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Summary Microbial electro- and photo-electrochemical CO2 fixation, in which CO2-reducing microorganisms are directly interfaced with a cathode material, represent promising approaches for sustainable fuel production. Although considerable efforts have been invested to optimize microorganism species and electrode materials, the microorganism-cathode interface has not been systematically studied. Here, investigation of the interface allowed us to optimize the CO2-reducing rate of silicon nanowire/Sporomusa ovata system. Tuning the bulk electrolyte pH and increasing its buffering capacity supported the formation of a close-packed nanowire-bacteria cathode. Consequently, the resulting close-packed biohybrid achieved a CO2-reducing current density of ∼0.65 mA cm−2. When coupled with a photovoltaic device, our system enabled solar-to-acetate production with ∼3.6% efficiency over 7 days.

Biological membranes are ideal for separations as they provide high permeability while maintaining high solute selectivity due to the presence of specialized membrane protein (MP) channels. However, successful integration of MPs into manufactured membranes has remained a significant challenge. Here, we demonstrate a two-hour organic solvent method to develop 2D crystals and nanosheets of highly packed pore-forming MPs in block copolymers (BCPs). We then integrate these hybrid materials into scalable MP-BCP biomimetic membranes. These MP-BCP nanosheet membranes maintain the molecular selectivity of the three types of β-barrel MP channels used, with pore sizes of 0.8 nm, 1.3 nm, and 1.5 nm. These biomimetic membranes demonstrate water permeability that is 20–1,000 times greater than that of commercial membranes and 1.5–45 times greater than that of the latest research membranes with comparable molecular exclusion ratings. This approach could provide high performance alternatives in the challenging sub-nanometre to few-nanometre size range. Protein channels are highly selective, but application in membranes is limited due to low protein content. Here, protein channels are embedded into block copolymers to form nanosheets using rapid solvent casting, with better water permeability and similar molecular exclusions relative to other membrane systems.

Combined organic and inorganic fouling is a primary barrier constraining the performance of reverse osmosis (RO) membrane. In this work, we conducted a systematic study focusing on the synergetic fouling effects of silica and humic acid (HA) in RO process, and found the critical silica concentration where the fouling pattern changed qualitatively. When the silica concentration was lower than 6 mM at a typical HA concentration of 50 mg·L−1, no severe fouling was observed, while silica reaching this critical point could cause severe synergetic fouling with HA. Concentrated silica above the critical point acted as the prior foulant with marginal fouling effect caused by HA. A variety of solutions and surface-based characterizations were performed to elucidate the synergistic fouling responsibility for silica and HA. Our study suggests that the carboxylic groups from HA formed hydrogen bonds with silica hydrate, inducing silica adsorption onto HA aggregates at low silica particle concentrations. The HA network was bridged together to form large foulants due to the silica-silica interaction above the silica critical concentration. These mechanisms were further confirmed by molecular dynamics simulations. This study provides an in-depth insight into the combined organic-inorganic fouling and can serve as a guideline to optimize feed conditions in order to mitigate fouling of RO in wastewater reusing industry.

Organic dyes have been considered as persistent pollutants to the water environment and remain a challenge for industrial wastewater treatment. Here we integrated environmental biotechnology and ad...

Bioinspired and biomimetic membranes that contain biological transport channels or attain their structural designs from biological systems have been through a remarkable development over the last two decades. They take advantage of the exceptional transport properties of those channels, thus possess both high permeability and selectivity, and have emerged as a promising solution to existing membranes. Since the discovery of biological water channel proteins aquaporins (AQPs), extensive efforts have been made to utilize them to make separation membranes-AQP-based membranes, which have been commercialized. The exploration of AQPs’ unique structures and transport properties has resulted in the evolution of biomimetic separation materials from protein-based to artificial channel-based membranes. However, large-scale, defect-free biomimetic membranes are not available yet. This paper reviews the state-of-the-art biomimetic membranes and summarizes the latest research progress, platform, and methodology. Then it critically discusses the potential routes of this emerging area toward scalable applications. We conclude that an appropriate combination of bioinspired concepts and molecular engineering with mature polymer industry may lead to scalable polymeric membranes with intrinsic selective channels, which will gain the merit of both desired selectivity and scalability.

