Now showing 1 - 10 of 50
  • 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
    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.
      880Scopus© Citations 15
  • Publication
    Interaction between Engineered Pluronic Silica Nanoparticles and Bacterial Biofilms: Elucidating the Role of Nanoparticle Surface Chemistry and EPS Matrix
    Nanoparticles (NPs) are considered a promising tool in the context of biofilm control. Many studies have shown that different types of NPs can interfere with the bacterial metabolism and cellular membranes, thus making them potential antibacterial agents; however, fundamental understanding is still lacking on the exact mechanisms involved in these actions. The development of NP-based approaches for effective biofilm control also requires a thorough understanding of how the chosen nanoparticles will interact with the biofilm itself, and in particular with the biofilm self-produced extracellular polymeric matrix (EPS). This work aims to provide advances in the understanding of the interaction between engineered fluorescent pluronic silica (PluS) nanoparticles and bacterial biofilms, with a main focus on the role of the EPS matrix in the accumulation and diffusion of the particles in the biofilm. It is demonstrated that particle surface chemistry has a key role in the different lateral distribution and specific affinity to the biofilm matrix components. The results presented in this study contribute to our understanding of biofilm-NP interactions and promote the principle of the rational design of smart nanoparticles as an important tool for antibiofilm technology.
      5Scopus© Citations 1
  • 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
    A physical impact of organic fouling layers on bacterial adhesion during nanofiltration
    Organic conditioning films have been shown to alter properties of surfaces, such as hydrophobicity and surface free energy. Furthermore, initial bacterial adhesion has been shown to depend on the conditioning film surface properties as opposed to the properties of the virgin surface. For the particular case of nanofiltration membranes under permeate flux conditions, however, the conditioning film thickens to form a thin fouling layer. This study hence sought to determine if a thin fouling layer deposited on a nanofiltration membrane under permeate flux conditions governed bacterial adhesion in the same manner as a conditioning film on a surface. Thin fouling layers (less than 50 μm thick) of humic acid or alginic acid were formed on Dow Filmtec NF90 membranes and analysed using Atomic Force Microscopy (AFM), confocal microscopy and surface energy techniques. Fluorescent microscopy was then used to quantify adhesion of Pseudomonas fluorescens bacterial cells onto virgin or fouled membranes under filtration conditions.It was found that instead of adhering on or into the organic fouling layer, the bacterial cells penetrated the thin fouling layer and adhered directly to the membrane surface underneath. Contrary to what surface energy measurements of the fouling layer would indicate, bacteria adhered to a greater extent onto clean membranes (24 ± 3% surface coverage) than onto those fouled with humic acid (9.8 ± 4%) or alginic acid (7.5 ± 4%). These results were confirmed by AFM measurements which indicated that a considerable amount of energy (10−7 J/μm) was dissipated when attempting to penetrate the fouling layers compared to adhering onto clean NF90 membranes (10−15 J/μm). The added resistance of this fouling layer was thusly seen to reduce the number of bacterial cells which could reach the membrane surface under permeate conditions. This research has highlighted an important difference between fouling layers for the particular case of nanofiltration membranes under permeate flux conditions and surface conditioning films which should be considered when conducting adhesion experiments under filtration conditions. It has also shown AFM to be an integral tool for such experiments.
      331Scopus© Citations 20
  • 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.
      181Scopus© Citations 21
  • Publication
    Understanding particle deposition kinetics on NF membranes: A focus on micro-beads & membrane interactions at different environmental conditions
    The significance of nanofiltration membrane surface properties when interacting with microbeads with and without permeate flux was investigated. This was achieved by characterising the surface tension and zeta potential of micro-beads and NF90 membranes to determine the colloid–membrane interaction forces. Dynamic adhesion assays under different ionic strengths (0.1 M and 0.01 M) and pH (5, 7, and 9) were conducted. Experimental results showed that at high ionic strength, pH does not have a significant effect on adhesion rates, while at low ionic strength the adhesion rate increased at pH 7 (4.56 s−1 cm−2) compared to pH 5 and pH 9, with rates of 2.69 and 3.66 s−1 cm−2 respectively. A model was devised to predict colloidal adhesion onto membranes under increasing permeate flux conditions, taking into account all interaction forces. Model predictions indicate that drag force overwhelms all other colloid–membrane interaction forces when the permeate flux increases to 7.2 L h−1 m−2. This study suggests that altering membrane surface properties for the prevention of fouling may be limited in its success as an antifouling strategy.
      248Scopus© Citations 12
  • Publication
    Antifouling activity of enzyme-functionalized silica nanobeads
    The amelioration of biofouling in industrial processing equipment is critical for performance and reliability. While conventional biocides are effective in biofouling control, they are potentially hazardous to the environment and in some cases corrosive to materials. Enzymatic approaches have been shown to be effective and can overcome the disadvantages of traditional biocides, however they are typically uneconomic for routine biofouling control. The aim of this study was to design a robust and reusable enzyme-functionalized nano-bead system having biofilm dispersion properties. This work describes the biochemical covalent functionalization of silica-based nanobeads (hereafter referred to as Si-NanoB) with Proteinase K (PK). Results showed that PK-functionalized Si-NanoB are effective in dispersing both protein-based model biofilms and structurally altering Pseudomonas fluorescens biofilms, with significant decreases in surface coverage and thickness of 30.1% and 38.85%, respectively, while increasing surface roughness by 19 % following 24 h treatments on bacterial biofilms. This study shows that enzyme-functionalized nanobeads may potentially be an environmentally friendly and cost effective alternative to pure enzyme and chemical treatments.
      331Scopus© 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.
      885Scopus© Citations 212
  • 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.
      382Scopus© Citations 12