Differential effects of sewage sludge and food waste biochars on Miscanthus × giganteus phytostabilization on acidic brownfield soil

Brownfield sites, often characterized by deteriorated marginal land and contamination resulting from industrial or agricultural activities, pose significant environmental and land-use challenges. Miscanthus × giganteus ( M × g ) is known to exhibit phytoremediation potential in contaminated soils, particularly when combined with biochar amendments. This study assessed the influence of sewage sludge biochar (SSB) and food waste biochar (FWB) on the M × g phytoremediation process, plant productivity, and microbial activity when applied at rates of 3.5% and 7% to acidic brownfield soil in Všebořice, Czech Republic. Results revealed that biochar applications significantly increased soil pH, cation exchange capacity and water holding capacity relative to the control, with more pronounced effects at the higher application rate (increases of 11.61%, 7.38%, and 8.22% for SSB, and 10.40%, 4.55%, 27.06% for FWB respectively). The highest dose of SSB enhanced the availability of P and K and significantly increased the dry biomass yield of M × g , particularly in stems, reaching 2.15 times that of the control. In contrast, biochar amendments had limited impact on plant stress and microbial activity in soil. The uptake of Al and Fe into the above-ground biomass was minimal, confirming the phytostabilization mechanism of M × g application. Despite these benefits, the incorporation of Zn-contaminated FWB substantially increased Zn availability in the soil by 598% and 914% for the 3.5% and 7% doses, respectively. The study demonstrated the potential of using biochar to support M × g phytostabilization as a nature-based solution for brownfield revitalization. However, FWB posed risks of increased Zn availability and accumulation, emphasizing the need for careful selection of biochar sources in phytoremediation strategies.