A major challenge facing widespread implementation of membrane-based water purification is fouling, which results in increased operating costs and reduced membrane lifetime. This thesis focuses on various methods, including novel membrane surface modifications and polymers that resist degradation when exposed to oxidizing agents used as disinfectants, to alleviate membrane fouling. Fouling-resistant ultrafiltration membrane coatings were prepared from poly(ethylene glycol) diglycidyl ether-crosslinked chitosan (chi-PEG hybrid). Composite membranes were prepared for oil-water emulsion filtration by coating the most promising chi-PEG hybrid onto a polysulfone ultrafiltration membrane. Optimization of the coating layer thickness led to composite membranes that exhibited water flux values more than 5 times higher than that of uncoated membranes after one day of oily-water crossflow filtration. The organic rejection of the coated membranes was also higher than that of the uncoated polysulfone membranes. Polydopamine (PDOPA) deposition was discovered to reduce fouling in water purification membranes. PDOPA was found to deposit from solution onto virtually any surface. When deposited on water purification membranes, PDOPA rendered the membrane more hydrophilic and less susceptible to fouling. Moreover, covalent binding of other molecules, such as amine-terminated poly (ethylene glycol) (PEG), to PDOPA is simple and performed using benign chemicals and conditions. Commercially-available polymeric membranes were modified with polydopamine, and all showed improved fouling resistance while filtering oil-water emulsions. To demonstrate the versatility and ease of PDOPA modification scalability, PDOPA was deposited on entire membrane modules, and the resulting modified module exhibited improved fouling resistance. Finally, high ion rejection, chlorine-tolerant sulfonated polysulfone thin-film composite membranes were prepared and characterized. Interestingly, freestanding thick sulfonated poly(arylene ether sulfone) (BPS) films exhibit nearly neutral electrostatic charge, even though sulfonation introduces fixed negative charge into the polymer structure. As a result, charge exclusion ion partitioning is not a dominant rejection mechanism in these films. However, composite membranes prepared from a BPS coating layer and a porous Udel polysulfone support exhibit a negatively charged surface and, presumably, charge exclusion would be a more important partitioning mechanism for these membranes. Therefore, thick BPS films do not exhibit certain drawbacks, such as reduced salt rejection of mixed-valence feeds, that are observed in BPS thin-film composite membranes. / text

With the aim of mitigating membrane fouling, an electrocoagulation (EC) based electrokinetic membrane bioreactor (EMBR) was developed and operated with real municipal wastewater under low temperatures. Both batch tests and continuous EMBR experiments demonstrated the significant advantages in membrane fouling reduction over the conventional antifouling strategies, ushering its potential applications as an attractive hybrid MBR technology for decentralized wastewater treatment in remote cold regions. The main research observations and findings could be summarized as follows: (1). Effective membrane fouling mitigation at low temperatures was due to destruction of extracellular polymeric substances (EPS) and subsequent reduction of the biocake resistance. The transmembrane pressure (TMP) increased at a much slower rate in EMBR and the filtration resistance was about one third of the control MBR prior to chemical cleaning cycle; (2). A new membrane parameter, the specific fouling rate (SFR) was proposed, relating the fouling rate with permeate flux and temperature-dependent viscosity. Pore clogging and biocake resistances were quantified for the first time with the same membrane module and operating conditions as in regular MBR, rather than resorting to the use of batch filtration setups; (3). The floc size in EMBR did not increase as a result of the air scouring shear force and decrease in the extracellular polymeric substances (EPS); (4). When current intensity was less than 0.2 A, polarity reversal had minimal impact on electrode passivation reduction due to insignificant hydrogen yield, however, if current intensity was above 0.2 A, frequent polarity reversal (< 5 min per cycle) was detrimental to electrode passivation if no sufficient mixing was provided; (5). Viability of the microorganisms in the EMBR system was found to be dependent on duration of the current application and current density. The bacterial viability was not significantly affected when the applied current density was less than 6.2 A/m2; (6). Significant abiotic ammonification was found in electrocoagulation (EC). DO in the treated liquid was depleted within an hour, under the anaerobic condition in EC, nitrate was chemometrically reduced to ammonium following a two-step first order reaction kinetics. Aeration (DO > 2 mg/L) was shown effective in suppressing abiotic ammonification; (7). Magnetic resonance imaging (MRI) technology was used for the first time as an in-situ non-invasive imaging tool to observe membrane fouling status in an EMBR. / October 2016

