Membrane Filtration System Research Articles

Exploring the transformation of polyethylene and polyamide microplastics during membrane filtration through FlowCam analysis

This study explored the applicability of fluid imaging microscopy (FlowCam) as a valuable tool for characterizing microplastic transformations, addressing the urgent need for rapid microplastic measurement techniques. FlowCam offers multiple measurement outputs, making it suitable for automated classification to separate polyethylene (PE) and polyamide (PA) microplastics in wastewater samples. Customized libraries for each type of microplastic were constructed using statistical analysis with appropriate confidence intervals, thus enhancing sorting accuracy. Comparing multiple FlowCam outputs before and after membrane filtration revealed limitations in dimensional outputs, particularly for irregularly shaped PA microplastics. Specifically, a marginal increase in the elongation of PA microplastics after filtration suggested their ability to longitudinally penetrate pores due to their high length relative to thickness. In contrast, PE microplastics with higher circularity, resembling ideal spheres, exhibited greater susceptibility to removal by the membrane pores. Therefore, membranes were more susceptible to wastewater containing PA microplastics, as these are complex and non-uniform particles, that are more likely to induce pore blockage and might form denser cake layers on the membrane surface by tightly filling interstitial spaces. These findings demonstrate the significant role of microplastic geometry and morphology in retention mechanisms and membrane fouling. Collectively, our findings highlight the potential of FlowCam for microplastic identification and provide a valuable basis for the characterization of microplastic transformations within membrane filtration systems, addressing a pressing concern in environmental science within engineered systems.

Investigation of the treatment and antibacterial properties of pollutant-containing water using black phosphorus blended polyethersulfone membranes (BP@PES)

The most important problem of membrane processes is clogging and therefore the reduction of their useful life. In order to eliminate such problems, the production of composite membranes is an option in membrane treatment systems. In this study, the usability of black phosphorus (BP) in membrane treatment systems, and its effect on antibacterial and treatment performance were studied. BP blended PES membranes (BP@PES) produced by loading BP into the polyethersulfone (PES) membranes were used for the treatment of bovine serum albumin (BSA) and Escherichia coli (E. coli). For this purpose, BP was added at three different amounts (0.5 %, 1.0 %, and 2.0 %) into PES membranes. Membranes with different BP amounts produced were named as 0.5%BP@PES, 1.0%BP@PES, and 2.0%BP@PES. After the production of these composite membranes, they were used in the dead-end filtration system and compared with the PES membrane without BP (bare PES). The removal effectiveness of bare PES was found to be 53.40 % in the BSA rejection results, and it was discovered to be 60.90 %, 97.15 %, and 100 % for 0.5%BP@PES, 1.0%BP@PES, and 2.0%BP@PES, respectively. The antioxidant activity of BP was 70.86% at 100 mg/L. Newly prepared BP caused single-strand DNA nuclease abilities at 50, 100, and 200 mg/L. BP showed the effective antimicrobial activity. The most antimicrobial activity was determined as a minimum inhibitory concentration (MIC) value of 8 mg/L against E. hirae and 100 % E. coli viability inhibition activity was achieved at 50 and 100 mg/L after 90 min exposure. BP also inhibited the biofilm formation of P. aeruginosa at 87.19 % and S. aureus at 90.28 % at 50 mg/L. Thus, both the effect of BP on membrane performance and its antibacterial properties were investigated. Pure water fluxes, BSA and E.coli rejection performances, and antibacterial properties of all membranes used in the membrane filtration system were investigated in detail. It is recommended to further investigate BP-containing membranes with different production techniques.

