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Theses and dissertations (Engineering and Built Environment)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/10

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Start date: 2022Subject: search.filters.subject.Biogas

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    Multiscale modelling of biogas purification using montmorillonite adsorbent
    (2024-05) Khuzwayo, Thandeka Ntombifuthi; Ngema, Peterson Thokozani; Ramsuroop, Suresh; Lasich, Madison M.
    Biogas, a renewable energy source derived from organic materials, offers significant potential for creating sustainable power sources and minimize environmental pollution. However, the presence of contaminants like carbon dioxide (CO2) and hydrogen sulfide (H2S) in biogas can reduce its usefulness and efficiency in a number of applications. To address this issue, this research focuses on the purification of biogas using clay adsorbent. This study investigates the adsorption capacity of clay minerals, such as montmorillonite, in removing CO2 and H2S from biogas. In this study, Grand Canonical Monte Carlo (GCMC) simulations were performed using a self-consistent forcefield to predict adsorption isotherms for methane, carbon dioxide, ethane, and hydrogen sulfide in montmorillonite lattice. The experimental setup involved a Pressure Swing Adsorption (PSA) column, where biogas passes through the adsorbent, leading to the adsorption of impurities while maintaining the methane content, thus enhancing the overall biogas quality. The model was fitted with Langmuir adsorption isotherms for all species at different pressures and ambient temperature, coupled with batch equilibrium approach to model the PSA system. The equilibrium modelling of a pressure swing adsorption system to purify CH4/CO2 feedstock was demonstrated in such that a system can be incorporated into a solar biogas reforming process, targeting purity of 93-96 mol-% methane, which was readily achievable. The modelling of PSA indicate that the system could produce over 96% of methane and a recovery of around 82% at low pressure. The findings suggest that the choice of clay adsorbent and optimization of process parameters can significantly enhance the purification efficiency of biogas via pressure-swing adsorption. The strong selectivity of the montmorillonite adsorbent has affinity to adsorb carbon dioxide and other species at low pressures, even though nitrogen require more pressure to be adsorbed onto the montmorillonite bed.
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    Application of synthesized magnetic nanoparticles for biogas production using anaerobic digestion
    (2023) Amo-Duodu, Gloria; Rathilal, Sudesh; Chollom, Martha Noro
    South Africa is encountering severe challenges in the areas of energy, water, and wastewater management in recent times. This study addresses both water and energy aspects. It aims at using synthesised magnetic nanoparticles (MNPs) on anaerobic digestion (AD) for biogas production from various wastewater sources in South Africa. The study experimented the feasibility of five different synthesized magnetic nanoparticles, magnetite (Fe3O4), copper ferrite (CuFe2O4), nickel ferrite (NiFe2O4), magnesium ferrite (MgFe2O4) and aluminium ferrite (AlFe2O4) on two different wastewater samples (industrial and municipal wastewater) from three sampling sources, Umbilo water works, Umgeni water and a sugar refinery industry. Five research objectives were accessed. The first objective was the synthesis and characterisation of MNPs using scanning electron microscopy/energy dispersive x-ray (SEM/EDX), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. The results showed a surface morphology of facecentred and monoclinic crystal structures with a size less than 20 nm. The nanostructures of ferrimagnetite and magnetite were obtained, and it had an O-H stretching and Fe-O vibration functional groups. The surface area obtained was found to be high for magnetite (Fe3O4) which was 27.597 m2 /g. The second objective was to evaluate the AD performance in terms of water quality and biogas production. This was carried out in two stages. The first was to evaluate the five MNPs with sugar refining wastewater. The second stage was to evaluate the performance of three best performing MNPs on two wastewater samples from Umbilo wastewater. The results for the first stage showed good degradation of organic matter for the bioreactors with MNPs which resulted in a higher yield of biogas and methane as compared to the control as well as good removal of contaminant (chemical oxygen demand (COD), colour and turbidity). Among the five MNPs used, Fe3O4, NiFe2O4 and CuFe2O4 had a contaminant removal efficiency of 60- 70% and a cumulative biogas yield of more than 140 ml/day with more than 85% methane composition, hence these three MNPs were found to be the best performed MNPs. The results obtained from the second stage for the three best performed MNPs indicated a high pollutant removal efficiency of more than 70% for