Browsing by Author "Bakari, Ramadhani"

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Analysis of Different Techniques for Improving Performance of Flat Plate Solar Collectors for Fruits Drying
(Tanzania Journal of Engineering and Technology (TJET), 2014-06) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
Fruits drying had become a broader technology in fruits and vegetables value addition. The technology is reported to be a promising way of dying without incurring higher cost but its adaptation has not been feasible in rural areas. Solar dryers have been developed but its poor performance limits its applicability. In this study, several techniques for modifications of traditional solar collector were addressed. It was observed that, varying collector designs in different techniques, a range of collector performances can be employing double duct counter flow, compared to conventional collectors. Likewise performance difference between conventional collectors and studied models were found to be 8%, 7.2%, 6.1% and 5.2% for model parked with charcoal 5 mm wire mesh, 4mm glass thickness and 8 baffles respectively. This study shows that, double duct counter flow system is the best option for improving the performance of the collectors, followed by charcoal and wire mesh. On the hand, using 4 mm glass thickness gave improved performance, however, it is recommended for collector size not exceeding 2 m in length.
Catalytic supercritical water gasification of biomass waste using iron-doped alkaline earth catalysts
(Springer Nature Switzerland AG., 2022-05-18) Bakari, Ramadhani; Kivevele, Thomas; Huang, Xiao; Jande, Yusufu
The objective of this study is to optimise the process of supercritical water gasification of rice husk biomass utilising a low-cost catalyst made from alkaline-earth materials. The interactions between catalyst loading and Fe content on gasification yield were investigated using response surface methodology. The catalyst characterisation findings revealed that the catalysts’ predominant reactive site is on iron oxide, calcium ferrite, and calcium oxide. Under all the conditions tested, the manufactured catalyst was highly active in promoting char gasification, gas volume, and gasification efficiency whilst the tar yield was substantially elevated. The maximum gasification efficiency of 69.57%, gas yield of 402.8 mL/g biomass, char yield 24.68 wt%, and gravimetric tar yield of 57.5 mg/g were obtained under the catalytic conditions of 15% catalyst loading with 5%Fe/limestone, 492 °C, 120-min residence time, and 9.5 wt% feed concentrations. Thus, the manufactured catalyst showed a potential for optimising gasification outputs.
Combatting toxic chemical elements pollution for Sub-Saharan Africa's ecological health
(Elsevier, 2025-02-08) Ripanda, Asha; Hossein, Miraji; Rwiza, Mwemezi; Nyanza, Elias; Selemani, Juma; Nkrumah, Salma; Bakari, Ramadhani; Alfred, Mateso; Machunda, Revocatus; Vuai, Said
With its booming mining, processing industries, agriculture, and increasing urbanization, sub-Saharan Africa experiences an alarming rise in accumulation of toxic chemical elements in all environmental matrices threatening entire ecology. Most toxic chemical elements are mercury, lead, cadmium, chromium, and arsenic. These toxic chemical elements are known human carcinogens, systemic toxicants and can induce multiple organ damage. The occurrences of toxic chemical elements in Sub-Saharan Africa are amplified by anthropogenic activities such as mining, industrial discharges, and agricultural practices. This study examined the extent of exposure to toxic chemical elements in surface and underground waters, sediments, soils, effluents, food crops, vegetables, aquatic organisms, industrial products, humans, and other animals in Sub-Saharan Africa. Results indicate occurrences of toxic chemical elements in surface and underground waters, sediments, soils, effluents, food crops, vegetables, aquatic organisms, industrial products, humans, and other animals above the recommended threshold. These findings highlight the persistent pollution of water, soil, sediments, food crops, aquatic organisms, and even industrial products, emphasizing the potential for bioaccumulation and exposure through the food chain. This requires interdisciplinary approaches, including updating and enforcing stricter regulations tailored to regional industrial and agricultural practices. Advanced remediation technologies, such as phytoremediation, and bioremediation, should be prioritized to remove toxic chemical elements from affected environments. Additionally, promoting sustainable practices, such as waste recycling programs, can help reduce anthropogenic contributions, strengthen environmental monitoring systems, nurture community awareness, and essentially encourage regional and international collaboration to protect ecosystems and safeguard human health in Sub-Saharan Africa.
