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  • Physical and economical evaluation of laboratory-scale membrane bioreactor by long-term relative cost–benefit analysis

    Ayub, Mariam; Saeed, Nadeeha; Chung, Shinho; Nawaz, Muhammad Saqib; Ghaffour, NorEddine (Journal of Water Reuse and Desalination, IWA Publishing, 2020-07-08) [Article]
    Two laboratory-scale single-stage submerged membrane bioreactors (MBRs) were operated in parallel to examine the effect of different flux conditions and several fouling mitigation methods. After control operation (filtration only), three fouling control methods (relaxation, standard backwash and chemical backwash) at 27 LMH flux and four different flux conditions (54, 36, 27 and 18 LMH) with standard backwash were applied. Physical performance of MBRs was evaluated based on the operational duration to reach maximum transmembrane pressure and the volume of permeate produced during the operational duration. Then relative cost–benefit analysis was carried out. Results showed that the combination of chemical backwash and standard backwash was the most effective for fouling mitigation in terms of physical improvement of MBR performance. However, the combination proved less economical (400% + α relative cost) than standard backwash alone (343% relative cost), because of the additional cost for pumps and chemical. It also showed that lower flux (18 LMH) is desirable as it showed better physical performance (1,770% improvement as compared to the highest flux, 54 LMH) and proved more economical than higher flux configuration. Therefore, it is concluded that the operation with standard backwash at the lowest possible flux is the best combination to improve MBR performance as well as long-term cost–benefit.
  • Biofouling control by phosphorus limitation strongly depends on the assimilable organic carbon concentration.

    Javier, Luisa; Farhat, Nadia M; Desmond, Peter; Linares, Rodrigo Valladares; Bucs,Szilard; Kruithof, Joop C; Vrouwenvelder, Johannes S. (Water research, Elsevier BV, 2020-07-05) [Article]
    Nutrient limitation is a biofouling control strategy in reverse osmosis (RO) membrane systems. In seawater, the assimilable organic carbon content available for bacterial growth ranges from about 50 to 400 μg C·L-1, while the phosphorus concentration ranges from 3 to 11 μg P·L-1. Several studies monitored biofouling development, limiting either carbon or phosphorus. The effect of carbon to phosphorus ratio and the restriction of both nutrients on membrane system performance have not yet been investigated. This study examines the impact of reduced phosphorus concentration (from 25 μg P·L-1 and 3 μg P·L-1, to a low concentration of ≤0.3 μg P·L-1), combined with two different carbon concentrations (250 C L-1 and 30 μg C·L-1), on biofilm development in an RO system. Feed channel pressure drop was measured to determine the effect of the developed biofilm on system performance. The morphology of the accumulated biomass for both carbon concentrations was characterized by optical coherence tomography (OCT) and the biomass amount and composition was quantified by measuring total organic carbon (TOC), adenosine triphosphate (ATP), total cell counts (TCC), and extracellular polymeric substances (EPS) concentration for the developed biofilms under phosphorus restricted (P-restricted) and dosed (P-dosed) conditions. For both carbon concentrations, P-restricted conditions (≤0.3 μg P·L-1) limited bacterial growth (lower values of ATP, TCC). A faster pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 250 μg C·L-1 was dosed. This faster pressure drop increase can be explained by a higher area covered by biofilm in the flow channel and a higher amount of produced EPS. Conversely, a slower pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 30 μg C·L-1 was dosed. Results of this study demonstrate that P-limitation delayed biofilm formation effectively when combined with low assimilable organic carbon concentration and thereby, lengthening the overall membrane system performance.
  • Effect of organic micropollutants on biofouling in a forward osmosis process integrating seawater desalination and wastewater reclamation

