Pierre Berube

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Practical considerations for ageing of drinking water membranes (2018)

This dissertation advances our understanding of practical considerations for ageing of membranes used in drinking water treatment. Fouling and cleaning of membranes are well understood, but knowledge of long-term changes (i.e. ageing) have not been fully explored. To date, changes in physical and chemical characteristics, and changes in membrane performance, have been attributed to ageing. The three major sections in this dissertation were structured around membrane performance.Firstly, the existing literature was comprehensively reviewed. Important membrane performance factors were identified via this review: resistance, fouling rate, cleaning rate, and susceptibility to breach. How chemical and physical characteristics impact these performance factors was also systematically assessed. Almost all of the reviewed research involved bench-scale ageing of membranes, with scant attention to full-scale ageing, and even less on how bench-scale ageing can be useful in understanding full-scale ageing. This recognition led to the two further research projects.Secondly, we investigated changes in performance factors and chemical characteristics for PVDF membranes aged in 8 full-scale water treatment plants (14 treatment trains ranging from new to 10 years of age). Membranes were harvested by plant operators regularly and analyzed in a standardized laboratory setting. Membranes exhibited stable behaviour until about 5 years of operation; after this time, performance factors and chemical characteristics began to change significantly. Clean membrane resistance and fouling rate increased for aged membranes. The mechanical properties of aged membranes deteriorated, suggesting that their susceptibility to breach was heightened. These performance changes correlated with the removal of hydrophilic additives from the membranes.The final research project sought to link performance changes observed at bench-scale with performance changes observed in the full-scale study. Two bench-scale ageing techniques were used to probe changes in performance and characteristics: soaking membranes in NaOCl cleaning agent, and cycling them with foulant and cleaning agent. The changes in membrane chemistry were similar for bench-scale and full-scale ageing, but performance differed. By comparing the two bench-scale techniques with the full-scale ageing findings, it was established that irreversible foulants are critical components of full-scale ageing, and the involvement of these can be approximated to some extent by cycling membranes.

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Nanofiltration and tight ultrafiltration membranes for drinking water treatment – system design and operation (2017)

Nanofiltration (NF) and tight Ultrafiltration (UF) membranes represent a technology that is well suited for high quality drinking water production from source waters with high concentrations of natural organic matter (NOM) or other contaminants. However, the application of these membranes is limited, mainly because of the challenges related to fouling, concentration polarization (CP), system complexity and cost. The aim of the present study was to address these issues and to enable a more widespread application of this technology. Opportunities for simplifying NF and tight UF systems by, for instance, operation in dead-end mode, were explored. Experiments were conducted to evaluate the contribution of CP and fouling to the increase in resistance to permeate flow when filtering raw waters containing NOM. Continuous and periodic hydraulic measures to control CP and fouling were assessed. When filtering model raw waters containing humic substances, the increase in resistance to permeate flow was dominated by CP. When humic substances are effectively rejected and are present at high concentrations, CP becomes extensive, leading to a significant increase in the resistance to permeate flow by the formation of a cake/gel layer at the membrane surface. In the presence of calcium and particulate matter, the increase in resistance to permeate flow was dominated by fouling rather than CP. Filtration tests using periodic hydraulic measures to control fouling indicated that it was difficult to hydraulically remove the accumulated material once a foulant layer had been formed. Therefore, cross-flow operation, which reduces CP and prevents the formation of a foulant layer, is recommended. To optimize cross-flow operation, a framework was developed to compare the performance of NF membranes of different configurations (i.e. spiral wound and hollow fiber configurations) and geometries in terms of the permeate flux that can be sustained, and to optimize the operating set point of NF membranes with respect to system configuration, cross-flow velocity and operating flux with respect to cost. The results suggest that, despite higher manufacturing costs for hollow fiber NF, hollow fiber NF can be cost competitive to spiral wound NF. Because of operational advantages, the application of hollow fiber configurations is recommended.

