Use of Recalcitrant Agriculture Wastes to Produce Biogas and Feasible Biofertilizer.

In the ongoing work, the digestion process of recalcitrant agricultural wastes (olive wastes and citrus pulps) mixed in different proportions with, livestock manures, milk serum and maize silage for biogas production was studied. Additionally, the chemical composition and the phytotoxicity of the digestates (each separated in liquid and solidfraction)wereevaluatedwiththepurposeofbeingused as organic fertilizer in agriculture. The results demonstrated that animal manure and recalcitrant agricultural wastes, if properly mixed, produced high percentage of biogas. The digestate chemical compositions differed and varied in respect to the kind of feedstock, and the ratio of their mixing to feed the digesters. The digestate from the digester named Fattoria,mainlypoweredwithanimalmanures(poultry,cow andsheep),containedlessphenolsandmoreactivemicrobial biomass than the digestate from the digester Uliva, mainly fed with olive waste and citrus pulp and in minor extent with animal manure and maize silage. Our data showed that the digestatecompositiondependedonthemixofbiomassinput. Additionally, the effects of digestate were plant speciesspecific and a positive correlation between the amount of phenols and the phytotoxic effects of digestate on plants was also well evident. These results suggest that the sustainable disposal of digestates requires a preliminary screening to select the one which better fits the demands of a particular species for optimizing crop production