Agronomic Potential of Digestates from Pig Slurry and Wine Vinasse Co-Digestion Under Temperature-Phased Anaerobic Digestion

The management of Pig Slurry (PS) and Wine Vinasse (WV) poses major environmental and economic challenges, Anaerobic co-digestion (AcoD) offers a promising approach, producing both renewable energy and nutrient-rich digestates with agronomic potential. This study evaluated digestates obtained from the AcoD of a 50:50 mixture of pig slurry and wine vinasse under Temperature-Phased Anaerobic Digestion (TPAD) conditions. The acidogenic reactor reached stability at a hydraulic retention time (HRT) of 5 days, achieving 51.34 ± 3.08% of tCOD removal and approximately 0.5 L of daily green hydrogen production, whereas the methanogenic stage reached stability at an HRT of 10 days with 89.14 ± 2.33% tCOD removal and recording daily biomethane production of up to 1 L. Digestates were tested in germination assays using Lepidium sativum (garden cress), Lactuca sativa (lettuce), and Raphanus sativus (radish) seeds to assess phytotoxicity, and pathogen analyses were conducted to confirm sanitary safety (contains 0.8 × 103 MPN/gTS E. coli). Results showed that agronomic performance was primarily influenced by dilution level, at 10D–15D% dilutions, germination and root growth remained stable, with Germination Index (GI) values above 80%. In contrast, concentrations above 25D% led to marked inhibition, with GI values below 50%. These findings demonstrate that the TPAD system operates effectively when treating pig slurry and winery vinasse, producing digestates that are safe and effective organic amendments. Moreover, given their compliance with sanitary standards, these digestates can be classified as Class A biosolids suitable for agricultural application, provided that adequate dilution is ensured.