Browsing by Author "Chaka, Bakari"

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    Publication
    Investigating the ohmic behavior of mediator-less microbial fuel cells using sewerage water as the bio-anode
    (Cogent OA, 2022-12-31) Mbarire, Thiong’o; Aloys, Osano; Chaka, Bakari
    There is a great challenge in ratification of electrochemical principles to energy-storage devices utilizing natural systems such as microbial fuel cells (MFCs). The purpose of this study is to investigate how increasing impedance affects key cell dynamics of MFCs at ambient conditions using untreated sewage as the bio-anode. A H-type mediator-less MFC of capacity 4,556.25 cm3 using porous graphite electrodes and raw sewage as the bio-anode was studied over one 10-day retention period. The results indicated an exponential increase in OCV up to the sixth day followed by its gradual reduction. ohmic behavior was observed in the current and power densities with the highest power density being 0.173 mW/cm3 for the 1,000 Ω resistor. The charge/discharge times ranged between 11.15 and 11.40 days with daily discharge rates of 8.77–8.96%. Ohmic behavior was also observed as the energy balance, capacity and density of the MFCs decreased with applied impedance. The highest values were obtained in the 1,000 Ω MFC (energy balance, 336.1 J/s; energy capacity, 4.227 Wh/cm3 and energy density, 17.237 Wh/kg, respectively). The MFCs ohmic behavior when using raw sewage proved to be quite novel and an inspiring finding to enhance applicability of MFCs using raw industrial effluents.
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    Publication
    Polycyclic Aromatic Hydrocarbon Emissions Arising from Domestic Combustion: A Kenyan Case Study
    (Research Gate, 2022-10-07) Forbes, Patricia; Osano, Aloys; Maghanga, Justin; Munyeza, Chiedza; Chaka, Bakari; Adeola, Adedapo; Nsibande, Sifiso
    A vast number of people in developing countries rely on solid fuels, including wood and charcoal, for domestic energy supply. We have studied the gaseous polycyclic aromatic hydrocarbon (PAH) concentrations in Kenyan homes in order to better understand the potential health risks associated with domestic combustion practices and to advise mitigation strategies. A comprehensive survey was conducted to elucidate the complex and multi-faceted factors governing fuel use in Kenyan coastal and inland regions. Results showed an almost equal distribution in fuel type usage between firewood, charcoal, kerosene and liquid petroleum gas (LPG). In rural areas, three-stone stoves were still predominant, whilst cleaner devices burning kerosene and LPG were used more widely in urban communities. Indoor air was subsequently sampled in a range of urban and rural households using portable polydimethylsiloxane sampling tubes. These were extracted using the plunger assisted solvent extraction (PASE) technique, followed by GC-MS analysis of the U.S. Environmental Protection Agency (EPA) priority PAHs. Total PAH concentrations in samples collected varied considerably (0.82-173.69 µg/m 3), which could be attributed to differences in fuel type, combustion device, climate, and nature of the households. Higher PAH concentrations were found in rural homes, although ambient PAH concentrations were higher in urban environments, likely due to traffic contributions and population density. Toxicity equivalent quotient values varied widely between households and emphasised the importance of good combustion practices to minimise human exposure.
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    Publication
    Seasonal variation in pesticide residue occurrences in surface waters found in Narok and Bomet Counties, Kenya
    (Springer Nature, 2023-08-17) Chaka, Bakari; Osano, Aloys M.; Wesley, Omwoyo N.; Forbes, Patricia B. C.
    Narok and Bomet are agricultural counties in Kenya which depend on flowing surface waters for farming activities. Agrochemicals have frequently been used to increase agricultural produce in this region. Occasionally, appropriate pesticide utilization measures are not followed. These surface waters are also consumed domestically by humans, livestock, and wild animals thus posing safety concerns to them. The current study sought to evaluate the levels and nature of pesticide residues found in surface waters in the dry and wet seasons of these counties. Eight water samples were collected in July (dry season) and October (wet season) at four different river sites in each of the two counties predetermined by the agricultural activity of its proximate environs. Pesticides extracted by solid phase extraction were analyzed by gas chromatography-mass spectrometry. At least 38 different pesticides were detected in the two counties with the highest concentration being recorded for chlorpyrifos and piperidine in Narok and Bomet counties, respectively. The pesticides chlorpyrifos, cypermethrin, cyfluthrin, and cyhalothrin were more prevalent in Narok County while triazine, semicarbazone, and epinephrine were more prevalent in Bomet County. There were significantly more pesticides detected during the wet season (P ≤ 0.05). Out of the nine prevalent pesticides detected, four of them posed serious ecotoxicology concerns with risk quotients above 1.0 (high risk); thus, there is a need for more government policy interventions in deterring farming near riparian lands and in training of famers regarding best practice for pesticide applications.
