PhD Theses and Dissertations

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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
The impacts of land use and climate change on Simiyu river discharge and the riverine sediment dynamics flowing towards lake Victoria
(NM-AIST, 2024-07) Shinhu, Renatus
This study aimed to trace the dominant sources of riverine sediments and assess climate change's current and future impacts on the river discharge at the critical agroecological region of the Simiyu catchment. Geochemical fingerprinting of the riverbed sediments and potential sediment sources were compared using a Bayesian mixing model (MixSIAR) to attribute the dominant riverine and land-use sources to the Simiyu Mainstem. The mixing model outputs showed that the Simiyu tributary was the dominant sediment source to the Simiyu Mainstem with 63.2%, while the Duma tributary accounted for 36.8%. Cultivated land was shown to be the main land-use source of riverine sediment, accounting for 80 % and 86.4% in the Simiyu and Duma sub-tributaries, respectively, followed by channel banks with 9% in both sub tributaries. The Soil and Water Assessment Tool (SWAT) under RCPs 4.5, 6.0, and 8.5 were also used to project the impacts of climate change on river discharge throughout 2030–2060. The selected three General Circulation Models (GCMs) predicted an increase in the annual average temperature of 1.4°C in 2030 to 2°C in 2060 and an average reduction of 7.8% in rainfall, which causes a decrease in river discharge. The simulated river discharge from the hydrological model under RCPs 4.5, 6.0 and 8.5 revealed a decreasing trend in annual average discharge by 1.6 m3s−1 from 5.66 m3s-1in 2019 to 4.0 m3s-1in 2060. Arbitrary, there will be an increase in frequent flood occurrence in the future (2030–2060) compared to the current period (1990–2019), with extreme discharges of 451.3 m3s−1and 232.8 m3s−1 at exceedance probabilities of 0.01% and 99.99%, respectively. The demonstrated application of sediment source tracing provides an important pathway for quantifying the dominant sediment sources in the rivers flowing towards Lake Victoria. This information is vital for designing catchment wide management plans that should focus on buffering the projected decreases in discharge, reducing soil erosion and sediment delivery from farming areas to the river networks, and ultimately supporting food security and water quality in the Lake Victoria Basin
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
Potential use of zero-valent iron in enhancing performance and resource recovery during the anaerobic digestion of domestic sewage
(NM-AIST, 2024-08) Bakari, Omari
Incorporating metallic iron (Fe 0 ) into anaerobic digesters can improve organics (chemical oxygen demand (COD)), phosphorus, and nitrogen from contaminated water. However, no study has systematically assessed Fe0 -supported anaerobic digestion (AD) systems for removing organic compounds and nutrients from domestic sewage (DS), limiting our understanding of their potential to replace tertiary treatment units. Besides, existing studies often focus on single contaminants at high concentrations, which may not reflect real-world effluents with multiple pollutants. Variations in experimental conditions and the type of wastewater effluent treated complicate comparisons across studies. Additionally, there is a lack of comprehensive evaluations of predictive models for methane (CH₄) yields in Fe0 -supported AD systems, hindering the identification of the most effective model and affecting future research and applications. Moreover, there is little information on sludge characteristics from Fe0 -aided AD systems and their potential applications. This research focused on three primary objectives: (i) assessing the impact of Fe0 type and dosage in AD systems for the simultaneous removal of COD and nutrients (orthophosphate (PO4 3- ), ammonium (NH4 + ), nitrate (NO3 - )), and (ii) characterizing the solids and biogas in Fe0 -supported AD of DS, and (iii) evaluating the Gompertz, Logistic, and Richard models for methane yield prediction. Two distinct experiments were conducted at various scales. In the first experiment, lab-scale reactors containing DS were subjected to varying dosages of Fe0 (0 to 30 g/L) over 32 experimental runs conducted for 76 days at a constant temperature of 37 ± 0.5℃. In the second experiment, bench-scale reactors with DS were fed with Fe0 and operated over 15 experimental runs for 53 days at 24 ± 3℃ temperature. Iron scraps (SI) and steel wool (SW) were used as the Fe0 sources. A control experiment was also conducted. It was found out that: (a) the optimal Fe0 dosage for organic and nutrient removal was 10 g/L SI, (b) NH4 + and NO3 - removal showed the lowest removal efficiency, and (c) maximum removal efficiencies for COD, PO4 3- , and NH4 + + NO3 - were 88.0%, 98.0%, and 40.0% for 10 g/L SI; 88.2%, 99.9%, and 25.1% for 10 g/L SW; and 68.9%, 7.3%, and 0.7% for the control system. Fe0 significantly enriched nutrients in the sludge, improved settling characteristics, and increased the percentage of methane content in biogas by over 12%. All tested methane prediction models showed good accuracy (error < 10%), with the Richard model demonstrating the highest level of fit (error < 1.6%). These findings confirm the effectiveness of Fe0 -supported AD in removing organics and nutrients from DS, producing agriculturally suitable sludge, and enhancing biogas methane content for potential energy recovery
