RSS 1.0Water Desalination and Reuse Research Center (WDRC)
Recent Submissions
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Unique stratification of biofilm density in heterotrophic membrane-aerated biofilms: An experimental and modeling study(Chemosphere, Elsevier BV, 2023-03-22) [Article]We consistently find a band of high cell density develop within heterotrophic membrane-aerated biofilms. This study reports and attempts to explain this unique behavior. Biofilm density affects volumetric reaction rates, biofilm growth rates, substrate diffusion, and mechanical behavior. Yet the mechanisms and dynamics of biofilm density development are poorly understood. In this study, a membrane-aerated biofilm, where O2 was supplied from the base of the biofilm and acetate from the bulk liquid, was used to explore spatial and temporal patterns of density development. Biofilm density was assessed by optical coherence tomography. After inoculation, the biofilm quickly increased in thickness, with a low density throughout. However, as the biofilm reached a stable thickness of around 1000 μm, a high-density layer developed in the biofilm interior. The layer slowly expanded over time. Oxygen microprofiles in the biofilm showed this layer coincided with the most metabolically active zone, resulting from counter-diffusing O2 and acetate. The formation of this dense layer appeared to be related to changes in growth rates. Initially, high growth rates throughout the biofilm presumably led to fast-growing, low-density biofilms. As the biofilm became thicker, and as substrates became limiting in the biofilm interior, growth rates decreased, resulting in new growth at a higher density. A 1-D mathematical model with variable biofilm density was developed by linking the rates of extracellular polymeric substances (EPS) production to the growth rate. The model captured the initial fast growth at a low density, followed by a slower, substrate-limited growth in the biofilm interior, producing a dense band within the biofilm. Together, these results suggest that low growth rates can lead to high-density zones within the interior of counter-diffusional biofilms. These findings should also be relevant to conventional, co-diffusional biofilms, although differences in density may be less obvious.
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Efficient in planta production of amidated antimicrobial peptides that are active against drug-resistant ESKAPE pathogens(Nature Communications, Springer Science and Business Media LLC, 2023-03-16) [Article]Antimicrobial peptides (AMPs) are promising next-generation antibiotics that can be used to combat drug-resistant pathogens. However, the high cost involved in AMP synthesis and their short plasma half-life render their clinical translation a challenge. To address these shortcomings, we report efficient production of bioactive amidated AMPs by transient expression of glycine-extended AMPs in Nicotiana benthamiana line expressing the mammalian enzyme peptidylglycine α-amidating mono-oxygenase (PAM). Cationic AMPs accumulate to substantial levels in PAM transgenic plants compare to nontransgenic N. benthamiana. Moreover, AMPs purified from plants exhibit robust killing activity against six highly virulent and antibiotic resistant ESKAPE pathogens, prevent their biofilm formation, analogous to their synthetic counterparts and synergize with antibiotics. We also perform a base case techno-economic analysis of our platform, demonstrating the potential economic advantages and scalability for industrial use. Taken together, our experimental data and techno-economic analysis demonstrate the potential use of plant chassis for large-scale production of clinical-grade AMPs.
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Fully Printed Dual-Layer Depolarizing Chipless RFID Tag for Wearable Applications(IEEE Journal of Radio Frequency Identification, Institute of Electrical and Electronics Engineers (IEEE), 2023-03-16) [Article]This work presents a cross-polar dual-layer chipless radio-frequency identification (RFID) tag based on a ladder-shaped resonator design. An integrated ground plane enables direct attachment to human skin without performance deterioration. Simulations show that the ladder-shaped resonator provides several advantages over traditional L-shaped and straight resonators, including a strong cross-polar radar cross section (-23.4 dBsm), third-order harmonics, orientation insensitivity, and compact size (0.062 λ2). The effects of the ground plane shape on the surface current distribution are investigated, and a circular tag of 20 mm radius is designed using ladder resonator groups and frequency shift encoding to provide an active area of 96.45 bits/λ2 and a unit frequency of 6.03 bits/GHz. The tag substrate is three-dimensionally (3D) printed with metallic resonator patterns that are subsequently screen-printed on the substrate. The maximum read range is measured at 40 mm using a cross-shaped, dual-polarized Vivaldi antenna connected to a network analyzer. The measured characteristics in free space are in good agreement with the simulation results, and practical on-body performance tests for the manufactured prototype using simulation and direct measurements indicate that the tag performance remains stable for both free space and on-body cases. The fully printed fabrication process makes the proposed tag design suitable for mass production at a low cost.
