The Stability And Mechanism Of Remediation On Cd Contaminated Soil By Sulfate Reducing Bacteria And Phosphate Solubilizing Bacteria

Soil safety involves in all aspects of people's daily life,however,the pollution of heavy metal Cd is more and more obvious with the double promotion of over irrigation and industrial wastewater discharge.In this research,cadmium resistant bacteria were isolated to a strain of sulfate reducing bacteria 2-2-5a and a strain of phosphate solubilizing bacteria 4-5a-1,and the remediation efficiencies of only 2-2-5?Group S?,4-5a-1?Group P?and 2-2-5a&4-5a-1?Group SP?were discussed.The stability and mechanism of this study were as follows:1.2-2-5a and 4-5a-1 can both grow well in Cd contamination soil and the Group SP had advantages compared with other groups?P<0.05?,specially,the maximum remediation efficiency of Group SP was 14.42%or 20.28%more than that of Group S or Group P.2.In addition,the extraction Cd²⁺of Group SP by TCLP method was less than risk value?0.5mg/L?and it suggested that remedying Cd in soil by the both strains had more stability.Then,many kinds of leach liquor were used to verify the stabilities on pH,organic acids and saline solutions.The strong acid environment?pH 3-5?,citric acid and Ca²⁺solution could extract more Cd²⁺and damage to the stability,but the stability of remediation for Group SP in this restrict environment was 48.86%more than other groups.3.Under Cd stress,the bacterial growth of 2-2-5a,4-5a-1 and combined bacteria were inhibited.Interestingly,the maximum bacteria colonies in the growth of Group SP didn't only increase by 1-2 orders of magnitude per one milliliter,moderate pH in the medium,but sulfate reduction ability,phosphate solubilizing ability and immobilization rates also increased 9.23%,16.57%and 20.86%,relatively.4.For the immobilization of microbial remediation,adsorption and precipitates are two main process of microbial remediation.The adsorption efficiencies were low and similar for three groups.By FTIR analysis of adsorption products,C-H,C=O,-NH₃ and phosphoric groups on the cell surface took part in adsorption.While for formed precipitates,the efficiency of Group SP was higher 16.98%or 28.44%than that of Group S or Group P.By SEM-EDX analysis of precipitates,more metabolites of cells like sulfate and phosphate were contributed to the higher precipitating rates.5.The cell adsorptions were sensitive to acid environment?pH 3-5?,critic acid and Ca²⁺solution,however,the released Cd²⁺content of Group SP was less than that of Group S or Group P,so it illustrated that the adsorption was the unstable part in microbial remediation and the desorption was contributed to the main release of Cd²⁺in Cd contaminated soil,so compared with the normal biosorption,the bacterial precipitates is more potential for immobilizing Cd in the soil.