Biomethanization of orange peel waste

Recent research has demonstrated that orange peel waste is a potentially valuable resource that can be developed into high value products such as methane. Following a pre-treatment to extract d-limonene, the anaerobic digestion of orange peel waste was evaluated at laboratory and pilot scale under mesophilic and thermophilic conditions. d-Limonene removals of 70% were reached with pre-treatment. The results showed the convenience of thermophilic conditions for treating this waste as the methane production rate and biodegradability were higher than at mesophilic temperature. At pilot scale, a thermophilic continuously stirred-tank reactor working in semi-continuous mode was employed. The OLR was found to be in the range of 1.20–3.67 kg COD/m3 d; the most appropriate range for working under stable conditions at SRT of 25 d. The methane yield coefficient was found to be 0.27–0.29 LSTP CH4/g added COD and the biodegradability 84–90% under these conditions. However, acidification occurred at the highest OLR.