Browsing by Author "Mahene, Wilson"

Now showing 1 - 7 of 7

Assessment of contamination level of a Tanzanian river system with respect to trace metallic elements and their fate in the environment
(IWA Publishing, 2022-04-01) Gebreyohannes, Netsanet; Rwiza, Mwemezi; Mahene, Wilson
The quality of water and sediments from a marginally-studied river was investigated with respect to As, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn including their fractionation behavior and environmental risk. Samples were collected along the Kou River that flows across two districts in the Manyara region of Tanzania. The leaching behavior of Fe was studied using sequential extraction fractionation and kinetics approach. The Kou water failed to meet the irrigation, aquatic, and biological life standards with respect to one of more trace metallic elements (TMEs). Fe concentration in the river water ranged from 4.1 to 5.38 mg/L, exceeding all the three standards. Six pollution indices were applied to assess the contamination and ecological risks of the nine trace metallic elements in the sediments. Overall, the metals were found to moderately contaminate the sediments. Cr, Fe, and Mn fell under the ‘severely polluted’ sediment quality class. Fe was the only metal that was found to significantly pollute both the river water and sediments. The Fe fractions in the sediments were in the order of residuals.Fe-Mn bound.or ganic bound.carbonate bound.water soluble.ion exchangeable; 7.8% of the total Fe content was bioavailable with a low potential to leach from the sediments. Under natural conditions, the sharpest release of the non-residual mobile fractions of Fe were identified to occur within the first 24 hours with the maximum Fe leached being 0.14% on the 12th day. None of the metals in the sediments were found with a poten tial to pose ecological risk
Cockle (Anadara granosa) shells-based hydroxyapatite and its potential for defluoridation of drinking water
(Elsevier, 2022-03-03) Mtavangu, Stanslaus; Mahene, Wilson; Machunda, Revocatus; Bruggen, Bart; Njau, Karoli
The present study describes the synthesis and characterization of a hydroxyapatite (HAp)-based adsorbent derived from biogenic cockle (Anadara granosa) shells for the defluoridation of drinking water. The raw cockle shells and synthesized HAp were characterized by X-ray fluorescence spectroscopy (XRF), attenuated total reflection-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopes-energy dispersive X-ray (FESEM-EDX) and Brunauer-Emmett-Teller (BET) surface area analysis. As demonstrated by FTIR, cockle shells were found to be composed of calcium carbonate (97.4%), an aragonite polymorphous type of carbonate mineral. XRD and SEM analysis supported the formation of a nanocrystalline HAp with an average crystal size of 19.08 nm and 57.1 nm, respectively, with a surface area of 105.8 m2/g and a pore size of 5.6 nm, as depicted by BET. Batch adsorption experiments were conducted using the Box-Behnken design (BBD) with five input parameters: adsorbent dose (2–10 g/L), initial fluoride concentration (10–80 mg/L), contact time (0.5–24 h), reaction temperature (303–333 K), and pH. (3–11). BBD revealed the following optimum conditions: adsorbent dose (6 g/L), initial fluoride concentration (45 mg/L), contact period 12.25 h, reaction temperature (303 K), and pH 3. Experimentally, the adsorption of fluoride on HAp fitted well with the non-linear Langmuir isotherm and linear pseudo-second order kinetics, signifying the chemisorption process. A maximum adsorption capacity (qm) of 15.374 mg/g, which is closer to the experimental value of 14.053 mg/g, was presented by the Langmuir isotherm. Thermodynamically, the adsorption process was spontaneous, endothermic, and stable in nature. The defluoridation mechanism was through electrostatic attraction, ion exchange, hydrogen bonding, and precipitation. Furthermore, the synthesized HAp and bone char were used to examine their efficacy in defluoridating field water: HAp performed better at natural pH, where the treated water met WHO and TBS standards, whereas bone char had insufficient fluoride removal, especially at high fluoride levels. As a result, this study suggests that HAp derived from Anadara granosa shells could be a viable adsorbent for the defluoridation of drinking water.
