Orange Peels as Substrate for Biogas Plants

In the industrialised countries of Northern Europe, orange juice is increasingly produced locally as direct juice from imported oranges rather than from concentrate. This produces a large amount of orange peel waste. As part of the planning for the construction of a direct juice production facility in Austria, it was investigated whether this waste could be revalorized and used to generate energy in biogas plants. For this purpose, the biogas yield of pressed oranges was tested with various inocula in batch tests in accordance with the VDI 4630 standard. The biogas quantities and the biogas quality were compared with the reference substrate maize silage. The results of the tests allowed for the conclusion that orange peels are a suitable substrate for biogas plants, although gas yields are not reaching reference values. The co-fermentation of maize silage and orange peels, renders, however, reasonable yields. This approach does not only transform the "waste" orange peel into an energy source, but compared to composting or even dumping into landfills, there is also a considerable mitigation of CO2.