Biofouling Control Strategies Research Articles

Zwitterionic functionalized chitosan with dual-antifouling for selective uranium extraction

Uranium adsorbents deployed in natural water environments rich in microorganisms for a long time are inevitably affected. Biofouling severely reduces the uranium adsorption performance and damages the structure of the adsorbents. Therefore, antifouling performance is necessary for adsorbents that extract uranium from seawater and uranium-containing groundwater. Previously reported antifouling uranium adsorbents mainly have two types: single antibacterial or anti-adhesion, and few studies have developed dual-antifouling adsorbents that combine the two antifouling pathways. In this study, a dual-antifouling adsorbent CS-MPC with both anti-adhesion and antibacterial properties was constructed. The synergistic effect of the superhydrophilic 2-methylacryloxyethyl phosphocholine (MPC) and the natural bactericidal chitosan (CS) enabled the inhibition rate of dual-antifouling CS-MPC against various bacteria to exceed 99 %. Furthermore, the uranium adsorption capacity of CS-MPC was 579 mg/g in simulated uranium-containing groundwater and 8.28 mg/g after immersion for 42 days in real seawater. The SA/CS-MPC composite beads prepared to solve powder defects also exhibited good dual-antifouling activity and uranium adsorption properties, making them potential candidates for uranium extraction. The construction of dual-antifouling adsorbents provides a new strategy for effective biofouling control.

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.

Enhancing quorum quenching media with 3D robust electrospinning coating: A novel biofouling control strategy for membrane bioreactors

Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality.

Biofouling Control in an Anaerobic Membrane Bioreactor with Indigenous Quorum Quenching Bacterium Micrococcus luteus Strain AnQ-m1

This study isolated and screened indigenous strains quenching the acyl homoserine lactone (AHL)-mediated quorum sensing system and investigated the effectiveness of a selected strain for biofouling control in a laboratory-scale anaerobic membrane bioreactor (AnMBR). Among the 11 facultative anaerobes isolated from anaerobic sludge, Micrococcus luteus strain AnQ-m1 was screened out as the most potent AHL degrader. Its AHL degradability was further examined while encapsulating the cells in polysulfone–alginate beads to optimize the encapsulation medium recipe. The QQ beads with immobilized AnQ-m1 cells retarded the apparent membrane fouling rate by 2.2 times compared with the AnMBR with vacant beads. C8-HSL, the dominant AHL in AnMBRs, was effectively (∼70%) quenched in the QQ-AnMBR before the membrane was fouled; however, its concentration was increased to the normal level when the membrane was fouled. Polysaccharides in a loosely bound extracellular polymeric substance were gradually reduced at a constant rate during the QQ stage, while the indigenous QQ strain barely affected the microbial community structure of the bulk sludge and the water treatment performance of the AnMBR. These findings provide new insights into the QQ-based biofouling control strategy and highlight the beneficial effects of indigenous QQ strains on AnMBR stability.

Hydrodynamic conditions affect the proteomic profile of marine biofilms formed by filamentous cyanobacterium

Proteomic studies on cyanobacterial biofilms can be an effective approach to unravel metabolic pathways involved in biofilm formation and, consequently, obtain more efficient biofouling control strategies. Biofilm development by the filamentous cyanobacterium Toxifilum sp. LEGE 06021 was evaluated on different surfaces, glass and perspex, and at two significant shear rates for marine environments (4 s−1 and 40 s−1). Higher biofilm development was observed at 4 s−1. Overall, about 1877 proteins were identified, and differences in proteome were more noticeable between hydrodynamic conditions than those found between surfaces. Twenty Differentially Expressed Proteins (DEPs) were found between 4 s−1 vs. 40 s−1. On glass, some of these DEPs include phage tail proteins, a carotenoid protein, cyanophynase glutathione-dependent formaldehyde dehydrogenase, and the MoaD/ThiS family protein, while on perspex, DEPs include transketolase, dihydroxy-acid dehydratase, iron ABC transporter substrate-binding protein and protein NusG. This study contributes to developing a standardized protocol for proteomic analysis of filamentous cyanobacterial biofilms. This kind of proteomic analysis can also be useful for different research fields, given the broad spectrum of promising secondary metabolites and added-value compounds produced by cyanobacteria, as well as for the development of new antibiofilm strategies.

