Effects of cations on biofilms in gravity-driven membrane system: Filtration performance and mechanism investigation.

The gravity-driven membrane (GDM) system is desirable for energy-efficient water treatment. However, little is known about the influence of cations on biofilm properties and GDM performance. In this study, typical cations (Ca2+ and Na+) were used to reveal the combined fouling behavior and mechanisms. Results showed that Ca2+ improved the stable flux and pollutant removal efficiency, while Na+ adversely affected the flux. Compared with GDM control, the concentration of pollutants was lower in Ca-GDM, as indicated by the low biomass, proteins, and polysaccharides. A heterogeneous and loose biofilm was observed in the Ca-GDM system, with roughness and porosity increasing by 43.06 % and 32.60 %, respectively. However, Na+ induced a homogeneous and dense biofilm, with porosity and roughness respectively reduced by 17.48 % and 22.04 %. The richness of bacterial communities increased in Ca-GDM systems, while it decreased in Na-GDM systems. High adenosine triphosphate (ATP) concentration in Ca-GDM system was consistent with the abundant bacteria and their high biological activity, which was helpful for the efficient removal of pollutants. The abundance of Apicomplexa, Platyhelminthes, Annelida and Nematoda increased after adding Ca2+, which was related to the formation of loose biofilms. Computational simulations indicated that the free volumes of the biofilms in Ca-GDM and Na-GDM were 13.7 and 13.2 nm3, respectively. The addition of cations changed intermolecular forces, Ca2+ induced bridging effects led to large and loose floc particles, while the significant dehydration of hydrated molecules in the Na-GDM caused obvious aggregation. Overall, microbiological characteristics and contaminant molecular interactions were the main reasons for differences in GDM systems.

Microplastics affect membrane biofouling and microbial communities during gravity-driven membrane filtration of primary wastewater.

Recently, gravity-driven membrane (GDM) filtration has been adopted as an alternative solution for decentralized wastewater treatment due to easy installation and maintenance, reduced energy and operation cost, and low global warming impact. This study investigated the influence of microplastic size (0.5-0.8 µm and 40-48 µm) and amount (0.1 and 0.2 g/L) on the membrane performance and microbial community in GDM systems for primary municipal wastewater treatment. The results showed that dosing microplastics in the GDM systems led to 9-54% lower permeate flux than that in the control. This was attributed to more cake formation (up to 6.4-fold) with more deposition of extracellular polymeric substances (EPS, up to 1.5-fold) and divalent cations (up to 2.1-fold) in the presence of microplastics, especially with increasing microplastic amount or size. However, the dosed microplastics promoted formation of heterogeneous cake layers with more porous nature, possibly because microplastics created void space in the cake and also tended to bind with divalent cations to reduce EPS-divalent cations interactions. In the biofilm of the GDM systems, the presence of microplastics could lower the number of total species, but it greatly enhanced the abundance of certain dominant prokaryotes (Phenylobacterium haematophilum, Planctomycetota bacterium, and Flavobacteriales bacterium), eukaryotes (Stylonychia lemnae, Halteria grandinella, and Paramicrosporidium saccamoebae), and virus (phylum Nucleocytoviricota), as well as amino acid and lipid metabolic functions. Especially, the small-size microplastics at a higher dosed amount led to more variations of microbial community structure and microbial metabolic functions.

High yield sterile filtration process for highly concentrated lentiviral vectors.

The development and manufacture of biopharmaceuticals are subject to strict regulations that specify the required minimum quality of the products. A key measure to meet these quality requirements is the integration of a sterile filtration step into the commercial manufacturing process. Whereas common procedures for most biologics exist, this is challenging for lentiviral vector (LVV) production for ex vivo gene therapy. LVVs nominal size is more than half the pore size (0.2 µm) of filters used for sterile filtration. Hence, highly concentrated virus solutions are prone to filter clogging if aggregation of viruses occurs or impurities attach to the viruses. Several filters were screened aiming to identify those which allow filtering highly concentrated stocks of LVVs of up to 1E + 9 transducing units mL-1 , which corresponds to 4.5E + 12 particles mL-1 . In addition, the effect of endonuclease treatment upstream of the purification process on filter performance was studied. In summary, three suitable filters were identified in a small-scale study (<15 mL) with virus yields >80% and the process was successfully scaled-up to a final scale of 100 mL LVV stock solution.

