Browsing by Author "Moyo, L.B."

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    Application of amine-modified tannins gels as coagulants in wastewater treatment
    (Research Square, 2024-08-28) Thelmmer, M.; Ncube, S.; Moyo, L.B.; Mamvura, T.A.; Danha, G.; Simate, G.S.; Tshuma, N.
    Tannin (T) is an organic substance that may potentially be used as an inexpensive, environmentally friendly, and effective bio-coagulant to remove impurities from residential and commercial wastewater. In this study, bio-coagulants were prepared using tannins obtained from the wattle tree (Acacia mearnsii). The bio-coagulants were modified using formalin and optionally, ethanolamine (ETA) and ammonium chloride (NH 4 Cl) as amine sources through the Mannich Reaction scheme. Three coagulants were prepared, T-ETA modified tannin, T-NH 4 Cl modified tannin and a mixture of T-ETA: T-NH 4 Cl in molar ratio 1: 1. Aluminium sulphate [Al 2 (SO 4) 3], a metal-coagulant was also used as the standard for comparison. The three coagulants were tested at varied concentrations (500–1250 mg/L) using jar tests on laundry wastewater to see their effect on remediation of wastewater. A mixture of bio-coagulant T-NH 4 Cl and T-ETA was most effective with highest removal efficiencies for turbidity (94%), COD (85%), Total solids (87%) and nitrates (99%). For colour removal T-NH 4 Cl modified tannin showed the highest removal efficiency of 92%. The results support the use of cheaper and environmentally friendly amine modified tannin-based flocculants in laundry wastewater treatment as they showed less toxicity on the treated water.
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    Application of response surface methodology for optimization of biodiesel production parameters from waste cooking oil using a membrane reactor
    (Elsevier, 2020-10-05) Moyo, L.B.; Iyuke, S.E.; Muvhiiwa, R.F.; Simate, G.S.; Hlabangana, N.
    In light of the growing concerns over depleting energy resources, alternative renewable fuels such as biodiesel have been identified as a possible means of addressing this crisis. In biodiesel production, waste cooking oil (WCO) is seen as the ideal alternative feedstock to vegetable oils, which are part of the food chain. The need to obtain high quality biodiesel at minimal cost has driven the idea to use membrane reactors, which offers the ability to achieve both reaction and separation processes simultaneously. Design and optimization studies were conducted using sulphated zirconia pre-treated WCO as feed stock. Response surface methodology modelling was used to investigate the effect of reaction temperature, catalyst concentration and circulation flow rate in biodiesel production using membrane reactors. This is because limited data is available, particularly considering circulation flow rate effect on biodiesel production using membrane reactors. Experimental results also show that the higher the catalyst to WCO ratio the higher the free fatty acids (FFA) content. A maximum biodiesel yield of 92. 6 mole % was obtained at a temperature of 61◦C, circulation flow rate of 26 mL/min using KOH catalyst concentration of 1.3 wt % over a TiO2/Al2O3 membrane. Upon membrane optimization, a biodiesel yield of 94.03 mol % was obtained at 58.5 ◦C, circulation flow rate of 18.78 ml/min and catalyst concentration of 1.24 wt %. This analysis clearly shows that RSM can be successfully used to model reacting membranes using temperature, catalyst concentration and circulation flow rate to achieve higher yields for biodiesel production.
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    Characterization, kinetics and thermodynamic evaluation of struvite produced using ferrochrome slag as a magnesium source
    (South African Journal of Chemical Engineering, 2023-10-24) Moyo, L.B.; Simate, G.S.; Hobane, N.; Dube, C.
    There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5◦C/min; 10◦C/min and 15◦C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µ m whilst, the lowest was 31 µ m at a pH of 9.5. The highest percent of fines (<10 µ m) was recorded at a pH of 9.5 using FCS as magnesium source in the metastable region of struvite precipitation whereas at a pH of 7.5 no fines (<10 µ m) were recorded. SEM images confirmed that the struvite underwent morphological changes when prepared with FCS in comparison to that produced using MgCl2. The surface morphology of the finished product demonstrated the presence of irregular shaped particles, due to presence of impurities. The kinetic data showed that struvite precipitation was limited by the chemical reaction step. Model fitting was used to determine the reaction control mechanism and the average activation energies obtained by four model free methods were FWO (56.2), KAS (51.67) Starink (49.61) and Tang (49.81) kJ/mol, indicating that the FWO method was the least accurate method. The thermodynamic data indicated that the thermal degradation of struvite crystals has a high degree of disorder, and the process is endothermic, irreversible, and non-spontaneous.
