PhD Theses and Dissertations

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Application of a constructed wetland for the removal of antibiotic residue, antibiotic-resistant bacteria, and antibiotic-resistance genes from pharmaceutically contaminated wastewater
(NM-AIST, 2024-06) Karungamye, Petro
The significant increases in abundance of pharmaceuticals, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the environment have drawn attention over public health. The presence of these contaminants in wastewaters is well-documented as a factor contributing to the decreased potency of antibiotics used in healthcare. These types of contaminants can be removed from wastewater using a number of techniques, including phytoremediation, which has demonstrated effectiveness. The removal of these contaminants by various aquatic plants has been explored, and the results are promising. The aim of this research was first, to analyze antibiotic resistance patterns of bacteria isolated from hospital wastewater effluent, which is a consequence of antibiotics occurrence in wastewater. Second, to investigate the removal of some selected antibiotics from synthetic wastewater in constructed wetland (CW) planted with Cyperus alternifolius, Canna indica, and one planted with both of these plant species, as well as the influence of antibiotics on microbial density and community in CW. Hospital wastewater samples were collected from the Benjamin Mkapa Hospital in Dodoma, Tanzania, where the hospital's wastewater is treated in a horizontal subsurface flow CW planted with Typha latifolia before being discharged into the environment. The results of hospital wastewater analysis showed that bacteria isolated from treated hospital wastewater were resistant to tested antibiotics and harbored antibiotics resistance genes. These findings demonstrate that CW can disseminate ARB and ARGs despite hospital wastewater treatment, which poses a risk to the public's health. In the pilot CW, the system planted with a single plant species (Cyperus alternifolius) outperformed those planted with mixed plant species or Canna indica alone in the removal of tested antibiotics from wastewater. This is supported by the observation of higher bacteria abundance in CW with Cyperus altenifolius than Canna indica, while the difference was not significant (p > 0.05). The findings of this investigation revealed that although there is a general decline in bacteria abundance, there is no significant change (p > 0.05) due to antibiotic presence in wastewater. It is concluded that, despite variations in performance, the plants studied play a significant role in pharmaceuticals remediation from wastewater
Climate and anthropogenic footprints implications on the surface and groundwater dynamics on the southern slopes of Mount Kilimanjaro, Tanzania
(NM-AIST, 2021-10) Said, Mateso
Climate and land use/cover changes impact water resources all over the world. This study aimed at developing a conceptual understanding and management of the impacts of present and future climate change and human activities on surface and groundwater resources on the Kikafu-Weruweru-Karanga (KWK) watershed. The methodology includes simulation of the present and prediction of the future hydrological fluxes and streamflow prediction under changing climate and land use/cover. Calibration and validation of the hydrological model, Soil and Water Assessment Tool (SWAT) showed satisfactory performance (Nash-Sutcliffe Efficiency (NSE)) > 0.50). A total of 22 parameters were used, and Curve number for soil moisture condition II, Baseflow alpha-factor, and average slope steepness were the most sensitive parameters. Future climate data for two Representative Concentration Pathway (RCPs) from Regional Atmospheric Climate Model -22T and Climate Limited Area Modeling 4 models were used. Land use/cover (LULC) maps were generated by classifying time-series (1996, 2006, and 2018) satellite images, selected spatial metrics were used to predict the LULC changes for the next decade using 2018 as a base year. Furthermore, the implications of selected staple crops production over the next decade was predicted. Simulated LULC shows expansion in built-up (by 32.55% and agriculture (by 39.52%) areas from 2018 to 2030, and the forest area is projected to shrink by 6.37%. However, the results suggest that farm size plays a minor role in increasing crop production. Expansion in cultivation land and built-up area attributed to the changes in water yield, surface runoff, evapotranspiration (ET), and groundwater flow. Rock-water interaction chiefly controls the groundwater quality in the presence of HCO3 enrichment and mixed CaNaHCO3 water types. The δ2H and δ18O values confirmed that recycled water is the primary recharge means, and glacier melts on Mt. Kilimanjaro sustains downstream water availability during the dry season. Furthermore, temperatures were projected to increase by 0.2ºC/year, and a decrease in precipitation was projected up to 2100 in both highland and lowland areas. The findings suggested the need to intensify the production per unit area rather than expanding the farm size. Also, improving the vegetation cover on the hillside and abandoned land area could help to reduce the direct surface runoff, and floods recurring in the area. The findings of this study are useful to facilitate sustainable water resources management in the watershed and other watersheds with or without modification.
