Life cycle assessment of a biogas-fed solid oxide fuel cell (SOFC) integrated in awastewater treatment plant

Abstract

This work assesses the environmental impacts of an industrial-scale Solid Oxide Fuel Cell (SOFC) plant fed by sewage biogas locally available from aWasteWater Treatment Plant (WWTP). Three alternative scenarios for biogas exploitation have been investigated and real data from an existing integrated SOFC-WWTP have been retrieved: the first one (Scenario 1) is the current scenario, where biogas is exploited in a boiler for thermal-energy-only production, while the second one is related to the installation of an efficient SOFC-based cogeneration system (Scenario 2). A thermal energy conservation opportunity that foresees the use of a dynamic machine for sludge pre-thickening enhancement is also investigated as a third scenario (Scenario 3). The life cycle impact assessment (LCIA) has shown that producing a substantial share of electrical energy (around 25%) via biogas-fed SOFC cogeneration modules can reduce the environmental burden associated to WWTP operations in five out of the seven impact categories that have been analyzed in this work. A further reduction of impacts, particularly concerning global warming potential and primary energy demand, is possible by the decrease of the thermal request of the digester, thus making the system independent from natural gas. In both Scenarios 2 and 3, primary energy and CO2 emissions embodied in the manufacture and maintenance of the cogeneration system are neutralized by operational savings in less than one year.