Valorization of heavy metal enriched phytoremediation biomass using a deep eutectic solvent (DES)

Phytoremediation is an in situ environmentally friendly and economically feasible remediation technology to treat heavy metal contaminated soil. However, the obtained heavy metal enriched biomass is treated as hazardous waste and disposed of traditionally via incineration, posing risks of secondary pollution. In this work, we developed a novel DES-based pretreatment and metal extraction process to enable the valorization of phytoremediation biomass such as genetically modified poplar as the potential feedstock for biomass refining. The results showed that the DES (choline chloride/lactic acid) could remove around 98.3% Cd accumulated in poplar as well as a notable amount of lignin, resulting in a cellulose-rich pulp with trace heavy metals and Cu-containing lignin nanoparticles with a high phenolic hydroxyl content. Moreover, the electrochemical properties of this DES were analyzed. The excellent electrochemical stability and high conductivity of this DES enable its cleaning up via electrochemical deposition and recycling. Furthermore, this DES-based treatment technology has been demonstrated successfully for the hyperaccumulator Sedum alfredii, providing evidence for its wide applicability and potential for scaling-up.

Automated summary

Phytoremediation is a viable method for treating heavy metal contaminated soil, but the resulting biomass is hazardous waste that is typically incinerated, leading to secondary pollution. This study developed a novel DES-based pretreatment and metal extraction process to utilize the biomass obtained from phytoremediation as a renewable feedstock. The DES effectively removed 98.3% of Cd from genetically modified poplar and produced cellulose-rich pulp with trace heavy metals, as well as Cu-containing lignin nanoparticles. The electrochemical properties of the DES allowed for efficient cleaning and recycling. This DES-based treatment technology was also successfully applied to Sedum alfredii, demonstrating its broad applicability and potential for scaling-up.