Filtration of a multi-serotype glycoconjugate vaccine drug product through sterilizing grade 0.2/0.22 µm pore size filters.

Glycoconjugate vaccines containing multiple serotypes of a bacterial capsular polysaccharide can provide strong immune protection against pathogenic infections. Sterile filtration is an important component of the fill and finish operations in the preparation of these vaccines, with the capacity of the sterile filter limited by membrane fouling. The objective of this study was to examine the performance of a range of commercial 0.2/0.22 µm nominal pore size sterilizing grade filters with both single-layer and dual-layer structures during filtration of a glycoconjugate vaccine drug product consisting of four polysaccharide serotypes. The highly asymmetric Millipore Express showed much higher capacity than the more homogeneous filters, with the support structure of the Express acting as a prefilter that was able to remove foulants thereby protecting the small pores in the size-selective skin layer. This behavior was confirmed by performing experiments with different batch prefilters and by examining the location of foulant deposition within the sterile filters using confocal microscopy. These results provide important insights into the factors controlling fouling by these multiserotype vaccines as well as a framework for increasing the capacity of the sterile filter.

Contributions of Chinese hamster ovary cell derived extracellular vesicles and other cellular materials to hollow fiber filter fouling during perfusion manufacturing of monoclonal antibodies.

Hollow fiber filter fouling is a common issue plaguing perfusion production process for biologics therapeutics, but the nature of filter foulant has been elusive. Here we studied cell culture materials especially Chinese hamster ovary (CHO) cell-derived extracellular vesicles in perfusion process to determine their role in filter fouling. We found that the decrease of CHO-derived small extracellular vesicles (sEVs) with 50-200 nm in diameter in perfusion permeates always preceded the increase in transmembrane pressure (TMP) and subsequent decrease in product sieving, suggesting that sEVs might have been retained inside filters and contributed to filter fouling. Using scanning electron microscopy and helium ion microscopy, we found sEV-like structures in pores and on foulant patches of hollow fiber tangential flow filtration filter (HF-TFF) membranes. We also observed that the Day 28 TMP of perfusion culture correlated positively with the percentage of foulant patch areas. In addition, energy dispersive X-ray spectroscopy-based elemental mapping microscopy and spectroscopy analysis suggests that foulant patches had enriched cellular materials but not antifoam. Fluorescent staining results further indicate that these cellular materials could be DNA, proteins, and even adherent CHO cells. Lastly, in a small-scale HF-TFF model, addition of CHO-specific sEVs in CHO culture simulated filter fouling behaviors in a concentration-dependent manner. Based on these results, we proposed a mechanism of HF-TFF fouling, in which filter pore constriction by CHO sEVs is followed by cake formation of cellular materials on filter membrane.

Removal of strontium by nanofiltration: Role of complexation and speciation of strontium with organic matter.

Strontium (Sr) removal from water is required because excessive naturally occurring Sr exposure is hazardous to human health. Climate and seasonal changes cause water quality variations, in particular quality and quantity of organic matter (OM) and pH, and such variations affect Sr removal by nanofiltration (NF). The mechanisms for such variations are not clear and thus OM complexation and speciation require attention. Sr removal by NF was investigated with emphasis on the role of OM (type and concentration) and pH (2-12) on possible removal mechanisms, specifically size and/or charge exclusion as well as solute-solute interactions. The filtration results show that the addition of various OM (10 types) and an increase of OM concentration (2-100 mgC.L-1) increased Sr removal by 10-15%. The Sr-OM interaction was enhanced with increasing OM concentration, implying enhanced size exclusion via Sr-OM interaction as the main mechanism. Such interactions were quantified by asymmetric flow field-flow fractionation (FFFF) coupled with an inductively coupled plasma mass spectrometer (ICP-MS). Both extremely low and high pH increased Sr removal due to the enhanced charge exclusion and Sr-OM interactions. This work elucidated and verified the mechanism of OM and pH on Sr removal by NF membranes.

