Immobilization of lead contaminated groundwater and loess soil using microbial-induced carbonate precipitation or phosphate precipitation and exploration of its influencing mechanism
Although the exploitations of metal deposits in northwest China have accelerated economic development,improper disposal of lead(Pb)contained wastewater may lead to site pollution,posing the great threat to the ecological environment and human health.In this study,the immobilization experiments in lead contaminated groundwater and loess soil of microbial-induced carbonate precipitation(MICP)and microbial-induced phosphate precipitation(MIPP)were investigated.The results show that the urea-releasing ability of Sporosarcina pasteurii may result in a lower degree of urea hydrolysis under acidic conditions,the immobilization efficiency of Pb is only 10.82％,and the mineralization products PbCO3 and Pb3(CO3)2(OH)2 have low chemical stability;while Bacillus megaterium has great potential for phosphate-releasing ability in acidic condition,achieving the immobilization efficiency of over 80％.In addition,the mineralized product Pbs(PO4)3 Cl has high chemical stability,and the mineralized product identified by the microscopic test is a co-precipitation(Ca2Pb3(PO4)3C1 and Phosphate mineral)structure with bacteria as the nucleation site,reducing the probability of Pb2+re-migrating and diffusing to the environment.The immobilization experiments in lead contaminated loess soil show that Bacillus megaterium has a high immobilization efficiency and the occurrence form of lead is Fe-Mn oxides bound.Compared with the carbonate bound,it has higher chemical stability and lower ecotoxicity.
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