This study evaluated the performance of a plug-flow reactor (PFR) for high-rate anaerobic co-digestion of complex agro-industrial wastes and used cooking oil or animal fat. The PFR was successfully operated up to an organic loading rate (OLR) of 21 g L-1 d-1, yielding biogas at 0.35 L g-1 chemical oxygen demand (COD) influent. During the study period, supernatant COD at the PFR effluent remained between 4 and 7 g L-1, with negligible volatile fatty acids' concentrations (<500 mg L-1) and no presence of foaming incidents. The biomass concentration inside the PFR, expressed as total suspended solids, remained between 30 and 60 g L-1. Moreover, the above-mentioned anaerobic digestion technology has been currently scaled-up at 50 m3 PFR, while a full-scale facility of 240 kW-el is under construction in the region of north-eastern Greece.
Keywords: Plug-flow reactor; anaerobic digestion; biogas; fat oil and grease; high-rate.