The current research attempts to elucidate fundamental mechanistic correlation between the complex chemical architecture of wastewater-derived biopolymers – EPS (extracellular polymeric substances) and their inherent thermal properties for fire-safety applications. By integrating thermogravimetric-infrared spectroscopy with two-dimensional correlation spectroscopy, we resolve intricate mass-loss profiles into three pseudo-components (PCs), each characterised by kinetic signatures and functional group transformations. PC1 (150–350 °C, activation energy (AE) = 140–150 kJ/mol), is primarily governed by the degradation of polysaccharides and release of early-stage volatiles (H₂O, CO₂, CH₄, NH₃, and HNCO). PC2 (210–450 °C, AE = 160–175 kJ/mol), represent the transition stage dominated by proteinaceous and lipid cross-linking, which produces nitrogenous species essential for promoting condensed-phase char development. PC3 (290–600 °C, AE > 180 kJ/mol) corresponds to the decomposition of humic-like substances and subsequent aromatic condensation of stable residues. Furthermore, comparative analysis reveals that EPS extracted from activated sludge exhibits higher thermal stability and a significantly increased char yield (33.5 %) than aerobic counterpart, attributed to higher AE during the middle decomposition stage. The persistent detection of C-O-C/P–O–C and aromatic C=C vibrations up to 700 °C confirms the formation of a phosphorus-rich aromatic char structure. This multi-dimensional analytical framework moves beyond conventional TG-based pseudo-component fitting, providing high resolution interpretation of the sequential evolution of volatile species and early-stage charring mechanisms of EPS. ... Read more

Limited understanding of the thermal properties and flammability of extracellular polymeric substances (EPS) from municipal sludge has constrained their use in fire safety applications. This study investigates the thermal stability and flame retardancy of EPS derived from secondary sludge, waste sludge, and digested sludges. Comprehensive analyses of chemical composition, activation energy, char formation, and heat and gas release during pyrolysis and combustion reveal potential flame-retardant mechanisms. All EPS from different types of sludge can release both free-radical scavenging compounds and non-flammable gases during combustion to reduce fire propagation in the gas phase. In the condensed phase, EPS demonstrate their char-forming capability as a major flame-retardant mechanism to diminish heat release rate due to the presence of nitrogen, phosphorus, and sulfur elements. While nitrogen-based compounds in EPS contribute to flame-retardant mechanisms in both phases, phosphorus and sulfur mainly act in the condensed phase. Additionally, EPS from secondary sludge show the highest activation energy (372.3 kJ/mol) and ignite 24 s later than other EPS. Cone calorimeter tests confirm that EPS from secondary sludge have superior fire-resistant properties, with increased char contents (31.2 %) and enhanced thermal stability compared to other EPS. This study provides the first comprehensive assessment of EPS as eco-friendly flame retardants, advancing wastewater sludge valorisation and fire safety applications. ... Read more

Various methods for recovering extracellular polymeric substances (EPS)-based biomaterials from wastewater sludge exist. However, the relationships between extraction methods and properties of biomaterials have not been fully explored. In this study, the thermal properties, including activation energy (AE) and thermal decomposition mechanism, of EPS-based biomaterials extracted by different methods have been determined by thermogravimetric analysis integrated with the deconvolution method. Simultaneously, the chemical properties of these biomaterials, such as the extraction yield, chemical composition, and functional groups, have been monitored to clarify the influences of extraction methods. Notably, proteins and humic-like substances have been found as the major components to determine thermal stability and AE. Moreover, the physicochemical method shows significant effects on enhancing extraction yield and AE, with the NaOH and heat methods proving to be outstanding by delivering the highest AE of 300 kJ/mol and a substantial char formation of 24%. The results have demonstrated the significant impact of extraction methods on the thermal stability of EPS-based biomaterials. Moreover, this finding provides insights into the linkages between the properties of EPS-based biomaterials and extraction methods to guide the selection of appropriate extraction methods tailored to specific applications, including flame-resistant materials. ... Read more