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Recent Submissions

  • Addition of a carbon fiber brush improves anaerobic digestion compared to external voltage application

    Baek, Gahyun; Saikaly, Pascal; Logan, Bruce (Water Research, Elsevier BV, 2020-10-26) [Article]
    Two methods were examined to improve methane production efficiency in anaerobic digestion (AD) based on adding a large amount of surface area using a single electrically conductive carbon brush, or by adding electrodes as done in microbial electrolysis cells (MECs) to form a hybrid AD-MEC. To examine the impact of surface area relative to electrodes, AD reactors were fitted with a single large brush without electrodes (FB), half a large brush with two electrodes with an applied voltage (0.8 V) and operated in closed circuit (HB-CC) or open circuit (HB-OC) mode, or only two electrodes with a closed circuit and no large brush (NB-CC) (equivalent to an MEC). The three configurations with a half or full brush all had improved performance as shown by 57-82% higher methane generation rate parameters in the Gompertz model compared to NB-CC. The retained biomass was much higher in the reactors with large brush, which likely contributed to the rapid consumption of volatile fatty acids (VFAs) and therefore improved AD performance. A different microbial community structure was formed in the large-size brushes compared to the electrodes. Methanothrix was predominant in the biofilm of large-size carbon brush, while Geobacter (anode) and Methanobacterium (cathode) were highly abundant in the electrode biofilms. These results demonstrate that adding a high surface area carbon fiber brush will be a more effective method of improving AD performance than using MEC electrodes with an applied potential.
  • Enrichment of salt-tolerant CO2-fixing communities in microbial electrosynthesis systems using porous ceramic hollow tube wrapped with carbon cloth as cathode and for CO2 supply.

    AlQahtani, Manal Faisal; Bajracharya, Suman; Katuri, Krishna; Ali, Muhammad; Xu, Jiajie; Alarawi, Mohammed S; Saikaly, Pascal (The Science of the total environment, Elsevier BV, 2020-10-20) [Article]
    Microbial inocula from marine origins are less explored for CO2 reduction in microbial electrosynthesis (MES) system, although effective CO2-fixing communities in marine environments are well-documented. We explored natural saline habitats, mainly salt marsh (SM) and mangrove (M) sediments, as potential inoculum sources for enriching salt-tolerant CO2 reducing community using two enrichment strategies: H2:CO2 (80:20) enrichment in serum vials and enrichment in cathode chamber of MES reactors operated at -1.0 V vs. Ag/AgCl. Porous ceramic hollow tube wrapped with carbon cloth was used as cathode and for direct CO2 delivery to CO2 reducing communities growing on the cathode surface. Methanogenesis was dominant in both the M- and SM-seeded MES and the methanogenic Archaea Methanococcus was the most dominant genus. Methane production was slightly higher in the SM-seeded MES (4.9 ± 1.7 mmol) compared to the M-seeded MES (3.8 ± 1.1 mmol). In contrast, acetate production was almost two times higher in the M-seeded MES (3.1 ± 0.9 mmol) than SM-seeded MES (1.5 ± 1.3 mmol). The high relative abundance of the genus Acetobacterium in the M-seeded serum vials correlates with the high acetate production obtained. The different enrichment strategies affected the community composition, though the communities in MES reactors and serum vials were performing similar functions (methanogenesis and acetogenesis). Despite similar operating conditions, the microbial community composition of M-seeded serum vials and MES reactors differed from the SM-seeded serum vials and MES reactors, supporting the importance of inoculum source in the evolution of CO2-reducing microbial communities.
  • Electrification at water–hydrophobe interfaces

