Integrated Sewage Sludge-to-Energy and CO2 Sequestration: Energy Intensity and Emission Characteristics

Abstract This study presents a comprehensive analysis of the integrated sewage sludge to energy with CO2 sequestration (ISSECS) process—a novel approach for converting sewage sludge into electricity, heat, and compressed CO2 for geological storage. The process integrates drying and pelletizing, plasma gasification, syngas cleaning, wet combustion, and CO2 capture and compression, forming a closed-loop energy and carbon management system. Using a functional unit of 1 Mg of dry sewage sludge, material and energy flows were quantified and scaled to assess the annual performance of a wastewater treatment plant processing 10,000 Mg of sludge. Results indicate that the ISSECS system generates 43.1 GWh of electricity and captures 11,405 Mg of CO2 annually, offsetting 10,080 Mg CO2-equivalent emissions from avoided methane release due to landfilling. Despite high energy demands (52.2 GWh), including 34.4 GWh of onsite electricity consumption, the process achieves a net CO2 reduction of 9,987 Mg. The study highlights the significant environmental benefits of the ISSECS process over conventional sludge disposal methods and identifies energy-intensive stages—such as drying and gasification—as key targets for efficiency improvements. The findings underscore the potential of ISSECS as a sustainable waste-to-energy technology that contributes to climate change mitigation and supports circular economy objectives.