Biofouling Mitigation Research Articles

Characterization of an N-acylhomoserine lactonase from Serratia sp. and its biofouling mitigation in a membrane bioreactor

Membrane biofouling is a process that can impede the development of membrane bioreactor (MBR), which constitutes an important system of the wastewater treatment process. Membrane biofouling is governed by quorum sensing (QS), a communication system heavily dependent on the activities of signal molecules. Certain bacteria, known as quorum quenching (QQ) bacteria, can quench the QS process by destroying the signal molecules. These QQ bacteria are considered a sustainable and feasible way of mitigating membrane biofouling in MBR. In this study, a QQ enzyme (designated as AisZ) from a Serratia sp. was first identified and characterized. Escherichia coli BL21 expressing AisZ was able to degrade different QS signal molecules. Furthermore, these cells could also mitigate membrane biofouling in MBR during a 29-day operation by reducing the transmembrane pressure from 31 to 21 kPa. The metal ions Co2+ and Ni2+ were relatively important to AisZ in that they could significantly enhance the activity of AisZ and restore the EDTA-inactivated AisZ. Expression of the aisA gene was not influenced by Co2+, Ni2+ and QS signal molecules. AisZ might, therefore, extend the diversity of potential candidates for the mitigation of biofouling associated with membrane filtration technologies.

Effects of Ethyl Lauroyl Arginate (LAE) on Biofilm Detachment: Shear Rate, Concentration, and Dosing Time

Biofilm formation is one of the main obstacles in membrane treatment. The non-oxidizing biocide ethyl lauroyl arginate (LAE) is promising for mitigating biofilm development on membrane surfaces. However, the operating conditions of LAE and their impact on biofilm detachment are not comprehensively understood. In this study, a real-time in vitro flow cell system was utilized to observe biofilm dispersal caused by the shear rate, concentration, and treatment time of LAE. This confirmed that the biofilm was significantly reduced to 68.2% at a shear rate of 3.42 s−1 due to the increased physical lifting force. LAE exhibited two different mechanisms for bacterial inactivation and biofilm dispersal. Biofilms treated with LAE at sub-growth inhibitory concentrations for a longer time could effectively detach the biofilm formed on the surface of the glass slides, which can be attributed to the increased motility of microorganisms. However, a high concentration (i.e., bactericidal concentration) of LAE should be seriously considered because of the inactivated sessile bacteria and their residual debris remaining on the surface. This study sheds light on the effect of LAE on biofilm detachment and provides insights into biofouling mitigation during the membrane process.

Intrinsically Disordered Protein Condensate-Modified Surface for Mitigation of Biofouling and Foreign Body Response.

Mitigation of biofouling and the host's foreign body response (FBR) is a critical challenge with biomedical implants. The surface coating with various anti-fouling materials provides a solution to overcome it, but limited options in clinic and their potential immunogenicity drive the development of more alternative coating materials. Herein, inspired by liquid-liquid phase separation of intrinsically disordered proteins (IDPs) to form separated condensates in physiological conditions, we develop a new type of low-fouling biomaterial based on flexible IDP of FUS protein containing rich hydrophilic residues. A chemical structure-defined FUS IDP sequence tagged with a tetra-cysteine motif (IDPFUS) was engineered and applied for covalent immobilization on various surfaces to form a uniform layer of protein tangles, which boosted strong hydration on surfaces, as revealed by molecular dynamics simulation. The IDPFUS-coated surfaces displayed excellent performance in resisting adsorption of various proteins and adhesion of different cells, platelets, and bacteria. Moreover, the IDPFUS-coated implants largely mitigated the host's FBR compared with bare implants and particularly outperformed PEG-coated implants in reducing collagen encapsulation. Thus, this novel low-fouling and anti-FBR strategy provides a potential surface coating material for biomedical implants, which will also shed light on exploring similar applications of other IDP proteins.

