Applied Science, Faculty of
Civil Engineering, Department of
DSpace
UBCV
Baskar, Varshini
Master of Applied Science - MASc
University of British Columbia
Passive membrane systems are ideal for use in small and remote communities; they are operated under a low permeate flux, thereby requiring limited energy, they have few passive fouling control measures, leading to limited mechanical complexity, and are relatively easy to operate. Their operation depends on the formation of a structurally loose and permeable biofilm on the membrane surface, which helps stabilize the permeate flux and aids the removal of organic material and other material of concern. However, their application is potentially hindered by intermittent loading conditions caused by periods of no inflow demand, a characteristic of small and remote systems. Periods of no inflow could stress biofilm in passive membrane systems and affect the overall system stability and performance. The current study investigated the impacts of the periods of no inflow on the throughput and in organic material removal the passive membrane systems. Passive membrane systems operated with various periods of no inflow were considered and compared to a passive membrane system operated with continuous inflow. The periods of no inflow considered were 3 hours per 24 hours, 8 hours per 24 hours and 2 days per week. For the passive membrane systems operated with periods of no inflow, both conditions with no permeate recycling (i.e., no flow through system) and permeate recycling (i.e., flow maintained through system by recycling permeate) were considered. Results indicate that the periods of no inflow do not negatively impact the performance of passive membrane systems. Rather, periods of no inflow could lead to better performance. The results also provided insight on the relationship between the length of the periods of no inflow, the recycling of the permeate during periods of no inflow, and the overall performance of passive membrane systems. In small and remote communities, the financial investment in equipment and operations for permeate recycling during periods of no inflow might be outweighed by the increased water production when operated with permeate recycling. Hence, for small and remote communities, operation of PGDMF systems without permeate recycling during the periods of no inflow is ideal.
INTERMITTENT OPERATIONS OF PASSIVE MEMBRANE SYSTEMS by VARSHINI BASKAR 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) February 2022 © Varshini Baskar, 2022 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: Intermittent operations of passive membrane systems submitted by Varshini Baskar in partial fulfilment of the requirements for the degree of Master of Applied Science in Civil Engineering Examining Committee: Dr. Pierre Bérubé, Professor, Department of Civil Engineering, UBC Supervisor Dr. Jongho Lee, Assistant Professor, Department of Civil Engineering, UBC Supervisory Committee Member iii Abstract Passive membrane systems are ideal for use in small and remote communities; they are operated under a low permeate flux, thereby requiring limited energy, they have few passive fouling control measures, leading to limited mechanical complexity, and are relatively easy to operate. Their operation depends on the formation of a structurally loose and permeable biofilm on the membrane surface, which helps stabilize the permeate flux and aids the removal of organic material and other material of concern. However, their application is potentially hindered by intermittent loading conditions caused by periods of no inflow demand, a characteristic of small and remote systems. Periods of no inflow could stress biofilm in passive membrane systems and affect the overall system stability and performance. The current study investigated the impacts of the periods of no inflow on the throughput and in organic material removal the passive membrane systems. Passive membrane systems operated with various periods of no inflow were considered and compared to a passive membrane system operated with continuous inflow. The periods of no inflow considered were 3 hours per 24 hours, 8 hours per 24 hours and 2 days per week. For the passive membrane systems operated with periods of no inflow, both conditions with no permeate recycling (i.e., no flow through system) and permeate recycling (i.e., flow maintained through system by recycling permeate) were considered. Results indicate that the periods of no inflow do not negatively impact the performance of passive membrane systems. Rather, periods of no inflow could lead to better performance. The results also provided insight on the relationship between the length of the periods of no iv inflow, the recycling of the permeate during periods of no inflow, and the overall performance of passive membrane systems. In small and remote communities, the financial investment in equipment and operations for permeate recycling during periods of no inflow might be outweighed by the increased water production when operated with permeate recycling. Hence, for small and remote communities, operation of PGDMF systems without permeate recycling during the periods of no inflow is ideal. v Lay Summary Passive membrane filtration is a well-established drinking water treatment technology that is easy to use and relatively low-cost to maintain and operate, making it well-suited for use in small and remote communities. Passive membrane filters use gravity to push water through the membranes and use simple passive measures to keep the membrane clean. The retained contaminants collect on the membrane surface and establish a microbial biofilm layer that is crucial to the stable operation. In small communities, the demand for water is such that the water treatment system might not be operated continuously. This could affect the biofilm layer in passive membrane filters and in turn affect the overall water output. The current study investigated the effect of varying operational periods in passive membrane filters. It was observed that periods of no inflow do not negatively impact the performance of passive membrane systems, but rather lead to overall better performance. vi Preface This dissertation is original, unpublished, independent work by the author, Varshini Baskar. vii Table of Contents Abstract ................................................................................................................................... iii Lay Summary .......................................................................................................................... v Preface ..................................................................................................................................... vi Table of Contents .................................................................................................................. vii List of Tables .......................................................................................................................... xi List of Figures ....................................................................................................................... xiii Lists of Abbreviations ........................................................................................................... xv Acknowledgements .............................................................................................................. xvi Dedication ............................................................................................................................ xvii Chapter 1. Introduction ......................................................................................................... 1 Chapter 2. Background and Literature Review .................................................................. 3 2.1 Membrane Filtration Systems ......................................................................................... 3 2.1.1 Low-pressure membrane filtration systems and their operation .............................. 3 2.1.2 Membrane Fouling ................................................................................................... 5 2.1.3 Membrane Fouling Control ...................................................................................... 6 2.2 Gravity Driven Membrane Systems ................................................................................ 8 2.2.1 Conventional Gravity Driven Membrane Filtration Systems ................................... 8 2.2.2 Passive Gravity Driven Membrane Filtration Systems .......................................... 11 2.3 Drinking Water Treatment in small and remote communities ...................................... 11 viii 2.3.1 Effect of periods of no inflow ................................................................................. 12 Chapter 3. Objectives ........................................................................................................... 17 Chapter 4. Materials and Methods...................................................................................... 18 4.1 Experimental Apparatus ................................................................................................ 18 4.1.1 Feed system ............................................................................................................ 19 4.1.2 Membrane System .................................................................................................. 20 4.1.3 Permeate system ..................................................................................................... 22 4.1.4 Air scouring system ................................................................................................ 23 4.1.5 Drain system ........................................................................................................... 23 4.1.6 Control system ........................................................................................................ 24 4.1.7 Monitoring system .................................................................................................. 24 4.1.8 Permeate recycling system ..................................................................................... 24 4.2 Feed Water .................................................................................................................... 24 4.3 Operating periods of inflow/ no inflow ......................................................................... 25 4.3.1 Daily (24-hour) repeating cycle: ............................................................................. 26 4.3.2 Weekly (7-day) repeating cycle: ............................................................................. 28 4.3.3 Summary of periods of inflow/no inflow ............................................................... 28 4.4. Analytical Methods ...................................................................................................... 29 4.4.1 Permeate flux and temperature ............................................................................... 29 4.4.2 Sample Collection................................................................................................... 29 ix 4.4.3 Organic Carbon Measurement ................................................................................ 30 4.4.4 Quality Assurance and Control............................................................................... 30 Chapter 5. Results and Discussion ...................................................................................... 34 5.1 Physical characteristics of membrane modules ............................................................. 34 5.2. Normalized Permeability.............................................................................................. 36 5.2.1 PGDMF systems operated with continuous inflow ................................................ 38 5.2.2 PGDMF systems operated with periods of no inflow – without permeate recycling ......................................................................................................................................... 41 5.2.3 Comparison of PGDMF systems operated with periods of no inflow without permeate recycling and with continuous inflow .............................................................. 43 5.2.4 PGDMF systems operated with periods of no inflow – with permeate recycling .. 48 5.2.5 Comparison of PGDMF systems operated with periods of no inflow with permeate recycling and continuous inflow ...................................................................................... 50 5.2.6. Comparison of PGDMF systems operated with periods of no inflow – with and without permeate recycling ............................................................................................. 54 5.3 Organic Matter Removal ............................................................................................... 58 5.3.1. PGDMF systems operated with continuous inflow ............................................... 59 5.3.2 PGDMF systems operated with periods of no inflow – without permeate recycling ......................................................................................................................................... 63 5.3.3 PGDMF systems operated with periods of no inflow – with permeate recycling .. 66 5.3.4 Comparison of Organic Material Removal between PGDMF systems .................. 69 x Chapter 6. Conclusions ......................................................................................................... 74 6.1. Engineering Implications ............................................................................................. 74 References .............................................................................................................................. 76 Appendix A: Timer Programming for automation of membrane systems ..................... 82 Appendix B: Calibration of Pressure Transducers ........................................................... 85 Appendix C: TMP Results ................................................................................................... 89 Appendix D: Calibration of TOC Analyser........................................................................ 91 Appendix E: TOC, DOC and POC Results ........................................................................ 92 Appendix F: UV254 Results ................................................................................................. 107 Appendix G: Clean Water Permeability Tests ................................................................. 108 Appendix H: Assessment of Normalized Permeability.................................................... 111 xi List of Tables Table 1. Applications and characteristics of low-pressure membranes .................................... 9 Table 2. Effects of periods of no inflow on biofilm-based membrane/filter technologies ..... 14 Table 3. Clean Water Permeabilities of the membrane modules ............................................ 22 Table 4. TOC/DOC of Raw Water, Filtered Water and Feed Water ...................................... 25 Table 5. Summary table for operating conditions ................................................................... 29 Table 6. Steady State Normalized Permeability ..................................................................... 40 Table 7 Assessment of differences between operation with of periods of no inflow (without permeate recycling) and continuous operation ....................................................................... 46 Table 8 Assessment of differences between operation with periods of no inflow ................. 52 Table 9 Assessment of differences between operation with periods of no inflow with permeate recycling and without permeate recycling .............................................................. 56 Table 10. Summary of average TOC and DOC concentrations and UV254 absorbances of feed water ........................................................................................................................................ 58 Table 11. Comparison of time series TOC, DOC, DOC/TOC and UV254 values for PGDMF C .............................................................................................................................................. 60 Table 12. Cumulative mass of organic material in PGDMF systems ..................................... 62 Table 13 Comparison of time series TOC, DOC and UV254 values in PGDMF NR .............. 64 Table 14 Comparison of time series TOC, DOC and UV254 values in PGDMF WR ............. 67 Table 15 Summary of TOC and DOC removal efficiencies ................................................... 69 Table 16. Assessment of differences in organic matter removal between PGDMF systems . 71 Table 17 Timer programming for PGDMF C ......................................................................... 82 Table 18 Timer programming for PGDMF NR ...................................................................... 82 xii Table 19 Timer Programming for PGDMF WR ..................................................................... 83 Table 20 Pressure transducer calibration for PGDMF C ........................................................ 85 Table 21 Pressure transducer calibration for PGDMF NR ..................................................... 86 Table 22 Pressure Calibration of PGDMF WR ...................................................................... 87 Table 23. p-values of ANOVA tests (99% significance) ........................................................ 98 Table 24. Cumulative mass of TOC, DOC and POC of PGDMF systems ............................. 99 xiii List of Figures Figure 1. Membrane Filtration Process ..................................................................................... 4 Figure 2. Schematic Representation of the PGDMF systems ................................................. 19 Figure 3. Membrane modules ................................................................................................. 21 Figure 4. Operation of the membrane systems with 24-hour cycle ........................................ 26 Figure 5. Operation of the membrane systems with 7-day cycle ............................................ 28 Figure 6. Images of membrane modules at the end of the study ............................................ 35 Figure 7. Normalized permeabilities of all PGDMF systems in the study ............................. 37 Figure 8. Average normalized permeabilities of PGDMF ...................................................... 39 Figure 9. Normalized Permeabilities of PGDMF NR ............................................................. 