Anaerobic co-digestion of agricultural residues produced in Southern Greece during the spring/summer season

• Published in: Biochemical engineering journal 2023-03, Vol.192, p.108826, Article 108826
• Main Authors: Aravani, Vasiliki P., Tsigkou, Konstantina, Papadakis, Vagelis G., Wang, Wen, Kornaros, Michael
• Format: Article
• Language: English
• Subjects: Alkalinity; Anaerobic digestion; Methane production; Organic loading rate; Propionic acid accumulation; Southern Greece spring/summer
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2023.108826

Anaerobic digestion (AD) is a well-known environmentally friendly technology, that even though has been investigated extensively, in Greece there is still a lack of experimental knowledge on locally available substrates’ valorisation. This study aimed to assess a continuous one-stage AD system for the valorization of Southern Greece’s spring/summer residual biomass. The most suitable substrate in Southern Greece during the spring/summer season is 10% corn silage, 14% cattle manure, 66% unsuitable for human consumption watermelons, and 10% tomato processing residues, in terms of methane yield maximization during anaerobic co-digestion. Regarding the system operational conditions, the hydraulic retention time (HRT) was set at 20 d, while the initial organic loading rate (OLR) of 2 g COD/(L·d) was applied, which was increased gradually, up to 7 g COD/(L·d). The reactor operated successfully for the applied OLRs 2–5 g COD/(L·d), while a further increase led to inhibition phenomena. Even if propionate accumulated up to 5 g/L, it successfully coped with the correction of alkalinity levels (up to 6.4 g CaCO3/L). The system’s efficient operation paves the way for residual biomass treatment in one-stage systems, without substrate dilution, at high OLRs, that can be applied in countries characterized by a surplus of the aforementioned residues. [Display omitted] •The one-stage anaerobic digester operated efficiently at OLR 2–5 g COD/(L·d).•The system operated successfully at OLR 5 g COD/(L·d) without substrate dilution.•Further OLR increase (7 g COD/(L·d)) led to process inhibition (VFAs accumulation).•At the run of 7 g COD/(L·d), constant washing out of the inoculum was observed.•Propionate accumulation was tackled via alkalinity levels fixation (>6 g CaCO3/L).