Photosynthetic semiconductor biohybrids integrate the best attributes of biological whole-cell catalysts and semiconducting nanomaterials. Enzymatic machinery enveloped in its native cellular environment offers exquisite product selectivity and low substrate activation barriers while semiconducting nanomaterials harvest light energy stably and efficiently. In this Review Article, we illustrate the evolution and advances of photosynthetic semiconductor biohybrids focusing on the conversion of CO2 to value-added chemicals. We begin by considering the potential of this nascent field to meet global energy challenges while comparing it to alternate approaches. This is followed by a discussion of the advantageous coupling of electrotrophic organisms with light-active electrodes for solar-to-chemical conversion. We detail the dynamic investigation of photosensitized microorganisms creating direct light harvesting within unicellular organisms while describing complementary developments in the understanding of charge transfer mechanisms and cytoprotection. Lastly, we focus on trends and improvements needed in photosynthetic semiconductor biohybrids in order to address future challenges and enhance their widespread adoption for the production of solar chemicals. Artificial photosynthetic technologies could potentially contribute to limiting global warming while providing useful chemicals for society. This Review Article covers photosynthetic semiconductor biohybrids—electrodes/nanomaterials coupled with microorganisms—for light-driven catalytic conversion of CO2 to fuels and other value-added chemicals.

The membrane bioreactor (MBR) technology is a rising star for wastewater treatment. The pollutant elimination and membrane fouling performances of MBRs are essentially related to the dissolved organic matter (DOM) in the system. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy, a powerful tool for the rapid and sensitive characterization of DOM, has been extensively applied in MBR studies; however, only a limited portion of the EEM fingerprinting information was utilized. This paper revisits the principles and methods of fluorescence EEM, and reviews the recent progress in applying EEM to characterize DOM in MBR studies. We systematically introduced the information extracted from EEM by considering the fluorescence peak location/ intensity, wavelength regional distribution, and spectral deconvolution (giving fluorescent component loadings/scores), and discussed how to use the information to interpret the chemical compositions, physiochemical properties, biological activities, membrane retention/fouling behaviors, and migration/ transformation fates of DOM in MBR systems. In addition to conventional EEM indicators, novel fluorescent parameters are summarized for potential use, including quantum yield, Stokes shift, excited energy state, and fluorescence lifetime. The current limitations of EEM-based DOM characterization are also discussed, with possible measures proposed to improve applications in MBR monitoring.

This study systematically investigated the correlations between fluorescence distributions characterized by the excitation-emission matrix (EEM) and hydrophobic/hydrophilic composition of dissolved organic matter (DOM) in membrane bioreactors (MBRs). On the basis of samples from 10 full-scale MBRs, we performed point-to-point comparisons among different components using an EEM fluorescence quotient (FQ) method and obtained a hydrophobic/hydrophilic fluorophore distribution map via Wilcoxon signed rank test. Hydrophobic acids/bases (HOA/HOB) concentrated in the low-wavelength region [excitation wavelength (Ex) 235 nm [especially with emission wavelength (Em) = 300-360 nm]. Quantitatively, EEM regional contribution to whole wavelength fluorescence was found to significantly correlate with the hydrophobic/hydrophilic proportions of DOM, with Pearson's coefficients of 0.94 and 0.78 ( p < 0.01) for HOA and HIS, respectively. We established a linear regression model showing the HOA proportion as a function of the EEM regional contribution at (Ex, Em) = (200-285, 340-465 nm), with R2 = 0.876, which was validated via leave-one-out cross-validation and Monte Carlo simulation. This study shows a statistically hydrophobicity-dependent fluorescence property across different MBRs, and it might be applied to provide a quick estimation of hydrophobic/hydrophilic composition of DOM in wastewater treatment systems based on EEM monitoring.

As water availability becomes a growing challenge in various regions throughout the world, desalination and wastewater reclamation through technologies such as reverse osmosis (RO) are becoming more important. Nevertheless, many open questions remain regarding the internal structure of thin-film composite RO membranes. In this work, fully aromatic polyamide films that serve as the active layer of state-of-the-art water filtration membranes were investigated using high-angle annular dark-field scanning transmission electron microscopy tomography. Reconstructions of the 3D morphology reveal intricate aspects of the complex microstructure not visible from 2D projections. We find that internal voids of the active layer of compressed commercial membranes account for less than 0.2% of the total polymer volume, contrary to previously reported values that are two orders of magnitude higher. Measurements of the local variation in polyamide density from electron tomography reveal that the polymer density is highest at the permeable surface for the two membranes tested and establish the significance of surface area on RO membrane transport properties. The same type of analyses could provide explanations for different flux variations with surface area for other types of membranes where the density is distributed differently. Thus, 3D reconstructions and quantitative analyses will be crucial to characterize the complex morphology of polymeric membranes used in next-generation water-purification membranes.

