Orange waste is a potential feedstock for biogas production. Orange waste contains ca 74.5% carbohydrate, 7.7% protein,
and 10.6% fat [20]. Even though the theoretical methane yield is 0.45Nm3/kgVS, the methane yields of 0.061 and
0.131Nm3/kgVS were obtained in this experiment from chopped and homogenized peel, respectively.This indicated
the strong inhibition by the limonene. Therefore, this compound should be separated from the orange peel before the
digestion process. In the current study, the limonene was recovered from the orange peel by solid-liquid pretreatment
using solvent to extract the limonene.