Now showing 1 - 10 of 39
  • Publication
    Comparative economic analysis of full scale MABR configurations
    The membrane-aerated biofilm reactor (MABR) is a technology that can deliver oxygen at high rates and transfer efficiencies. This paper provides a comparative cost analysis of the MABR compared to the activated sludge process. Membrane cost and electricity cost were found to be the critical parameters determining the relative feasibility of the conventional process to the membrane based process. The general downward trend in the market price of membranes and the steady increase in energy costs in recent years may prove to be a strong driver for the further development of this technology.
  • Publication
    Investigation of energy and operation flexibility of membrane bioreactors by using benchmark simulation model
    The aims of this study is to investigate operation and energy flexibility of membrane bioreactors for municipal wastewater treatment by mathematical modelling. Compared to conventional active sludge technology, membrane bioreactor has better treatment performance and it can achieve complete retention of solids and very high COD removal. Based on variable electricity price structure, appropriate optimization strategy can save 16% energy cost without violating exiting discharge standards.. The results showed that MBRs have a significant potential to create considerable commercial value by providing energetic flexibility.
  • 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
    Characterisitics of Streptomyces griseus biofilms in continuous flow tubular reactors
    The purpose of this study was to investigate the feasibility of cultivating the biotechnologically important bacterium Streptomyces griseus in single-species and mixed- species biofilms using a Tubular Biofilm Reactor (TBR). Streptomyces griseus biofilm development was found to be cyclical, starting with the initial adhesion and subsequent development of a visible biofilm after 24 hours growth, followed by the complete detachment of the biofilm as a single mass, and ending with the re-colonization of the tube. Fluorescence microscopy revealed that the filamentous structure of the biofilm was lost upon treatment with protease, but not DNase or metaperiodate, indicating that the extracellular polymeric substance is predominantly protein. When the biofilm was cultivated in conjunction with Bacillus amyloliquefaciens, no detachment was observed after 96 h, although once subjected to flow detachment occurred. Electron microscopy confirmed the presence of both bacteria in the biofilm and revealed a network of fimbriae-like structures that were much less apparent in single-species biofilm, and are likely to increase mechanical stability when developing in a TBR. This study presents the very first attempt in engineering Streptomyces griseus biofilms for continuous bioprocess applications.
      877Scopus© Citations 15
  • Publication
    Cicada Wing Surface Topography: An Investigation into the Bactericidal Properties of Nanostructural Features
    (American Chemical Society, 2015-11-09) ; ; ; ;
    Recently, the surface of the wings of the Psaltoda claripennis cicada species has been shown to possess bactericidal properties and it has been suggested that the nanostructure present on the wings was responsible for the bacterial death. We have studied the surface-based nanostructure and bactericidal activity of the wings of three different cicadas (Megapomponia intermedia, Ayuthia spectabile and Cryptotympana aguila) in order to correlate the relationship between the observed surface topographical features and their bactericidal properties. Atomic force microscopy and scanning electron microscopy performed in this study revealed that the tested wing species contained a highly uniform, nanopillar structure on the surface. The bactericidal properties of the cicada wings were investigated by assessing the viability of autofluorescent Pseudomonas fluorescens cells following static adhesion assays and targeted dead/live fluorescence staining through direct microscopic counting methods. These experiments revealed a 20-25% bacterial surface coverage on all tested wing species; however, significant bactericidal properties were observed in the M. intermedia and C. aguila species as revealed by the high dead:live cell ratio on their surfaces. The combined results suggest a strong correlation between the bactericidal properties of the wings and the scale of the nanotopography present on the different wing surfaces.
      861Scopus© Citations 208
  • Publication
    The significance of calcium ions on Pseudomonas fluorescens biofilms – a structural and mechanical study
    The purpose of this study was to investigate the effects of calcium ions on the structural and mechanical properties of Pseudomonas fluorescens biofilms grown for 48 h. Advanced investigative techniques such as confocal laser scanning microscopy and atomic force spectroscopy were employed to characterize biofilm structure as well as biofilm mechanical properties following growth at different calcium concentrations. The presence of calcium during biofilm development led to higher surface coverage with distinct structural phenotypes in the form of a granular and heterogeneous surface, compared with the smoother and homogeneous biofilm surface in the absence of calcium. The presence of calcium also increased the adhesive nature of the biofilm, while reducing its elastic properties. These results suggest that calcium ions could have a functional role in biofilm development and have practical implications, for example, in analysis of biofouling in membrane-based water-treatment processes such as nanofiltration or reverse osmosis where elevated calcium concentrations may occur at the solid–liquid interface.