41 Figure 10. Normalized Permeabilities of PGDMF C and PGDMF NR ................................. 44 Figure 11 Normalized Permeabilities of PGDMF WR ........................................................... 49 Figure 12 Normalized Permeabilities of PGDMF WR and PGDMF C.................................. 51 Figure 13. Transmembrane pressures of membrane systems during the study ...................... 90 Figure 14. Calibration curve from the TOC Analyser ............................................................ 91 Figure 15. a) TOC in feed water; b) DOC in feed water; c) POC in feed water .................... 93 Figure 16. a) DOC in permeate; b) DOC in drain; c) TOC in permeate; d) DOC in drain; e) POC in permeate; f) POC in drain .......................................................................................... 95 Figure 17. DOC/TOC ratios in (a) feed water, (b) permeate and (c) drain water ................... 96 Figure 18. Cumulative mass of TOC in a) PGDMF C; b) PGDMF NR and c) PGDMF WR............................................................................................................................................... 105 Figure 19. Cumulative mass of DOC in a) PGDMF C; b) PGDMF NR and ....................... 105 Figure 20. Cumulative mass of POC in a) PGDMF C; b) PGDMF NR and ........................ 106 xiv Figure 21. a) UV absorbance in feed; b) UV absorbance in permeate; c) UV absorbance in drain of the PGDMF systems ................................................................................................ 107 Figure 22. Membrane Integrity Test Setup (Khadem, 2016) ................................................ 109 Figure 23. Normalized Permeability vs cumulative flow ..................................................... 112 Figure 24. Normalized permeability vs fraction of time off ................................................. 112 Figure 25. Normalized permeability vs fraction of time on.................................................. 113 Figure 26. Normalized Permeability vs cumulative DOC removed ..................................... 114 xv Lists of Abbreviations DI Deionized DOC Dissolved Organic Carbon EPS Extracellular polymeric substances GDMF Gravity-driven membrane filtration HSD Honest Significant Difference LRV Log reduction value MF Microfiltration PGDMF Passive Gravity Driven Membrane Filtration PGDMF C PGDMF system with continuous operations PGDMF NR PGDMF system with no permeate recycling PGDMF WR PGDMF system with permeate recycling POC Particulate Organic Carbon TMP Transmembrane Pressure TOC Total Organic Carbon UF Ultrafiltration UV Ultraviolet xvi Acknowledgements I would like to thank my supervisor, Dr. Pierre Bérubé for his guidance and support throughout the course of my Master’s. Pursuing Master’s at UBC is a feat in itself and working under the mentorship of Dr. Bérubé on my thesis made it so much more rewarding. I will forever be grateful for his patience and trust. A thank you is not enough to convey my gratefulness to all the staff members at the Department of Civil Engineering: Felix Shuen, Simon Lee, Bill Leung, and Scott Jackson, who helped me with almost every aspect of my experimental setup, especially during the COVID-19 pandemic. Amanda Tobias, who’s setup I inherited, taught me various things that no textbook could have and got me ready for collecting water from Jericho Pond. Thank you for making the entire process less intimidating. You helped me take my first steps in the lab! Thank you to my parents, who quickly and thankfully came around to the idea of their daughter moving to one end of the world. You taught me to persevere and never give up. And to my sister, who always made me laugh no matter what state I was in! My girls from all over the world and my partner, who beat away my imposter syndrome when it surfaced, called me amazing when I was at my worst, and were my personal cheerleaders throughout, I am so grateful to have met you and am proud to call you mine! A tiny thank you to Tiktok and Netflix for providing me with constant entertainment, despite helping me procrastinate. xvii Dedication I dedicate this dissertation to all the women who made it possible for me to get here, and to all the women that come after me. 1 Chapter 1. Introduction Membrane filtration technologies like Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) are universally employed technologies for the treatment of drinking water. For freshwater treatment, UF membrane systems in particular are advantageous because of their ability to remove colloidal particles, pathogens like bacteria, viruses, protozoa, as well as other contaminants of concern. Unfortunately, their high costs of installation and maintenance, as well as their high mechanical complexity and uninterrupted energy requirements, have limited their implementation in small and remote communities (Peter-Varbanets et al., 2010). In the past decade, multiple studies have demonstrated the ability for membrane systems to be operated with low gravity head as the driving force for permeation and no fouling control measures (Derlon et al., 2012; Oka et al., 2017; Peter-Varbanets et al., 2010; Pronk et al., 2019, p. 201; Wang et al., 2008). Their operation depends on the formation of a structurally loose and permeable biofilm on the membrane surface, which helps stabilize the permeate flux and aids the removal of organic material amongst other pollutants. Although a steady permeate flux can be sustained with gravity driven membrane filtration (GDMF), it is low. However, by retaining a few fouling control measures, which can be implemented with limited to no mechanical complexity (i.e., passively), the permeate flux that can be sustained is increased. Because of their limited mechanical complexity and ease of operation, GDMF with passive fouling control, hereafter referred to as passive GDMF (PGDMF) systems, are ideal for use in small and remote communities (Peter-Varbanets et al., 2010). A key concern for water treatment systems in small communities are the periods of no/low flow demands, and corresponding periods of no/low inflow to the system. Periods of no/low 2 inflow conditions are expected to impact nutrient loading and therefore the biological activity in the biofilm of PGDMFs. Consequently, periods of no/low inflow could potentially negatively impact the performance of PGDMF systems. The current study investigated the impacts of the periods of no inflow on PGDMF systems. PGDMF systems operated with various periods with no inflow were studied and compared to operation with continuous inflow. Overall performance monitoring (i.e., permeability, organic carbon analysis) was used to assess the impacts of periods of no inflow. For the systems operated with periods of no inflow, both conditions with no permeate recycling (i.e., no flow through system during no inflow periods) and with permeate recycling (i.e., flow maintained through by recycling permeate during no inflow periods) were considered. Permeate recycling was considered to reduce potential negative impacts of periods of no inflow on the availability of nutrients for the biofilm in PGDMF systems. 3 Chapter 2. Background and Literature Review 2.1 Membrane Filtration Systems 2.1.1 Low-pressure membrane filtration systems and their operation Low-pressure membranes, such as microfiltration (MF) and ultrafiltration (UF) membranes, are typically used to produce drinking water from fresh (i.e., not salinated) water. When used for drinking water treatment, these membranes target the removal of contaminants such as natural organic matter (NOM) and pathogens (e.g. protozoa, viruses, bacteria etc.) (Huang et al., 2012). The removal efficiency can exceed 99.9999%, especially for protozoa and bacteria. During surface water treatment, MF and UF membranes work like extremely fine sieves, or strainers, with the membrane pore sizes in the order of 5 to 100 nm (Marcel Mulder, 1996). The particles that are larger than the size of the membrane pores are retained on the feed side of the membrane and some smaller material can also be retained inside the membrane pores. A driving force, such as pressure, is used to push water through the membrane pores. In MF and UF systems, the driving force is usually provided by a mechanical device, such as a pump as illustrated in Fig 1. 4 Figure 1. Membrane Filtration Process (Permeate is the water filtered through the membrane, reject stream contains the waste retained by the membrane system) The pressure between the feed (i.e. water to be filtered) side and the permeate (i.e., filtered water) side of the membrane is termed as the transmembrane pressure or TMP (John C. Crittenden et al., 2012). The flow of permeate through MF and UF membranes is typically quantified as the permeate flux (J). Permeate flux, which is the ratio of the permeate flow and the membrane filtration area, is a function of TMP, the dynamic viscosity of water, and the membrane resistance, as presented in Equation 1. The permeate flux can also be expressed in terms of transmembrane pressure and permeability (Equation 1). The structure of the membranes (e.g., porosity, pore size, wall thickness, etc.) affect the resistance (and permeability), and hence, the permeate flux. For MF and UF systems, the permeate flux typically ranges from 30 to170 l/m2-h under operating pressures of 0.2 to 10 bar. 5 Equation 1 𝐽 =𝑄𝐴௠= 𝑇𝑀𝑃µ௪𝑅= 𝑇𝑀𝑃 (𝐵்) where, J is the volumetric water flux through membrane (L/m2h), Q is the flow rate (L/h), Am is the membrane surface area (m2), TMP is the transmembrane pressure (kgm/s2), µ௪ is the dynamic viscosity of water (kg/ms), R is the resistance to permeate flow (m−1) and, BT is the membrane permeability (m) at a given temperature, T (℃). To account for the impact of temperature on the permeability, the permeability is usually reported for a standard temperature (e.g., 20℃) as presented in Equation 2. Equation 2 𝑩𝟐𝟎 = 𝑩𝑻( µ(𝒘,𝑻)µ(𝒘,𝟐𝟎) ) where, B20 is the permeability at the standard temperature of 20℃ (m), µ(𝒘,𝑻) is the dynamic viscosity of water at the measured temperature (kg/ms), and µ(𝒘,𝟐𝟎) is the dynamic viscosity of water at the standard temperature of 20℃ (kg/ms). 2.1.2 Membrane Fouling During membrane filtration, particles are retained on the surface of the membrane or within the pores of the membrane. This phenomenon is typically defined as membrane fouling (Cho et al., 1999). Fouling increases the resistance to the permeate flow through the membrane. To account for fouling, the resistance to permeate flow is typically considered as the sum of the intrinsic membrane resistance plus the resistance due to fouling. This resistance due to fouling is also typically considered as the sum of the resistance that is reversible (i.e., can be removed 6 with hydraulic and/or chemical membrane cleaning), and the resistance that is irreversible (i.e., cannot be removed with hydraulic and/or chemical membrane cleaning). Taking fouling into consideration, equation 1 can be modified as follows. Equation 3 𝐽 = 𝑄𝐴௠=𝑇𝑀𝑃µ (𝑅௠ + 𝑅ூோோ + 𝑅ோ) where, J is volumetric flux through the membrane (m/h), TMP is the transmembrane pressure (kgm/s2), µ is dynamic viscosity of water (kg/ms), R୫ is membrane resistance coefficient (m−1), R୍ୖୖ is irreversible fouling resistance coefficient (m−1) and, Rୖ is reversible fouling resistance coefficient (m−1). 2.1.3 Membrane Fouling Control In conventional membrane filtration, it is essential to prevent the accumulation of foulants to prevent an excessive increase in the resistance to the permeate flux. Fouling control measures, such as those outlined below, are usually used in parallel or in sequence. Cleaning can typically be classified as hydraulic or chemical cleaning (Gao et al., 2011;Ye et al., 2011). 2.1.3.1 Hydraulic Cleaning a) Backwashing Backwashing of a membrane system is a process in which the permeation through the membrane is periodically reversed to loosen/dislodge retained foulants. This loosened foulant layer can then be removed from the membrane by applying shear forces that scour and transport the loosened foulants (Pearce, 2011). 7 b) Relaxation Relaxation of a membrane is a process in which the permeation through the membrane is periodically interrupted to loosen retained foulants. As with backwashing, the loosened foulant later can be removed from the membrane by applying shear forces that scour and transport the loosened foulants (Pearce, 2011). c) Air sparging Air sparging, also known as air scouring or aeration, is often used to provide the shear forces to scour and transport foulants from the surface of the membrane. Air scouring is typically applied in parallel with backwashing or relaxation, but can also be applied on its own as a means of fouling control (Pearce, 2011). 2.1.3.2 Chemical cleaning Chemical cleaning is the process of employing chemical agents to remove retained foulants that cannot be removed hydraulically. Chemical cleaning typically occurs when the permeability of the membrane system cannot be recovered using hydraulic cleaning and becomes too low for the continued operation of the system. Some common chemicals used for chemical cleans in drinking water treatment are sodium hypochlorite, citric acid, and caustic soda. Chemical cleaning can typically be classified as mild cleaning and extensive cleaning. Mild cleaning, often referred to as maintenance cleaning, is typically performed frequently (every day to a week). Extensive cleaning, often referred to as recovery cleaning or clean in place, is more intense and is typically performed every 3 to 12 months depending upon the membrane filtration system (Porcelli & Judd, 2010). 8 2.2 Gravity Driven Membrane Systems Gravity-driven membrane filtration (GDMF) is a membrane filtration process where a low gravity head is used as the driving force (hydrostatic pressure ≤ 100 mbar) for permeation. GDMF systems typically employ no fouling control measures (i.e., hydraulic, and chemical cleaning). GDMF systems are well suited for small scale operations due to their limited mechanical complexity and ease of operation. In 2010, the first study on the stabilization of permeate flux in a GDMF system was published. In this study, a dead-end UF system was operated with gravity as the driving force without any hydraulic and/or chemical fouling control measures. The results demonstrated that a low flux, between 4 LMH and 10 LMH, could be sustained (Peter-Varbanets et al., 2010). Subsequent studies concluded that the flux stabilization occurred because of the development of a heterogeneous, permeable, and active biofilm layer on the surface of the membrane. Table 1 lists some of the recent studies that have considered GDMF systems for different types of raw water. 2.2.1 Conventional Gravity Driven Membrane Filtration Systems Conventional GDMF systems are typically operated without any hydraulic or chemical fouling control measures. Features of conventional GDMF include, i) low hydrostatic pressure, generated by a water column, which provides the driving force for permeation through the membranes; and ii) microorganisms, originating from the raw water, which form a highly porous biofilm that captures and degrades materials of concern. The lack of hydraulic or chemical fouling control measures limit the use of conventional of GDMF systems to low throughput and short-term applications (Jain, 2019; Oka, 2015). 9 Table 1. Applications and characteristics of low-pressure membranes Application TMP (mbar) Sustained Permeate Flux (L/m²·h) Membrane type (pore size) Materials removed Fouling control Duration of study (days) Reference Groundwater treatment 70 4 to 6 Hollow fiber (20 nm, 200 nm) Iron, manganese Aeration, chemical shock loading 100 (Tang et al., 2021) Secondary effluent treatment 45 2 to 4 Flat sheet membranes (20 kDA MWCO) Viruses Not applicable 91 (Wang et al., 2017) Pretreatment of seawater 40 18.6 Flat sheet membranes (80 Biopolymers, Assimilable organic carbon Not applicable 250 (Wu et al., 2017) 10 (before desalination) nm) Drinking water production from surface water 80 5 Hollow fibre (40 nm) Organics (TOC, DOC) Viruses Air sparging, backwashing, Relaxation 120 (Tobias Costa de Oliveira, 2019) Rainwater 50 3.3 to 4.7 Flat sheet (150 kDa) Organics (TOC, DOC) GAC Pretreatment 55 (Ding et al., 2018) Greywater 40 1.0 to 2.0 Hollow fibre (200 nm) Organics, Nitrogen, Phosphates No fouling control 183 (Jabornig & Podmirseg, 2015) 11 2.2.2 Passive Gravity Driven Membrane Filtration Systems Passive Gravity Driven Membrane Filtration Systems (PGDMF) are similar to GDMF systems, but are operated with passive hydraulic fouling control measures (e.g., gravity-induced air scouring, relaxation etc.). Features of PGDMF include, i) low hydrostatic pressure, generated by a water column, which provides the driving force for permeation through the membranes; ii) microorganisms, originating from the raw water, which form a highly porous biofilm that captures and degrades materials of concern; and iii) a vacuum, generated by a system tank drain, which generates air scouring that prevents the excessive build-up of microorganisms and foulants in the biofilm and on the membranes. Because of the limited mechanical complexity of PGDMF, the production of high-quality water and the ability to sustain a relatively high throughput, PGDMF systems are ideal to use for drinking water treatment in small and remote communities. 2.3 Drinking Water Treatment in small and remote communities There are currently no viable long-term solutions to provide high quality potable water to many small and remote communities (Omosule, 2017). Challenges for these communities include a limited access to funding, geographical isolation, and limited access to trained operators. These factors can negatively impact the quality of drinking water that is provided, and consequently, many of these communities are frequently on boil water advisories (FNHA, 2021). In Canada alone, currently there are approximately 600 small and remote water systems, many of them being in First Nation communities, that are on boil water advisories (INAC,2007). A major cause of concern for water systems in small and remote communities are periods of no/low flow demand for drinking water. Periods of low to no flow demand can occur during the day, at night, during weekends and holidays, as well as during maintenance periods. 12 No/low flow demand causes periods of low/no inflow periods to treatment systems. As mentioned previously, the flux stabilization capacity of PGDMF systems is highly dependent on the biological activity of the porous biofilm layer formed on the surface of the membranes. Hence, PGDMF systems perform best when a constant supply of nutrients is available through the feed (Gora & Walsh, 2011) as they reduce ‘stress’ on the biofilm. Periods of low/no inflow could impact nutrient loading, and hence, affect the formation and biological activity on the biofilm of PGDMF systems (Feng et al., 2019). Consequently, periods of no/low inflow could negatively impact the overall throughput of passive membrane systems (Álvarez-Hornos et al., 2008). 