Investigation of uranium derived from phosphate fertilizers on plants uptakes and bacterial diversity in selected agricultural soils of east africa
(NM-AIST, 2024-08) Mwalongo, Dennis
Different types of phosphate fertilizers (PFs) used in agriculture to increase soil fertility contain uranium (U) as an accompanying element. Uranium is both toxic and slightly radioactive. This study investigated the concentrations of U in phosphate rocks (PRs) and PFs used in growing tobacco (Nicotiana tabacum L.) and maize (Zea Mays L) plants from Burundi, Kenya, Rwanda, Tanzania, and Uganda. The results showed that the concentrations of U in phosphates from Burundi, Kenya, Tanzania and Uganda were statistically significant (P ≤ 0.01). The lowest U concentration was 10.7 mg kg−1 found at the Mrima Hill deposit in Kenya and the highest was 631.6 mg kg−1 found at the Matongo deposit in Burundi. Uranium concentrations for local and imported PFs was also statistically significant (P ≤ 0.01). Uranium concentration from PFs ranged from 107.88 ± 9.60 and 281.57 ± 15.82 mg kg−1 . The study also assessed the influence of U from PFs on the radioactivity of agricultural soils and uptake by tobacco plants. The results showed that applications of PFs in agricultural soils increased radioactivity in agricultural soil and tobacco crops. Tobacco smoking and snuffing behaviors resulted in an annual effective dose that was 2.41-6.53 and 1.14-2.45 times greater than annual recommended effective doses for snuffers and smokers. This work also investigated the influence of fertilizer derived U on maize plant uptake and bacterial diversity in soil after application of fertilizers with varying U concentrations. The pilot field experiments showed that application of PFs with different U concentrations influenced bacteria abundance and diversity in maize crops. Applications of Nafaka plus (NP) (3.93 mg kg-1 ) and Minjingu Powder (MP) (3.06 mg kg-1 ) PFs in soil increased bacteria abundance and diversity. Some bacteria were abundant on NP treated soil (high U content) because of their ability to tolerate higher U concentrations. Uptake from soil to crop for maize after applications of PFs of varying U concentrations was investigated by amending soil with Eucalyptus globulus ssp maideii bark and kaolin clay. The soil amendments in reduced U uptake from soil to plant in pot experiments. It is believed that the reduced U uptake is associated with eucalyptus globulus ssp maideni carboxyl groups that can reduce mobile hexa-uranyl ions to immobile tetra uranyl ions that can be absorbed by the kaolin clay. The study recommends further work in understanding the mechanisms of Eucalyptus ssp maidenii bark powder and kaolin U uptake reduction in soil complex matrix.
Valorisation of solid sisal leaves decortication wastes using black soldier fly (hermetia illucens l.) larvae
(NM-AIST, 2024-08) Konyo, Aziza
The amount of waste generated from sisal industries during sisal fiber production is huge and its management is still challenging and a menace to the environment. These wastes include sisal wastewater and sisal leaf decortication wastes (SLDW) which represent an opportunity for valorization into products. Nevertheless, the sisal leaf decortication wastes is suitable for resource recovery in order to reduce the impacts it causes by just being discarded in the environment without treatment. This study aimed at managing the SLDW using insect-based technology. Specifically, the study characterized the SLDW for its physical and chemical constituents, pretreatment of SLDW to render it suitable for the growth of the insects and optimization of the waste and other blends for production of livestock feed. The use of SLDW for various applications is limited due to its high acidic content and presence of saponin within it. This is the first study of its kind regarding the use the SLDW as a substrate for growth of BSFL. Pre-treatment was a necessary and challenging step done on the waste to meet minimum requirements for rearing of BSF. The resultant waste had Ca, P, K, Mn, Fe, Cu and Zn at varying levels which are all essential for animal growth. The SLDW contained 10 ± 0.01 percent of crude protein, 11 ± 0.02 moisture and energy (1615 kcal/g of Sisal de-corticated waste). The sun dried BSF larvae reared on SLDW contained 53 ± 0.005 percent crude protein, 4 ± 0.01 percent of crude fat, moisture content (10 ± 0.1) %, carbohydrate (43 ± 0.01) % and ash (37 ± 0.08) %. When rearing was done on SLDW, 3000 g of dried pre-treated waste yielded more wet BSF larvae (336 ± 41.3) g compared to 3000 g of fruit waste which yielded (244 ± 4.16) g of wet BSF larvae. Furthermore, the harvested BSFL after optimization process through blending of SLDW, RB and CDW improved growth rate of BSFL (2.2 gram per larvae) and contained sufficient nutritional value to feed poultry and fish, reducing the necessity to de-fatty the larvae as it is being practiced when market waste is being used. The SLDW is a promising feedstock for rearing BSFL because it has good reduction of the waste by 52%. This study eventually creates resource recovery sustainability in sisal industries.