The objective of drinking water treatment is to provide water which is free of pathogens, is chemically and biologically stable, and is of good aesthetic quality. Natural organic matter (NOM) is present in all natural waters and can make meeting these goals more challenging. Not only does it undergo adverse reactions with disinfectants such as chlorine, it also impacts the biological stability of water within the distribution system and contributes to undesirable aesthetic qualities such as taste and odour. NOM has also been implicated in membrane fouling, which continues to be a significant operational problem preventing wider implementation of this process. Due to its highly variable heterogeneous nature, NOM can be difficult to characterize in terms of its specific composition, however recent analytical advancements are allowing for a better understanding of its behaviour in water treatment. Two promising tools for NOM characterization include Liquid Chromatography Organic Carbon Detection (LC-OCD) and Fluorescence Excitation Emission Matrix (FEEM) analyses. In this research both techniques were applied to samples taken from five full scale facilities in Ontario, Canada over all four seasons. The source waters for these treatment locations consisted of both river (Grand River, Ottawa River) and Great Lake waters (Lake Huron, Lake Erie, Lake Ontario), and an additional raw source (Saugeen River) was also monitored. The plants all employed granular media filtration, but had differences including enhanced coagulation, ozonation, biofiltration and sand ballasted flocculation. Other relevant water quality parameters were also monitored (TOC, DOC, UV254, pH, conductivity etc.) as well as plant operating conditions (dosages, flows, filter run times etc.) to investigate their impact on removal of specific NOM fractions. Four of the waters (Grand River, Ottawa River, Lake Erie and Lake Ontario) were selected based on the initial survey due to their NOM composition, for bench scale ultrafiltration (UF) membrane fouling experiments. The experiments were run at constant flux for a period of five days, with an automated permeation cycle and backwash. The impact of biopolymers on hydraulically reversible and irreversible fouling was of specific interest. Important seasonal trends were identified for all waters, with biopolymer content increasing at higher temperatures. Useful comparisons could also be made between different treatment processes including conventional and enhanced coagulation. The enhanced process while significantly improving the removal of humic substances, was not beneficial in terms of biopolymer removal, suggesting a different removal mechanism for these two fractions. The removal of low molecular weight ozonation by-products during full scale biofiltration was well demonstrated, and other fractions (building blocks, biopolymers) had varying degrees of removal, which was more dependent on temperature. Principle component analysis (PCA), an advanced multivariate statistical method, was successfully applied to a FEEM data set containing five different waters at varying degrees of treatment. Three principle components related to humic-like, protein-like and particulate/colloidal material were identified, and served as useful complementary information to the LC-OCD results. The humic-like component was found to have relatively good correlation to the humic fraction from LC-OCD analysis, with some deviation in the post-ozonation samples (which underwent greater structural changes not captured by LC-OCD). The biopolymer fraction was shown to have good correlation to hydraulically reversible membrane fouling across all four waters. The same could not be said for hydraulically irreversible fouling for which a combined fouling layer (with particulate and colloidal material) is hypothesized. This research provides those working in the water treatment sector with greater insight into NOM behaviour during various levels of treatment. As biopolymers were demonstrated to impact hydraulically reversible fouling (relatively independent of water quality), their removal prior to membrane filtration could significantly extend operational cycles by extending time between backwashes, thereby reducing energy requirements. As biopolymers are also suspected in forming a combined fouling layer, their removal can potentially minimize chemical cleaning requirements (and extend the life cycle of the membranes). The removal of biopolymers through coagulation was well demonstrated. Biofiltration is also expected to perform well as a membrane pre-treatment due its ability to remove biopolymers and particulate/colloidal matter. The ability of biofiltration to control biological re-growth in the distribution system (by removing low molecular weight biodegradable products) was also shown using LC-OCD and FEEM analysis.