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Effect of bubble size and sparging frequency on the power transferred onto membranes for fouling control (2014)

Fouling control through air sparging in membrane systems is governed by the hydrodynamic conditions in the system and the resulting shear stress induced onto membranes. However, the relationship between hydrodynamic conditions and the extent of fouling control is not well understood. As a result, sparging approaches are designed using a capital and time intensive empirical trial-and-error approach that does not guarantee that optimal conditions are identified. To address this knowledge gap, the present research focused on characterizing the hydrodynamic conditions in a membrane system under different sparging conditions (bubble size and frequency) and on finding a correlation between the induced hydrodynamic conditions and fouling control efficiency. New concepts of zone of influence of bubbles and power transferred were defined to characterise the hydrodynamic conditions in the system. A non-homogenous fouling distribution was observed in the zone of influence of bubbles due to a non-homogenous distribution of velocity and shear stress in this zone. Fouling rates generally decreased with an increase in the area of the zone of influence, the root mean square of shear stress induced onto membranes and the rise velocity of bubbles. However, none of these parameters on their own could accurately describe the effect of the hydrodynamic conditions on fouling rate. On the other hand, power transferred onto fibers, which incorporates the effect of all the three parameters, could more effectively describe the effect of the hydrodynamic conditions on the rate of fouling. Power transfer efficiency into the system, defined as the ratio of power transferred onto membranes to the power input in the system, was used to identify optimal sparging approaches. For all cases investigated, the power transfer efficiency to the system was consistently much higher for pulse bubble than for coarse bubble sparging. The results also indicated that as sparging frequency and the size of the bubbles increased, the width of zone of influence increased, suggesting that the spacing between the spargers could be increased when sparging with larger bubbles or at higher frequencies. Increasing the spacing would not only decrease the number of spargers, but also the volume of the gas required for sparging.

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Membrane ageing due to chemical cleaning agent (2014)

Sodium hypochlorite is commonly used as a cleaning agent to remove adsorbed foulants from PVDF-based micro/ultra filtration membranes in water and wastewater treatment applications. Although effective for fouling control, extended sodium hypochlorite exposure can affect the physical/chemical characteristics and hinder the treatment performance of these membranes. In the present study, experiments were conducted to comprehensively quantify the effects of sodium hypochlorite exposure on changes in the physical/chemical characteristics and the filtration performances of blended PVDF-based supported hollow-fiber membranes and identifying the mechanism(s) responsible for the changes. Both the effect of the sodium hypochlorite concentration (C) and the duration of exposure (t) on the membrane characteristics are investigated. The physical/chemical characteristics and the filtration performances of virgin and aged (i.e., weathered due to exposure to sodium hypochlorite) membranes were compared. The membranes were characterized based on chemical composition (FTIR and NMR), mechanical strength (yield strength), surface hydrophilicity (contact angle), pore size and porosity (scanning electron microscopy and challenge test), membrane resistance (clean water permeation test), and affinity of the membrane for foulants (cleaning efficiency). The results indicated that exposure dose and concentration of the sodium hypochlorite used have a significant influence on the membrane characteristics. For the exposure conditions considered, the impact of sodium hypochlorite exposure on the parameters investigated could be most accurately and consistently correlated to an exposure dose relationship of the form Cnt (where, C=concentration and t=exposure time) rather than the Ct relationship commonly used to define the extent of exposure to cleaning agents. For all the parameters investigated, the power coefficient n was less than 1 indicating that time had a greater impact on the changes than did the concentration of the sodium hypochlorite. The results suggest that the use of sodium hypochlorite for chemical cleaning, at concentrations that are higher than those typically used for chemical cleaning would have less of an effect on the characteristics of the membrane materials. Changes in the characteristics were attributed to the oxidation of the hydrophilic additives (HA) present in blended PVDF membranes. A new non-destructive membrane characterization technique to evaluate the amount of membrane ageing is proposed.

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An investigation of hydrodynamic conditions inside gas-sparged hollow fiber membrane modules (2010)