Optimization of arsenic(III) and mercury(II) removal from non-competitive and competitive sorption systems onto activated carbon
(NM-AIST, 2024-07) Bayuo, Jonas
Heavy metals exist in the ecosystem both naturally and due to anthropogenic activities and as recalcitrant pollutants; they are non-biodegradable and cause acute and chronic diseases to human beings and many lifeforms. As a result, the removal of heavy metals from aqueous systems using sorbent materials produced from agricultural wastes is one of the new innovative treatment techniques. In this study, the biosorption and desorption characteristics of heavy metal ions from non-competitive and competitive aqueous solutions onto hybrid granular activated carbon produced from maize residues were investigated. The efficient sequestration of As(III) and Hg(II) ions from both monocomponent and bicomponent synthetic wastewater was found to show dependence on the physicochemical properties of the biosorbent and the studied independent biosorption process factors. The regenerated biosorbent could be reused up to the eighth cycle for the sequestration of As(III) and Hg(II) ions from the synthetic wastewater without significantly losing its adsorptive properties. The applicability of the biosorbent synthesized from the maize residues for the simultaneous decontamination of heavy metals found in real industrial wastewater as a function of several biosorption factors showed that the biosorbent could competitively decontaminate over 96% of As, Hg, Pb, Cd, and Cr in 100 mL textile wastewater in batch mode. The regeneration of the spent biosorbent using 0.10 M HCl showed that the biosorbent is capable of being recycled and reused severally for the sequestration of As, Hg, Pb, Cd, and Cr from the textile wastewater and even up to the ten cycles for a duration of 4 h. The optimization of the competitive removal of As and Hg ions in the co-existence of other heavy metals in the textile wastewater by the CCD-RSM resulted in maximum removal efficiencies of 97.72 and 99.99%, respectively. The characterization of the hybrid granular activated carbon using SEM, TEM, XRD, BET, and FTIR showed that the biosorbent surface characteristics could facilitate the removal of heavy metals from the non competitive and competitive biosorption media. The main biosorption mechanism of the heavy metal ions on the biosorbent was mainly chemisorption involving surface complexation. Therefore, this novel biosorbent is found to be promising and could effectively be employed for heavy metals remediation in aquatic environments. The outcomes of this study are expected to make a significant contribution to the design of low-cost and efficient industrial wastewater treatment systems such as a dynamic batch rector for heavy metal removal using locally available bio-adsorbents.
More than pollutant removal: constructed wetlands and waste stabilization ponds as biodiversity hotspots and community assets in Tanzania
(NM-AIST, 2024-05) Msaki, Gerubin
Waste stabilization ponds (WSPs) and constructed wetlands (CWs) are important ecotechnologies for wastewater treatment. Despite their potential and wastewater management being challenging in urban and peri-urban areas of Tanzania, their adoption and sustainability is not well developed. This study examined (a) social knowledge, attitude, and perceptions (KAPs) on wastewater treatment, technologies involved, and reuse across municipal wastewater treatment plants in four regions of Tanzania; (b) biodiversity of birds, insects, and reptiles in constructed wetlands (CWs) and waste stabilization ponds (WSPs), and (c) bacterial abundance and diversity in different types of CWs. A semi-structured household-level questionnaire (n=327) was used to collect quantitative and qualitative data. The survey involved observations and face-to-face interviews to assess social KAPs on wastewater treatment, technologies, reuse, and potential health risks. Key informants were selected purposively (n=8). The study also employed point counts, direct observations, and camera traps to assess bird diversity in WSPs and CWs. Direct observation and pitfall traps along established transects were used to collect and assess insects and reptiles. Fishnet was used to assess the reptiles living in the WSPs. Additionally, wastewater was collected in four different CWs for bacterial diversity establishment. Community KAPs were analyzed using SPSS, while Jamovi and PAST software were used to analyze the diversity and abundances of birds, insects, and reptiles, whereas bacterial community composition was characterized using Illumina-based sequencing of the V3 and V4 hypervariable region of 16S rRNA. The results show that social KAPs surrounding wastewater treatment and reuse were sufficient based on the KAPs score achieved from the asked questions. However, the general knowledge of treatment technologies, processes and reuse risks was found to be low. Over 90% of respondents were unaware of wastewater treatment technologies and the potential health risks associated with using treated wastewater (59%). Multivariate analysis of variance revealed significant differences (P < 0.05) in KAPs for treated wastewater across different demographic variables examined, i.e., age, sex and education level. Furthermore, results showed that birds exhibit high species abundance (n = 1132), high species richness, Margalef index (D = 4.266), evenness (E = 0.815), Shannon diversity (H = 2.881) and Simpson index (λ =0.903). The abundance and diversity of studied groups differed significantly (P<0.05) between WSPs and CWs. In addition, the results showed that the Proteobacteria were dominant (48.66%) phyla across all CWs. The Gammaproteobacteria class (27.67%), the family Comamonadaceae (35.79), and the genus Flavobacterium (4.35%) were dominant in all examined CWs.