Anaerobic membrane bioreactors may provide a sustainable technological solution for digestion of waste activated sludge due to their capacity to achieve substantial volatile solids (VS) destruction and positive energy balances with reduced digester volumes. However, membrane integrated anaerobic systems may have limitations that are imposed by membrane fouling and a decrease in biomass activity due to possible exposure of biomass to high shear conditions. This study characterised bioprocess and membrane performance under varying conditions, identified foulant type and origin and mechanism of fouling, and developed fouling control strategies by using low cross flow velocity and pressure anaerobic membrane systems. The study employed a pilot scale anaerobic digester integrated with negative and neutral tubular membranes; pilot and bench scale control digesters supported with bench scale filtration unit parametric studies. The membranes were polyvinylidene difluoride based with an average pore size of 0.02 micron and were operated at a constant cross flow velocity of 1 ms-1 and constant trans-membrane pressure of 30 kPa. Four operating conditions consisting of different combinations of HRT and SRT were evaluated. By integrating membranes into the digesters it was possible to simultaneously enhance digestion and increase throughput of the digesters without affecting its performance. The anaerobic membrane digester showed 48-49% volatile solids destruction at 30 days SRT under conventional and higher loadings of 1.2±0.4 and 2.1±0.6 kg COD m-3day-1. This was a 100% increase in performance compared to a control digester subjected to higher loading. This result was supported by the associated specific methane generation. The control digesters operated at a relatively higher SRT showed comparable VS destruction and gas generation to the anaerobic membrane running at a similar SRT. However the extra gas generated didn’t compensate heat required to maintain larger volume of the digester. In case of anaerobic membrane digesters due to the high rate feeding, increase biogas production and co-thickening, the energy balance increased by 144 and 200% under conventional and higher loading conditions respectively. Characterization of membrane performance showed that the average sustainable flux was 23.2±0.4 and 14.8±0.4 LMH during HRT-SRTs of 15-30 and 7-15 days respectively. The critical fluxes were in the range of 30-40, 16-17 and 20-22 LM-2H-1 during HRT-SRTs of 15-30, 7-30 and 7-15 days respectively. The decline in membrane performance at a higher loading was associated with the formation of cake layers on the membrane surface that led to reversible fouling. The additional decline in performance at extended SRT was attributed to irreversible fouling. The colloidal fraction of the sludge showed an overall higher fouling propensity during the long term pilot studies and short term filtration tests. The suspended solids fraction of the sludge showed a positive impact at concentration below 15 g/L but resulted in a decrease of membrane performance at higher concentrations. Further studies of foulant origin through a series of microscopic, membrane cleaning and sludge characterization studies showed that the colloidal proteins, soluble carbohydrates and inorganic materials such as iron, calcium and sulfur and their interaction to have a significant impact on membrane fouling. To control anaerobic membrane fouling by the digested sludge, integration of membrane relaxation techniques in the filtration cycle were found effective. By incorporating a unique relaxation technique to tubular membranes, it was possible to increase the sustainable flux to 29.2±1.8 and 34.5±2.5 LM-2H-1 for neutral and negative membranes during 15-30 HRT-SRT process condition. Addition of cationic polymers and sequential mechanical-citric acid membrane cleaning, that targeted both reversible and irreversible fouling was also found effective.