2.3.1 Effect of periods of no inflow Limited research has focused on the effects of periods of no inflow on the performance of PGDMF systems. X. Tang et al., (2016) assessed the impact of periods with no inflow, ranging from 3h/day to 12h/day, daily, over a period of 58 days in a GDMF system. The study concluded that periods of no inflow did not negatively impact the permeability, but rather increased the average stable flux. Similar results were observed by Peter-Varbanets (2012) in a study that assessed the impact of the flux interruptions ranging from 3h/day to 19h/day, daily, over a period of 60 days, in a GDMF system. No studies have considered periods of no inflow of greater than 19 hours/day over an extended period. In addition, no studies have considered the impacts of periods of no inflow for PGDMF, and no studies have considered permeate recycling (i.e., flow maintained through system by recycling permeate) as a means to mitigate the potential negative impacts of periods of no inflow on the performance of PGDMF systems. 13 A summary of the studies that assessed the impact of periods of no inflow on various membrane/filter-based technologies for drinking water treatment that rely on the presence of a biofilm for their successful operation, is presented in Table 2. 14 Table 2. Effects of periods of no inflow on biofilm-based membrane/filter technologies Technology – Source of Raw Water Length of periods of no inflow Effect on biofilm Effect on performance Duration of study Reference Biofiltration - River Water 8h or 12h OFF - daily cycle Less biomass density when compared to continuous system but higher enzyme activity – overall could be beneficial for biofilm. Increased DOC removal N/A (Singh Sidhu et al., 2018) BAC Filtration - River Water 6h OFF or 24h OFF - daily cycle Less biomass density,anaerobic conditions may be reached leading to prevalence of anaerobic organisms. Might degrade and lead to poor water quality. 60 (Niquette et al., 1998) 15 Biofiltration – lake water 8h to 16h OFF- daily cycle Less biomass density relative to continuously operated system. Increased DOC removal. 50 (McKie et al., 2019) PGDMF- Surface water 1h, 4h or 8h OFF -daily cycle Possibly less biomass density. Increase in normalized permeability. 60 (Oka et al., 2017) GDMF - Surface water 3h,6h,12h,19h OFF – daily cycle No inhibition to the biofilm formation process. Increase in average stable flux. 60 (Peter-Varbanets et al., 2012) 16 GDMF - Surface water 3h/6h/12h OFF - daily cycle Effectively decreased reversible membrane resistance with increase in period of no inflow when compared to a continuously operated system. Increase in average permeate flux, increase in net water production per day. 150 (Tang et al., 2016) 17 Chapter 3. Objectives The current research investigated the effects of periods of no inflow on the performance of PGDMF systems over an extended period of time (175 days). Performance was assessed in terms of system hydraulic throughput and DOC removal. The research also sought to assess if permeate recycling, during periods of no inflow. could mitigate the potential negative impacts of periods of no inflow on performance. The specific objectives of the current research are as follows: 1. Investigate whether operation with daily or weekly periods of no inflow (without permeate recycling) negatively impact the performance of PGDMF systems over an extended period. 2. Investigate if recycling the permeate during the periods of no inflow mitigates the potential negative impact of operation with periods of no inflow. 3. Investigate whether operation with daily or weekly periods of no inflow negatively impact the organic matter removal of PGDMF systems. 18 Chapter 4. Materials and Methods 4.1 Experimental Apparatus The experimental apparatus used in the current study consisted of 7 parallel systems operated under conditions that simulate the operation of PGDMF systems. Olivera et. Al. (2021) also used conditions that simulate those in PGDMF systems. Briefly, the PGDMF systems used in the current study were operated with vacuum-driven permeation rather than gravity driven permeation. This was not expected to affect the study outcomes because under low flux conditions, the material transport at the membrane for of systems operated with constant pressure and constant flux expected to be are similar (Miller et al., 2014; Oka, 2015). One PGDMF system was operated with continuous inflow (henceforth referred to as PGDMF C) and two sets of PGDMF systems were operated with periods of no inflow. For the sets operated with periods of no inflow, one set was operated with no permeate recycling during the period of no inflow (henceforth referred to as PGDMF NR) and the other set was operated with permeate recycling during the period of no inflow (henceforth referred to as PGDMF WR). Each set included 3 PGDMF systems, each operated with a different period of no inflow (see Section 4.3). The geometry of all of PGDMF systems was similar, with the exception of a permeate recycling line for PGDMF WR (Fig 2). 19 Figure 2. Schematic Representation of the PGDMF systems All PGDMF systems had the following components: feed system, membrane system, permeate system, monitoring system, air scouring system, drain system, and control system. In addition, PGDMF WR had an additional permeate recycling system. Details of each system are presented in the following sections. 4.1.1 Feed system The feed system consisted of 3 feed tanks, and an inflow valve. The 3 feed tanks were interconnected, with a combined working volume of approximately 85L. All PGDMF systems shared the same feed tanks. The feed tanks were filled with feed water (see Section 4.2) twice a week. The inflow valve was a normally closed ball valve (HSH-Flo 2 Way 1" 20 NPT ball valve; Model: T25-S2-B). A timer (see Section 4.1.6) and float switch (see Section 4.1.2) controlled the opening and closing of the inflow valve to maintain a constant water level in the membrane tank (see Section 4.1.2). 4.1.2 Membrane System The membrane system consisted of a tank, a float switch, 2 membrane modules (identical replicates) and an air diffuser. The membrane tank was a custom made, acrylic cylindrical container with an internal diameter of 5 cm and a height of 30 cm. Two (i.e., replicates) custom UF membrane modules were used in each membrane tank. Each membrane module consisted of 7x21 cm long ZeeWeed 500® hollow fibers (Nominal pore size – 0.04 μm; Suez Water Technologies & Solutions, Canada) potted into bulkheads at both ends. The bulk heads were made of polypropylene tubing and epoxy (Gorilla 4200101-2 Epoxy, 15 min set time). An image of the custom membrane modules is presented in Fig 3. Prior to use, a pressure decay test was performed to ensure that there were no breaches in the membrane modules (see Appendix F). The membrane tank had a working liquid level and volume of 25 cm and 490 mL, respectively. An air diffuser (McMaster-Carr, ¼ NPT Male, Muffler, 24 scfm Flow Rate), located below the membrane modules in the membrane tank, was used to generate air bubbles for hydraulic cleaning (see Section 4.1.4). 21 Figure 3. Membrane modules Clean water permeability tests were conducted for all the membrane modules prior to use (see Appendix G for methodology). The clean water permeability was calculated based on Equation 2 (see Section 2.1.1). The clean water permeability of all the membrane modules were statistically similar (significance = 99%), indicating that the membrane permeabilities did not vary significantly amongst the membrane modules. The average of the clean water permeabilities for each PGDMF system are summarized in Table 3. 22 Table 3. Clean Water Permeabilities of the membrane modules PGDMF System Clean water permeabilities corrected to 20℃ (m) PGDMF C 1.33E-12 ±1.55E-13 PGDMF 3hNR 1.07E-12 ± 2.34E-14 PGDMF 8hNR 1.03E-12 ± 1.31E-13 PGDMF 2dNR 7.94E-13 ± 6.14E-14 PGDMF 3hWR 1.31E-12 ± 4.15E-13 PGDMF 8hWR 1.39E-12 ± 2.12E-14 PGDMF 2dWR 1.42E-12 ± 1.7E-13 (Note: The clean water permeability value is the average from the replicate systems; ± corresponds to maximum and minimum of replicate systems.) 4.1.3 Permeate system The permeate system consisted of a permeate pump (peristaltic; Masterflex Pump series 7520-35) and a permeate tank. The permeate pump was used to provide the driving force for permeation, maintaining a constant flux for the membrane modules (see Section 4.1.2). Recall that, in the current study, vacuum driven permeation was used to simulate gravity driven permeation, as described in Tobias & Bérubé (2020). The permeate pump was connected to a timer that controlled the operations of the pump (see Section 4.1.6). The permeate tank had a volume of 2L and an overflow line connected to the drain tank (see 23 Section 4.1.5). The operating flux from day 0 to day 80 was 4 L/m2h, and 6 L/m2h from day 81 to the end of the study (day 175). 4.1.4 Air scouring system Air required for scouring in PGDMF systems can be provided by the vacuum that can be generated inside the membrane tanks during a tank drain (Tobias & Bérubé, 2020). In the current study, compressed air was used to simulate vacuum driven air addition. This was required because of the bench-top scale of the experimental apparatus which prohibited the development of a vacuum of relevant magnitude for air scouring during tank drains. The air scouring system consisted of an air-line, a pressure regulator, an airflow meter, an air valve, and an air diffuser (see Section 4.1.2). Compressed air was provided to the PGDMF systems via an air-line with a pressure regulator (HydraCheck pressure regulator, GP 8700). The flow of air was controlled with an airflow regulator/meter (Cole-Parmer, N082-03). The air valve (Solenoid valve, McMaster-Carr, Normally closed ½ “Male NPT Valve; Model: 4711K951) controlled the air flow to the air diffuser of the PGDMF systems during the aeration phase (see Section 4.3). The aeration rate was 4L/min, selected based on previous studies conducted with PGDMF systems (Oka et al.,2017; Jain, 2019). 4.1.5 Drain system The drain system consisted of a drain valve and a reject tank. The drain valve (HSH-Flo 2 Way 1" NPT ball valve; Model: T25-S2-B) was a normally closed ball valve. The valve was controlled with a timer (see Section 4.1.6). The reject tank had a working volume of 80L. All PGDMF systems shared a common reject tank in which the reject from the PGDMF systems collected. The reject tank was emptied twice a week. 24 4.1.6 Control system The control system consisted of a custom timer and float switches. A custom timer enabled operation as described in Section 4.3. A float switch controlled the liquid level in the membrane tank (see Section 4.1.2). The timer and/or float switch controlled the automated valves (ball and solenoid) as described in Sections 4.3.1 and 4.3.2. 4.1.7 Monitoring system The monitoring system consisted of 14 pressure transducers connected to a data logger. Each pressure transducer was located between a membrane module and its corresponding permeate pump. The pressure transducer measured the TMP every 5 seconds, and recorded the measurement using LabVIEW SignalExpress, a data logging software. Refer to appendix B for pressure transducer calibration. 4.1.8 Permeate recycling system The permeate recycling system, only present in PGDMF WR, consisted of a permeate recycling line and an automated permeate recycling valve (Solenoid valve, McMaster-Carr, normally closed ½ “Male NPT Valve; Model: 4711K951) which connected the permeate tank (see Section 4.1.3) to the influent of the membrane tank (see Section 4.1.1). A timer (see Section 4.1.6) controlled the permeate recycling tank. 4.2 Feed Water The feed water used throughout the study consisted of a mixture of raw water and tap water. The raw water was collected from Jericho Pond, located near Jericho beach in Vancouver, BC. Water from Jericho Pond has been used in previous studies that considered PGDMF systems (Oka, et. al. (2017) and, Tobias Costa de Oliveira (2019)). Tap water was collected 25 from the Environmental Engineering labs in the Department of Civil and Mechanical Engineering, at UBC. Raw water batches were collected on two occasions, one in July 2020 and one in Nov 2020. During collection, large suspended solids were removed by filtering with a 1mm screen. The collected water was then stored in the dark at T<4℃ until use. Before use, the screened raw water is filtered through a 5 μm cartridge filter and analysed for the TOC and DOC (see Table 4). The screened and filtered water was then mixed with tap water to achieve a DOC concentration of approximately 4 mg/L, prior to use as feed water. A concentration of 4 mg/L was used to enable the results from the current study to be comparable to those of previous studies on PGDMF systems that were performed with the same raw water source (Oka, et. al. (2017) and, Tobias Costa de Oliveira (2019)). Table 4. TOC/DOC of Raw Water, Filtered Water and Feed Water 4.3 Operating periods of inflow/ no inflow The operating conditions used were chosen to simulate those of PGDMF systems, as outlined in Tobias & Bérubé (2020). All systems were operated similarly, either with a 24-hour repeating cycle or a 7 -day repeating cycle. Month of Collection Filtered Jericho Pond Water Feed Water TOC (mg/L) DOC (mg/L) TOC (mg/L) DOC (mg/L) Batch 1 11.24 10.36 4.26 ± 0.491 3.54 ± 0.257 Batch 2 10.85 8.92 4.41 ± 0.141 3.63 ± 0.279 26 4.3.1 Daily (24-hour) repeating cycle: The phases of the 24-hour repeating cycle are illustrated in Figure 4. They consist of repeating cycles of permeation, passive cleaning (i.e., relaxation followed by an aerated tank drain), a system fill and where applicable followed by a period of no inflow (for PGDMF NR and PGDMF WR). Figure 4. Operation of the membrane systems with 24-hour cycle During permeation, the permeate pump was on (see Section 4.1.3) and the float switch controlled the opening and closing of the inflow valve to maintain a constant liquid level in the membrane tank. No air was added (air valve was closed; see Section 4.1.4) and no reject was withdrawn (drain valve was closed; see Section 4.1.5). For PGDMF WR, there was no permeate recycling (permeate recycling valve was closed; see Section 4.1.3). During relaxation, no permeation occurred (permeate pump was off) and the inflow valve was closed. No air was added (air valve was closed; see Section 4.1.4) and no reject was withdrawn (drain valve was closed; see Section 4.1.5). For PGDMF WR, there was no permeate recycling (permeate recycling valve was closed; see Section 4.1.8). During aeration, air was added for scouring. No permeation occurred (i.e., permeate pump was off) and inflow valve was closed. No reject was withdrawn (drain valve was closed; see 27 Section 4.1.5). For PGDMF WR, there was no permeate recycling (permeate recycling valve was closed; see Section 4.1.8). During drain, the drain valve was opened to purge the reject from the system. No permeation occurred (permeate pump was off) and the inflow valve was closed. No air was added (air valve was closed; see Section 4.1.4). For PGDMF WR, there was no permeate recycling (permeate recycling valve was closed; see Section 4.1.8). During fill, the inflow valve was opened to fill the membrane tank. No permeation occurred (i.e., permeate pump was off). No air was added (air valve was closed) and no reject was withdrawn (drain valve was closed). For PGDMF WR, there was no permeate recycling (permeate recycling valve was closed). During the daily period with no inflow, the inflow valve was closed. No air was added (air valve was closed), and no reject was withdrawn (the drain valve was closed). The following periods of no inflow were considered: i. 0-hr daily period of no inflow; corresponding to continuous inflow. ii. 3-hour daily period of no inflow; corresponding to daily recurring periods of short-term demand interruption. iii. 8-hour daily period of no inflow; corresponding to daily recurring periods of moderate-term demand interruption. For the systems with no permeate recycling during the period of no inflow (PGDMF NR), there was no permeation (permeate pump was off). For the systems with permeate recycling during the period of no inflow (PGDMF WR), there was permeation (permeate pump was on), and the permeate recycling valve was open. 28 4.3.2 Weekly (7-day) repeating cycle: The phases of the weekly (7-day) repeating cycles are illustrated in Figure 5. They consist of 5 consecutive 24-hour cycles (similar to that as described in section 4.3.1, with no daily period of no inflow) followed by a 2-day period of no inflow. Figure 5. Operation of the membrane systems with 7-day cycle 4.3.3 Summary of periods of inflow/no inflow A summary of the operating periods of inflow and no inflow considered for the daily and weekly repeating cycles is presented in Table 5. Note that no chemical cleaning was performed. 29 Table 5. Summary table for operating conditions 4.4. Analytical Methods 4.4.1 Permeate flux and temperature The permeate flux and temperature was manually monitored and recorded twice a week for the PGDMF systems with daily repeating cycles, at the start of the permeation phase. For the systems with weekly repeating cycles, the permeate flux and temperature was manually monitored and recorded twice a week, once at the start of permeation phase and once following the period of no inflow. The permeate flux was calculated based on the mass of permeate collected over approximately 180 minutes in a previously weighted Erlenmeyer flask (TP-1502 scale, Denver Instruments). 4.4.2 Sample Collection Samples of the permeate of each membrane module, the membrane system tank, the feed water, and the reject of all the PGDMF systems were collected on Monday (for daily Cycle Designation Daily permeation time (min) Daily relaxation time (min) Daily Aeration/ Drain time (min) Daily fill time (min) Period of no inflow Daily (h) Weekly (h) 24 hr C 1373 60 5/ 0.5 0.5 0 N/A 3h 1193 3 N/A 8h 893 8 N/A 7d 2d 1373 N/A 48 30 PGDMF systems), Tuesday (for weekly PGDMF systems) and Thursday (for all PGDMF systems). The permeate was sampled from the permeate flask used to measure the permeate flux (see Section 4.4.1). The feed tank and the permeate flask were sampled at mid-depth after their contents were fully mixed. The membrane tank was sampled at mid-depth prior to the end of a cycle. The reject from each PGDMF system was sampled by collecting all the reject during a drain after its contents were fully mixed. All samples were transferred into 25ml plastic vials and stored at 4℃ in the dark prior to analyses. 