Solvothermal liquefaction of orange peels and catalytic upgrading of biocrude into transportation fuel over a hybrid catalyst
(NM-AIST, 2024-08) Kariim, Ishaq
The efficient valorization of biomass for energy-derived biocrudes is essential for effective waste management. However, the production of biocrudes with high energy and reduced oxygen contents during the liquefaction process requires further improvement. This study investigates the impact of reaction temperature, residence time, and ratio of ethanol to acetone on the energy compositions and bio-product’s yield enhancement were investigated under non catalytic and catalytic process with further upgrading. The biocrudes obtained via the non catalytic liquefaction were characterized for elemental composition, bio-oil compositions, functional group, molecular weight and thermal stability to understand the effects of process parameters on the biocrudes’ compositions. An improved bio-oil with High Heating Value (HHV) (38.18 MJ/kg) and lower oxygen: carbon (O/C) ratio (0.11) were obtained at 430 ◦C, 35 min and 50% ethanol with a significant boost in the enhancement factor, deoxygenation, and percentage hydrogenation of 2.63, 36.88%, and 77.87%, respectively. The presence of ketones with composition of 32.58 area% suggests the needs for the removal of oxygen from the bio-oil. Using a central composite design (CCD), catalyst dosage (3-6 wt.%) and reaction temperature (330-430°C) were optimized, maintaining constant orange feedstock weight (10g), reaction time (15 minutes), and a solvent ratio of 3:1 (acetone to ethanol). Optimal biofuel yield (71.09 wt.%), solid residue (28.18 wt.%), biomass conversion (71.82 wt.%), and gas yield (40.14 mL/g) were achieved at 430°C and 3 wt.% catalyst loading. The Fe/CNSs catalysts possess high selectivity to acid formation. High correlation coefficients indicated the model’s strong fit with experimental data. The hydrodeoxygenation (HDO) of cyclohexanone under both catalytic and non-catalytic conditions involved mechanisms such as hydrogenation, decarboxylation, decarbonylation, and dehydration. The NiCeMo catalysts shows an even particle dispersion where 11.3 area % of hydrocarbon and highest conversion of ketones and phenols were obtained. However, the performance of NiCeMo catalysts for HDO was hampered by the Guerbet reaction, which led to the formation of side products which are primarily alcohols. Modifying the acidity and using water as a solvent could potentially increase the HHV of the biofuel hence, promote the usage for transportation purposes. Biofuel produced through the non-catalytic process demonstrated a higher energy value of 38.18 MJ/kg, highlighting orange peels as a viable renewable energy resource
Influence of rice husk derived nano-silica on performance, emissions, and combustion characteristics of diesel engine fueled with baobab biodiesel
(NM-AIST, 2024-08) Kapile, Fredrick
The increasing number of on-road automobiles as a result of an exponential increase in population and lifestyle places enormous strain on depleted fossil petroleum fuel, energy security, and environmental stability. This situation drives researchers to find an alternative source to replace petroleum diesel. Biodiesel is one of the promising viable substitutes. However, biodiesels may not always fulfill the EN 14214 standard due to differences in fuel properties. This could cause issues with engine operation and emissions. This study therefore aims to use novel nano-silica (SiO2) additives extracted from rice husk to improve its fuel properties. Also focuses on the influence of additives on the operation of the compression ignition (CI) engine. The Adansonia digitata methyl esters (ADME) were made by transesterification process, The physicochemical properties of the fuels with and without additives were measured as per ASTM D6751 and EN 14214 standards methods, and nano silica was analyzed by Thermogravimetry (TGA), Fourier transform infrared spectroscopy (FT-IR), Brunauer Emmett Teller (BET), X-ray diffractometer (XRD. Barret-Joyner Halenda (BJH) pore diameter, specific surface area, and pore volume of SiO2 were observed to be 19.3 nm, 502.24 m2 /g, and 0.761 cm3 /g, respectively. At 400 and 800 ppm dose levels, the oxidation induction period (OIP) increased dramatically, peaking at 10.03 h. The stability of ADME has significantly improved, as evidenced by these results, meeting the >3 h and >8 h standard limits set by ASTM D6751 and EN 14214, respectively. The viscosity of B100 decreased with increasing additive content, from 4.62 mm2 /s for neat B100 to 2.21 mm2 /s for 400 ppm. Cetane number (CN) (60 to 64). All nano-fuel blends used in engine tests were prepared by an ultrasonication process. The results revealed that the brake thermal efficiency (BTE) at maximum brake powers (BP) for B20, B20+SiO2, B100, and B100+SiO2 fuels were 29.9, 28.2, 28.44, and 27.1%, respectively, and brake-specific fuel consumption (BSFC) was reduced as the load increased. The peak heat release rate (HRR) of the B100+SiO2 and B20+SiO2 are slightly higher by 2.9 and 2.6%, respectively, than the neat B100 at medium BP. However, in-cylinder gas pressure (CGP) increased following the order of B20+SiO2
Emerging pollution, antimicrobial resistance, and the applicability of biochar adsorbents: A comprehensive study in African water systems
(NM-AIST, 2024-07) Ripanda, Asha
The impacts of antimicrobial resistance (AMR) extend far beyond clinical settings, permeating into agriculture and the economy, precipitating dire consequences such as compromised treatment efficacy, diminished agricultural productivity, and substantial economic burdens. This study aimed at investigating the occurrences, composition and distribution of antimicrobial pollutants and further study the remediation of lamivudine and ciprofloxacin from synthetic solutions onto JS biochar using a response surface methodology (RSM) based on optimal design. Results indicates identification of Klebsiella spp., Proteus spp., Pseudomonas aeruginosa, and Escherichia coli and were resistant to at least 1 of the tested antibiotics, indicating their presence in wastewater and urban receiving waters. Higher proportion of multi-drug resistance (MDR) in Escherichia coli,83%, than Klebsiella spp., 68.5% and Pseudomonas aeruginosa, 20%. All bacterial species highly resisted penicillin (P), while showed less resistance to gentamycin (CN). The isolates contained sulphonamide resistant genes (Sul 1 and Sul 2), tetracycline-resistant genes (Tet A, Tet B – 1, and Tet D) and β-lactamases (bla CTX-M and bla SHV), and Escherichia coli harboured more MDR genes (39%), followed by Klebsiella spp., 22%. JS biochar was amorphous, with porous, rough surface and potential functional groups for adsorption of contaminants. Further, results indicate increase in carbon content of JS biochar from 64.25-87.93 (wt.%) and nitrogen from 2-2.29 (wt.%) when calcination temperature increased from 400℃ to 600℃, with highest surface area of 261.2 m2/g and adsorption capacity of 555.55 mg/g for ciprofloxacin and 400 mg/g for lamivudine. Lamivudine removal had a model regression coefficient R2 , adjusted R2, and predicted R2 of 0.9934, 0.9761, and 0.8340, respectively. While for the ciprofloxacin model, the regression coefficient R2, adjusted R2,and projected R2 were 0.9968, 0.9891, and 0.8023, respectively. The maximum experimental removal efficiency of lamivudine and ciprofloxacin onto JS biochar reached 84.9% and 94.46%, respectively. Isotherm data indicated lamivudine and ciprofloxacin adsorption onto JS biochar followed the Freundlich isotherm. The study identified antimicrobial residues as well as the presence of antibiotic resistant bacteria in water. It also demonstrated the effectiveness of JS biochar adsorbent for remediation of lamivudine and ciprofloxacin from synthetic water, indicating future improvement and use in mitigating antimicrobial resistance.
