Membrane Biofouling Research Articles

Analysis of Tubular NF Plants in Scotland Indicates That Summer Temperatures and Redox-Sensitive Elements Are Correlated with Membrane Biofouling and Shortened Useful Life

Analysis of Tubular NF Plants in Scotland Indicates That Summer Temperatures and Redox-Sensitive Elements Are Correlated with Membrane Biofouling and Shortened Useful Life

Engineering dual-reinforced antibacterial and anti-fouling ultrafiltration membrane by in-situ synthesising super-dispersion and high-activity silver nanoparticles (AgNPs)

Membrane fouling, especially biofouling, would result in frequent cleaning and shorten membrane lifespan. Fabricating Ag nanoparticle (AgNP)-modified ultrafiltration (UF) membranes provided an innovative solution for in-situ membrane biofouling control. Inspired by the tongue’s taste generation mechanism, this study adopted sodium citrate and AgNO3 to in-situ synthesize AgNP-modified UF (i-Ag-UF) membrane with the characteristics of ‘super-dispersion and high-activity’ AgNPs, enhancing the antimicrobial and anti-fouling properties. Compared to the control, a perpendicular and rich macroporous finger-type structure was engineered in the i-Ag-UF membrane, which contributed to a 59 % permeability improvement (421.7 L m-2h−1 bar−1), thereby improving filtration efficiency and reducing operational costs. This enhancement was attributed to the in-situ synthesis of small-sized, super-dispersed AgNPs, improving compatibility and stability with membrane matrix, and enhancing resistance to interlayer shear stress during phase inversion. Furthermore, the i-Ag-UF membrane surface exhibited the highest hydrophilicity and surface polarity, which formed a hydration layer and increased pollutant repulsion, thereby greatly enhancing its anti-fouling performance and achieving a higher flux recovery rate of 98.64 %. Such enhancement could significantly improve the economic benefits and sustainability of the UF process. The i-Ag-UF membrane demonstrated exceptionally high antibacterial efficiency (>99.99 %), attributed to the widely dispersed, high-activity AgNPs with numerous exposure points. In addition, the i-Ag-UF membrane, with only 2.5 wt% Ag release after 50 days owing to the entanglement between AgNPs and polymer chains. These findings provide new insights into the fabrication of highly antibacterial and anti-fouling dual-enhanced UF membranes.

Innovative temperature-responsive membrane with an elastic interface for biofouling mitigation in industrial circulating cooling water treatment

To address the issues of scaling caused by heat and water evaporation in regard to circulating cooling water (CCW), TFC membrane filtration systems have been increasingly considered for terminal treatment processes because of their excellent separation performance. However, membrane biofouling phenomenon significantly hinders the widespread utilization of TFC membranes. In this study, to harness the thermal phenomenon of CCW and establish a stable and durable multifunctional antibiofouling layer, temperature-responsive Pnipam and the spectral antibacterial agent Ag were organically incorporated into commercially available TFC membranes. Biological experimental findings demonstrated that above the lower critical solution temperature (LCST), the contraction of Pnipam molecular chains facilitated the inactivation of bacteria by the antibacterial agent, resulting in an impressive sterilization efficiency of up to 99 %. XDLVO analysis revealed that below the LCST, the establishment of a hydration layer on the functional interface resulted in the creation of elevated energy barriers, effectively impeding bacterial adhesion to the membrane surface. Consequently, a high bacterial release rate of 98.4 % was achieved on the low-temperature surface. The alterations in the functional membrane surface conformation induced by temperature variations further amplified the separation between the pollutants and the membrane, creating an enhanced "elastic interface." This efficient and straightforward cleaning procedure mitigated the formation of irreversible fouling without compromising the integrity of the membrane surface. This study presents a deliberately engineered thermoresponsive antibiofouling membrane interface to address the issue of membrane fouling in membrane-based CCW treatment systems while shedding new light on the mechanisms of "inactivation" and "defense."

