Textile-Waste-Derived Biofuel Pellets for Coal Substitution: Combustion Emissions, Ash Characterization, Life Cycle of Carbon, and Economic Assessment

The increasing generation of textile cotton waste (TCW) and textile wastewater sludge (TWS) presents significant environmental management challenges. This study evaluates the conversion of TCW and TWS into biofuel pellets for waste recovery and coal substitution. Pellets were prepared at TWS ratios of 20:80, 40:60, 60:40, and 80:20 and assessed through combustion emission analysis, ash characterization, cradle-to-gate carbon assessment, and equal-energy cost comparison with imported bituminous coal. Increasing the TWS fraction prolonged combustion duration and increased SO2 and NOx emissions; however, all oxygen-normalized emissions remained within Sindh Environmental Quality Standards (SEQS) limits under the tested conditions. The 20:80 blend exhibited the lowest emission factors, with CO, SO2, NOx, and CO2 emissions of 1.03 g kg−1, 3.81 g kg−1, 1.57 g kg−1, and 1.42 kg kg−1, respectively. Ash analysis showed that Cd and Pb were not detected, while measured heavy-metal concentrations remained below U.S. EPA regulatory limits and relevant EU limit values. The 20:80 pellet achieved a cradle-to-gate carbon intensity of 6.6 g CO2e MJ−1, approximately 59% lower than upstream coal production. Equal-energy fuel-cost savings relative to imported coal were 37.6% for the binder-based 20:80 pellet and 83.1% for the binder-free 40:60 pellet. Overall, the results indicate that TCW–TWS pellets, particularly those containing 20–40% TWS, can support textile waste utilization and partial coal substitution while reducing fuel costs.