A multi-cycle pump for efficient separation of CO2 or other trace gas from a mixture of gases

An idealized gas separation pump is described for a membrane filtration system that conserves compressional energy by transferring it from one component to another operating at a different phase of the compression-decompression cycle. An example of the basic principle, we consider a pump that resembles an internal combustion engine with pistons in cylinders and three valves, one for mixed gas input, another for select gas output through a membrane, and a third for non-select gas output to the environment. With the transfer of compressional energy from the decompressing cylinder to the compressing cylinder, the energy required is the sum of frictional losses and the amount needed to compress only the trace gas that is to be separated. Compressional energy for the non-select is recovered. The mechanical energy required is the energy to compress the cylinder, NRT(lnC−1+1∕C)∼3NRT in the isothermal case for number of moles of select gas, N, gas constant R, temperature T, and compression factor C ∼ 50, multiplied by 1 + 2ϵ∕f ∼ 2 for frictional loss fraction ϵ ∼ 6% comparable to that in internal combustion engines and an input select gas molar fraction f ∼ 10% as for CO2 in flue gas. With T = 300 K and N = 2.3 × 104 per ton for CO2, this energy becomes ∼ 6NRT ∼ 94 kWh/tCO2. The advantages of a system like this are that the compression ratio through the membrane can be large and the timescale for compression can be adjusted to maximize the throughput for a given selectivity, overcoming the usual selectivity-permeance trade-off. A disadvantage is that the throughput is generally low for volumetric pumps at practical scales.

Application of biological early warning systems in wastewater treatment plants: Introducing a promising approach to monitor changing wastewater composition

Wastewater treatment plants (WWTPs) are a major source of micropollutants to surface waters. Currently, their chemical or biological monitoring is realized by using grab or composite samples, which provides only snapshots of the current wastewater composition. Especially in WWTPs with industrial input, the wastewater composition can be highly variable and a continuous assessment would be advantageous, but very labor and cost intensive. A promising concept are automated real-time biological early warning systems (BEWS), where living organisms are constantly exposed to the water and an alarm is triggered if the organism's responses exceed a harmful threshold of acute toxicity. Currently, BEWS are established for drinking water and surface water but are seldom applied to monitor wastewater. This study demonstrates that a battery of BEWS using algae (Chlorella vulgaris in the Algae Toximeter, bbe Moldaenke), water flea (Daphnia magna in the DaphTox II, bbe Moldaenke) and gammarids (Gammarus pulex in the Sensaguard, REMONDIS Aqua) can be adapted for wastewater surveillance. For continuous low-maintenance operation, a back-washable membrane filtration system is indispensable for adequate preparation of treated wastewater. Only minor deviations in the reaction of the organisms towards treated and filtered wastewater compared to surface waters were detected. After spiking treated wastewater with two concentrations of the model compounds diuron, chlorpyrifos methyl, and sertraline, the organisms in the different BEWS showed clear responses depending on the respective compound, concentration and mode of action. Immediate effects on photosynthetic activity of algae were detected for diuron exposure, and strong behavioral changes in water flea and gammarids after exposure to chlorpyrifos methyl or sertraline were observed, which triggered automated alarms. Different types of data analysis were applied to extract more information out of the specific behavioral traits, than only provided by the vendors algorithms. To investigate, whether behavioral movement changes can be linked to impact other endpoints, the effects on feeding activity of G. pulex were evaluated and results indicated significant differences between the exposures. Overall, these findings provide an important basis indicating that BEWS have the potential to act as alarm systems for pollution events in the wastewater sector.

Reactive electrochemical ceramic membrane filtration system for efficient treatment of enrofloxacin from wastewater: Mechanisms and applications

Reactive electrochemical ceramic membrane filtration system for efficient treatment of enrofloxacin from wastewater: Mechanisms and applications

One-step modification of MIL-88A(Fe) enhanced electro-Fenton coupled membrane filtration system for the removal of bisphenol A

