Conspectus Lipid nanoparticles (LNPs) are a type of lipid vesicles that possess a homogeneous lipid core. These vesicles are widely used in small-molecule drug and nucleic acid delivery and recently ...gained much attention because of their remarkable success as a delivery platform for COVID-19 mRNA vaccines. Nonetheless, the utility of transient protein expression induced by mRNA extends far beyond vaccines against infectious diseasesthey also hold promise as cancer vaccines, protein replacement therapies, and gene editing components for rare genetic diseases. However, naked mRNA is inherently unstable and prone to rapid degradation by nucleases and self-hydrolysis. Encapsulation of mRNA within LNPs protects mRNA from extracellular ribonucleases and assists with intracellular mRNA delivery. In this Account, we discuss the core features of LNPs for RNA delivery. We focus our attention on LNPs designed to deliver mRNA; however, we also include examples of siRNA-LNP delivery where appropriate to highlight the commonalities and the dissimilarities due to the nucleic acid structure. First, we introduce the concept of LNPs, the advantages and disadvantages of utilizing nucleic acids as therapeutic agents, and the general reasoning behind the molecular makeup of LNPs. We also briefly highlight the most recent clinical successes of LNP-based nucleic acid therapies. Second, we describe the theory and methods of LNP self-assembly. The common idea behind all of the preparation methods is inducing electrostatic interactions between the nucleic acid and charged lipids and promoting nanoparticle growth via hydrophobic interactions. Third, we break down the LNP composition with special attention to the fundamental properties and purposes of each component. This includes the identified molecular design criteria, commercial sourcing, impact on intracellular trafficking, and contribution to the properties of LNPs. One of the key components of LNPs is ionizable lipids, which initiate electrostatic binding with endosomal membranes and facilitate cytosolic release; however, the roles of other lipid components should not be disregarded, as they are associated with stability, clearance, and distribution of LNPs. Fourth, we review the attributes of LNP constructs as a whole that can heavily influence RNA delivery. These attributes are LNP size, charge, internal structure, lipid packing, lipid membrane hydration, stability, and affinity toward biomacromolecules. We also discuss the specific techniques used to examine these attributes and how they can be adjusted. Finally, we offer our perspective on the future of RNA therapies and some questions that remain in the realm of LNP formulation and optimization.
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•Biofouling is a long-standing problem in MBR for wastewater treatment.•Recent advances in anti-biofouling technologies in MBR are critically reviewed.•Integration of MBR with hybrid ...approach can mitigate biofouling effectively.•Biofouling properties are compared between aerobic and anaerobic MBR systems.•Biofouling is controlled by functionalized media in particle-sparged MBR.
Biofouling is a long-standing problem in membrane bioreactors (MBRs) for domestic wastewater treatment because it deteriorates membrane permeability, thus demanding frequent chemical cleaning which can shorten membrane life-time. Recently, several anti-biofouling strategies have been suggested under scientific and engineered attentions from aerobic or anaerobic MBR systems. Nevertheless, researches are still needed to better understand biofouling and develop novel approaches to control this inevitable phenomenon. In this review, recent advances and emerging issues associated with biofouling control in aerobic and anaerobic MBR technologies are critically discussed. Existing challenges and future research perspectives are also addressed to achieve MBR sustainability with biofouling control. This also suggests that integration of MBR with hybrid approach could effectively enhance MBR performance in terms of biofouling mitigation. Future works should elucidate biofouling behavior in integrated MBRs more clearly for sustainable wastewater treatment applications.
Membrane separations are powerful tools for various applications, including wastewater treatment and the removal of contaminants from drinking water. The performance of membranes is mainly limited by ...material properties. Recently, successful attempts have been made to add nanoparticles or nanotubes to polymers in membrane synthesis, with particle sizes ranging from 4
nm up to 100
nm. Ceramic membranes have been fabricated with catalytic nanoparticles for synergistic effects on the membrane performance. Breakthrough effects that have been reported in the field of water and wastewater treatment include fouling mitigation, improvement of permeate quality and flux enhancement. Nanomaterials that have been used include titania, alumina, silica, silver and many others. This paper reviews the role of engineered nanomaterials in (pressure driven) membrane technology for water treatment, to be applied in drinking water production and wastewater recycling. Benefits and drawbacks are described, which should be taken into account in further studies on potential risks related to release of nanoparticles into the environment.
