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.

This study investigates the influence of extracellular polymeric substances (EPS), recovered from wastewater sludge, on the flame-retardant and mechanical properties of wool-based fibreboards. The thermal properties of wool, resin, and EPS were analysed using thermogravimetric analysis and differential scanning calorimetry to determine manufacturing parameters and assess their impact on the thermal decomposition of the fibreboards. A specialised fibreboard manufacturing setup, incorporating a drum mixer, tube blender, and hot press, was developed to fabricate the composite boards. Results indicate that increasing the hot-pressing time enhances both flexural and internal bond strength. The incorporation of EPS significantly improves the internal bond strength compared to fibreboards without the biopolymer. Moreover, the combined effects of wool and EPS promote effective char formation and lead to a V-0 rating, showing self-extinguishing behaviour in vertical burn tests. Cone calorimeter analysis reveals that while EPS contributes to a reduction in the heat release rate, its effect reaches a saturation point. However, the fire growth index, along with barrier and protective effect values, demonstrates that EPS effectively mitigates fire spread and propagation. These findings highlight the potential of wastewater-derived EPS as a sustainable additive for enhancing the fire resistance and mechanical integrity of wool-based fibreboards.

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.