Inoculation with adapted bacterial communities promotes development of full scale slow sand filters for drinking water production.

Gravity-driven filtration through slow sand filters (SSFs) is one of the oldest methods for producing drinking water. As water passes through a sand bed, undesired microorganisms and chemicals are removed by interactions with SSF biofilm and its resident microbes. Despite their importance, the processes through which these microbial communities form are largely unknown, as are the factors affecting these processes. In this study, two SSFs constructed using different sand sources were compared to an established filter and observed throughout their maturation process. One SSF was inoculated through addition of sand scraped from established filters, while the other was not inoculated. The operational and developing microbial communities of SSFs, as well as their influents and effluents, were studied by sequencing of 16S ribosomal rRNA genes. A functional microbial community resembling that of the established SSF was achieved in the inoculated SSF, but not in the non-inoculated SSF. Notably, the non-inoculated SSF had significantly (p < 0.01) higher abundances of classes Armatimonadia, Elusimicrobia, Fimbriimonadia, OM190 (phylum Planctomycetota), Parcubacteria, Vampirivibrionia and Verrucomicrobiae. Conversely, it had lower abundances of classes Anaerolineae, Bacilli, bacteriap25 (phylum Myxococcota), Blastocatellia, Entotheonellia, Gemmatimonadetes, lineage 11b (phylum Elusimicrobiota), Nitrospiria, Phycisphaerae, subgroup 22 (phylum Acidobacteriota) and subgroup 11 (phylum Acidobacteriota). Poor performance of neutral models showed that the assembly and dispersal of SSF microbial communities was mainly driven by selection. The temporal turnover of microbial species, as estimated through the scaling exponent of the species-time relationship, was twice as high in the non-inoculated filter (0.946 ± 0.164) compared to the inoculated filter (0.422 ± 0.0431). This study shows that the addition of an inoculum changed the assembly processes within SSFs. Specifically, the rate at which new microorganisms were observed in the biofilm was reduced. The reduced temporal turnover may be driven by inoculating taxa inhibiting growth, potentially via secondary metabolite production. This in turn would allow the inoculation community to persist and contribute to SSF function.

Effects of running time on biological activated carbon filters: water purification performance and microbial community evolution.

Ozone-biologically activated carbon (BAC) filtration is an advanced treatment process that can be applied to remove recalcitrant organic micro-pollutants in drinking water treatment plants (DWTPs). In this study, we continuously monitored a new and an old BAC filter in a DWTP for 1 year to compare their water purification performance and microbial community evolution. The results revealed that, compared with the new filter, the use of the old BAC filter facilitated a slightly lower rate of dissolved organic carbon (DOC) removal. In the case of the new BAC filter, we recorded general increases in the biomass and microbial diversity of the biofilm with a prolongation of operating time, with the biomass stabilizing after 7 months. For both new and old BAC filters, Proteobacteria and Acidobacteria were the dominant bacterial phyla. At the genus level, the microbial community gradually shifted over the course of operation from a predominance of Herminiimonas and Hydrogenophaga to one predominated by Bradyrhizbium, Bryobacter, Hyphomicrobium, and Pedomicrobium, with Bradyrhizobium being established as the most abundant genus in the old BAC filter. Regarding spatial distribution, we detected reductions in the biomass and number of operational taxonomic units with increasing biofilm depth, whereas there was a corresponding increase in microbial diversity. However, compared with the effects of time, the influence of depth on the composition of the biofilm microbial community was considerably smaller. Furthermore, co-occurrence network analysis revealed that the microbial community network of the new filter after 11 months of operation was the most tightly connected, although its modular coefficient was the lowest of those assessed. We speculate that the positive and negative interactions within the network may be attributable to symbiotic or competitive relationships among species. Moreover, there may have been a significant negative interaction between SWB02 and Acidovorax, plausibly associated with a competition for substrates.