Aquaporins (AQPs) are naturally occurring water channel proteins. They can facilitate water molecule translocation across cellular membranes with exceptional selectivity and high permeability that are unmatched in synthetic membrane systems. These unique properties of AQPs have led to their use as functional elements in membranes in recent years. However, the intricate nature of AQPs and concerns regarding their stability and processability have encouraged researchers to develop synthetic channels that mimic the structure and properties of AQPs and other biological water-conducting channels. These channels have been termed artificial water channels. This article reviews current progress and provides a historical perspective as well as an outlook toward developing scalable membranes based on artificial water channels.

Biomimetic polymer/protein membranes are promising materials for DNA sequencing, sensors, drug delivery and water purification. These self-assembled structures are made from low molecular weight amphiphilic block copolymers (Nhydrophobic < 40 for a diblock copolymer), including poly(ethylene oxide)–1,2-polybutadiene (EO–1,2-BD) and poly(ethylene oxide)–poly(ethyl ethylene) (EO–EE). To examine these membranes' nanoscale structure, we developed a coarse-grained molecular dynamics (CG MD) model for EO–1,2-BD and assembled a CG MD model for EO–EE using parameters from two published force fields. We observe that the polymers' hydrophobic core blocks are slightly stretched compared to the random coil configuration seen at higher molecular weights. We also observe an increase in the interdigitation of the hydrophobic leaflets with increasing molecular weight (consistent with literature). The hydration level of the EO corona (which may influence protein incorporation) is higher for membranes with a larger area/chain, regardless of whether EE or 1,2-BD forms the hydrophobic block. Our results provide a molecular-scale view of membrane packing and hydrophobicity, two important properties for creating polymer–protein biomimetic membranes.

Artificial water channels are synthetic molecules that aim to mimic the structural and functional features of biological water channels (aquaporins). Here we report on a cluster-forming organic nanoarchitecture, peptide-appended hybrid[4]arene (PAH[4]), as a new class of artificial water channels. Fluorescence experiments and simulations demonstrated that PAH[4]s can form, through lateral diffusion, clusters in lipid membranes that provide synergistic membrane-spanning paths for a rapid and selective water permeation through water-wire networks. Quantitative transport studies revealed that PAH[4]s can transport >109 water molecules per second per molecule, which is comparable to aquaporin water channels. The performance of these channels exceeds the upper bound limit of current desalination membranes by a factor of ~104, as illustrated by the water/NaCl permeability-selectivity trade-off curve. PAH[4]'s unique properties of a high water/solute permselectivity via cooperative water-wire formation could usher in an alternative design paradigm for permeable membrane materials in separations, energy production and barrier applications.

Hydrophobicity and molecular weight (MW) are two fundamental properties of dissolved organic matter (DOM) in wastewater treatment systems. This study proposes fluorescence Stokes shift and specific fluorescence intensity (SFI) as novel indicators of hydrophobicity and MW. These indicators originate from the energy gap and photon efficiency of the fluorescence process and can be readily extracted from a fluorescence excitation-emission matrix (EEM). The statistical linkages between these indicators and hydrophobicity/MW were explored through investigation of DOM across 10 full-scale membrane bioreactors treating municipal wastewater. Stokes shift was found to exhibit a general rule among the hydrophobicity components in the order of hydrophilic substances (HIS) 100 kDa), SFI was found to be the most sensitive to the change of MW of 0.9). Hydrophobicity-related π conjugation and MW-dependent light exposure might be responsible for the correlations. These fluorescence indicators may be useful for convenient monitoring of DOM in wastewater treatment systems.

Graphene oxide (GO) membranes formed by stacked GO nanosheets can separate contaminants from water via nanosized capillaries, the properties of which, however, might be altered by intercalation of solutes. This study first reports the impacts of common inorganic ions on the structure and separation performance of non-covalently bonded GO membranes. When filtering NaCl, KCl, MgCl2, CaCl2, Na2SO4, and K2SO4 solutions, the flux of GO membranes, fabricated by vacuum filtration, exhibited significant increase over the filtration time in Na+ solutions, but maintained stable in the other electrolyte solutions. Rejection decline was observed for all the electrolytes with an order of Na+ > Mg2 + ≈ Ca2 + > K+ for the chlorides. X-ray diffraction indicated the GO membrane structure in K+ solutions was well maintained and slightly expanded in Mg2 +/Ca2 + solutions over time. However, the ordered structure of GO membranes disappeared after long exposure to Na+, explaining the significantly increased flux and reduced rejection. The effect of Na+ on the GO membrane structure was ascribed to its relatively large size but weak attraction with GO nanosheets. These findings highlight the importance of introducing strong covalent bonding between GO nanosheets to stabilize the structure and separation performance of GO membranes for water purification.