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    Investigating the feasibility of using agricultural waste as an adsorbent of gold ions in small scale gold processing plants.
    (2019) Tapfuma, A.; Chakawa, D.P.; Moyo, L.B.; Hlabangana, N.;; Danha, G.; Muzenda, E.
    The recovery of precious metals like gold is increasing each day due to its high market prices along with diverse applications. Bio-sorption represents a biotechnological innovation as well as a cost effective and excellent tool for recovery of precious metals from aqueous solutions. This study offers an overview of a recent scenario of bio-sorption studies carried out on the use of some promising bio-sorbents which could serve as an economical means for recovering gold for small scale gold processing plants. Results show that activated carbon (control) has the highest adsorption efficiency since it contains more active site on the carbon molecules. The activated maize corn cob had the highest adsorption efficiency (77.09%) compared to all other agricultural adsorbents. Banana peels showed a significant adsorption efficiency of 56.87%.
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    Optimisation of using a blend of plant based natural and synthetic coagulants for water treatment: ( Moringa Oleifera-Cactus Opuntia-Alum Blend)
    (2020) Gandiwa, B.I.; Moyo, L.B.; Ncube, S.; Mamvura, T.A.; Hlabangana, N.
    The research presents a comparative study on the effectiveness of blending plant based natural coagulants (Cactus Opuntia and Moringa Oleifera extracts) and a synthetic coagulant (aluminium sulphate or alum) in treatment of raw water. The low production rates of natural coagulants has derailed their commercialization this has driven the idea of blending synthetic coagulants which is envisaged to be the more appropriate means of application in this study. To measure the effectiveness of the coagulant, the following parameters were measured; turbidity, pH, conductivity and total alkalinity. The simplex lattice experimental design was applied using Minitab Software to obtain the optimal coagulant blend. The models were validated by statistical analysis which showed that the model was sufficient and no further modeling was required. The optimization results showed that a combination of alum, Moringa Oleifera and Cactus Opuntia in proportions of 13%, 42.6% and 44.4%, respectively with a total coagulant dosage of 45mg/L gave the best overall results with the resultant water having a turbidity, pH, conductivity and total alkalinity of 2.7 NTU, 6.99, 308 µS/cm and 137.7mg/L respectively. These physiochemical parameters are within required limits for potable water as per WHO guidelines. From the results, it was concluded that aluminum sulphate (alum) can be successfully blended with natural plantbased coagulants for raw water treatment.
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    Optimization of pulp production from groundnut shells using chemical pulping at low temperatures
    (2020) Musekiwa, P.; Moyo, L.B.; Mamvura, T.A.; Danha, G.; Simate, G.S.; Hlabangana, N.
    Paper production through chemical pulping has been identified as one of the ideal avenues of exploring the uses of groundnut shells as they are rich in cellulose. Ideally, the cellulose can be used to synthesize fibres that can be converted into useful paper products. In this study, chemical pulping was the chosen process for liberating the fibres as it is effective in dissolving lignin embedded within the cellulose. In addition, the fibres produced have superior physical properties compared to mechanical pulping. It is imperative that optimal conditions are identified for the chemical treatment process, in order to ensure that energy and chemical consumption are minimized. All these measures are aimed at reducing production costs and make chemical pulping economically viable, as compared to the mechanical pulping process which is less costly. Response surface methodology (RSM) was used in this study to evaluate the effect of three independent variables (cooking time, temperature, and sulphidity) on pulp yield and kappa number. These parameters are critical in the chemical pulping process and the optimal conditions obtained were 180 min, 100 C and 23.6 wt.%, respectively. At the optimal conditions, the pulp yield was 64.39wt% with a kappa number of 19.5. The results showed that all parameters investigated, had a statistically significant effect on the production of pulp. The increased cooking time was efficient in ensuring complete impregnation of the groundnut shells with chemicals for pulping and ensuring that the dissolution of lignin is not selective and does not result in dead spots inherently compromising the quality of the pulp. On the other hand, lower temperatures limited the peeling effect due to hydrolysis of carbohydrates which increased pulp yield due to a higher cellulose retention. Consequently, this contributed towards obtaining pulp that is well cooked, has a low bleach consumption and a higher quality.
