Valorisation of fresh olive oil pomace for biogas production

Abstract

Olive oil is a liquid fat obtained by pressing whole olives and directly extracting the virgin oil through mechanical processes. The remaining residue is a liquid/solid mixture called olive oil pomace, containing about 60 to 80% water. The current methods to treat and valorise this residue require an intensive use of energy for removing the excess water to facilitate the chemical extraction of remaining oil still present in the pomace (so-called olive pomace oil). The dry remainder after this secondary oil extraction is then burnt for production of electricity (e.g., through co-generation), for generating thermal energy (e.g., for heating of the olive mills), and for animal feeding. Due to the large increase in olive oil production, there are now several constraints to this process in terms of installed capacity. Alternative and more sustainable methods to valorise this residue were therefore investigated, namely evaluation of the potential for biogas production from fresh olive oil pomace. For this purpose, four samples of olive pomace were collected right after the exit of the decanter/centrifuge from two different mills in Portugal, located in the Alentejo and Douro regions. The preliminary results have shown promising gas yields, also when compared to other types of substrates. Further investigations are necessary to better understand the biogas potential of fresh olive oil pomace, and these experiments have thus provided an initial snapshot of the potential of such olive pomaces to produce biogas.