Computational and experimental performance analysis of a runner for gravitational water vortex power plant
(NM-AIST, 2024-08) Faraji, Adam
Energy generation through water is one of the most economic sources of power. On the other hand, isolated and rural communities can both benefit from using micro-hydropower to power their homes. The gravitational water vortex power plant (GWVPP) has recently attracted interest due to its low initial investment, straightforward design, simple maintenance requirements, and low head requirements. However, the technology suffers a low performance caused by unoptimised parameters of its crucial components, such as the GWVPP runner. This study presents the results of numerical simulation and experimental approaches for the GWVPP runner. To understand how each factor affected the efficiency of GWVPP runner, four parameters (hub-blade angle, speed, runner profile, and number of blades) were examined. The (custom) design tool of Design-Optimal Expert was used to create twenty-four (24) experimental runs. Commercial Computational Fluid Dynamics (CFD) software, specifically Ansys CFX, was employed to simulate these runs and assess the system's efficiency. R2 values of 0.9507 and 0.9603 for flat and curved profiles indicate a better model fitting to actual data. Additionally, the numerical analysis led to a 3.65% improvement in the efficiency of the curved blade profile runner, while the flat runner profile's efficiency increased by 1.69% compared to non-optimized scenarios. The validation process revealed that the comparison between the numerical investigation and experimental results demonstrated a promising agreement, further supporting the accuracy of the numerical analysis. The experimental finding depicts that the efficiency was 9.84 - 25.35%, torque was 0.08 – 0.23 Nm, and the output power was 2.96 – 7.33 W. Furthermore, the results portray the numerical efficiency to be slightly greater by 0.54% than the experimental efficiency, presumably because the frictional forces were not incorporated in the numerical analysis. Additionally, the exergy analysis of the system revealed a value of 43.58%. The power error range was between 0.1 and 0.5 W, with a low variation in the data points. The torque error range was relatively lower than the power error range, ranging from 0.01 to 0.03 Nm, and the torque measurements showed a low variation in the data points. The efficiency error range was generally low, with most errors falling within the 1.3-3.1% range. Therefore, the GWVPP runner efficiency can be improved significantly through numerical analysis and experimental studies. Also, based on the above results, the GWVPP runner and GWVPP system are recommended for energy generation in low-head and flowrate water sources.
Tin molybdenum mixed metal oxides catalyst for oxidative desulfurization of model diesel
(NM-AIST, 2023-08) Lesafi, Fina
This study reports on synthesis, characterization, and catalytic activity of mesoporous mixed metal oxides of tin (Sn) and molybdenum (Mo) for sulfur removal from model diesel. Variable synthesis conditions, namely calcination temperature and Sn/Mo mole ratios, have been on focus. Several techniques were used to characterize the catalysts, including powder X-ray diffraction (XRD) for the crystal structure, orientation, and particle size; scanning electron microscopy (SEM)-EDX for examining the morphological properties of the materials, N2 adsorption-desorption isotherms for textural properties, thermal gravimetric analysis (TGA) for thermal stability, the Fourier transform infrared spectroscopy (FT-IR) for functionality. Characterization results show that the adsorption-desorption isotherms are of type IV, indicative of mesoporous materials. The surface area of the synthesized materials decreased as calcination temperature increased due to the Ostwald ripening process and increased with the mole ratio Sn/Mo increase. The X-ray diffraction structural analyses revealed that the synthesized catalyst had a tetragonal structure. The presence of Mo=O and Sn‒O‒Mo bonds, which are responsible for the catalytic reaction, is confirmed by FT-IR and Raman analyses. The activity of the catalysts prepared at various calcination temperatures and mole ratios was analyzed for oxidative desulfurization of model diesel, dibenzothiophene (DBT). The optimal synthesis conditions were the calcination temperature of 450 °C and the mole ratio of Sn/Mo of (2:1). Other multiple parameters affecting the reduction of sulfur compounds were also investigated, including reaction temperature, catalyst loading, oxidant/sulfur ratio, and reaction time. The (DBT) removal efficiency was 99.8 % at 60 °C, 100 mg, 5, and 30 min, correspondingly. This high catalytic activity was due to the surface defects increase,resulting in a high surface area with high pore distribution around the mesopore region. Experiments examining the reaction kinetics have indicated that the reaction follows a pseudo first-order behaviour. The activation energy for the reaction has been determined to be 36 ± 4 kJ mol-1 . The rate of the heterogeneous reaction is governed by the Langmuir-Hinshelwood mechanism. Furthermore, the maximum rate constant value of SnO2-MoO3 catalyst with Sn/Mo (2:1) molar ratio is 0.057 min−1, which is higher than for pure SnO2 (0.017 min‒1 ) and MoO3 (0.007 min−1 ), confirming a synergy between SnO2 and MoO3, promoting oxidative desulfurization efficiency. The catalyst's high activity and reusability indicate enormous promise for industrial catalytic desulfurization.