Metal oxides modified Carbon electrode materials for Fluoride and Paraquat removal from water by capacitive deionization
(NM-AIST, 2024-06) Alfredy, Tusekile
Capacitive deionization (CDI) is an emerging water treatment technology with many advantages, including low energy consumption, high efficiency, low cost, green and pollution free electrode regeneration. However, the electrode material is the main controlling factor for achieving high CDI performance. For a long time, activated carbon (AC) has been a preferred electrode material for CDI due to its availability, ease of preparation, low cost, and tunable textural properties. However, the pristine AC lacks selectivity towards the targeted ions, resulting in unnecessary energy consumption for treating polluted water and decreasing the removal efficiency (RE) of the targeted pollutant. To improve ion selectivity, in this study, composites of AC with metal oxides have been synthesized through a simple and one-step co precipitation method at ambient temperature (23-27°C) for defluoridation and removing paraquat (PQ) from water. The composite properties were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X ray spectroscopy, and Brunauer-Emmett-Teller analysis. In competitive fluoride (Fˉ) removal CDI experiments, AC–Al4Fe2.5Ti4 composite reduced the Fˉ concentration from 5.15 to 1.18 mg/L, below the allowable limit of 1.5 mg/L set by the World Health Organization while pristine AC reduced the Fˉ concentration to 4.5 mg/L. Also, AC–Al4Fe2.5Ti4 composite demonstrated a high RE of 79% and excellent regeneration performance after continuous electric adsorption–desorption cycles. Furthermore, CDI batch experiments compared the electrosorption of paraquat (PQ) herbicide by the composite electrodes (AC-Al2O3: 1:1) and pristine AC. The performance of the composite electrodes showed that PQ RE and electrosorption capacity (EC) depend on aluminium content loading, applied potential, flow rate, and charging time. At 1.2 V, a flow rate of 15 mL/min, and a charging time of 3 h, the composite electrode demonstrated a RE, EC, and energy consumption of 95.5%, 1.27 mg/g, and 0.055 kWh/m3 , respectively, compared to 62%, 0.83 mg/g, and 0.11 kWh/m3 for the pristine AC. The presence of other ions/pollutants was found to have negligible interference on PQ pesticide removal as the RE of the AC/Al2O3-1:1 composite in both artificial and natural water were 95.5 and 87.5% while EC was 1.27 and 1.17 mg/g, respectively. Therefore, the modified AC-metal oxides electrodes are promising and efficient materials for removing inorganic pollutants from water, such as Fˉ and organic pollutants, including PQ pesticides for CDI technology
Optimization of sub- and supercritical water gasification of rice husk enhanced with iron-doped alkaline-earth catalysts
(NM-AIST, 2022-05) Bakari, Ramadhani
Biomass is a promising renewable energy source widely available worldwide, particularly in developing countries where clean and affordable energy is a major problem. Biomass gasification is an attractive technology that can transform biomasses into a more versatile fuel known as syngas, tar (bio-oil) and biochar. Syngas is a hydrogen-rich gas that could promote a clean and green energy and promote the agriculture sector. The utilisation of syngas would reduce dependence on fossil-based fuels and eventually reduce the carbon footprints. The gasification technology faces operational challenges; one of the problems is tar formation, slow char gasification reaction, and poor performance of catalysts. These challenges are influenced by inappropriate operating conditions and the precursors employed in catalyst synthesis. In this study, the optimisation of noncatalytic and catalytic gasification of rice husk is reported. The rice husk biomass was gasified under subcritical and supercritical water conditions in a batch autoclave reactor. The effect of temperature (350-500°C), residence time (30-120 minutes), and feed concentration (3-10 wt%) is optimised. Moreover, the effect of the addition of natural, calcined and Fe doped limestone and dolomite catalysts on the gasification yield is studied using a response surface methodology. The catalyst was prepared by a facile incipient wetness process using chlorine- and sulphur-free iron (III) ammonium citrate precursor. Optimisation of operating conditions suggests a quadratic model for gasification efficiency, gas volume, char yield, and gravimetric tar. The findings revealed that higher temperatures, longer residence times and lower feed concentrations favoured high gas yields. The lowest tar yield obtained was 2.98 wt%, while the highest gasification efficiency and gas volume attained was 64.27% and 423 mL/g, respectively. The findings of the catalyst characterisation revealed that the predominant reactive site of Fe/limestone catalyst is iron oxide, calcium ferrite, and calcium oxide. Under all conditions tested, the manufactured catalyst was highly active in promoting char gasification, gas volume and gasification efficiency. Tar yield was substantially promoted at low temperatures and high feed concentrations, but at high temperatures and low feed concentrations (500oC, 3 wt%), tar formation was suppressed by 22%, while char gasification was enormously enhanced by 65%. The maximum gas yield of 560 mL/g biomass was obtained under the catalytic conditions of 5%Fe/limestone, 15% catalyst loading, 500oC, 120 minutes, and 3 wt% feed concentrations. Therefore, these findings revealed that the rice husk's energy content could be harnessed using supercritical water gasification to obtain substantial fuel products.
