Feasibility study of biogas energy generation from refuse dump in a community-based distribution in Nigeria

Energy generation remains one of the biggest challenges of developing nations like Nigeria. The World Bank estimated that ~80 million (44.4%) out of 180 million Nigerians living in 8000 villages across the country lack access to electricity. Lack of access to electricity to stimulate small- and medium-scale enterprises in rural communities is believed to be a major factor responsible for rural—urban migration and the lingering emigration crises across the globe. In this study, three different wastes generated were combined in a locally fabricated digester and each singly loaded in respective digesters to generate energy in the form of biogas with an anticipation of redistribution for a community-based use. The biodegradability test of the substrates were studied ab initio by evaluating for ash and moisture contents, C/N ratio, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) for maize chaff, watermelon and cassava peels. The results showed 2.85, 0.66 and 2.40% for ash content, 11.18, 93.22 and 70.26% for moisture content, 12.10, 15.10 and 19.10% for C/N ratio, 155.07, 131.96 and 113.79 ppm for BOD, and 240.00, 212.00 and 264.00 ppm for the substrates, respectively. From the results, maize chaff with the highest ash content has the least biodegradable (organic) matter, while watermelon, with the least ash content, has the highest biodegradable matter. The moisture content results for maize chaff and watermelon were below and above the optimum value of ‘60–80%’ and this confirmed the low biogas volume produced when used alone. The ideal C/N ratio for anaerobic digestion is between ‘20:1 and 30:1’. A comparison of these sets of values from the study showed that the C/N ratios obtained from the research work are below the optimum values of the C/N ratios and could be responsible for the poor biogas yield for the disjoined substrates. The biogas volume of 2100 ml was produced at the end of the retention time for the combined substrates and, was higher compared with the 18, 25 and 29 ml produced for maize chaff, watermelon and cassava peels, (the disjoined) substrates, respectively. In this study, the COD value for each substrate is higher than the corresponding BOD values. Hence, co-digestion of unavoidable food wastes is economic and, a potentially viable option to generate alternative renewable energy for rural community-based use.

The biodegradability tests of the substrates are as shown in Tables 1 and 2 and in Figure 2. Table 1 shows the percentage ash, moisture, carbon and nitrogen contents of the substrates. From the table, maize chaff, watermelon and cassava peels have 2.85 ± 1.50%, 0.66±0.0.12% and 2.40 ± 0.61% ash content, respectively. It is evident from the results that maize chaff has the highest percentage ash content but with the least biodegradable (organic) matter, while watermelon has the least ash content with the highest organic matter.