Miscanthus phytotechnology of Cu- or Zn-spiked soils supported by contaminated Miscanthus biochar—is this a viable option for valorization?

Different agricultural practices can be beneficial in Miscanthus × giganteus (M × g) phytotechnology applied to post-military and post-mining lands. However, only limited research has focused on supportive treatments using biochar produced from M × g waste. Indeed, when M × g phytotechnology is applied to contaminated soil, the biochar produced through the pyrolysis of the obtained biomass is contaminated, raising concerns about its further application. The current study tested the use of biochar produced from M × g roots cultivated long-term in slightly contaminated soil in the M × g phytotechnology of Cu- or Zn-spiked soils which is important for finding the solution toward valorization of the contaminated biomass. Two biochar doses (1.67 and 5.00%) were evaluated with varying levels of Cu (200 to 416 mg kg⁻¹) or Zn (202 to 580 mg kg⁻¹) concentrations in the soils. This study revealed a beneficial influence of biochar on M × g development, specifically by increasing the plant height and aboveground biomass by up to 20.4 and 115%, respectively. However, the root dry weight increased by 31.8% only at the highest application rate of biochar. The option for valorization of the contaminated biochar in the next phytoremediation process applied to soil contaminated more than the biochar itself was tested. The finding showed the positive influence of biochar on the M × g phytoremediation metrics such as tolerance index, bioconcentration factor, translocation factor, and comprehensive bioconcentration index which ensured the perspective of the proposed approach in the implementation of post-remediation management practice.