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.

Abstract

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 oC, 53 min; D2: 161 oC, 62 min; D3: 191 oC, 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 oC, 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.