rate of chloride release corresponding to Batch 1 (meq/BV) Rate of chloride release corresponding to Batch 1(A) (meq/BV) Rate of chloride release considered for analysis (meq/BV) C 0.0113 ± 0.0004 0.0085 ± 0.0021 0.0107 ± 0.0007 3h (R) 0.0091 ± 0.0005 0.009 ± 0.0009 0.0099 ± 0.0004 8h (R) 0.0103 ± 0.0007 0.009 ± 0.0014 0.0101 ± 0.0007 2d (R) 0.0092 ± 0.0014 0.0106 ± 0.0005 0.0101 ± 0.0004 3h 0.0088 ± 0.0006 0.0092 ± 0.001 0.0096 ± 0.0003 8h 0.0103 ± 0.0011 0.0097 ± 0.0014 0.0107 ± 0.0006 2d 0.0116 ± 0.0016 0.011 ± 0.0029 0.0123 ± 0.0010 100 E.2 Sulphate removal during Phase 1 Figure E2 illustrates the rates of sulphate removal during Phase 1 corresponding to Batch 1 and Batch 1(A). Figure E2. Rate of sulphate removal during Phase 1 For Batch 1 (left) and Batch 1(A)(right). The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Table E2 summarizes the rates of sulphate removal during Phase 1, corresponding to Batch 1 and Batch 1(A) respectively, as well as the final rates considered for analysis in this study. Table E2. Summary of rates of sulphate removal in Phase 1 Systems Rate of sulphate removal corresponding to Batch 1 (meq/BV) Rate of sulphate removal corresponding to Batch 1(A) (meq/BV) Rate of sulphate removal considered for analysis (meq/BV) C 0.0005 ± 0.00002 0.0167 ± 0.0001 0.0118 ± 0.003 3h (R) 0.0004 ± 0.00005 0.0134 ± 0.0005 0.0121 ± 0.001 8h (R) 0.0005 ± 0.00003 0.013 ± 0.0013 0.0124 ± 0.001 2d (R) 0.0005 ± 0.00001 0.0133 ± 0.00008 0.0092 ± 0.002 3h 0.0004 ± 0.00001 0.0133 ± 0.0002 0.0111 ± 0.001 8h 0.0003 ± 0.0001 0.0133 ± 0.0002 0.0109 ± 0.001 2d 0.0006 ± 0.00003 0.0167 ± 0.0001 0.0121 ± 0.003 101 E.3 DOC removal during Phase 1 Figure E3 illustrates the rates of DOC removal during Phase 1 corresponding to Batch 1 and Batch 1(A). Figure E3. Rate of DOC removal during Phase 1 For Batch 1 (left) and Batch 1(A)(right). The negative y-axis indicates a net release of ions from the BIEX systems. Error bars in red represent a 95% confidence interval of the slope of the regression line. Table E3 summarizes the rates of DOC removal during Phase 1, corresponding to Batch 1 and Batch 1(A) respectively, as well as the final rates considered for analysis in this study. Table E3. Summary of rates of DOC removal in Phase 1 Systems Rate of DOC removal corresponding to Batch 1 (meq/BV) Rate of DOC removal corresponding to Batch 1(A) (meq/BV) Rate of DOC removal considered for analysis (meq/BV) C 0.0007 ± 0.00004 0.0003 ± 0.00002 0.0005 ± 0.00006 3h (R) 0.0006 ± 0.00001 0.0005 ± 0.00001 0.0005 ± 0.00001 8h (R) 0.0003 ± 0.0001 0.0005 ± 0.00002 0.0005 ± 0.00001 2d (R) 0.0006 ± 0.000008 0.0004 ± 0.00004 0.0005 ± 0.00004 3h 0.0005 ± 0.00001 0.0005 ± 0.00001 0.0005 ± 0.00001 8h 0.0005 ± 0.000009 0.0002 ± 0.00003 0.0003 ± 0.00004 2d 0.0007 ± 0.00001 0.0005 ± 0.00008 0.0006 ± 0.00005 102 E.4 Rate of release and/or removal during Phase 2 Table E4 summarizes the rates of release and/or removal during Phase 2. Table E4. Summary of rates of release and/or removal in Phase 2 Systems Rate of chloride release (meq/BV) Rate of sulphate release (meq/BV) Rate of DOC removal (meq/BV) C 0.0004 ± 0.00005 0.0012 ± 0.0001 0.0002 ± 0.00002 3h (R) 0.0004 ± 0.00006 0.0006 ± 0.0002 0.0002 ± 0.00004 8h (R) 0.0004 ± 0.00006 0.0003 ± 0.0002 0.0002 ± 0.00002 2d (R) 0.0003 ± 0.00005 0.0009 ± 0.0001 0.0003 ± 0.00002 3h 0.0005 ± 0.00009 0.0011 ± 0.0002 0.0001 ± 0.00001 8h 0.0004 ± 0.00008 0.0009 ± 0.0001 0.0002 ± 0.00001 2d 0.0006 ± 0.00008 0.0018 ± 0.0002 0.0003 ± 0.00002 E.5 Rate of release and/or removal during Phase 3 Table E5 summarizes the rates of release and/or removal during Phase 3. Table E5. Summary of rates of release and/or removal in Phase 3 Systems Rate of chloride release (meq/BV) Rate of sulphate release (meq/BV) Rate of DOC removal (meq/BV) C 0.00002 ± 0.00004 0.00022 ± 0.0001 0.0005 ± 0.00001 3h (R) 0.00001 ± 0.00001 0.00008 ± 0.0002 0.0002 ± 0.00001 8h (R) 0.00006 ± 0.00003 0.00041 ± 0.00005 0.0002 ± 0.00002 2d (R) 0.00006 ± 0.00002 0.00005 ± 0.00004 0.0003 ± 0.00001 3h 0.00004 ± 0.00003 0.00018 ± 0.00005 0.0003 ± 0.00001 8h 0.000001 ± 0.00001 0.00008 ± 0.0001 0.0001 ± 0.00001 2d 0.00004 ± 0.00002 0.00007 ± 0.0001 0.0003 ± 0.00001 103 Appendix F Anion loading in the BIEX systems, defined by phases of treatment Anion loading the BIEX systems, defined by Phase 1, 2, and 3, are presented below: 104 105 106 Figure F1. Normalized cumulative DOC removal, chloride release, and sulphate removal and/or release in all the BIEX systems. From left to right, the first vertical line indicates the change of feed from Batch 1 to Batch 1 (A) and the second vertical line indicates the change of feed from Batch 1 (A) to Batch 2 (A) Note that, towards the end of Phase 2, the normalized cumulative sulphate release approached the resin capacity for some BIEX systems. For System C, System 3h (R), System 8h (R), and System 3h, the normalized cumulative sulphate release approached the resin capacity of the BIEX systems (See Figure 8 and Figure D1 (a), (b), and (d)). However, for System 2d (R), System 8h, and System 2d, normalized cumulative sulphate release was significantly lower than the resin capacity of the BIEX systems (See Figure D1 (c), (e), and (f)). It is unclear why these three BIEX systems had a lower loading of sulphate on the resins, even though there appeared to be some resin capacity remaining in the BIEX systems. Table F1 summarizes the sulphate overloading or lack thereof, observed in some of the BIEX systems, 107 Table F1. Amount of sulphate overloading in the BIEX systems Systems Cumulative sulphate removed at end of Phase 1 (meq) Resin Capacity (meq) Sulphate overloading (%) C 13.469 11.29 19.3 3h (R) 12.676 12.28 8h (R) 11.648 3.17 2d (R) 10.604 (-) 12.37 3h 13.429 18.95 8h 10.824 (-) 4.13 2d 9.921 (-) 11.86 The negative sign indicates that there was an unloading of sulphate in those BIEX systems. 108 Appendix G Ion exchange during Phase 1 and Phase 2 G.1 Phase 1: Ion exchange Figure G1 presents the normalized cumulative sulphate removed to the normalized cumulative chloride released, and the normalized cumulative DOC removed to the normalized cumulative chloride during Phase 1. 109 110 111 Figure G1. Normalized cumulative sulphate removed to the normalized cumulative chloride released (left), and normalized cumulative DOC removed to the normalized cumulative chloride released (right) during Phase 1, in all the BIEX systems. The release ions are plotted on the x-axis and the uptake ions are plotted on the y-axis. The straight line indicates x = y. 112 G.2 Phase 2: Ion exchange Figure G2 illustrates the normalized cumulative DOC removed to the normalized cumulative chloride and/or sulphate released during Phase 2. 113 Figure G2. Normalized cumulative DOC removed to the normalized cumulative chloride and/or sulphate released during Phase 2, in all the BIEX systems The release ions are plotted on the x-axis and the uptake ions are plotted on the y-axis. The straight line indicates x = y. 114 Appendix H Summary of statistical analysis results in different phases of treatment Statistical analyses were performed on the release and/or removal data (in milliequivalents) to test the three hypotheses of the present study (See Chapter 3 and Section 4.4.2). H.1 Phase 1: Chloride release Results of statistical analysis on chloride release (in milliequivalents) during Phase 1 are presented below. Testing Hypothesis 1: Operation with periods of no inflow impacts DOC removal with BIEX systems. Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 6.307 6.374 6.753 6.120 6.087 6.370 6.399 Standard dev 3.486 3.683 3.732 3.303 3.648 3.583 3.324 Count 13 20 20 13 17 17 13 P-value N/A 0.997 0.774 0.858 0.836 1 0.983 T-critical N/A 2.051 2.051 2.063 2.055 2.055 2.063 Results Accept null Accept null Accept null Accept null Accept null Accept null Testing Hypothesis 2: The extent of the potential impacts of operation with periods of no inflow on DOC removal is affected by the duration and/or the frequency of the periods of no inflow ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 20 127.49 6.3746 14.282 8h (R) 20 135.08 6.7538 14.665 2d (R) 13 79.563 6.1202 11.822 Source of variation SS Df MS F P-value Fcrit Between groups 3.371 2 1.685 0.121 0.885 3.182 Within groups 691.86 50 13.68 Total 695.23 52 Result: Accept null ANOVA: Single factor (for BIEX systems operated without effluent recirculation) 115 Groups Count Sum Average Variance 3h 17 103.49 6.087 14.14 8h 17 108.3 6.370 13.641 2d 13 83.193 6.399 11.97 Source of variation SS Df MS F P-value Fcrit Between groups 0.953 2 0.476 0.035 0.965 3.209 Within groups 588.13 44 13.367 Total 589.08 46 Result: Accept null Testing Hypothesis 3: The extent of the potential impacts of operation with periods of no inflow on DOC removal can be mitigated by effluent recirculation Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 6.374 6.087 6.753 6.370 6.120 6.399 Standard dev 3.683 3.648 3.732 3.583 3.303 3.324 Count 20 17 20 17 13 13 P-value 0.818 0.759 0.838 T-critical 2.032 2.032 2.063 Results Accept null Accept null Accept null H.2 Phase 1: Sulphate removal Results of statistical analysis on sulphate removal (in milliequivalents) during Phase 1 are presented below. Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 4.456 5.721 5.738 3.590 2.529 2.036 3.928 Standard dev 4.405 2.783 2.976 3.314 3.186 2.659 3.637 Count 13 20 20 13 17 17 13 P-value N/A 0.451 0.438 0.591 0.209 0.106 0.751 T-critical N/A 2.055 2.055 2.073 2.086 2.100 2.068 116 Results Accept null Accept null Accept null Accept null Accept null Accept null Testing Hypothesis 2: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 20 114.43 5.721 22.396 8h (R) 20 114.76 5.738 20.849 2d (R) 13 46.671 3.590 11.903 Source of variation SS Df MS F P-value Fcrit Between groups 44.918 2 22.459 1.164 0.320 3.182 Within groups 964.48 50 19.29 Total 1009.4 52 Result: Accept null ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 17 43.008 2.529 10.072 8h 17 34.621 2.036 6.960 2d 13 51.072 3.928 14.337 Source of variation SS Df MS F P-value Fcrit Between groups 27.529 2 13.764 1.362 0.266 3.209 Within groups 444.56 44 10.104 Total 472.09 46 Result: Accept null Testing Hypothesis 3: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 5.721 2.529 5.738 2.036 3.590 3.928 Standard dev 2.783 3.186 2.976 2.659 3.314 3.637 Count 20 17 20 17 13 13 P-value 0.020 0.004 0.813 T-critical 2.034 2.039 2.063 Results Reject null Reject null Accept null 117 H.3 Phase 1: DOC removal Results of statistical analysis on DOC removal (in milliequivalents) during Phase 1 are presented below. Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 0.332 0.329 0.315 0.331 0.325 0.237 0.316 Standard dev 0.164 0.188 0.170 0.152 0.183 0.112 0.153 Count 13 20 20 13 17 17 13 P-value N/A 0.966 0.777 0.980 0.919 0.098 0.802 T-critical N/A 2.04 2.05 2.06 2.05 2.08 2.06 Results Accept null Accept null Accept null Accept null Accept null Accept null Testing Hypothesis 2: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 20 6.598 0.329 0.0373 8h (R) 20 6.301 0.315 0.305 2d (R) 13 4.303 0.331 0.025 Source of variation SS Df MS F P-value Fcrit Between groups 0.002 2 0.001 0.045 0.955 3.182 Within groups 1.589 50 0.031 Total 1.592 52 Result: Accept null ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 17 5.541 0.325 0.035 8h 17 4.034 0.237 0.013 2d 13 4.111 0.316 0.025 Source of variation SS Df MS F P-value Fcrit Between groups 0.078 2 0.039 1.565 0.220 3.209 118 Within groups 1.096 44 0.024 Total 1.174 46 Result: Accept null Testing Hypothesis 3: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 0.329 0.325 0.315 0.237 0.331 0.316 Standard dev 0.188 0.183 0.170 0.112 0.152 0.153 Count 20 17 20 17 13 13 P-value 0.950 0.115 0.814 T-critical 2.03 2.03 2.06 Results Accept null Accept null Accept null H.4 Phase 2: Chloride release To show that there was some chloride release from some of the BIEX systems in Phase 2, a t-test was performed on the normalized weekly composite chloride concentrations from the effluents of the BIEX systems. Results of statistical analysis are presented below. Hypothesis: The normalized cumulative effluent chloride concentration is not different from 1. Criteria C 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 1.408 1.93 1.873 1.562 1.779 1.84 1.54 Standard dev 0.622 0.886 0.933 0.78 0.867 0.981 0.848 Count 10 10 10 10 10 10 10 P-value 0.081 0.012 0.02 0.059 0.024 0.03 0.088 T-critical 2.26 2.26 2.26 2.26 2.26 2.26 2.26 Results Accept null Reject null Reject null Accept null Reject null Reject null Accept null Results of statistical analysis on chloride release (in milliequivalents) during Phase 2 are presented below. 119 Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 11.148 11.151 11.169 11.147 11.147 11.135 11.032 Standard dev 0.213 0.138 0.095 0.191 0.203 0.183 0.338 Count 23 15 14 23 19 21 26 P-value N/A 0.961 0.683 0.987 0.986 0.839 0.16 T-critical N/A 2.02 2.03 2.01 2.02 2.01 2.01 Results Accept null Accept null Accept null Accept null Accept null Accept null Testing Hypothesis 2: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 15 167.268 11.151 0.020 8h (R) 14 156.379 11.169 0.009 2d (R) 23 256.390 11.147 0.037 Source of variation SS Df MS F P-value Fcrit Between groups 0.004 2 0.002 0.091 0.912 3.186 Within groups 1.245 49 0.025 Total 1.249 51 Result: Accept null ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 19 211.798 11.147 0.043 8h 21 233.855 11.135 0.035 2d 26 286.836 11.032 0.119 Source of variation SS Df MS F P-value Fcrit Between groups 0.189 2 0.094 1.334 0.270 3.142 Within groups 4.463 63 0.070 Total 4.652 65 Result: Accept null 120 Testing Hypothesis 3: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 11.151 11.147 11.169 11.135 11.147 11.032 Standard dev 0.138 0.203 0.095 0.183 0.191 0.338 Count 15 19 14 21 23 26 P-value 0.948 0.490 0.152 T-critical 2.03 2.03 2.02 Results Accept null Accept null Accept null H.5 Phase 2: Sulphate release Results of statistical analysis on sulphate release (in milliequivalents) during Phase 2 are presented below. Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 12.441 12.280 11.298 8.701 12.535 10.053 8.142 Standard dev 0.684 0.238 0.105 0.564 0.500 0.410 1.014 Count 23 15 14 23 19 21 26 P-value N/A 0.323 6.3E-08 4.8E-23 0.616 3.2E-16 3.7E-21 T-critical N/A 2.04 2.06 2.01 2.02 2.02 2.01 Results Accept null Reject null Reject null Accept null Reject null Reject null Testing Hypothesis 2: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 12.280 12.535 11.298 10.053 8.701 8.142 Standard dev 0.238 0.500 0.105 0.410 0.564 1.014 Count 15 19 14 21 23 26 P-value 0.068 2.4E-12 0.021 T-critical 2.05 2.06 2.02 121 Results Accept null Reject null Reject null Testing Hypothesis 3: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 15 184.209 12.280 0.061 8h (R) 14 158.185 11.298 0.011 2d (R) 23 200.125 8.701 0.318 Source of variation SS Df MS F P-value Fcrit Between groups 130.69 2 65.345 399.838 4.5E-31 3.186 Within groups 8.008 49 0.163 Total 138.7 51 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h (R) vs 8h (R) 0.98 0.363 0.106 Statistically different 3h (R) vs 2d (R) 3.58 0.324 0.094 Statistically different 8h (R) vs 2d (R) 2.60 0.331 0.096 Statistically different ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 19 238.173 12.535 0.264 8h 21 211.122 10.053 0.176 2d 26 211.696 8.142 1.069 Source of variation SS Df MS F P-value Fcrit Between groups 211.93 2 105.964 190.514 1.9E-27 3.142 Within groups 35.041 63 0.556 Total 246.97 65 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h vs 8h 2.48 0.571 0.166 Statistically different 3h vs 2d 4.39 0.544 0.159 Statistically different 8h vs 2d 1.91 0.529 0.154 Statistically different 122 H.6 Phase 2: DOC removal Results of statistical analysis on DOC removal (in milliequivalents) during Phase 2 are presented below. Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 0.780 0.785 0.675 0.953 0.857 0.516 0.835 Standard dev 0.111 0.080 0.052 0.142 0.104 0.086 0.143 Count 23 15 14 23 19 21 26 P-value N/A 0.854 0.0007 6E-05 0.028 9E-11 0.142 T-critical N/A 2.03 2.03 2.01 2.02 2.01 2.01 Results Accept null Reject null Reject null Reject null Reject null Accept null Testing Hypothesis 2: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 0.785 0.857 0.675 0.516 0.953 0.835 Standard dev 0.080 0.104 0.052 0.086 0.142 0.143 Count 15 19 14 21 23 26 P-value 0.035 2E-07 0.007 T-critical 2.03 2.03 2.01 Results Reject null Reject null Reject null Testing Hypothesis 3: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 15 11.789 0.785 0.006 8h (R) 14 9.456 0.675 0.003 2d (R) 23 21.921 0.953 0.021 Source of variation SS Df MS F P-value Fcrit Between groups 0.712 2 0.356 28.957 5E-09 3.186 123 Within groups 0.602 49 0.012 Total 1.314 51 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h (R) vs 8h (R) 0.06 0.099 0.029 Not Statistically different 3h (R) vs 2d (R) 0.33 0.089 0.026 Statistically different 8h (R) vs 2d (R) 0.28 0.090 0.026 Statistically different ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 19 16.296 0.857 0.011 8h 21 10.848 0.516 0.007 2d 26 21.723 0.835 0.021 Source of variation SS Df MS F P-value Fcrit Between groups 1.548 2 0.774 54.518 2E-14 3.142 Within groups 0.894 63 0.014 Total 2.443 65 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h vs 8h 0.34 0.09 0.026 Statistically different 3h vs 2d 0.02 0.08 0.025 Not Statistically different 8h vs 2d 0.32 0.08 0.247 Statistically different H.7 Phase 3: Chloride release To show that there was no chloride release from the BIEX systems in Phase 3, a t-test was performed on the normalized weekly composite chloride concentrations from the effluents of the BIEX systems. Results of statistical analysis are presented below. 124 Hypothesis: The normalized cumulative effluent chloride concentration is not different from 1. Criteria C 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 1.025 1.028 1.018 1.039 1.034 1.032 1.028 Standard dev 0.057 0.046 0.091 0.064 0.069 0.095 0.068 Count 11 11 11 11 11 11 11 P-value 0.179 0.076 0.539 0.081 0.149 0.306 0.211 T-critical 2.22 2.22 2.22 2.22 2.22 2.22 2.22 Results Accept null Accept null Accept null Accept null Accept null Accept null Accept null H.8 Phase 3: Sulphate release To show that there was no sulphate release from the BIEX systems in Phase 3, a t-test was performed on the normalized weekly composite sulphate concentrations from the effluents of the BIEX systems. Results of statistical analysis are presented below. Hypothesis: The normalized cumulative effluent sulphate concentration is not different from 1. Criteria C 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 1.017 1.003 1.013 1.004 0.999 0.997 1.008 Standard dev 0.033 0.035 0.020 0.035 0.037 0.029 0.027 Count 11 11 11 11 11 11 11 P-value 0.128 0.752 0.066 0.673 0.982 0.807 0.358 T-critical 2.22 2.22 2.22 2.22 2.22 2.22 2.22 Results Accept null Accept null Accept null Accept null Accept null Accept null Accept null H.9 Phase 3: DOC removal Results of statistical analysis on DOC removal (in milliequivalents) during Phase 2 are presented below. 