Dissolved organic matter (DOM) plays a substantial role in wastewater treatment systems. Fluorescence is an important property of DOM and its use is promising for DOM characterization, but has rarely been extended to probing the basic physicochemical properties such as hydrophobicity and molecular weight. This study explores the possible linkages between the fluorescence properties and hydrophobicity/molecular weight of DOM, through case studies from three wastewater treatment plants (two membrane bioreactors and one oxidation ditch). The fluorescence properties of different hydrophobic/hydrophilic and molecular-weight fractions of DOM were obtained using excitation–emission matrix (EEM) spectroscopy and size-exclusion chromatography with fluorescence detection. The EEM spectra were interpreted using techniques of fluorescence regional integration, parallel factor analysis, fluorescence spectroscopic indices, and a novel energetic mapping based on fluorophore energy levels. It was found that for all the three plants, the hydrophobic fractions of DOM had a higher fluorescence intensity per UV absorbance (indicating a higher quantum yield) as well as a larger Stokes shifts than the hydrophilic fraction. The lower-molecular-weight fractions generally exhibited a higher fluorescence intensity per total organic carbon (indicating a higher fluorophore density), with the fluorescence distribution at slightly smaller excitation and emission wavelengths. These phenomena were explained via analysis of the fluorophore energy state during the excitation/emission process. The scale of the π-conjugated system in DOM molecules may serve as an intermediate factor in the correlations between the hydrophobicity/molecular weight and the fluorescence properties. These correlations may assist in developing fluorescent probes for the DOM characteristics during the process monitoring of wastewater treatment plants.

Artificial water channels are a practical alternative to biological water channels for achieving exceptional water permeability and selectivity in a stable and scalable architecture. However, channel-based membrane fabrication faces critical barriers such as: (1) increasing pore density to achieve measurable gains in permeability while maintaining selectivity, and (2) scale-up to practical membrane sizes for applications. Recently, we proposed a technique to prepare channel-based membranes using peptide-appended pillar[5]arene (PAP[5]) artificial water channels, addressing the above challenges. These multi-layered PAP[5] membranes (ML-PAP[5]) showed significantly improved water permeability compared to commercial membranes with similar molecular weight cut-offs. However, due to the distinctive pore structure of water channels and the layer-by-layer architecture of the membrane, the separation behavior is unique and was still not fully understood. In this paper, two unique selectivity trends of ML-PAP[5] membranes are discussed from the perspectives of channel geometry, ion exclusion, and linear molecule transport.

The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)-block-poly(ethylene oxide)-block-poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes.

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m−2 h−1 bar−1 compared with 4–7 L m−2 h−1 bar−1) over similarly rated commercial membranes. Synthetic polymeric membranes used for separations suffer from permeability-selectivity trade-offs. Here the authors demonstrate how a bioinspired pillar[5]arene artificial water channel embedded in a copolymer membrane can improve selectivity while still achieving high permeability.

The relative strengths of membrane bioreactors (MBR) versus conventional activated sludge (CAS) processes have long been debated, but never compared systematically at full scale. To this end, we monitored full-scale wastewater treatment performance and mixed-liquor characteristics (sludge biomass, extracellular polymeric substances (EPS), supernatant with molecular weight and hydrophilic/hydrophobic distribution) for parallel MBR and CAS (via oxidation ditch—OD), for a year. Ammonia and suspended solids were better removed by MBR; temperature affected ammonia removal in OD. At low temperatures, sludge settlement declined in both processes, but solid–liquid separation via membrane filtration continued, although the membrane fouled. EPS characteristics were similar, and organic components in EPS and supernatant varied seasonally, in both processes. MBR had a lower production rate, but higher concentration, of supernatant organics and accumulated large molecular-weight polysaccharides. Ammonia removal was correlated with tightly bound proteinaceous EPS. Polysaccharides, in loosely bound EPS and supernatant, were responsible for effective settlement (OD), and membrane fouling (MBR). These results demonstrate how mixed liquor intermediates process and performance, and that performance depends on effective solid–liquid separation. MBRs excel when stringent requirements for pollutant-removal and extreme environmental conditions exist. The much cheaper OD remains competitive under less demanding conditions.

Aquaporin based membranes (ABMs) are considered a promising biomimetic desalination technology and have been intensively studied over the last few years. The most common strategy to synthesize ABMs is to deposit the aquaporin incorporated lipid or block copolymer (BCP) vesicles onto porous substrates or more recently to integrate them within the active layer of polyamide membranes. However, ABMs with orders of magnitude improvement in permeability and perfect salt rejections proposed in initial work have not been realized. Early results were based on materials and methods that were rudimentary, especially considering the progress that has been made in this field. In particular, low signal to noise ratios (SNRs