4.4.3 Organic Carbon Measurement The total organic carbon (TOC) and dissolved organic carbon (DOC) in all samples (see Section 4.4.2) were quantified according to Standard Methods 5310 following the non-purgeable organic compound method (NPOC) using a Shimadzu Total Organic Carbon Analyser and was calibrated at the start of the study (see Appendix C). The UV254 Absorbance was also measured according to Standard Methods 5910 following the Ultraviolet Absorption method once every two weeks (see Appendix F). Prior to analysis, the DOC and UV254 samples were filtered through a 0.45μm membrane disc filter (Supor ®, Plain, 47mm diameter, No. 60173, Pall Laboratory). 4.4.4 Quality Assurance and Control 4.4.4.1 Data Analyses The temperature corrected permeability of the membrane modules was calculated as described in section 2.1.2. The temperature corrected permeability was used to take into consideration slight changes in ambient temperature which impacted the temperature of the water in PGDMF systems. The temperature corrected permeability was normalized to that on day 7 of the study. Day 7 was selected for normalization because prior to this day, the 31 temperature corrected normalized permeability fluctuated extensively for all PGDMF systems. The temperature corrected normalized permeability from the replicate membrane modules in each PGDMF system was similar (see Appendix H). For this reason, the average from replicate membrane modules was considered for the analysis of the permeability data (see Chapter 5). When relevant, the maximum and minimum temperature corrected normalized permeability from the replicate membrane modules for each PGDMF system were also considered for the analysis. In addition, for the analysis, weekly averages of the average temperature corrected normalized permeability from replicate membrane modules were considered. Weekly averages of the average temperature corrected normalized permeability from replicate membranes, hereafter referred to simply as normalized permeability, were considered to adequately compare the results for PGDMF systems that operate with daily and weekly cycles with periods of no inflow. The comparison of normalized permeabilities of the PGDMF systems was based on a paired t-test of the time-series normalized permeabilities for each timeline and, when applicable, a t-test of the steady state normalized permeability (see Section 5.2). If a difference was observed within the PGDMF systems being compared, Tukey’s Honest Significant Difference (HSD) test was performed to identify differences in the performance of the PGDMF systems in terms of normalized permeability (see Chapter 5). The TOC concentrations of the permeate from the replicate modules of each PGDMF system were statistically similar (see Appendix E) . For this reason, the average TOC from the replicate modules were considered for the analysis of the TOC concentrations of the permeate. The DOC concentrations of the permeate from the replicate modules of each 32 PGDMF system were statistically similar (see Appendix E). For this reason, the average DOC from the replicate modules were considered for the analysis of the DOC concentrations of the permeate. The UV254 Absorbance was estimated as described in Section 4.4.3. The UV254 Absorbance of the permeate from the replicate modules of each PGDMF system were statistically similar (see Appendix E). For this reason, the average UV254 Absorbance from the replicate modules were considered for the analysis of the UV254 Absorbance of the permeate. The comparison of the TOC concentrations, DOC concentrations, DOC/TOC ratios, and UV254 Absorbance between each PGDMF system (for PGDMF NR, between PGDMF 3hNR, PGDMF 8hNR and PGDMF 2dNR; for PGDMF WR, between PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR) were based a one-way ANOVA test of the time-series TOC concentrations and DOC concentrations for each timeline in the permeate, the drain and the feed water (see Section 5.3). Paired t-tests were also performed to compare the TOC and DOC concentrations of the permeate, drain and feed of the PGDMF system (see Section 5.3). If a difference was observed within the PGDMF systems being compared, a Tukey’s HSD test was performed to identify differences in the performance of the PGDMF systems, in terms of TOC and DOC removal (see Chapter 5). The paired t-tests and the one-way ANOVA tests were performed using the Data Analysis tool in Microsoft Excel while the linear regressions were performed using the Trendline tool of Microsoft Excel. A custom application was developed for the Tukey’s HSD tests using Microsoft Excel. 33 Steady state conditions were assumed when the slope of the regression line fitted to time series data was not different from zero. Values at steady state correspond to the average over the steady state period. 34 Chapter 5. Results and Discussion 5.1 Physical characteristics of membrane modules By the third week of operation, a biofilm layer was visible on all the PGDMF systems. From day 1 to day 80 of operation (Timeline 1; see Section 5.2), the biofilm layers on the membrane modules of all the PGDMF systems were light brown in color and unevenly distributed. When the operating flux was increased on day 81 (Timeline 2; see Section 5.2), the biofilm layers on all the membranes in the PGDMF systems became darker in color and more evenly distributed. When changing the feed water source (Timeline 3; see Section 5.2), the biofilm layers on all the membranes in the PGDMF systems were fully established and dark brown. The images of the membranes of all the PGDMF systems at the end of the study are presented in Fig 6. 35 Figure 6. Images of membrane modules at the end of the study a) PGDMF C; b) PGDMF 3hNR; c) PGDMF 8hNR; d) PGDMF 2dNR; e) PGDMF 3hWR; f) PGDMF 8hWR; g) PGDMF 2dWR 36 Qualitatively, the biofilm formation was not inhibited by operation with periods of no inflow. When comparing the biofilm layers in all three sets of PGDMF systems, the biofilm layer on the set of PGDMF WR and PGDMF C systems were darker in color and more homogeneous than those for the set of PGDMF NR system. The nonhomogeneous distribution of the biofilm on the membranes of PGDMF NR system was possibly due to the lack of permeation during the period of no inflow which can lead to the loosening and the detachment of the biofilm layer (Hong et al., 2002; Peter-Varbanets et al., 2012). When investigating the impacts of no inflow periods for a conventional GDMF system, Varbanets et al., (2012) reported results consistent with those of the current study. 5.2. Normalized Permeability The normalized permeability of the PGDMF systems throughout the study were calculated as described in Section 4.4.4. and are presented in Fig 7. As illustrated, the normalized permeability was considered over 3 timelines corresponding to the different combinations of the permeate flux (see Section 4.4.1) and feed water batches (see Section 4.2). i) During timeline 1 (days 1 to 80 of the study) the permeate flux was 4 L/m2h and the feed water used was from Batch 1; ii) During timeline 2 (days 81 to 101 of the study) the permeate flux was 6 L/m2h and the feed water used was from Batch 1; iii) During timeline 3 (days 102 to 175, end of study) the permeate flux was 6 L/m2h and the feed water used was from Batch 2. The timelines considered were the same for all PGDMF systems and are further described in detail below. 37 Timeline 1 Timeline 2 Timeline 3 Figure 7. Normalized permeabilities of all PGDMF systems in the study (Expected normalized permeability was adapted from Tobias Costa de Oliveira (2019).) A decreasing permeability to a sustained value is commonly reported for GDMF systems (Pronk et al., 2019). For this reason, the normalized permeability of the PGDMF systems was expected to decrease over time, eventually reaching quasi-steady-state magnitude (Tobias & Bérubé, 2020). However, as illustrated in Fig. 7, during timeline 1, no consistent decline in the normalized permeability was observed for any of the PGDMF systems. At low permeate flux operation, the fouling mechanisms are not expected differ for systems operated with constant pressure or constant flux (Miller et al., 2014; Oka, 2015). However, permeabilities can differ substantially (Tobias & Bérubé, 2020). This is because the mass flux of material towards the membrane is variable in constant pressure systems, while it is fixed in constant flux systems. It is likely that, in the current study, the mass flux of material towards the 38 membrane was lower than that of previous studies that considered PGDMF systems (Tobias Costa de Oliveira, 2019). These previous studies used a similar feed water, but with raw water (i.e., Jericho Pond water) collected at a different time. For comparison, results from a previous study with a similar experimental apparatus, operating conditions, and a raw water source identical to that used in the current study is included in Figure 7. The permeate flux was increased from 4 L/m2h to 6 L/m2h at the start of timeline 2 to generate a greater mass flux of material towards the membrane, with the aim of generating a normalized permeability expected of PGDMF systems (i.e., decrease to a sustained value). Within approximately 1 to 2 weeks of operation at a greater permeate flux, the normalized permeability began to decrease for all the PGDMF systems. At the start of timeline 3, the normalized permeability decreased more extensively for all PGDMF systems. This was likely because of the change in feedwater characteristics that occurred at the start of timeline 3. As previously discussed, changes in feedwater can impact mass flux, and consequently, the normalized permeability. Although the DOC concentration of the feed water for all timelines was similar, it is likely that other water quality parameters, which were not monitored, differed between timelines. Following an initial decline, relatively steady state normalized permeabilities were reached for all PGDMF systems in timeline 3. In the sections which follow, the normalized permeabilities of the PGDMF systems with continuous inflow and periods of no inflow are considered in detail. 5.2.1 PGDMF systems operated with continuous inflow As illustrated in Fig 8, during timeline 1, the normalized permeability remained constant (i.e., slope of regression line fitted to normalized permeability was not different from zero) at a steady state normalized permeability was 1.10± 0.04. 39 Figure 8. Average normalized permeabilities of PGDMF (Error bars correspond to maximum and minimum of replicate systems; Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated.) During timeline 2, there was a significant decrease in the normalized permeability for PGDMF C. As previously discussed, the decrease in normalized permeability at the start of timeline 2 was attributed to the greater mass flux of material towards the membrane when the permeate flux was increased from 4 L/m2h to 6 L/m2h at the start of timeline 2. During timeline 3, there was a further significant decrease in normalized permeability to an initial steady state value of 0.50±0.02. As previously discussed, the decrease in normalized permeability at the start of the timeline 3 was attributed to the change in feed water at the start of this timeline (see Section 4.2). Although the DOC concentration of the feed water for Timeline 1 Timeline 2 Timeline 3 40 all timelines was similar, it is likely that the other water quality parameters, which were not monitored, differed between timelines 1, 2 and 3. On day 110, the normalized permeability abruptly changed, decreasing to an interim steady state value of 0.40± 0.002. After one week, the normalized permeability once again abruptly changed, increasing to a steady state value of 0.50 ± 0.01, equivalent to that observed for the initial steady state value. The cause of the abrupt changes in the normalized permeability during timeline 3 are unknown and was not investigated in the current study. Table 6 summarizes the steady state normalized permeability of the PGDMF systems. Table 6. Steady State Normalized Permeability PGDMF system Timeline 1 Timeline 3 Steady state value Initial steady state value Interim steady state value Final Steady state value PGDMF C 1.10± 0.04 0.51±0.02 0.40±0.002 0.50±0.01 PGDMF 3hNR 0.97±0.10 0.52±0.05 0.40±0.02 0.50±0.02 8hNR 0.95±0.12 0.62±0.07 0.50±0.02 0.60±0.02 2dNR 1.00±0.09 0.71±0.07 N/A 0.70±0.03 PGDMF 3hWR 0.94±0.08 1.10±0.06 N/A 1.20±0.04 8hWR 1.00±0.05 0.97±0.03 N/A 1.03±0.04 2dWR 0.95±0.08 1.13±0.05 N/A 1.03±0.05 (Note: N/A indicates that steady state conditions were not achieved. No steady state value was sustained in timeline 2.) 41 5.2.2 PGDMF systems operated with periods of no inflow – without permeate recycling As illustrated in Fig 9, during timeline 1, for PGDMF 3hNR, PGDMF 8hNR and PGDMF 2dNR, the normalized permeability remained relatively constant (slope of regression line fitted to normalized permeability was not different from zero) with a steady state value of 0.97±0.10, 0.95±0.12 and 1.00±0.09 respectively (see Table 6). Timeline 1 Timeline 2 Timeline 3 Figure 9. Normalized Permeabilities of PGDMF NR (Error bars correspond to maximum and minimum of replicate systems; Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated) During timeline 2, within approximately 1 to 2 weeks of operation at a greater permeate flux, the normalized permeability began to consistently decrease for all the PGDMF systems. 42 However, the decrease was not significant. As previously discussed, the decrease in normalized permeability was attributed to the greater load on to the membrane when the flux was increased to 6 L/m2h at the start of timeline 2. During timeline 3, for PGDMF 3hNR and PGDMF 8hNR there was a sustained decrease in the normalized permeability for approximately 2 weeks to initial steady states value of 0.50±0.05 and 0.60±0.07, respectively. As previously discussed, the decrease in normalized permeability at the start of the timeline 3 was attributed to the change in feed at the start of this timeline (see Section 4.2). As observed for the PGDMF systems operated with continuous inflow, after approximately 2 weeks, the normalized permeability abruptly changed, decreasing to an interim steady state value of 0.40±0.02 for PGDMF 3hNR and 0.50±0.02 for PGDMF 8hNR. After approximately 1 week, the normalized permeability once again changed abruptly for PGDMF 3hNR and PGDMF 8hNR, increasing to steady state values of 0.50±0.02 and 0.60±0.02, respectively, equivalent to those observed for the initial steady state values. For PGDMF 2dNR, there was also a sustained decrease in membrane permeability for approximately 2 weeks, to an initial steady state value of 0.70±0.06 at the start of timeline 3. Again, the decrease in normalized permeability at the start of the timeline 3 was attributed to the change in feed water at the start of this timeline (see Section 4.2). However, for PGDMF 2dNR, the normalized permeability abruptly increased, in contrast to the abrupt decrease observed for PGDMF 3hNR and PGDMF 8hNR. After a period of 4 weeks, the normalized permeability once again changed, decreasing to a final steady state normalized permeability of 0.70±0.03, equivalent to that observed for the initial steady state value. The cause for the abrupt changes during timeline 3 is unknown and was not investigated in the current study. 43 5.2.3 Comparison of PGDMF systems operated with periods of no inflow without permeate recycling and with continuous inflow The first objective of the current study was to investigate whether periods of no inflow (without permeate recycling) negatively impact the performance of the PGDMF systems in terms of hydraulic throughput. The normalized permeability of the PGDMF systems operated with periods of no inflow (PGDMF 3hNR, 8hNR and 2dNR) was compared to that of the PGDMF system operated with continuous inflow (PGDMF C), as described in Section 4.4. The normalized permeabilities of PGDMF C and PGDMF NR throughout the study are presented in Fig 10 (Note: Figure 10 is a combination of Figures 8 and 9). 44 Timeline 1 Timeline 2 Timeline 3 Figure 10. Normalized Permeabilities of PGDMF C and PGDMF NR (Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated.) During timeline 1, there was no statistically significant difference between the pairwise comparison of the time series normalized permeabilities of PGDMF C and the PGDMF NR systems irrespective of the length of the periods of no inflow (see Table 7). There was also no statistically significant difference between the pairwise comparisons of steady state normalized permeabilities of PGDMF C (1.10±0.01) and PGDMF 3NR (0.97±0.10), and PGDMF C and PGDMF 8hNR (0.95±0.12), and PGDMF C and PGDMF 2dNR (1.00± 0.09), (see Table 7). 45 During timeline 2, there was again no statistically significant difference between the pairwise comparison of time series normalized permeabilities of PGDMF C and PGDMF NR, irrespective of the length of the periods of no inflow (see Table 7). No steady state normalized permeability was achieved for any of the PGDMF systems during timeline 2. 