Surface water – groundwater interactions: A case of a shallow semi-closed lake catchment in northern Tanzania
(NM-AIST, 2023-06) Okwir, Gustavio
Conjunctive use of surface water and groundwater is rapidly growing in many developing countries as an adaptation strategy to climate variability and change. However, the interactions between the groundwater and the surface water systems are not adequately understood, especially among the East African rift valley lakes, where data paucity has limited studies and reporting on the spatial influence of catchment heterogeneity. In its humble contribution to sustainable water development, this study aimed to present a platform for understanding the influence of climatic variation and anthropogenic activities on surface water–groundwater interactions. To be relevant locally, Lake Babati, a freshwater lake in Northern Tanzania that provides the community with fish, freshwater, and a habit for hippopotamus, was studied. The study applied hydrological simulation, grey relational analysis, and stepwise regression analysis to model the hydrological behaviour of the lake. Further, it used hydrogeochemistry and environmental isotopes to identify groundwater fluxes and draw the conceptual understanding of surface water – groundwater interaction and applied topography-based indices to spatially map groundwater potentials within the catchment. The results showed that Lake Babati level is significantly declining (p-value < 0.01) at a rate of 25 mm per annum. The lake level decline could not be explained by climatic variability since the decline occurred when both evaporation and rainfall showed no significant changes either seasonally or annually. Instead, the consistent decline of the lake level in all seasons could be due to the expansion of the spillway, which effectively lowered the lake reservoir level and increased the lake outflow in rainy seasons. The hydro-geochemistry and isotopes data showed that the lake water and groundwater interact and are in hydraulic connections. Further, using Height Above Nearest Drainage based and Topography Wetness Index based methods, the study developed two groundwater potential maps to predict groundwater spatial variability and guide groundwater prospecting efforts and subsequent development. Given that Lake Babati is in a hydraulic connection with the groundwater, its consistent decline will likely impact the groundwater system. Similarly, abstracting groundwater at unsustainable rates could lower the lake levels further. Therefore, integrated water resources management is required for sustainable water resources development and management in the catchment. Mandatory and continuous monitoring of the water resources (groundwater levels, river flows, and lake levels) is recommended to generate quality in situ data for future studies.
Short-term forecast techniques for energy management systems in microgrid applications
(NM-AIST, 2023-07) Mbuya, Benson
In the 2015 Paris Agreement, 195 countries adopted a global climate agreement to limit the global average temperature rise to less than 2°C. Achieving the set targets involves increasing energy efficiency and embracing cleaner energy solutions. Although advances in computing and Internet of Things (IoT) technologies have been made, there is limited scientific research work in this arena that tackles the challenges of implementing low-cost IoT-based Energy Management System (EMS) with energy forecast and user engagement for adoption by a layman both in off-grid or microgrid tied to a weak grid. This study proposes an EMS approach for short-term forecast and monitoring for hybrid microgrids in emerging countries. This is done by addressing typical submodules of EMS namely: load forecast, blackout forecast, and energy monitoring module. A short-term load forecast model framework consisting of a hybrid feature selection and prediction model was developed. Prediction error performance evaluation of the developed model was done by varying input predictors and using the principal subset features to perform supervised training of 20 different conventional prediction models and their hybrid variants. The proposed principal k-features subset union approach registered low error performance values than standard feature selection methods when it was used with the ‘linear Support Vector Machine (SVM)’ prediction model for load forecast. The hybrid regression model formed from a fusion of the best 2 models (‘linearSVM’ and ‘cubicSVM’) showed improved prediction performance than the individual regression models with a reduction in Mean Absolute Error (MAE) by 5.4%. In the case of the EMS blackout prediction aspect, a hybrid Adaptive Similar Day (ASD) and Random Forest (RF) model for short-term power outage prediction was proposed that predicted accurately almost half of the blackouts (49.16%), thereby performing slightly better than the stand-alone RF (32.23%), and ASD (46.57%) models. Additionally, a low-cost EMS smart meter was developed to realize the implemented energy forecast and offer user engagement through monitoring and control of the microgrid towards the goal of increasing energy efficiency.