Unveiling the impacts of salts on halotolerant bacteria during filtration: A new perspective on membrane biofouling formation in MBR treating high-saline organic wastewater

In recent decades, membrane bioreactor (MBR) has been prevalently employed to treat high-saline organic wastewater, where the halotolerant microorganisms should be intensively utilized. However, limited works were devoted to investigating the biofouling characteristics from the perspective of the relationship between halotolerant bacteria and salts. This work filled the knowledge gap by exploring the biofouling formation mechanisms affected by high salinity. The results showed that the amount of negative charge on halotolerant bacteria surface was significantly reduced by high content of NaCl, probably leading to the obvious cell agglomeration. Despite the normal proliferation, the halotolerant bacteria still produced substantial EPS triggered by high salinity. Compared with the case of control without salt addition, the enhanced biofouling development was observed under high-saline conditions, with the fouling mechanism dramatically transformed from cake filtration to intermediate blocking. It was inferred that the halotolerant bacteria initially adhered on membrane created an extra filter layer, which contributed to the subsequent NaCl retention, resulting in the simultaneous occurrences of pore blockage and cake layer formation because of NaCl deposition both on membrane pores as well as on biofilm layer. Under high-saline environment, remarkable salt crystallization occurred on the biofilm layer, with more protein secreted by the attached halotolerant bacteria. Consequently, the potential mechanisms for the enhanced biofouling formation influenced by high salinity were proposed, which should provide new insights and enlightenments on fouling control strategies for MBR operation when treating high-saline organic wastewater.

Long-term operation of a full-scale membrane bioreactor for industrial wastewater treatment using polyvinyl fluoride hollow fiber membranes: A systematic evaluation during 18-year operation

A membrane bioreactor (MBR) is a robust, high-performance technology for wastewater treatment that has been commercialized and disseminated worldwide since 1990. Despite broad implementation of this technology in the wastewater sector, ultralong operation beyond the membrane lifetime has rarely been reported. Therefore, the objectives of this study were to investigate (1) the effectiveness of a manually-operated feedback strategy to prevent membrane biofouling by dosing with sodium hypochlorite and oxalic acid and (2) the organic carbon removal of industrial wastewater treated by a full-scale MBR system in a chemical plant. The manually-operated feedback strategy consisted of monitoring the transmembrane pressure (TMP) by a test module in a bench-scale MBR to detect an inflection point, that is, the point (15 kPa) at which the TMP switched from growing gradually to exponentially in time. Biocake formation became noticeable at the inflection point, suggesting the TMP at which the membrane should be chemically washed to prevent severe biofouling. A full-scale MBR system was installed with a polyvinylidene fluoride (PVDF) membrane for organic carbon removal. The membrane was washed with 3000 mg/L of sodium hypochlorite and 1 wt% oxalic acid when the TMP reached 15 kPa during operation. The MBR was successfully operated for over 18 years without the PVDF membrane being damaged or compromised by biofouling. Characterization of the foulants on the membrane surface revealed that membrane washing removed inorganic (calcium and iron) and organic (acid amides and polysaccharides) foulants, plausibly by the action of oxalic acid and sodium hypochlorite, respectively. Installing a robust PVDF membrane and performing chemical washing at an inflection point in the TMP dynamics enabled ultralong MBR operation beyond the regular membrane lifetime. The implementation of the advocated strategy paves the way for the low CO2 footprint operation of a PVDF MBR, which does not require frequent membrane replacement and laborious membrane ex-situ cleaning.

Tourmaline triggered biofilm transformation: Boosting ultrafiltration efficiency and fouling resistance

Ultralow pressure filtration system, which integrates the dual functionalities of biofilm degradation and membrane filtration, has gained significant attention in water treatment due to its superior contaminant removal efficiency. However, it is a challenge to mitigate membrane biofouling while maintaining the high activity of biofilm. This study presents a novel ceramic-based ultrafiltration membrane functionalized with tourmaline nanoparticles to address this challenge. The incorporation of tourmaline nanoparticles enables the release of nutrient elements and the generation of an electric field, which enhances the biofilm activity on the membrane surface and simultaneously alleviates intrapore biofouling. The tourmaline-modified ceramic membrane (TCM) demonstrated a significant antifouling effect, with a substantial increase in water flux by 60 %. Additionally, the TCM achieved high removal efficiencies for contaminants (48.78 % in TOC, 22.28 % in UV254, and 24.42 % in TN) after 30 days of continuous operation. The fouling resistance by various constituents in natural water was individually analyzed using model compounds. The TCM with improved electronegativity and hydrophilicity exhibited superior resistance to irreversible fouling through increased electrostatic repulsion and reduced adhesion to foulants. Comprehensive characterizations and analyses, including interfacial interaction energies, redox reaction processes, and biofilm evolutions, demonstrated that the TCM can release nutrient elements to facilitate the development of functional microbial community within the biofilm, and generate reactive oxygen species (ROS) on the membrane surface to the degrade contaminants and mitigate membrane biofouling. The electric field generated by tourmaline nanoparticles can promote electron transfer in the Fe(III)/Fe(II) cycle, ensuring a stable and sustainable generation of ROS and bactericidal negative ions. These synergistic functions enhance contaminant removal and reduce irreversible fouling of the TCM. This study provides fundamental insights into the role of tourmaline-modified surfaces in enhancing membrane filtration performance and fouling resistance, inspiring the development of high-performance, anti-fouling membranes.