Core carbon fixation pathways associated with cake layer development in an anoxic-oxic biofilm-membrane bioreactor treating textile wastewater

Microbial carbon fixation pathways have not yet been adequately understood for their role in membrane case layer formation processes. Carbon fixation bacteria can play critical roles in either causing or enhancing cake layer formation in some autotrophic-prone anoxic conditions, such as sulfur-cycling conditions. Understanding the microbes capable of carbon fixation can potentially guide the design of membrane biofouling mitigation strategies in scientific ways. Thus, we used meta-omics methods to query carbon fixation pathways in the cake layers of a full-scale anoxic-oxic biofilm-MBR system treating textile wastewater in this study. Based on the wastewater constituents and other properties, such as anoxic conditions, sulfide-reducing and sulfur-oxidizing bacteria could co-exist in the membrane unit. In addition, low-light radiation conditions could also happen to the membrane unit. However, we could not quantify the light intensity or total energy input accurately because the whole experimental setup was a full-scale system. Potentially complete carbon fixation pathways in the cake layer included the Calvin-Benson-Bassham cycle, Wood-Ljungdahl pathway, and the 3-hydroxypropionate bicycle. We discovered that using aeration could effectively inhibit carbon fixation, which resulted in mitigating membrane cake layer development. However, the aeration resulted in the 3-hydroxypropionate bicycle pathway, presumably used by aerobic sulfur-oxidizing prokaryotes, to become a more abundant carbon fixation pathway in the cake layer under aerobic conditions.

Dopamine-Induced Surface Zwitterionization of Expanded Poly(tetrafluoroethylene) for Constructing Thermostable Bioinert Materials.

Although energy-demanding, the surface modification of polytetrafluoroethylene (PTFE) for biomedical applications is mandatory to mitigate irreversible biofouling that occurs whenever PTFE comes into contact with biological fluids. Here, we propose to take advantage of the adhesive properties of dopamine (DA) and of the antifouling ability of various zwitterionic monomers (sulfobetaine methacrylate (SBMA), sulfobetaine methacrylamide (SBAA), sulfobetaine acrylamide (SBAA'), and 4-vinylpyridine propylsulfobetaine (4VPPS)) and form antifouling coatings by copolymerization on the surface of expanded PTFE membranes. This simple, low-energy, and one-step coating procedure arises in significant biofouling mitigation. All zwitterionic coatings led to important reduction of biofouling by red blood cell conentrate (88-94%), platelet conentrate (70-90%), whole blood (40-66%), or bacteria (83-96%). Also, it is shown that the interactions of polydopamine with ePTFE are stable even at high temperatures. However, the zwitterionic monomers are differently affected. While the performance of SBMA coatings decreased (as SBMA is prone to hydrolysis), those of SBAA, SBAA', and 4VPPS coatings were generally maintained. All in all, this study illustrates that efficient and stable antifouling zwitterionic coatings can be generated onto PTFE membranes for biomedical applications, without the use of conventional high-energy-demanding surface modification processes.

Layered Antibiofouling Composite Membrane for Quenching Bacterial Signaling.

Bacterial quorum quenching (QQ) media with various structures (e.g., bead, cylinder, hollow cylinder, and sheet), which impart biofouling mitigation in membrane bioreactors (MBRs), have been reported. However, there has been a continuous demand for membranes with QQ capability. Thus, herein, we report a novel double-layered membrane comprising an outer layer containing a QQ bacterium (BH4 strain) on the polysulfone hollow fiber membrane. The double-layered composite membrane significantly inhibits biofilm formation (i.e., the biofilm density decreases by ~58%), biopolymer accumulation (e.g., polysaccharide), and signal molecule concentration (which decreases by ~38%) on the membrane surface. The transmembrane pressure buildup to 50 kPa of the BH4-embedded membrane (17.8 h ± 1.1) is delayed by more than thrice (p < 0.05) of the control with no BH4 in the membrane’s outer layer (5.5 h ± 0.8). This finding provides new insight into fabricating antibiofouling membranes with a self-regulating property against biofilm growth.