    Nauruzbayeva, Jamilya; Sun, Zhonghao; Gallo Junior, Adair; Ibrahim, Mahmoud; Santamarina, Carlos; Mishra, Himanshu (Nature Communications, Springer Science and Business Media LLC, 2020-10-20) [Article]
    Abstract The mechanisms leading to the electrification of water when it comes in contact with hydrophobic surfaces remains a research frontier in chemical science. A clear understanding of these mechanisms could, for instance, aid the rational design of triboelectric generators and micro- and nano-fluidic devices. Here, we investigate the origins of the excess positive charges incurred on water droplets that are dispensed from capillaries made of polypropylene, perfluorodecyltrichlorosilane-coated glass, and polytetrafluoroethylene. Results demonstrate that the magnitude and sign of electrical charges vary depending on: the hydrophobicity/hydrophilicity of the capillary; the presence/absence of a water reservoir inside the capillary; the chemical and physical properties of aqueous solutions such as pH, ionic strength, dielectric constant and dissolved CO2 content; and environmental conditions such as relative humidity. Based on these results, we deduce that common hydrophobic materials possess surface-bound negative charge. Thus, when these surfaces are submerged in water, hydrated cations form an electrical double layer. Furthermore, we demonstrate that the primary role of hydrophobicity is to facilitate water-substrate separation without leaving a significant amount of liquid behind. These results advance the fundamental understanding of water-hydrophobe interfaces and should translate into superior materials and technologies for energy transduction, electrowetting, and separation processes, among others.
  • Impact of osmotic and thermal isolation barrier on concentration and temperature polarization and energy efficiency in a novel FO-MD integrated module

    Son, Hyuk Soo; Kim, Youngjin; Nawaz, Muhammad Saqib; Al-Hajji, Mohammed Ali; Abu-Ghdaib, Muhannad; Soukane, Sofiane; Ghaffour, NorEddine (Journal of Membrane Science, Elsevier BV, 2020-10-18) [Article]
    In this study, a novel integrated forward osmosis - membrane distillation (FO-MD) module equipped with an isolation barrier carefully placed between the FO and MD membranes is experimentally investigated, and its performance is compared with a conventional hybrid module. The function of the isolation barrier is to osmotically and thermally separate the FO draw solution (DS) and MD feed channels. A systematic approach is adopted to compare the flux through both modules under (i) different and similar hydrodynamic conditions, (ii) different DS concentrations and temperatures, and (iii) different feed solution concentrations. All experiments were performed for 9 h each in batch mode using a custom-made compact module. New FO and MD membrane sheets were mounted for each experiment to ensure similarity in operating conditions. The proposed module design increased the flux by 22.1% using the same module dimensions but different hydrodynamic conditions. The flux increased by 16.6% using the same hydrodynamic conditions but different module dimensions. The FO/MD energy ratio reduced from 0.89 to 0.64 for the novel module, indicating better utilization of energy (primarily from MD). The gain output ratio (GOR) increased on average by 15.8% for the novel module compared to the conventional module, with a maximum increment of 20.7%. The temperature and concentration polarization coefficients in the MD operations showed improvements of 17.4% and 2.6%, respectively. The presence of the isolation barrier inside the integrated module indicated promising improvements of the flux and internal heat recovery, and further significant enhancements are expected for larger scale modules. Additionally, the novel module design offers unprecedented process integration opportunities for FO-MD as well as other membrane hybrid systems.
  • An Assistive Magnetic Skin System: Enabling Technology for Quadriplegics

