Recyclable cascading of arsenic phytoremediation and lead removal coupled with high bioethanol production using desirable rice straws

Abstract

Crop straws provide enormous lignocellulose residues convertible to biofuels, whereas Arsenic (As) and lead (Pb) pollute agricultural soil and water source. Hence, it becomes important to explore a compelling biomass process technology for both bioethanol production and trace metal remediation. In this study, we selected classic rice cultivars that distinctively accumulated As from 10.25 to 16.18 μg/g in their mature straws from the As-polluted farming soils, being up to 10-fold higher than those of the previously-reported rice straws and other crops. By performing various chemical pretreatments with the As-accumulated rice straws, this study sorted out that the optimal two-step 2%H2SO4 and 2%NaOH pretreatments could cause almost complete biomass enzymatic saccharification for high bioethanol production in all rice straws examined, along with a full As release for As recycling as potential high-value crystallized chemical. Furthermore, all remaining lignin-rich solid resides were finally examined to act as active biosorbent for Pb adsorption, with the optimal Pb adsorption conditions established (1 g/L adsorbent dose at pH6.0 and room temperature). Hence, this study has not only demonstrated a cascading-like strategy for efficient As and Pb remediation in agricultural soil and water source, but it has also provided a value-added approach for complete utilization of crop straws towards high bioethanol production.