Browsing by Author "Assefa, Birhanu (PhD)"

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    Comparison of Environmetal Performance and Economic Benefit of municipal Solid Waste Compost and Chemical Fertilizer
    (2011-07) Abate, Zerihun; Assefa, Birhanu (PhD); Negassa, Wakene (PhD)
    With the increasing rate of urbanization and industrialization, the current method of municipal solid waste (MSW) management cannot be effective and efficient to handle thousand tons of waste generated daily in big cities like Addis Ababa. The objectives of the present study were therefore, to (i) demonstrate the positive environmental effect of municipal solid waste composting and the negative impact of nitrogen (N) fertilizer (ii) compare the environmental performance of municipal solid waste compost and nitrogen fertilizer (iii) compare economic benefit of MSW compost and N- fertilizer from agricultural and environmental point of views. A series of experiments such as scenario analysis, incubation, leachate and effects of municipal solid waste compost on yield and yield components of wheat were conducted to achieve the stated objectives. The scenario analysis compared either disposing MSW in landfill or compositing for soil amendment to improve crop production. The results of the scenario analysis revealed that composting resulted in greenhouse gas reduction due to avoidance of methane emission from landfill. The addition of MSW compost significantly increased the soil total nitrogen (Nt), organic C, available P, pH and other microelements. Similarly, the leachate experiment revealed that the application of both MSW compost and N-fertilizer produced higher concentrations of NO3-N fluxes in the collected leachate that clearly showed fertilization during establishment poses serious threat to water quality in the absence of growing plants. Moreover, the application of both MSW compost and N-fertilizer had positively responded in improving wheat yield and yield component. The partial budget analysis with minimum acceptable rate of return 100% revealed that the highest net benefit (7038.35 Eth. Birr) was recorded with combined application of (20-kg N+3.33-t com) ha-1, however; the highest marginal rate of return (1024%) was registered for sole application of 5-t compost ha-1. The results of the present study revealed that using MSW as soil amendment along with appropriate composting techniques and soil management not only improve soil fertility and reduce investment on chemical fertilizers but also can alleviate the contribution of MSW to environmental pollution. Key words: MSW compost, incubation, leachate, economic analysis and urea
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    Evaluation of the Performance of Constructed Wetland System for the Treatment of Brewery Wastewater
    (Addis Ababauniversity, 2011-06) Angassa, kenatu; Assefa, Birhanu (PhD)
    Environmentally friendly way of handling industrial effluents is the most important concept for industries direct and/or indirect contribution of a country’s sustainable development. In order to achieve such goals biological processes considered to play the major role. The study to evaluate the treatment performance of horizontal subsurface flow constructed wetland (SSFCW) systems planted with selected emergent wetland plants for the removal of pollutants from brewery wastewater was initiated. For this purpose the treatment plant was fed with raw brewery wastewater collected from St. George Beer Industry of Ethiopia. The constructed wetland for wastewater treatment was operated for six months (August, 18/2010 to February, 20/2011).The four SSFCWs cells packed with gravel media and with HRT of 7 days. One bed was left unplanted and used as a control while each of the remaining beds was planted with Cana. indica, Phragmite. karka and Colocasia. gigantea to each unit. Each set of SSFCW cells had influent parameters such as hydraulic loading rates of 26 L/d with high-strength 4798 mg COD/L and 1714 mg BOD5/L from brewery wastewater. After six month operation, the laboratory analysis gave a witness that the average removal efficiencies for the planted and unplanted wetlands were as follows: COD (78.9 % and 76.8 %), BOD5 (74.4% and 70.5%), TN (77.4% and 59.8 %), NH4-N (62.8% and 58%), NO3-N (55.2% and 42.5%), TP (68 % and 56.1%), PO4 (81.4% and 58.4%), sulfate (36.1% and 30.1%), sulfide (97.3% and 93.4%), TSS (61.7% and 50%) ,TDS (54.1% and 45.5%) and EC (27.4% and 30%), respectively. While the amount of DO was increased for planted and unplanted (65.6% and 38.6%) respectively. Therefore, the influent concentration with the average composition of COD (4798 mg/L), BOD5 (1714 mg/L), TN (106 mg/L) and TP (83.3 mg/L) has a great effect on pollutant removal efficiency in horizontal subsurface flow constructed wetland systems. Keywords: Constructed wetlands, Horizontal subsurface flow, Wetland plants, Treatment Technology, Brewery wastewater