      356Scopus© Citations 31
  • 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.
      279Scopus© Citations 9
  • Publication
    Enhancing curcumin's solubility and antibiofilm activity via silica surface modification
    Bacterial biofilms are microbial communities in which bacterial cells in sessile state are mechanically andchemically protected against foreign agents, thus enhancing antibiotic resistance. The delivery of activecompounds to the inside of biofilms is often hindered due to the existence of the biofilm extracellularpolymeric substances (EPS) and to the poor solubility of drugs and antibiotics. A possible strategy toovercome the EPS barrier is the incorporation of antimicrobial agents into a nanocarrier, able topenetrate the matrix and deliver the active substance to the cells. Here, we report the synthesis ofantimicrobial curcumin-conjugated silica nanoparticles (curc-NPs) as a possibility for dealing with theseissues. Curcumin is a known antimicrobial agent and to overcome its low solubility in water it wasgrafted onto the surface of silica nanoparticles, the latter functioning as nanocarrier for curcumin intothe biofilm. Curc-NPs were able to impede the formation of modelP. putidabiofilms up to 50% anddisrupt mature biofilms up to 54% at 2.5 mg mL 1. Cell viability of sessile cells in both cases was alsoconsiderably affected, which is not observed for curcumin delivered as a free compound at the sameconcentration. Furthermore, proteomics of extracted EPS matrix of biofilms grown in the presence offree curcumin and curc-NPs revealed differences in the expression of key proteins related to celldetoxification and energy production. Therefore, curc-NPs are presented here as an alternative forcurcumin delivery that can be exploited not only to other bacterial strains but also to further biologicalapplications.
      157Scopus© Citations 18
  • Publication
    Disinfection of meticillin-resistant Staphylococcus aureus and Staphylococcus epidermidis biofilms using a remote non-thermal gas plasma
    The effective disinfection of hospital surfaces is recognised as an important factor in preventing hospital-acquired infections. The purpose of this study was to quantify the disinfection rate of a novel gas plasma system on clinically relevant biofilms. Clinical isolates of Staphylococcus epidermidis and methicillin-resistant Staphylococcus aureus (MRSA) were grown as biofilms on glass surfaces and tested in a disinfection container remote from the plasma source. The strains used in this study were known to produce substantial quantities of biofilm and average log10 counts were 9.0 and 9.1 cfu/cm2 for S. epidermidis and MRSA respectively. Counts were reduced by between 4 and 4.5 log10 after 1 h of exposure for MRSA and S. epidermidis respectively. More prolonged treatment in the case of MRSA biofilms resulted in a 5.5 log10 reduction after 90 min. Biofilm samples were also placed in medical device packaging bags and similar rates of disinfection were observed.
      1575Scopus© Citations 43
  • Publication
    Performance analysis of a pilot-scale membrane aerated biofilm reactor for the treatment of landfill leachate
    A 60 L membrane aerated biofilm reactor (MABR) was successfully employed to treat landfill leachate, which contained very high concentrations of refractory chemical oxygen demand (COD) and ammonium. Air or pure oxygen was supplied to the bioreactor through polydimethyl siloxane hollow fibre membranes. Over a year of operation with an average hydraulic retention time of about 5 days, and influent ammonium concentrations ranging from 500 to 2500 mg/L, the MABR achieved 80–99% nitrification. Simultaneously, the influent COD concentrations which ranged from 1000 to 3000 mg/L were reduced by approximately 200–500 mg/L. Oxygen transfer rates as high as 35 g O2/m2-day were achieved during the study. By operating at low gas flowrates, high oxygen transfer efficiencies were achieved without any negative impact on oxygen transfer rates. This suggested that the biofilm was not oxygen limited during this study. The very low gas flowrates and the low pressure losses required to move air through the membranes resulted in very high standard aeration efficiencies that exceeded 10 kg O2/kW h. The results indicate that mixing energy far exceeded that required for aeration in this study. Our results suggest that with process optimisation, MABR technology offers a low energy option for effective leachate treatment.
      900Scopus© Citations 67