Severe Biofouling Research Articles

Biofouling effect of different landfill leachates on high-density polyethylene pipe material

Pipelines used for collecting and transporting landfill leachates may be affected by biofouling, subsequently posing environmental risks. This study investigates the surface biofouling on high-density polyethylene (HDPE) pipes immersed in leachates acquired from operating (MSW-1) and closed (MSW-2) landfills and from a landfill containing incinerated bottom ash and municipal waste (MSW-3). Water quality monitoring, material characterization, and microbial high-throughput sequencing analysis were conducted to analyze the biofouling effects of different landfill leachates on HPDE pipes. The total fouling masses in the MSW-1, MSW-2, and MSW-3 leachates were 29.2 %, 35.2 %, and 24.5 %, respectively; MSW-2 depicted severe biofouling. The biofouling mass was dominated by living mycobacterial cells (69.93 % of the total biovolume). Proteobacteria was the dominant phylum (30.43 %) and the key bacteria group to cause biofouling. The leachates had a significant impact on the microbial community structure, with Castellaniella and Luteibacter being the endemic genera in MSW-3 and norank_f__Rhodothermaceae being the endemic genera in MSW-1 and MSW-2. Furthermore, Ca2+ was the dominant water-quality parameter to affect the distribution of microbial communities. This study provides valuable insights for pipeline disinfection and sterilization to mitigate bio-clogging in HDPE pipes.

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.

An antifouling electrochemical biosensor based on oxidized bacterial cellulose and quaternized chitosan for reliable detection of involucrin in wound exudate

The monitoring of biomarkers in wound exudate is of great importance for wound care and treatment, and electrochemical biosensors with high sensitivity are potentially useful for this purpose. However, conventional electrochemical biosensors always suffer from severe biofouling when performed in the complex wound exudate. Herein, an antifouling electrochemical biosensor for the detection of involucrin in wound exudate was developed based on a wound dressing, oxidized bacterial cellulose (OxBC) and quaternized chitosan (QCS) composite hydrogel. The OxBC/QCS hydrogel was prepared using an in-situ chemical oxidation and physical blending method, and the proportion of OxBC and QCS was optimized to achieve electrical neutrality and enhanced hydrophilicity, therefore endowing the hydrogel with exceptional antifouling and antimicrobial properties. The involucrin antibody SY5 was covalently bound to the OxBC/QCS hydrogel to construct the biosensor, and it demonstrated a low limit of detection down to 0.45 pg mL−1 and a linear detection range from 1.0 pg mL−1 to 1.0 μg mL−1, and it was capable of detecting targets in wound exudate. Crucially, the unique antifouling and antimicrobial capability of the OxBC/QCS hydrogel not only extends its effective lifespan but also guarantees the sensing performance of the biosensor. The successful application of this wound dressing, OxBC/QCS hydrogel for involucrin detection in wound exudate demonstrates its promising potential in wound healing monitoring.

Multi-layer structure toward simultaneous enhancement of forward osmosis membrane separation performance and anti-biofouling property

Biofouling is a critical issue in membrane-based water-treatment processes because the feed solution retains microorganisms despite rigorous pretreatment. The forward osmosis (FO) process has a drawback of severe biofouling tendency when the active layer faces the draw solution. Here, we fabricated a thin-film nanocomposite membrane with a multilayer structure consisting of an MXene/carbon nanotubes (MXene/CNT) interlayer and a CNT back layer (TFNi-CNT). The interlayer structure significantly enhanced the membrane separation performance whereas the CNT back layer did not significantly hamper the performance. The biofilm formed on the CNT back layer surface was reduced by approximately 90% compared to that on the pristine substrate, indicating that the CNT back layer has superior antibiofilm properties. The water flux of the TFNi-CNT membrane was well-maintained (approximately 46%) and reversibly recovered through facile physical flushing, even after four dynamic biofouling cycles, whereas that of the pristine membrane was reduced to approximately 10%. These results indicated that the TFNi-CNT membrane possesses excellent resistance to biofouling. The CNT layer acts as a barrier that effectively prevents bacteria from entering the inner porous substrate, thus alleviating the detrimental biofilm-enhanced internal concentration polarization. This study provides new insights into the rational design and fabrication of FO membranes to mitigate biofouling.

