Valorization of Agricultural Waste: Theoretical Estimation and Experimental Biomethane Yield from Cashew Nut Hulls

Biomethane potential production from cashew nut hulls, an agricultural waste, was carried out using old and fresh hulls as substrates. Samples were taken from old hulls (around 8 years old) and fresh hulls produced in cashew scale transformation units at Bobo Dioulasso/Burkina Faso. Physicochemical parameters showed that cashew hulls can be a good candidate for anaerobic digestion. But high acidity, total phenols and lignin tenor could be a constraint for anaerobic bacteria. Theoretical biochemical methane potential showed high value of 666.937 CH4 L. (Kg VS)-1 and 526.206 CH4 L. (Kg VS)-1 for crushed fresh and powdered old hulls, respectively. Experimental biochemical methane potential showed significantly low potential of 1.982 CH4 L. (Kg VM)-1 and 46.840 CH4 L. (Kg VM)-1 for fresh and hold hulls, respectively. Pretreatment for optimization, chemical composition and co-digestion system must be expected for a better anaerobic digestion performance.