Theses and Dissertations (Chemical Engineering)
http://hdl.handle.net/2263/32331
2024-03-28T17:50:38ZAdapting an existing batch pulp digester model for use in continuous digesters
http://hdl.handle.net/2263/90200
Adapting an existing batch pulp digester model for use in continuous digesters
A mathematical model of a continuous Kraft wood digester was developed and tested. The model relies heavily on the work done previously by Christensen, Albright & Williams (1982). The batch Kraft digester model developed by Christensen et al (1982) was adapted to model a continuous Kraft wood digester at Ngodwana, South Africa. This adaptation centres around utilizing the method of lines to account for changes in both time and height of the digester simultaneously. The model was able to simulate the Kappa number of the digester accurately to an average absolute error of 7.88 that was reduced to 2.87 after certain process parameters were optimized for. A moving horizon state estimator was introduced into the model in an effort to keep internal state prediction accurate. This addition brought the average absolute error down further to 2.75. Adaptive control was also implemented into the model. The plant data the model was compared against to determine its accuracy was filtered with the use of a rolling median filter to reduce the influence introduced by noisy and infrequent measurements.
Dissertation (MEng (Control Engineering))--University of Pretoria, 2020.
2020-01-01T00:00:00ZOptimizing Growth Conditions of Azolla pinnata R Brown for Phytoremediation
http://hdl.handle.net/2263/89680
Optimizing Growth Conditions of Azolla pinnata R Brown for Phytoremediation
Poor agricultural practices involving synthetic fertilizers have caused many environmental
issues which leads to the pollution of all biospheres of the earth. In order to meet the
ever-increasing demand of fertilizer it has been proposed to turn to eco-friendly biological
nitrogen fixation methods. The aquatic fern Azolla pinnata has a symbiotic relationship
with the nitrogen fixing bacteria Anabaena azollae. This relationship allows the plant to
live in low nitrogen environments due to the bacteria providing for the plant’s nitrogen
requirements. Optimally growing the plant would lead to increased use of biological
nitrogen fixation, thus decreasing the need for synthetic fertilizers. It is believed that
identifying an optimal combination of different growth conditions would be the best way
to improve the plants growth and thus it’s biological nitrogen fixation capabilities.
An investigation was undertaken to find the optimal growth conditions of the aquatic fern
A. pinnata. The growth conditions that were investigated were: light intensity, nitrogen
presence, pH control and humidity. The light intensity had three settings, i.e. low light
(5 000 lx), medium light (10 000 lx) and high light (20 000 lx), nitrogen was either added
to the system in the form of potassium nitrate or omitted, pH control to a pH of 6.5
was either done by daily manual dosing or the system was unaltered, and finally there
were three humidity settings – low humidity (60 %), medium humidity (75 %) and high
humidity at 90 %. A walk-in greenhouse was constructed so that each growth condition
could easily be adjusted to the different settings to facilitate a variety of growth condition
combinations. Using a 15 % strength Hoagland’s growth medium, it was found that a
high light intensity of 20 000 lx, pH control and 90 % humidity yielded the highest growth
rate of 0.321 d−1. It was found that the pH control must be used in conjunction with the
higher humidity values or else algal infection would occur and would negatively affect the
growth of the plant. The nitrogen presence did not have a significant effect on the growth
rate, this is likely due to the symbiosis between the A. pinnata and the A. azollae, proving
that the diazotroph fixates enough nitrogen to satisfy the plants nitrogen requirements.
A. pinnata has a variety of uses and since the optimal growth conditions study demonstrated
that A. pinnata can grow in low nitrogen environments, it was then decided to
investigate the plant’s phytoremediation properties of phosphorus under low nitrogen environments
and to observe if there was a pH response when the phosphorus was depleted.
i
Using the same set-up as in the optimal growth conditions study, the phosphate amounts
were varied between 0 ppm to 3.1 ppm in the Hoagland’s solution and different pH control
schemes were implemented to assess the feasibility of optimising phosphorus uptake in
a nitrogen absent environment. It was found that there was no significant difference in
growth or phosphorus uptake when the different pH control schemes were used. The pH 5
control scheme caused the A. pinnata to uptake phosphorus more readily than the pH 7.
This is due to the fact that phosphorus uptake is improved in acidic environments. The
A. pinnata did gain substantial mass when placed under low and no phosphate levels.
There was no significant pH response when the phosphate was depleted. In the natural
pH runs it was found that the pH behaved similarly, no matter the amount of phosphorus
added to the system. There was only a visual difference in the A. pinnata grown in
higher concentrations of phosphorus compared to the lower ones. The plants turned a
red colour and the fronds were much smaller in size for lower phosphorus levels. Since
the A. pinnata was grown optimally and the corresponding growth conditions found and
that the phytoremediation study proved the plants resilience to varying amounts of phosphorus
it is concluded that A. pinnata could be used for phytoremediation purposes in
nutrient-polluted systems.
Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2023.
