Targeting N-acyl-homoserine-lactones to mitigate membrane biofouling based on quorum sensing using a biofouling reducer

Exploring novel biological anti-quorum sensing (QS) agents to control membrane biofouling is of great worth in order to allow sustainable performance of membrane bioreactors (MBRs) for wastewater treatment. In recent studies, QS inhibitors have provided evidence of alternative route to control membrane biofouling. This study investigated the role of Piper betle extract (PBE) as an anti-QS agent to mitigate membrane biofouling. Results demonstrated the occurrence of the N-acyl-homoserine-lactone (AHL) autoinducers (AIs), correlate QS activity and membrane biofouling mitigation. The AIs production in bioreactor was confirmed using an indicator strain Agrobacterium tumefaciens (NTL4) harboring plasmid pZLR4. Moreover, three different AHLs were found in biocake using thin layer chromatographic analysis. An increase in extracellular polymeric substances (EPS) and transmembrane pressure (TMP) was observed with AHL activity of the biocake during continuous MBR operation, which shows that membrane biofouling was in close relationship with QS activity. PBE was verified to mitigate membrane biofouling via inhibiting AIs production. SEM analysis further confirmed the effect of PBE on EPS and biofilm formation. These results exhibited that PBE could be a novel agent to target AIs for mitigation of membrane biofouling. Further work can be carried out to purify the active compound of Piper betle extract to target the QS to mitigate membrane biofouling.     

Microbial population dynamics and proteomics in membrane bioreactors with enzymatic quorum quenching

Quorum sensing gives rise to biofilm formation on the membrane surface, which in turn causes a loss of water permeability in membrane bioreactors (MBRs) for wastewater treatment. Enzymatic quorum quenching was reported to successfully inhibit the formation of biofilm in MBRs through the decomposition of signal molecules, N-acyl homoserine lactones (AHLs). The aim of this study was to elucidate the mechanisms of quorum quenching in more detail in terms of microbial population dynamics and proteomics. Microbial communities in MBRs with and without a quorum quenching enzyme (acylase) were analyzed using pyrosequencing and compared with each other. In the quorum quenching MBR, the rate of transmembrane pressure (TMP) rise-up was delayed substantially, and the proportion of quorum sensing bacteria with AHL-like autoinducers (such as Enterobacter, Pseudomonas, and Acinetobacter) also decreased in the entire microbial community of mature biofilm in comparison to that in the control MBR. These factors were attributed to the lower production of extracellular polymeric substances (EPS), which are known to play a key role in the formation of biofilm. Proteomic analysis using the Enterobacter cancerogenus strain ATCC 35316 demonstrates the possible depression of protein expression related to microbial attachments to solid surfaces (outer membrane protein, flagellin) and the agglomeration of microorganisms (ATP synthase beta subunit) with the enzymatic quorum quenching. It has been argued that changes in the microbial population, EPS and proteins via enzymatic quorum quenching could inhibit the formation of biofilm, resulting in less biofouling in the quorum quenching MBR.     

Quorum sensing: an emerging link between temperature and membrane biofouling in membrane bioreactors

Lab-scale membrane bioreactors (MBRs) were investigated at 12, 18, and 25?°C to identify the correlation between quorum sensing (QS) and biofouling at different temperatures. The lower the reactor temperature, the more severe the membrane biofouling measured in terms of the transmembrane pressure (TMP) during filtration. More extracellular polymeric substances (EPSs) that cause biofouling were produced at 18?°C than at 25?°C, particularly polysaccharides, closely associated with QS via the production of N-acyl homoserine lactone (AHL). However, at 12?°C, AHL production decreased, but the release of EPSs due to deflocculation increased the soluble EPS concentration. To confirm the temperature effect related to QS, bacteria producing AHL were isolated from MBR sludge and identified as Aeromonas sp., Leclercia sp., and Enterobacter sp. through a 16S rDNA sequencing analysis. Batch assays at 18 and 25?°C showed that there was a positive correlation between QS through AHL and biofilm formation in that temperature range.     

