Application of organosolv technology to improve the anaerobic digestion of olive oil pomace

Abstract

So far, there are few sustainable alternatives to manage the exhausted olive pomace (EOP), a dangerous waste produced by the olive oil sector. In this work, EOP resulting from organosolv pretreatment was submitted to conventional anaerobic digestion (mono-AD) or co-digestion with sewage sludge (co-AD) at different ratios using a pilot-scale stirred tank reactor. Firstly, it was observed that a shortening of the acclimation phase improved performance allowing a methane specific productivity of 575.15 LCH4 kg VS−1 d−1. Even though the mono-AD strategy was more performant than co-AD in terms of biogas specific productivity (25.50 Lbiogas kgEOP−1 d−1), all tested conditions yielded 67–70% methane and a negligible H2S content. Likewise, no significant differences between these strategies were found in terms of methane specific productivity and biodegradability that reached maximum values of 230.85 ± 19.29 LCH4 kgVS−1 d−1 and 61.3 ± 5.1%, respectively. The main differences between them were observed in the overall chemical oxygen demand consumption rate (819.10 and 656.70 gCOD L−1 d−1 for Co-AD and mono-AD, respectively) and volatile solids removal (86.5% for Co-AD and 34.8% for mono-AD) when feeding 40 g of pretreated EOP. This work highlights the positive effect of organosolv to improve AD and the feasibility of the proposal to achieve the zero waste in this sector.