2023-01-01T00:00:00ZMicrobial precipitation of Pb(II) with wild strains of Klebsiella Pneumoniae and Paraclostridium Bifermentans isolated from an industrially obtained microbial consortium
http://hdl.handle.net/2263/89249
Microbial precipitation of Pb(II) with wild strains of Klebsiella Pneumoniae and Paraclostridium Bifermentans isolated from an industrially obtained microbial consortium
The study focused on determining the microbial precipitation abilities of two bacterial strains, Paraclostridium bifermentans and Klebsiella pneumoniae isolated from an industrially obtained microbial consortium. Previous research has demonstrated the effectiveness of the consortium in the bioprecipitation of Pb(II). The bioremediation of Pb(II) provides an alternative and less costly method for lead removal from solution. A proof of concept was determined in a long duration study over 100 h wherein the bioprecipitation abilities of the strains were determined. It was concluded that approximately 84 % and 100 % of Pb(II) was removed from solution in experiments containing 80 mg/L initial Pb(II) concentration over 100 h, with P. bifermentans and K. pneumoniae respectively. The mechanisms of precipitation were further investigated with a short-term study, since it was observed that precipitation occurred in under 18 h in the long duration study. This shorter study was conducted over 30 h with nine sampling intervals and indicated removal percentages of approximately 86 % and 91 % for samples containing 80 mg/L initial Pb(II) concentration after 30 h for P. bifermentans and K. pneumoniae respectively. The precipitate identity was determined to be PbS and Pb(0) for samples containing P. bifermentans while samples containing K. pneumoniae contained precipitates of PbO and either PbCl or Pb3(PO4)2. An investigation into the extracellular and intracellular Pb(II) concentration led to the observation that a rapid detoxification mechanism such as biosorption is present in the microbes within the first 6 h of the experiment. These mentioned factors provide a greater understanding of the mechanisms utilised by the bacteria in the bioprecipitation and adsorption of Pb(II), and can be used as a step towards applying the process on an industrial scale.
Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2022.
2022-01-01T00:00:00ZIn situ bioremediation of hexavalent chromium by permeable reactive barrier using wastewater sludge bacteria
http://hdl.handle.net/2263/89059
In situ bioremediation of hexavalent chromium by permeable reactive barrier using wastewater sludge bacteria
Environmental pollution is a global problem that affects both developed and developing countries by contaminating soil and water, threatening biodiversity, ecosystems, and human health. South Africa holds the largest chrome ore reserves in the world, and it is one of the largest producers of ferrochrome. During steel and chromate production, enormous quantities of ferrochrome wastes are generated and discarded in dumps. This waste has been shown to contain significantly higher levels of Cr(VI) than the maximum acceptable risk concentration that is allowed for waste disposal in South Africa, which becomes a serious concern for soil and groundwater pollution.
There are various conventional technologies available for minimizing the environmental impact of Cr(VI), including chemical reduction, ion exchange, electrochemical treatment, membrane separation, etc. However, most of these technologies are often ineffective and very expensive, especially for low concentrations of metals. Additionally, the use of chemical reagents produces an enormous amount of hazardous sludge that requires further treatment. The bioreduction of toxic Cr(VI) to less toxic Cr(III) using microbial organisms is considered a valuable, promising, and cost-effective approach for Cr(VI) remediation.
In this study, using batch and continuous flow bioreactor systems, the efficiency of the indigenous culture of bacteria from the local wastewater treatment plant located near the contaminated site was evaluated for Cr(VI) reduction potential.
The Cr(VI) reduction capability and efficiency of the isolated bacteria were investigated under a range of operational conditions, i.e., pH, temperature and Cr(VI) loading in a batch system. The culture showed great efficiency in reduction capability, with 100% removal in less than 4 h at a nominal loading concentration of 50 mg Cr(VI)/L. The culture showed resilience by achieving total removal at concentrations as high as 400 mg Cr(VI)/L. The consortia exhibited considerable Cr(VI) removal efficiency in the pH range from 2 to 11, with 100% removal being achieved at a pH value of 7 at a 37 ± 1 °C incubation temperature. The ability of the mixed bacterial consortium to treat Cr(VI) may be explored further in a continuous flow process for practical application.
The effectiveness of bioremediation of Cr(VI) contaminated water using biological permeable reactive barrier technology was evaluated through bench-scale studies. Successful Cr(VI) reduction was achieved with 95.9% removal over the 90 days operational period of the BPRB system. When glucose was used as the carbon source, a drastic decline in effluent pH from 6.91 to below 5.5 was observed in the effluent. The decrease in pH values was ascribed to the oxidation of glucose forming several types of organic acids by different Bacillus species and other bacterial species which result in a subsequent drop in medium pH. However, it did not influence the overall reactor performance. These results could also be effective in optimizing and improving the operation and performance of in situ bioremediation of Cr(VI) at target sites. Cr(VI) reduction kinetic parameters in both batch and continuous-flow systems were estimated using a modified non-competitive inhibition model with a computer program for simulation of the aquatic system (AQUASIM 2.0).
Further studies are required to understand the interaction of bacteria with other heavy metals that co-exist with Cr(VI) in the environment and also to evaluate the effect of operating the BPRB under various HRTs while occasionally backwashing or dislodging the accumulated precipitate from the system. Finally, experiments should be conducted with real contaminated groundwater to study the effect of different chemical compositions and conditions of contaminated water on the Cr(VI) removal efficiency by bacteria and the hydraulic behaviour of the used mixtures.
Thesis (PhD)--University of Pretoria, 2022.
2022-01-01T00:00:00Z