Turning sewage sludge into sintering fuel based on the pyrolysis I: lipid content and residual metal

The use of pyrolysis to produce oil from sludge by the evaporation-condensation process is a promising technique. However, the resulting lipids are prone to be acidized under exposure to oxygen, which can affect their quality and use. To eliminate the need for this oil separation process, the present work uses blended pyrolysis to preserve the oil in the char and to prevent it from deteriorating. At the same time, metals are eliminated to a secure level of combustion emissions. The sludge was pyrolyzed into a sintering fuel through blended pyrolysis with SiO₂, Al₂O₃, and sand. These materials are the main components of the sintered ceramsite obtained. Therefore, the influence of these substances and residence time on lipid formation and metal residue in the char were investigated. Non-blended pyrolysis required a 40-min duration, whereas sand-pyrolysis required 10 min to achieve the same yield. The concentration of C_16:0 produced by blended pyrolysis with sand reached 2177 mg kg^-1, which is 57% higher than that of non-blended pyrolysis. Blended pyrolysis with SiO₂ required at least 20 min to immobilize As metal. In summary, blended pyrolysis simplifies the process, reduces time, and produces char with lipid-rich and low metal leaching, which can be used as a sintering fuel.