Microbial consortium loaded tannery solid waste biochar application causes immobilization of nonessential metals in field-grown sunflower

Tannery solid waste poses significant environmental challenges owing to its high metal content, especially Cr. Converting this waste into value-added byproduct <i>i.e.,</i> biochar offers a sustainable management approach to reducing the waste load on landfill sites and also guarding the nearby fauna, flora and water bodies. This study aimed to develop metal-resistant microbial consortium loaded biochar (MCLB) by inoculating tannery solid waste biochar (BC) with consortium of ten <i>Bacillus</i> and/or five <i>Trichoderma</i> strains and their effect was evaluated on the morphological and biochemical attributes of sunflowers including metals immobilization. The soil amendment with BC at 2% rate improved the shoot height, dry biomass, and chlorophyll content in sunflowers but not in higher doses. However, the application of MCLB even at its highest concentration <i>i.e.,</i> 10% dose showed a significant increase in shoot length (61.2%) and dry weight (656.9%) over BC only. The findings of metal bioavailability indicated that the application of MCLB having metal-resistant strains decreased the mobility of Cd, Cr, Cu, Ni, Pb and Zn into the sunflower tissues compared to BC. Moreover, MCLB enhanced the uptake of Fe and Mg which are beneficial to the plant. In addition to that, the results for phenolic and proline content demonstrated a considerable decrease by MCLB indicating less stress response as compared to BC. Therefore, these findings highlight the potential of MCLB as a sustainable soil amendment for improving the growth attributes of oil-yielding sunflower varieties by using tannery solid waste biochar while decreasing the uptake of nonessential metals. By pyrolyzing the tannery solid waste into biochar, this approach contributes to a circular economy and environmental remediation practices.