46 Table 7 Assessment of differences between operation with of periods of no inflow (without permeate recycling) and continuous operation Comparison of PGDMF systems Comparison based on time-series normalized permeability Comparison based on steady state Normalized Permeability Timeline Timeline 1 2 3 1 3 Initial Interim Final 3hNR vs C No (p= 0.016) No (p= 0.062) No (p=0.082) No (p=0.021) No (p=0.055) No (p= 0.086) No (p=0.102) 8hNR vs C No (p= 0.048) No (p= 0.037) Yes (p= 0.0089) 8hNR vs 2dNR Yes (p= 4.9 E-07) No (p=0.04) Yes (p= 0.004) 8hNR vs 2dNR No (p= 0.02) Yes (p= 0.003) Yes (p= 0.002) 8hNR vs 2dNR Yes (p= 0.0003) 2dNR vs C No (p= 0.075) No (p= 0.023) Yes (p= 8.2E-11) Yes (p=0.009) Yes (p= 0.009) N/A Yes (p= 0.001) (Note: No steady state normalized permeability was observed during timeline 2; No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). During timeline 3, there was a statistically significant difference between the pairwise comparison of time series normalized permeabilities of PGDMF C and some of the PGDMF 47 NR systems. During this timeline, there is no statistically significant difference between the pairwise comparison of time series normalized permeabilities of PGDMF C and PGDMF 3hNR. However, Tukey’s HSD tests indicated that the time series normalized permeabilities of PGDMF 8hNR and PGDMF 2dNR were statistically greater than that of PGDMF C. Also, Tukey’s HSD tests indicated that the time series normalized permeability of PGDMF 2dNR was statistically greater than PGDMF 8hNR. When comparing steady state permeabilities, in the initial steady state, interim steady state and the final steady state, there was no statistically significant difference between the steady state normalized permeabilities of PGDMF C and PGDMF 3hNR (see Table 7). However, Tukey’s HSD tests indicated that the initial steady state normalized permeabilities of PGDMF 8hNR and PGDMF 2dNR were statistically greater than that of PGDMF C. Also, Tukey’s HSD tests indicated that the initial steady state normalized permeability of PGDMF 2dNR was statistically greater than that of PGDMF 8hNR. In the interim steady state, the steady state normalized permeability of PGDMF 8hNR was greater than that of PGDMF C. Note that no steady state normalized permeability was observed for PGDMF 2dNR during this interim period. In the final steady state period, Tukey’s HSD test indicated that the steady state normalized permeabilities of PGDMF 8hNR and PGDMF 2dNR were greater than that of PGDMF C. Also, Tukey’s HSD tests indicated that the final steady state normalized permeability of PGDMF 2dNR was statistically greater than that of PGDMF 8hNR. Considering that the cumulative hydraulic load to PGDMF 8hNR was lower than that for PGDMF 2dNR, which was in turn lower than PGDMF C, and that the normalized permeability of PGDMF C was lesser than that of PGDMF 8hNR, which was in turn lesser 48 than that of PGDMF 2dNR, the permeability is not expected to be governed by the cumulative hydraulic load. The results suggest that a short period of no inflow does not negatively impact the performance of the membrane system in terms of permeability. Rather, the results suggest that, for the conditions investigated, operation with period of no inflow of 8 hours/day or 2 days/week increases the membrane permeability. When investigating the impacts of no inflow periods for a conventional GDMF system, Varbanets et al., (2012) reported consistent results. They suggested that greater permeability when operated with periods of no inflow, could be attributed to reduced biological activity (i.e., secretion of soluble microbial products, excretion of extracellular polymeric substances, and other processes) in the biofilm layer during the periods of no inflow. Similarly, Tang et al., (2016) also reported that filtration resistance decreases with increasing periods of no inflow in a GDMF system. It can be concluded from the results that the periods of no inflow do not negatively impact the normalized permeability of PGDMF systems. Rather, it can be concluded that the periods of no inflow can increase the normalized permeability of PGDMF systems. The results also suggest that the normalized permeability is not impacted by greater hydraulic loads. 5.2.4 PGDMF systems operated with periods of no inflow – with permeate recycling As illustrated in Fig 11, during timeline 1, for PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR, the normalized permeability remained relatively constant (slope of regression line fitted to normalized permeability was not different from zero) with steady state values of 0.94±0.07, 1.00±0.05 and 0.95±0.08 respectively (see Table 6). 49 Timeline 1 Timeline 2 Timeline 3 Figure 11 Normalized Permeabilities of PGDMF WR (Error bars correspond to maximum and minimum of replicate systems; Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated) During timeline 2, within approximately 2 weeks of operation at a greater permeate flux, the normalized permeability began to consistently decrease for all the PGDMF WR systems. However, the decrease was not statistically significant. During timeline 3, for PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR there was a sustained decrease in the normalized permeability for approximately 2 weeks to initial steady state values of 1.10±0.06, 0.97±0.03 and 1.13±0.05, respectively. As previously discussed, the more extensive decrease in normalized permeability at the start of the timeline 3 was 50 attributed to the change in feed water at the start of this timeline (see Section 4.2). Unlike PGDMF NR and PGDMF C, an interim period of unsteady normalized permeability was observed for PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR for a period of 2 weeks, after which all PGDMF WR systems reached a final steady state values of 1.20±0.04 for PGDMF 3hWR, 1.03±0.03, for PGDMF 8hWR and 1.03±0.03, for PGDMF 2dWR, equivalent to those observed for the initial steady state values (see Table 6). The cause for the abrupt changes during timeline 3 is unknown and was not investigated in the current study. 5.2.5 Comparison of PGDMF systems operated with periods of no inflow with permeate recycling and continuous inflow The second objective of the current study was to investigate whether recycling the permeate during the periods of no inflow would mitigate the potential negative impact of periods of no inflow. As discussed in Section 5.2.3, operation with periods of no inflow did not negatively impact the throughput. Nonetheless, the results for PGDMF systems operated with permeate recycling during periods of no inflow were further considered. The normalized permeability of the PGDMF systems operated with periods of no inflow with permeate recycling (PGDMF 3hWR, 8hWR and 2dWR) was compared to that of the PGDMF system operated with continuous inflow (PGDMF C) as described in Section 4.4. The normalized permeabilities of PGDMF C and PGDMF WR throughout the study are presented in Fig 12. (Note: Figure 12 is a combination of Figures 8 and 11). 51 Timeline 1 Timeline 2 Timeline 3 Figure 12 Normalized Permeabilities of PGDMF WR and PGDMF C (Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated) In timeline 1, there was no statistically significant difference between the pairwise comparisons of the time series normalized permeabilities of PGDMF C and PGDMF WR irrespective of the length of the periods of no inflow (see Table 8). However, the steady state permeabilities of PGDMF WR were statistically different from PGDMF C, for all periods of no inflow (see Table 8). Also, Tukey’s HSD test indicated that there was no statistically significant difference between the steady state permeabilities of PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR. 52 Table 8 Assessment of differences between operation with periods of no inflow (with permeate recycling) and continuous operation Comparison of PGDMF systems Comparison based on time-series normalized permeability Timeline 1 2 3 3hWR vs C No (p= 0.305) Yes (p= 7.1E-09) 3hWR vs 2dWR 8hWR vs 2dWR No (p=0.076) No (p=6.3E-10) Yes (p= 4.6E-15) 3hWR vs 2dWR 8hWR vs 2dWR No (p=0.428) No (p=0.289) 8hWR vs C No (p= 0.091) Yes (p= 2.2E-09) Yes (p=3.6E-15) 2dWR vs C No (p= 0.014) Yes (p = 8.0E-08) Yes (p= 2.5E-24) (Note: No steady state normalized permeability was observed during timeline 2; No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). Comparison of PGDMF systems Comparison based on steady state normalized permeability Timeline 1 3 Initial Final 3hWR vs C Yes (p=9.9E-05) Yes (p= 0.001) 3hWR vs 8hWR 8hWR vs 2dWR No (p=0.428) No (p=0.289) Yes (p=9.3E-06) 3hWR vs 8hWR 8hWR vs 2dWR No (p=2.9 E-04) No (p=0.237) 8hWR vs C Yes (p=3.0E-4) Yes (p= 0.008) Yes (p= 9.2E-07) 2dWR vs C Yes (p= 9.6E-05) Yes (p= 0.003) Yes (p=2E-05) 53 During timeline 2, there was a statistically significant difference between pairwise comparisons of the time series normalized permeabilities of PGDMF C and PGDMF WR for all periods of no inflow (see Table 8). Tukey’s HSD tests indicated that the time series normalized permeabilities of PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR were statistically greater than that of PGDMF C. Also, Tukey’s HSD test indicated that the time series normalized permeability for PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR were statistically similar (see Table 8). During timeline 3, there was a statistically significant difference between the time series normalized permeabilities of PGDMF C and PGDMF WR, for all periods of no inflow. During this timeline, Tukey’s HSD test indicated that the time series normalized permeabilities of PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR were statistically greater than that of PGDMF C. Also, Tukey’s HSD tests indicated that the time series normalized permeability of PGDMF 3hWR was statistically greater than that of PGDMF 8hWR and PGDMF 2dWR. Tukey’s HSD tests also indicated that there was no statistically significant difference between the time series normalized permeabilities of PGDMF 8hWR and PGDMF 2dWR. When comparing steady state permeabilities, Tukey’s HSD indicated that the steady state permeabilities of PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR were statistically greater than that of PGDMF C for both the initial steady state and the final steady state (see Table 8). For PGDMF 3hWR, 8hWR and PGDMF 2dWR, Tukey’s test indicated that there was also no statistically significant difference between the systems in the initial steady state. However, in the final state period, Tukey’s HSD test indicated that there was a statistically significant difference between the PGDMF 3hWR and PGDMF 8hWR, while PGDMF 8hWR and PGDMF 2dWR were statistically similar. 54 It can be concluded from the results that the periods of no inflow, with permeate recycling, do not negatively impact the normalized permeability of PGDMF system. Rather, it can be concluded that, for the conditions investigated, operation with periods of no inflow, with permeate recycling, increases the normalized permeability of PGDMF systems. 5.2.6. Comparison of PGDMF systems operated with periods of no inflow – with and without permeate recycling As previously discussed, the second objective of the current study was to investigate whether recycling the permeate during the periods of no inflow would mitigate the potential negative impact of periods of no inflow on hydraulic throughput. The normalized permeability of the PGDMF systems operated with periods of no inflow, without permeate recycling (PGDMF 3hNR, 8hNR and 2dNR) was compared to that of the corresponding PGDMF system operated with periods of no inflow with permeate recycling (PGDMF 3hWR, 8hWR and 2dWR respectively), as described in Section 4.4. The normalized permeabilities of PGDMF NR and PGDMF WR throughout the study are presented in Fig 13. (Note: Figure 13 is a combination of Figures 9 and 11). 55 Timeline 1 Timeline 2 Timeline 3 Figure 13 Normalized Permeabilities of PGDMF WR and PGDMF NR (Note that the data presented is similar to that of Fig. 7, with only the data relevant to the present discussion being illustrated) During timeline 1, there was no statistically significant difference between the pairwise comparisons of the time series normalized permeabilities of PGDMF NR and PGDMF WR irrespective of the length of the periods of no inflow (see Table 9). Also, there was no statistically significant difference between the steady state permeabilities of PGDMF 3hWR and PGDMF 3hNR; PGDMF 8hWR and PGDMF 8hNR; and PGDMF 2dWR and PGDMF 2dNR, respectively (see Table 9). 56 Table 9 Assessment of differences between operation with periods of no inflow with permeate recycling and without permeate recycling Comparison of PGDMF systems Comparison based on time-series normalized permeability Comparison based on steady state normalized permeability Timeline Timeline 1 2 3 1 3 Initial Final 3hNR vs 3hWR No (p=0.013) Yes (p=6.0E-4) Yes (p=2.0E-7) No (p=0.282) Yes (p=0.001) Yes (p=8.4E-06) 8hNR vs 8hWR No (p=0.156) Yes (p=0.004) Yes (p=4.0E-12) No (p=0.029) Yes (p=0.003) Yes (p=3.2E-04) 2dNR vs 2dWR No (p=0.091) Yes (p=4.3E-09) Yes (p= 1.9E-12) No (p=0.032) Yes (p=0.002) Yes (p=5.8E-04) (Note: No steady state normalized permeability was observed during timeline 2; No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). During timeline 2, there was a statistically significant difference between the pairwise comparisons of time series normalized permeabilities of PGDMF 3hNR and PGDMF 3hWR; PGDMF 8hNR and PGDMF 8hWR; and PGDMF 2dNR and PGDMF 2dWR (see Table 9). Tukey’s HSD tests indicated that the time series normalized permeabilities of PGDMF WR were consistently greater than that of PGDMF NR. During timeline 3, there was a statistically significant difference between the pairwise comparisons of time series normalized permeabilities of PGDMF 3hNR and PGDMF 3hWR; 57 PGDMF 8hNR and PGDMF 8hWR; and PGDMF 2dNR and PGDMF 2dWR (see Table 9). Again, Tukey’s HSD test indicated that the time series normalized permeabilities of PGDMF WR were consistently greater than that of PGDMF NR (see Table 9). The difference in normalized permeabilities of the PGDMF systems and their correlation to operational conditions such as, cumulative hydraulic load (with and without permeate recycling during periods of no inflow), fraction of time on, and fraction of time off, were assessed to identify any possible trends (see Appendix H). The results suggested that the PGDMF systems operated with permeate recycling during periods of no inflow had a greater normalized permeability than PGDMF systems operated without permeate recycling during periods of no inflow. The results also suggested that the normalized permeabilities were not governed by the cumulative hydraulic load on the PGDMF systems (see Appendix H). Overall, with respect to normalized permeability, PGDMF WR performed better than PGDMF NR. When permeate is recycled, substrate near the biofilm could be depleted impacting biological activity in the biofilm at the membrane surface (Álvarez-Hornos et al., 2008; Feng et al., 2019). As previously discussed, permeate recycling was considered as a measure to mitigate potential negative impact of periods of no inflow. Although the normalized permeability was greater with operation with permeate recycling during periods of no inflow, it is not considered to be required because operation with periods of no inflow did not negatively impact the normalized permeability (see Section 5.2.3). Also, permeate recycling during periods of no inflow would significantly increase the complexity of PGDMF systems. Although operation with permeate recycling during periods of no inflow was not considered to be required, the conditions generated within the PGDMF system permeate recycling could be of interest for further studies (beyond the scope of the current study). This 58 is because operation with recycling the permeate during periods of no inflow consistently resulted in the highest normalized permeate flux and may offer insight into mechanisms that optimize normalized permeate flux. 5.3 Organic Matter Removal In contrast with the differences in permeability observed during the different timelines (section 5.2), single factor ANOVA tests with 99% significance concluded that the TOC and DOC concentrations, as well as UV254 absorbances, in each of the feed, permeate and reject, were statistically similar in all 3 timelines, as defined in Section 5.2, for all PGDMF systems (see Appendix F for p-values). For this reason, all of the TOC concentrations, DOC concentrations and UV254 absorbances were combined into a single timeline for the analyses which follow. The average TOC and DOC concentrations, as well as the UV254 absorbances of the feed water are summarized in Table 10. Table 10. Summary of average TOC and DOC concentrations and UV254 absorbances of feed water Average concentrations of feed water TOC (mg/L) DOC (mg/L) UVA 4.32 ± 0.29 3.44 ± 0.19 0.05 ± 0.001 59 Pairwise comparison of the time series TOC and DOC concentrations indicated that the feed TOC was significantly greater than the feed DOC (p= 3.68E-10). In the sections which follow, TOC and DOC concentrations, and UV254 absorbances, in the permeate and reject of the PGDMF systems with continuous inflow, and periods of no inflow, are considered in detail. 5.3.1. PGDMF systems operated with continuous inflow Pairwise comparisons indicated that the time series TOC concentrations of the permeate were statistically similar to the time series DOC concentrations of the permeate (p-value = 0.213). This is consistent with the DOC/TOC ratio of the permeate which was equivalent to 1.0 (i.e., not significantly different than 1.0; see Appendix E). Pairwise comparison tests also indicated that the time series TOC concentrations of the feed were statistically greater than the time series TOC concentrations of the permeate for PGDMF C (see Table 11), while pairwise comparison of the time series DOC concentrations of the feed and the permeate were statistically similar (see Table 11). This is also consistent with the greater DOC/TOC ratio of permeate than the feed, and consistent with results observed from comparing their corresponding cumulative mass of TOC and DOC in the feed and permeate (see Table 12). Overall, the results suggest that particulate organic material was completely removed by PGDMF C, while soluble organic matter was not. This is consistent with what is expected of GDMF systems, as the pore size of the membrane is much smaller than the size of particulate organic material (Tobias Costa de Oliveira, 2019). 60 Table 11. Comparison of time series TOC, DOC, DOC/TOC and UV254 values for PGDMF C Pairwise comparison of time series data Difference in TOC concentration Difference in DOC concentration Difference in DOC/TOC ratio Difference in UV254 absorbance Permeate vs Feed Yes (p=1.9E-4) No (p=0.128) Yes (p=1.6E-05) Yes (p=2.4E-15) Reject vs Feed Yes (p=0.008) Yes (p=0.002) Yes (p=9.8E-08) Yes (p=8.3E-17) Order Reject > Feed> Permeate (p=1.0E-06) Reject > (feed and permeate) (p=1.2E-06) Permeate > Reject > Feed (p=1.8E-07) Reject > Permeate > Feed (p=1.3E-16) (Note - No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). Pairwise comparisons indicated that the time series TOC concentrations of the reject were statistically greater than that of the time series DOC concentrations of the reject (p-value = 8.5E-11). This is consistent with the DOC/TOC ratio of the reject which was lesser than 1.0 (see Appendix E). Tukey’s HSD tests indicated that the time series TOC and DOC concentrations of the reject were greater than those of the feed and the permeate. Tukey’s HSD tests also indicated that the DOC/TOC ratio of the permeate was greater than of the reject, which was in turn greater than the feed. This is consistent with the results observed from comparing their corresponding TOC and DOC concentrations of the feed, permeate and reject, and consistent with results observed from comparing their corresponding TOC and 61 DOC cumulative mass in the feed, permeate and reject (see Table 13). Overall, the results suggest that TOC was accumulated in the membrane tanks after being removed from the feed water by membrane modules and/or after the detachment of the biofilm from the surface of the membrane modules, and that some of the TOC accumulated in the membrane tank was likely hydrolyzed into DOC due to biological activity in the foulant layer. The results are consistent with observations made by Oka (2015) in a study that considered PGDMF filtration. Although pairwise comparisons indicated that DOC concentrations of the feed and permeate were statistically similar, Tukey’s HSD tests indicated that the time series UV254 absorbance of the permeate was statistically greater than the that of the feed. Also, the UV254 absorbance of the reject was greater than that of the permeate and the feed. These results suggest that the permeate of PGDMF C had a greater fraction of aromatic compounds than the feed water. To obtain an accurate estimate of the overall TOC and DOC removal efficiencies for the PGDMF systems, mass balance analysis was performed which considered cumulative mass input of organic material into the PGDMF systems and cumulative mass output of organic material from the PGDMF systems, as described in Appendix E. The cumulative mass of organic material in the PGDMF systems are summarized in Table 12. 