On-site evaluation of DGT passive sampling for quantitatively measuring per- and polyfluoroalkyl substances in a river-estuary-sea water system

The passive sampling technique of diffusive gradients in thin-films (DGT) is promising for monitoring emerging contaminants such as per- and polyfluoroalkyl substances (PFAS). It is urgent to evaluate the impacts of salinity and exposure time on DGT sampling before it can be set as a standard method. Herein, DGT sampler based on the binding gel of weak anion exchanger (WAX) resin was deployed in a representative water system of the Xiaoqing river-estuary-sea for representative sampling windows (<1 day to 28 days) with high pH (8.18 ± 0.04 to 8.51 ± 0.17) and wide ranges of salinity (0.95 ± 0.07‰ to 14.37 ± 3.92‰), total dissolved solids (1.20 ± 0.09 g/L to 15.29 ± 3.91 g/L) and dissolved organic matter (2.8–32 mg/L). The results showed that the WAX-DGT sampler exhibited good performance for most target PFAS except for short-chain perfluorocarboxylates (C ≤ 5) in 14 days. When the exposure time was over 14 days, biofouling of the sampler may deflect the mass accumulation of the PFAS in the sampler. Salinity played an important role in the mass binding of PFAS by DGT. The shorter the carbon chain of the compound, the greater the influence of the salinity. PFAS with carboxyl groups had greater affinities for the biofouled membrane filter than those with sulfonic groups. In the river-estuary-sea system, where PFAS concentrations changed dynamically, the temporal resolution of the monitoring strategy has been demonstrated to be more important than spatial resolution. DGT provided a better integral of PFAS exposure than grab sampling in the dynamic water system and offered equivalent sensitivity of grab sampling with exposure time <10 d and greater sensitivity with exposure time ≥10 d. Thus, DGT has the advantage of providing high temporal resolution monitoring. This study provided support for the standardization of the DGT technique.

Quorum Quenching in Membrane Bioreactors for Fouling Retardation: Complexity Provides Opportunities.

The occurrence of biofouling restricts the widespread application of membrane bioreactors (MBRs) in wastewater treatment. Regulation of quorum sensing (QS) is a promising approach to control biofouling in MBRs, yet the underlying mechanisms are complex and remain to be illustrated. A fundamental understanding of the relationship between QS and membrane biofouling in MBRs is lacking, which hampers the development and application of quorum quenching (QQ) techniques in MBRs (QQMBRs). While many QQ microorganisms have been isolated thus far, critical criteria for selecting desirable QQ microorganisms are still missing. Furthermore, there are inconsistent results regarding the QQ lifecycle and the effects of QQ on the physicochemical characteristics and microbial communities of the mixed liquor and biofouling assemblages in QQMBRs, which might result in unreliable and inefficient QQ applications. This review aims to comprehensively summarize timely QQ research and highlight the important yet often ignored perspectives of QQ for biofouling control in MBRs. We consider what this "information" can and cannot tell us and explore its values in addressing specific and important questions in QQMBRs. Herein, we first examine current analytical methods of QS signals and discuss the critical roles of QS in fouling-forming microorganisms in MBRs, which are the cornerstones for the development of QQ technologies. To achieve targeting QQ strategies in MBRs, we propose the substrate specificity and degradation capability of isolated QQ microorganisms and the surface area and pore structures of QQ media as the critical criteria to select desirable functional microbes and media, respectively. To validate the biofouling retardation efficiency, we further specify the QQ effects on the physicochemical properties, microbial community composition, and succession of mixed liquor and biofouling assemblages in MBRs. Finally, we provide scale-up considerations of QQMBRs in terms of the debated QQ lifecycle, practical synergistic strategies, and the potential cost savings of MBRs. This review presents the limitations of classic QS/QQ hypotheses in MBRs, advances the understanding of the role of QS/QQ in biofouling development/retardation in MBRs, and builds a bridge between the fundamental understandings and practical applications of QQ technology.

