The immobilization effects on Pb, Cd and Cu by the inoculation of organic phosphorus-degrading bacteria (OPDB) with rapeseed dregs in acidic soil

Thirty-five organic phosphorus-degrading bacterial (OPDB) strains were screened from tailing-waste-contaminated soil. OPDB3-6-1 was selected based on its high ability to decompose organic phosphorus compounds and tolerance for heavy metals. OPDB3-6-1 was identified as Serratia marcescens by 16 s rDNA analysis. The immobilization effects of OPDB3-6-1 along with organic phosphorus compounds (rapeseed dregs) were examined in the remediation of heavy-metals-contaminated acidic soil. The results showed that inoculation of OPDB3-6-1 with rapeseed dregs in acidic heavy-metals-contaminated soil significantly reduced the bioavailability of Pb, Cd and Cu. In addition, the soil pH increased markedly, whereas the concentration of available phosphorus decreased over time. The reason may be that the phosphates released by OPDB3-6-1 reacted with the heavy metals in the soil. Furthermore, the mechanisms of the heavy metal immobilization by OPDB3-6-1 were investigated in this work. The data showed that OPDB3-6-1 could absorb heavy metals and its metabolites could precipitate heavy metals. Additionally, the bioprecipitation of each heavy metal was analyzed by X-ray diffraction (XRD), and the data showed that the bioprecipitations were mainly attributed to basic cupric chloride (Cu4(OH)6Cl2), cadmium carbonate (CdCO3), and pyromorphite (Pb5(PO4)3Cl). Moreover, the mechanisms of bio-adsorption were investigated by Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM). We found that PO, P-OH, PO43−, and CO played an important role in the adsorption of heavy metals. Overall, the mechanisms for heavy metal immobilization mainly involve bio-adsorption and bioprecipitation, and the inoculation of heavy metal tolerant OPDB with organic phosphorus compounds may have good application prospects in heavy metal pollution control and acid soil improvement in the future.