    Almansouri, Abdullah S.; Upadhyaya, Lakshmeesha; Nunes, Suzana Pereira; Salama, Khaled N.; Kosel, Jürgen (Advanced Engineering Materials, Wiley, 2020-10-15) [Article]
    People with quadriplegia no longer have control over their legs, neither the hands and cannot continue living their life independently. On top of that, severely injured quadriplegics (i.e., C1 and C2 injuries) suffer from speaking difficulties and minimal head and neck movements. With the advancement in wearable artificial skins and the Internet of Things, realizing comfortable and practical solutions for quadriplegics is more tangible than ever. Here, a comprehensive assistive magnetic skin system is presented that allows quadriplegics, including the severely injured ones, to move around individually and control their surroundings with ease. The system tracks facial expressions by tracking the movement of magnetic tattoos attached to the face, using magnetic field sensors incorporated into eyeglasses. The magnetic tattoos are made of highly flexible, stretchable, breathable, and biocompatible magnetic skins. In combination with smart-glasses, smart-wheelchair, and smart-gadgets, the users can move around and control their environment with their facial expressions. The system is also designed to allow quadriplegics to perform outdoor activities effortlessly. It supports line-of-sight communication and does not require pre-tethering to the smart-gadgets, unlike the existing solutions. Thus, enabling the user to walk on pathways, activate pedestrian lights, control public elevators, and perform various outdoor activities independently.
  • Biofilm removal efficacy using direct electric current in cross-flow ultrafiltration processes for water treatment

    Kerdi, Sarah; Qamar, Adnan; Vrouwenvelder, Johannes S.; Ghaffour, NorEddine (Journal of Membrane Science, Elsevier BV, 2020-10-14) [Article]
    Biofouling of membranes in water treatment is considered as one of the major practical problems. A novel and an efficient approach for cleaning biofilm grown on the membrane surface is proposed by applying a direct electric current (124 mA, 90 s) through platinum electrodes inside a cross-flow ultrafiltration channel. Depending on the electrochemical reactions occurring at the electrodes, either chlorine or hydrogen-producing configuration is realized by interchanging the current polarity. Baseline determination of the amount of chlorine generated and change in pH is assessed as a function of current intensity, linear cross-flow velocity, and duration of applied current. The efficiency of the proposed method is determined by investigating electrically treated biofilm through bacterial inactivation using Confocal Laser Scanning Microscopy (CLSM), bacterial cell structure changes through Scanning Electron Microscopy (SEM), and by estimating the amount of biomass removal through Optical Coherence Tomography (OCT). When a chlorine-producing electrode is placed at the inlet of the flow cell, 68% of bacterial inactivation is achieved without any modification of bacterial cell shape. Furthermore, a high and near-complete biomass removal is achieved (99%) after a subsequent forward flush of the electrically treated biofilm. However, placing a hydrogen-producing electrode at the inlet reveals a slightly lower bacterial inactivation (65%) and lower biomass removal (77%). Additional systematic experiments using individually sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), or gas microbubbles enabled to elucidate the cause of biofilm removal, synergic effect of caustic agent NaOH and microbubbles.
  • Innovative concentrated photovoltaic thermal (CPV/T) system with combined hydrogen and MgO based storage

    Burhan, Muhammad; Chen, Qian; Shahzad, Muhammad Wakil; Ybyraiymkul, Doskhan; Akhtar, Faheem; Ng, Kim Choon (International Journal of Hydrogen Energy, Elsevier BV, 2020-10-10) [Article]
    The intermittency of renewable energy resources which only have localized availability with low energy density, is the main reasons for our reliance on conventional fossil fuels. If steady supply and high energy quality can be achieved then solar energy potential is enough to meet the global energy demand. Heat and electricity both are equally important forms of derived energies. In this paper, an innovative configuration of solar energy system for simultaneous need of electricity and high grade thermal energy, is presented and discussed along with the long term energy storage solution. The proposed CPV/T system, with hydrogen based electrical and MgO based thermal storage, can produce electricity and high-temperature thermal energies at efficiency of 30% and 70% respectively. The CPV-Hydrogen configuration achieved Solar to Hydrogen efficiency of 19%. On the other hand, the MgO based TES system obtained 80% material storage efficiency at 400 °C which can be easily achieved with the concentrated thermal energy density of 240 Suns.
  • Counterintuitive Wetting Transitions in Doubly Reentrant Cavities as a Function of Surface Make-Up, Hydrostatic Pressure, and Cavity Aspect Ratio

