Masters Degrees (Microbiology)

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Browsing Masters Degrees (Microbiology) by browse.metadata.advisor "Bryant, Lee"

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    The effect of dissolved oxygen on the development of manganese oxidizing - and reducing biofilms in the lower blyde irrigation system
    (Stellenbosch : Stellenbosch University, 2018-12-11) Carstens, Alno; Wolfaardt, Gideon M.; Botes, Marelize; Bryant, Lee; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The Blyderiver dam in Mpumalanga is an important source of water for the irrigation of a variety of produce on farms in Limpopo and Mpumalanga. Water from this dam is used for gravity fed irrigation to farms via the Lower Blyde Irrigation System (LBIS), a network of pipelines of approximately 150 km. Biofilm development in the system causes a reduction in hydraulic capacity, leading to a reduction in water delivery for irrigation. It was hypothesized that high concentrations of manganese (Mn) in the water of the Blyderiver dam could potentially contribute to the development of these biofilms. Dissolved oxygen (DO) and Mn measurements taken during four sampling events from 2015 to 2017 indicated that the water of the Blyderiver dam has a distinct profile, with DO and Mn concentrations showing a strong inverse correlation. DO concentration typically remained constant between 8 and 9 mg l-1 in the upper 30 + meters of the water column, where after it decreased rapidly to below 2 mg l-1 at deeper depths. In contrast, total Mn concentration remained constant between 10 and 100 μg l-1 in the upper regions of the water column, followed by a rapid increase to higher than 8000 μg l-1 near the bottom. The current point of extraction for the LBIS is located near the bottom of the dam in this water with high Mn content. Mn concentration decreased with distance along the LBIS pipeline. For instance, results of the May 2016 sampling showed a decrease in the bulk aqueous phase Mn concentration from 8631 μg l-1 at the extraction point to 134 μg l-1 at 23 km downstream, while a decrease in Mn concentration could also be seen from 30105.4 mg kg-1 biofilm biomass at 4.5 km downstream to 13727.7 mg kg-1 at 28.4 km downstream. This decrease suggests ongoing incorporation of Mn into the biofilm, and thus potentially further loss in hydraulic capacity. Laboratory simulation experiments of the LBIS pipeline were conducted in which biofilms supplied with growth medium with different DO and Mn concentrations were cultivated. These biofilms were analysed by determining cell release into the effluent, Mn measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), automated ribosomal intergenic spacer analysis (ARISA) as well as confocal laser scanning microscopy (CLSM). Results obtained from colony counts and ARISA indicated that statistically significant differences did exist between biofilms cultivated under different growth conditions in some cases, but that these differences could not be attributed to the effects of different DO and Mn concentrations and were instead due to physical conditions such as shear and flux. These findings were confirmed by CLSM analysis. No statistically significant decrease in Mn concentration could be observed throughout the flow system, indicating that very little to no Mn was incorporated into the biofilm structure under any of the growth conditions tested in the laboratory simulations. SEM/EDS analysis of these biofilms further confirmed that the decreases in Mn concentration observed in both the bulk aqueous phase and biofilms with distance in the LBIS pipeline could not be replicated in these laboratory simulated flow systems. A number of factors were considered to explain this conclusion, including the time period of the experiment, nutrients used in the growth medium and biofilm sorption capacity. Future experimentation should include flow systems in which biofilms will be cultivated for longer time periods, and the use of microfluidic flow channels to provide shear values closer to that in the LBIS.