Chemical structure of hydrocarbons significantly affects removal performance and microbial responses in gas biotrickling filters.

The control of emissions of short-chain hydrocarbons with different structures is critical for the petrochemical industry. Herein, three two-carbon-containing (C2) hydrocarbons, ethane, ethylene, and acetylene, were chosen as pollutants to study the effects of chemical structure of hydrocarbons on removal performance and microbial responses in biotrickling filters. Results showed that the removal efficiency (RE) of C2 hydrocarbons followed the sequence of acetylene > ethane > ethylene. When the inlet loading rate was 30 g/(m3·h) and the empty bed residence time was 60 s, the RE of ethane, ethylene, and acetylene was 57 ± 4.0 %, 49 ± 1.0 %, and 84 ± 2.7 %, respectively. The high water solubility resulted in the high removal of C2 hydrocarbons, while a low surface tension enhanced the removal of C2 hydrocarbons. Additionally, the microbial community, enzyme activity, and extracellular properties of microorganisms also contributed to the difference in C2 hydrocarbon removal. These results could be referred for the effective control of light hydrocarbon emissions.

Biofilm rigidity, mechanics and composition in seawater desalination pretreatment employing ultrafiltration and microfiltration membranes.

The choice of appropriate biofilm control strategies in membrane systems for seawater desalination pretreatment relies on understanding the properties of the biofilm formed on the membrane. This study reveals how the biofilm composition, including both organic and inorganic, influenced the biofilm behavior under mechanical loading. The investigation was conducted on two Gravity-Driven Membrane reactors employing Microfiltration (MF) and Ultrafiltration (UF) membrane for the pretreatment of raw seawater. After a stabilization period of 20 days (Phase I), a biofilm behavior test was introduced (Phase II) to evaluate (i) biofilm deformation during the absence of permeation (i.e., relaxation) and (ii) biofilm resistance to detachment forces (i.e., air scouring). The in-situ monitoring investigation using Optical Coherence Tomography (OCT) revealed that the biofilms developed on MF and UF membrane presented a rigid structure in absence of filtration forces, limiting the application of relaxation and biofilm expansion necessary for cleaning. Moreover, under shear stress conditions, a higher reduction in biofilm thickness was observed for MF (-60%, from 84 to 34 µm) compared to UF (-30%, from 64 to 45 µm), leading to an increase of permeate flux (+60%, from 9.1 to 14.9 L/m2/h and +20 % from 7.8 to 9.5 L/m2/h, respectively). The rheometric analysis indicated that the biofilm developed on MF membrane had weaker mechanical strength, displaying lower storage modulus (-50 %) and lower loss modulus (-55 %) compared to UF. These differences in mechanical properties were linked to the lower concentration of polyvalent ions and the distribution of organic foulants (i.e., BB, LMW-N) found in the biofilm on the MF membrane. Moreover, in the presence of air scouring led to a slight difference in microbial community between UF and MF. Our findings provide valuable insight for future investigations aimed at engineer biofilm composition to optimize biofilm control strategies in membrane systems for seawater desalination pretreatment.

Removal of organic micropollutants in biologically active filters: A systematic quantitative review of key influencing factors.

Biofiltration utilizes natural mechanisms including biodegradation and biotransformation along with other physical processes for the removal of organic micropollutants (OMPs) such as pharmaceuticals, personal care products, pesticides and industrial compounds found in (waste)water. In this systematic review, a total of 120 biofiltration studies from 25 countries were analyzed, considering various biofilter configurations, source water types, biofilter media and scales of operation. The study also provides a bibliometric analysis to identify the emerging research trends in the field. The results show that granular activated carbon (GAC) either alone or in combination with another biofiltration media can remove a broad range of OMPs efficiently. The impact of pre-oxidation on biofilter performance was investigated, revealing that pre-oxidation significantly improved OMP removal and reduced the empty bed contact time (EBCT) needed to achieve a consistently high OMP. Biofiltration with pre-oxidation had median removals ranging between 65% and >90% for various OMPs at 10-45 min EBCT with data variability drastically reducing beyond 20 min EBCT. Biofiltration without pre-oxidation had lower median removals with greater variability. The results demonstrate that pre-oxidation greatly enhances the removal of adsorptive and poorly biodegradable OMPs, while its impact on other OMPs varies. Only 19% of studies we reviewed included toxicity testing of treated effluent, and even fewer measured transformation products. Several studies have previously reported an increase in effluent toxicity because of oxidation, although it was successfully abated by subsequent biofiltration in most cases. Therefore, the efficacy of biofiltration treatment should be assessed by integrating toxicity testing into the assessment of overall removal.