Membrane protein and membrane protein-mimic functionalized materials are rapidly gaining interest across a wide range of applications, including drug screening, DNA sequencing, drug delivery, sensors, water desalination, and bioelectronics. In these applications, material performance is highly dependent on activity-per-protein and protein packing density in bilayer and bilayer-like structures collectively known as biomimetic membranes. However, a clear understanding of, and accurate tools to study these properties of biomimetic membranes does not exist. This paper presents methods to evaluate membrane protein compatibility with biomimetic membrane materials. The methods utilized provide average single protein activity, and for the first time, provide experimentally quantifiable measures of the chemical and physical compatibility between proteins (and their mimics) and membrane materials. Water transport proteins, rhodopsins, and artificial water channels are reconstituted into the full range of current biomimetic membrane matrices to evaluate the proposed platform. Compatibility measurement results show that both biological and artificial water channels tested largely preserve their single protein water transport rates in biomimetic membranes, while their reconstitution density is variable, leading to different overall membrane permeabilities. It is also shown that membrane protein insertion efficiency inversely correlates with both chemical and physical hydrophobicity mismatch between membrane protein and the membrane matrix.

Membrane fouling remains a challenge for membrane bioreactor (MBR) application to wastewater treatment. The hydrophilic/hydrophobic organics present in MBR sludge supernatant form an important part of foulant. Their effects on fouling evolution and irreversibility were systematically investigated in this study. The organics, as fractionated into hydrophilic substances (HIS), hydrophobic acids (HOA), hydrophobic bases (HOB), and hydrophobic neutrals (HON), were subjected to fouling experiments using six microfiltration membranes covering the size range of 0.1–0.45 µm with varied hydrophobicity. Modeling methods were applied to quantitatively characterize the dynamic fouling process as consisting of the initial pore blocking and subsequent gel layer stages. The results demonstrated the importance of foulant concentration to fouling evolution: the apparent fouling rate on a same membrane followed the order HIS>HOA⪢HOB>HON, whereas the order became HOA>HIS with normalization of concentration to give the intrinsic propensity for fouling evolution (across the initial stage) as well as the specific resistance (for the gel layer stage). Foulant–membrane interactions (i.e. hydrophobic adsorption and size exclusion) and foulant–foulant interaction (polymer–metal–polymer complexation) were identified as key mechanisms for fouling at the initial pore blocking stage and the gel layer stage respectively, with the foulant properties of hydrophobicity, molecular size and carboxylic complexing groups closely involved in the interactions. Additionally, membrane properties were also important factors affecting the fouling behaviors of the hydrophilic/hydrophobic fractions, as suggested by the combined impact of membrane hydrophobicity and pore size on fouling evolution propensity, and the decisive role of membrane hydrophobicity in fouling irreversibility.

Supported biomimetic membranes hold potential for applications such as biosensors and water purification by filtration. The current paper reports on the preparation of a supported bolaamphiphile membrane on two polymeric nanofiltration membranes: NF-270 made of polyamide with carboxylic surface charges and NTR-7450 made of sulfonated polyethersulfone with sulfonic surface charges. The results, obtained using a proprietary microfluidic device, confirmed that the supported membrane coverage on the polymeric membranes was governed by the double-layer interactions, in agreement with previous studies on silica, mica, and gold. Remarkably, the formation of the biomimetic membrane was more favorable on the sulfonated polyethersulfone than on the polyamide surface, although both surfaces exhibit a similar surface charge density. It is suggested that the higher dissociation constant of sulfonic groups was the main reason for the higher coverage of NTR-7450. Finally, spinach aquaporins, which are trans-membrane proteins that facilitate the water transport, were incorporated into a supported membrane on NTR-7450. The incorporated aquaporin resulted in enhanced pressure-driven water transport through the membrane, however, for still unclear reasons, the transport was not selective. Despite this failure, the results provide new insights into formation of biomimetic membrane on water permeable polymeric substrates, as a generic approach towards biomimetic water filters

Biomimetic approaches to developing membranes for separations have seen a renewed interest in recent years. Biomimetic membranes incorporate biological elements or borrow concepts, ideas or inspiration from biological systems. Such membranes can take advantage of the strategies evolved by nature over billions of years for improving transport efficiency and specificity. This review covers biological paradigms that are relevant to membranes for separations and then presents an overview of strategies that are inspired by these paradigms. It also presents both fundamental and practical challenges to implementation of these strategies at application relevant scales.