An electro-Fenton coupled membrane filtration system (abbreviated as EF-MF system) was constructed for the efficient removal of bisphenol A (abbreviated as BPA, a kind of pharmaceuticals and personal care products, abbreviated as PPCPs). In the EF-MF system, a porous Fe3O4/FeO/Fe@C catalyst was synthesized and applied to enhance the electro-Fenton reaction, and polyvinylidene fluoride/carbon fiber cloth composite cathode membrane was used as both cathode electrode and membrane. Characterization results indicated the porous Fe3O4/FeO/Fe@C catalyst exhibited micron-level rod morphology and was in an encapsulated structure with Fe3O4/FeO/Fe composite nanoparticles covered by porous graphitic carbon. Degradation experiments indicated the EF-MF system exhibited great removal efficiency (approximately 96.97%) towards BPA within 70 min in the conditions of catalyst dosing at 0.500 g·L−1, the value of pH at 3 and the current density at 0.67 mA cm−2. Quenching experiments verified both OH radical and O2− radical played significant roles in the decomposition of BPA. The mass formation of reactive oxygen radicals was mostly owing to the easy access of H2O2 to the activated sites of the porous Fe3O4/FeO/Fe@C catalyst through the porous structure and the rapid cycle conversion between zero-valent iron (ZVI), Fe(Ⅱ) and Fe(Ⅲ). Based on the results of intermediates identification, three possible decomposition pathways were presented. Toxicity analysis exhibited most of the intermediates were in less toxicity than BPA. Moreover, the EF-MF system exhibited good stability after four-cyclic utilization. This work provides an efficient and energy-saving strategy for the removal of PPCPs.

Microfiltration, ultrafiltration and nanofiltration as a post-treatment of biological treatment process with references to oil field produced water of Moran oilfield of Assam

The selection of an apt technology for the treatment of Oilfield Produced Water (OFPW) depends mainly on the quality of OFPW and methods of pre-and post-treatment processes. The most challenging part of the OFPW treatment process is the removal of Suspended Solid (SS), Oil & Grease (O&G) and dissolved organics. SS and O&G pose an acute problem to the membrane filtration system by fouling the membrane surface which increases operation & maintenance costs and decreases the life of the membrane. Fouling of the membrane surface is mainly attributed to the presence of low molecular weight aromatic compounds and naphthenic acids in the suspended and dissolved organic compounds. Thus, the removal of these suspended and dissolved organic compounds before membrane filtration proffers a challenge to the researchers. In this research, bioremediation process has been applied to remove the organic compounds and the performance and fouling behaviour of hollow fibre Microfiltration (MF), Ultrafiltration (UF) and Nanofiltration (NF) membranes after the bioremediation process has been analyzed in detail. The level of toxicity was determined by comparing the pollutants with the safe discharge limit for disposal into the environment set by Central Pollution Control Board (CPCB), India. The research presents its novelty by using a hydrocarbon-degrading bacteria, Pseudomonas aeruginosa for the Reduction of Organic Loads (ROL) from OFPW of Moran oil field of Upper Assam as a pre-treatment to membrane filtration. The Total Sum Corrected Area (TSCA) method through chromatographic analyses was used for this. The organic loads removal from OFPW by the TSCA method was found to be 67–100%, 100% and 100% after 7, 14 and 21 days of bioremediation respectively. The major parameters in feed OFPW of Moran oil field were found to be pH (7.5–9.3), Total Dissolved Solid (TDS) (1.79–4.75) ppt, O&G (1.78–2.8) ppt, Salinity (2.94–6.98) ppt, Chloride (Cl−) (1.6–3.86) ppt, Bicarbonate (HCO3−) (2.89–4.03) ppt. It was observed that the ranges of pollutants removal by NF was highest such as TDS (26–86%), salinity (81–86%), turbidity (78–94%), hardness (67–75%), O&G (96–99%), Cl− (80–89%) and HCO3− (95–97%).

