Unlocking bioenergy potential in heavy metal polluted soils: synergistic advanced solid-state fermentation and combustion for valorization of sweet sorghum.

backgroundA novel co-disposal strategy integrating advanced solid-state fermentation (ASSF) and combustion was proposed to address the dual challenges of safe utilization and value-added conversion of heavy metal-enriched sweet sorghum (Sorghum bicolor (L.) Moench) biomass from phytoremediation.

resultsControlled field experiments demonstrated that Cd, Pb, and Cu concentrations in sweet sorghum organs increased significantly with elevated soil metal levels, following distinct accumulation patterns: roots > stems > leaves > grains for Cd and Cu, versus roots > leaves > stems > grains for Pb. Despite high metal loads in stalks (up to 7.00 ± 0.85 mg/kg Cd, 19.51 ± 2.1 mg/kg Pb, and 44.06 ± 3.4 mg/kg Cu), ASSF performance was not significantly inhibited, achieving a sugar utilization rate of 96.69 ± 0.81% and an ethanol conversion efficiency of 91.8 ± 1.2%. Subsequent combustion of fermentation residues at optimized condition (900 °C) effectively concentrated heavy metals in specific byproducts: Cd and Pb were primarily enriched in fly ash, with concentrations of 63.3 ± 18.09 mg/kg and 799.84 ± 97.25 mg/kg, respectively, whereas Cu accumulated in bottom ash at a concentration of 238.60 ± 67.13 mg/kg. This partitioning enables targeted metals recovery from fly ash while permitting the safe reuse of bottom ash as a soil amendment to improve soil environment.

conclusionsOur findings provide a closed-loop solution linking phytoremediation, bioenergy production, and resource recovery and utilization, offering both technical and economic viability for sustainable management of heavy metal-contaminated farmland.