Surface Microstructure Drives Biofilm Formation and Biofouling of Graphene Oxide Membranes in Practical Water Treatment.

Significant progress has been made previously in the research and development of graphene oxide (GO) membranes for water purification, but their biofouling behavior remains poorly understood. In this study, we investigated the biofilm formation and biofouling of GO membranes with different surface microstructures in the context of filtering natural surface water and for an extended operation period (110 days). The results showed that the relatively hydrophilic and smooth Fe(OH)3/GO membrane shaped a thin and spatially heterogeneous biofilm with high stable flux. However, the ability to simultaneously mitigate biofilm formation and reduce biofouling was not observed in the weakly hydrophilic and wrinkled Fe/GO and H-Fe(OH)3/GO membranes. Microbial analyses revealed that the hydrophilicity and roughness distinguished the bacterial communities and metabolic functions. The organic matter-degrading and predatory bacteria were more adapted to hydrophilic and smooth GO surfaces. These functional taxa were involved in the degradation of extracellular polymeric substances (EPS), and improved biofilm heterogeneity. In contrast, the weakly hydrophilic and wrinkled GO surfaces had reduced biodiversity, while unexpectedly boosting the proliferation of EPS-secreting bacteria, resulting in increased biofilm formation and aggravated biofouling. Moreover, all GO membranes achieved sustainable water purification during the entire operating period.

Vibrio neptunius-ULV11 cell-free supernatant as a promising antifouling approach in reverse osmosis systems

One of the most common problems observed in continuous operation of desalination plants, is the presence of biofouling in ultrafiltration (UF) modules and reverse osmosis membranes (ROMs), decreasing permeated water obtention and increasing energy consumption among other adverse effects. To solve this problem, desalination industry applied UF modules and ROMs cleaning procedures that aims to increase half-life operation time, however, many of the actual cleaning procedures are focused on the addition of chemical compounds that provokes secondary effects such as UF modules and ROMs disintegration leading to structural changes and a decrease in plant performance. Thus, new approaches to replace current cleaning compounds with new ecofriendly and less secondary effects technologies are necessary.In this study, we present a Vibrio neptunius strain ULV11 isolate, with a high capacity to remove fouling in RO systems. In detail, ULV11 cell-free supernatant (CFS) was used in replace of chemical agents as a cleaning solution according to standard operational protocol on 3-year-old membranes of continuous operation. The results showed that CFS can be used under operational conditions (such high pressure and flux) allowed us to recover permeate volumes similar to those observed in traditional chemical treatment with better conductivity. This recovery was accompanied by a reestablishment of membrane topology observed by atomic force microscopy and EPS remotion since concanavalin A signal trough confocal microscopy was decrease as compared with biofouling control.

Camellia sinensis leaf-derived magnetite nanoparticles as anti-biofouling nano-fillers in polymer electrolyte membrane for microbial fuel cell application

Membrane biofouling prevents one of the most promising bio-electrochemical systems known as microbial fuel cell (MFC) from operating at its fullest potential. Green tea leaf-mediated biosynthesized and sulphonated iron (II, III) oxide nanoparticles aim to serve as a nanofiller for polymer electrolyte membrane (PEM) to enhance the membrane physicochemical parameters and to improve the membrane anti-biofouling in MFC. Sulphonated polyether ether ketone (SPEEK) grafted styrene sulphonic acid (SSA) incorporated with biosynthesized-sulphonated Fe3O4 (BS-Fe3O4) nanoparticles is used as nanocomposite membranes in the MFC. The results show that 7.5 % BS-Fe3O4 integrated SPEEK/SSA membranes possessed high proton conductivity (8.4x10-2 S cm−1), water uptake (78.2 %), and ion exchange capacity (1.84 meq g−1) than plain SPEEK and commercially available Nafion-117 membrane. The results also reveal that SPEEK/SSA + 7.5 % BS-Fe3O4 membrane showed the highest maximum power density of 210.3 mW m−2 at 190 mA m−2 current density after 4 weeks of MFC operation. The heightened performance of the mentioned nanocomposite membranes is due to their exceptional anti-biofouling property as observed through zone of inhibition (10.25 mm) and biofilm inhibition tests (74.1 %). The prepared membranes also exhibited good mechanical and oxidative stability required for long-term operation. Finally, the phylogenetic analysis discloses the maximum presence of the Pseudomonas (∼54.75 %), Acidovax (∼9.5 %), Janthinobacteriu (∼4.84 %), Flavoacterium (∼2.77 %), and Thermomonas (∼2.66 %). This study provides avenues for interdisciplinary research in green synthesis, functionalization of nanomaterials, polymer synthesis, and MFCs to address current research gaps.

