Citrus waste for different applications such as production of pectin, flavonoid, fiber, and animal feed production has been proposed by several researchers [5–8]. However, a large amount of this waste is still dumped every year [9], which
causes both economic and environmental problems such as high transportation cost, lack of dumping site, and accumulation
of high organic content material [10].Therefore, more effective and sustainable alternatives for using orange peel wastes such as biogas are highly desirable.