Impact of polysaccharides, proteins, lipids, and humic-like substances on thermal stability and flammability of wastewater sludge extracellular polymeric substances

Abstract

The current study investigates the application of extracellular polymeric substances (EPS), recovered from municipal wastewater sludge, as sustainable flame-retardant materials. While EPS show significant fire-safety potential, their compositional complexity requires a clear understanding of fire performance. The primary objective of this research is to elucidate how key EPS components, such as proteins (PN), polysaccharides (PS), lipids (LP), and humic-like substances (HS), govern thermal decomposition and flammability. Thermogravimetric analysis reveals that PN and HS have higher activation energies than those of other components, enhancing EPS thermal stability. PS yield the highest char residue (48.7% at 900 °C), while PN achieve the highest graphitisation degree, highlighting their crucial roles in char formation of EPS. Pyrolysis gas analysis indicates that PN and HS are main sources of nitrogenous compounds, diluting oxygen. Moreover, flammability tests show PS have the lowest peak heat release rate (29.7 W/g), underlining the important role in increasing flame-retardancy of EPS. However, TGA-FTIR analysis indicates lipid as a primary source of combustible gases likely due to their hydrocarbon chains. This study provides valuable insight into the role of major EPS components in the flame-retardant properties and suggest a sustainable approach to enhance flame retardancy through targeted component optimisation.