The application of nitric oxide to control biofouling of membrane bioreactors

A novel strategy to control membrane bioreactor (MBR) biofouling using the nitric oxide (NO) donor compound PROLI NONOate was examined. When the biofilm was pre‐established on membranes at transmembrane pressure (TMP) of 88–90 kPa, backwashing of the membrane module with 80 μM PROLI NONOate for 45 min once daily for 37 days reduced the fouling resistance (R_f) by 56%. Similarly, a daily, 1 h exposure of the membrane to 80 μM PROLI NONOate from the commencement of MBR operation for 85 days resulted in reduction of the TMP and R_f by 32.3% and 28.2%. The microbial community in the control MBR was observed to change from days 71 to 85, which correlates with the rapid TMP increase. Interestingly, NO‐treated biofilms at 85 days had a higher similarity with the control biofilms at 71 days relative to the control biofilms at 85 days, indicating that the NO treatment delayed the development of biofilm bacterial community. Despite this difference, sequence analysis indicated that NO treatment did not result in a significant shift in the dominant fouling species. Confocal microscopy revealed that the biomass of biopolymers and microorganisms in biofilms were all reduced on the PROLI NONOate‐treated membranes, where there were reductions of 37.7% for proteins and 66.7% for microbial cells, which correlates with the reduction in TMP. These results suggest that NO treatment could be a promising strategy to control biofouling in MBRs.     

Microbial behaviors involved in cake fouling in membrane bioreactors under different solids retention times

Biomass characteristics and membrane performances in the MBRs operated at a high flux of 30 L/m² h under different SRTs (10, 30 days, and infinity) were monitored. Results showed that more serious cake-fouling happened in the SRT-infinity MBR, which correlated with the activated sludge characteristics such as smaller floc size and greater EPS amount. DGGE analysis indicated that the microbial community shifted in different ways under various SRTs, which also influenced EPS productions in the MBRs. Different microbial communities were developed on the membrane surfaces at various operating stages and SRTs. Possibly, the activated sludge characteristics (such as MLSS concentration, EPS properties) and hydrodynamic conditions influenced by the SRTs were associated with cake layer development and membrane fouling propensity. Insight into the EPS characteristics and deposition behaviors of bacterial flocs will be crucial to explore appropriate biofouling control strategies in MBRs.     

Mechanisms of Bacillus cereus biofilm formation: an investigation of the physicochemical characteristics of cell surfaces and extracellular proteins

Microbial biofilms contribute to biofouling in a wide range of processes from medical implants to processed food. The extracellular polymeric substances (EPS) are implicated in imparting biofilms with structural stability and resistance to cleaning products. Still, very little is known about the structural role of the EPS in Gram-positive systems. Here, we have compared the cell surface and EPS of surface-attached (biofilm) and free-floating (planktonic) cells of Bacillus cereus, an organism routinely isolated from within biofilms on different surfaces. Our results indicate that the surface properties of cells change during biofilm formation and that the EPS proteins function as non-specific adhesions during biofilm formation. The physicochemical traits of the cell surface and the EPS proteins give us an insight into the forces that drive biofilm formation and maintenance in B. cereus.     

Membrane biofouling behaviors at cold temperatures in pilot-scale hollow fiber membrane bioreactors with quorum quenching

Abstract

In this study, the seasonality of the biofouling behavior of pilot-scale membrane bioreactors (MBRs) run in parallel with vacant sheets and quorum quenching (QQ) sheets using real municipal wastewater was investigated. QQ media delayed fouling, but low temperatures caused severe biofouling. The greater amount of extracellular polymeric substances (EPSs) produced in cold weather was responsible for the faster biofouling of a membrane, even with QQ media. There were significant negative relationships between EPS levels and water temperature. Cold weather was detrimental to the degradation of quorum sensing signal molecules by QQ sheets, whose activity was restored with a higher dose of QQ bacteria. The QQ bacteria in the sheets experienced a slight loss in activity during the early stage of the field test, but survived in the pilot-scale MBR fed with real wastewater. There were no significant discrepancies in treatment efficiency among conventional, vacant, and QQ MBRs.     

Identifying pioneer bacterial species responsible for biofouling membrane bioreactors

More effective control of membrane biofouling in membrane bioreactors (MBRs) lies in the fundamental understanding of the pioneer microorganisms responsible for surface colonization that leads to biofilm formation. In this study, the composition of the planktonic and sessile microbial communities inhabiting four laboratory-scale MBR systems were compared using amplified ribosomal DNA restriction analysis (ARDRA) and 16S ribosomal DNA gene sequencing. The ARDRA results suggest that the microbial communities on membrane surfaces could be very different from the ones in the suspended biomass. Phylogenetic analysis based on the 16S rRNA gene sequences provided a list of bacteria that might be the pioneers of surface colonization on microfiltration membranes. The results further suggested that research on the mechanisms of cell attachment in such an engineering environment could be critical for future development of appropriate biofouling control strategies.     