Mechanistic insight into single-atom Fe loaded catalytic membrane with peracetic acid and visible light activation

Advanced oxidation is an effective method for removing hard-to-degrade organic pollutants from water. In this paper, a novel structure of a single atom Fe anchored g-C3N4 (FeCN) membrane was proposed to remove pollutants from water by coupling membrane technology with photocatalytic and peroxyacetic acid oxidation. The presence of zero-dimensional Fe atoms in FeCN membranes allows for the removal of acetaminophen (APAP) in mobile membrane filtration systems without compromising permeation performance by simultaneously possessing visible photocatalytic capability and peroxyacetic acid (PAA) activation. Existence of inter-membrane domain-limiting conditions led to 100 % degradation of APAP within 10.5 ms, which is 5 orders of magnitude faster than conventional catalytic systems. Notably, photo-generated electrons/holes generated by light and HClO generated by Cl- promote the conversion of Fe(V) and the removal of pollutants during the catalytic process. The spatial separation ability of the membrane catalytic layer surface mitigates the catalyst's passivation by macromolecular organics. Furthermore, surface photocatalysis of the membrane and interlayer catalysis generated by PAA mitigate the surface and interlayer pollutants of the membrane, respectively. This study explores a novel approach for the development of highly efficient atom-catalyzed membrane systems with multiple purposes.

Rejection of perfluoroalkyl acids by nanofiltration and reverse osmosis in a high-recovery closed-circuit membrane filtration system

Poly- and perfluoroalkyl substances (PFASs), especially perfluoroalkyl acids (PFAAs), have garnered broad attention due to their near ubiquitous presence in environmental and biological matrices, recalcitrant nature, and reported negative human health impacts. Processes using high-pressure membranes such as reverse osmosis (RO) and nanofiltration (NF) have been investigated as PFAA treatment technologies due to their ability to separate dissolved solutes such as inorganic ions, and small molecular weight organic compounds. The major drawback associated with high-pressure membranes is management of the concentrate stream produced during treatment. As a result, high recovery membrane system configurations have been developed with the goal of minimizing volume of concentrate requiring disposal. In the context of PFAS treatment, high-recovery membrane applications may be beneficial; PFAS residuals could be concentrated allowing advantages in terms of disposal, e.g., more effective application of PFAS destruction technologies. The objective of this study was to evaluate the PFAA rejection performance of commercially available high-pressure membranes in a pilot-scale closed-circuit membrane filtration (CCMF) system. The rejection of nine PFAAs by four spiral wound membrane products spanning characteristics ranging from loose NF to seawater RO was investigated during and through two closed-circuit sequences each operating up to 97% recovery. Mechanisms of PFAA rejection including steric and electrostatic exclusion were investigated through analysis of generated data, and ionic strength experiments. Additionally, short-term foulant accumulation during CCMF and normalized energy analysis were performed by monitoring the calculated temperature corrected specific flux (TCSF) and design software simulations, respectively. Results from this study demonstrate that tight NF and RO membranes are effective for separating and concentrating PFAAs during high recovery CCMF operation. During CCMF sequences to 97% water recovery, the NF90, CR100, and SW30 membranes evaluated exhibited overall rejection values of > 98.3% for the PFAAs quantified in this study. The loose NF membrane element investigated (NF270) exhibited the lowest PFAA rejection performance during the high recovery experiments, particularly at water recoveries > 90%. Diminished PFAA rejection performance of the NF270 is likely a result of both steric and electrostatic exclusion being significant separation mechanisms. Feed water amended with sodium sulfate yielded lower rejection for PFAAs by the NF270 compared to unamended feed water supporting the hypothesis that that high recovery CCMF operation may negatively impact PFAS rejection by loose NF membranes, particularly membranes that rely on electrostatic exclusion for separation of anions.

Application of different treatment systems for boron removal from industrial wastewater with extremely high boron content

The aim of the study is purification and environmental management of boron containing industrial wastewater wastewaters comparing the efficiency of chemical precipitation and membrane filtration systems on the removal of boron at high concentrations from wastewater coming from boric acid production process and ground water. In order to eliminate adverse effects and find optimum treatment system, chemical precipitation, electrocoagulation and reverse osmosis processes have been studied. Different chemical precipitants such as poly aluminum chloride (PACl), lime, calcium chloride (CaCl2) and barium chloride (BaCl2) and hydrogen peroxide as oxidant were used. When solution pH was adjusted at 10, boron removal increased to 99.5 %. With application of electrocoagulation, 9 % of SO42-, 80 % of Si and 45 % of B were removed from spring water. At membrane-system, single and double pass BWRO/SWRO membrane system operations were carried out in order. Boron-removal increased 98 % by increasing pH up to 10, and DP-SWRO membranes system at 10-pH was found to be the best system. Obtaining a sufficient result for boron removal from spring water, a hybrid membrane process which contains an electrocoagulation process as a pre-treatment method and a double pass RO membrane system has been developed as an attractive technology.