Anaerobic membrane bioreactors may provide a sustainable technological solution for digestion of waste activated sludge due to their capacity to achieve substantial volatile solids (VS) destruction and positive energy balances with reduced digester volumes. However, membrane integrated anaerobic systems may have limitations that are imposed by membrane fouling and a decrease in biomass activity due to possible exposure of biomass to high shear conditions. This study characterised bioprocess and membrane performance under varying conditions, identified foulant type and origin and mechanism of fouling, and developed fouling control strategies by using low cross flow velocity and pressure anaerobic membrane systems. The study employed a pilot scale anaerobic digester integrated with negative and neutral tubular membranes; pilot and bench scale control digesters supported with bench scale filtration unit parametric studies. The membranes were polyvinylidene difluoride based with an average pore size of 0.02 micron and were operated at a constant cross flow velocity of 1 ms-1 and constant trans-membrane pressure of 30 kPa. Four operating conditions consisting of different combinations of HRT and SRT were evaluated. By integrating membranes into the digesters it was possible to simultaneously enhance digestion and increase throughput of the digesters without affecting its performance. The anaerobic membrane digester showed 48-49% volatile solids destruction at 30 days SRT under conventional and higher loadings of 1.2±0.4 and 2.1±0.6 kg COD m-3day-1. This was a 100% increase in performance compared to a control digester subjected to higher loading. This result was supported by the associated specific methane generation. The control digesters operated at a relatively higher SRT showed comparable VS destruction and gas generation to the anaerobic membrane running at a similar SRT. However the extra gas generated didn’t compensate heat required to maintain larger volume of the digester. In case of anaerobic membrane digesters due to the high rate feeding, increase biogas production and co-thickening, the energy balance increased by 144 and 200% under conventional and higher loading conditions respectively. Characterization of membrane performance showed that the average sustainable flux was 23.2±0.4 and 14.8±0.4 LMH during HRT-SRTs of 15-30 and 7-15 days respectively. The critical fluxes were in the range of 30-40, 16-17 and 20-22 LM-2H-1 during HRT-SRTs of 15-30, 7-30 and 7-15 days respectively. The decline in membrane performance at a higher loading was associated with the formation of cake layers on the membrane surface that led to reversible fouling. The additional decline in performance at extended SRT was attributed to irreversible fouling. The colloidal fraction of the sludge showed an overall higher fouling propensity during the long term pilot studies and short term filtration tests. The suspended solids fraction of the sludge showed a positive impact at concentration below 15 g/L but resulted in a decrease of membrane performance at higher concentrations. Further studies of foulant origin through a series of microscopic, membrane cleaning and sludge characterization studies showed that the colloidal proteins, soluble carbohydrates and inorganic materials such as iron, calcium and sulfur and their interaction to have a significant impact on membrane fouling. To control anaerobic membrane fouling by the digested sludge, integration of membrane relaxation techniques in the filtration cycle were found effective. By incorporating a unique relaxation technique to tubular membranes, it was possible to increase the sustainable flux to 29.2±1.8 and 34.5±2.5 LM-2H-1 for neutral and negative membranes during 15-30 HRT-SRT process condition. Addition of cationic polymers and sequential mechanical-citric acid membrane cleaning, that targeted both reversible and irreversible fouling was also found effective.

The objective of drinking water treatment is to provide water which is free of pathogens, is chemically and biologically stable, and is of good aesthetic quality. Natural organic matter (NOM) is present in all natural waters and can make meeting these goals more challenging. Not only does it undergo adverse reactions with disinfectants such as chlorine, it also impacts the biological stability of water within the distribution system and contributes to undesirable aesthetic qualities such as taste and odour. NOM has also been implicated in membrane fouling, which continues to be a significant operational problem preventing wider implementation of this process. Due to its highly variable heterogeneous nature, NOM can be difficult to characterize in terms of its specific composition, however recent analytical advancements are allowing for a better understanding of its behaviour in water treatment. Two promising tools for NOM characterization include Liquid Chromatography Organic Carbon Detection (LC-OCD) and Fluorescence Excitation Emission Matrix (FEEM) analyses. In this research both techniques were applied to samples taken from five full scale facilities in Ontario, Canada over all four seasons. The source waters for these treatment locations consisted of both river (Grand River, Ottawa River) and Great Lake