Co-composting of the solid fraction of anaerobic digestates, to obtain added-value materials for use in agriculture

This work focuses on the viability of composting for the recycling of digestates, to obtain added-value organic materials with potential use in agriculture. Mixtures made from the solid fraction of a digestate (obtained from the anaerobic co-digestion of cattle slurry and silage), with or without vine shoot prunings as bulking agent, were composted by the Rutgers composting system. During composting, the temperature of the composting piles was monitored, as were physico-chemical, chemical, and maturity parameters. Potential added-value properties of the final composts, such as their physical characteristics and in vitro suppression of Fusarium oxysporum f. sp. melonis, were determined. The bulking agent had a positive effect, reducing the electrical conductivity and the N losses during composting and also diluting the heavy metal contents of the end-products. The composts obtained showed adequate degrees of stability and maturity, suitable physical properties for use as growing media, and suppression of F. oxysporum f. sp. melonis.

► Composting of the solid fraction of digestate is a suitable treatment to recycle it. ► Vine shoot pruning addition reduced N losses during composting. ► Composts from the solid fraction of digestate displayed suitable physical properties. ► The composts obtained showed a suppressive effect on F. oxysporum. f.sp. melonis.