Evaluation of the potential of bio-methane production from field-based crop residues in Africa

Africa is heavily dependent on solid biomass such as fuelwood for its energy requirements while low electricity access is a major issue in many African countries. This article evaluated the potential of bio-methane and bio-energy production from anaerobic digestion of field-based residues generated from 15 crops cultivated in Africa. The bio-energy potentials were evaluated using the residue-to-product ratios of the crops, the methane yields (L/g volatile solids) of the crop residues and the calorific value of methane gas. Among the residues investigated, rice straw produces the highest amount of bio-methane and bio-energy followed by wheat straw and maize stalk owing to the higher bio-methane yield of rice straw as opposed to the other two crop residues. The annual bio-methane and bio-energy potential from field-based crop residues in Africa is estimated at 31,303 Mm3 and 1141 PJ respectively while combustion of the bio-methane in a combined heat and power system is expected to generate 109.7 TWh of electricity and 133 TWh of thermal energy annually, with the 109.7 TWh of electricity potentially supplying 16.3% of Africa's electricity requirements. Comparing African countries, Egypt has the highest bio-methane potential while Djibouti has the lowest potential. On a per capita basis, Eswatini (formerly Swaziland) and Mauritius have the highest electrical energy potential of 424.2 kWh/capita and 297.3 kWh/capita respectively. With implementation of the technology still in its infancy stage, this article also elaborated on several recommendations and steps to facilitate the development of large-scale anaerobic digestion in Africa. Finally, the limitations of the current study were outlined and recommendations for future works were put forward.