Pyrolysis behaviour and kinetic analysis of food waste sludge cake

Abstract

Concerns regarding energy security are raised due to the conventional fossil fuel depletion, which drives the need of diversifying fuel sources for power generation. Sewage sludge, which is a waste product from the wastewater treatment plant, contains energy that could be retrieved and reused. Typically, these sludge are treated as a form of schedule waste and disposed of in a landfill. In this work, the valorisation potential of sludge cake to produce higher-value products was studied through thermogravimetric analysis.The thermal degradation behavior of the sludge cake under inert atmosphere was observed to possess two distinct zones: 1) moisture removal (62.86-131.76 °C) and 2) devolatilization (155.96-517.2 °C). The highest mass loss at 66.78 % was recorded during devolatilization. Kinetic analysis through model-free methods (Flynn-Wall-Ozawa (FWO) and Kissinger) revealed that an average activation energy in the range of 286.59 to 287.98 kJ/mol is required during pyrolysis. Characterisation of the sludge cake also revealed the potential of yielding a significant amount of bio-oil and gaseous products due to its high volatile content (72.3 %). The volatiles evolved were then sent to an FTIR instrument for further analysis. A variety of bio-oil compounds (phenols, alkanes, aromatics, acids, aldehydes, ketones, and carbonyl compounds) and gaseous products (CO, CH4, and CO2) were detected. In addition to these, the low ash content (6.68 %) measured portrayed the possibility of transforming this sludge cake feedstock into biochar with solid fuel properties. It has been demonstrated through this study that the sludge cake from food processing industries is a promising feedstock pyrolysis to yield bio-products of higher values.