Integration of thermal plasma with CCUS to valorize sewage sludge

The presented study addresses the threefold challenges namely, sustainable waste valorization of a difficult waste stream, climate change due to CO₂ emissions and clean energy crisis and it is a small step forward to achieve SDG-7. A hybrid DC thermal plasma was employed in a pilot scale facility (∼150 kW) to treat sewage sludge in the presence of waste CO₂ (according to the concept of CCUS, Carbon Capture Utilization and Storage) to produce syngas and assess the viability to retrieve phosphorus and other valuable materials from the generated ash. An equilibrium model was also developed to enhance the understanding about the dynamics of process. The H₂ generation was around 0.5 m³/kg fuel whereas the amount of char produced was negligible (0–0.013 kg/kg fuel) realizing an efficient transformation of carbon. It was promising to find a high amount of P₂O₅ in the ash retained in the filter (30 wt %) and reactor (9 wt %) as evaluated by XRF. An average value of 97 % was obtained for CCE (carbon conversion efficiency) depicting almost complete carbon conversion. The results are encouraging to valorize sewage sludge under the CCUS scheme to produce clean energy and reclaim valuable nutrients.