Influence of hydrothermal pretreatment conditions, typology of anaerobic digestion system, and microbial profile in the production of volatile fatty acids from olive mill solid waste

This study aimed to investigate the production of biobased volatile fatty acids (VFAs) from pretreated olive mill solid waste (OMSW). Three hydrothermal pretreatment (HP) conditions (D1: 125 degrees C, 53 min; D2: 161 degrees C, 62 min; D3: 191 degrees C, 83 min) were selected. The pretreated olive mill solid fraction (OMSF), pretreated olive mill liquid fraction (OMLF), and pretreated OMSW were evaluated as potential substrates for acidification in the anaerobic digestion (AD) in liquid (L-AD), semi-solid (Ss-AD), and solid (S-AD) phases. The best acidification efficiency (AE) observed in this study was 65%, for L-AD and HP condition D2 (161 degrees C, 62 min). However, the HP condition D2 applied to the Ss-AD provided a VFA concentration of 18218 mg L-1, about 6-fold higher than that observed in the L-AD system. Polyphenols changed the profile of VFAs, increasing the production of longer chain VFAs in the L-AD and S-AD systems. Also, the influence of the typology of the AD system and HP severity on the microbial community was evaluated. Proteobacteria and Firmicutes were the most representative phyla in acidogenic fermentation of OMSW substrates and the genera Enterobacter, Pseudomonas, Achromobacter, Clostridium, Ochrobactrum, and Peptoclostridium played an important role in the pretreated OMSW fermentation and, consequently, in the VFAs production profile.

Automated summary

This study investigated the production of biobased volatile fatty acids (VFAs) from pretreated olive mill solid waste (OMSW). Different hydrothermal pretreatment conditions and anaerobic digestion systems were evaluated, with significant impacts on the microbial community and VFA production profile. The study highlights the potential of using OMSW for sustainable VFA production and the importance of understanding the influence of pretreatment and digestion conditions on the process.