Assessment of the fertiliser potential of digestates from farm and agroindustrial residues

The sustainability of biogas production systems depends greatly on the appropriate disposal of the digestates produced. The main agrochemical characteristics of 12 digestates from the anaerobic co-digestion of farm and agroindustrial residues were determined and compared with quality standards to assess their potential use as fertilisers. The digestates have a high fertilising potential, associated mainly with their contents of NH4-N; however, their recycling in agriculture might be restricted by their Cu and Zn contents, salinity, biodegradability, phytotoxicity and hygiene characteristics, which must be addressed to obtain the maximum benefits. Such characteristics determine the need for applying pre- or post-treatments to increase digestate quality until acceptable levels. Therefore, digestate quality must be taken into account when managing the co-digestion process, including substrate selection, in order to use digestates as fertilisers without the additional cost of post-digestion conditioning treatments.