Simulation and performance analysis of municipal solid waste gasification in a novel hybrid fixed bed gasifier
(NM-AIST, 2022-06) Moshi, Robert
Municipal Solid Waste (MSW) is a main challenge to municipalities in developing countries due to the increase in its production caused by technology development, community culture, population growth, and urbanization. The challenge is heightened by the scarcity of dumping sites within municipalities and the environmental impact associated with improper disposal management. Thermo-chemical conversion technologies (gasification, pyrolysis and incineration) have become to be known as practicable technologies for municipal solid waste management (MSWM). In this study, the Hybrid Fixed Bed Gasifier (HFBG) model was developed using Aspen Plus in order to merge the advantages of both downdraft and cross draft gasifiers and suppress their disadvantages. Furthermore, experimental analysis of the flue gas was carried out on the HFBG. The TESTO 327- 1 flue gas analyzer was used to analyze the concentration of CO, CO2 and O2. The simulated results showed that the feedstock MC of about 59.8 wt% was lowered to 6.8 wt%. The developed hybrid fixed bed gasifier demonstrated an increase in 2 H and CO of about 29.29 % and 37.05 % mole fraction in the producer gas respectively. The syngas output was highly affected by the changes in the ER as well as change in temperature. The composition for 2 H and CO increases with increase in temperature while the composition decreases with ER between 0.1 to 0.4. However, at this ER CO2 and H O2 tend to increases but above 0.4 CO2 and H O2 decrease gradually. Experimental results show that after the elapse of 30 minutes CO and CO2 concentration was 9.69% and 5.85% respectively. Furthermore, after 150 minutes of the gasification process, the output concentration for O2 was 17.2 % while the concentration for CO and CO2 was 0.0 % and 3.77 % respectively. The experimental results revealed that, during the entire gasification process the concentration for CO and CO2 were decreasing with time while O2 concentration was increasing. This result shows diversion from the simulated results due to gasifier leakages. With high MC of MSW, the study has shown that, HFBG can handle up 60 wt% as compared to downdraft which is limited to 20 wt%.
Structural and biophysical characterization of cassava linamarase and the role of solvents on linamarin’s properties: a computational study
(NM-AIST, 2022-06) Paul, Lucas
Linamarase and linamarin mainly from cassava have many applications ranging from food, environmental to the medical industry. To better explore the potential of this enzyme and its substrate, one needs to understand its interaction mechanism at the molecular and atomistic level. In this thesis, the three‒dimensional (3D) structure of linamarase was built via homology modeling. The developed model was used to determine the binding orientation and mechanism of linamarin to the enzyme using molecular docking. Molecular dynamics simulation was used to determine the stability of the built model and when complexed with the ligand. It was interesting to note that complex 1 with the low binding‒free energy of ‒6.9 kcal/mol showed a larger Root Mean Square Deviation (RMSD) value with two maxima at 0.255 and 0.310 nm compared to complex 2 with the best binding‒free energy of ‒7.2 kcal/mol, whose RMSD value shows the maxima at 0.19 nm. The end‒point free energy method based on Molecular Mechanics Poisson Boltzmann Surface Area (MM/PBSA) was used to rescored binding free energy obtained from docking calculations. The ensemble structure was observed to be relatively stable compared to the modelled structure. Furthermore, the stability and conformational orientation preferences of linamarin in different solvents was established using classical molecular dynamics, and found to be solvent dependent. The effects of solvents on the stability and conformational preference is pronounced by different probability density maxima of the measured reaction coordinate/properties. Linamarin is observed to be stable in methanol followed by dimethyl sulfoxide (DMSO) and least stable in water. Solvent polarity was observed to influence the stability and conformation preference of the title compound. Linamarin exists in trans and gauche conformations, the former was observed to be more stable in water than other solvents and the latter in DMSO. The measured reaction coordinates, distance and dihedral angles ascertained that the conformational preference is due to rotation at 𝜙 = ± 180o and 𝜙 = ± 50o . Finally, the stability of linamarin was also attributed to different numbers of inter and intra hydrogen bonds formed in different solvents. Results presented in this thesis provides atomistic insights on the role of solvents polarity on linamarase‒linamarin complex interaction and stability. The findings provide important information on the application of linamarase and linamarin in different fields including food processing and in drugs.

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