Perlite as a Biocarrier for Augmentation of Biogas-Producing Reactors from Olive (Olea europaea) Waste

Abstract

Biogas is mainly produced by anaerobic digestion (AD), and in the EU, the widely used substrate for AD is maize silage. Due to a rise in silage prices, the intention is to gradually replace maize with lignocellulose biomass. In the Mediterranean area, the olive industry produces large amounts of lignocellulose wastes, namely olive cake and pruned biomass. Still, due to its high lignin content, it is resistant to biodegradation. This issue could be resolved by adding targeted microorganisms that enhance the substrate’s primary degradation, and the cells’ attachment to suitable biocarriers could boost the augmentation process. A microbial consortium customized for biodegradation of olive cake and pruned biomass was isolated, propagated and immobilized onto the biocarrier, perlite, a naturally occurring aluminosilicate material. The perlite proved to be a suitable biocarrier with numbers of immobilized bacteria as high as 2.1 ± 0.9 × 1011 and 3.4 ± 0.6 × 1010 CFU g−1 when preparation was performed in aerobic and anaerobic conditions, respectively. Bioaugmentation of AD reactors significantly increased the biogas yield, but only if olive cake, not the pruned biomass, was used as a substrate.