Permeation Increases Biofilm Development in Nanofiltration Membranes Operated with Varying Feed Water Phosphorous Concentrations.

Nutrient limitation has been proposed as a biofouling control strategy for membrane systems. However, the impact of permeation on biofilm development under phosphorus-limited and enriched conditions is poorly understood. This study analyzed biofilm development in membrane fouling simulators (MFSs) with and without permeation supplied with water varying dosed phosphorus concentrations (0 and 25 μg P·L−1). The MFSs operated under permeation conditions were run at a constant flux of 15.6 L·m2·h−1 for 4.7 days. Feed channel pressure drop, transmembrane pressure, and flux were used as performance indicators. Optical coherence tomography (OCT) images and biomass quantification were used to analyze the developed biofilms. The total phosphorus concentration that accumulated on the membrane and spacer was quantified by using microwave digestion and inductively coupled plasma atomic emission spectroscopy (ICP-OES). Results show that permeation impacts biofilm development depending on nutrient condition with a stronger impact at low P concentration (pressure drop increase: 282%; flux decline: 11%) compared to a higher P condition (pressure drop increase: 206%; flux decline: 2%). The biofilm that developed at 0 μg P·L−1 under permeation conditions resulted in a higher performance decline due to biofilm localization and spread in the MFS. A thicker biofilm developed on the membrane for biofilms grown at 0 μg P·L−1 under permeation conditions, causing a stronger effect on flux decline (11%) compared to non-permeation conditions (5%). The difference in the biofilm thickness on the membrane was attributed to a higher phosphorus concentration in the membrane biofilm under permeation conditions. Permeation has an impact on biofilm development and, therefore, should not be excluded in biofouling studies.

Novel strategy for membrane biofouling control in MBR with nano-MnO2 modified PVDF membrane by in-situ ozonation

In this study, ozonation catalyst nano-MnO2 blended polyvinylidene fluoride (PVDF) membrane was fabricated via phase inversion method and applied to membrane bioreactors (MBR), and then coupled with in-situ ozonation to study the anti-biofouling performance and reveal its mechanism. Results showed that, compared with pristine PVDF membrane (MBR_M0), 0.75 wt% and 1.00 wt% nano-MnO2 modified PVDF membrane (MBR_M0.75 and MBR_M1.00) could mitigate the membrane biofouling rate. Meanwhile MBR_M1.00 coupled with in-situ ozonation could increase the membrane cleaning cycle to 1.5 and 2.7 times, compared with MBR_M0 and MBR_M0.75 without in-situ ozonation. The possible mechanisms included that the nano-MnO2 modification coupled with in-situ ozonation directly removed the biofouling on the membrane surface, improved the hydrophilicity of the membrane surface and enhanced the chemical oxidation and biodegradation of membrane biofouling contaminants in the sludge mixture. The results of this work provide a new strategy for the control of membrane biofouling in MBR to treat industrial wastewater.

Phosphorus Concentration in Water Affects the Biofilm Community and the Produced Amount of Extracellular Polymeric Substances in Reverse Osmosis Membrane Systems.

Biofouling is a problem that hinders sustainable membrane-based desalination and the stratification of bacterial populations over the biofilm’s height is suggested to compromise the efficiency of cleaning strategies. Some studies reported a base biofilm layer attached to the membrane that is harder to remove. Previous research suggested limiting the concentration of phosphorus in the feed water as a biofouling control strategy. However, the existence of bacterial communities growing under phosphorus-limiting conditions and communities remaining after cleaning is unknown. This study analyzes the bacterial communities developed in biofilms grown in membrane fouling simulators (MFSs) supplied with water with three dosed phosphorus conditions at a constant biodegradable carbon concentration. After biofilm development, biofilm was removed using forward flushing (an easy-to-implement and environmentally friendly method) by increasing the crossflow velocity for one hour. We demonstrate that small changes in phosphorus concentration in the feed water led to (i) different microbial compositions and (ii) different bacterial-cells-to-EPS ratios, while (iii) similar bacterial biofilm populations remained after forward flushing, suggesting a homogenous bacterial community composition along the biofilm height. This study represents an exciting advance towards greener desalination by applying non-expensive physical cleaning methods while manipulating feed water nutrient conditions to prolong membrane system performance and enhance membrane cleanability.