Integrating gravity-driven ceramic membrane filtration with hydroponic system for nutrient recovery from primary municipal wastewater

In this study, a gravity-driven membrane (GDM) filtration system and hydroponic system (cultivating basil and lettuce) were combined for nutrient recovery from primary municipal wastewater. The GDM system was optimized by increasing the periodic air sparging flow rate from 1 to 2 L/min (∼15 hr per 3–4 days), resulting in a ∼52% reduction of irreversible fouling. However, the total fouling was not alleviated, and the water productivity remained comparable. The GDM-filtrated water was then delivered to hydroponic systems, and the effects of hydroponic operation conditions on plant growth and heavy metal uptake were evaluated, with fertilizer- and tap water-based hydroponic systems and soil cultivation system (with tap water) for comparison. It was found that (i) the hydroponic system under batch mode facilitated to promote vegetable growth with higher nutrient uptake rates compared to that under flow-through feed mode; (ii) a shift in nutrient levels in the hydroponic system could impact plant growth (such as plant height and leaf length), especially in the early stages. Nevertheless, the plants cultivated with the GDM-treated water had comparable growth profiles to those with commercial fertilizer or in soils. Furthermore, the targeted hazard quotient levels of all heavy metals for the plants in the hydroponic system with the treated water were greatly lower than those with the commercial fertilizer. Especially, compared to the lettuce, the basil had a lower heavy metal uptake capability and displayed a negligible impact on long-term human health risk, when the treated water was employed for the hydroponic system.

New approach to recycle and valorize the first filtrate of the LignoForce system™: Lignin extraction and its use in rigid lignin-based polyurethane foams

In this work, we report on the fractionation, recovery and characterization of softwood kraft lignin from the first filtrate of the LignoForce™ process. It is estimated that the lignin content in this stream could be >20–30 % of the lignin present initially in the black liquor. The use of a membrane filtration system was experimentally validated as an effective method for fractionating the first filtrate. Two membranes with different nominal molecular weight cut-offs (4000 and 250 Da) were tested. Higher lignin retention and recovery was obtained using the 250-Da membrane. This lignin (lignin_250) was found also to have a lower molecular weight and a tighter molecular weight distribution compared to the lignin obtained using the 4000-Da membrane (lignin_4000). The lignin_250 was characterized for it's hydroxyl group content and used to produce polyurethane (PU) foams. Up to 30 wt% petroleum-based polyol replacement by lignin_250, the resulting lignin-based PU (LBPU) foams presented the same thermal conductivity as the control (0.0303 W/m.K (control) vs 0.029 W/m.K (30 wt%)), as well as comparable mechanical (max stress: 145.8 kPa (control) vs 222.7 KPa (30 wt%), modulus 64.3 kPa (control) vs 75.1 (30 wt%)) and morphological properties to the petroleum polyol-based PU foams.