Blood compatible, fog-, frost- and bacterial-resistant dopamine-enabled zwitterionic glass interfaces

BackgroundHydration is at the core of the mechanisms rationalizing the ability of hydrophilic interfaces to resist fogging, frosting and biofouling, and to be hemocompatible. Although essential, very few biomedical interfaces and devices possess this set of properties. MethodsThis study sheds light on this combination of properties imparted to glass by a dopamine-enabled grafting of poly(sulfobetaine methacrylate) moieties. Water contact angle (WCA), fogging, frost resistance antifouling and blood compatibility tests were then conducted. Significant FindingsThe very low WCA measured on the glass surface (8.4°) permitted to inhibit condensation and maintain optical transparency, whereas other hydrophilic graftings prepared using hydroxyethylmethacyrlate (HEMA) or poly(ethylene glycol) methyl ether acrylate (PEGMA) lost 15% of their optical transparency. The strong hydration layer provided by the zwitterionic grafting almost entirely inhibited frost formation. While the virgin glass suffered from severe biofouling by various types of cells found in the medical field including Pseudomonas aeruginosa and whole blood, the grafted glass materials resisted biofouling efficiently (90% and 99% decrease using bacteria and whole blood, respectively). Hemocompatibility was supported by negligible haemolyis activity, and activated partial thromboplastin time (APTT, 32.1 s) and prothrombin time (PT, 10.4 s) comparable to those measured with whole blood. Stability was also proven by carrying out antifouling tests after 1 month-immersion in an ultrasonic bath. Thus, these zwitterionic glass materials have potential for application in the biomedical field.

Controls of Aurelia coerulea and Nemopilema nomurai (Cnidaria: Scyphozoa) blooms in the coastal sea of China: Strategies and measures

Outbreaks of scyphozoan Aurelia coerulea and Nemopilema nomurai in the coastal sea of China are managed in recent years because they have severely jeopardized local socioeconomic development and ecological health. In this study, we propose specific strategies to control these blooms based on the different physio-ecological characteristics of their polyps, which can produce medusae by strobilation. High densities of A. coerulea polyps can survive chronically on the surfaces of some artificial constructions submerged in harbors or bays, China. Through buddings, they can resist the invasion of biofouling organisms and proliferate on the surfaces of some fouling organisms (e.g., ascidians, and bryozoans). However, N. nomurai polyps have not been recorded in natural environment. The in situ experiments found that polyps on settling plates fail to survive via podocysts due to severe biofouling invasion and post-strobilated degeneration in late spring and summer. As a result, the population size following is strongly dependent on the sexual recruitment of medusae during late summer and autumn. Therefore, we suggest that the reasonable governance strategy is to manage polyp populations together with biofouling organisms for A. coerulea blooms, however, with a focus on the medusa stage (particularly young medusae) to decrease the sexual reproduction in N. nomurai blooms. Accordingly, massive occurrences of A. coerulea in Qingdao Middle Port, China were alleviated by eliminating polyps and biofouling organisms on the undersurfaces of floating docks and then brushing the surfaces with modified alloprene paints. Some applicable control measures, including resource utilization of N. nomurai medusae and more severe and earlier summer fishing moratoriums, were used to possibly help restrain outbreaks of N. nomurai in Chinese coastal waters.

Comparison of disinfection-residual-bacteria (DRB) after seven different kinds of disinfection: Biofilm formation, membrane fouling and mechanisms

Membrane fouling is the Achilles' heel of the reverse osmosis (RO) system for high-quality reclaimed water production. Previous studies have found that after the significant selection effect of traditional disinfection, the remaining disinfection-residual bacteria (DRB) may possess more severe biofouling potentials. To provide more constructive advice for the prevention of biofouling, we compared the RO membrane fouling characteristics of DRB after using five commonly used disinfection methods (NaClO, NH2Cl, ClO2, UV, and O3) and two novel disinfection methods (K2FeO4 and the flow-through electrode system (FES)). Compared with the control group (undisinfected, 21.1 % flux drop), the UV-DRB biofilm aggravated biofouling of the RO membrane (23.4 % flux drop), while the FES, K2FeO4, and NH2Cl treatments showed less severe biofouling, with final flux drops of 6.9 %, 8.1 %, and 8.1 %, respectively. Adenosine triphosphate (ATP) was found to be a capable indicator for predicting the biofouling potential of DRB. Systematic analysis showed that the thickness and density of the DRB biofilms were most closely related to the different fouling degree of RO membranes. Moreover, the relative abundance of bacteria with higher extracellular polymeric substance (EPS) secretion levels, such as Pseudomonas and Sphingomonas, was found closely related with the biofouling degree of RO membranes.

