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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    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).