Over the past decade, membrane filtration has emerged as a proven technology for waterand wastewater treatment applications. Despite its popularity, the problem of membranefouling remains the Achilles heel of membrane filtration. A common strategy to controlmembrane fouling is the use of gas sparging to prevent particle deposition on membranesurfaces. The efficiency of gas sparging for fouling control/prevention depends on theeffective distribution of sparged gas bubbles and bubble-induced flow across membranesurfaces. To date, there is very limited literature available that describes thishydrodynamic condition inside the submerged hollow fiber membrane modules. Thereason for this limited knowledge is the complex and transient nature of the geometry andhydrodynamics inside hollow fiber modules. The hydrodynamic conditions surroundinga hollow fiber under gas sparging, and the relationship between hydrodynamic conditionsand fouling control are not well understood. This presents an obstacle to optimizing theperformance of submerged hollow fiber modules with respect to energy costs associatedwith gas sparging. This thesis provides a comprehensive study of the hydrodynamicconditions inside a gas-sparged submerged hollow fiber membrane module, and therelationship between the observed hydrodynamic conditions and fouling control. Unlikewhat had been hypothesized by some, the results indicated that the hydrodynamicconditions inside a submerged hollow fiber membrane are different than those ofconfined tubular membrane systems. It was also observed that different types of shearprofiles exist inside the membrane module, and the different types of shear conditionsresult in different fouling, which suggests that different mechanisms are at play incontrolling particle transport near the membrane surface. This information opens theopportunity for further investigation in terms of optimization of the gas –sparging system,or other shear-generating devices that create shear conditions that offer the greatestbenefit minimizing fouling, while minimizing the energy demand associated withgenerating these shear conditions.

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Master's Student Supervision (2010 - 2018)
Chemically enhanced backwash as the only ultrafiltration fouling control approach in seawater applications (2018)

The use of ultrafiltration (UF) membranes as a pre-treatment technology for seawater applications, such as desalination and water production for deep sea oil extraction, has expanded in recent years. Controlling fouling during filtration remains a crucial operational challenge, particularly in applications with equipment footprint constraints. The present study sought to investigate a simplified fouling control approach where chemically enhanced backwash (CEB) was the only technique utilized.Short-term benchmarking trials were performed to evaluate a wide range of operating conditions. These included: CEB duration, CEB frequency, CEB make up solution, and sodium hypochlorite (NaClO) concentration. Long-term trials were then completed to determine the viability of this approach, and provide operational insight for future applications.NaClO concentrations as low as 8 ppm were effective in achieving sustainable fouling rates in low temperature UF operation with CEB as the only fouling control approach. Extended CEBs using 150 ppm NaClO solutions were effective at restoring lost permeability, though may not be required for periods of 6 months or more. Both outside-in, and inside-out membrane configurations were evaluated, with outside-in observed to have a lower fouling rate. No difference was observed when comparing UF permeate and nanofiltration concentrate as CEB make up solutions. A new measure, termed ‘cleaning effort’ (i.e. the product of CEB duration and NaClO concentration divided by CEB frequency), was proposed to compare fouling control efficiency for different CEB operating conditions. Fouling rate followed an exponential decay relationship with respect to cleaning effort. Accumulation of active biomass on membrane fibers was not observed after long-term trials. Residual chlorine in the CEB reject stream was observed to be above regulatory limits, and decayed slowly.

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Flux optimization in passive membrane systems with air sparging and relaxation (2016)

Traditional membrane filtration plants for drinking water require uninterrupted electricity for pumps and fouling control, thus making it unsuitable for small/rural communities and developing countries. Gravity driven passive membrane filtration systems can be a possible solution to this problem. Previous studies demonstrated that frequent air sparging is beneficial to maintaining a high permeate flux in passive membrane systems. Previous studies also reported that forward flushing after relaxation is also beneficial to maintaining a high permeate flux. Air sparging is an alternate solution to forward flushing after relaxation and considered in the present study.Four different air sparging rates were considered: no air sparging, continuous air sparging, 5 min/day and 5 min/2 days. Periodic air sparging significantly increased the steady-state permeability (0.39±0.003 B/Bi and 0.37±0.007 B/Bi for 5 min/ day and 5 min/2 days respectively) compared to conditions with no air sparging (0.21±0.006 B/Bi). The highest permeability (0.56±0.036 B/Bi) was achieved with continuous air sparging. Three different relaxation periods prior to periodic air sparging (5 min/day) were tested (1 hr, 4 hrs and 8 hrs). Relaxation prior to periodic air sparging increased the steady-state permeability (0.47±0.012 B/Bi and 0.41±0.023 B/Bi for 1 hr and 4 hrs relaxation period respectively) compared to condition without relaxation prior to air sparging (0.39±0.003 B/Bi). However, lower permeability was observed when a longer relaxation period (0.25±0.002 B/Bi for 8 hrs relaxation period) was considered.