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    Publication
    Synthesis and characterization of aluminium oxide nanoparticles from waste aluminium foil and potential application in aluminium-ion cell
    (Science Direct, 2021-07-01) Nduni, Mercy Njeri; Osano, Aloys Mosima; Chaka, Bakari
    Aluminium waste accumulated in landfills is a solid waste in abundance. Various methods have been employed to alleviate the waste only to yield secondary pollution effects. This study seeks to provide an alternative greener recycling procedure that is beneficial to society in terms of health and economics through energy storage materials. The study aimed to synthesize and characterize aluminium oxide nanoparticles from waste aluminium foil and its potential applications in fabricating aluminium-ion cell, FAIC.11Aluminium-ion cell. Aluminium oxide nanoparticles were obtained by co-precipitation of waste aluminium foils at constant annealing room temperature followed by mechanical milling to nanoparticulate range. The particles were then characterized for particle size and phases (X-ray diffraction), functional groups and optical activity (infra-red and ultra-violet-visible spectroscopy respectively). Cell assembling of FAIC was done using a graphite anode while the cathode had a standard and the synthesized aluminium oxide nanoparticles. Sulfuric acid and magnesium sulfate electrolytes were used with two binders; polyacrylate and silicone adhesives. The average synthesis yield was 40.64 ± 19.69%. Most of the particles had a α-Al2O3 and γ-Al2O3 phase with an average size of 63.763 nm and 66.5144 nm for the two polymorphs respectively. There were several OH-groups coupled to Al–O bonds. The optimal absorption peak was λmax = 237 nm corresponding to a band gap of 5.25eV. The synthesized nanoparticles exhibited great electrochemical potential, nearing the standard one in most of the parameters. The FAIC potential, current, power densities and polarization curves from sulfuric acid electrolyte and polyacrylate binder were significantly higher to those of magnesium sulfate and silicone binder (P > 0.05).
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    Publication
    The Influence of Biocatalytic Plant Extracts on Biogas Production from Kitchen Wastes at Cryo-mesophilic Temperature Regimes
    (Science Publishing Group, 2019-01) Chaka, Bakari; Osano, Aloys; Maghanga, Justin; Magu, and Martin
    Radicalization in waste-to-energy systems are on the rise to meet human energy demands. Biogas generation from kitchen wastes is one such scheme, though affected by poor yields and methane levels at low temperatures. In this research, biocatalytic extracts with fermentative properties were hereby assessed on their potential to fasten these processes and increase the biogas yield at ambient temperatures. The variations in kitchen waste substrate anaerobic parameters and elemental composition as well as biogas yields and methane levels were monitored in a 28-day retention period. Three 40-liter batch and unstirred bio-digesters containing biocatalysts Terminalia b., Acanthaceae spp. and a control setup were used. The results indicated rapid saccharification rates in the samples with additives. Terminalia b. additives exhibited high volatile solids hydrolysis rate of 98.3% followed by Acanthaceae spp. (50.8%) and control sample (29.4%). Similar trends were observed in organic carbon reduction as the levels of nitrogen, phosphorus and sulfur linearly increased. The biocatalysts did not affect substrate pH, volatile fatty acids and alkalinity levels. Terminalia b. sample produced 2.32 folds higher while Acanthaceae spp. sample produced 1.375 folds higher than the control sample. Terminalia b. methane levels were highest (45.475±0.922%) followed by the control sample (41.750±1.401) and Acanthaceae spp. sample (39.275±0.263%) after 28-day retention period at 19.5±0.5°C. Use of these biocatalysts in biofuel synthesis can thus optimize biogas production leading to greener economies.