Fe3O4, as well as a biogas yield of more than 1100 ml/day and a methane composition of approximately 98%. The third objective was the evaluation and optimisation of the anaerobic magnetised system for biogas production while the fourth objective involved a comparative study between the performances of magnetised biochemical methane potential (BMP) to non-magnetised biochemical methane potential. From the optimisation study, the predicted results obtained from the BBD-RSM showed an average contaminant removal of 70% and a biogas yield of 522 ml/day at an optimum MNP load of 0.5 g, retention time of 45 days, inoculum load of 500 ml, and a temperature of 35℃ with a desirability of 96% as the optimum conditions. With less than 2% deviation, the confirmatory test demonstrated equal performance at the optimum conditions. Findings from the fourth objective indicated that the BMP system with MF exposure exhibited a contaminant removal rate of over 80% and a biogas generation of 1715 ml/day with a 99.94% methane composition. Overall, the system that included both MF and MNP performed better than the other in terms of biogas yield and colour removal. The final objective was the kinetic study of the anaerobic magnetised system using modified Gompertz and first-order kinetic models. The results obtained from the kinetics showed that the modified Gompertz model described the kinetics and dynamics of the anaerobic magnetised system better than the firstorder kinetic model with a correlation co-efficient (R2 ) over 0.9999 and an error less than 0.0002. Therefore, the possibility of using MNPs, particularly magnetite (Fe3O4), in an AD system for biogas production from wastewater was found to be extremely feasible and without negative environmental consequences. Incorporating both MF and MNP in AD was also beneficial for wastewater treatment because it eliminated the need for post-treatment.
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    Wastewater treatment and photo-reduction of CO2 using an integrated magnetized TiO2 anaerobic- photocatalytic system
    (2022-09-29) Tetteh, Kweinor Emmanuel; Rathilal, Sudesh
    Conventionally, the treatment of municipal wastewater involves a sequence of treatment units aimed at reducing pollutants to acceptable discharge levels. Herein wastewater treatment plants in South Africa’s municipalities are being challenged recently due to emerging contaminants (nanomaterials, pesticides, antibiotics, COVID-19 RNA, etc.) that impede their efficiency. This calls for robust technological water solution systems targeted at promoting sustainable water supply and mitigating anthropogenic gas (CO2) emission via biogas production. Against this background, the novel of this study is aimed to develop an integrated AD-AOP (anaerobic digestion – advanced oxidation process) magnetized system to improve wastewater for reuse with biogas production and nanoparticles recoverability benefits. To obtain an optimal balance between robustness and cost-effectiveness of the integrated system, a series of feasibility and engineering works were explored. The first phase involved the synthesis via a co-precipitation technique, characterization, and applicability of the magnetized-photocatalysts (MPCs) for wastewater treatment. Analytically, the scanning electron microscopy and energy dispersive X-ray (SEM/EDX), Fourier transforms infrared spectra, X-ray diffraction (XRD), and Brunauer- Emmett-Teller (BET) techniques showed the tailored MPCs were successfully magnetized. Among the MPCs studied, Fe-TiO2 (with a BET surface area of 62.73 m2 /g) was found as the best with greater potential for above 75% decontamination of the wastewater and methane yield. In the technological design and evaluation, Fe-TiO2 was examined using biochemical methane potential (BMP), biophotocatalytic (BP), biomagnetic (BM), and biophotomagnetic (BPM) systems. Due to the external magnetic field influence on the BPMs, it was found very promising for future adventures. Above all, the novel integrated AD-AOP magnetized system proof of concept showed great potential for recoverability of the MPCs for reuse, reducing the toxicological effects of trace metals (27 elements considered), and improving water and biogas quality. The bioenergy economy of the integrated AD-AOP magnetized system demonstrated net energy being able to subsidize the energy required by the UV-lamp of the AOP system. Conclusively, this finding provides an insight into synthesizing novel MPCs and their applicability for wastewater remediation and biogas production. Also kinetics modeling and response surface methodology (RSM) optimization coupled with artificial neural network (ANN) predictability showed the potential to develop an optimized integrated AD-AOP magnetised system towards the treatment of industrial wastewater, biogas production , and CO2 emission reduction. The prospects necessitate a techno-scientific revolution to upscale the current integrated system into a pilot scale with smart-online monitoring towards improving the wastewater circular economy.