Environmental Engineering

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Browsing Environmental Engineering by Author "Abubeker, Yimam (PhD)"

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    Biomass Gasifier Process Simulation for Sustaibale Energy Production from Different Biomass Feedstock
    (Addis Ababa University, 2017-11) Seada, Mohammed; Abubeker, Yimam (PhD)
    With the gradual depletion of coal and petroleum resources, biomass is being perceived as a self-sustainable source of energy production. It is cheap and readily available as well. Gasification is one of the potential sources for production of clean and eco-friendly fuel. ASPEN PLUS simulator is a strong tool for investigating the behavior of a process and it can be readily used to access various aspects like feasibility of an operation, effect of operating parameters on the performance of a gasifier. In this paper, steady state simulation model of air gasification has been developed in Aspen plus for fixed bed biomass gasifier using rice husk, coffee husk and saw dust as a fuel and the analysis of fuel samples was done through ultimate and proximate properties of the biomass. Aspen plus is selected as a simulation tool due to its higher capability of handling solid feed using physical models. The fixed bed gasifier used here is an updraft type one with drying, Pyrolysis, gasification, and combustion stages. The gasifier has been modeled based on thermodynamic equilibrium model by Gibbs free energy minimization in four stages. In the first stage moisture content of biomass feed is reduce through drying. In the second stage biomass is decomposed into its elements by specifying yield distribution. In the third and fourth stages gasification and combustion reactions has been modeled using Gibbs free energy minimization approach. Simulation result include; sensitivity analysis of Air to fuel ratio, gasification temperature, gasification pressure, and, steam to biomass ratio have been varied over wide range and the effect of these parameters on syngas composition and lower heating value has been investigated. The sensitivity analysis results indicated that increase in air to fuel ratio decreases the heating value of the producer gas. Temperature increases the production of CO and H2 and enhances the heating value of the producer gas. Higher pressure reduces H2 rich syngas hence decreases the lower heating value of the producer gases. Steam as a gasifying agent favors hydrogen production which results in increase of hydrogen content in the syngas, while increase of the steam to biomass ratio had negative effects on lower heating value of syngas. Based on the simulation results, maximum lower heating value of syngas was found at the gasification temperature of 800ºC, steam flow rate of 0.3 kg/hr, and pressure of 1bar was obtained at air flow rate of 0.5 kg/hr for 1.5 kg/hr of each feed stocks.
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    Evaluating Penitential of “SUPHE” Soil as A Coagulating Agent in Primary Treatment of Asella Malt Factory Wastewater
    (Addis Ababa University, 2018-10) Arega, Getaneh; Abubeker, Yimam (PhD)
    Malt industries generate large amounts of wastewater effluent which contains a high concentration of biodegradable and non-biodegradable organic compounds which are poisonous to the environment and to eco system if discharged untreated. In this study, treatment performance of “Suphe” soil was evaluated first by treating composite malting waste water samples collected from different stages of production process at three different doses which were, 50mg/l, 500mg/l, 1000mg/l of “Suphe” soil in order to remove COD, BOD, TSS, then it was followed by adjusting the pH of waste water at acidic (pH 5), neutral (pH 7) and basic (pH9) medias. Sodium Hydroxide (NaOH) 0.1N and Sulfuric acid (H 2 SO 4 ) 0.1 N were used for adjusting the pH at the desired levels and the removal efficiency of “Suphe” soil was best recorded at pH of 7 and coagulant dose of 50 mg/l. Design-Expert 7.0.0 three-level-three-factor Box-Bhenken Design (BBD) was applied for experimental design and statistical analysis of results. Coagulant dose, pH of wastewater, and settling time had a significant effect on treatment process of malting wastewater samples process. For this treatment system, a set of experiments was performed to investigate removal of COD, BOD and TSS at different experimental phases. From these analyses, Results on overall efficiency had COD and BOD removal performance of 94.3% and 94.4 % for the first wet steep; 97.7%and 97.1% for the second wet steep and 96.3% and 96.1% for the composite treated effluent respectively. Andthe turbidity removal efficiency of the “Suphe” soil coagulant was 98.76%, 99% and 99.83% respectively for first wet steep, second wet steep and finally treated composite effluent at coagulant dose of 50 mg/l and pH of 7 On the other hand at the same pH level in which “suphe” soil was used, Alum turbidity removal efficiency was 96.2%, 96.6%and 99.4% respectively as mentioned above. Therefore, “Suphe” soil is found to lay a significant malting wastewater pretreatment agent which has the potential to replace the hydrated aluminum sulphate.