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    Pressurized torrefaction of waste biomass to improve bio coal quality: Synergistic effect between animal waste and wood chips
    (Elsevier, 2025-04-19) Tshuma, N.M.; Moyo, L.B.; Danha, G.; Mamvura, T.A.; Simate, G.S.; Artur, C.D.; Charis, G.
    This study aims to investigate the effect blending waste material to improve its fuel properties using pressurized torrefaction. This research explored the benefits of blending animal waste with wood chips to produce a bio-coal with improved fuel properties. The process conditions investigated were temperature and pressure intervals of 200◦C to 280◦C and atmospheric pressure (AP) to 4MPa, respectively. The results showed that an increase in temperature and pressure improved the fixed carbon content of the blend almost threefold from 19.87 % to 66.93 % and the higher heating value (HHV) to 27.32MJ/kg from 13.90MJ/kg at mild torrefaction temperature of 280◦C and gas pressure of 4MPa compared to atmospheric pressure conditions and the lowest temperature investigated. The HHV increased primarily due to a release of bound and unbound moisture and volatile matter. Wood chips had an HHV of 27.00MJ/kg at a torrefaction temperature of 280◦C due to the decomposition of hemicellulose and cellulose which enhanced the thermal stability, fixed carbon content and calorific value. However, animal waste had the least incremental increase in HHV (16.45MJ/kg) due to a high initial content of volatile matter and moisture. The improved properties of the blend of materials indicated that pressurized torrefaction was effective in increasing fixed carbon content through secondary polymerization reactions. Moreover, it facilitated the decomposition of cellulose at a lower temperature than the typical range of 315-400◦C if conducted at atmospheric pressure. This study elucidates the notable role of the synergistic effects of blending feed materials prior to torrefaction towards improving the properties and pyrolysis performance of biomass components.
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    Torrefaction of a mixture of animal waste and wood chips to produce sustainable bio coal: Kinetics and implications
    (2024) Tshuma, N.; Moyo, L.B.; Danha, G.; Mamvura, T; Geoffrey, S.; Artur, D.
    Perennial energy demands globally and the need to cut on fossil fuel based emissions has paved way for alternative energy sources such as raw biomass. However, raw biomass has faced challenges as a source of energy due to its low energy density and high moisture content compared to fossil coal. Consequently, pre-treatment of raw biomass has been deemed necessary to improve the aforementioned properties. The torrefaction process has been identified as an effective means to produce a sustainable solid fuel in the form of bio-coal from raw biomass. It is a promising technology that can be used to achieve a closed carbon cycle and mitigate greenhouse gas emissions. Characterization of bio-coal has shown comparative physical and chemical properties to fossil coal which can be synthesized by subjecting biomass to high-temperature thermo-chemical processing Biomass derived bio coal has shown excellent potential as a partial replacement for coal to achieve a closed carbon cycle and mitigate carbon dioxide emissions. Several drawbacks are associated with using animal waste as the sole feedstock for torrefaction processes. These issues encompass suboptimal energy yield, elevated ash levels and subpar bio coal quality. To counter these drawbacks, in this study, torrefaction on wood waste, animal waste and a mixture of the aforementioned materials at a ratio of 50: 50 by mass was investigated. The process conditions investigated included temperature and residence time intervals of 200 C to 500 C and 30 to 120 minutes respectively. The results showed that a positive adjustment in temperature and residence time increased the higher heating value (HHV) primarily due to release of moisture and volatile material. Wood and animal waste higher heating values were increased to 23.7 MJ/kg and 19.87 MJ/kg respectively from 17.9 MJ/Kg and 16.7 MJ/Kg respectively. Wood had a higher heating value upon treatment as the decomposition of hemicellulose and cellulose enhanced the thermal stability, fixed carbon content and calorific value. Whereas, animal waste had the least incremental increase in heating value due to a high initial content of volatile substances. The study showed that to overcome the drawbacks of having a low mass yield and heating value for animal waste, mixing animal waste with wood chips was effective in producing a product with a higher mass yield and calorific value. The kinetic analysis indicated that wood torrefaction is easily achievable compared to that of animal or mixed torrefaction as it had the lowest activation energy.