    Arunachalam, Sankara; Ahmad, Zain; Das, Ratul; Mishra, Himanshu (Advanced Materials Interfaces, Wiley, 2020-10-07) [Article]
    Surfaces that entrap air underwater serve numerous practical applications, such as mitigating cavitation erosion and reducing frictional drag. These surfaces typically rely on perfluorinated coatings. However, the non-biodegradability and fragility of the coatings limit practical applications. Thus, coating-free, sustainable, and robust approaches are desirable. Recently, a microtexture comprising doubly reentrant cavities (DRCs) has been demonstrated to entrap air on immersion in wetting liquids. While this is a promising approach, insights into the effects of surface chemistry, hydrostatic pressure, and cavity dimensions on wetting transitions in DRCs remain unavailable. In response, Cassie-to-Wenzel transitions into circular DRCs submerged in water are investigated and compared with those in cylindrical “simple” cavities (SCs). It is found that at low hydrostatic pressures (≈50 Pa), DRCs with hydrophilic (θo ≈ 40°) and hydrophobic (θo ≈ 112°) make-ups fill within 105 and 107 s, respectively, while SCs with hydrophilic make-up fill within <10−2 s. Under elevated hydrostatic pressure (P ≤ 90 kPa), counterintuitively, DRCs with hydrophobic make-up fill dramatically faster than the commensurate SCs. This comprehensive report should provide a rational framework for harnessing microtexturing and surface chemistry toward coating-free liquid repellency.
  • Effect of localized hydrodynamics on biofilm attachment and growth in a cross-flow filtration channel

    Kerdi, Sarah; Qamar, Adnan; Vrouwenvelder, Johannes S.; Ghaffour, NorEddine (Water Research, Elsevier BV, 2020-10-07) [Article]
    Biofilm attachment and growth in membrane filtration systems are considerably influenced by the localized flow inside the feed channel. The present work aims to map the biofilm attachment/growth mechanism under varying flow conditions. Effect of varying clearance region (space between the spacer filament and membrane surface) on biofouling pattern is investigated by using three 3D-printed pillar spacers having different filament diameters of 340, 500, and 1000 µm while maintaining the same pillar orientation, diameter and height. Direct Numerical Simulations (DNS) and Optical Coherence Tomography (OCT) were carried out to accurately predict the local hydrodynamics behavior and in-situ monitor the biofilm formation. On spacer filaments, biofouling attachment is primarily observed in the regions where low and non-fluctuating shear stresses are present. Conversely, on membrane surface, highest biofouling attachment was observed under spacer filaments where high shear stresses are prevalent along with low clearance height. Furthermore, as filtration time progresses, the biofilm grows faster on the membrane in the center of spacer cells where low shear stress with steady hydrodynamics conditions are prevalent. The proposed hydrodynamics approach envisages a full spectrum of spacer design constraints that can lead to intrinsic biofilm mitigation while improving filtration performance of membranes based water treatment.
  • Solar-heated submerged vacuum membrane distillation system with agitation techniques for desalination

    Bamasag, Ahmad; Alqahtani, Talal; Sinha, Shahnawaz; Ghaffour, NorEddine; Phelan, Patrick (Separation and Purification Technology, Elsevier BV, 2020-10-07) [Article]
    Submerged membrane distillation (S-MD) has been proposed as an alternative to conventional cross-flow MD systems to desalinate hypersaline water. In conventional S-MD systems, the hydrophobic membrane is submerged in the feed water tank that is directly heated by an electric heating element, eliminating the need for feed pumping. In this study, a solar-heated submerged vacuum membrane distillation (S-VMD) system that uses an evacuated tube collector as the feed container is proposed. Indoor tests under steady-state operating conditions and daily outdoor tests under ambient weather conditions were conducted to investigate the system’s functionality. The effect of two agitation techniques (aeration and internal circulation) to reduce temperature and concentration polarizations were studied. The daily performance tests revealed that the solarheated S-VMD system can achieve a permeate flux of 5.9 to 11.1 kg·m-2·h-1 depending on solar intensity. The permeate flux was enhanced by 9% under aeration and by 22% under circulation in the outdoor tests. The water production per solar absorbing area can be as high as 0.96 kg·m-2·h1. The system maintained a stable permeate flux and excellent water quality over a long-term operation. The small-scale system can provide fresh water in remote areas with limited natural resources.
  • Editorial perspective: Viruses in wastewater: wading into the knowns and unknowns