Remediation of soils contaminated with fluoride using seaweed-derived materials: case of slopes of mount Meru
(NM-AIST, 2023-08) Moirana, Ruth
While exposure to low fluoride is essential for stronger bones and teeth, exposure to high concentration (> 3 mg/L/day) leads to hyperostosis and osteoporosis. This research evaluated the role of fertilizer application on soil’s fluoride release, and assess the effectiveness of using seaweed (Eucheuma cottonnii) derived materials for remedial purposes. The soil characterization results in the study area, indicated the availability of diverse fluoride fractions and in different quantities in the soil such that; water-soluble (Ws-F) (39.5 ± 0.5 mg/kg), Exchangeable (Ex-F) (3.5 ± 0.5 mg/kg), bound to iron/manganese (Fe/Mn-F) (3.1 ± 1.0 mg/kg), and organic matter bound (Or-F) (9.1 ± 2.1 mg/kg) fluoride whereas the total fluoride (Tot-F) was 422 ± 52.9 mg/kg. The study further reports that the use of three studied fertilizers (diammonium phosphate (DAP), Urea, and farmyard manure) accelerates the bioavailability of fluoride in the soil by increasing Ws-F. These results deliver alerts to the plant health regulators suggesting proper management of the quality of fertilizers used for the enhancement of crop quality particularly those used in fluoride-contaminated agricultural soils. While fertilizer application accelerated the bioavailability of fluoride in the soil, soil amendment with dried seaweed (DSW) led to a decrement of Ws-F from 81.7 ± 3.1 mg/kg up to 28.5 mg/kg whereas the fermented seaweed (FSW) decreased Ws-F from 81.7 ± 3.1 mg/kg to 12 ± 1.3 mg/kg following 5 % (w/w) amendments. But unlike DSW and FSW, seaweed-derived biochar (SB) adsorbed fluoride at specific pH five (5) from 103.1 mg/kg to 91.2 ± 3.2 mg/kg whereas hydroxyapatite activated seaweed-biochar (HSB) exhibited defluoridation capabilities at varies pH (3 – 11) with a maximum Ws-F reduction from 103.1 mg/kg to 21.6 ± 2.1 mg/kg which is close to the recommended limit of 16.4 mg/kg. The DSW and FSW defluoridation was based on complexation reactions, alteration of soil properties, and increasing the soil-specific surface area, but SB and HSB defluoridation was through chemisorption. Therefore, seaweed-derived materials are capable of remediation of fluoride contaminated soils and the study recommends further investigation on fluoride uptake by crops in pot and field experiments post-amendment with seaweed derived materials.
Combination of natural betanidin dye with synthetic organic sensitiser towards dye-sensitised solar cell application
(NM-AIST, 2023-05) Costa, Rene
Betanidins belong to natural red-purple pigments betacyanins, which experimentally demonstrated good light adsorption in a visible range and might be suitable for the dye sensitised solar cell (DSSCs). Instability is a well-known drawback of natural dyes, which impedes their use for DSSCs. A thermodynamic approach helps to understand the betanidin (Bd) instability which occurs due to spontaneous decarboxylation reaction with decarboxylated betanidin (dBd) formation. The study considers the improvement of the sensitiser’s functionality via combination of natural Bd/dBd dyes and synthetic 4- (Diphenylamino)phenylcyanoacrylic acid (L0) dye. Novel complex D–π–A organic dyes, L0–Bd and L0–dBd with structural isomers, have been designed via esterification reactions. The DFT/B3LYP5/6‒31G(d,p) approach has been used to compute geometry, vibrational spectra and thermodynamic characteristics of the individual isomers and their complexes with L0. Implementation of TD–DFT method aids in obtaining optoelectronic properties. The broader coverage of the solar spectrum with greater light-harvesting efficiency was achieved for the complexes compared to individual dyes. The dyes attachment to the semiconductor TiO2 was simulated in terms of different adsorption modes to hydrogenated (TiO2)6 cluster. Binding energies and electronic spectra of the dye@TiO2 systems were computed, and electron density distributions over frontier molecular orbitals analysed. Binding energy magnitudes varied within 15‒21 eV for the dye@TiO2 systems.
Hydrologic responses to climate and land use/cover changes in world heritage site of Ngorongoro conservation area and surrounding catchments, northern Tanzania
(NM-AIST, 2023-01) Mwabumba, Mohamed
In Tanzania, various studies have analyzed the impact of climate and land use/cover changes on water resources. However, information on the interactions between climate and land use/cover change, temporal and spatial variability of hydrological components and water quality at the local scale is insufficient. The objective of this study was to evaluate the hydrological response to climate and land use/cover changes in Ngorongoro Conservation Area (NCA) and surroundings. The study performed climate change analysis using outputs from a multi-model ensemble of Regional Climate Models (RCMs) and statistically downscaled Global Climate Models (GCMs). The CA–Markov model applied to project Land use/cover for the future 2025 and 2035. This study further used the Soil Water Assessment Tool (SWAT) modelling approaches to analyse the hydrological responses and HYDRUS 1D to determine the change in Groundwater quality due to climate and land use/cover changes. The analysis of climate change between historical period (1982-2011) and future period (2021-2050) indicated an increase in the mean annual rainfall and temperature, seasonal rainfall except June to September (JJAS) season which showed a decreasing trend. Spatially, rainfall and temperatures would increase over the entire area. The projected Land use/cover change for the period 2025 to 2035 compared to the baseline 2016, showed a reduction in bushland, forest, water, and woodland, but an intensification in cultivated land, grassland, bare land, and the built-up area. The surface runoff, evapotranspiration, lateral flow, and water yield would significantly increase in the future, while groundwater would decrease under combined climate and land use/cover change. It is predicted that two anions (Cl− and PO4 −3 ) and two cations (Na+ and K+ ) would exceed the permissible limits for the drinking water set by the World Health organisation (WHO) and Tanzania Bureau of Standards (TBS), from 2036 to 2050. Changes in groundwater quality due to major cations and anions is significantly correlated to evapotranspiration and temperature with Pearson correlation (r) between 0.35 and 0.85. Furthermore, correlate to the changes in all land use/ cover types with Pearson correlation (r) between 0.56 and 0.96. The results obtained provide further insight into future water resources management planning and adaptation strategie