Data from the batch adsorption of ciprofloxacin and lamivudine from synthetic solution using jamun seed (Syzygium cumini) biochar: Response surface methodology (RSM) optimization
(Elsevier, 2023-02) Ripanda, Asha; Rwiza, Mwemezi; Nyanza, Elias; Bakari, Ramadhani; Miraji, Hossein; Njau, Karoli; Vuai, Said; Machunda, Revocatus
This dataset expresses the experimental data on the batch adsorption of ciprofloxacin and lamivudine from synthetic solution using jamun seed (JS) (Syzygium cumini) biochar. Independent variables including concentration of pollutants (10-500 ppm), contact time (30–300 min), adsorbent dosage (1-1000 mg), pH (1-14) and adsorbent calcination temperature (250,300, 600 and 750 °C) were studied and optimized using Response Surface Methodology (RSM). Empirical models were developed to predict the maximum removal efficiency of ciprofloxacin and lamivudine, and the results were compared with the experimental data. The removal of polutants was more influenced by concentration, followed by adsorbent dosagage, pH, and contact time and the maximum removal reached 90%.
Ecological Consequences of Antibiotics Pollution in Sub-Saharan Africa: Understanding Sources, Pathways, and Potential Implications
(KeAi, 2025-01-25) Ripanda, Asha; Rwiza, Mwemezi; Nyanza, Elias; Hossein, Miraji; Alfred, Mateso; Mahmoud, Alaa; Murthy, Ananda; Bakari, Ramadhani; Vuai, Said; Machunda, Revocatus
In Sub-Saharan Africa (SSA), the increasing use of antibiotics in human and veterinary medicine, combined with inadequate waste and water management systems, has intensified the problem of antibiotic pollution. Untreated or partially treated wastewater from industries, agricultural runoff, residential areas, and healthcare facilities is frequently discharged into the environment, often used for irrigation, contributing to antibiotic accumulation, the spread of resistance genes, and the rise of antibiotic resistance, posing serious threats to public health and environmental sustainability. The region's climatic conditions favour the survival and proliferation of microbial communities, including pathogens. Additionally, the high prevalence of infectious diseases such as HIV/AIDS, tuberculosis, and malaria, which often necessitate antibiotic use, further amplifies the issue. Systemic challenges, including poor waste management, inadequate or absent wastewater treatment infrastructure, weak regulatory enforcement, and the over-the-counter sale of antibiotics, exacerbate the crisis. Limited healthcare access often results in self-medication and improper antibiotic use, accelerating resistance spread. Evidence shows antibiotics in surface water, groundwater, effluents, food crops, environmental samples, and aquatic organisms, indicating their potential circulation through the food chain. However, a lack of comprehensive data on antibiotic pollution and its impacts on aquatic ecosystems in SSA hampers a thorough understanding of its scope and long-term effects. Addressing this crisis requires identifying contamination hotspots, evaluating ecological impacts, and establishing robust, region-specific regulatory frameworks to ensure environmental and public health safety
Ecological consequences of microplastic pollution in sub-Saharan Africa aquatic ecosystems: An implication to environmental health
(Elsevier Inc., 2023-12-01) Moto, Edward; Hossein, Miraji; Bakari, Ramadhani; Mateso, Alfred; Selemani, Juma; Nkrumah, Salma; Ripanda, Asha; Rwiza, Mwemezi; Nyanza, Elias; Machunda, Revocatus
Microplastic pollution (MPs) emerged as a significant environmental concern due to its persistent nature. These MPs particles endure in waters, soils, and even the atmosphere, posing potential threats to the entire ecosystem. Aquatic organisms are at risk of ingesting MPs, leading to accumulation in tissues, ultimately affecting entire food chain. This study aims to provide an overview of sources of MPs, distribution, and potential environmental impacts. MPs have been documented in various substances such as bottled water, salts, seafood, and even the air. However, the full extent of the health consequences on human exposure remains uncertain. Therefore, it is imperative that we draw public attention to the presence of these pollutants in the environment. To mitigate adverse effects of MPs, reducing plastic consumption, implementing improved waste management practices, and advocating sustainable behaviors are essential for well-being of natural ecosystems and the health human populations.