Despite the potentially important effect of temperature on membrane fouling, very few investigations have been conducted on full-scale membrane bioreactors (MBRs) regarding seasonal variation of fouling. In this study, fouling behavior in a full-scale MBR (capacity 60,000 m3/d) in northern China was monitored for a whole year. As the mixed liquor temperature dropped from 27 to 13 °C, the filtration resistance increased from 0.6×1013 to 2.6×1013 m−1, which was attributable to higher concentration of supernatant organics at lower temperatures. Humic substances were the predominant supernatant organics (10–25 mg/L) in comparison with polysaccharides and proteins (both 5–15 mg/L). The dependence of seasonal supernatant fouling potential on hydrophilic/hydrophobic composition and molecular weight distribution of the organics were analyzed based on statistical correlation. Humic substances in all hydrophobicity and molecular weight ranges correlated closely with the fouling potential. Hydrophilic polysaccharides and large-molecular-weight proteins were also found to contribute to the fouling potential.

Stirred dead-end filtration (SDEF) has been widely used for fundamental studies on membrane fouling caused by soluble and colloidal matter during microfiltration and ultrafiltration. Quantitative description of the SDEF fouling process which usually involves gel layer formation, however, has rarely been reported. In this study, an analytical model was derived based on theories of cake filtration and concentration polarization, to quantify the gel-associated fouling evolution process during constant pressure SDEF. The model formulates the relationship between filtration resistance ( R ) and specific permeate volume ( V ) as: V = C 1 + C 2 R + C 3 exp(− C 4 / R )+ V 0 ( C 2 dR / dV −1), where C 1 – C 4 and V 0 are constants. The model enables rigorous definition of characteristic points on the R vs. V curve to divide the fouling evolution process into the initial fouling stage, the gel layer growth stage and the gel layer mature stage. The model also gives a simplified piecewise expression: V = C 1 + C 2 R for the gel layer growth stage and V = C 1 + C 2 R + C 3 exp(− C 4 / R )− V 0 for the mature stage. A two-step fitting approach was proposed for the simplified expression to evaluate the C 1 – C 4 parameters. These parameters were found useful in determining the characteristic points of fouling evolution and further, in quantifying foulant and fouling layer properties including: hydrodynamic diameter and diffusion coefficient of foulant, mass transfer coefficient and boundary layer thickness of concentration polarization, and specific resistance and gel point concentration of gel layer. This model in combination with constant pressure SDEF experiments can serve as a tool for quantitative characterization of fouling propensity and foulant properties, and may thus assist in detailed analysis of fouling mechanisms.

Wastewater treatment plants are thought to be potential reservoirs of antibiotic resistance genes. In this study, GeoChip was used for analyzing multiple antibiotic resistance genes, including four multidrug efflux system gene groups and three β-lactamase genes in ten large-scale membrane bioreactors (MBRs) for municipal wastewater treatment. Results revealed that the diversity of antibiotic genes varied a lot among MBRs, but about 40% common antibiotic resistance genes were existent. The average signal intensity of each antibiotic resistance group was similar among MBRs, nevertheless the total abundance of each group varied remarkably and the dominant resistance gene groups were different in individual MBR. The antibiotic resistance genes majorly derived from Proteobacteria and Actinobacteria. Further study indicated that TN, TP and COD of influent, temperature and conductivity of mixed liquor were significant (P

International audience; Aquaporins (AQPs) are biological water channels known for fast water transport (similar to 10(8)-10(9) molecules/s/channel) with ion exclusion. Few synthetic channels have been designed to mimic this high water permeability, and none reject ions at a significant level. Selective water translocation has previously been shown to depend on water-wires spanning the AQP pore that reverse their orientation, combined with correlated channel motions. No quantitative correlation between the dipolar orientation of the water-wires and their effects on water and proton translocation has been reported. Here, we use complementary X-ray structural data, bilayer transport experiments, and molecular dynamics (MD) simulations to gain key insights and quantify transport. We report artificial imidazole-quartet water channels with 2.6 angstrom pores, similar to AQP channels, that encapsulate oriented dipolar water-wires in a confined chiral conduit. These channels are able to transport 106 water molecules/s, which is within 2 orders of magnitude of AQPs' rates, and reject all ions except protons. The proton conductance is high (similar to 5 H+/s/channel) and approximately half that of the M2 proton channel at neutral pH. Chirality is a key feature influencing channel efficiency.

The exquisite selectivity and unique transport properties of membrane proteins can be harnessed for a variety of engineering and biomedical applications if suitable membranes can be produced. Amphiphilic block copolymers (BCPs), developed as stable lipid analogs, form membranes that functionally incorporate membrane proteins and are ideal for such applications. While high protein density and planar membrane morphology are most desirable, BCP-membrane protein aggregates have so far been limited to low protein densities in either vesicular or bilayer morphologies. Here, we used dialysis to reproducibly form planar and vesicular BCP membranes with a high density of reconstituted aquaporin-0 (AQP0) water channels. We show that AQP0 retains its biological activity when incorporated at high density in BCP membranes, and that the morphology of the BCP-protein aggregates can be controlled by adjusting the amount of incorporated AQP0. We also show that BCPs can be used to form two-dimensional crystals of AQP0.