waters (Lake Huron, Lake Erie, Lake Ontario), and an additional raw source (Saugeen River) was also monitored. The plants all employed granular media filtration, but had differences including enhanced coagulation, ozonation, biofiltration and sand ballasted flocculation. Other relevant water quality parameters were also monitored (TOC, DOC, UV254, pH, conductivity etc.) as well as plant operating conditions (dosages, flows, filter run times etc.) to investigate their impact on removal of specific NOM fractions. Four of the waters (Grand River, Ottawa River, Lake Erie and Lake Ontario) were selected based on the initial survey due to their NOM composition, for bench scale ultrafiltration (UF) membrane fouling experiments. The experiments were run at constant flux for a period of five days, with an automated permeation cycle and backwash. The impact of biopolymers on hydraulically reversible and irreversible fouling was of specific interest. Important seasonal trends were identified for all waters, with biopolymer content increasing at higher temperatures. Useful comparisons could also be made between different treatment processes including conventional and enhanced coagulation. The enhanced process while significantly improving the removal of humic substances, was not beneficial in terms of biopolymer removal, suggesting a different removal mechanism for these two fractions. The removal of low molecular weight ozonation by-products during full scale biofiltration was well demonstrated, and other fractions (building blocks, biopolymers) had varying degrees of removal, which was more dependent on temperature. Principle component analysis (PCA), an advanced multivariate statistical method, was successfully applied to a FEEM data set containing five different waters at varying degrees of treatment. Three principle components related to humic-like, protein-like and particulate/colloidal material were identified, and served as useful complementary information to the LC-OCD results. The humic-like component was found to have relatively good correlation to the humic fraction from LC-OCD analysis, with some deviation in the post-ozonation samples (which underwent greater structural changes not captured by LC-OCD). The biopolymer fraction was shown to have good correlation to hydraulically reversible membrane fouling across all four waters. The same could not be said for hydraulically irreversible fouling for which a combined fouling layer (with particulate and colloidal material) is hypothesized. This research provides those working in the water treatment sector with greater insight into NOM behaviour during various levels of treatment. As biopolymers were demonstrated to impact hydraulically reversible fouling (relatively independent of water quality), their removal prior to membrane filtration could significantly extend operational cycles by extending time between backwashes, thereby reducing energy requirements. As biopolymers are also suspected in forming a combined fouling layer, their removal can potentially minimize chemical cleaning requirements (and extend the life cycle of the membranes). The removal of biopolymers through coagulation was well demonstrated. Biofiltration is also expected to perform well as a membrane pre-treatment due its ability to remove biopolymers and particulate/colloidal matter. The ability of biofiltration to control biological re-growth in the distribution system (by removing low molecular weight biodegradable products) was also shown using LC-OCD and FEEM analysis.

The performance of a submerged membrane bioreactor for the duty of gas field produced water treatment was appraised. The system was operated under steady state conditions at a range of mixed liquor suspended solids (MLSS) concentrations and treatment and membrane performance examined. Organics removal (COD and TOC) display removal rates between 90 and 97%. Removal of specific target compounds Benzene, Toulene, Ethylbenzene and Xylene were removed to above 99% in liquid phase with loss to atmosphere between 0.3 and 1%. Comparison of fouling rates at a number of imposed fluxes has been made between long term filtration trials and short term tests using the flux step method. Produced water fed biomass displays a greater fouling propensity than municipal wastewater fed biomass from previous studies. Results indicate an exponential relationship between fouling rate and flux for both long and short term trials, although the value was an order of magnitude lower during long term tests. Moreover, operation during long term trials is characterised by a period of pseudo stable operation followed by a catastrophic rise in TMP at a given critical filtration time (tfi, ) during trials at 6 g. L"1. This time of stable operation, tfit, is characterised by a linear relationship between fouling rate and flux. Results have been compared with the literature. Data for membrane fouling prior to the end of t fit yielded a poor fit with a recently proposed model. Trends recorded at t> trlt revealed the fouling rate to follow no definable trend with flux. The system showed resilience to free oil shocking up to an oil concentration of 200ppmv. Following an increase in oil concentration to 500 ppmv, rapid and exponential fouling ensued.