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Impact of electrochemically generated iron on the performance of an anaerobic wastewater treatment process.(The Science of the total environment, Elsevier BV, 2023-03-07) [Article]Anaerobic treatment of domestic wastewater has the advantages of lower biomass yield, lower energy demand and higher energy recover over the conventional aerobic treatment process. However, the anaerobic process has the inherent issues of excessive phosphate and sulfide in effluent and superfluous H2S and CO2 in biogas. An electrochemical method allowing for in-situ generation of Fe2+ in the anode and hydroxide ion (OH−) and H2 in the cathode was proposed to overcome the challenges simultaneously. The effect of electrochemically generated iron (e‑iron) on the performance of anaerobic wastewater treatment process was explored with four different dosages in this work. The results showed that compared to control, the experimental system displayed an increase of 13.4–28.4 % in COD removal efficiency, 12.0–21.3 % in CH4 production rate, 79.8–98.5 % in dissolved sulfide reduction, 26.0–96.0 % in phosphate removal efficiency, depending on the e‑iron dosage between 40 and 200 mg Fe/L. Dosing of the e‑iron significantly upgraded the quality of produced biogas, showing a much lower CO2 and H2S contents in biogas in experimental reactor than that in control reactor. The results thus demonstrated that e‑iron can significantly improve the performance of anaerobic wastewater treatment process, bringing multiple benefits with the increase of its dosage regarding effluent and biogas quality.
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Inventions, innovations, and new technologies: Solar Desalination(Solar Compass, Elsevier BV, 2023-03-04) [Article]This article is a brief review of inventions, innovations, and commercialization aspects of solar desalination technology for clean water supply. It is estimated that by the year 2025, nearly two-thirds of the global population will be affected by clean water scarcity. Solar desalination is one of the most sustainable ways of facing this global challenge with emerging technological advancements. Highly efficient interfacial solar evaporation that localizes the heat on the evaporating surface has attracted tremendous research interest within the last few years. In addition, notable innovations can be found in adsorption desalination and energy-efficient freeze desalination. The mini review is followed by a list of notable recent patents and articles. However, the list is by no means exhaustive or complete, and quite possibly some important patents and articles are not cited. The mini review and the lists support the objective of this section: to draw attention to the topic of inventions, innovations and new technologies, which can be a major contributor to the global goal of net zero carbon emissions.
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SARS-CoV-2 wastewater-based epidemiology in an enclosed compound: A 2.5-year survey to identify factors contributing to local community dissemination(The Science of the total environment, Elsevier BV, 2023-03-01) [Article]Long-term (>2.5 years) surveillance of SARS-CoV-2 RNA concentrations in wastewater was conducted within an enclosed university compound. This study aims to demonstrate how coupling wastewater-based epidemiology (WBE) with meta-data can identify which factors contribute toward the dissemination of SARS-CoV-2 within a local community. Throughout the pandemic, the temporal dynamics of SARS-CoV-2 RNA concentrations were tracked by quantitative polymerase chain reaction and analyzed in the context of the number of positive swab cases, the extent of human movement, and intervention measures. Our findings suggest that during the early phase of the pandemic, when strict lockdown was imposed, the viral titer load in the wastewater remained below detection limits, with <4 positive swab cases reported over a 14-day period in the compound. After the lockdown was lifted and global travel gradually resumed, SARS-CoV-2 RNA was first detected in the wastewater on 12 August 2020 and increased in frequency thereafter, despite high vaccination rates and mandatory face-covering requirements in the community. Accompanied by a combination of the Omicron surge and significant global travel by community members, SARS-CoV-2 RNA was detected in most of the weekly wastewater samples collected in late December 2021 and January 2022. With the cease of mandatory face covering, SARS-CoV-2 was detected in at least two of the four weekly wastewater samples collected from May through August 2022. Retrospective Nanopore sequencing revealed the presence of the Omicron variant in the wastewater with a multitude of amino acid mutations, from which we could infer the likely geographical origins from which the variants were imported. This study demonstrated that long-term tracking of the temporal dynamics and sequencing of variants in wastewater would aid in identifying which factors contribute the most to SARS-CoV-2 dissemination within the local community, facilitating an appropriate public health response to control future outbreaks as we now live with endemic SARS-CoV-2.
