The VS content of the treated orange peel is 11% and the methane yield was 0.177Nm3/kgVS. Thus, every ton of
orange wastes produced 19.47Nm3 of biogas and 1.4 L of limonene as by-product. The best pretreatment condition
obtained in this work increased the methane yield by 350% compared to the untreated peel. This improvement is lower
than that obtained fromsteam-explosion pretreatment which could increase the methane yield by 426% . However, in
this current work the pretreatment was conducted at room temperature for 10 minutes, whereas the steam explosion
pretreatment was carried out at 150∘C for 20 minutes . Thus, this pretreatment can be considered as low energy
demanding. However, selection of the solvent is a critical point to avoid inhibition problem from the solvent on
anaerobic digesting system.