Integrating biofouling sensing with fouling mitigation in a two-electrode electrically conductive membrane filtration system

Biofouling detection enables the adoption of effective cleaning strategies for biofouling prevention. This work investigates the use of electrical impedance spectroscopy (EIS) to monitor the biofilm development and the use of electric fields to mitigate biofouling on the surface of gold-coated membranes. The multi-bacterial suspension was injected into a two-electrode crossflow filtration system where the permeate flux and impedance spectra were recorded to monitor the biofilm growth. Permeate flux declined over time while the impedance at low frequency regions (<10 Hz) rapidly decreased with fouling at the early stages of fouling, and then gradually decreased as biofilm matured. The normalized diffusion-related impedance (Rd), an EIS-derived parameter, was extracted to determine the sensitivity of EIS detection. We observed that impedance-based detection was more sensitive to changes as compared to the decline of permeate flux during the early stage of biofouling. With early detection of fouling, fouling mitigation strategies could be applied more effectively. Further, under the same conditions as fouling detection, either applying an intermittent cathodic potential (−1.5 V) or cross-flow flushing delayed the biofilm growth on the electrically conductive membranes (ECMs). EIS sensitivity was repeatably recovered across four cycles of mechanical fouling removal. Hence ECMs were demonstrated to play a dual function: EIS-enabled detection of biofouling evolution and surface biofouling mitigation.

Affordable Pretreatment Strategy for Mitigation of Biofouling in Drinking-Water Systems

AbstractBiofouling triggers a chain of events that are deleterious to engineered systems providing safe water to the population and industry. The frequent use of dissolved biocides to combat biofil...

Anti-barnacle biofouling coatings for the protection of marine vessels: synthesis and progress.

Marine biofouling has gnawed both mobile and non-mobile marine structures since time immemorial, leading to the deterioration of designed operational capabilities as well as a loss of valuable economic revenues. Mitigation of biofouling has been the primary focus of researchers and scientists from across the globe to save billions of dollars wasted due to the biological fouling of marine structures. The availability of an appropriate environment along with favorable substrata initiates biofilm formation within a few minutes. The crucial element in establishing a gelatinous biofilm is the excreted metabolites of destructive nature and exopolymeric substances (EPSs). These help in securing as well as signaling numerous foulants to establish themselves on this substrate. The larvae of various benthic invertebrates adhere to these suitable surfaces and transform from juveniles to adult barnacles depending upon the environment. Despite biofouling being characteristically witnessed for a month or lengthier timeframe, the preliminary phases of the fouling process typically transpire on a much lesser timescale. A few natural and synthetic additives had demonstrated excellent non-toxic anti barnacle establishment capability; however, further development into commercial products is still far-fetched. This review collates the specific anti-barnacle coatings, emphasizing natural additives, their sources of extraction, general life cycle analysis, and concluding future perspectives of this niche product.

Mitigation of Biofouling in MBR by Interference in Microbial Metabolisms with a Bioactive Substance

Mitigation of Biofouling in MBR by Interference in Microbial Metabolisms with a Bioactive Substance

Strategies for Mitigating MBR Membrane Biofouling

Membrane biofouling is a roadblock to the application of membrane bioreactors (MBR) for wastewater treatment and reuse. Strategies for the mitigation of membrane biofouling have been extensively reviewed in this paper. The review was focused on feedwater pretreatment, modified membranes, suppression of the secretion and discharge of extracellular polymeric substances (EPSs) and soluble microbial products (SMPs), and novel MRB systems. The three identified novel strategies for mitigating membrane biofouling in an MBR for wastewater reclamation are lower EPS concentration by adding D-amino acids (D-AAs) and a cationic polymer flucculant; introducing a modified membrane in an MBR; and applying a novel algae-bacteria system. Experimental results have shown that membrane biofouling has been mitigated to some extent via these strategies.

Surface PEGylation via Ultrasonic Spray Deposition for the Biofouling Mitigation of Biomedical Interfaces.