    Kim,Youngjin; Kim, Lan Hee; Vrouwenvelder, Johannes S.; Ghaffour, NorEddine (Journal of Hazardous Materials, Elsevier BV, 2020-07-04) [Article]
    This study systematically investigated the effect of organic micropollutants (OMPs) on biofouling in forward osmosis (FO) integrating wastewater treatment and seawater dilution. Synthetic seawater (0.6 M sodium chloride) was used as a draw solution and synthetic municipal wastewater as a feed solution. To evaluate the impact of OMPs in a replicate parallel study, wastewater was supplemented with a mixture of 7 OMPs (OMPs-feed) and without OMPs (control) during 8 batch filtration cycles with feed and draw solution replacement after each filtration. The FO performance (water flux), development and microbial composition properties of biofilm layers on the wastewater side of the FO membrane were studied. Compared to the control without OMPs, the FO fed with OMPs containing wastewater showed (i) initially the same water flux and flux decline during the first filtration cycle, (ii) with increasing filtration cycle a lower flux decline and (iii) lower concentrations for the total cells, ATP, EPS carbohydrates and proteins in biofilm layers, and (iv) a lower diversity of the biofilm microbial community composition (indicating selective pressure) and (v) increasing rejection of 6 of the 7 OMPs. In essence, biofouling on the FO membrane showed (i) a lower flux decline in the presence of OMPs in the feed water and (ii) a higher OMPs rejection, both illustrating better membrane performance. This study has a significant implication for optimizing osmotic dilution in terms of FO operation and OMPs rejection.
  • A Robust, Safe and Scalable Magnetic Nanoparticle Workflow for RNA Extraction of Pathogens from Clinical and Environmental Samples

    Ramos Mandujano, Gerardo; Salunke, Rahul; Mfarrej, Sara; Rachmadi, Andri Taruna; Hala, Sharif; Xu, Jinna; Alofi, Fadwa S; Khogeer, Asim; Hashem, Anwar M; Almontashiri, Naif AM; Alsomali, Afrah; Hamdan, Samir; Hong, Pei-Ying; Pain, Arnab; Li, Mo (Cold Spring Harbor Laboratory, 2020-06-29) [Preprint]
    <jats:p>Diagnosis and surveillance of emerging pathogens such as SARS-CoV-2 depend on nucleic acid isolation from clinical and environmental samples. Under normal circumstances, samples would be processed using commercial proprietary reagents in Biosafety 2 (BSL-2) or higher facilities. A pandemic at the scale of COVID-19 has caused a global shortage of proprietary reagents and BSL-2 laboratories to safely perform testing. Therefore, alternative solutions are urgently needed to address these challenges. We developed an open-source method called Magnetic- nanoparticle-Aided Viral RNA Isolation of Contagious Samples (MAVRICS) that is built upon reagents that are either readily available or can be synthesized in any molecular biology laboratory with basic equipment. Unlike conventional methods, MAVRICS works directly in samples inactivated in acid guanidinium thiocyanate-phenol-chloroform (e.g., TRIzol), thus allowing infectious samples to be handled safely without biocontainment facilities. Using 36 COVID-19 patient samples, 2 wastewater samples and 1 human pathogens control sample, we showed that MAVRICS rivals commercial kits in validated diagnostic tests of SARS-CoV-2, influenza viruses, and respiratory syncytial virus. MAVRICS is scalable and thus could become an enabling technology for widespread community testing and wastewater monitoring in the current and future pandemics.</jats:p>
  • Flow field in fouling spiral wound reverse osmosis membrane modules using MRI velocimetry

    Bristow, Nicholas W.; Vogt, Sarah J.; O'Neill, Keelan T.; Vrouwenvelder, Johannes S.; Johns, Michael L.; Fridjonsson, Einar O. (Desalination, Elsevier BV, 2020-06-26) [Article]
    Magnetic Resonance Imaging (MRI) velocimetry was applied to study non-invasively the water flow field inside a spiral-wound desalination membrane module (diameter: 2.5 in.; length: 18.5 in.), located in a pressure vessel, at typical practice operational conditions as a function of alginate fouling, simulating extracellular polymeric substances (EPS). Cross-sectional velocity images were acquired at an in-plane spatial resolution of 0.137 mm at multiple locations along the length of the reverse osmosis module and were acquired as a function of alginate concentration. At a total system alginate concentration of 3.25 mg/l, significant changes in the cross-sectional velocity map were observed near the module inlet due to alginate fouling, with limited changes observed in the middle and outlet regions of the module. When the total system alginate concentration was increased to 75 mg/l, it caused the module brine seal to fail resulting in significant local water flow by-passing the membrane module. This was clearly discernible in this opaque membrane system using MRI and resulting in dramatic changes in fluid velocity distribution through the membrane module. These observations of significant flow field heterogeneity as fouling develops are consistent with ‘irreversible’ fouling effects noted frequently in practice by the water treatment industry.
  • Enhanced Pollutant Adsorption and Regeneration of Layered Double Hydroxide-Based Photoregenerable Adsorbent.

