Evaluation of the physico-chemical development of kitchen food wastes through torrefaction - a biodiversity case study

Abstract

This study evaluated the change in physical and chemical properties of sun-dried food waste, during torrefaction in a fixed bed reactor. Torrefaction was carried out at different temperatures 230 °C, 260 °C, and 290 °C, for different residence times of 15, 30, 45, 60, 75, and 90 min in a fixed bed reactor. The solid torrefied products were analyzed by elemental analysis, proximate analysis, compositional analysis, and thermogravimetric analysis (TGA), and it was found that most suitable residence time for torrefaction was 60 min as torrefaction beyond 60 min did not yield much improvement in changing the properties of kitchen food waste. Carbon content increased from 46.0 to 58.5%, consecutively increasing higher heating value (HHV) from 16.1 to 21.9%. Compositional analysis demonstrated that there was not much hemicellulose left in the raw food waste after cooking; however, it had cellulose in significant proportion which went through decomposition during torrefaction. Lignin was not affected much. Various process parameters such as mass yield, energy yield, and energy density were also studied, and it was found the mass and energy yield decreased by 65.0% and 47.5%, respectively, and energy density increased by 35%. Van Krevelen indicated clearly that torrefied char had achieved coal characteristics.