Ricerc@Sapienza

The effects of an industrial scale, mechanical pretreatment were determined on the methane yield of Giant reed stems. The feedstock was pretreated using a two stages dry milling process and the experiments were performed for two different mass flow rates (600 and 900 kg h-1). Untreated and pretreated stems were both anaerobically digested in batch reactors under mesophilic conditions for 28 days. The cumulative biogas production from the pretreated materials exceeded 212 Nm3t-1of volatile solids, showing a 137% gain compared to the raw material. Such a gain resulted far above the known range for size reduction pretreatments. Processed stems also showed a significant decrease in the acid detergent fiber content. The specific electric energy requirement for pretreatment decreased from 97.8 to 76.5 kWh t-1of processed material with increasing the mass flow rate. The net primary energy output from pretreated stems was enhanced by about 118% compared to the raw material. The cost for the extra energy produced by pretreatment was estimated at 0.034 € kWh-1, resulting fully compatible with the selling price for the electric energy produced from biogas in force in Italy.