Impact of monoterpenes in the stability of the anaerobic digestion of Mediterranean Wholesale Market Waste

Abstract

The stability and robustness of long-term anaerobic digestion process of fruit and vegetable waste (FVW) generated in Mediterranean wholesale markets were assessed, monitoring potential inhibitory volatile organic compounds (VOCs) such as volatile fatty acids (VFAs) and/or monoterpenes. Particle size (4 and 10 mm) and organic loading rate (OLR) were evaluated during the experimentation. Anaerobic digestion remained stable at OLR of 1.0 g VS L−1 d−1 (VS, total volatile solids) regardless of the feedstock particle size. At this OLR, methane yield was 254 ± 8 and 229 ± 11 mL CH4 g VS−1 for 4 and 10 mm, respectively. As the OLR increased above 1.0 g VS L−1 d−1, the system rapidly destabilized, and a high accumulation of VFAs was observed. In parallel of to the VFAs accumulation, other VOCs such as fenchone also reached concentrations that contributes to the destabilisation of the process. The destabilization process at an OLR of 3.0 g VS L−1 d−1 also resulted in a drastic reduction in the relative abundance and species diversity of methanogenic archaea in all digesters.