    Suh, Min-Jeong; Weon, Seunghyun; Li, Renyuan; Wang, Peng; Kim, Jae-Hong (Environmental science & technology, American Chemical Society (ACS), 2020-06-20) [Article]
    Efforts to combine photocatalysts with organic and inorganic adsorbents in engineered composite materials have been pursued extensively to harness sunlight for a green, sustainable regeneration of exhausted adsorbent. Recent advances combining benchmark photocatalyst, titanium dioxide (TiO2), with an inorganic adsorbent, layered double hydroxides (LDHs), have shown potential for an inorganic adsorbent-photocatalyst system but faced critical limitations in realizing practical applications: low adsorption capacity and slow, inefficient photocatalytic regeneration. This study presents an enhanced TiO2/LDH based material that demonstrates a dramatically increased efficiency for both decontamination through adsorption and subsequent solar, photocatalytic regeneration. The combination of delamination and high temperature treatment of LDH is utilized to drastically enhance the adsorption capacity toward model contaminant Methyl Orange to 1450-1459 mg/g, which is even higher than most commercial and lab-synthesized carbon-based adsorbents. Light-active plasmonic nanoparticles are employed to increase the photocatalytic regeneration performance, and experimental results show that the synthesized composite material regains above 97% of its adsorption capacity for 5 cycles of regeneration and readsorption. Overall, the results of this study demonstrate potential for the development of inorganic multifunctional adsorbents that can harness a variety of chemical reactions without the loss of adsorptivity over long-term use.
  • Photothermoelectric Response of Ti3C2Tx MXene Confined Ion Channels

    Hong, Seunghyun; Zou, Guodong; Kim, Hyunho; Huang, Dazhen; Wang, Peng; Alshareef, Husam N. (ACS Nano, American Chemical Society (ACS), 2020-06-15) [Article]
    With recent growing interest in biomimetic smart nanochannels, a biological sensory transduction in response to external stimuli has been of particular interest in the development of biomimetic nanofluidic systems. Here we demonstrate the MXene-based subnanometer ion channels that convert external temperature changes to electric signals via preferential diffusion of cations under a thermal gradient. In particular, coupled with a photothermal conversion feature of MXenes, an array of the nanoconfined Ti3C2Tx ion channels can capture trans-nanochannel diffusion potentials under a light-driven axial temperature gradient. The nonisothermal open-circuit potential across channels is enhanced with increasing cationic permselectivity of confined channels, associated with the ionic concentration or pH of permeant fluids. The photothermoelectric ionic response (evaluated from the ionic Seebeck coefficient) reached up to 1 mV·K–1, which is comparable to biological thermosensory channels, and demonstrated stability and reproducibility in the absence and presence of an ionic concentration gradient. With advantages of physicochemical tunability and easy fabrication process, the lamellar ion conductors may be an important nanofluidic thermosensation platform possibly for biomimetic sensory systems.
  • A Calibration Procedure for Field and UAV-Based Uncooled Thermal Infrared Instruments.

    Aragon Solorio, Bruno Jose Luis; Johansen, Kasper; Parkes, Stephen; Malbeteau, Yoann; Almashharawi, Samir; Al-Amoudi, Talal; Andrade, Cristhian F; Turner, Darren; Lucieer, Arko; McCabe, Matthew (Sensors (Basel, Switzerland), 2020-06-14) [Article]
    Thermal infrared cameras provide unique information on surface temperature that can benefit a range of environmental, industrial and agricultural applications. However, the use of uncooled thermal cameras for field and unmanned aerial vehicle (UAV) based data collection is often hampered by vignette effects, sensor drift, ambient temperature influences and measurement bias. Here, we develop and apply an ambient temperature-dependent radiometric calibration function that is evaluated against three thermal infrared sensors (Apogee SI-11(Apogee Electronics, Santa Monica, CA, USA), FLIR A655sc (FLIR Systems, Wilsonville, OR, USA), TeAx 640 (TeAx Technology, Wilnsdorf, Germany)). Upon calibration, all systems demonstrated significant improvement in measured surface temperatures when compared against a temperature modulated black body target. The laboratory calibration process used a series of calibrated resistance temperature detectors to measure the temperature of a black body at different ambient temperatures to derive calibration equations for the thermal data acquired by the three sensors. As a point-collecting device, the Apogee sensor was corrected for sensor bias and ambient temperature influences. For the 2D thermal cameras, each pixel was calibrated independently, with results showing that measurement bias and vignette effects were greatly reduced for the FLIR A655sc (from a root mean squared error (RMSE) of 6.219 to 0.815 degrees Celsius (℃)) and TeAx 640 (from an RMSE of 3.438 to 1.013 ℃) cameras. This relatively straightforward approach for the radiometric calibration of infrared thermal sensors can enable more accurate surface temperature retrievals to support field and UAV-based data collection efforts.
  • Fouling investigation of a full-scale seawater reverse osmosis desalination (SWRO) plant on the Red Sea: Membrane autopsy and pretreatment efficiency