In order to fill the knowledge gaps between lab/pilot-scale and full-scale operations and contribute basic information to long-term and stable operation of large-scale membrane bioreactors (MBRs), a systematic investigation was first conducted focused on soluble microbial products (SMPs) in 10 large-scale MBRs (capacity over 10,000 m3/d) for municipal wastewater treatment distributed in 4 different areas of China from fall to winter. The majority of these MBR plants had been operated stably for at least 1 year. Fundamental properties of SMPs were investigated, including composition, molecular weight distribution, hydrophobicity, fluorescent characteristics and fouling potential. The results showed that the concentration of SMPs ranged roughly from 5 to 25 mg TOC/L, with the major component being polysaccharides (ca. 3–18 mg/L) followed by humic substances (ca. 2–10 mg/L); while the protein concentration was relatively low (

It is believed that the presence of calcium ions causes more severe organic fouling during nanofiltration, since they serve as bridges near the membrane surface between foulants and the surface through complexation. However, complexation can also occur in the solution (bulk complexation), leading to the formation of aggregates. This study used alginate as a model foulant to investigate the potential for bulk complexation to lower organic fouling. Results demonstrated that two regimes existed with regard to initial fouling, i.e., flux decline. As the concentration of calcium increases from zero, the initial rate of fouling increased until a critical calcium concentration was reached. Increasing the calcium concentration above this point decreased the initial rate of fouling. Analysis of the size distribution in the alginate solution revealed that at very high calcium concentrations, significant formation of aggregates occurred and reduced the amount of dissolved organic carbon. Thus, effective transportation of alginate toward the membrane and the fouling it causes occur more slowly. The accumulative total organic carbon at the membrane surface was similar to the initial fouling with respect to the concentration of calcium. This strengthens the slower effective transportation of alginate at very high calcium concentrations. Moreover, the stabilized flux and specific resistance of the fouling layer varied monotonically with calcium concentrations over all concentrations tested. Both depend on intermolecular forces between foulants, which is enhanced at increased calcium concentration.

Since the introduction of the membrane bioreactor (MBR) in China in the early 1990s, remarkable progress has been achieved on the research and application of this technology. China has now become one of the most active fields in the world in this regard. This review outlines the development of MBR-based processes in China and their performance of treating municipal and industrial wastewaters. Since membrane fouling is a critical operational problem with MBR processes, this paper also proposes updated understanding of fouling mechanisms and strategies of fouling control, which are mainly compiled from publications of Chinese researchers. As for the commercial application of MBR in the country, the latest statistics of large-scale MBR plants (>10000 m3·d−1) are provided, and the growth trend of total treatment capacity as well as its driving force is analyzed.

Synthetic polymer membranes, critical to diverse energy-efficient separations, are subject to permeability-selectivity trade-offs that decrease their overall efficacy. These trade-offs are due to structural variations (e.g., broad pore size distributions) in both nonporous membranes used for Angstrom-scale separations and porous membranes used for nano to micron-scale separations. Biological membranes utilize well-defined Angstrom-scale pores to provide exceptional transport properties and can be used as inspiration to overcome this trade-off. Here, we present a comprehensive demonstration of such a bioinspired approach based on pillar[5]arene artificial water channels, resulting in artificial water channel-based block copolymer membranes. These membranes have a sharp selectivity profile with a molecular weight cutoff of ~ 500 Da, a size range challenging to achieve with current membranes, while achieving a large improvement in permeability (~65 L m−2 h−1 bar−1 compared with 4–7 L m−2 h−1 bar−1) over similarly rated commercial membranes., Synthetic polymeric membranes used for separations suffer from permeability-selectivity trade-offs. Here the authors demonstrate how a bioinspired pillar[5]arene artificial water channel embedded in a copolymer membrane can improve selectivity while still achieving high permeability.

Soluble microbial products (SMPs) contained in membrane bioreactor (MBR) supernatant have been proved to be main foulants. To obtain a comprehensive understanding of the fouling potential of SMPs on the basis of both hydrophilic/hydrophobic properties and molecular size, MBR supernatant of a pilot-scaled system treating municipal wastewater was partitioned into different hydrophilic/hydrophobic fractions by DAX-8 resins, with joint size partition of hydrophilic fraction also undertaken. A series of stirred dead-end filtration tests were conducted to investigate the flux decline. Hydrophilic fraction was found the dominant foulant responsible for flux deterioration, which was mainly attributed to the subclass of molecular weight above 100 kDa. The molecular weight distribution and atomic force microscopy images indicated that large molecules in hydrophilic fraction plugged the membrane pores. The backwash tests showed the flux decline caused by hydrophilic fraction was much less recoverable by hydraulic cleaning. It can be inferred that steric factor, i.e. size exclusion was the primary cause in the initial stage of fouling, while the role of hydrophobic interaction was of less significance. Additional modeling work indicates that the main fouling mechanism was complete blocking, further confirming the predominance of size exclusion contributing to membrane fouling by SMPs in MBR supernatant.

