Co-digestion of Theobroma cacao (Cocoa) pod husk and poultry manure for energy generation: Effects of pretreatment methods

[Display omitted] •Two low-cost acidic and alkaline pretreatments were applied to Cocoa pod husk.•H2O2 pretreatment removed 81% of the lignin composition of Cocoa pod husk.•H2O2 pretreated Cocoa pod produced 68% more biogas than the acidic treatment.•High net heat and electrical energy make H2O2 pretreatment economically viable.•The resulting digestate could serve as biofertilizer for increasing crop yield. In this study, biogas was produced from the anaerobic co-digestion of Cocoa pod husk (CPH) and poultry manure. Pretreatment of the CPH was carried out using sulfuric acid and hydrogen peroxide. The physicochemical, elemental and structural analyses were carried out on the CPH before and after pretreatment. The microbial composition of the fermenting materials were also determined using standard method while the Fourier Transform Infra-red (FTIR) spectroscopy was used to identify the structural changes that took place after pretreatments. Use of alkaline hydrogen peroxide caused high solubilization of the lignin component of the CPH and reduced up to 81% of lignin i.e. initial value of 21.7% m.m−1 to final value of 4.2% m.m−1. Similarly, the alkali reduced the hemicellulose content of the CPH from 27.0% m.m−1 to 8.5% m.m−1. Overall, there was 68% increase in biogas volume from the alkaline pretreated CPH.