Now showing 1 - 10 of 30
  • Publication
    Simulation studies of process scale membrane aerated biofilm reactor configurations
    In the membrane aerated biofilm reactor oxygen diffuses through the membrane into the biofilm where oxidation of pollutants, supplied from the biofilm side of the membrane takes place. Despite numerous studies at the laboratory scale showing the potential of the technology, efforts to scale-up the technology to process scale have been hampered by problems such as excessive biofilm growth and consequent flow distribution problems. This paper presents results of simulation studies which utilise Computational Fluid Dynamics (CFD) to examine performance of several technical scale MABR design configurations. The simulations suggest that plate-and-frame membrane configuration with a suitable liquid inlet distributor will deliver superior performance compared to hollow fibre configuration with respect to liquid flow distribution.
  • Publication
    Biofilm Development in a Membrane Aerated Biofilm Reactor: Effect of Flow Velocity on Performance
    The effect of liquid flow velocity on biofilm development in a membrane-aerated biofilm reactor was investigated both by mathematical modeling and by experiment, using Vibrio natriegens as a test organism and acetate as carbon substrate. It was shown that velocity influenced mass transfer in the diffusion boundary layer, the biomass detachment rate from the biofilm, and the maximum biofilm thickness attained. Values of the overall mass transfer coefficient of a tracer through the diffusion boundary layer, the biofilm, and the membrane were shown to be identical during different experiments at the maximum biofilm thickness. Comparison of the results with published values of this parameter in membrane attached biofilms showed a similar trend. Therefore, it was postulated that this result might indicate the mechanism that determines the maximum biofilm thickness in membrane attached biofilms. In a series of experiments, where conditions were set so that the active layer of the membrane attached biofilm was located close to the membrane biofilm interface, it was shown that the most critical effect on process performance was the effect of velocity on biofilm structure. Biofilm thickness and effective diffusivity influenced reaction and diffusion in a complex manner such that the yield of biomass on acetate was highly variable. Consideration of endogenous respiration in the mathematical model was validated by direct experimental measurements of yield coefficients. Good agreement between experimental measurements of acetate and oxygen uptake rates and their prediction by the mathematical model was achieved.
      735Scopus© Citations 65
  • Publication
    Studies on the effect of concentration of a self-inhibitory substrate on biofilm reaction rate under co-diffusion and counter diffusion configurations
    (Elsevier, 2009-06-15) ; ;
    A simple mathematical model was developed to investigate the utilization rate of a self-inhibitory substrate in idealised biofilm reactors operating with either counter-diffusion or co-diffusion of oxygen and phenol. This study has implications for the development of membrane-supported biofilm technologies, such as the membrane-aerated biofilm reactor. An unsteady-state formulation of the model was used to investigate the effect of shock loads of phenol on biofilm performance. It was found that the counter-diffusion configuration may be advantageous under high phenol concentrations provided the biofilm thickness is above a critical value. The performance advantage of the counter-diffusion configuration is gained by the presence of an oxygen depleted layer, adjacent to the liquid–biofilm interface which acts as a diffusive barrier to phenol transport to the region of respiratory activity.
      380Scopus© Citations 12
  • Publication
    A Review of Nanomaterials and Technologies for Enhancing the Antibiofilm Activity of Natural Products and Phytochemicals
    (American Chemical Society, 2020-08-04) ;
    Biofilms are communities of microorganisms encased in a self-produced matrix constituted of extracellular polymeric substances (EPS). The recalcitrant and often harmful nature of biofilms, particularly in the biomedical field, motivates a search for antibiofilm compounds and materials. Within this context, nanoparticles (NPs) represent a promising platform for antibiofilm technologies due to their increased penetration into biofilms and facility of tailoring type, size, shape, and surface functionalization. The association of NPs with natural products and phytochemicals is even more appealing as an antibiofilm strategy, since the antimicrobial activity of essential oils, extracts, and isolated compounds can be improved when they are carried on the surface of NPs or encapsulated within them, as well as combined in formulations such as in nanoemulsions. This review article aims to provide an overview of recent methodologies for natural product delivery using nanomaterials and nanoformulations for the effective combat and eradication of bacterial and fungal biofilms. The nano-based technologies are categorized based on the type of antimicrobial delivery (NP coating, encapsulation, or nanoemulsions), and a selection of some widely reported natural substances (curcumin, propolis, and cinnamon components) is explored in more depth.
      6Scopus© Citations 25
  • Publication
    Model-based comparative performance analysis of membrane aerated biofilm reactor configurations
    (Wiley, 2008-04-15) ;
    The potential of the membrane aerated biofilm reactor (MABR) for high-rate bio-oxidation was investigated. A reaction-diffusion model was combined with a preliminary hollow-fiber MABR process model to investigate reaction rate-limiting regime and to perform comparative analysis on prospective designs and operational parameters. High oxidation fluxes can be attained in the MABR if the intra-membrane oxygen pressure is sufficiently high, however the volumetric oxidation rate is highly dependent on the membrane specific surface area and therefore the maximum performance, in volumetric terms, was achieved in MABRs with relatively thin fibers. The results show that unless the carbon substrate concentration is particularly high, there does not appear to be an advantage to be gained by designing MABRs on the basis of thick biofilms even if oxygen limitations can be overcome.