Air plasma and spray technology are common methods for surface modification. In this study, air plasma is used to generate hydroxyl groups on various material surfaces. Then random copolymers of styrene and ethylene glycol methacrylate (PS-r-PEGMA) are spray-coated to achieve coating densities ranging between 0.1 and 0.6 mg/cm2. PS50-r-PEGMA50 led to the best overall antifouling properties, while a coating density of 0.3 mg/cm2 was enough to significantly reduce biofouling. This surface modification technique enabled efficient modification of a wide range of materials and biofouling reduction by at least 75% on polymeric surfaces (polystyrene, polyvinylidene fluoride, poly(tetrafluoroethylene), polydimethylsiloxane), metallic surfaces (steel, titanium alloy), or ceramic surface (glass). Applied to the modification of well plate used for blood-typing, this antifouling modification permitted to greatly increase the signal sensitivity (×4).

Mitigation of membrane biofouling via immobilizing Ag-MOFs on composite membrane surface for extractive membrane bioreactor

The extractive membrane bioreactor (EMBR) combines an extractive membrane process and bioreactor to treat highly saline recalcitrant organic wastewater, in which the organic contaminations diffuse through a semi-permeable polydimethysiloxane (PDMS) composite membrane from the feed wastewater to the receiving biomedium. During the long-term EMBR operation, membrane biofouling is an inevitable phenomenon, which is one of the main obstacles impeding its wide applications. The excessive biofilm deposited on membrane surface could significantly reduce the organic mass transfer coefficient of composite membranes by more than 40%. Therefore, in this work, the silver (Ag)-metal organic frameworks (MOFs) were synthesized and immobilized on the PDMS surface of nanofibrous composite membranes to mitigate the membrane biofouling. The robustness of Ag-MOFs coating on membrane surface was well demonstrated by ultrasonic treatment. In addition, the silver nanoparticles (AgNPs) were coated on the PDMS surface of composite membranes for comparison. In contrast with the unmodified composite membrane #M0, the AgNPs-coated (#M1) and Ag-MOFs modified (#M2) composite membranes possessed less hydrophobic and negatively charged surfaces due to the coating layers. Although the modified membranes exhibited lower phenol mass transfer coefficients (k0’s) in the aqueous-aqueous extractive membrane process due to these additional modification layers, both #M1 and #M2 displayed better long-term performance in the 12-days continuous EMBR operations due to their excellent anti-biofouling properties. Moreover, #M2 exhibited the most stable EMBR performance among the composite membranes developed in this work and other reported membranes with a finally stabilized k0 of 33.0 × 10–7 m/s (89% of initial k0). The least amounts of proteins, polysaccharides and total suspended solids (TSS) on the surface of tested #M2 also demonstrated its outstanding biofouling resistance. This excellent anti-biofouling performance should be attributed to the stable, controlled and long-lasting Ag+release from Ag-MOFs, as well as its less hydrophobic and negative charged surface properties, which made #M2 undergo the k0’s increasing and gradual stabilization stages in the long-term EMBR operations.

Photolytic quorum quenching effects on the microbial communities and functional gene expressions in membrane bioreactors

Photolytic quorum quenching by ultraviolet A (UVA) irradiation is an effective strategy for controlling membrane bioreactor (MBR) biofouling; however, its effects on MBR microbial communities and functional genes have not yet been explored. Here, we report on the effects of the UVA irradiation, which mitigates membrane biofouling, on the microbial community structures, alpha and beta diversities, and functional gene expressions in the MBR mixed liquor and biocake (membrane fouling layer) for the first time. The results show that the microbial communities become less diversified when alternating UVA is applied to the MBRs. The changes in the community structure are highly influenced by spatiotemporal factors, such as microbial habitats (mixed liquor and biocake) and reactor operation time, although UVA irradiation also has some impacts on the community. The relative abundance of the Sphingomonadaceae family, which can decompose the furan ring of autoinducer-2 (AI-2) signal molecules, becomes greater with continuous UVA irradiation. Xanthomonadaceae, which produces biofilm-degrading enzymes, is also more abundant with UVA photolysis than without it. Copies of monooxygenase and hydroxylase enzyme-related genes increase in the MBR with longer UVA exposures (i.e., continuous UVA). These enzymes seem to be inducible by UVA, enhancing the AI-2 inactivation. In conclusion, UVA irradiation alters the microbial community and the metabolism in the MBR, contributing to the membrane biofouling mitigation.

