Advancing safe bioenergy production from cadmium-contaminated sweet sorghum through mild synergistic pretreatment

Phytoremediation is an eco-friendly and cost-effective method for treating cadmium (Cd)-contaminated soil. However, safe disposal of harvested hyperaccumulators remains scarce. Herein, a mild synergistic pretreatment combining dilute acid and alkali pretreatment was developed for safe biorefining of the Cd-containing sweet sorghum, and Cd was centrally extracted into the acid pretreatment liquid in the first step. The results showed that the synergistic pretreatment was more effective in removing Cd from the biomass and overcoming biomass recalcitrance. During the synergistic pretreatment, the Cd concentration in biomass dramatically decreased from 4.03 to 0.00626 mg/kg, and a considerable amount of lignin and hemicelluloses in biomass was removed, facilitating enzymatic saccharification and safe bioenergy production. The optimal conditions of the synergistic pretreatment resulted in a total sugar yield of 81.6 wt %, which was 4.7-fold higher than that of the original biomass. This strategy holds promise for reducing the cost of industrial saccharification and is a valuable inspiration for the safe handling and resource utilization of Cd-containing biomass.