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Engineered ketocarotenoid biosynthesis in the polyextremophilic red microalga Cyanidioschyzon merolae 10D(Cold Spring Harbor Laboratory, 2023-02-28) [Preprint]The polyextremophilic Cyanidiales are eukaryotic red microalgae with promising biotechnological properties arising from their low pH and elevated temperature requirements which can minimize culture contamination at scale. Cyanidioschyzon merolae 10D is a cell wall deficient species with a fully sequenced genome that is amenable to nuclear transgene integration by targeted homologous recombination. C. merolae maintains a minimal carotenoid profile and here, we sought to determine its capacity for ketocarotenoid accumulation mediated by heterologous expression of a green algal beta-carotene ketolase (BKT) and hydroxylase (CHYB). To achieve this, a synthetic transgene expression cassette system was built to integrate and express Chlamydomonas reinhardtii (Cr) sourced enzymes by fusing native C. merolae transcription, translation and chloroplast targeting signals to codon-optimized coding sequences. Chloramphenicol resistance was used to select for the integration of synthetic linear DNAs into a neutral site within the host genome. CrBKT expression caused accumulation of canthaxanthin and adonirubin as major carotenoids while co-expression of CrBKT with CrCHYB generated astaxanthin as the major carotenoid in C. merolae. Unlike green algae and plants, ketocarotenoid accumulation in C. merolae did not reduce total carotenoid contents, but chlorophyll a reduction was observed. Light intensity affected global ratios of all pigments but not individual pigment compositions and phycocyanin contents were not markedly different between parental strain and transformants. Continuous illumination was found to encourage biomass accumulation and all strains could be cultivated in simulated summer conditions from two different extreme desert environments. Our findings present the first example of carotenoid metabolic engineering in a red eukaryotic microalga and open the possibility for use of C. merolae 10D for simultaneous production of phycocyanin and ketocarotenoid pigments.
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The evolution of feed spacer role in membrane applications for desalination and water treatment: A critical review and future perspective(Desalination, Elsevier BV, 2023-02-28) [Article]The membrane research community has witnessed a significant research growth on feed spacers since 2010, both in quantity and scope. Increasingly novel spacer geometries and spacer chemistries are being reported in literature to tackle key challenges facing membrane processes, including concentration polarization, energy consumption, low flux, and fouling. This review aims to analyze the recent developments of spacer research, starting with a review of the various roles spacers can and do play in membrane systems and their increased prominence in tackling membrane fouling and scaling. We then review the continued need for novel spacer designs, discuss the contribution spacers can make to energy saving, and the necessity for new generations of spacers to facilitate the deployment of next generation, ultra-permeable membranes. Qualitative and quantitative spacer performance assessment tools are described. The key trends in spacer modifications over the period of 2010 to 2021 are categorized into: i) design modifications of both conventional and novel geometries, and ii) spacer surface modifications, including chemical coatings and new spacer materials. Finally, the future trends of spacer research are highlighted, with an emphasis on the development of functionalized feed spacers and new spacers made via 4D printing and smart materials.
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Solution-Diffusion-Electromigration Approximation Model (Sde-A) for Strongly Charged, Weakly Charged and Effectively Uncharged Reverse Osmosis Membranes(Elsevier BV, 2023-02-28) [Preprint]The solution-diffusion-electromigration approximation model (SDE-A) was formulated to describe the salt permeability of effectively uncharged, weakly charged and strongly charged reverse osmosis (RO) membranes. The model uses three of fewer parameters, depending on the type of charge behavior that a particular membrane exhibits under the allowable experimental conditions regarding feedwater salinity and acidity. The resulting algebraic equation is an approximation of an analytical solution of the Nernst-Planck equations for a 1:1 salt where the membrane charge depends on the feedwater conditions. The SDE-A model was compared to the more complex solution-friction (SF) model, by converting SF parameters to SDE-A parameters, resulting in a typical difference in computed salt permeability of less than 20%. Furthermore, the SDE-A model was applied to datasets from literature, corresponding to strongly charged, weakly charged and uncharged membranes. The SDE-A model can describe the effect of salinity and pH in these datasets comparably to the SF model. Because the model parameters can be easily determined experimentally and the algebraic model equation does not require elaborate solvers, the model is suitable for process design and optimization.