Improved Reliability of Raman Spectroscopic Imaging of Low-Micrometer Microplastic Mixtures in Lake Water by Fractionated Membrane Filtration

Low-micrometer microplastics (LMMPs), typically in the size range, 1–10 μm, are emerging contaminants ubiquitously present in aquatic systems. However, the quantification of LMMP mixtures in environmental waters is hindered by the limitations of current analytical methods. In this study, we developed a novel analytical method that couples a fractionated membrane filtration with Raman microspectroscopy (μ-Raman) to reliably quantify LMMPs in lake water. The fractionated membrane filtration system recovered >90% of the mixed polystyrene (PS) and poly(methyl methacrylate) (PMMA) LMMPs (i.e., 1.5, 3, 5, and 8 μm) from water. By separating LMMPs into 1–5 and 5–10 μm size fractions, the quality of the Raman images of small LMMPs (i.e., 1.5 and 3 μm particles) acquired directly on the membrane filters improved substantially. The reliability of LMMP Raman imaging was further improved by tracking the sum and product of their three characteristic Raman bands. In this way, the interferent Raman signals from the lake water matrix and membrane filters were significantly suppressed. This method provides a reliable tool to recover, separate, and quantify LMMP mixtures in complex water matrices, paving the way toward a deeper understanding of their environmental implications.

Improvement of Saccharomyces propagation performance through oxygen-enriched air and aeration parameter variation

A variety of yeast applications in the food and beverage industry require individual and reproducible yeast propagation at high yields and consistent quality. One quality-determining parameter for yeast propagation is effective aeration to avoid oxygen depletion. Therefore, this work investigated three important aeration parameters: airflow, pulse time, and oxygen concentration, for their influence on yeast propagation. The aeration of a propagator involves phase transitions which are gradient-driven processes and can be accelerated with higher gradients between the liquid medium and the gas bubbles. In this study, oxygen-enriched air generated with membrane filters was used to aerate the system in an easy and cost-efficient way without the need for expensive technical gas usage. Propagation experiments were carried out in a pilot-scale reactor equipped with a membrane filter system for enhanced oxygen concentrations in ingas and online sensors for representative monitoring of the process. The membrane filter system is based on the separation of nitrogen in compressed air, leading to oxygen enrichment. Using oxygen-enriched air for propagation aeration showed higher oxygen transfer into the medium and the anaerobic process time caused by oxygen depletion due to high cell numbers was reduced by an average of 7.4% for pulsed aeration. Additionally, we conducted experiments with controlled measures of dissolved oxygen using different oxygen concentrations for aeration. The main objective of this study is to present a new and affordable optimization of propagation aeration using membrane filtration to enrich process air. The results showed increased cell counts for higher ingas oxygen concentrations and no negative impact on cell vitality was observed. Hence, our investigations showed that using oxygen-enriched air reduced the frequency of pulsed aeration, thus hindering foam formation, a limiting factor of the yeast propagation process.

Water treatment membranes embedded with a stable and bactericidal nanodiamond material.

Filtration has emerged as a critical technology to reduce waterborne diseases caused by poor water quality. Filtration technology presents key challenges, such as membrane selectivity, permeability and biofouling. Nanomaterials can offer solutions to these challenges by varying the membranes' mechanical and bactericidal properties. This research uses nanodiamond particles with facile surface functionality and biocompatibility properties that are added to membranes used for filtration treatments. Scanning and transmission electron microscopy (SEM and TEM) and Fourier transform infrared spectroscopy (FTIR) were performed to study the membrane surface. FTIR spectra confirms an increase in oxygen functional groups onto the ultradispersed diamond's (UDD) surface following acid treatment. SEM images show particle deagglomeration of functionalized UDD at the membrane surface. Tensile strength tests were done to measure the UDD mechanical properties and Coliscan membrane filtration characterization was performed to determine the filter effectiveness. Polyether sulfone (PES) and polyvinylidene (PVDF) membranes expressed a change in their yield point when UDD was incorporated into the porous matrix. A significant microorganism reduction was obtained and confirmed using t-test analysis at a 95% level of confidence. UDD-embedded membranes exhibit a significant bactericidal reduction compared to commercial membranes suggesting these membranes have the potential to enhance current membrane filtration systems.