Effect of Glass Thickness on Performance of Flat Plate Solar Collectors for Fruits Drying
(Hindawi Publishing Corporation, 2014) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
This study aimed at investigating the effect of thickness of glazing material on the performance of flat plate solar collectors. Performance of solar collector is affected by glaze transmittance, absorptance, and reflectance which results into major heat losses in the system. Four solar collector models with different glass thicknesses were designed, constructed, and experimentally tested for their performances. Collectors were both oriented to northsouth direction and tilted to an angle of 10° with the ground toward north direction. The area of each collector model was 0.72 m2 with a depth of 0.15 m. Low iron (extra clear) glass of thicknesses 3 mm, 4 mm, 5 mm, and 6 mm was used as glazing materials. As a control, all collector performances were analysed and compared using a glass of 5 mm thickness and then with glass of different thickness. The results showed that change in glass thickness results into variation in collector efficiency. Collector with 4 mm glass thick gave the best efficiency of 35.4% compared to 27.8% for 6 mm glass thick. However, the use of glass of 4 mm thick needs precautions in handling and during placement to the collector to avoid extra costs due to breakage.
Experimental analysis of air flow patterns in perfomance of flat plate solar collectors
(African Journal of Agricultural Research, 2015-02-05) Bakari, Ramadhani; Minja, Rwaichi; Njau, Karoli
Solar drying is one of the promising methods of reducing post-harvest losses in rural areas. Studies have shown that, heat transfer mechanisms in a solar collector influences the performance of solar dryers. This study aims at improving heat transfer in flat plate solar collectors by designing different air flow patterns inside the collector. Three flat plate solar collectors were constructed by using Pterocarpus timber (Mninga) and tested for their effect in heat transfer at various flow patterns. Three different flow patterns namely: single duct front pass, double duct parallel flow and double duct counter flow were designed and tested. Experimental results show that collector efficiency of single duct front pass, double duct front pass and double duct counter flow were 30.6, 36.1 and 38.2% respectively. It was found that, double duct flow gives improved performance compared to single duct flow due to the increased heat transfer area. In additional, double duct counter flow showed superior performance compared to double duct parallel flow due to extended heat transfer area and the advantage of air preheating at the inlet which reduces heat losses through glazing. Through this study, it was concluded that, solar collector designs with double duct counter flow can improve collector performance for up to 8.3% compared to single duct front pass.
Fluoride contamination a silent global water crisis: A Case of Africa
(Elsevier, 2024-11-20) Hossein, Miraji; Rwiza, Mwemezi; Nyanza, Elias; Bakari, Ramadhani; Ripanda, Asha; Nkrumah, Salma; Selemani, Juma; Machunda, Revocatus
Fluoride contamination in drinking water poses a global health risk, affecting millions worldwide, with Africa bearing a disproportionate burden due to unique geological factors like the East African Rift Valley. High fluoride levels in groundwater in these regions contribute to widespread health problems, notably dental and skeletal fluorosis, which impair quality of life and economic productivity. This study aims to evaluate the scope of fluoride contamination across continents, examining how Africa compares to regions like Asia, North America, and Europe. While some countries have mitigated contamination through advanced water treatment and regulatory measures, Africa still faces significant challenges due to limited infrastructure and resources. Findings highlight that addressing fluoride contamination in Africa requires a targeted approach, involving affordable treatment solutions, regulatory reforms, and community awareness programs. By outlining these strategies and emphasizing international cooperation, this study underscores the urgency of safeguarding health and well-being across affected African communities.
