Browsing by Author "Lubwama, M."

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    Effect of alkaline pretreatment on the thermal behavior and chemical properties of rice husk varieties in relation to activated carbon production
    (Springer, 2019-07-19) . Menya, E; Olupot, P. W.; Storz, H.; Lubwama, M.; Kiros, Y.; John, M. J.
    Thermal behavior and chemical properties of selected raw and NaOH-pretreated rice husk varieties were investigated. NaOH- pre treatment process involved soaking 5 g rice husk samples in 40 mL of 2%w/v NaOH, shaking (400 rpm) and heating (50 C) for 3 h. NaOH- pretreated samples were water-washed, oven-dried, and milled for use in the determination of their thermal behavior and surface functional groups. Alkaline wash water was also analyzed for sugar components. Thermal decomposition temperatures, degradation rates, and the subsequent mass losses varied from one rice husk variety to another. These thermal properties increased after NaOH pretreatment of the rice husk varieties, reducing their char yields (17.1–20.4% db). These changes mainly had to do with the lignin, hemicellulose, and ash removal from the rice husk varieties, as confirmed by their FTIR analysis, as well as by the sugar composition analysis of their alkaline wash-water. Consequently, the FTIR spectra differed between the raw and NaOH-pretreated rice husk varieties
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    Optimization of pyrolysis conditions for char production from rice husks and its characterization as a precursor for production of activated carbon
    (Springer, 2019-03-13) Menya, E.; Olupot, P. W.; Storz, H.; Lubwama, M.; Kiros, Y.; John, M. J.
    Response surface methodology was employed to optimize pyrolysis conditions for the production of char with maximum yield, fixed carbon content, and minimum ash content from Uganda’s New Rice for Africa (NERICA) 1 rice husk variety. The aim was to obtain rice husk char with more suitable properties as an activated carbon precursor. Mathematical models were developed to explain the relationships between the experimental responses and the pyrolysis parameters of temperature (400–600 °C), heating rate (10–25 °C min−1), and heating period (60–120 min). The optimized rice husk char was further characterized for elemental and proximate compositions, thermal behaviour, specific surface area, as well as surface functional groups. Results from the analysis of variance (ANOVA) revealed that the quadratic model best fits each of the responses. Pyrolysis temperature had the greatest influence on each of the responses, followed by heating period, and lastly heating rate. Optimum pyrolysis conditions were found to be temperature (406 °C), heating rate (10 °C min−1), and heating period (60 min), resulting in char yield, fixed carbon, and ash contents of 35.26, 55.39, and 35.01% dry basis, respectively. Compared to raw rice husk, the resulting rice husk char was found more suited as activated carbon precursor, due to its enriched carbon content (60.35%) and specific surface area (123.9 m2g−1). Thermogravimetric analysis of the rice husk char revealed that thermal activation temperatures were higher than 400 °C may be required to considerably devolatilize the char, forming a more porous activated carbon.
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    Optimization of pyrolysis conditions for char production from rice husks and its characterization as a precursor for production of activated carbon
    (Springer, 2019-03-13) Menya, E.; Olupot, P. W.; Storz, H.; Lubwama, M.; Kiros, Y.; John, M. J.
    Response surface methodology was employed to optimize pyrolysis conditions for production of char with maximum yield, fixed carbon content, and with minimum ash content from Uganda’s New Rice for Africa (NERICA) 1 rice husk variety. The aim was to obtain rice husk char with more suitable properties as an activated carbon precursor. Mathematical models were developed to explain the relationships between the experimental responses and the pyrolysis parameters of temperature (400–600 °C), heating rate (10–25 °C min−1), and heating period (60–120 min). The optimized rice husk char was further characterized for elemental and proximate compositions, thermal behavior, specific surface area, as well as surface functional groups. Results from the analysis of variance (ANOVA) revealed that the quadratic model best fits each of the responses. Pyrolysis temperature had the greatest influence on each of the responses, followed by heating period, and lastly heating rate. Optimum pyrolysis conditions were found to be temperature (406 °C), heating rate (10 °C min−1), and heating period (60 min), resulting in char yield, fixed carbon, and ash contents of 35.26, 55.39, and 35.01% dry basis, respectively. Compared to raw rice husk, the resulting rice husk char was found more suited as activated carbon precursor, due to its enriched carbon content (60.35%) and specific surface area (123.9 m2 g−1). Thermogravimetric analysis of the rice husk char revealed that thermal activation temperatures higher than 400 °C may be required to considerably devolatilize the char, forming a more porous activated carbon.
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    Production and performance of activated carbon from rice husks for removal of natural organic matter from water:
    (Elsevier, 2017-11-02) Menya, E.; Olupot, P.W.; Storz, H.; Lubwama, M.; Kiros, Y.
    Adsorption by activated carbon has great potential to improve natural organic matter (NOM) removal from water. However, the high production and regeneration costs limit its wide scale application. To address these limitations, research efforts have been focused on finding low-cost materials that can be transformed into activated carbon. Rice husk is one of such material of research focus, especially in developing countries, where over 96% of rice husks are generated globally. Although numerous investigations have been made concerning the production of activated carbon from rice husks, the existing scientific information still remains widely scattered in the literature. Furthermore, the scientific information regarding the performance of rice husk-activated carbon during NOM removal from water still remains poorly documented. This review article, therefore, provides ample information on efforts made by various researchers concerning the production of activated carbon from rice husks and its adsorption performance in relation to NOM removal from water. The properties and pretreatment of rice husks in relation to the production of activated carbon are discussed. Activation of rice husks by physical and chemical methods under numerous conditions is reviewed. Factors affecting NOM adsorption by activated carbon are briefly discussed. The adsorption performance of rice husk activated carbon is also reviewed with respect to NOM removal from water, and where possible compared with other source-derived activated carbons. The data from the literature revealed that NOM removal by rice husk activated carbon can be as effective as commercial activated carbon. Consequently, rice husk-activated carbon has the potential to serve as an alternative to commercial-activated carbon.
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    Synthesis and evaluation of activated carbon from rice husks for removal of humic acid from water
    (Springer, 2020-11-26) Menya, E.; Olupot, P. W.; Storz, H.; Lubwama, M.; Kiros, Y.
    Activated carbon was synthesized from the New Rice for Africa (NERICA) rice husk variety, followed by its evaluation for removal of humic acid from water. Product values of carbon yield, C and total specific surface area, as,BET were employed as the performance criterion. The best physically activated carbon resulted from char activation at 800 °C for 10 min, leading to as,BET and C×as,BET values of 756.8 and 402.7 m2 g−1, respectively. The best chemically activated carbon resulted from 30 wt% H3PO4 activation of rice husk at 400 °C for 30 min, leading to as,BET and C×as,BET values of 2258.4 and 1058.7 m2 g−1, respectively. Despite the higher as,BET value, the maximum adsorption capacity of the best chemically activated carbon (5.3 mg g−1) was found lower than 8.9 and 27.2 mg g−1 exhibited by the chemically activated carbons prepared at 500 and 600 °C, respectively. The best adsorption conditions included carbon dose of 0.5 g, solution pH of 2, and contact time of 60 min. The adsorption capacity of the prepared activated carbons (27.2 mg g−1) was comparable to that of the commercial activated carbon (30.40 mg g−1). The analyses of the adsorption isotherms and kinetics revealed that the experimental data fits well the Langmuir isotherm model, as well as the pseudo-second-order kinetic model. The latter suggests that the adsorption of humic acid onto the activated carbon was controlled by the chemisorption process. Overall, the study revealed that the NERICA rice husk variety has good prospects for preparation of activated carbons for humic acid adsorption.