The Immobilization Effects And Mechanism Of Pb,Cd And Cu By The Inoculation Of Organic Phosphorus-degrading Bacteria(OPDB) In Acidic Soil

In this study,the organic phosphorus-degrading bacteria?OPDB?and rapeseed dregs were applied to acidic soil contaminated by lead,cadmium and copper.The immobilization effect and mechanism of inoculation organic phosphorus-degrading bacterial?OPDB?on heavy metals in acid soil was was examined.The OPDB used in this experiment was?Serratia marcescens?OPDB3-6-1 which has a high phosphorus-resolving capacity of167.62 mg/L,and the pH of the medium increased from 7 to 8.95 in the process of degrading organic phosphorus.OPDB3-6-1 grew well at the condition of 400 mg/L Pb²⁺,100 mg/LCd²⁺,and 200 mg/L Cu²⁺.At the same time,OPDB3-6-1 can tolerance to various antibiotics and can secrete indole acetic acid IAA.The strain has a high activity of ACC deaminase,and it also has the growth promoting effect on plant.OPDB3-6-1 and rapeseed dregs were added to acidic soil contaminated by lead,cadmium and copper with different gradients?three high,medium and low gradients?,and the changes of heavy metals fraction were tested after each repair cycle for 30 days.Experimental studies have shown that in Pb-treated soils,the concentration of Pb is 200mg/kg,600 mg/kg,and 1200 mg/kg,after the addition of rapeseed dregs and OPDB3-6-1,the acid extractable fraction decreased from the 14.37.%,19.97%,34.15% to 4.90%,7.43%,10.46%;and the residual fraction increased from 2.89%,11.55%,10.53% to 8.76%,17.37%,23.76%;after the second addition of OPDB3-6-1,the residue fraction has risen to 11.37%,28.12%,and 28.14%.In the contaminated soil with Cd,and the Cd concentration was 1,5,20 mg/kg,respectively.After the first remediation,the acid extraction fraction was reduced from the 36.80%,37.39%,43.39%to 18.46%,20.08% and 33.56%,respectively,and the residual fraction increased from 3.55%,5.41%,1.31%to 13.1%,7.59%,8.89%;after the second remediation,the residual state increased to 19.94%,12.84%,19.20%.In the Cu-contaminated soil,the initial water-soluble fraction decreased from initial 5.17%,2.25%,3.20%to 1.81%,0.37%,and 1.68%,and the residual fraction increased from the initial 5.67%,5.68%,and 3.72% to 10.2%.10.99%,5.59%,the residue fraction increased to 24.52%,16.76%,and 13.07% after the second addition.The immobilization effect of the composite pollution was also significant.After the second round of bacteria?60^th day?,the changes of soil pH and soil nutrients were as follows:the pH of all gradient heavy metal contaminated soils increased significantly after amendment,the maximum increase was 4.5-6.1,and it has a significant effect on the acid soil.At the same time,the increase of soil enzyme activity,cation exchange capacity and other parameters indicates a significant increase in soil activity.The immobilization mechanism of OPDB3-6-1 on heavy metals was explored.The adsorption and precipitation efficiency experiments of Pb,Cd and Cu with different concentration gradients show that OPDB3-6-1 can quickly remove metal ions in solution within 1 h,and the best adsorption rate of Cu?concentration:200 mg/L?can reach 97%,and the precipitation rate of Pb?concentration of 200mg/L?is the best,reaching 73%.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 P=O,P-OH,PO₄^3-,and C-O 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 3-6-1 with organic phosphorus compounds may have good application prospects in heavy metal pollution control and acid soil improvement in the future.