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles.

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Revolutionizing Airborne Virus Defense: Electromagnetic MXene-Coated Air Filtration for Superior Aerosol Viral Removal.

The COVID-19 pandemic sparked public health concerns about the transmission of airborne viruses. Current methods mainly capture pathogens without inactivation, leading to potential secondary pollution. Herein, we evaluated the inactivation performance of a model viral species (MS2) in simulated bioaerosol by an electromagnetically enhanced air filtration system under a 300 kHz electromagnetic induction field. A nonwoven fabric filter was coated with a 2D catalyst, MXene (Ti3C2Tx), at a coating density of 4.56 mg·cm-2 to absorb electromagnetic irradiation and produce local heating and electromagnetic field for microbial inactivation. The results showed that the MXene-coated air filter significantly enhanced the viral removal efficiency by achieving a log removal of 3.4 ± 0.15 under an electromagnetic power density of 369 W·cm-2. By contrast, the pristine filter without catalyst coating only garnered a log removal of 0.3 ± 0.04. Though the primary antimicrobial mechanism is the local heating as indicated by the elevated surface temperature of 72.2 ± 4 °C under the electromagnetic field, additional nonthermal effects (e.g., dielectrophoresis) on enhanced viral capture during electromagnetically enhanced filtration were investigated by COMSOL simulation to delineate the potential transmission trajectories of bioaerosol. The results provide unique insights into the mechanisms of pathogen control and thus promote alternative solutions for preventing the transmission of airborne pathogens.

Addition of (bio)surfactants in the biofiltration of hydrophobic volatile organic compounds in air.

The removal of volatile organic compounds (VOCs) in air is of utmost importance to safeguard both environmental quality and human well-being. However, the low aqueous solubility of hydrophobic VOCs results in poor removal in waste gas biofilters (BFs). In this study, we evaluated the addition of (bio)surfactants in three BFs (BF1 and BF2 mixture of compost and wood chips (C + WC), and BF3 filled with expanded perlite) to enhance the removal of cyclohexane and hexane from a polluted gas stream. Experiments were carried out to select two (bio)surfactants (i.e., Tween 80 and saponin) out of five (sodium dodecyl sulfate (SDS), Tween 80, surfactin, rhamnolipid and saponin) from a physical-chemical (i.e., decreasing VOC gas-liquid partitioning) and biological (i.e., the ability of the microbial consortium to grow on the (bio)surfactants) point of view. The results show that adding Tween 80 at 1 critical micelle concentration (CMC) had a slight positive effect on the removal of both VOCs, in BF1 (e.g., 7.0 ± 0.6 g cyclohexane m-3 h-1, 85 ± 2% at 163 s; compared to 6.7 ± 0.4 g cyclohexane m-3 h-1, 76 ± 2% at 163 s and 0 CMC) and BF2 (e.g., 4.3 ± 0.4 g hexane m-3 h-1, 27 ± 2% at 82 s; compared to 3.1 ± 0.7 g hexane m-3 h-1, 16 ± 4% at 82 s and 0 CMC), but a negative effect in BF3 at either 1, 3 and 9 CMC (e.g., 2.4 ± 0.4 g hexane m-3 h-1, 30 ± 4% at 163 s and 1 CMC; compared to 4.6 ± 1.0 g hexane m-3 h-1, 43 ± 8% at 163 s and 0 CMC). In contrast, the performance of all BFs improved with the addition of saponin, particularly at 3 CMC. Notably, in BF3, the elimination capacity (EC) and removal efficiency (RE) doubled for both VOCs (i.e., 9.1 ± 0.6 g cyclohexane m-3 h-1, 49 ± 3%; 4.3 ± 0.3 g hexane m-3 h-1, 25 ± 3%) compared to no biosurfactant addition (i.e., 4.5 ± 0.4 g cyclohexane m-3 h-1, 23 ± 3%; hexane 2.2 ± 0.5 g m-3 h-1, 10 ± 2%) at 82 s. Moreover, the addition of the (bio)surfactants led to a shift in the microbial consortia, with a different response in BF1-BF2 compared to BF3. This study evaluates for the first time the use of saponin in BFs, it demonstrates that cyclohexane and hexane RE can be improved by (bio)surfactant addition, and it provides recommendations for future studies in this field.

