Biomethane production tests on ensiled orange peel waste

Oranges represent one of the most relevant fruits in the global market and nearly 70% of them is used in industrial processes to produce juices, jams and other products, returning huge quantities of residues known as Orange Peel Waste (OPW). Currently, many possible uses have been proposed for its management, one of the most promising options is methane production through the anaerobic digestion process; however, each valorisation proposal must consider that oranges production, and so the OPW one, is strictly influenced by the fruit seasonal spread. For this reason, this paper analyses at lab scale the effects of a form of storage, the ensiling, generally used for fodders, on the bio-methane production from anaerobic digestion processes. Different samples of OPW have been ensiled for increasingly long periods, then bio-methane production (BMP) tests were carried out and the results have been compared with those of fresh OPW. The results have been evaluated also in terms of global balance of the whole process (ensiling and anaerobic digestion). The results have shown that OPW ensiled for longer periods has the most promising methane production. However, the same sample has also shown the highest volatile solids reduction during ensiling and thus the highest potential reduction of bio-methane production.