ENERGY RECOVERY FROM ORANGE PEEL FOR HYDROGEN AND METHANE PRODUCTION

Brazil is the world leader producer and exporter of orange juice. During the industrial processing, about 50% of the orange fruit is discarded as a residue which includes seeds and peels; however, substantial economic and environmental benefits might be achieved with the revaluation of those residues. The objective of this work was to obtain combustible gases: hydrogen and methane from orange peel derived of the juice processing through anaerobic digestion in two-stage reactors. Three anaerobic digesters were used in experimental set: two for the acidogenic and methanogenic stages and the other as control. The operating parameters follow: mesophilic conditions at 35 °C, continuous feeding (65 ml of orange peel and 35 ml of water), and pH range 5.0-6.0 in the acidogenic reactor and 7.0-8.0 in the methanogenic and control reactors. The initial characterization of orange peel residue indicated 23% pectin, 16% total lignin, 72% moisture and 7% protein. A higher production of hydrogen and methane, with peaks of 30% and 70%, respectively, during the experimental time, was observed in two-stage reactors, while the control reactor produced 50% of methane. Additionally, this study estimated the potential of electric energy generation from biogas burning in a stationary engine (34% efficiency). For São Paulo State, the main orange producer in Brazil, the whole citrus industry residues could produce 90x103 MWh/ton of orange peels, which might be used in the industry’s own facilities and in case of surplus, it could be sold to the energy grid. The use of two-stage reactors efficiently reduces the organic load avoiding side effects related to the residue disposal. Moreover, the biogas burning may subsidize a clean development mechanism by means of a more renewable energy supply for the citrus industry.