Improvement of cadmium immobilization in contaminated paddy soil by using ureolytic bacteria and rice straw

Cadmium (Cd) in paddy soil can be immobilized via microbially induced carbonate precipitation (MICP), but it poses a risk to the properties and eco-function of the soil. In this study, rice straw coupled with Sporosarcina pasteurii (S. pasteurii) was used to treat Cd-contaminated paddy soil with minimizing the detrimental effects of MICP. Results showed that the application of rice straw coupled with S. pasteurii reduced Cd bioavailability. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that Cd immobilization efficiency was increased in the rice straw coupled with S. pasteurii treatment via co-precipitating with CaCO₃. Moreover, rice straw coupled with S. pasteurii enhanced soil fertility and ecological functions as reflected by the high amount of alkaline hydrolysis nitrogen (AN) (14.9 %), available phosphorus (AP) (13.6 %), available potassium (AK) (60.0 %), catalase (9.95 %), dehydrogenase (736 %), and phosphatase (214 %). Further, the relative abundance of dominant phyla such as Proteobacteria and Firmicutes significantly increased when applying both rice straw coupled with S. pasteurii. The most significant environmental factors that affected the composition of the bacterial community were AP (41.2 %), phosphatase (34.2 %), and AK (8.60 %). In conclusion, using rice straw mixed with S. pasteurii is a promising application to treat Cd-contaminated paddy soil due to its positive effects on treating soil Cd as well as its ability to reduce the detrimental effects of the MICP process.