62 Table 12. Cumulative mass of organic material in PGDMF systems PGDMF systems TOC DOC Cumulative mass in feed (mg) Cumulative mass in permeate (mg) Cumulative mass in reject (mg) Cumulative mass in feed (mg) Cumulative mass in permeate (mg) Cumulative mass in reject (mg) PGDMF C 279.5 135.5 110.7 222.2 129.1 98.6 PGDMF NR 244.5 154.3 114.6 194.5 152.4 108.2 PGDMF WR 244.5 139.5 110.2 194.5 121.8 102.1 Based on the mass balance analysis, TOC removal efficiency was estimated to be 44.8%, while the DOC removal efficiency was 36.9% for PGDMF C. UF membranes used for drinking water treatment are usually expected to have low organic matter removal due to their relatively large pore sizes (Schafer, 2001; Tobias Costa de Oliveira, 2019). One previous study that considered PGDMF systems (Oka, 2015) reported organic matter removal of up to 50 percent for a feed water similar to that used in the current study (mix of tap water and Jericho Pond water). However, the feed water used in this previous study was not pre-filtered using a 5µm cartridge filter as done in the current study (see Section 4.2). The ratio of TOC/DOC of the feed water in the previous study was approximately 1.5 times greater than that used in the current study. These differences are likely what led to the greater removal of organic matter reported by Oka (2015). 63 5.3.2 PGDMF systems operated with periods of no inflow – without permeate recycling Single factor ANOVA tests with 99% significance concluded that the time series TOC, DOC and UV254 of all 3 PGDMF NR systems were statistically similar in the permeate (p = 0.016 for TOC, p= 0.082 for DOC, p = 0.469 for UV254) and in the reject (p = 0.023 for TOC, p= 0.044 for DOC, p= 0.638 for UV254). For this reason, the average of the time series TOC and DOC concentrations, and UV254 absorbances of PGDMF 3hNR, PGDMF 8hNR and PGDMF 2dNR were considered for the analysis which follow. Pairwise comparisons indicated that the time series TOC concentrations of the permeate were statistically similar to the time series DOC concentrations of permeate (p-value = 0.237). This is consistent with the DOC/TOC ratio of the permeate which was equivalent to 1.0 (i.e., not significantly different than 1; see Appendix E). Pairwise comparisons also indicated that the time series TOC concentrations of the feed were statistically greater than the time series TOC concentrations of the permeate for PGDMF NR as observed for PGDMF C (see Table 14). However, unlike for PGDMF C, the time series DOC concentrations of the permeate were statistically greater than the time series DOC concentrations of the feed (see Table 13). This is consistent with the greater DOC/TOC ratio of permeate than the feed, and consistent with results observed from comparing their corresponding TOC and DOC cumulative mass in the feed and permeate (see Table 12). Overall, the results suggest that particulate organic material was completely removed by PGDMF NR as observed for PGDMF C, while soluble organic material was partially removed (unlike the absence of removal for PGDMF C). As previously discussed, this is consistent with what is expected of GDMF systems, as the pore size of the membrane is much smaller than the size of particulate organic material (Tobias Costa de Oliveira, 2019). 64 Table 13 Comparison of time series TOC, DOC and UV254 values in PGDMF NR Comparison of time series data Difference in TOC concentration Difference in DOC concentration Difference in DOC/TOC ratio Difference in UV254 absorbance Permeate vs Feed Yes (p=3.1E-05) Yes (p=5.0E-04) Yes (p=0.006) Yes (p=1.1E-14) Reject vs Feed Yes (p=2.1E-05) Yes (p=1.2E-05) Yes (p=8E-4) Yes (p=3.2E-18) Order Reject > Feed> Permeate (p=1E-04) Reject > Permeate > Feed (p=2.2E-05) Permeate > Reject > Feed (p=4.2E-03) Reject > Permeate > Feed (p=4.4E-18) (Note - No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). Pairwise comparisons of the time series TOC and DOC concentrations of the reject indicated that the time series TOC concentrations of the reject were statistically greater than that of the time series DOC concentrations of reject (p-value = 1.9E-04). This is consistent with the DOC/TOC ratio of the reject was lesser than 1.0 (see Appendix E). Tukey’s HSD tests indicated that the time series TOC and DOC concentrations of the reject were greater than those of the feed and the permeate. Tukey’s HSD tests also indicated that the DOC/TOC ratio of permeate was greater than of the reject, which was in turn greater than the feed. This is consistent with the results observed by comparing their corresponding TOC and DOC concentrations of the feed, permeate and reject, and consistent with results observed from comparing their corresponding TOC and DOC cumulative mass in the feed, permeate and 65 reject (see Table 13). Overall, as previously discussed, the results suggest that TOC was accumulated in the membrane tanks after being removed from the feed water by membrane modules and/or after the detachment of the biofilm from the surface of the membrane modules, and that some of the TOC accumulated in the membrane tank was likely hydrolyzed into DOC due to biological activity in the foulant layer, as observed for PGDMF C. The results are consistent with observations made by Oka (2015) in a study that considered PGDMF filtration. Tukey’s HSD tests indicated that the time series UV254 absorbance of the permeate was statistically greater than that of the feed. Also, the UV254 absorbance of the reject was greater than that of the permeate and the feed. These results were in accordance with the observations made by comparing the time series DOC concentrations of the feed and permeate of PGDMF NR. To obtain an accurate estimate of the overall TOC and DOC removal efficiencies for the PGDMF systems, mass balance analysis was performed, which considered, cumulative mass input of organic material into the PGDMF systems and cumulative mass output of organic material from the PGDMF systems, as described in Appendix E. The cumulative mass of organic material in the PGDMF systems are described in Table 12. Based on the mass balance analysis, TOC removal efficiency was estimated to be 36.9%, while the DOC removal efficiency was 21.6 % for PGDMF NR. Low organic material removal was also observed for PGDMF C (see Section 5.3.1). UF membranes used for drinking water treatment are usually expected to have low organic matter removal due to their relatively large pore sizes (Schafer, 2001; Tobias Costa de Oliveira, 2019). One previous study that considered PGDMF systems (Oka, 2015) reported organic matter removal of up to 50 percent 66 for a feed water similar to that used in the current study (mix of tap water and Jericho Pond water). However, the feed water used in this previous study was not pre-filtered using a 5µm cartridge filter as done in the current study (see Section 4.2). The ratio of TOC/DOC of the feed water in the previous study was approximately 1.5 times greater than that used in the current study. These differences are likely what led to the greater removal of organic matter reported by Oka (2015). 5.3.3 PGDMF systems operated with periods of no inflow – with permeate recycling Single factor ANOVA tests with 99% significance concluded that the time series TOC, DOC and UV254 of all 3 PGDMF WR systems were statistically similar in the permeate (p = 0.515 for TOC, p= 0.013 for DOC, p = 0.508 for UV254) and in the drain (p = 0.043 for TOC, p= 0.057 for DOC, p= 0.422 for UV254). For this reason, the average of the time series TOC and DOC concentrations, and UV254 absorbances of PGDMF 3hWR, PGDMF 8hWR and PGDMF 2dWR are considered for the analyses which follow. Pairwise comparisons indicated that the time series TOC concentrations of the permeate were statistically similar to the time series DOC concentrations of permeate (p-value = 0.294). This is consistent with the DOC/TOC ratio of the permeate which was equivalent to 1.0 (i.e., not significantly different than 1.0; see Appendix E). Pairwise comparisons also indicated that the time series TOC concentrations of the feed were statistically greater than the time series TOC concentrations of the permeate for PGDMF WR (see Table 14), while pairwise comparisons of the time series DOC concentrations of the feed and permeate were statistically similar (see Table 15). This is also consistent with the greater DOC/TOC ratio of permeate than of the feed and consistent with results observed from comparing their corresponding TOC and DOC cumulative mass of the feed and permeate (see Table 12). 67 Overall, the results suggest that particulate organic material was completely removed by PGDMF WR, while organic material was not, as observed for PGDMF C and PGDMF NR (see Section 5.3.1 and 5.3.2). As previously discussed, this is consistent with what is expected of GDMF systems, as the pore size of the membrane is much smaller than the size of particulate organic material (Tobias Costa de Oliveira, 2019). Table 14 Comparison of time series TOC, DOC and UV254 values in PGDMF WR Comparison of time series data Difference in TOC concentration Difference in DOC concentration Difference in DOC/TOC ratio Difference in UV254 absorbance Permeate vs Feed Yes (p=2.3E-05) No (p=0.226) Yes (p=1.43E-06) Yes (p=9.44E-16) Reject vs Feed Yes (p=3.98E-06) Yes (p=1.06E-08) Yes (p=9.59E-05) Yes (p=3.5E-18) Order Reject > Feed> Permeate (p=0.003) Reject > (Feed and Permeate) (p=2.16E-05) Permeate > Reject > Feed (p=0.002) Reject > Permeate > Feed (p=8E-18) (Note - No: No statistically significant difference; Yes: Statistically significant difference with relevant p-value provided in parentheses). Pairwise comparisons indicated that the time series TOC concentrations of the reject were statistically greater than that of the time series DOC concentrations of reject (p-value = 5.96E-10). This is consistent with the DOC/TOC ratio of the reject which was lesser than 1.0 (see Appendix E). Tukey’s HSD tests indicated that the time series TOC and DOC concentrations of the reject were greater than those of the feed and the permeate. Tukey’s 68 HSD tests also indicated that the DOC/TOC ratio of permeate was greater than of the reject, which was in turn greater than the feed. This is consistent with the results observed by comparing their corresponding TOC and DOC concentrations of the feed, permeate and reject, and consistent with results observed from comparing their corresponding TOC and DOC cumulative mass in the feed, permeate and reject (see Table 12). Overall, as previously discussed, the results suggest that TOC was accumulated in the membrane tanks after being removed from the feed water by membrane modules and/or after the detachment of the biofilm from the surface of the membrane modules, and that some of the TOC accumulated in the membrane tank was likely hydrolyzed into DOC due to biological activity in the foulant layer, as observed for PGDMF C and PGDMF NR (see Section 5.3.1 and 5.3.2). The results are consistent with observations made by Oka (2015) in a study that considered PGDMF filtration. Although pairwise comparisons indicated that DOC concentrations of the feed and permeate are statistically similar, Tukey’s HSD tests indicated that the time series UV254 absorbance of the permeate was statistically greater than the feed. Also, the UV254 absorbance of the reject was greater than the permeate and the feed. These results suggest that the permeate of PGDMF WR had a greater fraction of aromatic compounds than the feed water. To obtain an accurate estimate of the overall TOC and DOC removal efficiencies for the PGDMF systems, mass balance analysis was performed which considered cumulative mass input of organic material into the PGDMF systems and cumulative mass output of organic material from the PGDMF systems, as described in Appendix E. The cumulative mass of organic material in the PGDMF systems are summarized in Table 12. Based on the mass balance analysis, TOC removal efficiency was estimated to be 42.9%, while the DOC 69 removal efficiency was 37.3% for PGDMF WR. Low organic material removal was also observed for PGDMF C and PGDMF NR (see Sections 5.3.1 and 5.3.2). UF membranes used for drinking water treatment are usually expected to have low organic matter removal due to their relatively large pore sizes (Schafer, 2001; Tobias Costa de Oliveira, 2019). One previous study that considered PGDMF systems (Oka, 2015) reported organic matter removal of up to 50 percent for a feed water similar to that used in the current study (mix of tap water and Jericho Pond water). However, the feed water used in this previous study was not pre-filtered using a 5µm cartridge filter as done in the current study (see Section 4.2). The ratio of TOC/DOC of the feed water in the previous study was approximately 1.5 times greater than that used in the current study. These differences are likely what led to the greater removal of organic matter reported by Oka (2015). 5.3.4 Comparison of Organic Material Removal between PGDMF systems The third objective of the current study was to investigate whether operation with periods of no inflow negatively impact the organic matter removal of PGDMF systems. A summary of the TOC and DOC removal efficiencies calculated based on cumulative mass balances (see Sections 5.3.1 to 5.3.3), are summarized in Table 15. Table 15 Summary of TOC and DOC removal efficiencies PGDMF systems TOC removal efficiency DOC removal efficiency PGDMF C 44.8% 41.9% PGDMF NR 36.9% 21.6% PGDMF WR 42.9% 37.3% 70 The TOC and DOC removal efficiencies for the different PGDMF systems were also assessed based on time series data. As discussed below, the assessment of TOC and DOC removal, based on time series data, is similar to that based on cumulative mass balance. Tukey’s HSD tests indicated that the time series TOC concentrations of the permeate of PGDMF NR were statistically greater than that of PGDMF C and PGDMF WR, while pairwise comparisons indicated that the time series TOC concentrations of PGDMF C and PGDMF WR were statistically similar (see Table 16; see appendix E for figures). Also, Tukey’s HSD tests indicated that the time series DOC concentrations of the permeate of PGDMF NR was statistically greater than that of PGDMF C and PGDMF WR, while pairwise comparisons indicated that the time series DOC concentrations of the permeate of PGDMF C and PGDMF WR were statistically similar (see Table 16; see appendix E for figures). 71 Table 16. Assessment of differences in organic matter removal between PGDMF systems PGDMF systems Comparison based on TOC Comparison based on DOC Permeate Reject Permeate Reject PGDMF NR vs PGDMF C Yes (p= 1.0E-4) Yes (p= 5.9E-05) Yes (p= 4.8E-06) Yes (p= 0.004) PGDMF WR vs PGDMF C No (p= 0.253) Yes (p= 6.8E-07) No (p= 0.109) No (p= 0.092) Order NR >(C, WR) (p= 1.3E-07) NR > C > WR (p= 0.001) NR >(C, WR) (p= 1.8E-07) NR >(C, WR) (p= 7.0E-04) Comparison based on TOC removal efficiency Comparison based on DOC removal efficiency PGDMF NR vs PGDMF C Yes (p= 2.0E-04) Yes (p= 1.6E-06) PGDMF WR vs PGDMF C No (p= 0.2204) No (p= 0.265) Order WR > C > NR (p= 1.8E-04) (WR,C) > NR (p= 9.1E-09) Tukey’s HSD tests indicated that the time series TOC concentrations of the reject of PGDMF NR was statistically greater than that of PGDMF C, which was in turn greater than that of PGDMF WR (see Table 16; see appendix E for figures). Tukey’s HSD tests also indicated that the time series DOC concentrations of the reject of PGDMF NR was statistically greater 72 than that of PGDMF C and PGDMF WR, while pairwise comparisons indicated that the time series DOC concentrations of the reject of PGDMF C and PGDMF WR were statistically similar (see Table 16; see appendix E for figures). Overall, the results from the Tukey’s HSD tests indicated that the TOC removal efficiencies of PGDMF WR were greater than that of PGDMF C, which was in turn greater than that of PGDMF NR and were in accordance with the observed results (see Table 15). Also, the results from the Tukey’s HSD tests indicated that the DOC removal efficiency of PGDMF NR was lesser than that of PGDMF C and PGDMF WR and were consistent with the observed results. The lower DOC removal for PGDMF NR was likely due to the release of soluble microbial products during nutrient starvation of the biofilm during the periods of no inflow (Zhang & Bishop, 2003). As previously discussed, the time series TOC and DOC concentrations of the reject of PGDMF NR were statistically greater than those of PGDMF C and PGDMF WR (see Table 15). This may have been due to the greater detachment of the biofilm from the membrane surface during the periods of no permeation for PGDMF NR. Recall that for PGDMF C and PGDMF WR, permeation was not interrupted by periods of no inflow. The expanded biofilm layer of PGDMF NR may have been easier to detach from the membrane surface during aeration when compared to PGDMF C and PGDMF WR resulting in greater TOC and DOC concentrations of the reject. The greater removal of biofilm in PGDMF NR likely resulted in a thinner biofilm in PGDMF NR than PGDMF C and PGDMF WR. Tobias & Bérubé (2020) reported that the biofilm in PGDMF systems significantly contributes to the removal of material. This is consistent with the greater TOC and DOC concentrations found in the permeate of PGDMF NR than PGDMF C and PGDMF WR. van Loosdrecht et al., (2002) reported that the biofilm concentrations decrease with decreasing 73 hydraulic (i.e., substrate) loads. This suggests that the biofilm of PGDMF C would have been more extensive than those of PGDMF WR and PGDMF NR, and that there is potentially less biofilm in PGDMF NR than PGDMF WR. It can be concluded from the results that periods of no inflow, without permeate recycling, reduce the organic material removal efficiencies of PGDMF systems, and periods of no inflow, with permeate recycling, do not negatively impact the organic material removal efficiencies of PGDMF systems. The results also suggest that the length of the periods of no inflow, with and without permeate recycling, had no effect on the organic material removal of PGDMF systems. As previously discussed, low organic material removal is expected of PGDMF systems (see Sections 5.3.1, 5.3.2 and 5.3.3). Although the organic material removal was reduced with operations with periods of no inflow, without permeate recycling, the reduced organic material removal is not considered to be consequential because TOC and DOC removal is typically not expected in PGDMF systems. In the present study, TOC and DOC was monitored to gain insight into the overall performance of PGDMF systems. Hence, the negative impact of periods of no inflow, without permeate recycling, on organic matter removal is not expected to be consequential in terms of overall system performance. 