Jamun Seed (Syzygium Cumini) Biochar as a Potential Adsorbent for Environmental Applications
(Engineered Science Publisher, 2025-02-18) Ripanda, Asha; Rwiza, Mwemezi; Giridhar Reddy, S.; Nyanza, Elias; Bakari, Ramadhani; Miraji, Hossein; Ravikumar, C. R.; Ananda Murthy, H. C.; Vuai, Saidi; Machunda, Revocatus; Annamareddy, Sri Hari
This study investigates the properties and adsorption performance of jamun seed biochar (JS biochar) produced through calcination at varying temperatures. Elemental analysis reveals that the carbon content significantly increases from 64.25 to 87.93 wt.% as calcination temperature rises from 400 to 600 °C, while nitrogen content remains within the range of 2 to 2.29 wt.%. The biochar's surface characteristics, with a maximum specific surface area of 261.2 m²/g, demonstrate strong adsorption capacity for small organic molecules, including ciprofloxacin (555.55 mg/g) and lamivudine (400 mg/g). The identified functional groups, including hydroxyl and carbonyl groups, enhance adsorption through mechanisms such as hydrogen bonding and electrostatic interactions. The observed porous, rough surface morphology supports the material's effectiveness as an adsorbent. The results demonstrate JS biochar’s high adsorption capacity, governed by a synergistic interplay of physisorption and chemisorption. This research underscores the potential of JS biochar as a sustainable and effective solution for environmental remediation, particularly in mitigating aqueous pollutants. The findings offer valuable insights for optimizing biochar properties to improve adsorption efficiency, thereby promoting sustainable waste management and environmental remediation.
Optimization of solvothermal liquefaction of water hyacinth over PTFE-acid mediated kaolin catalyst for enhanced biocrude production
(Elsevier, 2024-03-01) Kariim, Ishaq; Bakari, Ramadhani; Waidi, Yusuf; Kazmi, Wajahat; Swai, Hulda; Kivevele, Thomas; Malla, Sunita
The invasive nature of water hyacinth and the need for renewable energy sources have necessitated this research. Catalyst development through enhanced pore structure and process parameters optimization are requirements for effective mass transport during the biomass valorization and improved biocrude formation during solvothermal liquefaction process. In this present study, the effects of temperature (250–340 °C), residence time (10–20 min) and catalyst loading (10–13 wt%) on biocrude, biochar, gas yield, and biomass conversion were optimized using a Box-Behnken experimental design. The developed catalyst through the application of polytetrafluoroethylene (PTFE) for pore structure enhancement was characterized using SEM, BET and XRD techniques. The process optimization found maximum biocrude yield (32.0 wt%), minimum biochar yield (19.4 wt%) and maximum conversion efficiency (80.6%) at 340 °C, 20 min residence time, and 13 wt% catalyst loading. The GC-MS result of the biocrude produced at the optimum conditions (13 wt% catalyst loading) consists of ketones (32.2%), acids (22.3%) and had 65.2% carbon, 7.3% hydrogen, HHV of 29.4 MJ/kg and H/C ratio of 1.34 while an increment in catalyst loading of 20 wt% enhanced the overall biocrude properties with HHV of 35.50 MJ/kg. This result depicts the suitability of the PTFE modified acid treated kaolin for high quality biocrude production through valorization of water hyacinth into a candidate for renewable energy material.
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.
