Uranium compounds are toxic and radioactive. Its poisonous properties can be fatal. So, it is necessary to prevent its excessive entry into nature due to uranium's chemical toxicity and radioactivity. Waste from industrial-nuclear centers also has different amounts of uranium; therefore, the removal of this element from the effluent of these centers is essential. On the other hand, due to the importance and limited resources, uranium recovery from waste has economic value. In the present study, the Response Surface Method (RSM) based on the central composite design was used to evaluate and optimize different parameters affecting the bioremediation process of Shewanella RCRI7 in real waste. The proposed second-order model with a correlation coefficient R2 = 0.94 appropriately predicted the experimental data and the maximum uranium reduction efficiency by Shewanella RCRI7 under optimal conditions (pH = 5.7-6.5, Temperature 26.63 °C and Time 117 hours) was estimated to be about 98%. In the next step to interact between the variables, three-dimensional procedures with pH and temperature; temperature and time; pH and time interactions were obtained; finally, the uranium reduction in real effluent was investigated by XRD and spectrophotometric methods. Based on the results, Shewanella RCRI7 is determined as a valuable candidate for uranium bioreduction processes in the determined industrial wastewater. On the other hand, using the response surface methodology can provide a comprehensive understanding of the process, the mechanism of uranium bioremediation by Shewanella RCRI7, and the theoretical support for this process.
Native Shewanella sp. RCRI7 is recently counted as an operative bacterium in the uranium bioreduction. The aim of this study was to investigate the effect of uranium tolerance on the morphology and population of RCRI7 following its potential removal capacity in different time intervals. Accordingly, the bacterial growth and uranium removal kinetic were evaluated in aerobic TSB medium, uranium reducing condition (URC), aerobic uranium containing (AUC) and anaerobic uranium free (AUF) solutions, following evaluations of omcAB gene expressions. In addition, spectrophotometry analyses were performed in URC con rming the bioreduction mechanism.It was found that the bacteria can grow e ciently in the presence of 0.5 mM uranium anaerobically, unlike AUC and AUF solutions during 92 h incubation. The bacteria can kinetically remove a large amount of soluble uranium through adsorption pathway in the rst 12 h in URC. This occurs in a circumstance that the removal process keeps on increasing via reduction lane up to 84 h, when the most amount of uranium removal has been indicated. In 92 h, the adsorbed uranium containing unreduced and reduced (U (IV) monomeric), was released to the solution due to either the increased pH or bacterial death. In AUC and AUF, improper conditions lead to reduced bacterial size and increased bacterial aggregations, however, membrane vesicles produced by the bacteria avoid the uranium incrustation in AUC.
Native Shewanella sp. RCRI7 is recently counted as an operative bacterium in the uranium bioreduction. The aim of this study was to investigate the effect of uranium tolerance on the morphology and population of RCRI7 following its potential removal capacity in different time intervals. Accordingly, the bacterial growth and uranium removal kinetic were evaluated in aerobic TSB medium, uranium reducing condition (URC), aerobic uranium containing (AUC) and anaerobic uranium free (AUF) solutions, following evaluations of omcAB gene expressions. In addition, spectrophotometry analyses were performed in URC confirming the bioreduction mechanism. It was found that the bacteria can grow efficiently in the presence of 0.5 mM uranium anaerobically, unlike AUC and AUF solutions during 92 h incubation. The bacteria can kinetically remove a large amount of soluble uranium through adsorption pathway in the first 12 h in URC. This occurs in a circumstance that the removal process keeps on increasing via reduction lane up to 84 h, when the most amount of uranium removal has been indicated. In 92 h, the adsorbed uranium containing unreduced and reduced (U (IV) monomeric), was released to the solution due to either the increased pH or bacterial death. In AUC and AUF, improper conditions lead to reduced bacterial size and increased bacterial aggregations, however, membrane vesicles produced by the bacteria avoid the uranium incrustation in AUC.
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