Evaluation and risk communication of the effects of alcohol exposure on disposable procedure masks and portable air purifiers in hospital environments.

Electret technology was widely used to prevent the airborne transmission of bioaerosols during the COVID-19 pandemic and improve the filtration efficiency of masks and high-efficiency particulate air (HEPA) filters. As alcohol disinfectants are widely used in medical and welfare institutions, concerns about alcohol exposure inactivating electret exist. However, comprehensive alcohol exposure tests have not been conducted on masks and HEPA filters distributed in Japan. Twenty-five types of masks and five types of HEPA filters were subjected to a discharging process according to ISO 16890 to quantitatively elucidate the resistance to alcohol exposure. Measurements of changes in filtration efficiency and pressure drop before and after discharge show that 17 masks (68%) and four HEPA filters (80%) exhibited a significant decrease in filtration efficiency, confirming their vulnerability to alcohol. In addition, a survey (n = 500 Japanese adults, including 30 healthcare professionals) revealed that ∼90% of the general public were unaware that alcohol exposure could degrade masks and air purifiers. Furthermore, 36% of the surveyed healthcare professionals had sprayed alcohol directly onto their masks. The effectiveness of user warnings through product labels and instructions was investigated from the perspective of ensuring the safety of patients and healthcare professionals. Results revealed that the best approach was to describe the extent and duration of the adverse effects caused by disregarding precautions. Increase in awareness of healthcare professionals and general public by authorities and manufacturers through guidelines and warning labels would reduce the risk of inhaling bioaerosols caused by unintentional electret inactivation.

Evaluation of commercial nanofiltration and reverse osmosis membrane filtration to remove per-and polyfluoroalkyl substances (PFAS): Effects of transmembrane pressures and water matrices.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are now widely found in aquatic ecosystems, including sources of drinking water and portable water, due to their increasing prevalence. Among different PFAS treatment or separation technologies, nanofiltration (NF) and reverse osmosis (RO) both yield high rejection efficiencies (>95%) of diverse PFAS in water; however, both technologies are affected by many intrinsic and extrinsic factors. This study evaluated the rejection of PFAS of different carbon chain length (e.g., PFOA and PFBA) by two commercial RO and NF membranes under different operational conditions (e.g., applied pressure and initial PFAS concentration) and feed solution matrixes, such as pH (4-10), salinity (0- to 1000-mM NaCl), and organic matters (0-10 mM). We further performed principal component analysis (PCA) to demonstrate the interrelationships of molecular weight (213-499 g·mol-1 ), membrane characteristics (RO or NF), feed water matrices, and operational conditions on PFAS rejection. Our results confirmed that size exclusion is a primary mechanism of PFAS rejection by RO and NF, as well as the fact that electrostatic interactions are important when PFAS molecules have sizes less than the NF membrane pores. PRACTITIONER POINTS: Two commercial RO and NF membranes were both evaluated to remove 10 different PFAS. High transmembrane pressures facilitated permeate recovery and PFAS rejection by RO. Electrostatic repulsion and pore size exclusion are dominant rejection mechanisms for PFAS removal. pH, ionic strength, and organic matters affected PFAS rejection. Mechanisms of PFAS rejection with RO/NF membranes were explained by PCA analysis.

Highly Efficient Fabrication of Biomimetic Nanoscaled Tendrils for High-Performance PM0.3 Air Filters.