Coke wastewater is an extremely toxic industrial effluent that requires treatment before discharge. A bench-scale, anaerobic–anoxic–oxic membrane bioreactor (A 1 /A 2 /O-MBR) system was utilized to treat real coke wastewater with complete sludge retention. In a 160-d test, the A 1 /A 2 /O-MBR system stably removed 87.9 ± 1.6% of chemical oxygen demand, 99.4 ± 0.3% of turbidity, and 99.7 ± 3.5% of NH 4 + -N from coke wastewater. The membrane rejected almost all suspended solids; hence, a low food-to-microorganism environment was created to degrade refractory substances and reduce sludge production rates. The microbial diversity in the MBR system declined over time; however, neither pollutant removal efficiency nor total biological activity was adversely affected. Membrane fouling, which occurred during the operation of the MBR system, was principally resulted from the colloidal fraction of supernatant in suspension. Physical cleaning removed initial deposits of particles; however, prolonged operation resulted in severe clogging that can only be removed by chemical cleaning. An A 1 /A 2 /O-MBR system with short intermittent physical cleaning was recommended for coke wastewater treatment.

Bioinspired artificial water channels aim to combine the high permeability and selectivity of biological aquaporin (AQP) water channels with chemical stability. Here, we carefully characterized a class of artificial water channels, peptide-appended pillar[5]arenes (PAPs). The average single-channel osmotic water permeability for PAPs is 1.0(± 0.3) × 10(-14) cm(3)/s or 3.5(± 1.0) × 10(8) water molecules per s, which is in the range of AQPs (3.4 ∼ 40.3 × 10(8) water molecules per s) and their current synthetic analogs, carbon nanotubes (CNTs, 9.0 × 10(8) water molecules per s). This permeability is an order of magnitude higher than first-generation artificial water channels (20 to ∼ 10(7) water molecules per s). Furthermore, within lipid bilayers, PAP channels can self-assemble into 2D arrays. Relevant to permeable membrane design, the pore density of PAP channel arrays (∼ 2.6 × 10(5) pores per μm(2)) is two orders of magnitude higher than that of CNT membranes (0.1 ∼ 2.5 × 10(3) pores per μm(2)). PAP channels thus combine the advantages of biological channels and CNTs and improve upon them through their relatively simple synthesis, chemical stability, and propensity to form arrays.

Large-scale membrane bioreactors (MBRs) have been widely used for the municipal wastewater treatment, whose performance relies on microbial communities of activated sludge. Nevertheless, microbial functional structures in MBRs remain little understood. To gain insight into functional genes and their steering environmental factors, we adopted GeoChip, a high-throughput microarray-based tool, to examine microbial genes in four large-scale, in-operation MBRs located in Beijing, China. The results revealed substantial microbial gene heterogeneity (43.7-85.1% overlaps) among different MBRs. Mantel tests indicated that microbial nutrient cycling genes were significantly (P 0.05) correlated to influent COD, [Formula: see text] -N, TP or sulfate, which signified the importance of microbial mediation of wastewater constituent removal. In addition, functional genes shared by all four MBRs contained a large number of genes involved in antibiotics resistance, metal resistance and organic remediation, suggesting that they were required for degradation or resistance to toxic compounds in wastewater. The linkages between microbial functional structures and environmental variables were also unveiled by the finding of hydraulic retention time, influent COD, [Formula: see text] -N, mixed liquid temperature and humic substances as major factors shaping microbial communities. Together, the results presented demonstrate the utility of GeoChip-based microarray approach in examining microbial communities of wastewater treatment plants and provide insights into the forces driving important processes of element cycling.

This chapter focuses on lipid and polymer-based biomimetic membranes for separations. We first discuss the structure, organization, and transport properties of biological membranes that form the inspiration for biomimetic membranes with a focus on aspects relevant to synthetic membrane development. This is followed by a description of the novel properties and current strategies for synthesis of biomimetic membranes. Lipid and polymer-based membranes are discussed as well as the emerging area of artificial-channel-based membranes. A short outlook on the advancements needed for commercialization of biomimetic membranes is also presented. Keywords: lipid bilayers; membrane proteins; block copolymers; ionophores; ion channels; aquaporins; artificial channels; desalination