Investigation of a full scale, mechanical pretreatment for enhanced biomethane production from giant reed (Arundo Donax)

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.