Combined mild chemical pretreatments for complete cadmium release and cellulosic ethanol co-production distinctive in wheat mutant straw†
Wheat is a major food crop providing substantial biomass straw applicable for heavy metal phytoremediation and cellulosic ethanol production. In this study, we observed that wheat mutant straw could accumulate a maximum cadmium (Cd) concentration of 8.29 µg g−1 dry straw, whereas wheat wild type (WT) contained Cd at a concentration of 6.43 µg g−1, while grown in soil pots supplied with 75 mg CdCl2 per kg soil. Due to the Cd accumulation, the wheat mutant and WT straws distinctively showed a reduced cellulose level and degree of polymerization (DP) with increased soluble sugar stock compared to the control (without Cd), which led to much improved cellulose surface accessibility for relatively higher biomass enzymatic saccharification and bioethanol production under various chemical pretreatments. Notably, compared to the one-step pretreatment of a strong alkali or acid, the two-step pretreatment of a mild alkali and acid could cause an effective wall polymer extraction for a complete Cd release and collection from the mature straw typical in the wheat mutant. Therefore, this study has demonstrated a green-like technology for Cd collection and cellulosic ethanol co-production by employing a mild chemical pretreatment. It has also suggested a potential biotechnology for Cd phytoremediation by selecting cell wall-altered mutants and transgenic crops.