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The Microbial Growth Potential of Antiscalants used in Seawater Desalination(Water Research, Elsevier BV, 2023-02-25) [Article]20 years since the first report on the biofouling potential of chemicals used for scale control, still, antiscalants with high bacterial growth potential are used in practice. Evaluating the bacterial growth potential of commercially available antiscalants is therefore essential for a rational selection of these chemicals. Previous antiscalant growth potential tests were conducted in drinking water or seawater inoculated with model bacterial species which do not represent natural bacterial communities. To reflect better on the conditions of desalination systems, we investigated the bacterial growth potential of eight different antiscalants in natural seawater and an autochthonous bacterial population as inoculum. The antiscalants differed strongly in their bacterial growth potential varying from ≤ 1 to 6 μg easily biodegradable C equivalents/mg antiscalant. The six phosphonate-based antiscalants investigated showed a broad range of growth potential, which depended on their chemical composition, whilst the biopolymer and the synthetic carboxylated polymers-based antiscalants showed limited or no significant bacterial growth. Moreover, nuclear magnetic resonance (NMR) scans enabled antiscalant fingerprinting, identifying components and contaminants, providing a rapid and sensitive characterization, and opening opportunities for rational selection of antiscalants for biofouling control.
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Impact of Forestation and Land-use Changes on Desert Climate(Copernicus GmbH, 2023-02-22) [Poster]Growing forests is an effective way of removing CO2 from the atmosphere. Forestation projects were started in China, Germany, and the Middle East. Saudi Arabia announced its ambitious “Saudi Green Initiative,” intending to plant ten billion trees. Given the insufficient rainfall to support the initiative, vegetated areas will require irrigation, effectively increasing evaporation. In addition, those areas have a lower albedo than bare land, absorbing more solar radiation. Enhancing precipitation due to the recycling of evaporated water is important as it reduces the amount of freshwater required for irrigation. In this study, we focus on the regional climate impact of irrigated forested or vegetated areas on temperature and precipitation over the Arabian Peninsula to quantify their effect on livability and evaluate the water recycling potential. First, we studied the climate effect of irrigated farming developing over vast areas in Saudi Arabia since the 1980s. The agricultural areas were mapped using available satellite-based observations from the Landsat platforms, which capture optical and thermal data every 16 days at a resolution of 30 m to 100 m. Second, we projected the climate impact of widespread forestation over the Arabian Peninsula. The analysis of the long-term precipitation changes caused by irrigated farming is hindered by the lack of in situ observations and the limitations of global-scale observation data sets. Most reanalysis products have contradictory evaporation trends and indicate an overall reduction in rainfall since the 1980s. The recycled precipitation cannot be estimated reliably because of reanalysis increments and background rainfall variability. Presumably, the local increase in rains occurs downstream of the irrigated areas rather than over them. Along with the analysis of observations, we conducted numerical experiments mimicking the effect of irrigated agricultural fields using a non-hydrostatic regional meteorological model (WRF), covering the whole Arabian Peninsula by a 9x9 km2 grid, with 3x3 km2 nesting over the irrigated areas. Irrigation water is accounted for by tagging moisture evaporated from agricultural regions. The amount of tagged water vapor falling as rain represents recycled precipitation. The simulated evaporation and local temperature response strongly depends on the level of irrigation. Large-scale subsidence suppresses the local deep convection over most parts of the Arabian Peninsula. Strong turbulence quickly mixes evaporated water vapor within a six km thick atmospheric boundary layer, preventing precipitation in shallow convection so that the fraction of recycled rainfall appears to be low.
