Limonene is present in orange peelwastes and is known as an antimicrobial agent,which impedes biogas productionwhen digesting
the peels. In this work, pretreatment of the peels to remove limonene under mild condition was proposed by leaching of limonene
using hexane as solvent. The pretreatments were carried out with homogenized or chopped orange peel at 20–40∘C with orange
peel waste and hexane ratio (w/v) ranging from 1 : 2 to 1 : 12 for 10 to 300 min. The pretreated peels were then digested in batch
reactors for 33 days. The highest biogas production was achieved by treating chopped orange peel waste and hexane ratio of 12 : 1
at 20∘C for 10 min corresponding to more than threefold increase of biogas production from 0.061 to 0.217m3 methane/kgVS.The
solvent recovery was 90% using vacuum filtration and needs further separation using evaporation.The hexane residue in the peel
had a negative impact on biogas production as shown by 28.6% reduction of methane and lower methane production of pretreated
orange peel waste in semicontinuous digestion system compared to that of untreated peel.