Now showing 1 - 8 of 8
  • 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.
    Scopus© Citations 86  1253
  • Publication
    A novel approach to model a gas network
    The continuous uninterrupted supply of Natural Gas (NG) is crucial to today's economy, with issues in key infrastructure, e.g., Baumgarten hub in Austria in 2017, highlighting the importance of the NG infrastructure for the supply of primary energy. The balancing of gas supply from a wide range of sources with various end users can be challenging due to the unique and different behaviours of the end users, which in some cases span across a continent. Further complicating the management of the NG network is its role in supporting the electrical network. The fast response times of NG power plants and the potential to store energy in the network play a key role in adding flexibility across other energy systems. Traditionally, modelling the NG network relies on nonlinear pipe flow equations that incorporate the demand (load), flow rate, and physical network parameters including topography and NG properties. It is crucial that the simulations produce accurate results quickly. This paper seeks to provide a novel method to solve gas flow equations through a network under steady-state conditions. Firstly, the model is reformulated into non-linear matrix equations, then the equations separated into their linear and nonlinear components, and thirdly, the non-linear system is solved approximately by providing a linear system with similar solutions to the non-linear one. The non-linear equations of the NG transport system include the main variables and characteristics of a gas network, focusing on pressure drop in the gas network. Two simplified models, both of the Irish gas network (1. A gas network with 13 nodes, 2. A gas network with 109 nodes) are used as a case study for comparison of the solutions. Results are generated by using the novel method, and they are compared to the outputs of two numerical methods, the Newton-Raphson solution using MATLAB and SAINT, a commercial software that is used for the simulation of the gas network and electrical grids.
      538Scopus© Citations 23
  • 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.
      494Scopus© Citations 14
  • Publication
    Hydrodynamics and gas transfer performance of confined hollow fibre membrane modules with the aid of computational fluid dynamics
    The use of gas permeable membranes for bubbleless aeration is of increasing interest due to the energy savings it affords in wastewater treatment applications. However, flow maldistributions are a major factor in the impedance of mass transfer efficiency. In this study, the effect of module configuration on the hydrodynamic conditions and gas transfer properties of various submerged hollow fibre bundles was investigated. Flow patterns and velocity profiles within fibre bundles were predicted numerically using computational fluid dynamics (CFD) and the model was validated by tracer-response experiments. In addition, the effect of fibre spacing and bundle size on the aeration rate of various modules was evaluated experimentally. Previous studies typically base performance evaluations on the liquid inlet velocity or an average velocity, an approach which neglects the effect of geometric features within modules. The use of validated CFD simulations provides more detailed information for performance assessment. It was shown that specific oxygen transfer rates declines significantly with increasing numbers of fibres in a bundle. However, the same trend was not observed when the fibre spacing is increased. A correlation was proposed for the prediction of the overall mass transfer coefficient utilizing the local velocity values obtained from the validated CFD model.
      902Scopus© Citations 23
  • Publication
    Membrane aerated biofilms for high rate biotreatment : performance appraisal, engineering principles, scale-up and development requirements
    (ACS, 2008-03-15) ;
    Diffusion of the electron acceptor is the rate controlling step in virtually all biofilm reactors employed for aerobic wastewater treatment. The membrane-aerated biofilm reactor (MABR) is a technology that can deliver oxygen at high rates and transfer efficiencies, thereby enhancing the biofilm activity. This paper provides a comparative performance rate analysis of the MABR in terms of its application for carbonaceous pollutant removal, nitrification/denitrification and xenobiotic biotreatment. We also describe the mechanisms influencing process performance in the MABR and the inter-relationships between these factors. The challenges involved in scaling-up the process are discussed with recommendations for prioritization of research needs.
      2368Scopus© Citations 238
  • 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.
      935Scopus© Citations 40
  • 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.
      966Scopus© Citations 26
  • 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.