    Fortunato, Luca; Alshahri, Abdullah; Farinha, Andreia S.F.; Zakzouk, Islam; Jeong, Sanghyun; Leiknes, TorOve (Desalination, Elsevier BV, 2020-06-10) [Article]
    In this study, the membrane autopsy was performed on a full-scale seawater reverse osmosis (SWRO) desalination plant located on the Red Sea. Several techniques were employed to characterize the nature and the fate of the foulants in the process, including LCOCD, ICP-MS, SEM-EDS, TSS, and ATP. The efficiency of the pretreatment in removing the fouling potential was assessed by analyzing the seawater after the intake feed pump, after the spruce media filter (SMF) and after the cartridge filter (CF). The autopsy of the membrane modules and CF operated for long-term revealed the presence of a heterogeneous fouling layer. The organic fraction composition of the fouling layer depended on the module position in the vessel. The inorganic deposits embedded in the layer were mainly composed of aluminum, iron, and magnesium silicate. The inorganic sediments entered the plants from the shoreline seawater intake and accumulated on the CF filter and the membrane. The analysis of the pretreatment performance showed an increase of TSS and ATP after CF, highlighting the inappropriate CF filter replacement time.
  • Organic composition in feed solution of forward osmosis membrane systems has no impact on the boron and water flux but reduces scaling

    Kim, Lan Hee; Bucs,Szilard; Witkamp, Geert Jan; Vrouwenvelder, Johannes S. (Journal of Membrane Science, Elsevier BV, 2020-06-09) [Article]
    This study aimed to characterize the impact of organic and inorganic compounds in the feed solution on the membrane fouling and the boron flux in a forward osmosis (FO) membrane system. Lab-scale FO membrane systems were operated in batch mode, with a solution containing organic compounds (humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA)), scaling constituents (calcium chloride, sodium sulfate), and boric acid as feed solution, and with concentrated sodium chloride as draw solution. Preparations of membrane sample for scanning electron microscopy and energy dispersed spectroscopy (SEM-EDX) by freeze- and by oven-drying showed different results and can therefore not be considered as suitable for the evaluation of the samples. Results showed that the organic fouling layer did not have an impact on water and boron fluxes, but reverse salt flux (RSF) was reduced in the presence of BSA and HA. The molar flux ratio between water and boron was roughly 105, regardless of the presence of the fouling. The hydrophobicity and surface charge of the fouling layer were not related to the boron transport rate. A thicker and more uniform organic fouling layer, as observed, caused a reduced RSF. The organic compounds in the feed solution impeded the crystallisation of gypsum, which can lead to reduce scaling.
  • Mini Review: Metagenomics as a tool to monitor reclaimed water quality.

    Hong, Pei-Ying; Mantilla Calderon, David; Wang, Changzhi (Applied and environmental microbiology, American Society for Microbiology, 2020-06-07) [Article]
    Many biological contaminants are disseminated through water, and their occurrence has potential detrimental impacts on public and environmental health. Conventional monitoring tools rely on cultivation and are not robust in addressing modern water quality concerns. This review proposes metagenomics as a means to provide a rapid, nontargeted assessment of biological contaminants in water. When further coupled with the appropriate methods (e.g., quantitative PCR and flow cytometry) and bioinformatic tools, metagenomics can provide information concerning both the abundance and diversity of biological contaminants in reclaimed waters. Further correlation between the metagenomic-derived data of selected contaminants and the measurable parameters of water quality can also aid in devising strategies to alleviate undesirable water quality. Here, we reviewed metagenomic approaches (i.e., both sequencing platforms and bioinformatic tools) and studies that demonstrated their use for reclaimed water quality monitoring. We also provide recommendations on areas of improvement that will allow metagenomics to significantly impact how the water industry performs reclaimed water quality monitoring in the future.
  • A self-sustainable solar desalination system using direct spray technology