Functional DNA-peptide conjugates with enhanced antifouling capabilities for electrochemical detection of proteins in complex human serum

Electrochemical biosensors with high sensitivity and cost-effectiveness, are considered as a promising alternative to existing clinical diagnostic techniques, but their practical assaying application in complex biological samples was significantly limited by the severe biofouling. Herein, an electrochemical biosensing platform with enhanced antifouling abilities was constructed based on a designed DNA-peptide conjugate, which was synthesized with an anchoring DNA and a difunctional (antifouling and recognizing) peptide. The DNA-peptide conjugates were easily immobilized onto an electrode, which was modified with poly(3,4-ethylenedioxythiophene) (PEDOT) and gold nanoparticles (AuNPs), through the interaction between the anchoring DNA and AuNPs, and the recognizing peptide was specific for the binding of target human immunoglobulin G (IgG). As both the anchoring DNA and the difunctional peptide possessed antifouling abilities, the IgG biosensor based on the DNA-peptide conjugates exhibited enhanced antifouling properties, and it was capable of detecting IgG directly in real human serum, with a wide linear range from 0.1 ng·mL−1-10 μg·mL−1 and a low limit of detection (0.037 ng·mL−1). The strategy of developing biosensors with functional DNA-peptide conjugates as antifouling materials offered an effective and simple way to achieve low fouling protein detection in complex human serum.

Functionalization of PEG-AgNPs Hybrid Material to Alleviate Biofouling Tendency of Polyethersulfone Membrane.

Membrane-based processes are a promising technology in water and wastewater treatments, to supply clean and secure water. However, during membrane filtration, biofouling phenomena severely hamper the performance, leading to permanent detrimental impacts. Moreover, regular chemical cleaning is ineffective in the long-run for overcoming biofouling, because it weakens the membrane structure. Therefore, the development of a membrane material with superior anti-biofouling performance is seen as an attractive option. Hydrophilic-anti-bacterial precursor polyethylene glycol-silver nanoparticles (PEG-AgNPs) were synthesized in this study, using a sol-gel method, to mitigate biofouling on the polyethersulfone (PES) membrane surface. The functionalization of the PEG-AgNP hybrid material on a PES membrane was achieved through a simple blending technique. The PES/PEG-AgNP membrane was manufactured via the non-solvent induced phase separation method. The anti-biofouling performance was experimentally measured as the flux recovery ratio (FRR) of the prepared membrane, before and after incubation in E. coli culture for 48 h. Nanomaterial characterization confirmed that the PEG-AgNPs had hydrophilic-anti-bacterial properties. The substantial improvements in membrane performance after adding PEG-AgNPs were evaluated in terms of the water flux and FRR after the membranes experienced biofouling. The results showed that the PEG-AgNPs significantly increased the water flux of the PES membrane, from 2.87 L·m−2·h−1 to 172.84 L·m−2·h−1. The anti-biofouling performance of the PES pristine membrane used as a benchmark showed only 1% FRR, due to severe biofouling. In contrast, the incorporation of PEG-AgNPs in the PES membrane decreased live bacteria by 98%. It enhanced the FRR of anti-biofouling up to 79%, higher than the PES/PEG and PES/Ag membranes.

The critical role of feed spacer channel porosity in membrane biofouling: Insights and implications

Membrane biofouling is a major hindrance limiting the efficiency of spiral wound membrane (SWM) module for water treatment. Feed spacer is an imperative component of SWM module which creates feed channels, determines fluid field and thus influences biofilm development via its geometry. Yet, the role of feed spacer channel porosity in biofilm development remains unclear. In this study, 16 feed spacers of varied geometric parameters and thus different channel porosities were used for both numerical simulations and biofouling experiments. Results showed that the hydraulic and anti-biofouling performances were more sensitive to the variation of filament diameter and spacer thickness. Feed channel porosity as a gross parameter played a pivotal role in biofouling development. The high-porosity (> 0.85) feed spacer channels exhibited a slower increase of feed channel pressure drop when biofouling occurred, but with more biomass accumulated in the middle of spacer meshes because of lower shear stress. For the low-porosity (< 0.75) channels, biofilm incipiently developed from the interspace region between spacer filaments and membrane surface due to “block effect”, which aggravated “narrow channeling” and induced a larger area of dead zone, leading to more severe biofouling ultimately. An appropriate channel porosity was suggested at ∼0.85 based on the hydraulic and anti-biofouling performances conjointly in this study.