Nanoparticles show a great potential for application in polymeric and ceramic membrane structures, in view of fouling mitigation and catalytic breakdown processes.
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•Cleaning with scouring agent generates favorable and energy-efficient MBR.•Involvement of factors impacting mechanical cleaning is necessary to understand.•Optimum size of scouring ...agent and its dosage permit to maximize fouling control.•Beneficial effect is counter balanced due to energy cost and sludge breaking up.•Universal model is able to optimize hydrodynamics of mechanical cleaning in MBR.
Membrane bioreactor (MBR) is a reliable and promising technology for wastewater treatment and reclamation applications. In spite of more than a decade of significant advances in developing fouling mitigation methods, different physical and cleaning protocols are still necessary to be developed to limit the membrane fouling. The use of scouring agents in MBR applications has been paid attention as a new approach as an energy-efficient way to control membrane fouling. Recently, mechanical cleaning by scouring agents is becoming an intense research area considering high efficiency of fouling reduction while requiring low energy consumption. In this review, fundamental and comprehensive assessments of the mechanical cleaning concepts and their applications with porous and nonporous scouring agents for MBR system are critically reviewed. The existing challenges and future research prospects on the mechanical cleaning technology associated with scouring agents for the MBR applications are also discussed.
•Domestic wastewater was treated with an anaerobic fluidized membrane bioreactor at 8–30°C.•GAC fluidization prevented membrane fouling over the 485days of operation.•With HRT of 4.5–6.8h, effluent ...COD was below 25mg/L and BOD5 below 10mg/L.•Biosolids production of 0.051gVSS/g COD is much less than with aerobic systems.•Methane energy potential was sufficient for modified plant operation.
A pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) was operated continuously for 485days, without chemical cleaning of membranes, treating primary-settled domestic wastewater with wastewater temperature between 8 and 30°C and total hydraulic retention time (HRT) between 4.6 and 6.8h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals averaged 81% and 85%, respectively, during the first winter at 8–15°C before full acclimation had occurred. However, subsequently when fully acclimated, summer and winter COD removals of 94% and 90% and BOD5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23mg/L nor BOD5 higher than 9mg/L. Operational energy requirement of 0.23kWh/m3 could be met with primary and secondary methane production, and could be reduced further through hydraulic change. Biosolids production in all seasons averaged 0.051g volatile suspended solids per g COD removed.
Abstract
When a low-viscosity fluid displaces into a higher-viscosity fluid, the liquid-liquid interface becomes unstable causing finger-like patterns. This viscous fingering instability has been ...widely observed in nature and engineering systems with two adjoined fluids. Here, we demonstrate a hitherto-unrealizable viscous fingering in a single fluid-solid interface. In a single polyelectrolyte fluid on a charge selective surface, selective ion rejection through the surface initiates i) stepwise ion concentration and viscosity gradient boundaries in the fluid and ii) electroconvective vortices on the surface. As the vortices grow, the viscosity gradient boundary pushes away from the surface, resulting viscous fingering. Comparable to conventional one with two fluids, i) a viscosity ratio (
$$M$$
M
) governs the onset of this electroconvective viscous fingering, and ii) the boundary properties (finger velocity and rheological effects) - represented by
$$M$$
M
, electric Rayleigh (
$${{Ra}}_{E}$$
R
a
E
), Schmidt (
$${Sc}$$
S
c
), and Deborah (
$${De}$$
D
e
) numbers - determine finger shapes (straight v.s. ramified, the onset length of fingering, and relative finger width). With controllable onset and shape, the mechanism of electroconvective viscous fingering offers new possibilities for manipulating ion transport and dendritic instability in electrochemical systems.
•Ceramic membrane was applied in anaerobic fluidized MBR for low-strength wastewater.•Membrane net flux of 17LMH was achieved with only periodic maintenance cleaning.•No adverse effect of the ...maintenance cleaning on organic removal was observed.•Average SCOD in membrane permeate of 23mg/L was achieved.•Electrical energy required to operate the AFCMBR was only about 0.038kWh/m3.
