Biochemical conditions for anaerobic digestion of agricultural feedstocks: A full-scale study linking elements concentration and residual methane potential

Agricultural biogas plants should operate at the highest biological efficiency, with a fast anaerobic conversion of organic feedstocks leading to a low Residual Methane Potential (RMP). Optimal biochemical conditions boost the metabolic activity of microorganisms, providing better process performances. In this study, RMP of 16 full scale agricultural biogas plants operating with different agri-based feedstock categories was used as indicator of biological efficiency and linked to their operational parameters such as Organic Loading Rate (OLR), Hydraulic Retention Time (HRT) and to chemical elements concentration in the digestate. RMP ranged between 1% and 26% of the total biomethane produced revealing a clear relation with HRT. The Principal Component Analysis (PCA) showed how specific trace elements supplementation, in the order Se > Mo > Co, and their concentration ratios (Ni/Co and Ni/Se) lead to RMP reduction in full-scale agricultural biogas plants with low HRT (<48 days) and high OLR (>3.61 kgVS m � 3 day-1) mainly fed with manure and agro-industrial by-products.

Automated summary

Agricultural biogas plants should aim for high biological efficiency by quickly converting organic feedstocks to minimize residual methane potential. Optimal biochemical conditions can enhance microorganism activity and improve process performance.