CEST2025

The replacement of fossil fuels by renewable energy sources is one of the most important steps for the reversal of climate crisis through circular economy. The contribution of solar and wind energy has been continually increasing in the recent years to this end. To fully exploit their potential, their storage as chemical energy in the form of green hydrogen or methane is of paramount importance. Green hydrogen generated via electrolysis of water using the surplus electricity generated by photovoltaic cells is employed in this work for the reduction of the carbon dioxide contained in biogas to methane. This leads to almost complete upgrading of the biogas generated via anaerobic digestion of the wastewater generated by a potato processing industry. The upgraded biogas may then be injected into the natural gas network, used in a combined heat and power (CHP) process or used as transportation fuel in the form of bioCNG. Two alternative approaches are examined. The first is an ex situ process: biogas is generated in a UASB reactor and co-fed with green hydrogen to a mesophilic trickling bed reactor (TBR) in order to be upgraded to biomethane via hydrogenotrophic methanogenesis. In the second alternative, green hydrogen is fed as microbubbles to a wastewater processing UASB reactor for an in-situ enrichment of biogas to biomethane. A third alternative also examined is the direct use of the generated electricity with or without hydrogen addition in a microbial electrolysis cell anaerobic digestion (MEC-AD) system.