Removal of lamivudine from synthetic solution using jamun seed (Syzygium cumini) biochar adsorbent
(Emerging Contaminants, 2023-09-01) Ripanda, Asha; Rwiza, Mwemezi; Nyanza, Elias; Bakari, Ramadhani; Bakari, Ramadhani; Miraji, Hossein; Njau, Karoli; Vuai, Said; Machunda, Revocatus
Antiviral drugs such as lamivudine have been globally identified in the environment and marked as emerging pollutants of concern due to their bioactive extremity. Following therapeutic uses, approximately 70% of the oral dose of lamivudine is eliminated renally as the parent drug. Concerns has been raised for neighbouring aquatic bodies due to effluent produced from production plants containing high concentrations of antiviral drugs. Antiviral drugs, such as lamivudine, are extremely bioactive, prompting interest in their urgent removal from the environment. The purpose of the present study was to optimize the removal of lamivudine from the synthetic solution using jamun seed (JS) (Syzygium cumini) biochar. The influence of sorption parameters such as pH, lamivudine concentration, adsorbent dosage, contact time, and calcination temperatures on the removal of lamivudine was investigated and optimized using a response surface methodology (SRM) based on optimal design. The results indicated that, a quadratic model best fits data with a model regression coefficient R2, adjusted R2, and predicted R2 of 0.9934, 0.9761 and 0.8340, respectively. The JS biochar calcined at 750 °C, at pH 8, initial lamivudine concentration of 10 ppm and contact time of 30 min indicated a maximum experimental removal efficiency of 84.9%. The residual standard error (RSE) value was 3.5% implying that the model was reliable. Isotherm data for the adsorption of lamivudine on JS biochar followed the Freundlich isotherm, with an R2 value of 0.9977 while R2 for the modified Langmuir model was 0.9852. These findings indicated that JS biochar is potentially useful for removal of lamivudine, and other organics from contaminated water and wastewater effluents. Therefore, this study presents an environmentally friendly remedy against lamivudine for a healthier ecology.
Simulation and optimisation of the pyrolysis of rice husk: Preliminary assessment for gasification applications
(Elsevier B.V., 2020-09) Bakari, Ramadhani; Kivevele, Thomas; Huang, Xiao; Jande, Yusufu
Thermochemical conversion of biomass into useful products is a promising route to harness biofuels. This process is clean, renewable and can reduce the use of fossil fuel. In this study, SuperPro Designer (SPD) software and response surface methodology (RSM) is used to simulate and optimize rice husk pyrolysis process. The SPD simulator was built to handle kinetics and stoichiometric reaction of lignocellulosic composition of rice husk into final products. The SPD simulation and RSM optimization were performed at a temperature ranging from 350 to 800 °C and residence time of 0.25−60 s. The simulated results were in agreement with product yield published in the literature at an average relative error of 6.8 %. The combined effect of temperature and residence time were analysed by using RSM and analysis of variance (ANOVA). A cubic model for bio-oil and quartic model for char and gas yield were proposed. The desirability function in Design-Expert showed that the optimum bio-oil yield (36.72 %) could be attained at a temperature 588 °C and a residence time 0.25 s while the optimum gas yield (73.25 %) could be achieved at a temperature 798.8 °C and a residence time 15.47 s. These findings therefore revealed that the energy content of the rice husk could be harnessed by pyrolysis/gasification to obtain substantial fuel products.
Sub- and Supercritical Water Gasification of Rice Husk: Parametric Optimization Using the I-Optimality Criterion.
(ACS Publications, 2021-05-18) Bakari, Ramadhani; Kivevele, Thomas; Huang, Xiao; Jande, Yusufu
In this study, rice husk biomass was gasified under sub- and supercritical water conditions in an autoclave reactor. The effect of temperature (350-500 °C), residence time (30-120 min), and feed concentration (3-10 wt %) was experimentally studied using the response surface methodology in relation to the yield of gasification products. The quadratic models have been suggested for both responses. Based on the models, the quantitative relationship between various operational conditions and the responses will reliably forecast the experimental outcomes. The findings revealed that higher temperatures, longer residence times, and lower feed concentrations favored high gas yields. The lowest tar yield obtained was 2.98 wt %, while the highest gasification efficiency and gas volume attained were 64.27% and 423 mL/g, respectively. The ANOVA test showed that the order of the effects of the factors on all responses except gravimetric tar yield follows temperature > feed concentration > residence time. The gravimetric tar yield followed a different trend: temperature > residence time > feed concentration. The results revealed that SCW gasification could provide an effective mechanism for transforming the energy content of RH into a substantial fuel product.