Sustainable management of post-phytoremediation biomass

Abstract Organic and inorganic contaminants are entrained into environmental systems through natural and anthropogenic processes, such as mining activities, manufacturing, and waste disposal. In terrestrial and aquatic environments, the contaminant(s) remediation can be achieved by immobilization, thereby inhibiting their dispersal and bioavailability. Mobilization, through leaching and plant uptake, is another process of pollutant removal. Phytoremediation has attracted attention as an eco-friendly alternative for the remediation of contaminated environments. However, the safe management of post-phytoremediation contaminated biomass poses many practical challenges. Understanding the fate of the pollutants in the plants allows the estimation of the possible transfer of the contaminants to the food chain ascertain by-products or residues during biofuel production. Metal-enriched fractions could be used as a valuable source of novel catalysts or reusable materials. The safe conversion of biomass into energy may require sequestering contaminants at any step of the process, preferably upstream of the energy conversion or as a pre-treatment of plant biomass. Through gasification or pyrolysis of post-remediation biomass, bioenergy products (including syngas, oil, hydrogen gas, biochar, and hydrochar) can be used for heating and electricity generation. A comparative evaluation among pyrolysis, gasification, combustion, and liquefaction/fermentation processes for biofuel production from post-phytoremediation biomass suggests that pyrolysis is the strategy with the lowest transfer of toxic metals to the final products. This review presents critical discussions of the processes involved in phytoremediation of contaminated environments, the redistribution of contaminants within plant biomass, the sustainable management of post-phytoremediation biomass, and the unintended environmental consequences of phytoremediation.