Co-combustion of

Fossil-based solid fuel dependency is characterized by supply scarcity and environmental hazards, underscoring the need for cleaner, renewable energy sources. Spirulina (Arthrospira) platensis (SP) cyanobacterium is a promising source of energy due to its abundance and high calorific value. However, co-combustion is one of several methods to reduce environmental impact by utilizing unmanaged plastic or synthetic waste (SW) with high volatility and combining it with SP. Circulating fluidized bed combustor (CFBC) technology is one of the effective thermal methods to convert various types of feedstocks into a heat source. There is limited study about the co-combustion of microalgae and plastic waste in CFBC. This study aims to examine the ash characteristics of 30% SP and 70% SW. Ash characterization is important to mitigate ash buildup and evaluate its potential for valorization. Morphology analysis showed that combustion significantly alters the feedstock's physical structure, resulting in more porous, coarser ash. The main compositions of ash are O, Si, Cl, P, Na, and Fe. Fourier transform infrared (FTIR) spectroscopy revealed the loss of specific peaks in the 3700-2000 cm⁻1 region after combustion, indicating the decomposition of proteins and lipids from SP, whereas the SW component showed significant polymer degradation.