Browsing by Author "Mwegoha, W. J. S."

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    Effectiveness of activated groundnut shells to remove chromium from tannery wastewater
    (Science Publishing Group, 2016) Mwegoha, W. J. S.; Lema, M. W. J.
    This paper presents results of the investigation of Chromium III removal from tannery wastewater using groundnut shells under laboratory scale batch experiments. The effects of pH, contact time, particle size and dosage of the adsorbent on the adsorption of Cr (III) were studied. Determination of Chromium ion concentration in the wastewater was done using Atomic Absorption Spectrophotometer (AAS). Results show that removal mechanism is dominantly adsorption, which is dependent of the physical and chemical characteristics of the material. The main constituent of groundnut shell is carbon, potentially making it suitable for making activated carbon for adsorption experiments. From the initial concentration of 6.643 ppm, optimum Cr (III) removal was obtained at pH of 4, particle size of 0.25mm, contact time of 180 minutes and adsorbent dosage of 20g, with highest efficiency of 98.013%, corresponding to final concentration of 0.132ppm. The adsorption process was found to obey the Freundlich adsorption isotherm with R2 being 0.9613. Overall, the adsorption capacity of the activated groundnut shell was found to be 2.6172mg/g which ensures that they can be used for the removal of Chromium III from tannery wastewater.
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    Heavy metal contamination in agricultural soils and water in Dar es Salaam city
    (Academic Journals, 2010) Mwegoha, W. J. S.; Kihampa, C.
    Heavy metals in soil and water were determined at four points along Msimbazi River valley in Dar es Salaam city, which is popular for vegetable farming. Results indicated that the concentration of chromium in water ranged from (1.414±0.922) to 0.01 mg/L. Maximum and minimum lead concentrations of 0.113 and 0.083 mg/L were detected. The concentration of copper was generally low at all sites, ranging from (0.013±0.005) to (0.016±0.005) mg/L. The concentration of lead in water throughout the river exceeds the WHO (2004) drinking water limit of 0.01 mg/L, ranging from (0.113±0.104) to (0.083±0.059) mg/L. Cadmium concentration at all sampling points was below detection limit of 0.01 mg/L. Soil analysis indicated that the concentrations of heavy metals are highest at the top soil and decreased with depth. Lead had the highest concentration of (22.85±1.502) mg/kg; which did not exceed the TZS (2003) maximum limit of 200 mg/kg for soils. Chromium had maximum and minimum concentrations of (502.33±150.991) and (174.707±168.278) mg/kg, respectively, with most of samples exceeding the TZS (2003) permissible limit of 200 mg/kg. The maximum and minimum concentrations of copper were (21.073±2.881) and (4.513±1.713) mg/kg, respectively, lower than the TZS (2003) permissible limit of 100 mg/kg. Cadmium concentrations at all sampling points were lower than the permissible concentration of 100 mg/kg in soils (TZS, 2003). The presence of heavy metals in soil and water indicates the potential for pollution transfer from these media to the food chain, especially since this valley is popular for vegetable cultivation.
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    Leaching behaviour and speciation of Pb, Zn and Cu in stabilized Gold mine tailings.
    (Open Science Online, 2018) Mapinduzi, R. P.; Pancras, M. S. B.; Mwegoha, W. J. S.