Cockle (Anadara granosa) shells-based hydroxyapatite and its potential for defluoridation of drinking water
(Elsevier, 2022-02-27) Mtavangu, Stanslaus; Mahene, Wilson; Machunda, Revocatus; Bruggen, Bart; Njau, Karoli
The present study describes the synthesis and characterization of a hydroxyapatite (HAp)-based adsorbent derived from biogenic cockle (Anadara granosa) shells for the defluoridation of drinking water. The raw cockle shells and synthesized HAp were characterized by X-ray fluorescence spectroscopy (XRF), attenuated total reflection-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopes-energy dispersive X-ray (FESEM-EDX) and Brunauer-Emmett-Teller (BET) surface area analysis. As demonstrated by FTIR, cockle shells were found to be composed of calcium carbonate (97.4%), an aragonite polymorphous type of carbonate mineral. XRD and SEM analysis supported the formation of a nanocrystalline HAp with an average crystal size of 19.08 nm and 57.1 nm, respectively, with a surface area of 105.8 m2/g and a pore size of 5.6 nm, as depicted by BET. Batch adsorption experiments were conducted using the Box-Behnken design (BBD) with five input parameters: adsorbent dose (2–10 g/L), initial fluoride concentration (10–80 mg/L), contact time (0.5–24 h), reaction temperature (303–333 K), and pH. (3–11). BBD revealed the following opti- mum conditions: adsorbent dose (6 g/L), initial fluoride concentration (45 mg/L), contact period 12.25 h, re- action temperature (303 K), and pH 3. Experimentally, the adsorption of fluoride on HAp fitted well with the non-linear Langmuir isotherm and linear pseudo-second order kinetics, signifying the chemisorption process. A maximum adsorption capacity (qm) of 15.374 mg/g, which is closer to the experimental value of 14.053 mg/g, was presented by the Langmuir isotherm. Thermodynamically, the adsorption process was spontaneous, endo- thermic, and stable in nature. The defluoridation mechanism was through electrostatic attraction, ion exchange, hydrogen bonding, and precipitation. Furthermore, the synthesized HAp and bone char were used to examine their efficacy in defluoridating field water: HAp performed better at natural pH, where the treated water met WHO and TBS standards, whereas bone char had insufficient fluoride removal, especially at high fluoride levels. As a result, this study suggests that HAp derived from Anadara granosa shells could be a viable adsorbent for the defluoridation of drinking water.
In-situ synthesis of calcium/magnesium phosphate system for water de-fluoridation: Clay ceramic materials
(Elsevier, 2022-02-15) Mahene, Wilson; Hilonga, Askwar; Machunda, Revocatus
Clay ceramic water filters impregnated with silver colloids have been used to purify water in many parts of East Africa disregarding the removal of fluoride, which is a health-threatening ion in water supplies. This paper presents a synthesis of clay ceramic materials containing in-situ generated calcium/magnesium phosphate system as an adsorbent for water de-fluoridation. The materials were prepared in varied ratios of clay (K) to heat-pretreated dolostone (R) (K:R = 0:100, 90∶10, 85∶15, 75∶25 and 100:0), sintered at temperatures between 500 °C and 900 °C, and characterized using XRF, AAS, CHNS–O analyzer and X-ray PDF analysis. The materials improved in de-fluoridation performance with increase in sintering temperature at 500–700 °C, before exhibiting a sharp drop at 800 °C. The adsorption performance of K:R = 75:25 was higher than that of K:R = 0:100, signifying the effect of clay. The adsorption data obeyed Freundlich isotherm model, suggesting multi-layer adsorption. Fluoride uptake follows pseudo-second-order and intra-particle diffusion models, which suggests a chemisorption process involving rate-limiting intra-particle diffusion.