Predictive Maintenance of Floating Offshore Wind Turbine Mooring Lines using Deep Neural Networks

Abstract The recent massive deployment of onshore wind farms has caused controversy to arise mainly around the issues of land occupation, noise and visual pollution and impact on wildlife. Fixed offshore turbines, albeit beneficial in those aspects, become economically unfeasible when installed far away from coastlines. The possibility of installing floating offshore wind turbines is currently hindered by their excessive operation and maintenance costs. We have developed a comprehensive model to help companies plan their operations in advance by detecting failure in mooring lines in almost real time using supervised deep learning techniques. Given the lack of real data, we have coupled numerical methods and OpenFAST simulations to build a dataset containing the displacements and rotations of a turbine’s floating platform across all directions. These time series and their corresponding frequency spectra are used to obtain a set of key statistical parameters, including means and standard deviations, peak frequencies, and several relevant momenta. We have designed and trained a Deep Neural Network to understand and distinguish amongst a series of common failure modes for mooring lines considering a range of metocean and structural conditions. We have obtained promising results when monitoring severe changes in the line’s mass and damping using short time spans, achieving a 95.7% validation accuracy when detecting severe biofouling failure.

Antifouling Electrochemical Biosensor Based on the Designed Functional Peptide and the Electrodeposited Conducting Polymer for CTC Analysis in Human Blood.

Circulating tumor cells (CTCs) are considered reliable cancer biomarkers for the liquid biopsy of many types of tumors. The direct detection of CTCs in human blood with normal biosensors, however, remains challenging because of severe biofouling in blood that contains various proteins and a large number of cells. Herein, we report the construction of an antifouling electrochemical biosensor capable of assaying CTCs directly in blood, based on a designed multifunctional peptide and the electrodeposited conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The designed peptide possesses antifouling capability in complex biological media and specific recognition ability to capture breast cancer cells MCF-7. Meanwhile, electrodeposited PEDOT can promote electron transfer at the sensing interface, improve the signal-to-noise ratio for the detection, and thus enhance the sensitivity of the biosensor. The integration of the multifunctional peptide and conducting polymer PEDOT ensures that the developed biosensor is able to perform directly in blood samples without purification or separation. The antifouling electrochemical biosensor for the detection of MCF-7 cells exhibits a wide linear range over 4 orders, with a limit of detection (LOD) of 17 cells mL-1. More interestingly, even when performing in 25% human blood, the biosensor still retains a linear response with an LOD of 22 cells mL-1, without suffering significantly from biofouling in real blood. This work provides a promising strategy for the direct analysis of CTCs in human blood without a complicated pretreatment, and it may find practical application in the liquid biopsy of cancers.

Effects of reverse solute diffusion on membrane biofouling in pressure-retarded osmosis processes

Biofouling is a critical bottleneck in pressure-retarded osmosis (PRO), as the feed solution inevitably contains microorganisms. Reverse solute diffusion (RSD) from the draw solution may alter biofouling tendency. However, no study has yet explored the relationship between RSD and biofouling in PRO. Here, we investigated the influence of applied hydraulic pressure (ΔP) and draw solution types on RSD properties and solute concentrations in the support layer. RSD of Na+ induced a similar biofouling extent under different ΔP values because the solute concentrations were similar at the support-active layer interface, despite an increased reverse solute flux. Contrarily, RSD of Ca2+ triggered increased water flux decline and severe biofouling in PRO because Ca2+ induced increased bacterial growth and extracellular polymeric substance formation. RSD of Mg2+ exhibited insignificant effects on biofouling in PRO due to the negligible effects of Mg2+ on biofilm formation. We further revealed the roles of influencing factors (ΔP, draw solution type and concentration) on biofouling in PRO. Although ΔP had no significant influence on biofouling, draw solution type and concentration markedly altered biofouling extent in PRO. Collectively, this study provides a comprehensive understanding of the effects of RSD on biofouling and novel insights into biofouling control strategies in PRO.