Biofouling behaviors of reverse osmosis membrane in the presence of trace plasticizer for circulating cooling water treatment: Characteristics and mechanisms

Reverse osmosis (RO) system has been increasingly applied for circulating cooling water (CCW) reclamation. Plasticizers, which may be dissolved into CCW system in plastic manufacturing industry, cannot be completely removed by the pretreatment prior to RO system, possibly leading to severe membrane biofouling. Deciphering the characteristics and mechanisms of RO membrane biofouling in the presence of trace plasticizers are of paramount importance to the development of effective fouling control strategies. Herein, we demonstrate that exposure to a low concentration (1 − 10 μg/L) of three typical plasticizers (Dibutyl phthalate (DBP), Tributyl phosphate (TBP) and 2,2,4-Trimethylpentane-1,3-diol (TMPD)) detected in pretreated real CCW promoted Escherichia coli biofilm formation. DBP, TBP and TMPD showed the highest stimulation at 5 or 10 μg/L with biomass increasing by 55.7 ± 8.2 %, 35.9 ± 9.5 % and 32.2 ± 14.7 % respectively, relative to the unexposed control. Accordingly, the bacteria upon exposure to trace plasticizers showed enhanced adenosine triphosphate (ATP) activity, stimulated extracellular polymeric substances (EPS) excretion and suppressed intracellular reactive oxygen species (ROS) induction, causing by upregulation of related genes. Long-term study further showed that the RO membranes flowing by the pretreated real CCW in a polypropylene plant exhibited a severer biofouling behavior than exposed control, and DBP and TBP parts played a key role in stimulation effects on bacterial proliferation. Overall, we demonstrate that RO membrane exposure to trace plasticizers in pretreated CCW can upregulate molecular processes and physiologic responses that accelerate membrane biofouling, which provides important implications for biofouling control strategies in membrane-based CCW treatment systems.

Benefits of fungal-to-bacterial quorum quenching as anti-biofouling strategy in membrane bioreactors for wastewater treatment and water reuse

This study addresses membrane biofouling in membrane bioreactors (MBRs) by exploring fungal-to-bacterial quorum quenching (QQ) strategies. While most research has been focused on bacterial-to-bacterial QQ tactics, this study identified fungal strain Vanrija sp. MS1, which is capable of degrading N-acyl-homoserine lactones (signaling molecules of Gram-negative bacteria). To determine the benefits of fungal over bacterial strains, after immobilization on fluidizing spherical beads in an MBR, MS1 significantly reduced the fouling rate by 1.8-fold compared to control MBR, decreased extracellular polymeric substance levels in the biofilm during MBR operation, and favorably changed microbial community and bacterial network, resulting in biofouling mitigation. It is noteworthy that, unlike Rhodococcus sp. BH4, MS1 enhanced QQ activity when switching from neutral to acidic conditions. These results suggest that MS1 has the potential for the effective treatment of acidic industrial wastewater sources such as semiconductor and secondary battery wastewater using MBRs.