74 Chapter 6. Conclusions From the results of the current study, the following conclusions could be made: 1) Periods of no inflow, without permeate recycling, do not negatively impact the normalized permeability of PGDMF systems. Rather the periods of no inflow can increase the normalized permeability of PGDMF systems. 2) Periods of no inflow, with permeate recycling, do not negatively impact the performance of the membrane system in terms of permeability. Rather, the results suggest that, for the conditions investigated, operation with period of no inflow, with permeate recycling, can increase the normalized permeability of PGDMF systems. 3) When comparing PGDMF systems with and without recycling during the periods of no inflow, the PGDMF systems, with permeate recycling, perform better, and exhibit greater normalized membrane permeability. 4) Periods of no inflow, without permeate recycling, reduce the organic material removal efficiencies of PGDMF systems. Periods of no inflow, with permeate recycling, do not negatively impact the organic material removal efficiencies of PGDMF systems. 6.1. Engineering Implications Conventional GDMF systems are only ideal for low throughput and short-term application due to their lack of fouling control measures (see Section 2.2.1). As previously discussed, passive fouling control measures, including relaxation and gravity induced air scouring, add no substantial mechanical or operational complexities to the conventional GDMF systems, yet increase the normalized permeability by almost two-fold (Oka et al., 2017; Tobias Costa 75 de Oliveira, 2019). Periods of no inflow are a characteristic of water treatment systems in small and remote communities and were a cause for concern for PGDMF systems as they impact nutrient loading (see Section 2.3). The results from the current study conclude that operation with periods of no inflow, without permeate recycling, do not negatively impact normalized permeability of PGDMF systems. Therefore, no remedial action is needed to address periods of no inflow. 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Chemosphere, 50(1), 63–69. https://doi.org/10.1016/S0045-6535(02)00319-3 82 Appendix A: Timer Programming for automation of membrane systems The timer programming for systems with continuous operation and periods of no inflow (with and without permeate recycling) are presented in Table 17, 18 and 19, respectively. Table 17 Timer programming for PGDMF C Operation Time (min) Cycle Feed Pump Drain Air On Off Fill 0.5 0 30 On Off Off Off Permeate 1373.5 30 82440 On On Off Off Relaxation 60 82440 86040 On Off Off Off Aerate 5 86040 86340 Off Off Off On Drain 0.5 86340 86370 Off Off On Off Fill (Permeate feed) 0.5 86370 86400 On Off Off Off Table 18 Timer programming for PGDMF NR PGDMF 3hNR Operation Time (min) Cycle Feed Pump Drain Air On Off Fill 0.5 0 30 On Off Off Off Permeate 1193.5 30 71640 On On Off Off Relaxation 60 71640 75240 On Off Off Off Aerate 5 75240 75540 Off Off Off On Drain 0.5 75540 75570 Off Off On Off Fill (Permeate Feed) 0.5 75570 75600 On Off Off Off No permeation 180 75600 86400 On Off Off Off PGDMF 8hNR 83 Operation Time (min) Cycle Feed Pump Drain Air On Off Fill 0.5 0 30 On Off Off Off Permeate 893.5 30 53640 On On Off Off Relaxation 60 53640 57240 On Off Off Off Aerate 5 57240 57540 Off Off Off On Drain 0.5 57540 57570 Off Off On Off Fill (Permeate Feed) 0.5 57570 57600 On Off Off Off No permeation 480 57600 86400 On Off Off Off PGDMF 2dNR Operation Time (min) Cycle Feed Pump Drain Air On Off Fill 0.5 0 30 On Off Off Off Permeate 7133.5 30 428040 On On Off Off Relaxation 60 428040 431640 On Aerate 5 431640 431940 Off Off Off On Drain 0.5 431940 431970 Off Off On Off Fill (Perm) 0.5 431970 432000 On Off Off Off No operation 2880 432000 604800 On Off Off Off Table 19 Timer Programming for PGDMF WR PGDMF 3hWR Operation Time (min) Cycle Feed Pump Drain Air Permeate feed On Off Fill 0.5 0 30 On Off Off Off Off Permeate 1193.5 30 71640 On On Off Off Off Relaxation 60 71640 75240 On Off Off Off Off Aerate 5 75240 75540 Off Off Off On Off Drain 0.5 75540 75570 Off Off On Off Off Fill (Perm. feed) 0.5 75570 75600 Off Off Off Off On 84 Permeate (Perm. feed) 180 75600 86400 Off On Off Off On PGDMF 8hWR Operation Time (min) Cycle Feed Pump Drain Air Permeate feed On Off Fill 0.5 0 30 On Off Off Off Off Permeate 893.5 30 53640 On On Off Off Off Relaxation 60 53640 57240 On Off Off Off Off Aerate 5 57240 57540 Off Off Off On Off Drain 0.5 57540 57570 Off Off On Off Off Fill (Perm. feed) 0.5 57570 57600 Off Off Off Off On Permeate (Perm. feed) 480 57600 86400 Off On Off Off On PGDMF 2dWR Operation Time (min) Cycle Feed Pump Drain Air Permeate feed On Off Fill 0.5 0 30 On Off Off Off Off Permeate 7133.5 30 428040 On On Off Off Off Relaxation 60 428040 431640 On Off Off Off Off Aerate 5 431640 431940 Off Off Off On Off Drain 0.5 431940 431970 Off Off On Off Off Fill (Perm. Feed) 0.5 431970 432000 Off Off Off Off On Permeate (Perm. Feed) 2880 432000 604800 Off On Off Off On 85 Appendix B: Calibration of Pressure Transducers The calibration of the pressure transducers was performed by connecting the pressure transducers to a pressure calibrator set to the required pressure. The pressure transducers were calibrated to provide accurate measurements of transmembrane pressure from 0.1 psi to 5.5 psi. Once the desired pressure was set, the corresponding electrical signal from the pressure transducer was measured using the LabView SignalExpress software. This was done for 5 different pressures within the calibration range and the signal values were recorded. The slope and intercept of the calibration line were calculated by fitting the 5 measured signals into a line. The signals, pressures, slopes, and intercepts for PGDMF C, PGDMF NR and PGDMF WR are presented below in Table 20, Table 21, and Table 22, respectively. Table 20 Pressure transducer calibration for PGDMF C Continuous System Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) 0.0046 0.1 0.0046 0.1 0.0050 0.2 0.0050 0.2 0.0063 0.81 0.0086 0.84 0.0079 1 0.0102 1.05 0.0171 3.02 0.0205 3.05 0.0263 5 0.0329 5.36 Slope 221.06 185.85 Intercept -0.79 -0.77 86 Table 21 Pressure transducer calibration for PGDMF NR PGDMF 3h NR Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) 0.0056 0.1 0.0060 0.1 0.0060 0.2 0.0069 0.22 0.0096 0.84 0.0102 0.83 0.0112 1.05 0.0112 1.07 0.0221 3.05 0.0217 3.02 0.0326 5.36 0.0329 5.36 Slope 192.23 Slope 195.4 Intercept -1.02 Intercept -1.13 PGDMF 8h NR Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) 0.0063 0.1 0.0066 0.11 0.0066 0.21 0.0069 0.22 0.0099 0.81 0.0102 0.8 0.0112 1.02 0.0112 1.02 0.0221 3.01 0.0221 2.99 0.0326 5.03 0.0329 5.05 Slope 185.81 Slope 186.4 Intercept -1.05 Intercept -1.09 PGDMF 2dNR Module 1 Module 2 87 Signal Pressure (psi) Signal Pressure(psi) 0.0060 0.1 0.0060 0.09 0.0063 0.2 0.0063 0.2 0.0096 0.8 0.0099 0.81 0.0112 1.1 0.0119 1 0.0211 3.01 0.0204 3.08 0.0316 5.01 0.0323 5.04 Slope 191.04 Slope 191.7 Intercept -1.03 Intercept -1.07 Table 22 Pressure Calibration of PGDMF WR PGDMF 3hWR Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) -0.0062 0.11 -0.0062 0.09 -0.0069 0.21 -0.0069 0.2 -0.0095 0.8 -0.0103 0.8 -0.0115 1.04 -0.0118 1.01 -0.0223 3.03 -0.0223 3.03 -0.0331 5.09 -0.0338 5.09 Slope -180.57 Slope -182.2 Intercept -0.99 Intercept -1.07 PGDMF 8hWR Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) 88 -0.0063 0.09 -0.0062 0.11 -0.0066 0.2 -0.0069 0.21 -0.0105 0.8 -0.0095 0.8 -0.0115 1.09 -0.0115 1.04 -0.0237 3.27 -0.0223 3.03 -0.0342 5.25 -0.0331 5.09 Slope -184.06 Slope 186.4 Intercept -1.06 Intercept -1.03 PGDMF 2dWR Module 1 Module 2 Signal Pressure (psi) Signal Pressure(psi) 0.0050 0.09 0.0046 0.1 0.0056 0.21 0.0053 0.2 0.0086 0.8 0.0086 0.8 0.0096 1 0.0099 1 0.0208 3.03 0.0208 3.03 0.0313 5.01 0.0316 5.01 Slope 186.16 Slope 182.8 Intercept -0.82 Intercept -0.77 89 Appendix C: TMP Results The transmembrane pressures of membrane modules of PGDMF C, PGDMF NR and PGDMF WR are presented below in Figure 13. (a) (b) 90 (c) Figure 13. Transmembrane pressures of membrane systems during the study (a) PGDMF C; (b) PGDMF NR and (c) PGDMF WR 91 Appendix D: Calibration of TOC Analyser The TOC analyser was calibrated using 5 standard TOC samples prepared with concentrations of 0, 5, 10, 15 and 20 mg/L of TOC. The samples were loaded in the TOC Analyser and the calibration curve was analysed and stored in a calibration curve file. The calibration curve was used in all TOC and DOC sample analyses. The calibration curve results are present in Figure 14. Figure 14. Calibration curve from the TOC Analyser 92 Appendix E: TOC, DOC and POC Results The time series TOC, DOC and POC concentrations of the feed water throughout the study are presented in Fig 15. a) b) 93 c) Figure 15. a) TOC in feed water; b) DOC in feed water; c) POC in feed water The TOC, DOC concentrations of the permeate and the drain of PGDMF systems are presented in Figure 16. a) 94 b) c) d) 95 e) f) Figure 16. a) DOC in permeate; b) DOC in drain; c) TOC in permeate; d) DOC in drain; e) POC in permeate; f) POC in drain The DOC/TOC ratios of the feed water, membrane tanks, permeate and drains in all the membrane systems are presented in Fig 17. 96 a) b) c) Figure 17. DOC/TOC ratios in (a) feed water, (b) permeate and (c) drain water 97 Pairwise comparisons of the TOC, DOC and UV254 concentrations for replicate modules of the PGDMF systems: Pairwise comparisons of the TOC, DOC and UV254 concentrations for the replicate modules were statistically similar. Their p-values are: - For TOC: for PGDMF C, p=0.379; for PGDMF 3hNR, p=0.498; for PGDMF 8hNR, p=0.159; for PGDMF 2dNR, p=0.041; for PGDMF 3hWR, p = 0.364; for PGDMF 8hWR, p = 0.217; and for PGDMF 2dWR, p= 0.013. - For DOC: for PGDMF C, p=0.129; for PGDMF 3hNR, p=0.418; for PGDMF 8hNR, p=0.825; for PGDMF 2dNR, p=0.029; for PGDMF 3hWR, p = 0.111; for PGDMF 8hWR, p = 0.046; and for PGDMF 2dWR, p= 0.087 - For UV254: for PGDMF C, p=0.035; for PGDMF 3hNR, p=0.644; for PGDMF 8hNR, p=0.056; for PGDMF 2dNR, p=0.598; for PGDMF 3hWR, p = 0.198; for PGDMF 8hWR, p = 0.355; and for PGDMF 2dWR, p= 0.162 Comparison of time series concentrations in different timelines: Single factor ANOVA tests with 99% significance concluded that the TOC and DOC concentrations, as well as UV254 absorbances, in each of the feed, permeate and reject, were statistically similar in all 3 timelines, as defined in Section 5.2, for all PGDMF systems. The p-values are presented in Table 23. 98 Table 23. p-values of ANOVA tests (99% significance) PGDMF systems Feed Permeate Reject TOC DOC UVA TOC DOC UVA TOC DOC UVA PGDMF C 0.656 0.363 0.134 0.659 0.829 0.226 0.569 0.154 0.796 PGDMF NR 0.054 0.929 0.237 0.155 0.017 0.327 PGDMF WR 0.294 0.638 0.21 0.796 0.013 0.484 Mass balance analysis: Mass balance analyses were performed on the time series TOC and DOC concentrations of the feed, permeate, and reject of the PGDMF systems to estimate TOC and DOC removal efficiencies (see Table 24). The TOC removal efficiency was estimated by dividing the difference of cumulative mass input into the PGDMF system and the cumulative mass output from the PGDMF system (DOC in permeate) divided by the cumulative mass input into the system. Similarly, the DOC removal efficiency was estimated by dividing the difference of cumulative mass input into the PGDMF system and the cumulative mass output from the PGDMF system (DOC in permeate) divided by the cumulative mass input into the PGDMF system. 99 Table 24. Cumulative mass of TOC, DOC and POC of PGDMF systems 31-Aug 03-Sep 07-Sep 10-Sep 14-Sep 17-Sep 21-Sep 24-Sep 28-Sep 01-Oct 05-Oct 08-Oct 12-Oct 15-Oct 19-Oct 22-Oct 26-Oct 29-Oct 02-Nov 05-Nov 09-Nov TOC (mg) Mass Feed PGDMF C 4.42 3.35 3.47 3.85 3.89 3.90 3.39 3.34 4.04 4.34 4.21 3.38 4.67 5.05 4.20 4.90 5.72 7.55 7.06 5.99 6.08 PGDMF NR/ WR 3.86 2.93 3.04 3.37 3.41 3.41 2.97 2.92 3.53 3.79 3.68 2.96 4.08 4.42 3.67 4.29 5.01 6.60 6.18 5.24 5.32 Permeate PGDMF C 2.07 2.04 2.33 3.19 2.37 2.93 2.82 2.14 1.51 1.16 1.22 1.57 2.44 2.72 1.68 3.91 1.18 1.50 2.62 2.62 2.74 PGDMF NR 3.44 3.32 3.51 3.72 3.54 3.05 3.73 1.95 1.92 1.63 1.50 1.65 3.05 3.44 1.64 3.43 2.72 1.86 2.09 2.22 2.69 PGDMF WR 2.45 2.42 2.61 2.70 2.50 3.08 2.92 1.94 1.94 1.37 1.46 1.47 2.78 3.20 1.87 2.97 1.85 1.94 2.64 2.41 2.55 Drain PGDMF C 3.36 3.34 3.34 3.42 3.76 3.61 3.72 3.50 2.02 3.44 1.70 1.96 1.73 1.77 1.73 1.70 2.35 1.76 2.63 2.77 2.60 PGDMF NR 3.37 3.35 3.35 3.43 3.77 3.62 3.73 3.51 3.67 3.45 1.76 1.98 1.69 1.73 1.72 2.22 2.32 1.72 2.56 2.72 2.79 PGDMF WR 3.17 3.16 3.16 3.23 3.54 3.40 3.51 3.30 4.69 3.25 1.60 1.88 1.79 1.84 1.56 2.40 1.97 1.83 2.35 2.50 2.37 Cumulative mass Feed PGDMF C 4.42 7.76 11.23 15.08 18.97 22.87 26.26 29.60 33.64 37.98 42.19 45.57 50.24 55.29 59.48 64.38 70.10 77.65 84.71 90.69 96.77 PGDMF NR/ WR 3.86 6.79 9.83 13.19 16.60 20.01 22.98 25.90 29.43 33.23 36.91 39.87 43.96 48.38 52.05 56.33 61.34 67.94 74.12 79.36 84.67 Permeate PGDMF C 2.07 4.11 6.44 9.64 12.01 14.94 17.77 19.90 21.42 22.58 23.80 25.37 27.81 30.54 32.22 36.13 37.31 38.81 41.43 44.05 46.79 PGDMF NR 3.44 6.77 10.28 14.00 17.54 20.58 24.31 26.27 28.19 29.82 31.32 32.97 36.02 39.47 41.11 44.54 47.26 49.12 51.21 53.43 56.11 PGDMF WR 2.45 4.87 7.48 10.18 12.67 15.75 18.67 20.61 22.54 23.92 25.38 26.85 29.63 32.83 34.70 37.68 39.53 41.47 44.11 46.51 49.06 Drain PGDMF C 3.36 6.70 10.04 13.46 17.22 20.83 24.55 28.05 30.07 33.51 35.21 37.16 38.89 40.66 42.39 44.10 46.44 48.20 50.83 53.60 56.21 PGDMF NR 3.37 6.72 10.06 13.50 17.27 20.89 24.62 28.13 31.79 35.24 37.00 38.99 40.68 42.41 44.13 46.35 48.67 50.39 52.95 55.67 58.47 PGDMF WR 3.17 6.33 9.49 12.72 16.26 19.66 23.17 26.47 31.16 34.41 36.01 37.89 39.69 41.52 43.08 45.49 47.46 49.29 51.64 54.14 56.51 Permeate + Drain PGDMF C 5.43 10.81 16.48 23.10 29.23 35.77 42.32 47.95 51.49 56.09 59.01 62.53 66.70 71.20 74.61 80.23 83.75 87.02 92.27 97.66 103.00 PGDMF NR 6.81 13.49 20.34 27.49 34.80 41.47 48.93 54.39 59.98 65.06 68.32 71.96 76.70 81.88 85.24 90.88 95.93 99.51 104.16 109.10 114.58 PGDMF WR 5.62 11.20 16.97 22.89 28.93 35.41 41.84 47.07 53.70 58.33 61.39 64.74 69.31 74.35 77.79 83.17 86.99 90.75 95.74 100.65 105.57 DOC (mg) Mass Feed PGDMF C 3.86 3.83 3.99 4.12 3.93 4.02 3.76 3.81 3.76 3.89 3.80 3.78 3.67 3.88 3.89 3.89 3.86 3.82 3.77 3.68 3.80 PGDMF NR/ WR 3.37 3.35 3.49 3.61 3.44 3.52 3.29 3.33 3.29 3.40 3.33 3.30 3.21 3.39 3.41 3.40 3.37 3.35 3.30 3.22 3.32 Permeate PGDMF C 1.93 1.82 2.05 2.80 3.06 2.98 2.89 2.09 1.64 1.18 1.17 1.55 2.55 2.85 1.71 3.10 1.33 1.42 2.30 2.47 2.70 PGDMF NR 1.90 1.83 1.95 2.06 3.34 3.07 3.42 1.93 2.13 1.68 1.52 1.61 2.69 3.13 1.78 2.87 2.29 1.49 1.95 1.93 2.36 PGDMF WR 1.84 1.79 1.92 1.98 3.13 2.87 2.41 1.88 1.89 1.28 1.22 1.47 2.29 2.60 1.79 2.61 1.53 1.27 2.39 2.03 2.25 Drain PGDMF C 2.20 2.20 2.59 2.66 3.19 3.36 3.32 3.25 1.81 2.66 1.57 1.51 1.44 1.47 1.53 1.67 1.66 1.46 1.49 1.50 2.12 PGDMF NR 2.33 2.32 2.87 2.95 3.54 3.72 3.81 3.60 3.39 2.95 1.63 1.69 1.59 1.63 1.63 2.10 2.19 1.62 1.65 1.66 2.35 PGDMF WR 2.05 2.07 2.75 2.82 3.39 3.34 3.34 3.45 3.04 2.83 1.52 1.59 1.72 1.76 1.58 2.49 1.78 1.75 1.79 1.80 2.13 Cumulative mass Feed PGDMF C 3.86 7.68 11.68 15.80 19.73 23.75 27.52 31.33 35.08 38.97 42.77 46.54 50.21 54.09 57.99 61.87 65.73 69.55 73.32 77.00 80.80 PGDMF NR/ WR 3.37 6.72 10.22 13.83 17.26 20.78 24.08 27.41 30.70 34.10 37.42 40.73 43.94 47.33 50.74 54.14 57.51 60.86 64.16 67.38 70.70 Permeate PGDMF C 1.93 3.74 5.79 8.59 11.66 14.64 17.53 19.62 21.26 22.44 23.61 25.16 27.71 30.56 32.27 35.37 36.70 38.11 40.42 42.89 45.58 PGDMF NR 1.90 3.73 5.69 7.75 11.09 14.16 17.57 19.50 21.63 23.31 24.83 26.44 29.13 32.26 34.03 36.91 39.20 40.69 42.64 44.57 46.93 100 PGDMF WR 1.84 3.63 5.55 7.53 10.66 13.53 15.94 17.81 19.70 20.98 22.20 23.67 25.96 28.56 30.34 32.96 34.49 35.76 38.15 40.18 42.43 Drain PGDMF C 2.20 4.40 6.99 9.65 12.84 16.20 19.52 22.77 24.58 27.24 28.81 30.33 31.76 33.23 34.76 36.43 38.09 39.55 41.05 42.55 44.67 PGDMF NR 2.33 4.65 7.52 10.47 14.00 17.72 21.54 25.14 28.53 31.48 33.10 34.80 36.39 38.01 39.64 41.74 43.93 45.55 47.20 48.87 51.21 PGDMF WR 2.05 4.12 6.87 9.69 13.08 16.42 19.76 23.22 26.25 29.08 30.60 32.19 33.91 35.67 37.25 39.74 41.52 43.27 45.06 46.86 48.98 Permeate + Drain PGDMF C 4.25 8.39 13.31 19.06 25.66 32.36 39.07 44.76 49.79 53.91 56.71 59.96 64.10 68.57 71.91 77.11 80.63 83.66 87.62 91.75 96.80 PGDMF NR 4.10 8.13 12.68 17.40 23.93 30.35 37.09 42.27 46.21 50.55 53.64 56.76 60.89 65.49 68.80 73.34 77.29 80.24 83.69 87.12 91.61 PGDMF WR 3.89 7.75 12.42 17.22 23.74 29.95 35.70 41.03 45.95 50.06 52.80 55.86 59.87 64.23 67.59 72.69 76.01 79.03 83.20 87.03 91.41 POC (mg) Mass Feed PGDMF C 0.92 0.70 0.72 0.80 0.81 0.81 0.71 0.70 0.84 0.90 0.88 -0.28 0.97 1.05 0.88 1.02 1.19 1.57 1.47 1.25 1.27 PGDMF NR/WR 0.81 0.61 0.63 0.70 0.71 0.71 0.62 0.61 0.74 0.79 0.77 -0.24 0.85 0.92 0.77 0.89 1.04 1.38 1.29 1.09 1.11 Permeate PGDMF C 0.10 0.10 0.11 0.15 0.11 0.14 0.13 0.10 0.07 0.06 0.06 0.07 0.12 0.13 0.08 0.19 0.06 0.07 0.13 0.12 0.13 PGDMF NR 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.02 0.02 0.02 0.02 0.02 0.04 0.04 0.02 0.04 0.03 0.02 0.02 0.03 0.03 PGDMF WR 0.31 0.30 0.33 0.34 0.31 0.39 0.37 0.24 0.24 0.17 0.18 0.18 0.35 0.40 0.23 0.37 0.23 0.24 0.33 0.30 0.32 Drain PGDMF C 0.37 0.37 0.37 0.38 0.41 0.40 0.41 0.38 0.22 0.38 0.19 0.21 0.19 0.19 0.19 0.19 0.26 0.19 0.29 0.30 0.29 PGDMF NR 0.19 0.19 0.19 0.19 0.21 0.20 0.21 0.20 0.21 0.19 0.10 0.11 0.10 0.10 0.10 0.13 0.13 0.10 0.14 0.15 0.16 PGDMF WR 0.23 0.23 0.23 0.23 0.26 0.25 0.26 0.24 0.34 0.24 0.12 0.14 0.13 0.13 0.11 0.17 0.14 0.13 0.17 0.18 0.17 Cumulative