Sustainable recycling of residues from the food waste (FW) composting plant via pyrolysis: Thermal characterization and kinetic studies

Residues from the food waste (FW) composting factories are an important component of solid waste and commonly treated by landfill and incineration approaches, posing serious environmental and social challenges. In this work, pyrolysis was proposed as a potential alternative method to sustainably recycle FW composting residues as value-added byproducts (bio-char, bio-oil and syngas). To obtain reliable operating and designing parameters for the pyrolytic reactor, the characteristics of the composting residues, the thermal behaviors and kinetic parameters were investigated. The results show that the composting residues mainly consisted of lignin (69%), bone (18%) and plastic (12%), with the lower heat value of around 15.72 MJ/kg. The final pyrolysis temperature of over 500 °C was needed for the complete decomposition of the lignin, bone, and plastic components. According to the comparison between the experimental and calculated thermogravimetric/derivative thermogravimetric curves, only slight interactions were observed in the decomposition of the lignin, bone, and plastic components. The byproducts from lignin/bone pyrolysis might deposit on the plastic material and slightly slow down the mass loss rate. However, the catalytic role of the byproducts were also observed which prompted further investigations. The thermal behavior of the FW composting residues could be successfully modelled by first and third-order chemical reactions respectively in the temperature ranges of 200-360 and 360-510 °C, with activation energy ranging from 25.68 to 41.89 kJ/mol. The results from this study have not only proved the feasibility of the proposed pyrolysis technique for diverting FW composting residues away from landfilling and incineration for enhancing resource recovery from FW, but also provided basic information for further pyrolysis reactor design and operation.