Microbe-surface interactions in biofouling and biocorrosion processes.

The presence of microorganisms on material surfaces can have a profound effect on materials performance. Surface-associated microbial growth, i.e. a biofilm, is known to instigate biofouling. The presence of biofilms may promote interfacial physico-chemical reactions that are not favored under abiotic conditions. In the case of metallic materials, undesirable changes in material properties due to a biofilm (or a biofouling layer) are referred to as biocorrosion or microbially influenced corrosion (MIC). Biofouling and biocorrosion occur in aquatic and terrestrial habitats varying in nutrient content, temperature, pressure and pH. Interfacial chemistry in such systems reflects a wide variety of physiological activities carried out by diverse microbial populations thriving within biofilms. Biocorrosion can be viewed as a consequence of coupled biological and abiotic electron-transfer reactions, i.e. redox reactions of metals, enabled by microbial ecology. Microbially produced extracellular polymeric substances (EPS), which comprise different macromolecules, mediate initial cell adhesion to the material surface and constitute a biofilm matrix. Despite their unquestionable importance in biofilm development, the extent to which EPS contribute to biocorrosion is not well-understood. This review offers a current perspective on material/microbe interactions pertinent to biocorrosion and biofouling, with EPS as a focal point, while emphasizing the role atomic force spectroscopy and mass spectrometry techniques can play in elucidating such interactions.     

Pressure drop increase by biofilm accumulation in spiral wound RO and NF membrane systems: role of substrate concentration,flow velocity,substrate load and flow direction

In an earlier study, it was shown that biofouling predominantly is a feed spacer channel problem. In this article, pressure drop development and biofilm accumulation in membrane fouling simulators have been studied without permeate production as a function of the process parameters substrate concentration, linear flow velocity, substrate load and flow direction. At the applied substrate concentration range, 100–400 μg l^?1 as acetate carbon, a higher concentration caused a faster and greater pressure drop increase and a greater accumulation of biomass. Within the range of linear flow velocities as applied in practice, a higher linear flow velocity resulted in a higher initial pressure drop in addition to a more rapid and greater pressure drop increase and biomass accumulation. Reduction of the linear flow velocity resulted in an instantaneous reduction of the pressure drop caused by the accumulated biomass, without changing the biofilm concentration. A higher substrate load (product of substrate concentration and flow velocity) was related to biomass accumulation. The effect of the same amount of accumulated biomass on the pressure drop increase was related to the linear flow velocity. A decrease of substrate load caused a gradual decline in time of both biomass concentration and pressure drop increase. It was concluded that the pressure drop increase over spiral wound reverse osmosis (RO) and nanofiltration (NF) membrane systems can be reduced by lowering both substrate load and linear flow velocity. There is a need for RO and NF systems with a low pressure drop increase irrespective of the biomass formation. Current efforts to control biofouling of spiral wound membranes focus in addition to pretreatment on membrane improvement. According to these authors, adaptation of the hydrodynamics, spacers and pressure vessel configuration offer promising alternatives. Additional approaches may be replacing heavily biofouled elements and flow direction reversal.     

Nitric Oxide Treatment for the Control of Reverse Osmosis Membrane Biofouling

Biofouling remains a key challenge for membrane-based water treatment systems. This study investigated the dispersal potential of the nitric oxide (NO) donor compound, PROLI NONOate, on single- and mixed-species biofilms formed by bacteria isolated from industrial membrane bioreactor and reverse osmosis (RO) membranes. The potential of PROLI NONOate to control RO membrane biofouling was also examined. Confocal microscopy revealed that PROLI NONOate exposure induced biofilm dispersal in all but two of the bacteria tested and successfully dispersed mixed-species biofilms. The addition of 40 μM PROLI NONOate at 24-h intervals to a laboratory-scale RO system led to a 92% reduction in the rate of biofouling (pressure rise over a given period) by a bacterial community cultured from an industrial RO membrane. Confocal microscopy and extracellular polymeric substances (EPS) extraction revealed that PROLI NONOate treatment led to a 48% reduction in polysaccharides, a 66% reduction in proteins, and a 29% reduction in microbial cells compared to the untreated control. A reduction in biofilm surface coverage (59% compared to 98%, treated compared to control) and average thickness (20 μm compared to 26 μm, treated compared to control) was also observed. The addition of PROLI NONOate led to a 22% increase in the time required for the RO module to reach its maximum transmembrane pressure (TMP), further indicating that NO treatment delayed fouling. Pyrosequencing analysis revealed that the NO treatment did not significantly alter the microbial community composition of the membrane biofilm. These results present strong evidence for the application of PROLI NONOate for prevention of RO biofouling.     