125 Testing Hypothesis 1: Criteria C C vs 3h(R) C vs 8h(R) C vs 2d(R) C vs 3h C vs 8h C vs 2d 3h (R) 8h (R) 2d (R) 3h 8h 2d Average 1.580 1.028 0.874 1.418 1.257 0.710 1.339 Standard dev 0.318 0.099 0.095 0.178 0.166 0.051 0.157 Count 27 29 30 26 26 26 25 P-value N/A 1.5E-09 6.5E-12 0.029 4.9E-05 1.1E-13 0.001 T-critical N/A 2.03 2.04 2.01 2.02 2.05 2.02 Results Reject null Reject null Reject null Reject null Reject null Reject null Testing Hypothesis 2: ANOVA: Single factor (for BIEX systems operated with effluent recirculation) Groups Count Sum Average Variance 3h (R) 29 29.815 1.028 0.010 8h (R) 30 26.241 0.874 0.009 2d (R) 26 36.875 1.418 0.033 Source of variation SS Df MS F P-value Fcrit Between groups 4.302 2 2.151 127.152 7.4E-26 3.107 Within groups 1.387 82 0.016 Total 5.690 84 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h (R) vs 8h (R) 0.15 0.081 0.023 Statistically different 3h (R) vs 2d (R) 0.39 0.084 0.024 Statistically different 8h (R) vs 2d (R) 0.54 0.082 0.024 Statistically different ANOVA: Single factor (for BIEX systems operated without effluent recirculation) Groups Count Sum Average Variance 3h 26 32.682 1.257 0.028 8h 26 18.471 0.710 0.002 2d 25 33.488 1.339 0.025 Source of variation SS Df MS F P-value Fcrit 126 Between groups 6.021 2 3.010 158.757 1.7E-27 3.120 Within groups 1.403 74 0.189 Total 7.424 76 Result: Reject null Tukey’s Honesty Test Comparison Absolute difference Critical range S.E Results 3h vs 8h 0.55 0.091 0.027 Statistically different 3h vs 2d 0.08 0.092 0.027 Not Statistically different 8h vs 2d 0.63 0.092 0.027 Statistically different Testing Hypothesis 3: Criteria 3h (R) vs 3h 8h (R) vs 8h 2d (R) vs 2d 3h (R) 3h 8h (R) 8h 2d (R) 2d Average 1.028 1.257 0.874 0.710 1.418 1.339 Standard dev 0.099 0.166 0.095 0.051 0.178 0.157 Count 29 26 30 26 26 25 P-value 4.7E-07 2.6E-10 0.107 T-critical 2.02 2.01 2.00 Results Reject null Reject null Accept null H.10 Comparing Rates of DOC removal in Phase 2 and Phase 3 To compare the rates of DOC removal in Phase 2 and Phase 3, a t-test at 95% confidence interval was performed on the rates of DOC removal. Results of statistical analysis are presented below. Hypothesis: Rates of DOC removal during Phase 2 is similar to that during Phase 3 Criteria Phase 2 Phase 3 Average 0.00023 0.0003 Count 7 7 P-value 0.1695 T-critical 2.446 Results Accept null 127 Appendix I Results of organic mass balance I.1 Organic mass balance based on normalized cumulative DOC removed Figure I1 Organic mass balance based on normalized DOC removed Systems Normalized cumulative mass of DOC removed (mg/BV) Normalized cumulative mass of DOC removed (meq/BV) Distribution of DOC removal mechanisms (%) Ion Exchange Biodegradation Phase1 Phase2 Phase3 Phase1 Phase2 Phase3 C 0.048 0.022 0.045 0.0005 0.0002 0.0005 48% 50% 3h (R) 0.048 0.025 0.020 0.0005 0.0003 0.0002 72% 26% 8h (R) 0.045 0.022 0.022 0.0005 0.0002 0.0002 72% 28% 2d (R) 0.047 0.027 0.032 0.0006 0.0003 0.0003 66% 32% 3h 0.047 0.025 0.032 0.0005 0.0003 0.0003 64% 33% 8h 0.033 0.018 0.011 0.0002 0.0002 0.0001 81% 18% 2d 0.057 0.028 0.031 0.0003 0.0003 0.0003 66% 30% I.2 Organic mass balance based on resin regeneration