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Passive membrane systems for small communities (2015)

Submerged hollow fibre ultrafiltration (SHFUF) is an established drinking water treatment technology viable for community-scale use. It can effectively treat surface water up to 4-log removal of colloids, pathogenic bacteria, and viruses. However, current use of SHFUF in small/ remote communities is hindered by the system’s complexity and high construction and operating costs. The present study focuses on the development of a novel and simple SHFUF system that can operate passively and with limited mechanical complexity for the production of drinking water in small/ remote communities.The experimental program was divided into four main stages; each stage was instrumental in eliminating component of a SHFUF system that contributes to its complexity (ie. backwash, permeate pump, aeration and recovery cleaning) and achieving an optimized state feasible for a small community use. Surface water containing 6-7 ppm dissolved organic carbon (DOC) was used for the pilot-scale experiments. In Stage 1, the contributions of periodic backwash in SHFUF were assessed through a comparative study of with and without backwash systems at sub-critical fluxes of 10, 20 and 30 L/m²h. While the benefits of backwash were clearly observed at 30 L/m²h, backwash was less necessary at lower permeate fluxes. At 10 L/m²h, flux was successfully maintained over the 2-month operation without backwash, indicating that backwash can be eliminated when operating at a low flux. Elimination of backwash reduces power requirements, increases throughput, and simplifies the system. In Stage 2, further simplification to the system was achieved through gravity permeation at a constant hydrostatic pressure. Gravity permeation at 10 L/m²h could be maintained with a head of 37 mbar. In stage 3, further reduction in energy consumption was achieved through operations under reduced air sparging conditions. Although reduced aeration decreased the permeate flux that could be maintained, this decrease can be compensated by proportionally increasing the number of membrane modules. In stage 4, recovery cleaning was confirmed to recover all of the permeability loss during the 2-month operation. Results from the present study confirm that technical complexity and energy requirements of SHFUF can be substantially reduced and made feasible for use in small/ remote communities.

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Reducing operational costs in membrane bioreactors using slug bubbles (2015)

Membrane bioreactors (MBRs) are commonly used in wastewater treatment processes.In fact, the demand is expected to increase with more than double digitgrowth annually over the next decade [5]. However, operational costs of MBRs arestill higher compared to operational costs of conventional treatment plants due tothe additional aeration and pumping required in MBRs. This study examines thefeasibility of using excess air that was used to clean the membrane for water conveyance(known as airlift pump), for a minimized energy use in MBR processes.In order to meet the objective, prototypes of airlift pumps were built with differentdimensions. The experimental results of each prototype were comprehensivelycompared to existing models in the literature. The models were modified for a betterfit of the experimental data.It was determined whether a new apparatus, where many riser tubes were bundledtogether, would behave like many individual riser tubes. While the air was injectedat the bottom of the individual riser tube previously, the bundled riser tubes of thenew apparatus would be attached to a rubber sheet; this, was attached to a frame.The rubber sheet was added to the apparatus in order to trap the air in the tankand lead it to the bundle of riser tubes. Different collector angles of the rubber aswell as different water heights were investigated. The experimental results werecompared to the previously modified models.The last step was to design a system that redirects the pumped water so that it canbe transported back to the head of the MBR plant.The results suggest that air exiting to the atmosphere from an MBR can be used totransport the water. However, the models are only able to predict water flows forindividual airlift pumps that consist of a single riser tube, where the air is injected at its bottom. Further research needs to be done in order to be able to predict water flows that can be achieved in systems, such as the one proposed in this present study, which uses a bundle of riser tubes.

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Shear stress and fouling control in hollow fiber membrane systems under different gas sparging conditions (2012)

The shear stress created by gas sparging has been widely recognized as a controlling factor in the fouling of submerged membrane systems. Effective gas sparging can significantly reduce the fouling and improve the membrane performance. Several factors, such as membrane module configuration, gas sparging tank configuration, gas sparging pattern and temperature, affect the hydrodynamic conditions around the membrane. Chan et al. (2011) reported that different types of shear profiles exist inside the submerged hollow fiber membrane module, and the different types of shear conditions have different effects on fouling control. In this thesis, the relationship between the shear stress generated by conventional sparging and a novel sparging approach on fouling control were studied. The results indicate that, to achieve the similar fouling control (fouling rate), only a quarter of energy (i.e air flow rate) input was required for the novel slug bubble sparger, compared to the conventional coarse bubble sparger.