    Cao, Bin; Gu, April Z.; Hong, Pei-Ying; Ivanek, Renata; Li, Baikun; Wang, Aijie; Wu, JingYi (Environmental Research, Elsevier BV, 2020-10-06) [Article]
    The COVID-19 pandemic has posed immense challenges to the fields of public health, economy and education worldwide. Yet, its transmission and attenuation in the environment are not fully elucidated. What we do know is that the water and wastewater treatment plants (WTPs/WWTPs) are most susceptible to viral contamination specifically during the current COVID-19 outbreak. Although knowledge about SARS-CoV-2 in sewage and WWTPs is limited (Foladori et al., 2020), SARS-CoV-2 is likely to be rapidly inactivated under increased temperature and by disinfectants such as bleach, ethanol, benzylalkonium chloride, povidone-iodine and chloroxylenol (Chin et al., 2020). The application of secondary disinfection measures, like dosing of chloramines to maintain a certain residual chlorine level in the distribution network adds to further protection from contamination (Bhowmick et al., 2020). However, as municipal network receives huge amount of wastewater from asymptomatic patients and treated sewage from hospitals, SARS-CoV-2 from improperly disinfected wastewater might persist for a prolonged time in pipelines, in turn becoming a secondary source of transmission (Zhang et al., 2020). Therefore, we must make sure the wastewater coming out of the SARS-CoV-2 infected areas should be properly disinfected in order to reduce the impact on the receiving water bodies. This brings in the need for careful consideration of disinfection and removal strategies for SARS-CoV-2 from contaminated waters (Kitajima et al., 2020).
  • Fluorescence-assisted real-time study of magnetically immobilized enzyme stability in a crossflow membrane bioreactor

    Gebreyohannes, Abaynesh Yihdego; Geens, T.; Kubarev, A.; Roeffaers, M.; Naessens, W.; Swusten, T.; Verbiest, T.; Nopens, I.; Nunes, Suzana Pereira; Vankelecom, I. F.J. (Colloids and Surfaces A: Physicochemical and Engineering Aspects, Elsevier BV, 2020-10-04) [Article]
    The detailed structures and distribution of enzymatically active magnetic-responsive dynamic layers (EnzSP) were investigated for the first time in a crossflow superparamagnetic biocatalytic membrane reactor (XF-BMRSP). The trade-off between a higher mass transfer rate, lower fouling tendency, and preventing washout of the dynamic layer, highly depends on the balance of the various forces that act on the EnzSP. The real-time visual inspection of the biointerface was realized through the design and fabrication of an adapted crossflow system, guided by computational fluid dynamics (CFD) simulations. Time-resolved images of the dynamic layer under a broad range of operational conditions was obtained using fluorescence microscopy. The deposition, dispersion and stability of the dynamic layer was mainly governed by the external magnetic force. The shear force did not cause significant particle washout when a buffer solution was recirculated without permeation even under a turbulent flow regime (6.4 cm/s ∼ Re = 5200). The removal of the external magnetic force after initial magnetic immobilization of the EnzSP, or the substitution of a smooth flow velocity by the propagation of an impulse flow, significantly affected the stability of the dynamic layer. Although membrane fouling occurs at the membrane-solution interface, where a laminar flow regime prevails, most membrane fouling models are based on turbulent flow. Therefore, the detailed, time-resolved images obtained here can provide solid foundation for the development of theoretical models that can describe the membrane fouling under the more representative laminar flow regime.
  • Role of dissolved air flotation (DAF) and liquid ferrate on mitigation of algal organic matter (AOM) during algal bloom events in RO desalination

