Remediation of As and Cd contaminated sediment by biochars: Accompanied with the change of microbial community

As and Cd pollution in sediment has posed a potential threat to ecosystem owing to their high toxicity. Fixing heavy metals and transforming their speciation into stable forms can be a sustainable method. In this study, nine biomass feedstocks were pyrolyzed into biochars for immobilization of As and Cd in sediment, and the accompanied changes in the microbial community were analyzed to evaluate their effect on bioavailability. The heavy metal immobilization capacity of biochars in sediment were assessed by measuring the change of As and Cd concentrations in aqueous phases (overlying water (COW) and pore water (CPW)) and the leachate of Toxicity Characteristic Leaching Procedure (TCLP), and metal speciation after biochar treatment. The maximum reduction of As and Cd concentrations could reach 95% and 78% (COW), 73% and 59% (CPW), 81% and 37% (leachate), respectively, and the F1, F2, F3 fraction (bioavailable form) of As and Cd significantly decreased (up to 18.0%) in the biochar-treated sediments. The ACE (Abundance-based Coverage Estimator) and Shannon index results revealed that biochars efficiently enriched the microbial biodiversity and population in the sediment. Water hyacinths biochar (WHB) exhibited the better performance among all biochar samples mainly due to the abundant oxygen-containing functional groups on the surface and the higher O/C. The overall results highlighted the inhibition effects of biochar on heavy metal mobility and bioavailability, and helped to provide guidance for optimization of biochars for sediment remediation.