Enhanced indigenous consortia for the remediation of uranium-contaminated groundwater by bioaugmentation: Reducing and phosphate-solubilizing consortia.

To investigate the strengthening effects and mechanisms of bioaugmentation on the microbial remediation of uranium-contaminated groundwater via bioreduction coupled to biomineralization, two exogenous microbial consortia with reducing and phosphate-solubilizing functions were screened and added to uranium-contaminated groundwater as the experimental groups (group B, reducing consortium added; group C, phosphate-solubilizing consortium added). ß-glycerophosphate (GP) was selected to stimulate the microbial community as the sole electron donor and phosphorus source. The results showed that bioaugmentation accelerated the consumption of GP and the proliferation of key functional microbes in groups B and C. In group B, Dysgonomonas, Clostridium_sensu_stricto_11 and Clostridium_sensu_stricto_13 were the main reducing bacteria, and Paenibacillus was the main phosphate-solubilizing bacteria. In group C, the microorganisms that solubilized phosphate were mainly unclassified_f_Enterobacteriaceae. Additionally, bioaugmentation promoted the formation of unattached precipitates and alleviated the inhibitory effect of cell surface precipitation on microbial metabolism. As a result, the formation rate of U-phosphate precipitates and the removal rates of aqueous U(VI) in both groups B and C were elevated significantly after bioaugmentation. The U(VI) removal rate was poor in the control group (group A, with only an indigenous consortium). Propionispora, Sporomusa and Clostridium_sensu_stricto_11 may have played an important role in the removal of uranium in group A. Furthermore, the addition of a reducing consortium promoted the reduction of U(VI) to U(IV), and immobilized uranium existed in the form of U(IV)-phosphate and U(VI)-phosphate precipitates in group B. In contrast, U was present mainly as U(VI)-phosphate precipitates in groups A and C. Overall, bioaugmentation with an exogenous consortium resulted in the rapid removal of uranium from groundwater and the formation of U-phosphate minerals and served as an effective strategy for improving the treatment of uranium-contaminated groundwater in situ.

[Efficiency and mechanism on reduction of U(VI) by sulfate reducing bacteria].

Under anaerobic conditions, the characteristics of sulfate reducing bacteria (SRB) were applied to reduce U(VI) under different temperature, pH values, U(VI) concentrations and coexisting ions. The results showed that the optimum reduction condition was the temperature 35 degrees C, pH 7.0 and U(VI) concentration 25 mg x L(-1). The maximum reduction capacity of SRB was 179.1 mg x g(-1). Mo(VI) or Ca2+ did not affect SRB on the reduction process of U(VI) under the concentration less than 5 g x L(-1), but they strongly inhibited the process under the concentration more than 20 g x L(-1). The main inhibition of Mo (VI) was physiological inhibition and the inhibition of Ca2+ was competitive inhibition through the stable complex formation, Ca-UO2-CO3. The results also showed that lag phase did not appear on the concentration of Ca2+ less than 5 g x L(-1), but the lag phase of 24 hours appeared on the concentration of Ca2+ more than 20 g x L(-1).