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.

Biological-based control strategies for MBR membrane biofouling: a review.

Membrane bioreactor (MBR) technology has been paid extensive attention for wastewater treatment because of its advantages of high effluent quality and minimized occupation space and sludge production. However, the membrane fouling is always an inevitable problem, which causes high operation and maintenance costs and prevents the wide use of MBR technology. The membrane biofouling is the most complicated and has relatively slow progress among all types of fouling. In recent years, many membrane biofouling control methods have been developed. Different from the physical or chemical methods, the biological-based strategies are not only more effective for membrane biofouling control, but also milder and more environment-friendly and, therefore, have been increasingly employed. This paper mainly focuses on the mechanism, unique advantages and development of biological-based control strategies for MBR membrane biofouling such as quorum quenching, uncoupling, flocculants and so on. The paper summarizes the up-to-date development of membrane biofouling control strategies, emphasizes the advantages and promising potential of biological-based ones, and points out the direction for future studies.

Experimental Assessment of a Conducting Polymer (PEDOT) and Microbial Biofilms as Deterrents and Facilitators of Macro-Biofouling: Larval Settlement of the Barnacle Notobalanus flosculus (Darwin, 1854) from Central Chile

Maritime enterprises have long sought solutions to reduce the negative consequences of the settlement and growth of marine biofouling (micro- and macro-organisms) on virtually all surfaces and materials deployed at sea. The development of biofouling control strategies requires solutions that are cost-effective and environmentally friendly. Polymer-based coatings, such as the poly (3,4-ethylenedioxythiophene) (PEDOT) and its potential applications, have blossomed over the last decade thanks to their low cost, nontoxicity, and high versatility. Here, using multiple-choice larval settlement experiments, we assessed the efficacy of PEDOT against the balanoid barnacle Notobalanus flosculus one of the most common biofouling species in Southeastern Pacific shores, and compared results against a commercially available antifouling (AF) coating, and biofilms at different stages of succession (1, 2, 4 and 8 weeks). We show that larval settlement on PEDOT-coated surfaces was similar to the settlement on AF-coated surfaces, while larvae settled abundantly on roughened acrylic and on early-to-intermediate stages of biofilm (one to four weeks old). These results are promising and suggest that PEDOT is a good candidate for fouling-resistant coating for specific applications at sea. Further studies to improve our understanding of the mechanisms of barnacle larval deterrence, as well as exposure to field conditions, are encouraged.

Novel strategy for membrane biofouling control in MBR with CdS/MIL-101 modified PVDF membrane by in situ visible light irradiation

Novel control strategies for membrane biofouling with eco-friendly photocatalytic technology are critically needed in practical operation of membrane bioreactors (MBRs). In this study, a metal-organic frameworks (MOF) based photocatalytic membrane was firstly applied in an anammox MBR for a long-term biofouling control, where bacteria were inactivated and foulants were degraded simultaneously, with environmentally friendly and renewable visible light energy. By physicochemical characterization, the synthesized photocatalyst of CdS/MIL-101 showed superior visible-light photocatalytic ability, and the 1 wt% CdS/MIL-101 modified membrane C2 showed enhanced hydrophilicity and water permeability compared with the pristine membrane C0. In the long-term operation of anammox MBRs under waterproof lights irradiation, the filtration cycles of C2 (25–26 d) were obviously extended compared with C0 (10–14 d), while their average total nitrogen removal efficiencies were comparable up to 84%, indicating an excellent biofouling alleviation effect by using C2 with a satisfactory nitrogen removal performance maintained. By analysis of the biofilm on the fouled membranes, the organic foulants (especially extracellular polymeric substances) were degraded, and the live bacteria were inactivated effectively by the photocatalytic reactions of CdS/MIL-101 on C2. In the antimicrobial tests against model bacteria, C2 exhibited remarkable antimicrobial effect against both Gram-negative and Gram-positive bacteria with visible light irradiation by destruction of cell integrity with the inhibition rate of 92% for Escherichia coli and 95% for Staphylococcus aureus, respectively. In the model foulants (bovine serum albumin, sodium alginate, and humic acid) filtration tests, C2 showed higher antifouling capabilities, lower flux declining rates, and higher foulants rejection rates under visible light irradiation compared with C0. The reactive species of ·OH, e– and h+ generated on C2 were verified to play the predominant role in the anti-biofouling processes by simultaneous bacteria inactivation and foulants degradation. The findings offer a novel insight into the biofouling controlling in MBRs by simultaneous bacteria inactivation and foulants degradation with an eco-friendly method.

