Assessing the potential of different biochars to support Miscanthus × giganteus phytoremediation in petroleum hydrocarbons-contaminated soil

Soil contamination by petroleum hydrocarbons (PHs) poses a persistent environmental challenge. This study evaluated the phytoremediation of Miscanthus × giganteus ( M×g ) in PHs-contaminated soil (0, 10, and 20 g kg −1 ) using a semi-controlled pot experiment. Biochars derived from M×g waste biomass (MB) and sewage sludge (SSB) were applied at 0, 3.5, and 7.0 % doses to assess the effects of these amendments on soil agrochemical properties, PHs degradation, total carbon (TC), microbial abundance, and plant growth parameters. Targeted biochars influenced soil and plant parameters, with SSB having a stronger impact. At a contamination level of 10 g PHs kg −1 , 3.5 % and 7 % SSB increased the TC by 47.5 % and 30.3 %, respectively, whereas no significant effect was observed at 20 g PHs kg −1 . Similarly, 3.5 % MB increased the TC by 58.7 % at a contamination level of 10 g PHs kg −1 . PHs contamination inhibited plant growth indicators by up to 75.2 %; however, SSB mitigated this effect more effectively than MB. At a contamination level of 20 g PHs kg −1 , SSB restored plant height, stem diameter, and root biomass up to control levels and simultaneously increased leaves and stems biomass by 71.5 % and 74.3 %, respectively. The incorporation of biochars did not influence PHs degradation rates in the presence or absence of plant vegetation. The detected shifts in microbial biomass were driven primarily by PHs degradation, while the presence of M×g had almost no effect on microbial parameters. Although targeted biochars minimally influenced microbial communities, SSB fostered greater microbial diversity. The results of the current study highlight the potential of biochars in M×g phytoremediation when applied to PHs-contaminated soil. Future research should explore microbial dynamics and nutrient cycling at specific biochar doses, considering broader PHs contamination levels, process cost-effectiveness, and the full cycle of the M×g biomass value chain. • Miscanthus developed satisfactory in the PH-spiked soil until 20 g kg −1 . • Sewage sludge biochar mitigated the contamination with an optimal dose of 3.5 %. • Miscanthus biochar was less effective in mitigating soil contamination with PHs. • During vegetation soil pH, P, and N content changed, K and S altered slightly. • Variation in TC, TOC, and TN contents were determined in biochar-amended soils.