    Alshahri, Abdullah; Fortunato, Luca; Zaouri, Noor A.; Ghaffour, NorEddine; Leiknes, TorOve (Separation and Purification Technology, Elsevier BV, 2020-09-28) [Article]
    Harmful Algal Blooms (HABs) are considered a major contributor to membrane biofouling in Seawater Reverse Osmosis (SWRO) desalination plants. The presence of HABs in the raw feed water leads to an increase in membrane fouling rate, increase of chemical consumption, and can cause temporary shutdown of plants. Effective pretreatment can reduce the amount of organic foulants reaching the RO membrane and alleviate the problem of flux decline during RO operation and frequent membrane cleaning using chemicals. This study compared the effect of in-situ generated liquid ferrate and ferric chloride in combination with dissolved air flotation (DAF) as a pretreatment strategy to remove algal cells and algal organic matter (AOM) during algal bloom events. Experiments were performed using a bench-scale DAF unit. HABs conditions were simulated by harvesting AOM from cultivating Chaetoceros affinis (CA) in raw seawater to a concentration of around 10 mg C/L of dissolved organic carbon (DOC). The liquid ferrate was generated in-situ by wet oxidation of ferric chloride in analkaline media. The best performance was achieved with the combined use of liquid ferrate and DAF, removing up to 100% of algal cells, 99.99% of adenosine tri-phosphate (ATP), and up to 92% of AOM.
  • Resistance assessment of microbial electrosynthesis for biochemical production to changes in delivery methods and CO2 flow rates

    Bian, Bin; Xu, Jiajie; Katuri, Krishna; Saikaly, Pascal (Bioresource Technology, Elsevier BV, 2020-09-28) [Article]
    Microbial electrosynthesis (MES) for CO2 valorization could be influenced by fluctuations in CO2 mass transfer and flow rates. In this study, we developed an efficient method for CO2 delivery to cathodic biofilm by directly sparging CO2 through the pores of ceramic hollow fiber wrapped with Ni-foam/carbon nanotube electrode, and obtained 45% and 77% higher acetate and methane production, respectively. This was followed by the MES stability test in response to fluctuations in CO2 flow rates varying from 0.3 ml/min to 10 ml/min. The biochemical production exhibited an increasing trend with CO2 flow rates, achieving higher acetate (47.0 ± 18.4 mmol/m2/day) and methane (240.0 ± 32.2 mmol/m2/day) generation at 10 ml/min with over 90% coulombic efficiency. The biofilm and suspended biomass, however, showed high resistance to CO2 flow fluctuations with Methanobacterium and Acetobacterium accounting for 80% of the total microbial community, which suggests the robustness of MES for onsite carbon conversion.
  • Longitudinal vibration analysis of sucker rod based on a simplified thermo-solid model

    Wang, Xiaobing; Lv, Leigang; Li, Sen; Pu, Hui; Liu, Yang; Bian, Bin; Li, Dong (Journal of Petroleum Science and Engineering, Elsevier BV, 2020-09-19) [Article]
    The longitudinal vibration of a sucker rod may change plunger stroke, thus affecting the pumping efficiency. In the study, a simplified thermo-solid coupling model of the longitudinal vibration of a sucker rod is established based on the consideration of the effect of the temperature along the well depth. Then, with the finite element method, the influence of longitudinal vibration of a continuous steel sucker rod on plunger stroke is studied. The calculation model involves two stages. In the first stage, the polished rod position remains stationary, whereas the sucker rod vibrates only under its gravity and liquid column gravity. The final stable state of the sucker rod is the initial state of the second stage. This stage aims to eliminate the effect of the initial tensile vibration. The longitudinal vibration characteristics of the sucker rod in the second stage are calculated based on the consideration of the excitations of both the polished rod displacement and the liquid column load in order to ensure the accuracy of calculation results. The influences of the frequency of stroke, stroke, and the length of sucker rod on plunger displacement are studied. The plunger displacement is slightly lagged behind the excitation on the polished rod due to the joint action of elasticity and load. The frequency of stroke, stroke, and the length of sucker rod affect the overtravel. When the sucker rod length is 2000 m, the overtravel reaches 0.12 m. Other parameters can also be optimized with this model.
  • Effect of phosphate availability on biofilm formation in cooling towers.