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    Evaluation of Sugarcane Straw Derived Biochar for the Remediation of Chromium and Nickel Contaminated Soil
    (Addis Ababa University, 2018-12-06) Selam, Masresha; Abubeker, Yimam (PhD)
    Soil constitutes a crucial component of rural and urban environments. This fact is making role of heavy and trace elements in the soil system an issue of global concern. Heavy metals constitute an ill-defined group of inorganic chemical hazards, whose main source is anthropogenic activities mainly related to fabrications. This accumulation of heavy metals soils can prove toxic to the environment. The application of biochar to soil is one way of immobilizing these contaminants through sorption by exploiting the high surface area of this material among its other essential properties. This research examined the ability of sugar cane straw, an organic waste material from sugar farm, derived biochar and ash to remediate soil contaminated with heavy metals mainly Chromium and Zinc from the effluent of electroplating industry. Biochar was produced by varying the temperature from 300°C to 500°C and ash at 700°C. The highest yield (50%) was obtained at the lowest temperature (300°C). The proximate analysis showed ash content of 42.8%, ultimate analysis with carbon content of 67.18%, the Hydrogen to Carbon ratio of 0.54 and the results from FTIR analysis disclosed the organic nature of biochar. Methylene blue absorption indicated its fine surface area and pore structure which increases with severity of temperature. Biochar was mixed with soil with at a ration varying from 4%w/w to 10%w/w of soil and the response variables was determined at a time interval of 150 days, 180days and 210days. As for ash (10% w/w), the characterization was performed at incubation time of 210days. The results of pH indicated that biochar (9.24) had a notable liming capacity of acidic soil (4.8) by increasing it to 6.89 whereas ash increased it to 7.5. The immobilization capacity of biochar was found to effected mostly by the highest production temperature (500°C) which was 75.5% for Chromium and 80.5% for Nickel. In addition, ash was shown to possess an outstanding immobilization capacity of 95.5% and 90.5% for Chromium and Nickel respectively. All in all, The results from these methods showed that biochar produced from this specific biomass possesses the typical functional groups that enable it to store carbon, the appropriate pH that could remediate acidic soil, a fine amount of macro and micro nutrients that would aid plant growth.
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    Investigation of Acid Treated Lemna minor as Adsorbent for Removal of Cu and Pb from aqueous solution
    (Addis Ababa University, 2018-06) Yalembrhan, Debebe; Abubeker, Yimam (PhD)
    The release of wastewater with heavy metals of Cu, Pb, Zn, Cd etc. Particularly in areas with expansion of industries can pose a significant threat to human health and environment due to their toxicity. This paper deals with bio sorption of heavy metals (copper and lead) using acid treated dried lemna minor powder. The adsorbent after treated with hydrochloric acid was dried and ground to a particle size range of (820-850) µm. Characterization of the adsorbent such as proximate analysis, surface charge, FTIR spectroscopy, surface area and XRD was done prior to bio sorption process. A batch adsorption experiment was carried out using central composite design expert 6.0.8 and the effect of adsorption parameters: pH, initial metal concentration, and adsorbent dose was studied. The result indicated that maximum percentage removal of 92.45 % for Lead (II) was obtained at pH = 11. Similarly, 88.4 % removal was found for Copper (II) at pH = 9. Temperature effects showed that the adsorption process was endothermic with positive enthalpy and negative free Gibbs energy values. The Removal efficiency of lemna minor increased with increase in temperature. Data‘s from the adsorption were analyzed with Temkin, Langmuir and Freundlich isotherm models. Desorption of Cu +2 and Pb +2 were carried out by using a 100ml of 0.1M HCl in to 250 volumetric flasks with 0.1 g of 43.86 ppm of copper and 42.38 ppm of Lead loaded sun dried lemna minor. The percent desorption increased with time for both metals and maximum desorption observed at 60-minute contact time with 80% for Lead and 72.2% for Copper.