    Chen, Qian; Alrowais, Raid Naif; Burhan, Muhammad; Ybyraiymkul, Doskhan; Shahzad, Muhammad Wakil; Li, Yong; Ng, Kim Choon (Energy, Elsevier BV, 2020-06-07) [Article]
    Solar desalination offers a sustainable solution to growing global water demand due to the geographical coincidence between high solar availability and severe water scarcity. This paper presents a self-sustainable solar desalination system combining a spray-assisted low-temperature desalination system, solar thermal collectors, and heat storage tanks. A mathematical model is firstly developed and validated with laboratory pilot for the proposed large-scale solar-powered desalination system. Afterward, the long-term productivity and energy efficiency of the system is evaluated under the climatic conditions of Makkah, Saudi Arabia. The proposed solar desalination system is able to provide an uninterrupted water supply of 20 kg/day for per square meter solar collector area, and the value can be further increased by optimizing the interactions of the three subsystems, i.e. efficiency of the solar collectors, temperature and heat losses in the storage tank, and energy efficiency of the desalination system. With a collector area of 360 m2, the annual productivity is maximized when the feed flowrate is 1.7 kg/s and the diameter of the heat storage tank is 1.9 m. The desalination cost is estimated to be $1.29/m3, which is much lower than other solar thermal desalination systems.
  • Green Synthesis of Thin-Film Composite Membranes for Organic Solvent Nanofiltration

    Ong, Chi Siang; Falca, Gheorghe; Huang, Tiefan; Liu, Jiangtao; Manchanda, Priyanka; Chisca, Stefan; Nunes, Suzana Pereira (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2020-06-04) [Article]
    Membrane-based liquid filtration systems are key process engineering platforms for chemical industry, particularly for solvent intensive processes. While they are used in large-scale for desalination, water treatment and in the food industry, polymeric membranes are mostly fabricated from solutions in organic solvents with concerning toxicity. Herein, we report a green fabrication method using decanoic acid as an alternative green solvent. The low vapor pressure, relative to common organic solvents, reduces the toxicity and the harm to the environment. The decanoic acid was used to dissolve trimesoyl chloride and reacted with polyethylenimine in the aqueous solution via an interfacial polymer reaction to produce a thin film composite membrane. The resultant membrane had high permeances for water (~52 L m-2 h-1 bar-1) and organic solvents (16 to 124 L m-2 h-1 bar-1) and selectivity in the nanofiltration range. Therefore, our method of membrane preparation can offer an excellent and green platform for molecular separations for the chemical and biochemistry industry.
  • Numerical analysis of the effect of surface recombination on N-atom in discharge and post-discharge region

    Li, Sen; Wang, Xiaobing; Liu, Yang; Cheng, Qinglin; Bian, Bin; Pu, Hui; Ma, Tingting; Tang, Bo (Physics of Plasmas, AIP Publishing, 2020-06-01) [Article]
    In this paper, the effect of surface recombination on N-atom production is discussed through a one-dimensional simulation of Townsend dielectric barrier discharge in pure N2 based on a fluid model. By comparison of the experimental results, the recommended value of the sticking coefficient of N–N surface recombination is 0.5–1. The spatial-temporal distribution of N-atom of simulation results in discharge and post-discharge agree with experimental results. When the sticking coefficient is 0.5, the primary active species include N, N2(A), and N2(a0). N4 þ is the densest positive ion, which can reach 4.77 109 cm3. N-atom can reach the saturation level within about 30 ms. The highest number density is 3.14 1014 cm3 at the position 0.25 mm away from the surface. The numerical simulation results are very consistent with the experimental results. The contribution of surface recombination and three-body recombination for the decay of N-atom are roughly equal in the post-discharge region.
  • Fouling control in a gravity-driven membrane (GDM) bioreactor treating primary wastewater by using relaxation and/or air scouring

