The development and validation of a novel, parameter-free, modelling strategy for electromembrane processes: Electrodialysis

As the global water crisis worsens and natural resources of strategic inorganic elements dwindle, the need for efficient and effective salt separation methods is becoming ever more important. Electromembrane processes, and in particular electrodialysis, are emerging as efficient and effective separation technologies that use an electric field to drive the transport of ions against a concentration gradient. Modelling electromembrane processes allows for process design and optimisation, as well as the identification of what technological improvements would have the greatest effect. However, the wide use of empirical fitting parameters in most existing models greatly limits their globality. The presence of complex and confounding phenomena within electromembrane processes greatly exacerbates this. In this work, a novel, circuit-based modelling strategy for electromembrane processes is presented, avoiding the use of any fitting parameters. Conventional electrodialysis is adopted as a case study. The implementation of a novel transport number model and membrane resistance model are crucial for model accuracy over a wide range of process conditions. The model was experimentally validated and showed excellent agreement with experimental data across a range of concentrations and voltages. Consequently, this model will prove to be an excellent tool for researchers and process designers

The Investigation, Development, and Analysis of Models of Electrodialysis

Electrodialysis is an emerging electromembrane salt separation technology, industrial implementation of which is currently inhibited by the risk-averse nature of industry and poor optimisation of units. The work presented in this thesis involves understanding how electrodialysis is modelled, rigorously testing one of the most basic assumptions, and developing more advanced modelling strategies. A review of existing published literature revealed there is a wide variety of models both in their fundamental construction and the assumptions taken to neglect phenomena. Despite this, good agreement with empirical data is near ubiquitous but attributed to an over-reliance on fitting parameters. One assumption taken by all researchers is channel uniformity whereby the repeating geometry is leveraged to significantly reduce model complexity. In Part I, this assumption was investigated through computational fluid dynamics simulations through which significant flow maldistribution between channels was revealed. Further, an analytical model was found to capture the degree of maldistribution well in a dimensionless number and revealed how it can be influenced. A study on the impact of maldistribution revealed that while the electric resistance is marginally affected, the limiting current density is significantly reduced. Particle image velocimetry experiments empirically demonstrated the presence of maldistribution and transport experiments validated its impact. In Part II, an advanced process model of electrodialysis was developed using the analogy of an electric circuit. This model was designed to be adaptable and avoid the use of empirical fitting parameters. A membrane transport number and resistance model proved vital in ensuring predictive accuracy over a range of concentrations and voltages. To demonstrate the generality of the model, it was extended to describe bipolar membrane electrodialysis which similarly showed good agreement with experimental data. Overall, this work has contributed significant advancements to how electrodialysis is analysed, designed, and modelled

The development and evaluation of a parameter-free circuit-based model of bipolar membrane electrodialysis for process design and optimisation

Bipolar membrane electrodialysis (BPMED) is an emerging electromembrane technology which has the potential to replace existing pH manipulation process units among others and take advantage of the benefits posed by process electrification. The development of robust and flexible process models of BPMED for design and optimisation is paramount in derisking potential instillations and improving commercial viability. Herein, a circuit-based model of BPMED is presented which avoids reliance on empirical fitting parameters and training data. The resulting model is flexible enough that extension to account for added complexities may be readily adopted. The mass transfer and electrical resistance of six different domains (three membranes and three streams) were computed by applying fundamental laws such as Ohm’s law and Faraday’s first law. Acid-base reactions and their effect releasing current within the membranes were also considered. Furthermore, the stack model can be readily embedded in a broader process model. To this end, the stack model is applied to a recirculating-batch experiment using a delayed differential material balance to account for dead-time within the tubing and measurement flow-cells. Two orthogonal methods of experimental validation were conducted to assess the performance of the model over a range of concentrations and applied voltages. These involved running a recirculating-batch experiment and collecting current–voltage polarisation data, respectively, and both showed good agreement with the model predictions. Overall, a robust model of BPMED has been produced which is able to accurately predict system performance and will prove useful for the design and optimisation of industrial systems

Persistent bacterial infections: the interface of the pathogen and the host immune system

Persistent bacterial infections involving Mycobacterium tuberculosis, Salmonella enterica serovar Typhi (S. typhi) and Helicobacter pylori pose significant public-health problems. Multidrug-resistant strains of M. tuberculosis and S. typhi are on the increase, and M. tuberculosis and S. typhi infections are often associated with HIV infection. This review discusses the strategies used by these bacteria during persistent infections that allow them to colonize specific sites in the host and evade immune surveillance. The nature of the host immune response to this type of infection and the balance between clearance of the pathogen and avoidance of damage to host tissues are also discussed