Investigation of co-combustion characteristics of distillery sludge and sugar mill waste: kinetics, synergy, and ash characterization

The co-combustion characteristics and synergy of distillery effluent sludge (DES) and sugar mill waste (SMW) were studied by thermogravimetric (TG) analysis. TG data were used to evaluate the combustion indices, synergy, kinetic parameters, and heterogeneous reaction mechanisms. The blend D1S3 (25% DES and 75% SMW) exhibited optimal combustion parameters (C_i = 2.69 × 10⁻⁴% min⁻³, C_b = 1.34 × 10⁻⁶% min⁻⁴, and CCI = 13.02 × 10⁻⁷%² °C⁻³ min⁻²). Mixing DES with SMW resulted in a positive synergy that facilitated effective combustion owing to the presence of Fe, Ca, and Mg in DES, which served as catalysts during combustion. For D1S3, the apparent activation energy (^*E_a) calculated using FWO, KAS, and ST iso-conversional methods were 173.3, 172.4, and 172.7 kJ mol⁻¹, respectively. The master plots revealed that the combustion process was governed by the D1, D3, F2, and F3 solid-state kinetic models in different conversion (α) ranges for the wastes and their blends. Finally, the presence of alkaline and alkaline-earth elements (Na, K, Mg, and Ca) was confirmed through ash characterization. Thus, the ash can be considered a possible supplementary cementing material for end-use applications.