Preservation and reactivation strategies for quorum quenching media to combat membrane biofouling

Microbial quorum quenching (QQ), which addresses biofouling resistant to physical and chemical methods, presents a compelling solution. Enhancements in sustainability are imperative to ensure its long-term stability. This study explores QQ media preservation for extended use. Three media types were tested over 150 days: fresh BH4 cells, preserved/reactivated BH4 cells, and BH4 cell extracts. Initial QQ activities ranged in the appropriate levels from 1.08 to 1.24 h−1. Preservation in 50 mM Tris-HCl at 4 °C showed that media with whole cells retained approximately 60 % activity after 60 days, unlike cell extract media, which lost all activity. However, the dehydration and reactivation of BH4 cell media fully recovered the initial QQ activity while maintaining it for 150 days. In MBR tests, reactivated QQ media performed as effectively as those prepared with freshly cultured BH4 cells, delaying membrane fouling by 2-fold. Revitalizing QQ media in combination with chlorine-based chemically enhanced backwashing (CEB) further delayed fouling by 2.5 times compared to CEB alone. Reactivated QQ media retained robust activity even after prolonged MBR use. This study showcases the effectiveness of dehydration and reactivation techniques for preserving QQ media, ensuring its reliable long-term storage and utilization. However, further enhancements are necessary to optimize cell viability.

Mitigation of biofouling in membrane bioreactors by quorum-quenching bacteria during the treatment of metal-containing wastewater.

Quorum quenching (QQ) is an efficient way to mitigate membrane biofouling in a membrane bioreactor (MBR) during wastewater treatment. A QQ bacterium, Lysinibacillus sp. A4, was isolated and used to mitigate biofouling in an MBR during the treatment of wastewater containing metals. A QQ enzyme (named AilY) was cloned from A4 and identified as a metallo-β-lactamase-like lactonase. The QQ activity of A4 and that of Escherichia coli BL21 (DE3) overexpressing AilY could be promoted by Fe2+, Mn2+, and Zn2+ while remaining unaffected by other metals tested. The two bacteria effectively mitigated biofouling by reducing the transmembrane pressure from around 30 to 20kPa without negative influence on the COD, NH4+-N, or total phosphorus of the effluent. The relative abundance of Lysinibacillus sp. A4 increased greatly from 0.04 to 8.29% in the MBR with metal-containing wastewater, suggesting that Lysinibacillus sp. A4 could multiply quickly and adapt to this environment. Taken together, the findings suggested that A4 could tolerate metal to a certain degree, and this property could allow A4 to adapt well to metal-containing wastewater, making it a valuable strain for mitigating biofouling in MBR during the treatment of metal-containing wastewater.

Development, growth, and function of biofilm communities on reverse osmosis membranes desalinating tertiary effluent

Efficient tertiary effluent desalination is hindered by membrane biofouling, leading to plant downtime, shortened membrane lifespan, heightened energy consumption, and reduced permeability. While the composition of these biofouling layers is studied, little is known about bacterial succession and function. To address this, we used a benchtop reverse osmosis (RO) system to process synthetic tertiary effluent with diluted sludge. System flux monitoring tracked biofouling layer development, and RO biofilm samples were collected at early and mature stages (48, 72, 120 h). Scanning electron microscopy visualized the samples, and their 16S rRNA genes were sequenced. DNA-stable isotope probing with labeled glucose identified growing taxa in early and late biofouling stages (48, 120 h). Over time, biofouling layer biomass increased, with shifts in bacterial diversity and composition. Proteobacteria, notably oligotrophic genera, dominated early stages along with Bacteriodota, while Actinobacteria increased in mature biofilms. Functional changes included a shift from biosynthesis of cellular components like DNA, peptidoglycan, membrane lipids, and antimicrobials, to production of extracellular polysaccharides and reactive oxygen scavenging agents. In conclusion, our research enhances the understanding of biofouling dynamics within tertiary effluent desalination processes, providing insights that could improve biofouling management strategies in RO desalination systems, potentially applicable to larger-scale operations.

Compact and water flushing resistant mesh biofilms forming at short SRT disappeared naturally under extended SRT in dynamic membrane bioreactor

