Environmental impact assessment of pyrolysis and incineration including end-of-life of sewage sludge by-products

Incineration and pyrolysis have been proposed for sewage sludge treatment. However, most studies have overlooked the environmental impacts of by-products from thermal processes. This study compared the applicability of incineration and pyrolysis, with a detailed environmental impact assessment of by-products. The long-term stability of heavy metals in ash and biochar was investigated through an accelerated aging process, while their potential as fertilizers was evaluated in terms of phosphorus availability and other functions. Both incineration ash and pyrolyzed biochar demonstrated high heavy metal stability even after aging and exhibited potential as substitutes for chemical fertilizers. Consequently, the life cycle assessment determined that the environmental impacts of incineration were more severe than those of pyrolysis due to increased biogenic CO₂ emissions and greater mobility of heavy metals during incineration. Therefore, pyrolysis is suggested as the more environmentally sustainable option for sewage sludge treatment, considering both environmental impacts and by-product implications.