    Fortunato, Luca; Ranieri, Luigi; Naddeo, Vincenzo; Leiknes, TorOve (Journal of Membrane Science, Elsevier BV, 2020-05-21) [Article]
    Gravity-driven membrane bioreactors (GD-MBR) have been proposed as a sustainable water treatment due to the low energy requirements in terms of operation. The objective of this study is to investigate the effect of different physical cleaning strategies on the membrane performance in a gravity-driven membrane bioreactor treating primary wastewater. The Optical Coherence Tomography (OCT) allowed evaluating the impact of the physical cleaning on the biomass developed on the membrane surface. Applying relaxation did not enhance the membrane performance, however, it led to an increase in thickness and a decrease in the biomass specific hydraulic resistance. Using air scouring under continuous filtration increased the biomass specific hydraulic resistance by compressing the biomass (~50% decrease in thickness). When air scouring was applied at the end of a relaxation cycle, a higher biomass removal and a significant increase in flux (250%) were observed. Biopolymers were found to constitute 55% of the fouling layer. This study highlighted the suitability of an in-situ monitoring approach as a key tool to evaluate the impact of different physical cleaning strategies on the biomass removal in membrane filtration process.
  • Mapping the condition of macadamia tree crops using multi-spectral UAV and WorldView-3 imagery

    Johansen, Kasper; Duan, Qibin; Tu, Yu-Hsuan; Searle, Chris; Tu, Yu Hsuan; Phinn, Stuart; Robson, Andrew; McCabe, Matthew (ISPRS Journal of Photogrammetry and Remote Sensing, Elsevier BV, 2020-05-20) [Article]
    Australia is one of the world’s largest producers of macadamia nuts. As macadamia trees can take up to 15 years to mature and produce maximum yield, it is important to optimize tree condition. Field based assessment of macadamia tree condition is time-consuming and often inconsistent. Using remotely sensed imagery may allow for faster, more extensive, and more consistent assessment of macadamia tree condition. To identify individual macadamia tree crowns, high spatial resolution imagery is required. Hence, the objective of this work was to develop and test an approach to map the condition of individual macadamia tree crowns using both multispectral Unmanned Aerial Vehicle (UAV) and WorldView-3 imagery for different macadamia varieties and three different sites located near Bundaberg, Australia. A random forest classifier, based on all available spectral bands and selected vegetation indices was used to predict five condition categories, ranging from excellent (category 1) to poor (category 5). Various combinations of the developed models were tested between the three sites and over time. The results showed that the multi-spectral WorldView-3 imagery produced the lowest out of bag (OOB) classification errors in most cases. However, for both the UAV and the WorldView-3 imagery, more than 98.5% of predicted macadamia condition categories were either correctly mapped or offset by a single category out of the five condition categories (excellent, good, moderate, fair and poor) for trees of the same variety and at one point in time. Multi-temporally, the WorldView-3 imagery performed better than the UAV data for predicting the condition of the same macadamia tree variety. Applying a model from one site to another site with the same macadamia tree variety produced OOB classification between 31.20 and 42.74%, but with > 98.63% of trees predicted within a single condition category. Importantly, models trained based on one type of macadamia tree variety could not be successfully applied to a site with another variety. The developed classification models may be used as a decision and management support tool for the macadamia industry to inform management practices and improve on-demand irrigation, fertilization, and pest inspection at the individual tree level.
  • Biomimetic Coating-free Superomniphobicity.

    Das, Ratul; Ahmad, Zain; Nauruzbayeva, Jamilya; Mishra, Himanshu (Scientific reports, Springer Science and Business Media LLC, 2020-05-15) [Article]
    Superomniphobic surfaces, which repel droplets of  polar and apolar liquids, are used for reducing frictional drag, packaging electronics and foods, and separation processes, among other applications. These surfaces exploit perfluorocarbons that are expensive, vulnurable to physical damage, and have a long persistence in the environment. Thus, new approaches for achieving superomniphobicity from common materials are desirable. In this context, microtextures comprising "mushroom-shaped" doubly reentrant pillars (DRPs) have been shown to repel drops of polar and apolar liquids in air irrespective of the surface make-up. However, it was recently demonstrated that DRPs get instantaneously infiltrated by the same liquids on submersion because while they can robustly prevent liquid imbibition from the top, they are vulnerable to lateral imbibition. Here, we remedy this weakness through bio-inspiration derived from cuticles of Dicyrtomina ornata, soil-dwelling bugs, that contain cuboidal secondary granules with mushroom-shaped caps on each face. Towards a proof-of-concept demonstration, we created a perimeter of biomimicking pillars around arrays of DRPs using a two-photon polymerization technique; another variation of this design with a short wall passing below the side caps was investigated. The resulting gas-entrapping microtextured surfaces (GEMS) robustly entrap air on submersion in wetting liquids, while also exhibiting superomniphobicity in air. To our knowledge, this is the first-ever microtexture that confers upon intrinsically wetting materials the ability to simultaneously exhibit superomniphobicity in air and robust entrapment of air on submersion. These findings should advance the rational design of coating-free surfaces that exhibit ultra-repellence (or superomniphobicity) towards liquids.
  • Minimum Net Driving Temperature Concept for Membrane Distillation