    Leaching and speciation of heavy metals in stabilized gold mine tailings were investigated by using leaching tests and leaching model (Visual MINTEQ 3.1®) respectively. Results indicate that the Stabilized/Solidified (S/S) tailings has high acid neutralizing capacity, which is dependent on binder content used. The dissolution of alkaline metals and oxyanions (such as SO42-, HCO32-) raises both the pH and electric conductivity of the leachant and, in-turn, affects leaching of the heavy metals. Higher leaching rates were observed with low pH leachants. Speciation modeling reveals that under acidic conditions, the solution is dominated by (Cu2+, CuCl and CuSO4(aq)), (Zn2+, ZnCl+, ZnCl42-(aq), ZnCl3-, ZnCl2(aq)) and Zn(SO4)2-) and (Pb(OH)2(aq) and PbOH+) for Cu, Zn and Pb respectively. Under alkaline condition, metal hydroxides are mostly leached into the solution. Adsorption simulation results reveal that only <1% of each metal is immobilized on either HFO or Gibbsite, with a pH dependent sorption process. The maximum adsorption occurs between pH 6 and 9. Based on the observed cumulative amount of metals sorbed, the affinity trend appears to be Pb2+ > Cu2+ > Zn2+ for HFO and Zn2+ > Pb2+ > Cu2+ for Gibbsite. It was further observed that the major leaching mechanism for Cu2+, Zn2+ and Pb2+ in stabilized, non-dissolving cylindrical monolithic tailing samples is surface washout, which is dominant during the whole leaching period. It was also observed that the leaching of the soluble fraction of metals is through surface washout. It can be concluded that that the leaching of the three metals in both granular and monolithic material is pH dependent.
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    Nitrogen dynamics in a maturation waste stabilization pond system receiving industrial wastewater in Mabibo area Dar es salaam, Tanzania
    (Fortune, 2015) Mwegoha, W. J. S.
    A mathematical model describing the dynamics of Nitrogen transformation and removal in a maturation Waste Stabilization Pond (MWSP) system receiving industrial wastewater was developed. Simulation of the processes was done using STELLA 8_1®, based on the principle of conservation of mass. Besides, measurement of different parameters input to the model was made. Model simulation and mass balance analysis results show that nitrification was responsible for the majority of nitrogen transformation at 36.9% (38.1 mgl-1d-1), followed by plant uptake at 31.6% (32.55 mgl-1d-1); mineralization at 21.05% (21.65 mgl-1d-1); sedimentation/accretion at 9.3% (9.1 mgl-1d-1) transformation. Regression analysis indicates a good agreement between simulation results and actual measurements with R2 of 0.749 for NO3-N, 0.709 for NH3-N, 0.985 for Org-N, and 0.973 for Soil/Sediment-N. These results suggest that the developed model is capable of simulating the dynamics of nitrogen transformation and removal in a Maturation Waste Stabilization Pond system receiving industrial wastewater, and can be utilized as a tool in assessing nitrogen levels at various pollution scenarios to aid decision making as regard to protecting water bodies receiving effluent from these systems.
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    Sorption-desorption tests on the performance of non-hazardous industrial wastes in decreasing leachability of trace metals on contaminated lands
    (Open Science Online, 2015) Mwegoha, W. J. S.; Muhondwa, J.
    Soil stabilization by addition of industrial solid wastes in order to increase trace metals retention and (a minor secondary effect) to dilute their concentrations is an environmentally friendly and attractive soil remediation process that attenuates trace metals impact. In this study, non-hazardous industrial by-products (sugar foam, gypsum, zeolitic materials and fly ashes) were tested using laboratory scale experiments to assess their performance on the remediation of acidic soil that has been affected by a pyritic source of contamination at Aljaraque, Spain. In this soil, the concentration of metals in the Aqua Regia and soil-water extracts confirmed the extent of the soil contamination since all seven trace metals (Cu, Cd, As, Pb, Zn, Co and Sb) analyzed from the Aqua Regia extracts and nine trace metals (Cu, As, Cd, Zn, Pb, Co, Sb, Ni and Cr) analyzed in soil-water extract were found above the intervention limits specified in the Junta de Andalucía (Spain) and Germany National Standard (DIN) respectively for both Agriculture and Industrial activities. Metal sorption and desorption capacity of the industrial wastes were estimated in a soil water extract medium. Fly ashes and zeolitic material were found to be the best candidate materials for soil remediation due to their ability to increase soil pH, exhibiting greater solid-liquid distribution coefficient (Kd), lower sorption reversibility (Kd, des) and lower desorption yields to almost all trace metals analyzed.