A simple reaction-diffusion model for initial stages of biofouling in reverse osmosis membranes

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes and consequently increases operational and maintenance costs. It is difficult to control this operational challenge, so the development of effective biofouling monitoring and control methods and strategies is a critical issue for membrane technology and applications. In this work, we develop a simulation approach for evaluating the operational time of reverse osmosis (RO) membranes based on a reaction-diffusion (RD) type of model. This approach would help to understand different factors involved in the formation of biofilms including microbial population dynamics (replication and death rates of microbial cells) and nutrient consumption. The model is focused on the initial stages of the membrane biofouling that is initiated by attachment of microbial species to the membrane leading to pore blocking followed by the formation of thick cake layer. We applied this approach to study the RO membrane biofouling by Picochlorum algae, the most common biofouling agent in the seawater of the Arabian Gulf, at known contents of total organic carbon and essential nutrients. We found that the biofilm growth dynamics on an RO membrane is mainly defined by the ratio of the replication and death rates of microbial cells. The proposed approach should be useful for fast evaluation of the RO membrane performance in different environmental conditions without using significant computational resources. This methodology allows generalization for multi-microbial and multi-nutrient systems. The establishment of effective fouling control strategies should decrease operational and maintenance costs of RO membrane systems.

Biofouling control by phosphorus limitation strongly depends on the assimilable organic carbon concentration

Nutrient limitation is a biofouling control strategy in reverse osmosis (RO) membrane systems. In seawater, the assimilable organic carbon content available for bacterial growth ranges from about 50 to 400 μg C·L−1, while the phosphorus concentration ranges from 3 to 11 μg P·L−1. Several studies monitored biofouling development, limiting either carbon or phosphorus. The effect of carbon to phosphorus ratio and the restriction of both nutrients on membrane system performance have not yet been investigated.This study examines the impact of reduced phosphorus concentration (from 25 μg P·L−1 and 3 μg P·L−1, to a low concentration of ≤0.3 μg P·L−1), combined with two different carbon concentrations (250 C L−1 and 30 μg C·L−1), on biofilm development in an RO system. Feed channel pressure drop was measured to determine the effect of the developed biofilm on system performance. The morphology of the accumulated biomass for both carbon concentrations was characterized by optical coherence tomography (OCT) and the biomass amount and composition was quantified by measuring total organic carbon (TOC), adenosine triphosphate (ATP), total cell counts (TCC), and extracellular polymeric substances (EPS) concentration for the developed biofilms under phosphorus restricted (P-restricted) and dosed (P-dosed) conditions.For both carbon concentrations, P-restricted conditions (≤0.3 μg P·L−1) limited bacterial growth (lower values of ATP, TCC). A faster pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 250 μg C·L−1 was dosed. This faster pressure drop increase can be explained by a higher area covered by biofilm in the flow channel and a higher amount of produced EPS. Conversely, a slower pressure drop increase was observed for P-restricted conditions compared to P-dosed conditions when 30 μg C·L−1 was dosed. Results of this study demonstrate that P-limitation delayed biofilm formation effectively when combined with low assimilable organic carbon concentration and thereby, lengthening the overall membrane system performance.