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Prediction of particulate fouling in full-scale reverse osmosis plants using the modified fouling index – ultrafiltration (MFI-UF) method(Desalination, Elsevier BV, 2023-02-22) [Article]This study aims at applying and verifying the MFI-UF method to predict particulate fouling in RO plants. Two full-scale RO plants treating surface water, with average capacity of 800–2000 m3/h, were studied. Firstly, the MFI-UF of RO feed and concentrate was measured using 5–100 kDa membranes at same flux applied in the RO plants (20–26 L/m2.h). Subsequently, the particle disposition factor (Ω) was calculated to simulate particle deposition in RO cross-flow filtration. Finally, particulate fouling rates were predicted based on MFI-UF and Ω, and compared with the actual fouling rates in the plants. For plant A, the results showed that the fouling rates predicted using MFI-UF measured with 100 kDa membrane have the best agreement with the actual fouling (with 3–11 % deviation). For plant B, the fouling rates predicted based on both 10 and 100 kDa membranes agree well with the actual fouling (with 2 % and 15 % deviation, respectively). However, the fouling predicted based on 5 kDa membrane is considerably overestimated for both plants, which is attributed to the effect of the low surface porosity of 5 kDa membrane. More widespread applications of MFI-UF in full-scale RO plants are required to demonstrate the most suitable MFI-UF membranes for fouling prediction.
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Solar desalination: A review of recent developments in environmental, regulatory and economic issues(Solar Compass, Elsevier BV, 2023-02-19) [Article]The aim of the current study was to provide a review of recent developments in solar desalination from the viewpoint of environmental, regulatory, and economic aspects. The analysis attempted to give better insight into the larger question of why more solar desalination plants are not being established by reviewing different technologies, drivers, barriers, and markets. Critical barriers which were dependent on the level of regional development were found to be uncertainty of government subsidies and a lack of regulatory policies. A new tool called a Pareto frontier may be utilized to generate optimal points in complex scenarios with a high number of variables. This all-inclusive method should be employed in any major decision-making process. Furthermore, in exciting innovative research studies, a sustainable Janus wood evaporator was developed that overcame many of the current solar desalination problems. While subsidies were crucial in the growth of renewable energy programs, barriers in deployment of solar desalination systems still exist such as low electricity tariff structures and fragmented energy policies. The overall trend was towards integration of renewable energy with conventional sources and energy storage systems.
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Hybrid salt-enriched micro-sorbents for atmospheric water sorption(Journal of Water Process Engineering, Elsevier BV, 2023-02-16) [Article]Water shortage severely impacts drought-stricken regions, with estimates indicating that almost half a billion people are affected yearly. Composites of Salt and Porous Matrix (CSPMs) are promising functional materials for water vapor sorption. Here, CSPMs were synthesized by loading SAPO-34 porous crystals with highly hygroscopic salts, namely LiCl and CaCl2, individually (mono-salt systems) or combined (binary salt systems) to enhance water sorption capacity and cyclability. The LiCl and CaCl2 content in the impregnation solution impacted the sorption behavior and equilibrium capacity of the resulting composites. Physicochemical, morphological, textural, and sorption properties were evaluated showing that the confinement of binary salts yielded the highest water uptake (0.88 gw/gads at 25 °C and 90 % RH), which was four times higher than that of the parent SAPO-34. The shape of the obtained water vapor isotherms revealed that the salts introduced into the porous structure led to significant changes in the sorption mechanism, with SAPO-34 following a Langmuir behavior (type I isotherm) and the composites a type II isotherm with associated multilayer formation due to the presence of the salts. Kinetic studies also revealed that the materials follow a PSO model dominated by water-surface interactions. Embedding different salts into the same hosting pores to support atmospheric water harvesting was therefore found to enhance capacity and cyclability compared to single inorganic porous structures toward more efficient water sorption processes.