    Pinel, Ingrid S M; Kim, Lan Hee; Proença Borges, Vitor R; Farhat, Nadia M; Witkamp, Geert Jan; van Loosdrecht, Mark C M; Vrouwenvelder, Johannes S. (Biofouling, Informa UK Limited, 2020-09-05) [Article]
    Phosphate limitation has been suggested as a preventive method against biofilms. P-limited feed water was studied as a preventive strategy against biofouling in cooling towers (CTs). Three pilot-scale open recirculating CTs were operated in parallel for five weeks. RO permeate was fed to the CTs (1) without supplementation (reference), (2) with supplementation by biodegradable carbon (P-limited) and (3) with supplementation of all nutrients (non-P-limited). The P-limited water contained ≤10 µg PO4 l-1. Investigating the CT-basins and coupons showed that P-limited water (1) did not prevent biofilm formation and (2) resulted in a higher volume of organic matter per unit of active biomass compared with the other CTs. Exposure to external conditions and cycle of concentration were likely factors that allowed a P concentration sufficient to cause extensive biofouling despite being the limiting compound. In conclusion, phosphate limitation in cooling water is not a suitable strategy for CT biofouling control.
  • Removal of Bacteria and Organic Carbon by an Integrated Ultrafiltration—Nanofiltration Desalination Pilot Plant

    Rehman, Zahid Ur; Khojah, Bayan; Leiknes, TorOve; Alsogair, Safiya; Alsomali, Mona (Membranes, MDPI AG, 2020-09-04) [Article]
    Fouling caused by organic matter and bacteria remains a significant challenge for the membrane-based desalination industry. Fouling decreases the permeate quality and membrane performance and also increases energy demands. Here, we quantified the amount of organic matter and bacteria at several stages along the water-treatment train of an integrated ultrafiltration–nanofiltration seawater treatment pilot plant. We quantified the organic matter, in terms of Total Organic Carbon (TOC) and Assimilable Organic Carbon (AOC), and evaluated its composition using Liquid Chromatography for Organic Carbon Detection (LC-OCD). The bacterial cells were counted using Bactiquant. We found that ultrafiltration (UF) was effective at removing bacterial cells (99.7%) but not TOC. By contrast, nanofiltration (NF) successfully removed both TOC (95%) and bacterial cells. However, the NF permeate showed higher amounts of AOC than seawater. LC-OCD analysis suggested that the AOC was mostly composed of low molecular weight neutral substances. Furthermore, we found that the cleaning of the UF membrane using chemically enhanced backwash reduced the amount of AOC released into the UF permeate. By implementing the cleaning-in-place of the NF membrane, the pressure drop was restored to the normal level. Our results show that the UF and NF membrane cleaning regimes investigated in this study improved membrane performance. However, AOC remained the hardest-to-treat fraction of organic carbon. AOC should, therefore, be monitored closely and regularly to mitigate biofouling in downstream processes.
  • Conceptual design of a dynamic turbospacer for efficient low pressure membrane filtration