mass Feed PGDMF C 0.92 1.62 2.34 3.15 3.96 4.77 5.48 6.18 7.02 7.93 8.80 8.53 9.50 10.55 11.43 12.45 13.65 15.22 16.69 17.94 19.21 PGDMF NR/ WR 0.81 1.42 2.05 2.75 3.46 4.18 4.80 5.41 6.14 6.94 7.70 7.46 8.31 9.23 10.00 10.90 11.94 13.32 14.61 15.70 16.81 Permeate PGDMF C 0.10 0.20 0.31 0.46 0.57 0.71 0.85 0.95 1.02 1.08 1.13 1.21 1.33 1.46 1.54 1.72 1.78 1.85 1.98 2.10 2.23 PGDMF NR 0.04 0.08 0.12 0.16 0.21 0.24 0.29 0.31 0.33 0.35 0.37 0.39 0.42 0.47 0.48 0.52 0.56 0.58 0.60 0.63 0.66 PGDMF WR 0.31 0.61 0.94 1.27 1.59 1.97 2.34 2.58 2.82 2.99 3.18 3.36 3.71 4.11 4.34 4.72 4.95 5.19 5.52 5.82 6.14 Drain PGDMF C 0.37 0.74 1.10 1.48 1.89 2.29 2.69 3.08 3.30 3.68 3.86 4.08 4.27 4.46 4.65 4.84 5.10 5.29 5.58 5.88 6.17 PGDMF NR 0.19 0.38 0.57 0.76 0.97 1.18 1.39 1.59 1.79 1.99 2.09 2.20 2.29 2.39 2.49 2.61 2.74 2.84 2.99 3.14 3.30 PGDMF WR 0.23 0.46 0.69 0.93 1.18 1.43 1.69 1.93 2.27 2.51 2.62 2.76 2.89 3.02 3.14 3.31 3.46 3.59 3.76 3.94 4.11 Permeate + Drain PGDMF C 0.47 0.93 1.41 1.94 2.46 3.00 3.54 4.03 4.32 4.75 5.00 5.29 5.59 5.92 6.19 6.56 6.88 7.14 7.55 7.98 8.40 PGDMF NR 0.23 0.46 0.69 0.93 1.18 1.42 1.67 1.90 2.12 2.34 2.46 2.59 2.72 2.86 2.97 3.14 3.30 3.42 3.59 3.77 3.96 PGDMF WR 0.54 1.07 1.63 2.20 2.77 3.40 4.02 4.51 5.09 5.50 5.80 6.12 6.60 7.13 7.48 8.03 8.40 8.78 9.28 9.76 10.26 12-Nov 16-Nov 19-Nov 23-Nov 26-Nov 30-Nov 03-Dec 07-Dec 10-Dec 14-Dec 17-Dec 21-Dec 24-Dec 28-Dec 31-Dec 04-Jan 07-Jan 11-Jan 14-Jan 18-Jan 21-Jan TOC (mg) Mass Feed PGDMF C 6.73 5.74 6.53 6.79 6.61 6.71 5.54 5.76 6.56 6.17 6.21 6.41 6.82 5.92 6.78 6.02 6.00 7.08 6.94 5.99 5.70 PGDMF NR/ WR 5.89 5.02 5.72 5.95 5.79 5.87 4.85 5.04 5.74 5.40 5.43 5.61 5.97 5.18 5.93 5.27 5.25 6.19 6.08 5.24 4.99 Permeate PGDMF C 3.15 2.97 4.03 3.31 4.08 4.17 1.84 1.90 3.73 4.01 3.53 4.18 4.34 3.16 4.22 3.17 2.02 4.45 4.33 2.00 1.92 PGDMF NR 2.66 4.05 3.77 3.25 3.82 3.87 2.40 2.49 4.01 4.31 3.80 4.52 4.02 4.28 3.96 4.37 2.66 4.19 4.07 2.64 2.38 PGDMF WR 3.04 2.86 3.72 2.87 3.76 3.82 2.19 2.28 3.37 3.62 3.20 3.81 4.07 2.91 3.92 3.10 2.45 4.32 4.20 2.52 2.31 Drain PGDMF C 1.82 2.07 1.84 1.91 1.86 1.89 1.75 1.83 1.85 1.73 1.73 1.77 1.80 2.12 1.87 2.05 1.81 1.89 1.89 1.83 1.87 PGDMF NR 2.15 2.41 1.80 1.90 1.82 1.85 1.82 1.89 1.80 1.69 1.69 1.73 1.76 2.46 1.82 2.38 1.88 1.85 1.85 1.90 1.94 101 PGDMF WR 2.22 1.81 1.91 1.89 1.93 1.96 1.65 1.72 1.91 1.79 1.80 1.83 1.87 1.85 1.93 1.79 1.71 1.96 1.96 1.73 1.76 Cumulative mass Feed PGDMF C 103.50 109.24 115.77 122.57 129.18 135.89 141.43 147.18 153.75 159.91 166.12 172.54 179.36 185.28 192.06 198.08 204.09 211.16 218.11 224.10 229.80 PGDMF NR/ WR 90.56 95.58 101.30 107.25 113.03 118.90 123.75 128.78 134.53 139.92 145.36 150.97 156.94 162.12 168.06 173.32 178.58 184.77 190.84 196.09 201.07 Permeate PGDMF C 49.94 52.90 56.94 60.25 64.32 68.49 70.33 72.22 75.96 79.96 83.49 87.68 92.02 95.17 99.39 102.56 104.58 109.02 113.35 115.35 117.27 PGDMF NR 58.78 62.83 66.60 69.85 73.66 77.54 79.94 82.43 86.44 90.75 94.55 99.07 103.09 107.36 111.32 115.69 118.35 122.54 126.61 129.25 131.63 PGDMF WR 52.10 54.95 58.67 61.54 65.30 69.12 71.31 73.59 76.96 80.57 83.78 87.58 91.65 94.55 98.47 101.57 104.02 108.34 112.54 115.07 117.38 Drain PGDMF C 58.03 60.11 61.95 63.86 65.72 67.61 69.37 71.19 73.04 74.77 76.50 78.27 80.07 82.19 84.05 86.10 87.91 89.81 91.69 93.53 95.40 PGDMF NR 60.62 63.03 64.83 66.73 68.55 70.40 72.22 74.11 75.91 77.60 79.30 81.03 82.79 85.25 87.08 89.46 91.34 93.18 95.03 96.93 98.87 PGDMF WR 58.73 60.54 62.45 64.33 66.26 68.22 69.88 71.60 73.51 75.30 77.10 78.93 80.80 82.65 84.59 86.38 88.09 90.05 92.01 93.73 95.50 Permeate + Drain PGDMF C 107.97 113.01 118.89 124.10 130.05 136.10 139.69 143.42 148.99 154.73 159.99 165.94 172.09 177.36 183.45 188.67 192.49 198.83 205.05 208.88 212.67 PGDMF NR 119.39 125.86 131.43 136.58 142.22 147.94 152.15 156.54 162.35 168.35 173.85 180.09 185.88 192.62 198.40 205.14 209.69 215.72 221.64 226.18 230.50 PGDMF WR 110.82 115.50 121.12 125.87 131.57 137.34 141.19 145.19 150.47 155.88 160.88 166.51 172.45 177.21 183.06 187.95 192.11 198.39 204.55 208.80 212.88 DOC (mg) Mass Feed PGDMF C 4.12 4.82 4.83 4.82 4.83 4.83 4.84 4.83 4.84 4.85 4.87 4.94 5.15 4.87 4.94 5.11 5.09 5.09 5.00 5.01 4.67 PGDMF NR/ WR 3.61 4.21 4.22 4.22 4.22 4.23 4.24 4.23 4.23 4.25 4.26 4.32 4.51 4.26 4.32 4.47 4.45 4.45 4.38 4.39 4.08 Permeate PGDMF C 3.14 3.01 4.02 2.73 4.07 4.15 1.76 1.82 4.23 3.98 4.00 3.77 3.93 2.91 3.82 2.92 1.76 4.03 3.92 1.74 1.67 PGDMF NR 3.12 3.49 4.41 3.17 4.46 4.53 2.42 2.52 5.14 4.72 4.87 4.95 4.69 3.67 4.62 3.77 2.69 4.90 4.76 2.67 2.40 PGDMF WR 2.66 2.61 3.24 2.69 3.28 3.33 1.84 1.91 3.68 3.46 3.50 3.64 3.54 2.65 3.41 2.83 2.05 3.62 3.52 2.03 1.86 Drain PGDMF C 2.15 1.89 2.17 1.80 2.19 2.22 1.62 1.69 1.53 1.43 1.44 1.47 2.12 1.93 2.20 1.87 1.67 2.23 2.22 1.69 1.73 PGDMF NR 2.38 1.72 2.40 1.87 2.43 2.46 1.68 1.75 1.69 1.59 1.59 1.62 2.35 1.75 2.43 1.70 1.73 2.46 2.46 1.76 1.79 PGDMF WR 1.99 1.64 2.01 1.78 2.03 2.06 1.56 1.63 1.83 1.72 1.72 1.76 1.96 1.67 2.03 1.62 1.62 2.06 2.06 1.64 1.67 Cumulative mass Feed PGDMF C 84.93 89.74 94.57 99.39 104.22 109.05 113.89 118.72 123.56 128.41 133.28 138.22 143.37 148.24 153.18 158.29 163.37 168.46 173.46 178.48 183.14 PGDMF NR/ WR 74.31 78.52 82.75 86.97 91.19 95.42 99.66 103.88 108.12 112.36 116.62 120.94 125.45 129.71 134.03 138.50 142.95 147.40 151.78 156.17 160.25 Permeate PGDMF C 48.72 51.73 55.75 58.48 62.55 66.70 68.46 70.28 74.51 78.49 82.49 86.27 90.20 93.11 96.93 99.86 101.62 105.64 109.57 111.31 112.99 PGDMF NR 50.05 53.55 57.96 61.12 65.58 70.11 72.53 75.05 80.19 84.91 89.77 94.72 99.41 103.09 107.71 111.48 114.17 119.07 123.82 126.49 128.89 PGDMF WR 45.09 47.70 50.94 53.63 56.91 60.23 62.07 63.98 67.66 71.12 74.62 78.27 81.81 84.47 87.88 90.71 92.77 96.39 99.91 101.94 103.81 Drain PGDMF C 46.82 48.70 50.87 52.67 54.86 57.09 58.71 60.40 61.93 63.36 64.80 66.26 68.38 70.31 72.51 74.37 76.05 78.27 80.49 82.19 83.92 PGDMF NR 53.59 55.31 57.70 59.57 62.00 64.46 66.14 67.89 69.59 71.17 72.76 74.39 76.73 78.49 80.92 82.62 84.35 86.81 89.28 91.03 92.82 PGDMF WR 50.97 52.61 54.62 56.40 58.43 60.49 62.05 63.68 65.52 67.23 68.95 70.71 72.67 74.35 76.38 78.00 79.62 81.68 83.74 85.38 87.05 Permeate + Drain PGDMF C 102.31 107.04 113.46 118.06 124.55 131.16 134.60 138.17 144.10 149.66 155.26 160.65 166.93 171.60 177.85 182.47 185.97 192.46 198.84 202.34 205.81 PGDMF NR 96.87 102.25 108.83 113.80 120.45 127.19 131.24 135.44 142.11 148.27 154.57 160.99 167.80 173.40 180.22 185.85 190.22 197.34 204.32 208.68 212.81 PGDMF WR 96.06 100.31 105.55 110.02 115.33 120.72 124.12 127.66 133.18 138.36 143.58 148.98 154.49 158.82 164.26 168.72 172.38 178.07 183.65 187.32 190.85 POC (mg) Mass Feed PGDMF C 1.40 1.20 1.36 1.42 1.38 1.40 1.16 1.20 1.37 1.29 1.30 1.34 1.42 1.24 1.41 1.26 1.25 1.48 1.45 1.25 1.19 PGDMF NR/WR 1.23 1.05 1.19 1.24 1.21 1.23 1.01 1.05 1.20 1.13 1.13 1.17 1.25 1.08 1.24 1.10 1.10 1.29 1.27 1.10 1.04 Permeate PGDMF C 0.15 0.14 0.19 0.16 0.19 0.20 0.09 0.09 0.18 0.19 0.17 0.20 0.21 0.15 0.20 0.15 0.10 0.21 0.21 0.10 0.09 102 PGDMF NR 0.03 0.05 0.04 0.04 0.05 0.05 0.03 0.03 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.03 0.05 0.05 0.03 0.03 PGDMF WR 0.38 0.36 0.46 0.36 0.47 0.48 0.27 0.29 0.42 0.45 0.76 0.48 0.51 0.36 0.49 0.39 0.31 0.52 0.51 0.30 0.28 Drain PGDMF C 0.20 0.23 0.20 0.21 0.20 0.21 0.19 0.20 0.20 0.19 0.19 0.19 0.20 0.23 0.21 0.23 0.20 0.21 0.21 0.20 0.21 PGDMF NR 0.12 0.14 0.10 0.11 0.10 0.10 0.10 0.11 0.10 0.10 0.10 0.10 0.10 0.14 0.10 0.13 0.11 0.10 0.10 0.11 0.11 PGDMF WR 0.16 0.13 0.14 0.14 0.14 0.14 0.12 0.13 0.14 0.13 0.13 0.13 0.14 0.13 0.14 0.13 0.12 0.14 0.14 0.13 0.13 Cumulative mass Feed PGDMF C 20.61 21.81 23.17 24.59 25.97 27.37 28.53 29.73 31.10 32.39 33.68 35.02 36.45 37.68 39.10 40.35 41.61 43.08 44.53 45.78 46.97 PGDMF NR/ WR 18.04 19.08 20.28 21.52 22.73 23.95 24.96 26.01 27.21 28.34 29.47 30.64 31.89 32.97 34.21 35.31 36.40 37.70 38.97 40.06 41.10 Permeate PGDMF C 2.38 2.52 2.71 2.87 3.07 3.27 3.35 3.44 3.62 3.81 3.98 4.18 4.39 4.54 4.74 4.89 4.99 5.20 5.41 5.50 5.59 PGDMF NR 0.69 0.74 0.79 0.82 0.87 0.91 0.94 0.97 1.02 1.07 1.12 1.17 1.22 1.27 1.31 1.36 1.40 1.45 1.49 1.52 1.55 PGDMF WR 6.52 6.88 7.34 7.70 8.17 8.65 8.93 9.21 9.63 10.09 10.85 11.32 11.83 12.20 12.69 13.07 13.38 13.90 14.41 14.71 14.99 Drain PGDMF C 6.37 6.60 6.80 7.01 7.21 7.42 7.61 7.81 8.02 8.21 8.40 8.59 8.79 9.02 9.22 9.45 9.65 9.86 10.06 10.26 10.47 PGDMF NR 3.42 3.55 3.66 3.76 3.87 3.97 4.07 4.18 4.28 4.38 4.47 4.57 4.67 4.81 4.91 5.04 5.15 5.25 5.36 5.47 5.58 PGDMF WR 4.28 4.41 4.55 4.68 4.82 4.97 5.09 5.21 5.35 5.48 5.61 5.75 5.88 6.02 6.16 6.29 6.41 6.56 6.70 6.82 6.95 Permeate + Drain PGDMF C 8.75 9.12 9.51 9.88 10.28 10.69 10.97 11.26 11.64 12.02 12.38 12.77 13.18 13.56 13.97 14.34 14.64 15.06 15.47 15.77 16.06 PGDMF NR 4.11 4.30 4.44 4.59 4.74 4.89 5.02 5.15 5.30 5.45 5.59 5.74 5.89 6.07 6.22 6.41 6.55 6.70 6.85 6.99 7.13 PGDMF WR 10.80 11.29 11.89 12.39 13.00 13.62 14.01 14.42 14.98 15.57 16.46 17.07 17.71 18.21 18.84 19.36 19.79 20.46 21.11 21.53 21.94 25-Jan 28-Jan 01-Feb 04-Feb 08-Feb 11-Feb 15-Feb 18-Feb TOC (mg) Mass Feed PGDMF C 7.30 6.21 6.14 5.89 5.87 6.03 6.08 6.18 PGDMF NR/ WR 6.39 5.43 5.37 5.15 5.13 5.28 5.32 5.41 Permeate PGDMF C 4.43 2.00 2.04 1.95 1.95 1.93 1.95 1.98 PGDMF NR 4.35 2.76 2.63 2.52 2.51 2.60 2.62 2.65 PGDMF WR 4.45 2.62 2.59 2.48 2.47 2.49 2.51 2.54 Drain PGDMF C 1.96 1.90 1.92 1.84 1.84 1.93 1.94 1.99 PGDMF NR 1.91 1.96 1.99 1.91 1.90 2.00 2.01 2.06 PGDMF WR 2.03 1.79 1.81 1.74 1.73 1.82 1.83 1.88 Cumulative mass Feed PGDMF C 237.10 243.31 249.45 255.34 261.20 267.23 273.31 279.49 PGDMF NR/ WR 207.46 212.89 218.27 223.42 228.55 233.83 239.15 244.56 Permeate PGDMF C 121.70 123.71 125.74 127.70 129.64 131.58 133.53 135.51 PGDMF NR 135.97 138.73 141.36 143.89 146.40 149.00 151.62 154.27 PGDMF WR 121.83 124.46 127.05 129.53 132.00 134.49 137.00 139.54 Drain PGDMF C 97.36 99.25 101.17 103.02 104.85 106.79 108.73 110.72 PGDMF NR 100.78 102.75 104.74 106.65 108.56 110.56 112.57 114.64 PGDMF WR 97.53 99.31 101.13 102.86 104.60 106.42 108.25 110.12 PGDMF C 219.06 222.96 226.92 230.72 234.50 238.36 242.26 246.23 103 Permeate + Drain PGDMF NR 236.76 241.48 246.11 250.54 254.96 259.56 264.19 268.91 PGDMF WR 219.36 223.77 228.17 232.40 236.60 240.91 245.25 249.67 DOC (mg) Mass Feed PGDMF C 5.08 5.02 4.90 4.90 4.90 4.79 4.80 4.76 PGDMF NR/ WR 4.44 4.39 4.28 4.28 4.28 4.19 4.20 4.17 Permeate PGDMF C 4.02 1.75 1.78 1.70 1.78 1.61 1.70 1.72 PGDMF NR 5.08 2.79 2.66 2.54 2.67 2.50 2.64 2.68 PGDMF WR 3.74 2.11 2.08 1.99 2.09 1.91 2.02 2.05 Drain PGDMF C 2.30 1.75 1.78 1.70 1.79 1.70 1.80 1.84 PGDMF NR 2.55 1.82 1.84 1.76 1.85 1.77 1.86 1.91 PGDMF WR 2.13 1.69 1.72 1.64 1.72 1.65 1.73 2.78 Cumulative mass Feed PGDMF C 188.22 193.24 198.14 203.03 207.93 212.71 217.51 222.28 PGDMF NR/ WR 164.69 169.09 173.37 177.65 181.94 186.12 190.32 194.49 Permeate PGDMF C 117.00 118.75 120.53 122.23 124.01 125.62 127.32 129.05 PGDMF NR 133.97 136.76 139.41 141.95 144.62 147.12 149.77 152.45 PGDMF WR 107.55 109.66 111.74 113.73 115.82 117.73 119.75 121.80 Drain PGDMF C 86.22 87.97 89.75 91.44 93.23 94.93 96.73 98.57 PGDMF NR 95.37 97.19 99.03 100.79 102.64 104.41 106.27 108.17 PGDMF WR 89.18 90.87 92.59 94.23 95.95 97.60 99.33 102.11 Permeate + Drain PGDMF C 212.38 215.94 219.56 223.01 226.65 230.03 233.59 237.22 PGDMF NR 220.19 224.73 229.16 233.39 237.85 242.06 246.50 260.62 PGDMF WR 196.72 200.53 204.33 207.95 211.77 215.33 219.08 223.91 POC (mg) Mass Feed PGDMF C 1.52 1.30 1.28 1.23 1.22 1.26 1.27 1.29 PGDMF NR/WR 1.33 1.13 1.12 1.08 1.07 1.10 1.11 1.13 Permeate PGDMF C 0.21 0.10 0.10 0.09 0.09 0.09 0.09 0.09 PGDMF NR 0.05 0.03 0.03 0.03 0.03 0.03 0.03 0.03 PGDMF WR 0.54 0.32 0.31 0.30 0.30 0.30 0.30 0.31 Drain PGDMF C 0.21 0.21 0.21 0.20 0.20 0.21 0.21 0.22 PGDMF NR 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.12 PGDMF WR 0.15 0.13 0.13 0.13 0.13 0.13 0.13 0.14 Cumulative mass Feed PGDMF C 48.50 49.79 51.07 52.30 53.53 54.78 56.05 57.34 PGDMF NR/ WR 42.43 43.57 44.69 45.76 46.84 47.94 49.05 50.18 Permeate PGDMF C 5.81 5.90 6.00 6.09 6.19 6.28 6.37 6.47 PGDMF NR 1.60 1.64 1.67 1.70 1.73 1.76 1.79 1.82 PGDMF WR 15.53 15.84 16.15 16.45 16.75 17.05 17.35 17.66 104 Drain PGDMF C 10.68 10.89 11.10 11.31 11.51 11.72 11.93 12.15 PGDMF NR 5.68 5.79 5.91 6.01 6.12 6.23 6.35 6.46 PGDMF WR 7.10 7.23 7.36 7.49 7.61 7.75 7.88 8.02 Permeate + Drain PGDMF C 16.49 16.79 17.10 17.40 17.69 18.00 18.30 18.62 PGDMF NR 7.29 7.43 7.57 7.71 7.85 7.99 8.14 8.28 PGDMF WR 22.63 23.07 23.52 23.94 24.37 24.80 25.23 25.68 105 The cumulative masses of the TOC, DOC and POC concentrations in the PGDMF systems are presented in Fig. 18, 19 and 20. Figure 18. Cumulative mass of TOC in a) PGDMF C; b) PGDMF NR and c) PGDMF WR Figure 19. Cumulative mass of DOC in a) PGDMF C; b) PGDMF NR and c) PGDMF WR 106 Figure 20. Cumulative mass of POC in a) PGDMF C; b) PGDMF NR and c) PGDMF WR 107 Appendix F: UV254 Results The UV absorbance measured in the feed water, the permeate and the drain of all the PGDMF systems are presented in Fig 21. a) b) c) Figure 21. a) UV absorbance in feed; b) UV absorbance in permeate; c) UV absorbance in drain of the PGDMF systems 108 Appendix G: Clean Water Permeability Tests Each new membrane module was cleaned prior to the beginning of the study using a specific chemical cleaning protocol. The cleaning agent used was sodium hypochlorite prepared with a mixture of bleach (Javex ® 12, Clorox Commercial Solutions) and DI water. As soon as new membrane modules were potted, they were cleaned using the following protocol (Robinson, 2018): 1. New membrane modules were soaked in a tank containing 500 ppm sodium hypochlorite solution for 24h. 2. The membrane tanks were filled with fresh 500 ppm sodium hypochlorite solution and the membrane modules were permeated for 15 min. 3. The water tanks were drained and refilled with DI water, and the modules are permeated for 30 min. 4. If not immediately used, the membrane modules were stored in a Ziploc bag with 5 ppm sodium hypochlorite solution at T<4℃. Membrane integrity test: Before the start of the study, the integrity of the cleaned membrane modules is verified using the pressure hold test. The pressure hold test setup is illustrated in Fig 22. The protocol for membrane integrity test is as follows (Jain, 2019): 1. Each membrane module was submerged in DI water and pressurized using compressed air (8 psi). 2. The pressure in the pressurized module was then monitored for 2 minutes using a pressure gauge. 109 If any drastic pressure drops or bubble formation was identified, the module was considered breached and was discarded. Figure 22. Membrane Integrity Test Setup (Khadem, 2016) Clean Water Permeability Tests: Following the membrane cleaning and the membrane integrity tests clean water permeability tests were performed to measure their intrinsic permeability. The clean water permeability test was performed as follows: 1. The membrane modules were permeated with DI water for approximately 3 hours with the permeate pumps operating at 50 rpm. 2. The TMP was measured over the course of 3 hours and the temperature and flux were measured at the end according to sections 4.2. 110 3. The membrane permeability was calculated and corrected to 20℃ according to equations 1 and 2. The results of the clean water tests are presented in Section 4.2. 111 Appendix H: Assessment of Normalized Permeability Pairwise comparison of normalized permeabilities for replicate membrane modules: The p-values for the pairwise comparisons of replicate membrane modules of the PGDMF systems are: for PGDMF C, p=0.992; for PGDMF 3hNR, p=0.132; for PGDMF 8hNR, p=0.15; for PGDMF 2dNR, p= 0.046; for PGDMF 8hWR, p = 0.243; and for PGDMF 2dWR, p= 0.414. Assessment of normalized permeability: The difference in normalized permeabilities of the PGDMF systems and their correlation to operational conditions such as, cumulative flow (with and without permeate recycling during periods of no inflow), fraction of time on, and fraction of time off were assessed. Correlation between normalized permeability and cumulative flow: The plot between normalized permeability and cumulative flow of PGDMF systems are illustrated in Fig 23. Fig 23. suggests that cumulative flow (thereby cumulative hydraulic loading) does not impact the normalized permeability of PGDMF systems. 112 Figure 23. Normalized Permeability vs cumulative flow Correlation between normalized permeability and fraction of time off: The plot between normalized permeability of PGDMF systems and fraction of time off are illustrated in Fig 24. Fig 24. suggests that PGDMF systems operated with permeate recycling during periods of no inflow had a greater normalized permeability than PGDMF systems operated without permeate recycling during periods of no inflow. Figure 24. Normalized permeability vs fraction of time off 00.20.40.60.811.21.40 0.2 0.4 0.6 0.8 1 1.2Normalized PermeabilityCumulative flow (day)Continuous 3hNR 8hNR 2dNR 3hWR 8hNR 2dWR00.20.40.60.811.21.40 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4Normalized PermeabilityFraction of time off (average time off/day)Continuous 3hNR 8hNR 2dNR 3hWR 8hNR 2dWR 113 Correlation between normalized permeability and fraction of time on: The plot between normalized permeability of PGDMF systems and fraction of time off are illustrated in Fig 25. Figure 25. Normalized permeability vs fraction of time on Fig 25. suggests that PGDMF systems operated with permeate recycling during periods of no inflow had a greater normalized permeability than PGDMF systems operated without permeate recycling during periods of no inflow, as previously discussed. Correlation between normalized permeability and cumulative DOC removed: The plot between normalized permeability of PGDMF systems and cumulative doc removal are illustrated in Fig 26. 00.20.40.60.811.21.40 0.2 0.4 0.6 0.8 1 1.2Normalized PermeabiityFraction of time on (average time on/day)Continuous 3hNR 8hNR 2dNR 3hWR 8hNR 2dWR 114 Figure 26. Normalized Permeability vs cumulative DOC removed Fig 26. suggests that PGDMF systems operated with permeate recycling during periods of no inflow had greater cumulative DOC removal than PGDMF systems operated without permeate recycling during periods of no inflow, as previously discussed. Also, PGDMF systems operated continuously had a similar DOC removal to PGDMF systems operated with permeate recycling during periods of no inflow. These results suggest that there is possibly more than one governing mechanism that causes differences in membrane permeability in PGDMF systems. 00.20.40.60.811.21.40 10 20 30 40 50 60 70 80Normalized PermeabilityCumulative DOC removed (mg)Continuous 3hNR 8hNR 2dNR 3hWR 8hNR 2dWR
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Bérubé, Pierre R.
Intermittent operations of passive membrane systems
Text