Biogas Production From Exhausted Pomace After Polyphenol Recovery

Italy ranks second in Mediterranean basin as for production and export of olive oil. Oil production means proportional volumes of organic waste that need to be disposed of. Assuming that to be sustainable in the long term a production process must have a circular flow of energy and raw material, a system has been studied for organic waste valorization so to create a technical cycle where waste of olive production is used to a) extract polyphenols, b) produce energy through anaerobic digestion (AD), c) use organic residual from AD as a fertilizer for olive grove. The study was based on the assumption that the vegetation waters and the exhausted pomace have a high content of polyphenol molecules with high value added potential. The polyphenols, however, if left in the exhausted pomace give it bactericidal capacity which prevents extensive use as soil fertilizer as it interferes with soil microbiome. For the same bactericidal activity the exhausted pomace could show difficulty in AD for the production of biogas. For these reasons, at present a common destination for depleted pomace is incineration with consequent loss of organic matter and energy. Both for economic and environmental reasons the study was developed to manage the exhausted pomace in a circular economy perspective: extraction of polyphenols and subsequent anaerobic digestion of residual pomace with energy and digestate production. Data used in the study refer to an olive treatment plant of average medium/small dimensions. Results demonstrate the possibility to put in place an economically sustainable production cycle.