Evaluation of Posidonia oceanica residues as feedstock for anaerobic digestion

The suitability of Posidonia oceanica as feedstock for anaerobic digestion process was evaluated carrying out several biochemical methane potential tests. No clear evidence of process inhibition were observed during tests. Nevertheless, the very high lignin content of Posidonia did not allow the organic matter solubilization by microbial lithic enzymes, thus limiting the effectiveness of the anaerobic digestion process. Therefore, Posidonia was subjected to thermal (132 °C) and thermo-chemical pre-treatment in order to increase its anaerobic digestibility. The opportunity of reducing biomass stress due to the high salinity of Posidonia suspension (performing a washing operation before anaerobic digestion) was also evaluated. Thermal treatment and salt removal allowed only a limited increase in anaerobic digestion process efficiency. Whilst thermo-chemical pre-treatment at 132 °C in presence of HCl 0.40% resulted in a relevant increase of Posidonia biodegradability leading to a specific methane production higher than 90 mL/gVS and a VS removal efficiency of about 50%.