Designing a fault detection classifier framework for an industrial dynamic ultrafiltration membrane process using wavelet-based feature analysis

In recent years, due to the increase in population and the number of industrial sites, water reclaim has become more relevant. Dynamic membrane filtration systems can play an important role for water reuse. Therefore, process monitoring of dynamic membrane systems is of great importance to ensure the water quality while considering environmental and economic factors. The exploitation of on-line monitoring of dynamic membrane systems in industrial operation is challenged by intentional disturbances such as backflush and backshock (i.e. used as cleaning strategies) and unintentional input fluctuations. Consequently, process inherent behaviour is hidden within very complex sensors signals. Therefore, critical flux identification or fouling characterization for process monitoring is not straightforward, leading to suboptimal operation. The present study establishes a fault detection framework from a classification viewpoint, capable of handling industrial data that is prone to noise and disturbances, while offering an effective yet straightforward approach. The case study is a pilot-scale dynamic ultrafiltration process which has been tested previously within an industrial facility for produced water reclamation. The dataset contains 18 experiments, where three of the experiments are faulty. These experiments were implemented in an oil recovery facility located in the Orinoquía region, Colombia. A feature analysis approach based on wavelets is developed to identify the key characteristics of the installed sensors while alleviating the noise effects. The process conditions are pinpointed by feeding the extracted features into several widely used classification methods including Multilayer Perceptron Neural Network (MLPNN), Support Vector Machine (SVM), and Principal Component Analysis (PCA) based classifiers. The results indicated that the MLPNN classifier has the highest detection accuracy of 99.7% with a low percentage of false alarms. The framework developed in this study is a vital part of a membrane system digitalization strategy, which can be integrated into automated surveillance strategies for monitoring of membrane systems toward effective fault detection.

The improvement of heavy metals removal by wood membrane in drinking water treatment: Comparison with polymer membrane and associated mechanism

The application of commercial membranes is limited by the secondary pollution such as the usage of toxic chemicals for the membrane preparation and the disposal of aged membranes. Therefore, the green and environmentally friendly membranes are extremely promising for the sustainable development of membrane filtration in water treatment. In this study, the comparison of wood membrane with the pore size of tens microns (μm) and polymer membrane with the pore size of 0.45 μm was made to study the heavy metals removal in drinking water treatment by gravity-driven membrane (GDM) filtration system, and there was an improvement in the removal of Fe, Cu and Mn by wood membrane. The sponge-like structure of fouling layer for wood membrane made the retention time of heavy metals prolonged in contrast to the cobweb-like structure of polymer membrane. The carboxylic group (-COOH) content of fouling layer for wood membrane was greater than that for polymer membrane. Additionally, the population abundance of heavy metal-capturing microbes on the surface of wood membrane was higher compared with polymer membrane. The wood membrane provides a promising route to producing facile, biodegradable and sustainable membrane as a green alternative to polymer membranes in heavy metal removal from drinking water.

In Situ Visualization of Membrane Fouling Evolution during Ultrafiltration Using Label-Free Hyperspectral Light Sheet Fluorescence Imaging.

Profound understanding of fouling behaviors and underlying mechanisms is fundamentally important for fouling control in membrane-based environmental applications. Therefore, it entails novel noninvasive analytical approaches for in situ characterizing the formation and development of membrane fouling processes. This work presents a characterization approach based on hyperspectral light sheet fluorescence microscopy (HSPEC-LSFM), which is capable of discriminating various foulants and providing their 2-dimensional/3-dimensional spatial distributions on/in membranes in a label-free manner. A fast, highly sensitive and noninvasive imaging platform was established by developing a HSPEC-LSFM system and further extending it to incorporate a laboratory-scale pressure-driven membrane filtration system. Hyperspectral data sets with a spectral resolution of ∼1.1 nm and spatial resolution of ∼3 μm as well as the temporal resolution of ∼8 s/plane were obtained, and the fouling formation and development process of foulants onto membrane surfaces, within the pores and on the pore walls were clearly observed during the ultrafiltration of protein and humic substances solutions. Pore blocking/constriction at short times while cake growth/concentration polarization at longer times was found to have coupled effects for the flux decline in these filtration tests, and yet the contribution of each effect as well as the transition of the governing mechanisms was found distinct. These results demonstrate in situ label-free characterization of membrane fouling evolution with the recognition of foulant species during filtration and provide new insights into membrane fouling. This work offers a powerful tool to investigate dynamic processes for a wide range of membrane-based explorations.

