L'impiego della frazione separata solida del liquame digerito e non per l'alimentazione dei digestori anaerobici

Effluents from biomasses anaerobic digestion (known as digestate) are mainly composed from water ( over 90%) and organic and inorganic materials. They are generally stored in uncovered tanks and regularly land applied as organic fertilizer, or mixed with water for crop irrigation. Digestate management can cause problems as the volumes daily produced are high and, in some cases, storage tanks have insufficient capacity to hold the produced volumes over the required period. Moreover, digestate transport to fields to outside farm areas can be very expensive. For these reasons, in many Italian anaerobic digestion plants, digestate is mechanically separated in order to obtain a solid and a liquid fraction. The liquid phase contains most of the potassium and ammoniacal nitrogen, whereas the solid fraction mainly presents the insoluble organic matter compounds and the phosphorus. Since the solid fraction still retains a high amount of volatile solids it could be used as a feedstock for anaerobic digestion plants. The present study was carried out with the aim to assess the biogas and methane yield of five different mechanically separated solid fractions of co-digested slurry and of a solid fraction sample obtained from the mechanic separation of raw pig slurry.