Photocatalytic quorum quenching: A new antifouling and in-situ membrane cleaning strategy for an external membrane bioreactor coupled to UASB

Microbial quorum sensing (QS) induces biofilm formation on the membrane surfaces leading to severe biofouling, which remains a major bottleneck for membrane-based systems. Here, we report an effective UV photocatalytic quorum quenching (QQ) strategy in an integrated upflow anaerobic sludge blanket – photocatalytic membrane reactor (UASB-PMR) system, where TiO2 nanoparticles immobilized in porous polymeric beads were kept in suspension as the photocatalysts. The UASB unit reached a methane yield of 0.30 ± 0.05 L CH4/g COD removal while treating the synthetic wastewater, slightly higher than a typical internal anaerobic membrane bioreactor (AnMBR). This novel system showed 7-fold higher efficacy in membrane fouling control than the UV photolytic QQ system (19.1 ± 2.4 d vs. 2.7 ± 1.0 d) under intermittent UV irradiation (17% of total operation time). Continuous UV irradiation, both in photolytic and photocatalytic QQ, significantly alleviated membrane biofouling, while long-term UV exposure exerted some changes in the surface properties of the membranes, which were not observed under intermittent UV irradiation. The reactive oxygen species (ROS) generated by the UV-excited TiO2 not only oxidized the foulants on the membrane surface, but also quenched acyl-homoserine lactones (AHLs), the QS signal molecules, thus retarding membrane fouling to the maximum extent. Additionally, in-situ membrane cleaning, enhanced COD removal, and almost complete disinfection of the effluent were realized in the photocatalytic QQ system. Equipped with these advantages, this innovative photocatalytic QQ can be a readily implementable strategy to prevent fouling in external membrane bioreactors (MBRs) for the pilot- and/or full-scale applications.

Considerations to Approach Membrane Biofouling in Microbial Fuel Cells

Among bioelectrochemical systems, those referred to as microbial fuel cells (MFCs) are widely implemented for wastewater management and simultaneous recovery of electrical energy. MFCs are fundamentally assisted by bacterial populations, mostly mixed cultures to be more exact that, after oxidizing the substrate, are capable of facilitating the passage of electrons to an electron acceptor, usually the anode. However, certain undesired bacterial strains often colonize not only the electrode but the membrane separator over time and cause severe biofouling. The membrane is an architectural element of many MFCs and determines the efficiency of the system. In this paper, this issue is overviewed briefly and some considerations concerning how to approach the problem are presented.

Nanofiltration in pilot scale for wastewater reclamation: Long-term performance and membrane biofouling characteristics

Nanofiltration (NF) has been recognized as a cost-effective membrane technology for wastewater reclamation, while little information is available about its performance in pilot scale for practical engineering application. In addition, the biofouling issue is always a barrier to membrane process for its long-term stable operation which requires further investigations. In this study, the performance of a pilot-scale two-stage NF system was continually monitored for three months. The membrane autopsy characterization was conducted when the irreversible membrane fouling occurred. The rejections of COD, TOC and TP by NF were 96.5 ± 1.2%, 91.9 ± 1.9% and 97.7 ± 2.1%, respectively. A total of 23 emerging contaminants have been detected in NF influent, including 19 pharmaceuticals and personal care products (PPCPs) and four environmental estrogens (EEs). Except for bisphenol A (57.6%) and ibuprofen (69.9%), the rejections of other 21 emerging contaminants were all higher than 80% by the NF system. Microbial community structure analysis showed that Proteobacteria and Bacteroidetes were the two predominant bacteria on the membrane surface with percentages of 34.1%-41.0% and 23.4%-30.6% at phylum level, respectively. At genus level, Stenotrophomonas and Pseudoxanthomonas were primarily dominant in the first stage, while Cloacibacterium and Methyloversatilis showed higher relative abundances in the second stage. Sphingopyxis was an extremely stubborn genus on the membrane surface. Besides, the biodiversity of microbial communities in the first stage was higher than that in the second stage, possibly showing more severe biofouling in the first stage of the two-stage NF system. This study has provided insights to understand the practical performance of NF technology in pilot scale and could give guideline for biofouling control in NF engineering application.

Stimulatory effects on bacteria induced by chemical cleaning cause severe biofouling of membranes

Abstract Chemical cleaning with hypochlorite is routinely used in membrane-based processes. However, a high-transient cleaning efficiency does not guarantee a low biofouling rate when filtration is restarted, with the physiological mechanisms largely remaining unknown. Herein, we investigated the microbial regrowth and surface colonization on membrane surfaces after NaOCl cleaning had been completed. Results of this study showed that the regrowth of model bacteria, Pseudomonas aeruginosa, was initially subject to inhibition due to the damage of key enzymes' activity and the accumulation of intracellular reactive oxygen species although the oxidative stress induced by NaOCl had been removed. However, with the resuscitation ongoing, the stimulatory effects became obvious, which was associated with the enhanced production of N-acyl homoserine lactones and the secretion of eDNA that ultimately led to more severe biofouling on the membrane surface. This study elucidates the inhibition–stimulation mechanisms involved in biofilm reformation (membrane biofouling) after membrane chemical cleaning, which is of particular significance to the improvement of cleaning efficiency and application of membrane technologies.