An aluminum dioxide (Al2O3) ceramic membrane was used in a single-stage anaerobic fluidized bed ceramic membrane bioreactor (AFCMBR) for low-strength wastewater treatment. The AFCMBR was operated continuously for 395days at 25°C using a synthetic wastewater having a chemical oxygen demand (COD) averaging 260mg/L. A membrane net flux as high as 14.5–17L/m2h was achieved with only periodic maintenance cleaning, obtained by adding 25mg/L of sodium hypochlorite solution. No adverse effect of the maintenance cleaning on organic removal was observed. An average SCOD in the membrane permeate of 23mg/L was achieved with a 1h hydraulic retention time (HRT). Biosolids production averaged 0.014±0.007gVSS/gCOD removed. The estimated electrical energy required to operate the AFCMBR system was 0.039kWh/m3, which is only about 17% of the electrical energy that could be generated with the methane produced.
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•Challenges and opportunities of AnMBRs are critically reviewed.•Novel configurations of AnMBRs are presented to overcome technology limitations.•Energy demand and energy production ...potential with different AnMBRs are analyzed.•Innovative strategies to reduce energy demands and fouling are critically discussed.•Future perspectives and key issued required urgent attention are highlighted.
Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.
With the increasing need for particulate matter (PM) monitoring, the demand for light-scattering sensors that allow for real-time measurements of PM is increasing. This light-scattering method ...involves irradiating light to the aerosols in the atmosphere to analyze the scattered light and measure mass concentrations. Humidity affects the measurement results. The humidity in an outdoor environment may exist as gas or steam, such as fog. While the impact of humidity on the light-scattering measurement remains unclear, an accurate estimation of ambient PM concentration is a practical challenge. Therefore, this study investigated the effects of humidity on light-scattering measurements by analyzing the variation in the PM concentration measured by the sensor when relative humidity was due to gaseous and steam vapor. The gaseous humidity did not cause errors in the PM measurements via the light-scattering method. In contrast, steam humidity, such as that caused by fog, resulted in errors in the PM measurement. The results help determine the factors to be considered before applying a light-scattering sensor in an outdoor environment. Based on these factors, directions for technological development can be presented regarding the correction of measurement errors induced by vapor in outdoor environments.
Aluminum dioxide (Al2O3) flat-tubular ceramic membrane was applied in a novel staged anaerobic fluidized bed ceramic membrane bioreactor (SAF-CMBR) for low-strength wastewater treatment. Granular ...activated carbon (GAC) particles were fluidized by bulk recirculation through the membrane reactor to control membrane fouling without any biogas sparging. The SAF-CMBR was operated for 350 days at 25 °C with total hydraulic retention time (HRT) between 1.3 and 2.1 h. A net permeate flux of 22 L/m2 h was achieved during the reactor operation combined with periodic maintenance cleaning using 25 mg/L of sodium hypochlorite solution under GAC fluidization. The overall chemical oxygen demand (COD) removal efficiency was 93%; with average SCOD was less than 30 mg/L in membrane permeate. Energy requirement to operate the SAF-CMBR was 0.024 kWh/m3 and it was only 10% of the electrical energy converted from methane produced by the reactor. Biosolids production averaged 0.01 g volatile suspended solids per g COD removed. With SAF-CMBR, microbial classification revealed that anaerobic treatment was achieved mainly by microbial communities grown on the GAC particles fluidized in which propionate-degrading syntrophs, aceticlastic/DIET-dependent CO2 reduction methanogens Methanothrix and exoelectrogenic Geobacter were dominated.
•Staged anaerobic fluidized bed ceramic membrane bioreactor was developed.•Net flux of 22 LMH was achieved under GAC fluidization and maintenance cleaning.•Overall COD removal of 93% was achieved with less than 30 mg/L COD in permeate.•Only 10% of electrical energy produced by the reactor was required for system operation.•Methanothrix and Geobactor were dominantly grown on GAC particles as fluidized media.
