Utilization of wasted sardine oil as co-substrate with pig slurry for biogas production – A pilot experience of decentralized industrial organic waste management in a Portuguese pig farm

This work aimed to demonstrate in a pig farm and in real conditions, the possibilities to co-digest wasted sardine oil (WSO) and pig slurry (PS) at farm scale. A biogas mobile pilot plant, was set up in the farm and operated in real conditions during 4 months. Dynamic mesophilic (35–37 °C) continuous pilot trials were performed during four different periods of time. In each period a different organic loading rate (OLR) based on the chemical oxygen demand (COD) was operated sequentially, with pig slurry (PS) (OLR = 1.6 kg COD/m3 d−1) and with mixtures of WSO:PS with a volumetric composition (% v/v) of 2:98 (OLR = 3.0 kg COD/m3 d−1), 3:97 (OLR = 3.7 kg COD/m3 d−1) and 5:95 (OLR = 5.2 kg COD/m3 d−1). Biomass adapted very fast in metabolise the WSO and biogas productivity was raised substantially for different compositions of WSO:PS. Process stability indicators pH and Total volatile fatty acids/bicarbonate alkalinity (T-VFA/BA) ratio, suggests that the co-digestion process was robust. It was concluded that WSO could be easily co-digested in farm scale biogas plants.