Mechanism of biofilm formation on a hydrophobic polytetrafluoroethylene membrane during the purification of surface water using direct contact membrane distillation (DCMD), with especial interest in the feed properties

The impact of feed water quality on biofilm formation during membrane distillation (MD) was investigated in this study, particularly emphasizing the interrelationship between organics, salts, and microbes. Two types of typical natural surface waters in Nanjing, China, were chosen as feed solutions for long-term MD operation, including the Qinhuai River and Xuanwu Lake. The biofilms that developed under different feed water qualities exhibited distinct Foulant compositions and structures, causing different flux decline trends for the MD system. Accordingly, two typical patterns of biofilm formation were suggested for the MD operation of the two different kinds of surface waters in this study. Organics from a primal feed solution and dead bacteria were the key to the establishment of a biofilm on the membrane, and this needs to be effectively removed from the MD system through pre-treatment and process control strategies. Finally, a feasible strategy for MD biofouling control was suggested.

Integrated Pest Management for Fouling Organisms on Boat Hulls

AbstractBoating is a major vector for aquatic invasive species that cause significant economic and ecological impacts, necessitating biofouling control that goes beyond simply maintaining boat operations. However, new regulations restricting the use of antifouling paints—a common control tactic along with hull cleaning—have not considered the consequences to invasive species management. As a result, there is a critical need for a biofouling control strategy that both protects water quality and minimizes invasive species transport. We compared recruitment of fouling organisms to experimental plates (1) treated with hull coatings after 1 month and, for copper‐based paint, after 1‐, 3‐, 6‐, and 12‐month submersion times; (2) after application of California's in‐water hull cleaning practices; and (3) among locations within and between geographically separated harbors. Copper‐based paint was initially effective at reducing fouling but lost effectiveness over time and was fouled heavily within 12 months. On plates with copper‐based paint, nonnative species typically recruited first and facilitated the recruitment of other species. Nontoxic coatings were readily fouled, and invasive species (Watersipora subatra and Hydroides spp.) settled more often on ceramic epoxy and/or siliconized epoxy (“slick”) coatings. Recruitment was higher in the harbor in the warmer water region. Depending on the harbor, W. subatra, Ciona spp., and Filograna implexa recruitment was correlated with water flow, the presence of conspecifics on the docks, or both factors. Strong seasonal recruitment was evident for Ciona spp., F. implexa, and Bugula neritina. Algae dominated the light‐exposed surfaces of plates, and invertebrates dominated the shaded surfaces. California's hull cleaning practices did not stimulate fouling, which contradicted previous findings. Our findings informed the development of an integrated pest management framework for biofouling control on boat hulls that is adaptable to different regions and boater needs. This novel approach balances effective boat operations and protection of ecosystem health while simultaneously addressing water quality and invasive species transport.

Inhibition of biofouling in membrane bioreactor by metabolic uncoupler based on controlling microorganisms accumulation and quorum sensing signals secretion.

Biofouling is a limiting bottleneck in the development of membrane bioreactor (MBR) since the birth of this technology. Recently, the biofouling control strategy based on interfering with the bacterial quorum sensing (QS) system is highly desirable for biofouling control in MBR. In this study, three lab-scale parallel MBR systems were operated over 100 days to investigate the inhibitory effect of a metabolic uncoupler (3,3',4',5-tetrachlorosalicylanilide, TCS) on biofouling and the potential mechanism for biofouling control. Compared to the control MBR, the fouling cycle duration of MBR 2 with 100μg/L TCS extended over two times. The attached biomass on membrane in MBR 2 decreased over 50% at the end of each operating period, which indicated that the addition of TCS significantly mitigated microorganisms accumulation on membrane. The content of interspecies QS signal (autoinducer-2) and intraspecific QS signals (N-octanoyl-dl-homoserine lactone, C8-HSL) was reduced by the TCS, suggesting the secretion of QS signals in MBR were affected by uncoupler. Although the addition of TCS induced brief fluctuations of extracellular proteins and polysaccharides, microorganisms seemed to rapidly acclimatize to the presence of TCS and then the secretion of extracellular polymeric substances (EPS) was inhibited by 100μg/L TCS. The continuous operation of MBR was not be affected by the low-concentration uncoupler via the analysis of substrate removal and sludge growth. This study systematically evaluated the effect and inhibitory efficiency of TCS on biofouling, biomass accumulation, QS signals, EPS and treatment performances, demonstrating the feasibility of metabolic uncoupler for biofouling control in MBR.