Extending the solids retention time (SRT) has been demonstrated to mitigate membrane biofouling. Nevertheless, it remains an intriguing question whether the compact and water flushing resistant mesh biofilms developed at short SRT can undergo biodegradation and be removed with extended SRT. In present study, the bio-fouled mesh filter in the 10d-SRT dynamic membrane bioreactor (DMBR), with mesh surfaces and pores covered by compact and water flushing resistant biofilms exhibiting low water permeability, was reused in the 40d-SRT DMBR without any cleanings. After being reused at 40d-SRT, its flux driven by gravity occurred from the 10th day and recovered to a regular level of 36.7 L m−2·h−1 on the 27th day. Both scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM) analyses indicated that the compact mesh biofilms formed at10d-SRT biodegraded and were removed at 40d-SRT, with the residual biofilms becoming removable by water flushing. As a result, the hydraulic resistance of the bio-fouled mesh filter decreased from 4.36 × 108 to 6.97 × 107 m−1, and its flux fully recovered. The protein and polysaccharides densities in mesh-biofilms decreased from 24.4 to 9.7 mg/cm2 and from 10.7 to 0.10 mg/cm2, respectively, which probably have contributed to the disappearance of compact biofilms and the decrease in adhesion. Furthermore, the sludge and mesh-biofilms in the 40d-SRT reactor contained a higher relative abundance of dominant quorum quenching bacteria, such as Rhizobium (3.52% and 1.35%), compared to those in the 10d-SRT sludge (0.096%) and mesh biofilms (0.79%), which might have been linked to a decline in extracellular polymeric substances and, consequently, the biodegradation and disappearance of compact biofilms.

Membrane biofouling control by D-ribose in membrane bioreactor

BackgroundMembrane biofouling is still one major obstacle in the application of membrane bioreactor (MBR). Because of similar chemical structure to quorum sensing (QS) signaling molecule autoinducer-2 (AI-2), D-ribose might be an ideal QS inhibitor to inhibit membrane biofouling. Methods100 μM of D-ribose were periodically added to MBR to investigate the effect of D-ribose on membrane biofouling in MBR. Significant findingsThe fouling cycle was prolonged significantly, and the membrane was covered with larger and looser foulants with the addition of D-ribose. The soluble microbial products (SMP) content were reduced slightly and the secretions of extracellular polymeric substances (EPS) in activated sludge were effectively inhibited by the addition of D-ribose. Moreover, D-ribose could promote catalase (CAT) and superoxide dismutase (SOD) activity of activated sludge, and reduce the accumulation of malondialdehyde (MDA). Furthermore, long-term addition of D-ribose could increase the abundance of quorum-sensing quenching (QQ) bacteria, strengthen the quenching ability of the system and effectively inhibit membrane biofouling.

Biofouling-focused assessment of a novel, cellulose-based ionogel membrane applied in a microbial fuel cell

In this work, a novel ionogel membrane was prepared on polyethersulfone physical support from the mixture of microcrystalline cellulose and [BMIM][Cl] (1-Butyl-3-methylimidazolium chloride) ionic liquid and used in a microbial fuel cell (MFC). The ionogel membrane was characterized in terms of its morphology, mass- (substrate, oxygen) and ion transfer features and compared to Nafion 115. The membranes were deployed in acetate-fed two-chamber MFC, where the MFC equipped with the ionogel membrane showed a Coulombic efficiency and peak current density of 49.4 % and 369 mA m−2, respectively. Through three weeks of experiments, the electrode and membrane biofouling layers were studied by 16S amplicon metagenomics and correspondence analysis. It turned out that a cellulose-degrading species, Clostridium termitidis was present with a relatively large, 23.2 % relative abundance on the surface of the ionogel membrane, which may have caused its deterioration and the consequent colonization of the cathodic compartment.

Photocatalytic Zinc Oxide Nanoparticles in Antibacterial Ultrafiltration Membranes for Biofouling Control.

Global water scarcity is a threat that can be alleviated through membrane filtration technologies. However, the widespread adoption of membranes faces significant challenges, primarily due to membrane biofouling. This is the reason why membrane modifications have been under increasing investigation to address the fouling issues. Antibacterial membranes, designed to combat biofouling by eliminating microorganisms, offer a promising solution. Within this study, flat sheet ultrafiltration (UF) membranes with integrated photocatalytic zinc oxide (ZnO) nanoparticles were developed, characterized, and assessed through filtration and fouling tests. The antibacterial properties of the membranes were conducted in static tests using Gram-negative bacteria-Escherichia coli-and natural tap water biofilm. The results demonstrated a notable enhancement in membrane surface wettability and fouling resistance. Furthermore, the incorporation of ZnO resulted in substantial photocatalytic antibacterial activity, inactivating over 99.9% of cultivable E. coli. The antibacterial activity persisted even in the absence of light. At the same time, the persistence of natural tap water organisms in biofilms of modified membranes necessitates further in-depth research on complex biofilm interactions with such membranes.