Particulate matter pollution has become a serious public health issue, especially with the outbreak of new infectious diseases. However, most existing air filtration materials face challenges such as being too bulky, having high resistance, and a trade-off between filtration efficiency and air permeability. Here, a unique electro-blown spinning technique is used to prepare an air filter made of biomimetic nanoscaled tendril nonwovens (Nano-TN). The introduction of an airflow field significantly increases the whipping frequency and the strain mismatch of composite jets, achieving large-scale and highly efficient preparation of Nano-TN. The resultant Nano-TN has an ultrahigh porosity (97%) and a small pore size (2.9 µm). At the same filtration level, its air resistance is 37% lower than that of traditional straight nanofibrous nonwovens and has a higher dust-holding capacity. Moreover, compared with traditional three-dimensional air filters, the Nano-TN filter is thinner, offering tremendous application prospects in various environmental purification and personal protection fields.

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles.

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl3 and AlCl3 coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl3 and 1 mg/L for AlCl3. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Size-based analysis of virus removal filter fouling using fractionated protein aggregates.

Fouling by protein aggregates reduces virus removal filter performance. In the present study, we investigated the effects of different-sized protein aggregates on fouling and aggregate retention in order to better understand the fouling mechanisms. Human immunoglobulin G was denatured by heating to produce aggregates of various sizes and then fractionated by size exclusion chromatography into different-sized aggregates with a narrow size distribution. The fractionated aggregates were filtered on Planova 20N, a virus removal filter known for its stable filtration capability. Analysis of flux behavior demonstrated different flux decrease patterns for different-sized aggregates. Observation of aggregate retention by staining revealed that larger aggregates were captured closer to the inner surface of the membrane while smaller aggregates penetrated farther into the membrane. These findings demonstrate that Planova 20N has a gradient structure with decreasing pore size from the inner to the outer surface of the membrane. This structure minimizes fouling and enables stable filtration by protecting the smaller pores located closer to the outer surface from clogging by large aggregates. Applying the predominant clogging models to the present filtrations revealed that clogging behavior transitioned from complete blocking to cake filtration as filtration progressed. In this combination model, after a certain number of pores are blocked by complete blocking, newly arrived aggregates begin to accumulate on previously captured aggregates, generating cake between capture layers within the membrane. Application of the approaches described here will facilitate elucidation of membrane fouling and virus removal mechanisms.

Optimizing backwash control using data on seasonal changes in the invertebrate community of granular activated carbon filters.

Problems associated with the colonization and leakage of invertebrates in the granular activated carbon (GAC) filters of waterworks have received increased attention in recent years. To study the effect of environmental factors and water quality on invertebrate abundances, and the backwash control for minimizing invertebrate abundance. A survey of the invertebrate community of GAC filters was carried out monthly from March 2021 to May 2022. A pilot-scale GAC system established in the laboratory alongside a lake, with a volume of 35.3 L. 45 invertebrate species were detected, and 40 of these were rotifers. Significant variation in abundance was observed among seasons before and after GAC filtration, the average invertebrate abundance in the inlet water was 11.1 times that in the filtrate. The GAC filter contained invertebrates that might be responsible for the large number of organisms in the filtrate. Invertebrate abundance in the GAC filter decreased gradually with the carbon layer depth, which the mean invertebrate abundances were 6,926, 5,232, and 3818 ind./kg in the top layer (TL), middle layer (ML), and bottom layer (BL), respectively. Invertebrate abundance was correlated with water temperature and varied seasonally. Among eight water quality parameters, chlorophyll a (Chla) and the total plate count (TPC) were most significantly correlated with invertebrate abundance. According to the statistical modeling and the optimization process of response surface methodology (RSM). The predicted optimal values were a flow rate of 6.36 L/h, a backwash cycle of 3.26 d, and a backwash intensity of 14.97 L/(m2·s) for a minimum invertebrate abundance of 3013 ind./kg in the GAC filter. To maintain invertebrate abundance within an acceptable range, some of these measures might need to be modified depending on the actual conditions.