Produced water (PW), or water associated with crude oil extraction, is the largest oily wastewater stream generated worldwide. The reuse and reclamation of these important water volumes are critical for more sustainable operation in the oilfield. Ceramic membrane filtration is a promising technology for PW treatment; however, fouling is the major drawback for a broader application. Fouling leads to higher resistance to flow, reducing membrane lifetime, and ultimately leading to higher capital expenditures and operating expenses. Further understanding of the interactions between PW foulants and the ceramic materials is needed for designing fouling control strategies and cleaning protocols for ceramic membranes. This work explored different techniques to characterize, visualize, and quantify the submicron PW contaminants content and its adsorption interactions with metal oxides. We visualized and characterized submicron oil droplets in oilfield PW samples by applying suitable advanced microscopy techniques. For the first time, crude oil droplets as small as 20 nm were found in oilfield PW together with other submicron contaminants. The adsorption studies performed by quartz crystal microbalance with dissipation (QCM-D) showed that the interactions of organic surface-active compounds with the metal oxides are driven by the nature of the surfactant and not by the surface properties. This has implications in the selection of the ceramic membrane material, wherein electrostatic interactions should not be taken as the only predicting factor of adsorption and fouling during PW treatment. Furthermore, our results suggested that the more fluid or viscoelastic-like the contaminant layer, the more difficult the cleaning process from the metal oxide. It demonstrates that the mechanical property of the attached films is a crucial factor in designing appropriate cleaning protocols for ceramic membranes. Finally, QCM-D and advanced microscopy techniques were applied to analyze adsorption and cleaning of contaminants in a complex Bahraini PW into alumina as a case study. Bacteria were found to attach irreversibly on the alumina surface, promoting nucleation points for calcium precipitates. The protocols developed in this work are suitable for understanding membrane fouling phenomena in the micron scale and could be implemented before filtration pilot testing to save time and expenses at larger scales.

Low-pressure membrane systems such as Microfiltration (MF) and Ultrafiltration (UF) have been presented as viable option to pre-treatment systems in potable water applications. UF membranes are sporadically backwashed with ultra-filtered water to remove deposited matter from the membrane and restore it. Several factors that may cause permeability and selectivity decrease are involved and numerous procedures are applicable to achieve this objective. Membrane cleaning is the most important step required to maintain the characteristics of the membrane. This research was made with the purpose of investigating the effects of acid cleaning during chemically enhanced backwashing (CEB) on the performance of ultrafiltration (UF) membranes in seawater reverse osmosis (SWRO) pretreatment. To accomplish this, the questions made were: Does the acid addition (before or after the alkali CEB) influence the overall CEB cleaning effectiveness on Dow UF membrane? Does the CEB order of alkali (NaOCl) and acid (H2SO4) affect the overall CEB cleaning effectiveness? If yes, which order is better/worse? What is the optimal acid CEB frequency that will ensure the most reliable performance of the UF?. To answer this queries, a series of sequences were carried out with different types of chemical treatments: Only NaOCl, daily NaOCl plus weekly acid, daily NaOCl plus daily acid, and weekly acid plus daily NaOCl. To investigate the consequence of acid by studying the effect of operational data like the trans-pressure membrane, resistance or permeability and support that by the analytical experiments (organic, inorganic and microbial characterization). Microorganisms were removed almost completely at hydraulic cleaning and showed no difference with addition of acid. As a conclusion of the operational data the organic and inorganic chatacterization resulted in the elimination of the first sequence due to the acummulation of fouling over time, which produces that the cleaning increases downtime, productivity diminishes, Increases water cost, shortens membrane lifespan and the frequency of cleaning in place (CIP). The elimination of the third sequence, NaOCl followed by daily acid, resulted in excessive dosing of acid which affects fibers and increases the water cost. The removal of organic carbon and inorganic fractions for the second and third sequence were investigated. The better removal of Iron was in the last sequence with value of 11.52 mg/l due to acid was dose first which target inorganic foulants. The better removal of bio polymers was obtained at the second sequence with a value of 0.95 mg/l owed to the influence of chorine CEB to acid which oxidized biopolymers with higher molecular weight to smaller, then when the acid CEB removed it in a larger amount. While the last sequence was 0.57 mg/l. It can be concluded that second sequence provided a better removal that the last sequence. To support this conclusion, the operational data was compared to the second sequence is operationally sustainable, therefore in this revision the best sequence was the second.

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