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Assessment of causes of irreversible fouling in powdered activated carbon/ultrafiltration membrane (PAC/UF) systems (2011)

Powdered Activated Carbon (PAC) has been successfully used in conjunction with membrane ultrafiltration (UF) to reduce taste, odour, colour and other concerns caused by organic material present in raw drinking water sources. PAC addition also typically significantly reduces the extent of fouling in hybrid PAC/UF systems. However, in some cases, PAC addition can have a significant negative effect by increasing irreversible membrane fouling. The present study was developed to assess the cause of irreversible fouling in a system for which PAC addition had a negative effect. The first part of the study evaluated if irreversible fouling could potentially be due to the breakdown of PAC particles in a PAC/UF membrane system. Particle size analysis of the virgin PAC suggested that pore plugging was unlikely because the PAC was too large. However, when exposed to relatively high shear conditions typical of UF systems, the size of the PAC was observed to decrease to a range comparable to that of the size of the pores in the UF membranes used. However results from the analysis of a bench scale PAC/UF system suggested that irreversible fouling was not solely due to the direct plugging of membrane. The decrease in the permeability for the irreversibly fouled system with PAC was observed to be linear over time, suggesting that irreversible fouling was possible due to the formation of a cake layer by PAC. This was confirmed with FESEM imaging.The second part of the study aimed to characterize the foulants in the cake layer on PAC/UF hollow fibres. FESEM and SEM-EDX were performed to obtain insight on the characteristics of the membrane surface of the hollow fibres. Sonication and a novel solubilisation technique were used to analyze the foulants in/on the membrane surface of the hollow fibres. Organic and inorganic material extracted from the fouled membrane suggested that these have great influence on the PAC cake layer formation on membrane fibres. The results from the study indicate that PAC does not cause irreversible membrane fouling in PAC/UF systems by itself, but it may facilitate the absorption of organic and inorganic material causing irreversible fouling.

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Effect of biological activated carbon (BAC) filtration on the removal and biodegradation of natural organic matter (NOM) (2011)

Natural organic matter is a complex mixture of various organics including humic substances, carbohydrates, amino acids and carboxylic acids that exist in natural waters. Integrated treatment processes that combine oxidation processes and activated carbon biofilters have been shown to be effective at reducing natural organic matter (NOM) levels. The current research project investigated the effect of ozone and advanced oxidation at various doses on specific parameters including: biodegradability of NOM, formation of disinfection by-products (DBPs), change in apparent molecular weight (AMW) of NOM and dissolved organic carbon content (DOC). Overall, ozonation of the raw water at 2mg O₃/mg DOC resulted in significant reductions in aromatic material, resulting in lowered DBPFP. In addition, ozonation was successful at transforming NOM from high AMW to low AMW, rendering the organic material more biodegradable and preferentially removed during biofiltration. While the high-dose oxidants (ozonation at 25mg O₃/mg DOC and AOP treatment at 4000mJ/cm² and 10mg/L H₂0₂) were successful at reducing DOC, UVA, AMW and DBPFP, the elevated dose required make these options less realistic. Ozonation at 2mg O₃/mg DOC and AOP treatment at 2000mJ/cm² and 10mg/L H₂O₂ provide good reduction of UVA, AMW and DBPFP. The high dose oxidants are unsuitable as pre-treatment options for biofiltration given that they result in highly oxidized NOM that exhibited very little biodegradation during biofiltration. The lower dose oxidants are suitable pre-treatment options for biofiltration given the high reductions in UVA, AMW and DBPFP exhibited, and the similar biodegradation kinetics observed. Pre-oxidation prior to biofiltration is essential for removal of non-biodegradable DOC. The rate kinetics governing biodegradation were not sensitive to oxidant type or dose. Overall, this project provided beneficial insight into the operation of integrated treatment processes and the effect of these on several NOM characteristics including biodegradation.  

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