Co-digestion of Waste Coffee and Cocoa Hulls: Modeling of Biogas Production by the Particle Swarm Method

Energy is a crucial material for the development of our economy. Access to sufficient energy remains a major concern for developing countries, particularly those in sub-Saharan Africa. The major challenge lies in access to clean, environmentally friendly, quality and low-cost energy in different households in our municipalities. To cope with this vast energy gap, many households are dependent on fossil fuels. In Cameroon, the consumption of wood for the supply of energy is increasing by 4% per year. Overall, approximately 80% of households in Cameroon depend on woody biomass as the sole main source of energy supply in Cameroon and demand is growing over time. In view of the climatic variations that our countries, particularly Cameroon, undergo through deforestation, the use of wood as a source of energy is expensive and harmful to the environment, hence the urgency of replacing wood with renewable energy. Biogas is one of the most versatile sources of renewable energy. On an industrial scale, it is important to automate the process control. The main objective of the present work is to model the anaerobic digestion of coffee and cocoa hulls using the particle swarm optimisation method. Pretreatment using the organosolv process was done. This resulted in 48% lignin removal and 22% cellulose increase. For the pretreated biomass, the maximum production rate was 21 NmLCH₄ per day with a biomethane yield of 90 NmLCH₄/gVS. This represents an enhancement of 117% in biomethane yield. A positive flammability test was recorded after the 10th day of retention time. Moreover, the data collected during anaerobic digestion allowed implementation of a two-phase mathematical model. The thirteen parameters of the model were estimated with particle swarm optimisation method in Matlab. The model was able to simulate the biomethane production kinetics and variation of volatile fatty acid concentration.