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A Fouling Comparison Study of Algal, Bacterial and Humic Organic Matters in Seawater Desalination Pretreatment Using Ceramic UF Membranes(Membranes, MDPI AG, 2023-02-15) [Article]This study investigates three types of organic matter, namely algal organic matter (AOM), bacterial organic matter (BOM), and humic organic matter (HOM). These organics are different in properties and chemical composition. AOM, BOM and HOM were compared in terms of organic content, fouling behavior, and removal efficiency in ceramic UF filtration. UF experiments were conducted at a constant flux mode using 5 kDa and 50 kDa ceramic membranes. Results showed that 5 kDa membrane removed more transparent exopolymer particles (TEP)/organics than 50 kDa membranes, but less fouling formation for all the three types of organic matters tested. Membranes exhibited the lowest trans-membrane pressure (TMP) during the filtration of HOM, most probably due to the high porosity of the HOM cake layer, contributed by big HOM aggregates under Ca bridging effect. AOM shows the highest MFI-UF (modified fouling index-ultrafiltration) and TMP (transmembrane pressure) values among the three organics and during all filtration cycles for both membranes. The AOM fouling layer is well known for having high fouling potential due to its compressibility and compactness which increase the TMP and eventually the MFI values. AOM and BOM organics exhibited a similar fouling behavior and mechanism. Furthermore, the divalent cations such as calcium showed a significant impact on membrane fouling. That is probably because calcium ions made the membranes and organic matter less negatively charged and easier to deposit on membranes, thus, enhancing the membrane fouling significantly.
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Supercritical carbon dioxide extraction of oils from Andean lupin beans: Lab-scale performance, process scale-up, and economic evaluation(Journal of Food Process Engineering, Wiley, 2023-02-13) [Article]Oil extraction from Andean lupin beans (Lupinus mutabilis SWEET) via supercritical carbon dioxide (scCO2) was studied on both lab scale and pilot scale. On the lab scale, the effect of pressure, solvent-to-feed ratio (S/F), sample particle size and temperature on oil yield were evaluated. The oil quality (fatty acid [FA] composition and tocopherol content) were investigated. Five-hour scCO2 extraction yielded about 86% oil of Soxhlet extraction (using hexane as solvent). The fraction of unsaturated FA rose with extraction pressure at specific time. High tocopherol contents were detected in oils extracted at low pressure. An increase in temperature was unfavorable to oil and tocopherol yield, thereby confirming the validity for preserving oil extract quality under a mild scCO2 extraction condition. Oil quality and yield did not have identical optimum settings, opening up possibilities for producing different qualities of oils. Pilot-scale extraction offered comparable oil yield to lab-scale extraction at similar S/F ratio. Economic evaluation showed that it is promising to implement industrial scale scCO2 process for lupin oil extraction. It was predicted that, at a specific industrial scale of extraction (2 × 1000 L, 550 bar, 40°C and S/F of 24), the manufacturing cost of oils got close to actual commercial production cost. Practical Application: This study applied an environment-friendly high-pressure extraction method, supercritical carbon dioxide (scCO2) extraction, to separate oils from Andean lupin beans (Lupinus mutabilis SWEET). ScCO2 extraction can serve as an alternative oil extraction method to conventional ones that use fossil-derived organic solvents as the extractant. Up-scaled scCO2 processing was estimated to be economically viable for commercial lupin oil production.
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Electrochemical and Hydraulic Analysis of Thin-Film Composite and Cellulose Triacetate Membranes for Seawater Electrolysis Applications(Elsevier BV, 2023-02-13) [Preprint]Thin film, reverse osmosis (RO) membranes can be used in saltwater electrolysis to minimize chlorine ion crossover and chlorine gas generation without significantly increasing the potential requirement for electrolysis in comparison to a cation exchange membrane (CEM). Optimizing membrane performance requires a better understanding of membrane properties that impact electrical resistances and ion retention. Twelve RO membranes, one nanofiltration (NF) membrane, and one cellulose triacetate forward osmosis (FO) membrane were examined for their electrical resistances under conditions typically used for CEMs. Resistances measured at low current densities (0.07 to 0.3 mA/cm2) varied between different membranes by over an order of magnitude in 1 M NaCl at neutral pH, from 6.1 ± 0.1 W cm2 to 70 ± 30 W cm2. There was no significant correlation between membrane resistance and applied potential during saltwater electrolysis at 20 mA/cm2 (p=0.44), or between membrane resistance and water permeability (p=0.35). These results indicate traditional CEM resistance characterization methods do not predict RO membrane electrolysis performance because proton and hydroxide transport, which is important during electrolysis when large pH gradients develop, must be considered separately from salt ion and water molecule transport through size selective RO, NF, and FO membranes during water electrolysis.
