Determining Biogas Energy Generation from Municipal Wastes and Designing an Appropriate Biogas digester (Case of Adama city)

Abstract

Fast growing cities are subjected to projected urbanization accompanied with increased number of population and income. This has resulted in increasing demand for energy and other services. Use of conventional type sources of energy such as wood, cow dung cake, charcoal etc. which are meant for domestic use have led to environmental deterioration and increased green house gas effect. Adama city is one of the fast growing cities in Ethiopia with increased number of population. It is clear that the rate of growth of population is directly proportional to solid wastes generated from the household of the urban cities such as Adama. The purpose of this study is to determine the size of energy generated from Adama Municipal biodegradable wastes and design an appropriate bio-digester suitable for the city. For this study the first step was identification of major sources of municipal biodegradable wastes; Thus, four categories such as domestic animal wastes, food wastes, household wastes, Fruit and Vegetable wastes, were identified. To determine the size of the wastes sample data collection was done. Further, data collection from literatures, documents of organizations in Adama and Addis Ababa was done. For a close study data of sample weight for each of identified major waste categories were collected for one week (or successive seven days); Average weight of wastes per day, and average weight of wastes per source per day were calculated. From this the average total weight of the biodegradable solid wastes was determined. The average total weight of biodegradable solid wastes in Adama city was found to be 1,323,938.24 kgs per day (or 1,323.938 metric tons per day). The biogas potential of the above total weight of biodegradable wastes was resulted to be in a range of 49,767.23 m3 – 96,805.07 m3 of biogas yield per day; The calorific value ranges from 1,094,879MJ - 2,129,711.54 MJ per day which can generate 84.6-164.6 MWh electricity per day. With this result and other parameters such as waste Total solid, Total influent etc. the total volume of the digester had been designed and was found to be 63,916.53 m3. Having this result the location for construction of the digester, means of segregation, collection and transporting of wastes had been suggested. From this all we can conclude that the size of biodegradable waste in Adama city is very high and proper management and use will benefit the society otherwise will harm the society and environment.