Browsing by Author "Broughton, James Kuan"

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    Modelling biofilm structure and biofilm-micropollutant interactions using an individual-based Model
    (Stellenbosch : Stellenbosch University, 2019-04) Broughton, James Kuan; Louw, Tobias M.; Wolfaardt, Gideon M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Micropollutants are emerging contaminants that have received considerable attention in recent years due to environmental concerns. Diclofenac is a nonsteroidal anti-inflammatory drug that is commonly detected in South African surface waters and has been shown to be persistent and harmful to the environment. Biofilms, which are composed of sessile, mixed microbial communities, play a key role in wastewater treatment and functioning of natural ecosystems. There is, however, a poor understanding of biofilm-micropollutant interactions in this context. Biofilm structure is a useful indicator of the effect of micropollutant exposure on a biofilm and its activity. Recently, individual-based models have been developed that can simulate biofilm structure from first principles and show potential as a tool to provide mechanistic understanding of these interactions. The aim of the project was to develop and validate an individual-based model capable of describing biofilm structural development of a sample, as well as reproducing observed effects of diclofenac exposure on biofilm structure. A further aim was to investigate the feasibility of observed biofilm structure for validation of the biofilm model. Lumped biokinetic parameters of an environmental sample were estimated using batch respirometric methods and regression of model parameters. Heterotrophic growth was found to dominate in the sampled culture. The estimated parameters were thus used to calibrate lumped heterotrophic growth in the biofilm model. Mixed-species biofilms were cultivated in flow cells under control conditions and exposed to diclofenac at 0.1 and 10 mg.L-1. Confocal laser scanning microscopy was used to examine morphological changes in biofilm structure over time. Biofilm structural parameters were derived from microscopy data and compared to the simulation output. Observed structure of biofilms were successfully used to validate the proposed biofilm model. Experimental results indicated a dose-dependent response to diclofenac. Diclofenac at 10 mg.L-1 significantly inhibited biofilm growth over the exposure period compared to a control. Exposure at 0.1 mg.L-1 resulted in an increase in biofilm growth after 24 h. The biofilm model successfully reproduced observed trends in structure at 10 mg.L-1 and 0.1 mg.L-1. More work is required to elucidate the complex microbial interactions of diclofenac in the μg.L-1 range. This study showed that an individual-based model can reproduce in vitro biofilm structure development based on emergent structural parameters. Individual-based models coupled with comparative experimental methods show potential as a tool for investigating biofilm interactions and improving model development. However, areas of improvement were identified including model parameter uncertainties, limitations in the biofilm model, and reproducibility in experimental methods.