Role of feed water biodegradable substrate concentration on biofouling: Biofilm characteristics, membrane performance and cleanability

Biofouling severely impacts operational performance of membrane systems increasing the cost of water production. Understanding the effect of critical parameters of feed water such as biodegradable substrate concentration on the developed biofilm characteristics enables development of more effective biofouling control strategies.In this study, the effect of substrate concentration on the biofilm characteristics was examined using membrane fouling simulators (MFSs). A feed channel pressure drop (PD) increase of 200 mbar was used as a benchmark to study the developed biofilm. The amount and characteristics of the formed biofilm were analysed in relation to membrane performance indicators: feed channel pressure drop and permeate flux. The effect of the characteristics of the biofilm developed at three substrate concentrations on the removal efficiency of the different biofilms was evaluated applying acid/base cleaning.Results showed that a higher feed water substrate concentration caused a higher biomass amount, a faster PD increase, but a lower permeate flux decline. The permeate flux decline was affected by the spatial location and the physical characteristics of the biofilm rather than the total amount of biofilm. The slower growing biofilm developed at the lowest substrate concentration was harder to remove by NaOH/HCl cleanings than the biofilm developed at the higher substrate concentrations.Effective biofilm removal is essential to prevent a fast biofilm regrowth after cleaning. While substrate limitation is a generally accepted biofouling control strategy delaying biofouling, development of advanced cleaning methods to remove biofilms formed under substrate limited conditions is of paramount importance.

Influent salinity conditions affect the bacterial communities of biofouling in hybrid MBBR-MBR systems

The system performance, biomass kinetics and microbial community structure in biofouling and suspended biomass of a hybrid MBBR-MBR system operating at 6 h of hydraulic retention time subjected to four different scenarios of salinity wastewater -constant 6.5 mS cm−1, and tidal-like variable at 4.5, 6.5 and 8.5 mS cm−1 was studied. The performance of the bioreactors in terms of organic matter removal was efficient, nevertheless only the scenario of variable 4.5 mS cm−1 showed good nitrogen removal (59.59%). The salinity conditions exerted an effect over the kinetics of the system, with rates of substrate utilization dependent on substrate for variable salinity conditions and non-dependent for constant salinity conditions. Also, higher peak salinities lead to lower rates of substrate utilization. Massive parallel sequencing showed that Xanthomonadaceae family (2.57–33.00%) and Mycobacterium genus (4.70%) dominated biofouling under variable and constant salinity conditions, respectively. Principal component analyses showed higher community similarity between biofouling and suspended biomass under variable salinity conditions than for constant salinity. However, differences in biofouling-related OTUs were observed between attached and suspended communities by the means of effect size quantification. The composition of oligotypes of OTUs important for biofouling showed no differences between biofouling and suspended biomass at all salinity scenarios. The results suggested that biofouling process could be mainly determined by increases in relative abundance of biofouling-related OTUs in the attached biomass with respect to suspended biomass (25.76–204.63% increase). The results obtained will be of importance for future design and implementation of strategies for operation and biofouling control of salinity wastewater treatment systems.

Bacterial Adhesion to Ultrafiltration Membranes: Role of Hydrophilicity, Natural Organic Matter, and Cell-Surface Macromolecules.

Insight into the mechanisms underlying bacterial adhesion is critical to the formulation of membrane biofouling control strategies. Using AFM-based single-cell force spectroscopy, we investigated the interaction between Pseudomonas fluorescens, a biofilm-forming bacterium, and polysulfone (PSF) ultrafiltration (UF) membranes to unravel the mechanisms underlying early stage membrane biofouling. We show that hydrophilic polydopamine (PDA) coatings decrease bacterial adhesion forces at short bacterium-membrane contact times. Further, we find that adhesion forces are weakened by the presence of natural organic matter (NOM) conditioning films, owing to the hydrophilicity of NOM. Investigation of the effect of adhesion contact time revealed that PDA coatings are less effective at preventing bioadhesion when the contact time is prolonged to 2-5 s, or when the membranes are exposed to bacterial suspensions under stirring. These results therefore challenge the notion that simple hydrophilic surface coatings are effective as a biofouling control strategy. Finally, we present evidence that adhesion to the UF membrane surface is mediated by cell-surface macromolecules (likely to be outer membrane proteins and pili) which, upon contacting the membrane, undergo surface-induced unfolding.