Mitigation of membrane biofouling using quorum-quenching bacteria in a continuously operated membrane bioreactor

Quorum-quenching (QQ) has become an attractive strategy for the mitigation of membrane biofouling known as biocake or biofilm. In this study, a QQ system, which exploited two QQ bacteria (Serratia sp. Z4 and Klebsiella sp. Q2) and γ-caprolactone (GCL), was established and used to effectively mitigate biofouling. This system could delay the increase in transmembrane pressure by half during a 40-day operation in a continuous membrane bioreactor (MBR) with low effluent chemical oxygen demand and ammonium nitrogen. GCL improved the biofouling-mitigation ability of the QQ bacteria without stimulating bacterial growth. The reduction in soluble microbial products was consistent with the delay in transmembrane pressure increase. Furthermore, soluble microbial products (SMP) in the reactors were significantly influenced by the QQ system, suggesting that SMP was important for the occurrence of biofouling. Microbial community analysis showed that the relative abundance of some main genera was not greatly influenced by the QQ system. The two most abundant genera of quorum sensing (QS)-related bacteria found in the sludge mixture were Alicycliphilus and Thauera. The results indicated that a QQ strategy based on the disturbance of QS among the microbes should be effective for biofouling mitigation in MBR.

Non-chemical biofouling mitigation systems for seawater cooling tower using granular activated carbon biofiltration and ultrafiltration

Biofouling is a serious problem in industrial cooling tower. It damages equipment through bio-corrosion, causes blockages, and increases energy consumption by decreased heat transfer. One of the most popular methods used in the cooling tower process to control the biofouling is disinfection by chlorination. However, chlorination forms harmful disinfection byproducts in the presence of organic. The research aims to remove the nutrients and microorganisms from seawater for biofouling mitigation in seawater cooling towers (SCTs) without chemical usage. Granular activated carbon (GAC) biofiltration and ultrafiltration (UF) membrane pretreatment systems were employed to reduce the amount of nutrients and the number of microorganisms in seawater entering the main process, respectively. Assimilable organic carbon (AOC) levels in the feed seawater are directly linked with a bacterial growth, thus it can be used as an indicator of biofouling potential after pretreatment. GAC biofilter exhibited a high efficiency in the reducing of biofouling potential by removing AOC in seawater feed. UF could minimize the initial microbial growth. Further, a hybrid GAC/UF system achieved the removal of DOC up to 78% with enhanced AOC reduction (less than 60% compared to value without pretreatment). It indicates that the GAC/UF hybrid is a promising process minimizing the chemical usage and mitigating the biofouling growth. This study can provide the useful information to operator of SCTs to manage the biofouling problems without chemical and to operate it environmentally-friendly.

Star polymer-mediated in-situ synthesis of silver-incorporated reverse osmosis membranes with excellent and durable biofouling resistance

Biofouling mitigation for water purification membranes is critically important for the efficient separation process. Most anti-biofouling thin-film nanocomposite (TFN) membranes have been incorporated with biocidal nanomaterials via ex-situ hybridization, often leading to performance deterioration and ineffective nanomaterial incorporation. Here, we present a new in-situ hybridization strategy for the fabrication of silver-incorporated TFN (CD-Ag-TFN) reverse osmosis (RO) membranes exhibiting excellent anti-biofouling and separation performance by utilizing an amine-functionalized star polymer. CD-Ag-TFN membranes were formed by adding a Ag precursor (AgNO3) to an aqueous solution containing poly(acryloyl hydrazide)-branched star polymers (CD-PAHs) prior to interfacial polymerization with trimesoyl chloride (TMC). Numerous amine groups in CD-PAH strongly adsorbed Ag+ ions via complexation, which were subsequently converted to Ag or AgCl nanoparticles, while simultaneously forming a polyamide (PA) selective layer via the reaction with TMC, consequently creating a uniform PA-Ag hybrid network. Due to its greater hydrophilicity and high crosslinking density, the optimized CD-Ag-TFN membrane exhibited RO performance, which is better than that of the CD-PAH-assembled control (CD-TFC) and comparable to than that of recently reported other lab-made RO membranes. Importantly, the robust and effective incorporation of Ag endowed the CD-Ag-TFN membrane with remarkably long-lasting anti-bacterial activity and greater anti-biofouling performance than control CD-TFC.