      788Scopus© Citations 37
  • Publication
    Bacterial adhesion onto nanofiltration and reverse osmosis membranes: Effect of permeate flux
    The influence of permeate flux on bacterial adhesion to NF and RO membranes was examined using two model Pseudomonas species, namely Pseudomonas fluorescens and Pseudomonas putida. To better understand the initial biofouling profile during NF/RO processes, deposition experiments were conducted in cross flow under permeate flux varying from 0.5 up to 120 L/(h m2), using six NF and RO membranes each having different surface properties. All experiments were performed at a Reynolds number of 579. Complementary adhesion experiments were performed using Pseudomonas cells grown to early-, mid- and late-exponential growth phases to evaluate the effect of bacterial cell surface properties during cell adhesion under permeate flux conditions. Results from this study show that initial bacterial adhesion is strongly dependent on the permeate flux conditions, where increased adhesion was obtained with increased permeate flux, until a maximum of 40% coverage was reached. Membrane surface properties or bacterial growth stages was further found to have little impact on bacterial adhesion to NF and RO membrane surfaces under the conditions tested. These results emphasise the importance of conducting adhesion and biofouling experiments under realistic permeate flux conditions, and raises questions about the efficacy of the methods for the evaluation of antifouling membranes in which bacterial adhesion is commonly assessed under zero-flux or low flux conditions, unrepresentative of full-scale NF/RO processes.
      488Scopus© Citations 20
  • Publication
    Detachment characteristics of a mixed culture biofilm using particle size analysis
    Detachment is a critically important aspect of biofilm processes; it impacts not only on the characteristics of the biofilm itself but also has general implications for the dissemination of pathogenic bacteria and the operation of biofilm reactors. The mechanisms of biofilm detachment are of fundamental importance in the analysis of biofilm processes. However the complexity of biofilm detachment creates difficulties in performing and analyzing experiments. It is necessary to identify if, under steady conditions, biofilms experiments are reproducible with respect to detachment. In this study mixed culture biofilms were cultivated under low shear conditions over four days in glass flow cells in triplicate under non-recirculation conditions. Detached particles were regularly sampled, were stained, filtered and analyzed using a fluorescence microscope to establish size distributions of detached cells and cell clumps. This study has shown that, despite the existence of a complex particle size distribution, reproducibility is possible in four day old mixed culture biofilms. This has important implications for the study of active or passive detachment in biofilm systems. This study also distinguished between erosion and sloughing following step increases in shear stress.
      765Scopus© Citations 22
  • Publication
    Treatment of fluoroacetate by a Pseudomonas fluorescens biofilm grown in membrane aerated biofilm reactor
    Fluorinated organic compounds have widespread applications, and their accumulation in the environment is a concern. Biofilm reactors are an effective technology for the treatment of contaminated wastewater, yet almost no research has been conducted on the effectiveness of biofilms for the biodegradation of fluorinated aliphatic compounds. In this paper we describe experiments undertaken to investigate the degradation of fluoroacetate using a membrane aerated biofilm reactor (MABR) by Pseudomonas fluorescens DSM8341. The concentration of fluoroacetate in the medium influenced biofilm structure, with less dense biofilm observed at lower fluoroacetate loading rates. As biofilm thickness increased, oxygen utilization decreased, probably as a consequence of increased resistance to oxygen transfer. Furthermore, most of the biofilm was anaerobic, since oxygen penetration depth was less than 1000 μm. Biofilm performance, in terms of fluoroacetate removal efficiency, was improved by decreasing the fluoroacetate loading rate, however increasing the intramembrane oxygen pressure had little effect on biofilm performance. A mathematical model showed that while fluoroacetate does not penetrate the entire biofilm, the defluorination intermediate metabolite glycolate does, and consequently the biofilm was not carbon limited at the biofilm−membrane interface where oxygen concentrations were highest. The model also showed the accumulation of the free fluoride ion within the biofilm. Overflow metabolism of glycolate was identified to be most likely a result of a combination of oxygen limitation and free fluoride ion inhibition. The study demonstrated the potential of MABR for treating wastewater streams contaminated with organofluorine compounds.
      730Scopus© Citations 22
  • Publication
    Tracer measurements reveal experimental evidence of biofilm consolidation
    (Wiley, 2007-11-01)
    The ability to simultaneously measure both biofilm thickness and the mass transfer coefficient of an inert tracer through it provides a powerful method to study biofilm development. In this communication previously published data has been collated to interpret global trends in biofilm structure during the transition towards steady-state. It appears that sudden changes in biofilm structure (directly related to the rate of change of biofilm mass transfer resistance) may occur following transitions in rate of biomass production. These observations are consistent with the concept of consolidation, recently introduced into spatially structured biofilm mathematical models to account for structural realignment of the biofilm under dynamic conditions.
      330Scopus© Citations 13
  • Publication
    Upon impact: the fate of adhering Pseudomonas fluorescens cells during Nanofiltration
    (American Chemical Society, 2014-07-29) ; ;
    Nanofiltration (NF) is a high-pressure membrane filtration process increasingly applied in drinking water treatment and water reuse processes. NF typically rejects divalent salts, organic matter, and micropollutants. However, the efficiency of NF is adversely affected by membrane biofouling, during which microorganisms adhere to the membrane and proliferate to create a biofilm. Here we show that adhered Pseudomonas fluorescens cells under high permeate flux conditions are met with high fluid shear and convective fluxes at the membrane-liquid interface, resulting in their structural damage and collapse. These results were confirmed by fluorescent staining, flow cytometry, and scanning electron microscopy. This present study offers a 'first-glimpse' of cell damage and death during the initial phases of bacterial adhesion to NF membranes and raises a key question about the role of this observed phenomena during early-stage biofilm formation under permeate flux and cross-flow conditions.
      281Scopus© Citations 9