Waste to Energy: Comparison of the Quantity and Quality of Biogas Produced From Fruit Waste and Slurries Prepared with Slaughter and Human Wastes

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Waste management has become one of the major challenges facing today’s world cities. The waste management problem is more pronounced in the cities of developing countries especially those of the Sub-Saharan Africa including Ghana. The high rate of rural-urban migration coupled with weak enforcement of settlement laws have led to the springing up of slums in most parts of these cities. However, the low commitment of city authorities to enforce environmental laws coupled with lack of funds has worsened the waste management challenges which are more pronounced in slums. Meanwhile, the current technologies (open-dumping and disposal into the ocean) employed in managing the wastes generated in these cities are non-sustainable and highly detrimental to the environment. Also, the high organic fraction content of wastes generated in the developing countries coupled with high capital cost make it difficult to treat wastes with the technologies used by the developed countries. There is therefore the need to search for and employ organic waste treatment technology that is sustainable and thus best fitting for developing countries. This is the anaerobic digestion process in which waste is converted to energy (in the form of biogas) and bio-fertilizer. This study was conducted to determine the amount of biogas (digester-specific and substrate-specific biogas production) and quality of biogas that will be produced by fruit wastes and slurries prepared with slaughter waste and human waste.The study was also to determine the slurry that will be suitable for optimum commercial biogas production. A composite of mango, pineapple and papaw wastes was digested in a 450 m3 digester at Adeiso while four different slurries (S1 to S4) prepared with varying proportions of slaughter and human wastes were digested anaerobically in two 8 m3 fixed-dome (WASAZA design) digesters built at GIDA site in Ashaiman. The data obtained were analyzed with the 2007 version of Microsoft Excel. Results obtained showedthatthe digester-specific biogas production of slurries S1, S2, S3, S4 and S5 produced are0.167, 0.120, 0.278, 0.325 and 0.723 m3 biogas/m3 digester volume/dayrespectively while the substrate-specific biogas production was 0.121, 0.344, 0.432, 0.327 and 0.270 m3 biogas/kg ODM/day respectively. The daily average methane (CH4) produced by the slurries range from 52 to 66 % biogas by volume while their carbon dioxide (CO2) production was from an average value of 32 to 38 % biogas by volume. Also, hydrogen sulphide (H2S) produced by the slurries was from an average value of 216 ppm to 625 ppm. Slurry prepared with about 50%HW and 50%SW was found to be the most suitable for optimum commercial biogas production.
A Thesis submitted to the Department of Agricultural Engineering, Kwame Nkrumah University of Science and Technology in fulfilment of the requirements for the degree of Master of Science in Agro-Environmental Engineering.