The role of textural properties and surface chemistry of activated carbon support in catalytic deoxygenation of triglycerides into renewable diesel
(Elseiver, 2023-07) Mahene, Wilson; Kivevele, Thomas; Machunda, Revocatus
The textural properties and surface chemistry of activated carbon support are commonly known to have influ- ence on the catalytic performance of catalysts. Many authors have assessed the effect of textural properties and surface chemistry of activated carbon support in the deoxygenation of triglycerides. This review focuses on reconciling literature on the role/relevance of textural properties and surface chemistry of activated carbon support in deoxygenation of triglycerides into diesel-like hydrocarbons. It is revealed that different activated carbon (AC) exhibit distinct effects on the catalytic behaviors of the supported catalyst. The degree of influence of both textural properties and surface chemistry of AC support varies with the nature of the supported catalyst.
Synthesis and FTIR Characterization of Mg-Hydroxylapatite Derived from Dolostone with High Dolomite Mineral Content
(University of Dar es Salaam, 2020-08-24) Mahene, Wilson; Gervas, Charles; Hilonga, Askwar; Machunda, Revocatus
We present the synthesis of magnesium-substituted hydroxylapatite starting from locally available dolostone. The apatite was prepared by a reaction between heat pre-treated dolostone powder with phosphoric acid, maintained at the pH of 12.5 using sodium hydroxide. The resultant material was then calcined at 500 °C, 600 °C, 700 °C, 800 °C and 900 °C. The precursor dolostone was characterized by organic elemental analyser (CHNS-O analyser), X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR), while the synthesized material was characterized by using FTIR. Results indicated that the dominant mineral in the carbonate rock materials was near-stoichiometric dolomite, while the synthesized material was found to be (carbonate, magnesium)-substituted hydroxylapatite. The synthesized material did not exhibit hydroxylapatite diagnostic peaks until after being calcined at 600 °C. The peaks became more distinct with increase in calcination temperature. The prepared material exhibited a low degree of crystallinity and low conversion temperature to beta-tricalcium phosphate, 700–800 °C. These characteristics are typical of a magnesium-substituted hydroxylapatite (Mg-substituted β-tricalcium phosphate). This work has demonstrated the feasibility of synthesizing magnesium-substituted hydroxylapatite (Mg-HA), with potential applications in water purification, using dolostone as a calcium/magnesium source
Tracking animal movements using biomarkers in tail hairs: a novel approach for animal geolocating from sulfur isoscapes.
(Movement Ecology, 2020-09-18) Kabalika, Zabibu; Morrison, Thomas; McGill, Rona A; Munishi, Linus; Ekwem, Divine; Mahene, Wilson; Lobora, Alex; Newton, Jason; Morales, Juan; Haydon, Daniel; Hopcraft, Grant
Background Current animal tracking studies are most often based on the application of external geolocators such as GPS and radio transmitters. While these technologies provide detailed movement data, they are costly to acquire and maintain, which often restricts sample sizes. Furthermore, deploying external geolocators requires physically capturing and recapturing of animals, which poses an additional welfare concern. Natural biomarkers provide an alternative, non-invasive approach for addressing a range of geolocation questions and can, because of relatively low cost, be collected from many individuals thereby broadening the scope for population-wide inference. Methods We developed a low-cost, minimally invasive method for distinguishing between local versus non-local movements of cattle using sulfur isotope ratios (δ34S) in cattle tail hair collected in the Greater Serengeti Ecosystem, Tanzania. Results We used a Generalized Additive Model to generate a predicted δ34S isoscape across the study area. This isoscape was constructed using spatial smoothers and underpinned by the positive relationship between δ34S values and lithology. We then established a strong relationship between δ34S from recent sections of cattle tail hair and the δ34S from grasses sampled in the immediate vicinity of an individual’s location, suggesting δ34S in the hair reflects the δ34S in the environment. By combining uncertainty in estimation of the isoscape, with predictions of tail hair δ34S given an animal’s position in the isoscape we estimated the anisotropic distribution of travel distances across the Serengeti ecosystem sufficient to detect movement using sulfur stable isotopes. Conclusions While the focus of our study was on cattle, this approach can be modified to understand movements in other mobile organisms where the sulfur isoscape is sufficiently heterogeneous relative to the spatial scale of animal movements and where tracking with traditional methods is difficult.