Effects of Fenton’s reagent treatment on biomethane production of olive pomace

In this research work we have investigated the effects of oxidative treatments, based on Fenton’s reagent, to improve the biochemical methane potential (BMP) of two types of olive solid residues coming from a two-phase extraction system: the wet olive pomace (WOP) and the destoned wet olive pomace (DWOP). In the nineties, the spread of the horizontal centrifuge separator provided of two outlets has had the shortcoming to hinder the exploitation of olive pomace for the industrial extraction of residual oil. For this reason, the olive oil industry is facing the problem to valorize a huge quantity of biomass, lacking the traditional way to use it. One of the most promising technologies to valorize the residual biomass is the anaerobic digestion (AD), capable to provide renewable energy (biogas) and stabilized organic matter able to be used as soil improver. The major obstacle for the exploitation of the olive pomace in the AD processes is the high phenols content present in it. Those substances have a bacteriostatic effect on the microbial community present in the digesters. The hydroxyl radical produced during the Fenton’s reaction can react with the phenols. The treatments proposed are capable to produce two effects in the treated matrices: improving the speed of biomethane production in the AD process and reducing the H2S content in biogas. E.g., in the tests with the WOP we have observed that the matrix treated with Fe (II) and 4.4 M H2O2 showed an intense production of methane almost immediately, with a peak production (over 11 NmL/gVS), during the 8th and the 9th days whereas, the untreated WOP starts the biogas production in the 8th day of test with a daily peak of production of CH4 (13.46 NmL/gVS) during the 14th day. The treatment proposed has the potential to eliminate the environmental impacts associated with olive oil industry and permits a fully exploitation of the whole biomass that came from the olive food processing.