Loading organic phosphorus-degrading bacteria enhanced biochar performance for heavy metals adsorption

Abstract

As a porous material, biochar has been endowed with high expectations to be the carrier for heavy metals-tolerant microorganism loading due to its excellent performance. Therefore, the biochar derived from green walnut husk was used in this study to load a screened heavy metal-tolerant organic phosphorus-degrading bacteria OPB3–6–1 for heavy metals remediation. The results suggested that biochar loaded with OPB3–6–1 (IOPB) exhibited a synergistic effect in adsorbing of Pb2+, Cu2+ and Cd2+, while IOPB500 (carrier prepared under 500℃ of pyrolysis temperature) obtained the highest adsorption potential as its adsorption capacities for Pb2+, Cu2+ and Cd2+ reached 591.0, 300.0 and 20.0 mg/g under a certain initial concentration, respectively. In addition, the carrier dosage, reaction temperature and pH posed different effects on IOPB500 in heavy metals adsorption, and the top adsorption capacity obtained under the condition of 1 g/L of dosage, 30℃ of reaction temperature and 6–7 of pH. The adsorption kinetics and isotherms suggested that monolayer chemical reaction dominated the whole adsorption process of IOPB500 for Pb2+, Cu2+ and Cd2+, while intra-particle diffusion process played a greater role in rate control. Compared with intracellular uptake, extracellular complexation accounted for the major contribution for Pb2+, Cu2+ and Cd2+ adsorption of OPB3–6–1, which facilitated the adsorption of heavy metals in IOPB since such functional groups as PO, P-OH and PO43- were detected in IOPB by FTIR. After applying IOPB500 into heavy metal contaminated soil, the exchangeable fraction of Pb2+, Cu2+ and Cd2+ decreased by 15.7%, 19.0% and 23.24%, while the residual content increased by 15.9%, 9.3% and 11.5%, respectively, thereby alleviated the toxicity and risks of heavy metals. Overall, the conclusion of this study proved the potential of biochar-bacteria coupled systems on heavy metal remediation applications.