Energy recovery from Ginkgo biloba urban pruning wastes: pyrolysis optimization and fuel property enhancement for high-grade charcoal productions

Abstract

Ginkgo biloba trees are widely planted in urban areas of developed countries for their resilience, longevity and aesthetic appeal. Annual pruning to control tree size, shape and interference with traffic and pedestrians generates large volumes of unutilized Ginkgo biomass. This study aimed to valorize these pruning residues into charcoal by optimizing pyrolysis conditions and evaluating its fuel properties. The pyrolysis experiment was conducted at 400–600°C, after oven drying pretreatment. The mass yield of charcoal was found to vary from 27.33 to 32.05% and the approximate volume shrinkage was found to be 41.19–49.97%. The fuel properties of the charcoals were evaluated using the moisture absorption test, proximate and ultimate analysis, thermogravimetry, calorimetry and inductively coupled plasma optical emission spectrometry. The calorific value improved from 20.76 to 34.26 MJ kg−1 with energy yield up to 46.75%. Charcoal exhibited superior thermal stability and better combustion performance. The results revealed satisfactory properties compared with other biomass, coal and biochar standards. The product complied with first-grade standards at 550 and 600°C and second-grade wood charcoal standards at other temperatures. However, higher concentrations of some heavy metals like Zn indicate the need for pretreatment and further research on co-pyrolysis for resource optimization. This study highlights the dual benefits of waste management and renewable energy, providing insights for urban planning and policymaking.