Figure I2 Organic mass balance based on resin regeneration Systems Total mass of DOC recovered from the BIEX resins (mg/L)* Normalized cumulative mass of DOC (mg) Normalized mass of DOC recovered (mg/BV) Mass of DOC removed (mg) by Feed Effluent Total DOC removed Ion exchange Assumed biodegradation C 1760 517 206 312 0.038 174 (56%) 138 (44%) 3h (R) 1197 300 119 181 0.030 70 (39%) 111 (61%) 8h (R) 1012 281 103 179 0.030 91 (51%) 88 (49%) 2d (R) 1253 346 168 178 0.035 126 (71%) 52 (29%) 3h 1546 336 151 184 0.033 137 (75%) 47 (25%) 8h 811 286 77 210 0.020 81 (38%) 129 (62%) 2d 1190 394 156 238 0.029 129 (54%) 109 (46%) *DOC concentration in 1L of regenerating solution The distribution of DOC removal mechanism in System 3h (R) and System 8h has been marked as inconclusive, as the amount of DOC recovered from the regenerated solutions from 128 these two systems was most likely an underestimate (potentially not all DOC were recovered from the resins). 129 Appendix J Time-series results Every 5-6 weeks of operation, dynamic time-series samples were collected from the BIEX systems, at the end of a period of no inflow (time = 0), and every 2 hours thereafter for a total of 6 hours. The effluent samples acted as a snapshot of the BIEX systems’ performance immediately after the end of a period of no inflow. The volume of water in the effluent tank at the time of sample collection was also recorded. Figure J1 illustrates the sampling schedule for the time-series samples from the BIEX systems. Figure J1. Summary of composite and time-series sampling schedule for the BIEX systems. Figure J2 illustrates raw data of the effluent DOC concentrations as a function of BIEX systems’ run time after flow was restored in the systems (time = 0), and every 2 hours thereafter for a total of 6 hours. On Week 11 and 20, time-series samples were also collected at t=22 hours. 130 Figure J2. Raw time-series data of effluent DOC concentrations 131 Overall, as presented in Figure J2, the raw data for the time-series samples indicated that immediately after flow is restored following a period of no inflow in a BIEX system, the effluent DOC concentration was higher than the feed DOC concentration (irrespective of the operating conditions investigated). The results from the time-series analysis were similar to other studies. Niquette et al., (1998) also reported high values of DOC in BAC filter effluents immediately after filtration was resumed following filter shutdown without backwash. As the amount of time since restoration of flow increased, the effluent DOC concentrations decreased gradually in most of the operating conditions investigated. The effluent DOC concentrations in all the operating conditions investigated appeared to become stable after 4-6 hours restoration of flow. Similar results were also reported by McKie et al., (2019) who suggested that biofilms can recover after exposure to the intermittent period which is a “stressful condition” for the biofilm communities. Additionally, at 22 hours after restoration of flow, the effluent DOC concentration was similar to the effluent DOC concentration at 4-6 hours after restoration of flow. Only in BIEX systems operated with a daily and long (~8h) period of no inflow (System 8h (R) and System 8h), the effluent DOC concentration at t=22 hours was slightly higher, similar to the effluent DOC concentration at 2 hours after restoration of flow. The reason for the heightened effluent DOC concentration is unknown and beyond the scope of the present study.
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Bérubé, Pierre R.
Impact of periods of no inflow on dissolved organic carbon (DOC) removal by Biological Ion Exchange (BIEX) systems
Text