    Blankert, Bastiaan; Vrouwenvelder, Johannes S.; Witkamp, Geert Jan; Ghaffour, NorEddine (Membranes, MDPI AG, 2020-05-14) [Article]
    <jats:p>In this study, we analyzed the heat requirement of membrane distillation (MD) to investigate the trade-off between the evaporation efficiency and driving force efficiency in a single effect MD system. We found that there exists a non-zero net driving temperature difference that maximizes efficiency. This is the minimum net driving temperature difference necessary for a rational operational strategy because below the minimum net driving temperature, both the productivity and efficiency can be increased by increasing the temperature difference. The minimum net driving temperature has a similar magnitude to the boiling point elevation (~0.5 °C for seawater), and depends on the properties of the membrane and the heat exchanger. The minimum net driving temperature difference concept can be used to understand the occurrence of optimal values of other parameters, such as flux, membrane thickness, and membrane length, if these parameters are varied in a way that consequently varies the net driving temperature difference.</jats:p>
  • Experimental investigation of a solar-heated direct contact membrane distillation system using evacuated tube collectors

    Bamasag, Ahmad; Alqahtani, Talal; Sinha, Shahnawaz; Ghaffour, NorEddine; Phelan, Patrick (Desalination, Elsevier BV, 2020-05-12) [Article]
    Solar-powered membrane distillation (SP-MD) is examined as a promising renewable solution in the desalination and water treatment industry. In this study, an innovative direct contact membrane distillation (DCMD) module to directly utilize solar thermal energy is proposed. While previous studies focused more on utilizing solar energy indirectly (i.e. to heat the feed water outside the MD module), the proposed system integrates hollow fiber membranes inside evacuated tube solar collectors in order to achieve a more compact system. The performance of the direct SP-MD module is measured first indoors in a bench-scale experiment, and then tested outdoors under sunlight. Results show that applying radiation directly can enhance the efficiency and permeate flux up to 17% compared to the same process when radiation is not applied under the same operating conditions. The daily operation of a stand-alone, directly heated SP-MD unit equipped with 0.035 m2 membrane area achieved a permeate flux of 2.2 to 6.5 kg·m−2·h−1 depending on solar intensity.
  • Photovoltaic panel cooling by atmospheric water sorption–evaporation cycle

    Li, Renyuan; Shi, Yusuf; Wu, Mengchun; Hong, Seunghyun; Wang, Peng (Nature Sustainability, Springer Science and Business Media LLC, 2020-05-11) [Article]
    More than 600 GW of photovoltaic panels are currently installed worldwide, with the predicted total capacity increasing very rapidly every year. One essential issue in photovoltaic conversion is the massive heat generation of photovoltaic panels under sunlight, which represents 75–96% of the total absorbed solar energy and thus greatly increases the temperature and decreases the energy efficiency and lifetime of photovoltaic panels. In this report we demonstrate a new and versatile photovoltaic panel cooling strategy that employs a sorption-based atmospheric water harvester as an effective cooling component. The atmospheric water harvester photovoltaic cooling system provides an average cooling power of 295 W m–2 and lowers the temperature of a photovoltaic panel by at least 10 °C under 1.0 kW m–2 solar irradiation in laboratory conditions. It delivered a 13–19% increase in electricity generation in a commercial photovoltaic panel in outdoor field tests conducted in the winter and summer in Saudi Arabia. The atmospheric water harvester based photovoltaic panel cooling strategy has little geographical constraint in terms of its application and has the potential to improve the electricity production of existing and future photovoltaic plants, which can be directly translated into less CO2 emission or less land occupation by photovoltaic panels. As solar power is taking centre stage in the global fight against climate change, atmospheric water harvester based cooling represents an important step toward sustainability.

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