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    Treatment of efuent from a malting processing plant using bio‑coagulants
    (Discover Civil Engineering, 2024-07-05) Murisa, V.; Murisa, V.,; Ncube, S.; Moyo, L.B.; Danha, G.; Mamvura, T.A.
    Stringent measures by water authorities worldwide on water clarification has resulted in the use of chemical-based coagulants to be a formidable challenge. This has driven the need to find alternative sustainable coagulants such as plant-based bio coagulants which are readily available, abundant and cost effective in developing countries such as Zimbabwe. In this regard, the effectiveness of treating effluent from a brewery malting processing plant using bio-coagulants (Aloe Vera, Cactus opuntia and Okra seeds) was investigated compared to that of a chemical coagulant (Alum). The water pollution parameters that were investigated include turbidity, total dissolved solids, electrical conductivity, temperature and pH. The results showed that Alum was the most effective coagulant as it reduced the turbidity from 734 NTU to 68.3 NTU and Total Dissolved Solids (TDS) from 19,800 ppm to 880 ppm at a dosage of 40 mg/L. Okra seeds had an optimum dosage of 35 mg/L with a turbidity and TDS removal of 88.83% and 95.25% respectively. Aloe Vera had an optimum dosage of 40 mg/L with a turbidity and TDS removal of 74.25% and 95.40% respectively. For Cactus opuntia it was 50 mg/L obtaining turbidity and TDS removal of 74.66% and 95% respectively. The best blend of the bio coagulants had a ratio of (0.17, 0.17, and 0.67) for Aloe Vera, Cactus opuntia and Okra seeds respectively. At a dosage of 40 mg/L the turbidity removal was 83.92% and TDS removal was 95.12%. The results indicated that blending the plant-based coagulants had a positive synergistic effect. Highlights Aluminum sulphate (Alum) is more effective in reduction of suspended solids and dissolved solids compared to Aloe Vera, Cactus and Okra seeds. The effectiveness of Aloe Vera, Cactus and Okra seeds as plant-based coagulants indicates that they have active compounds effective as coagulation agents. There were positive synergistic effects upon blending Aloe Vera, Cactus and Okra seeds this was observed in the reduction of turbidity this was higher than when Aloe Vera and Cactus were used individually as coagulants.
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    Utilization of cellulose in tobacco (Nicotiana tobacum) stalks for nitrocellulose production
    (Heliyon, 2021-07-13) Muvhiiwa, R.; Mawere, E.; Moyo, L.B.; Tshuma, L.
    This research explains the conversion of waste tobacco stalks into nitrocellulose to try to recover as much chemical potential contained in the biomass material as possible. Simple pioneering experiments were conducted using pulping tobacco stalks with a moisture content of 10.17 wt% and the soda pulping method being applied to produce cellulose pulp. The cellulose pulp was bleached using calcium hypochlorite to produce a dry white lignin-free pulp, which was subjected to nitration. The mixture used was 67% nitric acid and 98% sulphuric acid, and the acid ratio was varied between 3:7 and 7:3 v/v. Nitration time was varied between 5 and 25 min. This process produced nitrocellulose with all the various conditions. The nitrocellulose obtained with nitrogen content between 11 – 11.5% v/v was characterized using its solubility in acetone. An optimum nitrating mixture of 1:1 v/v with a nitration time of 5 min was used to produce nitrocellulose from tobacco stalks using soda pulping. The results show a great potential for tobacco farming countries to reduce their nitrocellulose import bill using this process.