Superior sewage sludge disposal with minimal greenhouse gas emission via fast pyrolysis in a fluidized bed reactor

In response to global carbon footprint reduction efforts, the promising waste-to-energy sludge disposal is assessed according to greenhouse gas emissions and biofuel production. Life cycle assessment and ^GEsTABouses were used in quantifying the CO ₂ eq emissions of sludge disposal routes. In energy content assessment, fast pyrolysis experiment was done using a fluidized bed reactor, and the energy contents of derived biofuels were accounted for. The result shows that sewage sludge disposal through fast pyrolysis is the most environmentally sustainable route with the lowest emissions (696.7 kg CO ₂ eq) compared to liming and land application (833.3 kg CO ₂ eq), composting and land application (756.3 kg CO ₂ eq), and incineration with household wastes (2805.3 kg CO ₂ eq) per ton of dried sludge. The fast pyrolysis supremacy is illustrated by net negative emission balance (–1070.9 kg CO ₂ eq), manifesting its significant contribution to emission mitigation. Fast pyrolysis has a high bio-oil yield (35.68 wt%) with a high heating value of 36.43 MJ/kg. Energy contents per ton of dried sludge are: bio-oil = 13.0 GJ, biogas = 2.73 GJ, biochar = 1.75 GJ. Overall, this study demonstrated fast pyrolysis as a superior sludge disposal route contributing to the environment and energy sustainability.