CARBON FOOTPRINT OF ELECTRICITY FROM BIOGAS WITH STEAM EXPLOSION PRETREATMENT

In the absence of appropriate pretreatment, maize stover is a widely available but poorly fermentable agricultural residue. With stover pretreatment using the novel steam explosion (SE) technology, this study calculates the carbon footprint of 1 kWh electricity from maize stover biogas. The system includes a 500 kWel-biogas plant with a combined heat-and-power (CHP) unit (50% external off-heat utilization), as well as substrate production and digestate management. Total GHG-emissions are 239 g CO2-eq/kWh, with the most important contributors being methane slip in the CHP exhaust (133 g CO2-eq/kWh), electricity for plant operation (43 g CO2-eq/kWh) and construction materials (24 g CO2-eq/kWh). Constructing and operating the SE unit contributes little (0.5 g CO2-eq/kWh) if the heat requirements can be covered by off-heat from the CHP unit. Hence, SE pretreatment can allow the use of agricultural residues for biogas as a suitable alternative to the use of energy crops.