Biochar immobilized Proteus mirabilis Ch8 to enhance the Cd phytoremediation potential of woody plant Robinia pseudoacacia L

Abstract

The resource-oriented utilization of agricultural solid wastes as biochar is eco-friendly and cost-effective, but the application of biochar for Cd-polluted soil remediation hindered by their efficiency and complicated field condition. This study used three types of raw materials i.e. oil tea (Camellia oleifera Abel) shell, reed straw, and urban sludge to prepare pyrolysis biochar. Meanwhile, a Cd highly resistant Proteus mirabilis Ch8 isolated from Robinia pseudoacacia L. rhizosphere was immobilized to form a biochar-bacteria composite for the remediation of Cd-polluted soil. The pyrolysis configurations and adsorption curves were studied and sludge biochar prepared at 700 °C was the most suitable for Cd adsorption which could be further accelerated to 79.97 mg g⁻¹ Cd adsorption concentration as sludge biochar-bacteria composite (CHB). After CHB treated the rhizosphere of R. pseudoacacia L. under Cd stress soil, it was shown that the CHB could synergistically (E-value > 0) enhance the Cd root enrichment level (BCF = 3.21), while soil Cd availability decreased by 78%, showing effective soil remediation potential. Further plant growth parameters indicated that plant biomass and photosynthesis level increased up to 2.25 and 2.34 folds compared to the untreated control. In addition, CHB largely improved the rhizosphere bacterial community diversity and functional species, with 13 types of rhizobia that might have N-fixing and growth promoting effects on plants. The study thoroughly explored how biochar interacts with microorganisms to improve Cd adsorption, enhance soil quality, and promote plant growth. By coupling biochar preparation configurations with enhanced Cd soil remediation efficiency, the study connects the utilization of waste biomass with the restoration of heavy metal. This highlights the potential of integrated biological and carbon-based technologies to address global environmental challenges.