Roles of initial bacterial attachment and growth in the biofouling development on the microfiltration membrane: From viewpoints of individual cell and interfacial interaction energy

In this study, bacterial adhesion and growth behaviors during biofouling development on the polyvinylidene fluoride (PVDF) microfiltration (MF) membrane were investigated. It is recognized that abundance of biomass is essential to the serious biofouling occurrence. The irreversible resistance of membrane increased to 5.2 × 1011 m−1 after filtration of 22 days, and then to 1.42 × 1012 m−1 at the end of 68 days. The growth of bacteria on the membrane surface conformed well to the pseudo second-order kinetic equation, and was mainly determined by the substrates concentration in the feeding. Based on the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory, the interfacial energy between MF membrane and typical bacteria (Pseudomonas aeruginosa) decreased continuously from 11800 KT (0 h) to −8100 KT (16 h), and the energy barrier decreased gradually after short-term filtration. By chemical cleaning with NaClO and NaOH, the flux of MF membrane recovered to 92.3% and 80.2% of the initial flux, respectively, but the interface energy between membrane and bacteria decreased to −2550 KT and −280 KT, respectively, which accelerated the adhesion of bacteria. This work helps to understand the biofouling mechanisms and provides guidance for the mitigation and control of biofouling for membrane filtration.

Mitigation of membrane biofouling in membrane bioreactor treating sewage by novel quorum quenching strain of Acinetobacter originating from a full-scale membrane bioreactor

A novel quorum quenching (QQ) strain, Acinetobacter guillouiae ST01, was isolated from a full-scale membrane bioreactor (MBR) and characterized for its QQ activities. Batch reactor studies at lab-scale showed that A. guillouiae ST01 exhibited higher QQ activity against acyl homoserine lactones (AHLs) with an oxo group compared to those without an oxo group. The organism was then inoculated (10%) in an MBR (Q-MBR) treating sewage over 48 days and was found to reduce quorum sensing (QS) activity by reducing AHL concentrations in the sludge and the biofilm of the Q-MBR. The concentration of polysaccharides was reduced up to 30% in both the biofilm and sludge relative to the control, whereas protein concentrations were reduced by 40% and 47% in the sludge and biofilm, respectively. The Q-MBR fouling rates were halved. These results indicate that A. guillouiae ST01 is a promising strain for biofouling reduction in MBR treating real wastewater.

Self-assembly and regeneration strategy for mitigation of membrane biofouling by the exploitation of enzymatic nanoparticles

Biofouling of membranes is an unresolved problem in the water industry. Numerous anti-biofouling membrane technologies have been proposed but the duration of their anti-fouling properties is short relative to the required lifetime of the membrane.The present work investigated a facile renewable anti-biofouling layer strategy whereby smart enzymatic nanomaterials are self-assembled onto a commercial membrane surface, creating a pH-triggered releasable and regenerable anti-biofouling system. The Proteinase-K-functionalized-PEGylated-silica (SPK) nanoparticles were characterized both chemically and biologically. These smart enzymatic particles demonstrated an excellent capability of against Pseudomonas fluorescens biofilms, and their activity persisted for at least 45 days in synthetic wastewater. Surface morphology and analysis of chemical compositions showed that these smart nanoparticles generated an anti-biofouling layer on the cellulose-based membrane surface through a submersion method, attributed to the strong noncovalent affinity-interactions between the particles and membrane. The SPK anti-biofouling layer stably attached to the membrane surfaces in synthetic wastewater (pH 7.4), whilst having the capacity to be released for regeneration in a pH 10 solution. Regeneration was accomplished by simple reloading of fresh particles on the membrane. Filtration tests revealed that the SPK anti-biofouling layer negligibly affected on membrane permeance while effectively mitigated membrane biofouling. Besides significant improvement in filtration fluxes, the SPK assembled membrane efficiently reduced the irreversible fouling and bacterial coverages on the membrane surface.