Modelling and Control

“An implementation framework for wastewater treatment models requiring a minimum programming expertise”

The freely available download (from here) is a Matlab-Excel platform for implementation of WWT plant models.

Mathematical modelling in environmental biotechnology has been a traditionally difficult resource to access for researchers and students without programming expertise. The great degree of flexibility required from model implementation platforms to be suitable for research applications restricts their use to programming expert users. More user friendly software packages however do not normally incorporate the necessary flexibility for most research applications. This work presents a methodology based on Excel and Matlab-Simulink for both flexible and accessible implementation of mathematical models by researchers with and without programming expertise.

The models are almost fully defined in an Excel file in which the names and values of the state variables and parameters are easily created. This information is automatically processed in Matlab to create the model structure and almost immediate model simulation, after only a minimum Matlab code definition, is possible. The framework proposed also provides programming expert researchers with a highly flexible and modifiable platform on which to base more complex model implementations. The method takes advantage of structural generalities in most mathematical models of environmental bioprocesses while enabling the integration of advanced elements (e.g. heuristic functions, correlations). The methodology has already been successfully used in a number of research studies.

Modelling Microbial Fuels Cells

A comprehensive mathematical model for microbial fuel cells (MFCs) was developed and demonstrated. The model, with a structure based on mass balance equations, describes the dynamics of complete microbial fuel cells. Both anodic and cathodic bulk compartments are assumed as perfectly mixed reactors and an anode biofilm is described using a one dimensional discretisation approach into perfectly mixed layers. The model represents in detail, among other elements, electrode kinetics and complete electrical circuit; a comprehensive acid-base chemical speciation and charge neutrality; mass transport of all species inside the biofilm and through the specifically modelled separation membrane; microbial metabolism (and yield) in function of local energetics. Multiple electron transport mechanisms, interlinked by bioenergetic considerations, are theoretically introduced and discussed.

A number of representative case studies are presented in order to demonstrate the model capabilities to describing experimentally observed behaviour in MFCs. Based on the model simulations it was possible to mechanistically represent phenomena observed experimentally at high currents like that of current decrease at increasing voltage in MFC polarization curves. By analysis of model simulations this was attributed to severe pH gradients and inhibition inside the biofilm. Confirming early studies, the model also reproduces the positive effect of higher buffer concentrations on MFC performance at high currents. Variable microbial growth yield and metabolism as function of local energetics establishes a relationship between electroactive biomass growth and biofilm thickness with electrode potential and local concentrations. The model is implemented in a highly flexible platform for structural modifications which enables model implementation for alternative BES configurations.