2.2. Methods. Pretreatment of the wastes by leaching was
conducted in Erlenmeyer flasks. Four different solvents
including hexane, diethyl ether, dichloromethane, and
ethyl acetate were used. These chemicals are toxic and/or
inflammable and should be treated properly. In the experiment
to select the solvent, each solvent was added to the
orange peel with orange peel waste and hexane ratio of 1 : 4.
The mixture of solvent and orange peel was shaken vigorously
for 10 minutes followed by incubation for 20 minute at room
temperature. In the optimization of pretreatment study,
hexane was used as a solvent. Two levels of four parameters
including temperature (20∘C and 40∘C), time (10 min and
300min), orange peel wastes and hexane ratio (1 : 2 and 1 : 12),
and the wastes size (homogenized or chopped) were selected.
Forty grams of the wastes was dissolved with a certain amount
of hexane in the flasks, followed by shaking vigorously for a
determined period of time. After the settlement, the extracts
were removed from residuals by vacuum filtration. The
residual, pretreated orange waste was then washed three
times with water in order to remove remaining hexane.
Finally, the pretreated waste was digested to produce biogas.