Characterization and effect of biofouling on polyamide reverse osmosis and nanofiltration membrane surfaces

Biofouling is a major reason for flux decline in the performance of membrane-based water and wastewater treatment plants. Initial biochemical characterization of biofilm formation potential and biofouling on two commercially available membrane surfaces from FilmTec Corporation were investigated without filtration in laboratory rotating disc reactor systems. These surfaces were polyamide aromatic thin-film reverse osmosis (RO) (BW30) and semi-aromatic nanofiltration (NF270) membranes. Membrane swatches were fixed on removable coupons and exposed to water with indigenous microorganisms supplemented with 1.5 mg l(-1) organic carbon under continuous flow. After biofilms formed, the membrane swatches were removed for analyses. Staining and epifluorescence microscopy revealed more cells on the RO than on the NF surface. Based on image analyses of 5-μm thick cryo-sections, the accumulation of hydrated biofoulants on the RO and NF surfaces exceeded 0.74 and 0.64 μm day(-1), respectively. As determined by contact angle the biofoulants increased the hydrophobicity up to 30° for RO and 4° for NF surfaces. The initial difference between virgin RO and NO hydrophobicities was ～5°, which increased up to 25° after biofoulant formation. The initial roughness of RO and NF virgin surfaces (75.3 nm and 8.2 nm, respectively) increased to 48 nm and 39 nm after fouling. A wide range of changes of the chemical element mass percentages on membrane surfaces was observed with X-ray photoelectron spectroscopy. The initial chemical signature on the NF surface was better restored after cleaning than the RO membrane. All the data suggest that the semi-aromatic NF surface was more biofilm resistant than the aromatic RO surface. The morphology of the biofilm and the location of active and dead cell zones could be related to the membrane surface properties and general biofouling accumulation was associated with changes in the surface chemistry of the membranes, suggesting the validity of the combination of these novel approaches for initial assessment of membrane performance.     

Characteristics of flux and gel layer on microfilter and non-woven fabric filter surface based on anoxic–aerobic MBRs

Non-woven fabric filter- (NWFF) and microfilter-MBR modules were made using 100?μm polypropylene and 0.25?μm polyethylene materials, respectively. The performances and mechanisms of the two processes were investigated, including additional batch filtration tests to find the function of the dynamic gel layer on the membrane surface. The HRT of both MBRs was 9?h and the operating permeate flux was 13?L/m(2)/h. The two MBRs consisted of an anoxic and aerobic reactor. The NWFF or microfilter (MF) was submerged in each of the aerobic reactors. The two MBRs showed similar performances for the removal of organic matters, suspended solids and nitrogen. Cake formation on the NWFF contributed to major resistance, while the gel layer on the microfilter or internal fouling of the pores played a key role in the fouling of the membrane surface. The amount of soluble extracellular polymer substances (EPS) (13?mg/L) of the attached sludge on the NWFF surface was larger than that (11?mg/L) of that suspended sludge. Consequently, the functional gel layer for the coarse and microfilter is established based on the relationship among the EPS, transmembrane pressure and MLSS.     

Biofouling development and rejection enhancement in long SRT MF membrane bioreactor

This study was conducted to investigate the development and extracellular polymeric substances (EPS) distribution in biofouling layer and biofouling effect on permeate quality. The experimental results suggested that formation of biofouling layer was started by the attachment of polysaccharides and formed a biogel like layer on top of membrane surface (adhesive attachment). It further induced the attachment of protein, polysaccharides and bioparticles, and formed cake layer (cohesive attachment). As evidenced in SEM photos and permeates quality, the formed biofouling layer had changed the properties of membrane surface such as the pore and porosity, and hence produce the better permeates quality. A great enhancement of rejection performance occurred at the early filtration period, and followed by a slight enhancement in rejection throughout the entire filtration. This enhancement of rejection performance by biofouling layer can be mathematically expressed by the logarithm function with the degree of membrane fouling.     

