Experimental assessment of the energetic potential of the anaerobic co-digestion of different agricultural and agro industrial residuals and waste

The residuals and waste arising from the zootechnical, the agricultural and the agro industrial activities, represent for many different Italian sites a serious environmental and economical problem. The intensive livestock represent a serious threat for the water, for the soil and for the air, as a consequence of the relevant production of nitrate and GHG gas. The increased restriction, imposed by the recent rules to cattle breeding and to the practice of spreading manure on agricultural soils, constrains the breeders to find some alternative solutions, generally represented by the adoption of aerobic and/or anaerobic facilities, that can lead to an higher sustainability of the whole activity. Other important activities, particularly diffused in the Italian regions, are represented by the viticulture, by the production of the olive oil and chees. Generally the grapes are harvested for wine production but, in some years, the values of the grapes imposed by the market makes this activity not economically sustainable. For this reason, the investigation of feasible alternative exploitation of this biomass, able to give to the farmer the adequate revenues, represent an interesting issue to be analysed. From the other hand, the extra-virgin oil production is associated with the production of an high amount of solid olive residues, that can affects significantly the economical sustainability of the whole process as a consequence of the disposal fee. Furthermore, the viticulture as the olive oil production, takes place in quite similar periods of the year, represented by the end of September to the end of November. The global waste and residual production of these two activities, is hence narrowed in these two/three months. The chees manufacturing causes the production of a significant fraction of whey, that has to be managed and disposed in a correct way. This study concerns the possibility of exploiting, for energetic uses, the grapes, the residues of the olive oil production and the whey, in an existing anaerobic/aerobic swine manure facility (Di Maria et al., 2010a; Di Maria et al., 2010b), situated in the Umbria region. Currently, in this aerobic/anaerobic facility, also other agricultural residues are co-treated together with the swine manure. The study has been performed by the aid of an experimental apparatus, direct to evaluate the biogas production potential, of the different biodegradable material currently exploited and exploitable in the considered plant. In particular, the whey dhows a bio-gasification potential (Fig. 1) able to achieve also 700 Nl/kgVS, when co-digested with about 10% of swine manure (Fig. 1). As the amount of whey exploited in co-digestion rises the biogas production generally decreases. The solid residues of olive oil production, seems able to produce about 170-260 Nl per each kg of VS solids (Fig. 2). In any case the co-digestion process and the biogas yield are significantly influenced by other process parameters that can be strongly affected by the ratio between the different residuals exploited in the tests.