Potential Bioenergy and Biofertiliser Production from Livestock Waste in Mediterranean Islands Within Circular Bioeconomy

The livestock sector can generate a steady stream of manure biomass, that can be subjected to different transformation technologies. Moreover, EU must also play an important role in developing a policy framework for the Mediterranean islands, in order to offer equality of development opportunities to all its territories, by designing and implementing adequate measures for reducing their dependency on fossil fuels. Therefore, this study evaluates the potential biogas and digestate production through the Anaerobic Digestion (AD) process of livestock manure on a selection of Mediterranean islands, sharing characteristics such as the costs of waste management and energy production, that are much higher than in mainland Europe: Balearic Islands, Corsica, Sardinia, Sicily, Malta, Crete and Cyprus. The potential manure generation from cattle and pigs was estimated by using available livestock statistical data, so that the potential biogas, bioenergy and digestate production was quantified by applying established conversion factors. It was possible to estimate a yearly potential generation of 10.9 million t of livestock manure, that corresponds to a potential biogas production of 269.28 million m3, equivalent to a total bioenergy of 5234.77 thousand GJ. The bioenergy generated from livestock manure in Sardinia and Sicily can potentially satisfy 17.20 and 9.18% of the energy demand, respectively. Moreover, it was possible to estimate a yearly potential production of 4.69 million t of digestate, that can be separated into a liquid fraction, to be used as biofertiliser, instead of conventional inorganic/mineral/chemical fertilisers, and a solid fraction, to be used as growing substrate for the soilless cultivation of Mediterranean crops, instead of peat, according to Circular Bieconomy (CBE) principles. The islands of Malta and Corsica, having high livestock population and low availability of Utilised Agricultural Area, will have to deal with an oversupply of nitrogen equivalent to a double and triple, respectively, rather than the amount that can be applied to soils. Therefore, AD needs to be complimented with other technologies to process the excess nitrogen inside the digestate, i.e. combustion and pyrolysis.