Biofilms of As(III)-oxidising bacteria: formation and activity studies for bioremediation process development

The formation and activity of an As(III)-oxidising biofilm in a bioreactor, using pozzolana as bacterial growth support, was studied for the purpose of optimising fixed-bed bioreactors for bioremediation. After 60 days of continuous functioning with an As(III)-contaminated effluent, the active biofilm was found to be located mainly near the inflow rather than homogeneously distributed. Biofilm development by the CAsO1 bacterial consortium and by Thiomonas arsenivorans was then studied both on polystyrene microplates and on pozzolana. Extra-cellular polymeric substances (EPS) and yeast extract were found to enhance bacteria attachment, and yeast extract also appears to increase the kinetics of biofilm formation. Analysis of proteins, sugars, lipids and uronic acids indicate that sugars were the main EPS components. The specific As(III)-oxidase activity of T. arsenivorans was higher (by ninefold) for planktonic cells than for sessile ones and was induced by As(III). All the results suggest that the biofilm structure is a physical barrier decreasing As(III) access to sessile cells and thus to As(III)-oxidase activity induction. The efficiency of fixed-bed reactors for the bioremediation of arsenic-contaminated waters can be thus optimised by controlling different factors such as temperature and EPS addition and/or synthesis to increase biofilm density and activity.     

Effect of hydraulic retention time on membrane fouling and biomass characteristics in submerged membrane bioreactors

In this paper, three identical membrane bioreactors (MBRs) were operated in parallel in order to specify the influence mechanism of hydraulic retention time (HRT) on MBR. The results showed that the removal efficiency of chemical oxygen demand (COD) was stable though it decreased slightly as HRT decreased, but biomass activity and dissolved oxygen (DO) concentration in sludge suspension decreased as HRT decreased. The filamentous bacteria grew easily with decreasing HRT. The extracellular polymeric substances (EPS) concentration and sludge viscosity increased significantly as filamentous bacteria excessively grew. The over growth of filamentous bacteria, the increase of EPS and the decrease of shear stress led to the formation of large and irregular flocs. Furthermore, the mixed liquid suspended solids (MLSS) concentration and sludge viscosity increased significantly as HRT decreased. The results also indicated that sludge viscosity was the predominant factor that affecting hydrodynamic conditions of MBR systems.     

Exopolysaccharide sugars contribute to biofilm formation by Salmonella enterica serovar typhimurium on HEp-2 cells and chicken intestinal epithelium

Recently, we demonstrated that Salmonella enterica serovar Typhimurium can form biofilm on HEp-2 cells in a type 1 fimbria-dependent manner. Previous work on Salmonella exopolysaccharide (EPS) in biofilm indicated that the EPS composition can vary based upon the substratum on which the bacterial biofilm forms. We have investigated the role of genes important in the production of colanic acid and cellulose, common components of EPS. A mutation in the colanic acid biosynthetic gene, wcaM, was introduced into S. enterica serovar Typhimurium strain BJ2710 and was found to disrupt biofilm formation on HEp-2 cells and chicken intestinal tissue, although biofilm formation on a plastic surface was unaffected. Complementation of the wcaM mutant with the functional gene restored the biofilm phenotype observed in the parent strain. A mutation in the putative cellulose biosynthetic gene, yhjN, was found to disrupt biofilm formation on HEp-2 cells and chicken intestinal epithelium, as well as on a plastic surface. Our data indicate that Salmonella attachment to, and growth on, eukaryotic cells represent complex interactions that are facilitated by species of EPS.     

A novel approach to evaluate the permeability of cake layer during cross-flow filtration in the flocculants added membrane bioreactors

In order to obtain a better understanding of the cake layer formation mechanism in the flocculants added MBRs, a model was developed on the basis of particle packing model considering cake collapse effect and a frictional force balance equation to predict the porosity and permeability of the cake layers. The important characteristic parameters of the flocs (e.g., floc size, fractal dimensions) and operating parameters of MBRs (e.g., transmembrane pressure, cross-flow velocity) are considered in this model. With this new model, the calculated results of porosities and specific cake resistances under different MBR operational conditions agree fairly well with the experimental data.