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W2N-MXene composite anode catalyst for efficient microbial fuel cells using domestic wastewater(Chemical Engineering Journal, Elsevier BV, 2023-02-09) [Article]Microbial fuel cells (MFCs) have enormous potential to treat wastewater and reduce the energy demands of wastewater treatment plants while generating electricity using active microorganisms as biocatalysts. However, the practical application of MFCs is limited by the low power density produced, mainly due to poor anode performance. Herein, a tungsten nitride (W2N)-MXene composite catalyst is introduced to modify the anode surface for use in microbial fuel cells during domestic wastewater treatment. The aim is to improve the wettability, electrical conductivity, electron transfer efficiency, and microorganism attachment capability of the anode and ultimately increase the overall performance of the microbial fuel cell to produce electricity during wastewater treatment. In detail, a hydrofluoric acid etching approach is used to synthesize the Ti3C2Tx MXene, the urea glass technique is used to prepare the W2N particles, and an adequate mixing and heat treatment approach is used to produce the W2N-Ti3C2Tx composite catalyst. The W2N-Ti3C2Tx composite on carbon cloth anode provides one of the best performances recorded for MXene in this type of fuel cells and using real domestic wastewater: with a 523% increase in the power density (548 mW m-2), an 83% decrease in the chemical oxygen demand (COD), and a 161% increase in the electron transfer efficiency compared to those of the plain carbon cloth. We demonstrate that this outstanding performance is due to the improvements in hydrophilicity and microorganism attachment, particularly nanowires (or pili) which promote electron transfer. The present work offers an interesting avenue towards the process scale-up and optimization of single-chamber microbial fuel cells.
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Space-Air-Ground-Sea Integrated Networks: Modeling and Coverage Analysis(IEEE Transactions on Wireless Communications, Institute of Electrical and Electronics Engineers (IEEE), 2023-02-07) [Article]Due to its potential to enable global connectivity in remote locations, such as rural areas and islands, Space-Air-Ground networks have become an ambitious solution for terrestrial communication in the sixth generation (6G) wireless communication network. In this paper, we propose a novel structure of Space-Air-Ground-Sea integrated networks (SAGSINs) to study and derive the coverage probability (CP) of users who are annotated as surface stations (SSs) on the far-reaching ocean surface that is far away from the coastline. By incorporating different types of relays such as onshore stations (OSs), tethered balloons (TBs), high altitude platforms (HAPs), and satellites (SATs), communication links between the terrestrial core connected base stations (CCBSs) and SSs are established via one of the four types of relay stations. Considering practical scenarios with a random distribution of SSs, we model the channel using the point-to-area model, which is recommended by ITU (for OSs to SS), the Rician model (for TBs or HAPs to SS), and the Shadowed-Rician model (for SATs to SS). When the SS’s distance from the coastline continues to increase from zero, since different channel models are considered, different relay stations will result in specific received signal strengths at SSs. The most powerful relay station will be chosen as the relay at one time. Hence, as we move away from the coastline, the respective strengths of the different types of relay stations vary, and hence, the association preference (among HAPs, OSs, TBs, and SATs) of the SSs changes leading to a CP value high enough even at locations far away from the coastline into the ocean. We analyze the CP using tools from stochastic geometry. Comparisons of CP between the integrated system with four types of relay stations and the single relay station system (only one type of relay station available) are represented. Numerical results verified by Monte-Carlo simulations reveal insights into the applicability of SAGS...
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A Via-less Fully Screen-Printed Reconfigurable Intelligent Surface for 5G Millimeter Wave Communication(arXiv, 2023-02-07) [Preprint]In this paper, we propose a via-less fully screen-printed reconfigurable intelligent surface which can establish a second line-of-sight communication from 23.5GHz to 29.5GHz. By serially connecting the H shaped resonator along the H field of the incident wave, we minimize the effect of the biasing lines and make a via-less design, which reduces the fabrication difficulty and cost. The unit-cell simulation of the array with screen-printed VO2 switches shows a 215° to 160° phase shift difference between the ON and OFF states within bandwidth. During the field testing of the ideal arrays, we verify that the array can redirect the 45° incident wave to 0° reflection with a signal enhancement of at least 10 dB as compared to the array which has all unit cells in the OFF condition.