    Ali, Syed Muztuza; Qamar, Adnan; Phuntsho, Sherub; Ghaffour, NorEddine; Vrouwenvelder, Johannes S.; Shon, Ho Kyong (Desalination, Elsevier BV, 2020-09-03) [Article]
    This study presented a conceptual design of a novel dynamic turbospacer to enhance the performance of a low pressure membrane filtration process. It consists of ladder type filaments and a series of microturbine networks within the filament cells. The rotation of the turbines leads to the formation of turbulence in the feed channel that prevents foulants accumulation. Direct numerical simulation (DNS) was conducted to characterize the fluid flow behaviors of the feed channel for the proposed turbospacer and compared with a standard symmetric non-woven feed spacer. Further, their performances were investigated for a low pressure ultrafiltration (UF) process in a lab-scale experimental setup using 2.8 mm thick 3D printed prototypes of the turbospacer and the standard spacer. Experiments for the proof of this concept were conducted at 173 mL/min and 250 mL/min feed solution inlet velocity when Reynolds number of the flow is 160 and 230 respectively. Substantial reductions in fouling effects using the turbospacer was confirmed by the in-situ Optical Coherence Tomography (OCT) scans of the fouling cake layer accumulated over the membrane during the filtration of seawater with high fouling potential. The proposed turbospacer also lowered the average pressure drop by 4 times and enhanced the specific permeate flux by more than 3 times at 173 mL/min inlet flowratre. At the same operating condition, the specific energy consumption for the turbospacer was found about 2.5 folds lower than the standard spacer.
  • Antibacterial rGO-CuO-Ag film with contact- and release-based inactivation properties.

    Alayande, Abayomi Babatunde; Kim, Chang-Min; Vrouwenvelder, Johannes S.; Kim, In S (Environmental research, Elsevier BV, 2020-09-02) [Article]
    To reduce the high operational costs of water treatment because of membrane biofouling, next-generation materials are being developed to counteract microbial growth. These modern anti-biofouling strategies are based on new membrane materials or membrane surface modifications. In this study, antimicrobial films comprising rGO, rGO-CuO, rGO-Ag, and rGO-CuO-Ag were synthesized, evaluated, and tested for potential biofouling control using Pseudomonas aeruginosa PAO1 as the model bacterium. The combined rGO-CuO-Ag film displayed enhanced reduction (10-log reduction) in biofouling in comparison to the rGO film (control), followed by the rGO-Ag film (8-log reduction) and rGO-CuO film (0-log reduction). This demonstrated that the use of mixed antimicrobial agents is more effective in reducing biofouling than that of a single agent. The rGO-Cu-Ag film exhibited consistent, controlled, and moderate release of silver (Ag) ions. The release of Ag ions produced a long-lasting antimicrobial effect. These results underscore the potential applications of combined antimicrobial surface-based agents in practice and further research.
  • Sacrificial coating development for biofouling control in membrane systems

    Nava Ocampo, Maria F.; Bucs,Szilard; Farinha, Andreia S.F.; Son, Moon; Logan, Bruce E.; Vrouwenvelder, Johannes S. (Desalination, Elsevier BV, 2020-08-28) [Article]
    Current cleaning strategies for biofouling control on spiral wound membrane systems used for seawater desalination are not effective and can hinder long-term membrane performance. To enable effective cleaning of a membrane, we examined the in-situ application and the use of a sacrificial multilayer polyelectrolyte coating on the membrane surface. The membrane coating was based on a layer-by-layer assembly approach using two non-toxic linkers, poly (diallyl-dimethyl ammonium chloride) and poly(sodium-4-styrene sulfonate). This polyelectrolyte coating was effectively applied on the membrane surface under cross-flow conditions, and it was stable on the membrane surface under continuous operation. Coating removal requires only a concentrated sodium chloride solution (synthetic brine in our study) adjusted to pH 11. Using this procedure, both the biofilm and the sacrificial layer could be simultaneously removed, leaving a clean surface compared to the non-coated membrane. Biofouling tests showed that the coated membrane had two-fold higher permeate flux recovery than the control non-coated membrane. The used polyelectrolyte sacrificial coatings avoided the use of toxic linkers and harsh cleaning chemicals, and thus it is a suitable technique for biofouling control on reverse osmosis spiral wound membranes.

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