Biomethane production using an integrated anaerobic digestion, gasification and CO2 biomethanation process in a real waste water treatment plant: A techno-economic assessment

The biomethanation of CO2 from anaerobic digestion within the power to gas concept has recently emerged as a promising technology to upgrade biogas, to decarbonise the domestic and industrial heat sector, provide long term energy storage and deliver grid balancing services. In addition, the utilisation of the digestate, through a process such as gasification, offers a circular economy approach and has the potential to enhance the deployment of power to gas systems. To this direction, the study focuses on exploring the techno-economic feasibility of coupling biomethanation with digestate gasification for the wastewater industry. The study constitutes the first endeavour to assess the viability of such an integrated energy system. Four different scenarios have been designed and assessed. The energy efficiency of the concepts lies between 26.5% and 35.5% while the minimum selling price (MSP) of biomethane is in the range of 135–183 £/MWh. The implementation of appropriate policy mechanisms and the inclusion of by-products revenues reduces the MSPs by approximately 32%–42%. The conduction of a typical sensitivity analysis has identified the electricity price as the prime cost driver and this is followed by the cost of the electrolyser or the gasification plant depending on the scenario. Finally, a 2030 analysis, that incorporates projected techno-economic advances, has been carried out and revealed that under certain circumstances profits can be generated.