Tin halide perovskites: computational modeling of structural, electronic and thermodynamic properties towards solar cell applications
(NM-AIST, 2021-07) Paschal, Catherine
In the photovoltaic field, significant attention has been drawn to lead organo-halide perovskite materials because of their higher ability to convert sun energy to electricity and relatively simple process of fabrication as compared to silicon materials. Among the issues which hinder the lead perovskites solar cells (PSCs) application, are lead toxicity and instability of the PSCs in presence of moisture and light. The tin perovskites are thought over as the foremost fitting substitute due to their comparable chemical nature and high-power conversion efficiency. In this work, the methylammonium tin iodide CH3NH3SnI3 (MASnI3) and guanidinium tin halides C(NH2)3SnX3 (GUASnX3), X = Cl, Br, I, are considered; the electronic, structural as well as thermodynamic properties of the perovskites’ orthorhombic phase (O-phase) have been investigated using various theoretical DFT approaches. For the MASnI3, a direct band gap has been proved; in gamma symmetrical point of the band structure, the band gap value Eg is computed using three different exchange-correlation (XC) functionals: LDA 0.46 eV, PBEsol 0.98 eV and for PBE 1.12 eV; the best result has been obtained with the PBE which follows from the comparison of the computed Eg and lattice parameters with available experimental data. The enthalpy of the decomposition reaction of the MASnI3 into the solid-state materials, SnI2 and CH3NH3I, with reaction enthalpy, ΔrH°(0 K) = 37 kJ mol–1 , and enthalpy of formation ΔfH°(CH3NH3SnI3, 0 K) = –390 kJ mol–1 , have been evaluated showing the stability of the O-phase perovskite at low temperature. For the guanidinium-tin perovskites GUASnX3, the lattice parameters are optimized using the GGA PBE functional. Computations of the materials’ band structures was carried out, and band gaps at the gamma symmetry points were obtained: 3.00, 2.47 and 1.78 eV for the C(NH2)3SnCl3, C(NH2)3SnBr3 and C(NH2)3SnI3, respectively. The projected state densities are visualized, and the s-and p-states contribution of the halogens and tin to valence and conduction bands of the perovskites assessed. For the GUASnX3 compounds, the thermodynamic stability to different decomposition routes is examined, the standard enthalpies of formation are obtained: –673 (GUASnCl3), –541 (GUASnBr3), and –401 kJ mol–1 (GUASnI3). The interface between the hole transport material Cu2O and perovskite MASnI3 has been built and analyzed; the predicted binding energy shows strong binding between the two layers.
Evaluation of selected botanicals as insecticides against cabbage insect pests in Tanzania
(NM-AIST, 2022-06) Mpumi, Nelson
Synthetic pesticides are frequently and unwisely used to control cabbage insect pests by smallholder farmers despite the environmental pollution and insect pests’ resistance development. This work assessed the insecticidal efficacy of botanicals from Tephrosia vogelii, Croton dichogamus and Syzygium aromaticum against cabbage insect pests in Northern Tanzania. Firstly, larvicidal action of extracts against Crocidolomia binotalis and Plutella xylostella larvae was assessed in the laboratory. Secondly, insecticidal and synergistic actions of aqueous extracts against cabbage insect pests were assessed in field experiment. Lastly, chemical compounds in S. aromaticum and in C. dichogamus were determined. The larvicidal activities of extracts were assessed for mortality of ten larvae into 9 cm Petri-dishes for 24 hours of exposure. Chlorpyrifos and acetone were used as a positive and negative control, respectively. The insecticidal efficacy of 10%, 5% and 1% w/v of T. vogelii, C. dichogamus and S. aromaticum aqueous extracts and their mixture (2.5% and 5%) was assessed against cabbage insect pests in the field. Chlorpyrifos was used as a positive control, and water and water plus soap were used as negative controls. The GC-MS was used for compounds identification in C. dichogamus and in S. aromaticum. Results from the study revealed that S. aromaticum extract (16, 24 and 32 mg/mL), T. vogelii (24 and 32 mg/mL) and C. dichogamus (32 mg/mL) gave 100 ± 0.0% mortality of C. binotalis larvae after 24 hours of exposure. Moreover, S. aromaticum extract (8, 16, 24 and 32 mg/mL), T. vogelii (16, 24 and 32 mg/mL) and C. dichogamus (32 mg/mL) gave 100 ± 0.0% mortality of P. xylostella larvae after 24 hours of exposure. The aqueous extracts from those plants significantly (P ≤ 0.05) lowered the population of cabbage insect pests compared with negative controls. The 5% of aqueous extract from mixed plants possessed significantly (P ≤ 0.01) lower population of cabbage insect pests in both wet seasons compared with other concentrations. Then, it was followed by 10% of S. aromaticum, C. dichogamus and T. vogelii aqueous extracts and 1% and 5% of aqueous extracts of S. aromaticum, C. dichogamus and T. vogelii and 2.5% of aqueous extracts from the mixed plants significantly lowered the population of insect pests compared with negative controls in both seasons. The compounds identified in S. aromaticum, at higher percent were Eugenol (52.66%); Eugenol acetate (20.46%) and β-caryophyllene (7.52%). Moreover, the compounds identified in C. dichogamus at higher percent were 4,6-Bis (4-chloro-3-(trifluoromethyl) phenoxy)-2-pyrimidinol (25.08%); Cholestan-6-en-3-ol (18.63%) and 1-Heptadecene (7.34%). These compounds could be responsible for larvicidal and insecticidal activities against cabbage ii insect pests. Therefore, these plants can be recommended to be used by smallholder farmers for cabbage insect pest control at higher concentrations and development of insecticides.

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