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    Optimum Production of Biogas from Bio-Municipal Solid Wastes Using Two Stages Anaerobic Digester
    (2011-06) Assefa, Gizachew; Assefa, Birhanu (PhD)
    Various aspects of Anaerobic Digestion (AD) have been became a promising technology for the management of Municipal Solid Waste. Thus, the objective of this study was to optimize the production of biogas from these wastes by using two-stage anaerobic digester. To achieve this, batch anaerobic digestion experiments were conducted to determine the optimum methane produced from the digestion and co-digestion of Organic Fraction of Municipal Solid Waste (OFMSW) and Cow Manure (CM) in different mix operated under ambient condition. Moreover, this study presents several runs of experiment and analysis with the aim of substrate mix and the duration of overall stage of digestion process while optimizing the biogas generation with higher methane content. The physical and chemical characteristic of the sample done by analytical method, volume of biogas produced and methane composition of different mix of the feed stock were determined by water displacement and digital gas (SR2-BIO gas analyzer), respectively. The highest specific gas production observed was 353 L/Kg VS added for the digestions of 1:2 mix of OFMSW: CM. It was observed that the independent variable – mix ratio significantly affect (p-value 4.18*10-9) the dependent variable – amount of methane produced since the p-value is less than the chosen α-level usually 0.05. The calculated volume of methane in the biogas produced per Kg of volatile solid removed were 510L, 355L, 375L, 435L and 600L for OFMSW (100%), 2:1 mix of OFMSW: CM, CM (100%), 1:1 and 1:2 mix of OFMSW: CM, respectively. In general From the digestion of 1:2 mix of OFMSW: CM: 0.47 m3/d/m3 biogas with 51.5% methane content was produced; 0.45 m3/d/m3, 0.35 m3/d/m3, 0.26 m3/d/m3, and 0.23 m3/d/m3, biogas with 31.4%, 42.9%, 20.3% and 33.7 % methane composition is produced from 1:1 mix of OFMSW: CM, CM alone, OFMSW alone and 2:1 1 mix of OFMSW: CM respectively. The mix ratio significantly affects the biogas production (p-value<<0.05).
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    Pressure Modelling for Leakage Reduction In Addis Ababa Water Supply System Mains (Saint Paul And Rufael Sub Systems
    (Addis Ababauniversity, 2008-07) Meressa, Mosissa; Assefa, Birhanu (PhD)
    The city of Addis Ababa is suffering from shortage of water - the city is receiving only 48% of its demand in 2007; at the same time losing 35.73% of its supply in its distribution systems. Financial, management and technical constraints are the main bottlenecks that hamper the city from satisfying the highly growing needs of its residents while loosing such a large amount of treated water within its system. This Masters Thesis focuses on modelling water supply pressure for leakage reduction in the mains of Addis Ababa Water Supply System, especially in Rufael and Saint Paul sub systems. EPANET modelling software prepared by the Environmental Protection Authority of America is used for the purpose. In so doing, first of all water balance at both city and the stated sub-city levels was conducted to visualize the loss of water and for the purpose of indexing the leakage level, at their respective levels. Water supply for the entire city and water consumption as aggregated from individual customer bills was used to evaluate the total water loss at city level and at the sub distribution system levels, respectively. Finally, potential Environmental effects of leakage in the city water supply system are assessed. Quantifying, characterizing and modelling the factors that lead to water leakage in a city water supply system is by its nature a complex task requiring well managed network and reliable data which is scarce in Addis Ababa city water supply system. As a result, cross checking and verification of data was the most significant problem faced during the study. The paper comprises two major parts; namely Leakage Analysis part and Pressure Modelling part. It was found out from leakage analysis part that water leakage in the city was 35.67%. The ILI value was obtained to be 4.74 which is far from an ideal value of 1. Thus, there is a room for AAWSA to target for leakage reduction without affecting the current pressure system. Besides, there is similar room for leakage reduction due to excessive pressure at some nodes with pressure above the recommended maximum for leakage of 80m almost all the day as pointed out from the modelling part