Fouling properties of reverse osmosis membranes along the feed channel in an industrial-scale system for wastewater reclamation

Membrane fouling is an inevitable disadvantage of the reverse osmosis (RO) process for wastewater reclamation. In order to clarify the development process of membrane fouling, all the fouled membranes along a feed channel of a two-stage industrial-scale RO system for wastewater reclamation (six elements in each stage) were autopsied and analyzed.The water flux and salt rejection efficiency of the fouled membranes at the head and tail were the lowest among 12 elements, thereby indicating more severe fouling on these membranes. In this RO system, most of the organic compounds deposited on the head elements of each stage were mainly composed of proteins, polysaccharides, and fulvic acid. The ATP concentrations of the foulants on the first and twelfth elements were much higher than those of the other elements, suggesting severe biofouling. Although microbes can cause organic fouling owing to extracellular polymeric substances production, no clear correlation was found between organic fouling and biofouling in this study. For example, the ATP concentrations on the second element and seventh element were similar (1.16 ng/cm2 and 1.26 ng/cm2, respectively), thereby suggesting a similar extent of biofouling, but organic fouling of the second element was relatively slight (DOC: 24.8 mg/m2) compared with that of the seventh element (DOC: 46.2 mg/m2). The seventh element (ATP: 1.26 ng/cm2) was more severely biofouled than the eighth element (ATP: 0.15 ng/cm2), but they suffered from the same level of organic fouling (DOC: 46.2 mg/m2 and 47.1 mg/m2, respectively). Approximately 70% of metallic elements, predominantly Fe, were deposited on the first element. Although the concentration of Fe in the feed water was much lower than those of Ca and Mg, the concentration of Fe on the first three elements was significantly higher than that of any other element, suggesting that Fe was more easily deposited on the RO membranes.

Universal surface modification using dopamine-hyaluronic acid conjugates for anti-biofouling

Various materials are used to make implantable devices such as pumps, catheters, and stimulators. However, such implants inevitably undergo biofouling, which is associated with non-specific proteins and cell adhesion on the material surfaces. Severe biofouling often leads to adverse tissue reactions, such as foreign body responses, and thick scar tissue formation around the implantation, which in turn hampers the function and performance of the implants. Herein, a simple and effective surface modification method using dopamine-hyaluronic acid conjugate (DA-HA) is demonstrated to implement anti-biofouling in various biomaterials. DA-HA was synthesized and utilized as a coating material and five commonly used implantable substrates (i.e., polyimide (PI), gold (Au), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE), and polyurethane (PU)) were tested for modification with DA-HA. Highly hydrophilic HA chains were immobilized on the substrate surfaces through self-polymerization of DA-HA at an alkaline pH. The DA-HA-modified substrates displayed significant resistance to both non-specific protein adsorption and cell adhesion on the surfaces. In addition, a reduction in scar tissue formation was observed in the DA-HA-coated substrates compared to the unmodified bare substrates after a 4-week subcutaneous implantation. This universal surface coating can be further implemented in various biomedical applications in which severe biofouling is highly undesirable.

Improved anti-biofouling performance of polyamide reverse osmosis membranes modified with a polyampholyte with effective carboxyl anion and quaternary ammonium cation ratio

Biofouling is a serious problem in reverse osmosis (RO) membrane processes. In this paper, a polyamide RO membrane was modified with a polyampholyte composed of anionic 2-carboxyethyl acrylate (CAA) and cationic [2-(acryloyloxy)ethyl] trimethyl ammonium chloride (TMA) by surface-initiated atom transfer radical polymerization, in order to improve its anti-biofouling properties. The anti-biofouling properties of membranes with different CAA/TMA surface ratios were evaluated by protein adsorption, static bacterial attachment, and long-term dynamic biofouling filtration experiments. It was found that an electrostatic attraction resulted in a severe biofouling, even if the water contact angle was 5–20° and the membrane hydrophilicity was sufficiently high. However, the RO membrane with CAA/TMA surface ratio of 1:1, fabricated from a mixed monomer solution with 3:1 CAA/TMA ratio showed an excellent anti-biofouling performance even in long-term dynamic biofouling filtration experiments. These good anti-biofouling properties derive from the high hydrophilicity of the membrane surface, resulting from its large content of ionic groups, and the almost complete lack of electrostatic attractions with charged bacteria, because the net surface charge is close to zero.