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    Removal of Some Selected Heavy Metal Using Modified Bagasse and Eucalyptus Bark from Gold Mining Waste Water: Case Study of Ezana (Meli) Gold Mining Development Plc Industries
    (Addis Ababa University, 2018-06) Mebrahtom, Hagos; Abubeker, Yimam (PhD)
    This study investigated the potential use of modified bagasse (MSB) and eucalyptus Bark (EB) treated from sample wastewater in batch mode experiments. The discharge of untreated gold mining wastewater contaminates with heavy metals such as Cu (II) and Pb (II), which is threatening ecosystems, carcinogenic to the human & hinder development of plants. Since the removal by adsorption is cost effective, not time consuming and environmentally friendly, it has been widely studied by many scholars for remediation of heavy metals. Characterization of bagasse and eucalyptus bark were analyzed using proximate analysis like MC (%), Ash value (%), ƍ b (g/cm 3 ), VM (%), fixed carbon (%) and % (C, N 2 ). FTIR analysis revealed the presence of multiple functional groups in the adsorbent, some of which were involved in the sorption process and x-ray diffraction (XRD) used to measure the crystalline content of adsorbent materials. The result indicated that the effluents discharged from Ezana Gold extraction were mainly contains the following: TSS (ppm), turbidity (NTU), EC (µs/cm), TDS (ppm), COD (ppm), temperature(°C), pH, cyanide WAD with <11°C (ppm) and heavy metals such as Fe > Cu >Pb >Mn > Cr (VI) >Zn > Co > Ni > Cd (ppm). They were determined by atomic absorption spectroscopy. The major pollutants selected from the process effluent were Cu 2+ and Pb 2+ due to exceeded standard discharge limits. The objective of the study was removal of Cu 2+ and Pb 2+ from rich Ezana wastewater using modified sugarcane bagasse and eucalyptus bark powder as an adsorbent. The selected parameters were pH, adsorbent dose and time. A maximum removal of (Cu 2+ , Pb 2+ ) by modified bagasse (88.45%, 94%) and eucalyptus bark (92%, 99%) respectively was achieved. The adsorption data were well fitted to the Langmuir isotherm model and pseudo-second order kinetic model for both modified bagasse (Cu, Pb) and eucalyptus bark (Cu, Pb). This indicated that Eucalyptus bark powder was more effective than modified bagasse (MSB) and it can be used as an alternative low cost adsorbent for the removal of copper and lead from Ezana mining wastewater.
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    Synthesis, Process Parameters Optimization and Characterization of Banana Peel Based Bio-plastic
    (Addis Ababa University, 2019) Aster, Taddele; Abubeker, Yimam (PhD)
    In this study, a small scale laboratory bioplastic was synthesized and investigated using banana peel as raw material. The effect of HCL concentrations, concentrations Glycerol, drying temperature and residence time for hydrolysis were analyzed. Design of experiment for response surface methodology (RSM) was used to analyze and optimize the simultaneous effect of HCl concentration (4%, 12%, 20% v/w), Glycerol concentration (4%, 8%, 12% v/w), drying temperature (40⁰C, 50⁰C, 60⁰C) and Residence time of (5, 15, 25 minutes). A four-factor and three-level Box-Behnken design was used to develop a statistical model to describe the relationship between physical and mechanical property of banana peel based bio film and the chosen independent variables and to optimize the production parameters of banana peel based bio-film. The model was statistically significant (p ˂0.0001). A relatively good quality bioplastic with 9.348MPA of tensile strength, 13.523% Elongation at break, 62.883% water absorption and 48.388% biodegradability was synthesized at optimum parameters of 52.424⁰C temperature, HCl concentration of (2.937ml HCl/25g of banana peel), glycerol concentration of (2.096ml of glycerol/25g of banana peel) and 14.50 minutes of residence time for hydrolysis with high value of combined desirability (95.1%). Validation of the statistical model showed an insignificant difference between experimental and model-predicted results. After analyzing the results of the primary synthesized bioplastic, a new modified bioplastics was produced with 27 % improved water/moisture absorption using a Calcium carbonate as filler at the optimum conditions from the earlier experiments.