Co-combustion of multiple blends of coal, sewage sludge, and bamboo: thermal behaviors, kinetic evaluation, and heavy-metal migration

The co-combustion of sludge and coal in power plant boilers is widely employed to address waste-disposal challenges. Sludge, however, is characterized by its low calorific value and high heavy-metal content. This study demonstrates that incorporating bamboo into coal and sludge mixtures for ternary co-combustion can significantly improve combustion performance. Thermogravimetric experiments indicate that adding bamboo reduces the ignition temperature and accelerates the combustion rate. At a mass ratio of 95:5:5 (coal:sludge:bamboo), the comprehensive combustion characteristics are enhanced, and activation energy is reduced compared to coal alone. Ash analysis highlighted significant synergistic interactions during co-combustion. At 1000 °C, the concentrations of Cu, Zn, As, Cr, and Mn in the ash were elevated by 57.6%, 58.1%, 6.6%, 11.89%, and 3.6%, respectively, relative to combustion without bamboo. Thermodynamic equilibrium calculations combined with experimental data suggest that heavy metals are stabilized through the formation of stable compounds or encapsulation within inorganic matrices. This study provides theoretical guidance for cleaner combustion in power plants, promoting improved biomass utilization, enhanced fuel efficiency, and mitigation of heavy-metal emissions.