Sharing of Moonlighting Proteins Mediates the Symbiotic Relationship among Intestinal Commensals.

The human gastrointestinal tract is inhabited by trillions of symbiotic bacteria that form a complex ecological community and influence human physiology. Symbiotic nutrient sharing and nutrient competition are the most studied relationships in gut commensals, whereas the interactions underlying homeostasis and community maintenance are not fully understood. Here, we provide insights into a new symbiotic relationship wherein the sharing of secreted cytoplasmic proteins, called "moonlighting proteins," between two heterologous bacterial strains (Bifidobacterium longum and Bacteroides thetaiotaomicron) was observed to affect the adhesion of bacteria to mucins. B. longum and B. thetaiotaomicron were cocultured using a membrane-filter system, and in this system the cocultured B. thetaiotaomicron cells showed greater adhesion to mucins compared to that shown by monoculture cells. Proteomic analysis showed the presence of 13 B. longum-derived cytoplasmic proteins on the surface of B. thetaiotaomicron. Moreover, incubation of B. thetaiotaomicron with the recombinant proteins GroEL and elongation factor Tu (EF-Tu)-two well-known mucin-adhesive moonlighting proteins of B. longum-led to an increase in the adhesion of B. thetaiotaomicron to mucins, a result attributed to the localization of these proteins on the B. thetaiotaomicron cell surface. Furthermore, the recombinant EF-Tu and GroEL proteins were observed to bind to the cell surface of several other bacterial species; however, the binding was species dependent. The present findings indicate a symbiotic relationship mediated by the sharing of moonlighting proteins among specific strains of B. longum and B. thetaiotaomicron. IMPORTANCE The adhesion of intestinal bacteria to the mucus layer is an important colonization strategy in the gut environment. Generally, the bacterial adhesion process is a characteristic feature of the individual cell surface-associated adhesion factors secreted by a particular bacterium. In this study, coculture experiments between Bifidobacterium and Bacteroides show that the secreted moonlighting proteins adhere to the cell surface of coexisting bacteria and alter the adhesiveness of the bacteria to mucins. This finding indicates that the moonlighting proteins act as adhesion factors for not only homologous strains but also for coexisting heterologous strains. The presence of a coexisting bacterium in the environment can significantly alter the mucin-adhesive properties of another bacterium. The findings from this study contribute to a better understanding of the colonization properties of gut bacteria through the discovery of a new symbiotic relationship between them.

Modeling of Organic Fouling in an Ultrafiltration Cell Using Different Three-Dimensional Printed Turbulence Promoters.

Designing turbulence promoters with optimal geometry and using them for ultrafiltration systems has been a key challenge in mitigating membrane fouling. In this study, six different turbulence promoters were created using three-dimensional printing technology and applied in dead-end ultrafiltration. Three-dimensional-printed (3DP) turbulence promoter configurations were integrated into a classical batch ultrafiltration cell. The effects of these configurations and the stirring speeds on the permeate filtration flux, organic rejections, and membrane resistances were investigated. The fouling control efficiency of the 3DP promoters was evaluated using two polyethersulfone membranes in a stirred ultrafiltration cell with model dairy wastewater. The Hermia and resistance-in-series models were studied to further investigate the membrane fouling mechanism. Of the Hermia models, the cake layer model best described the fouling in this membrane filtration system. It can be concluded that the 3DP turbulence promoters, combined with intense mechanical stirring, show great promise in terms of permeate flux enhancement and membrane fouling mitigation. Using a well-designed 3DP turbulence promoter improves the hydrodynamic flow conditions on the surface of the stirred membrane separation cells based on computational fluid dynamics modeling. Therefore, the factors effecting the fabrication of 3DP turbulence promoters are important, and further research should be devoted to revealing them.