The effect of bacterial growth phase and culture concentration on U(VI) removal from aqueous solution

Abstract

Bacteria play a key role in controlling the mobility of contaminants, such as uranium (U), in the environment. Uranium could be sourced from disposed radioactive waste, derived either from surface disposal trenches for Low Level Waste (LLW) that, because of the waste type and disposal concept, would typically present acidic conditions (both aerobic and anaerobic), or from the geological disposal of LLW or Intermediate Level Waste (ILW) that, because of the waste type and the disposal concept, would typically present alkaline conditions (anaerobic only). In disposed radioactive waste, there could be variable amounts of cellulosic material. Bacterial cells may be living in a range of different growth phases, depending on the growth conditions and nutrients available at the time any waste-derived U migrated to the cells. A key knowledge gap to date has been the lack of a mechanistic understanding of how bacterial growth phases (exponential, stationary, and death phase) affect the ability of bacteria to remove U(VI) from solution. To address this, we first characterised the cells using potentiometric titrations to detect any differences in proton binding to proton active sites on Pseudomonas putida cells at each growth phase under aerobic conditions, or under anaerobic conditions favourable to U(IV) reoxidation. We then conducted batch U(VI) removal experiments with bacteria at each phase suspended in 1 and 10 ppm U aqueous solutions with the pH adjusted from 2-12 as well as with culture concentrations from 0.01-10 g/L, to *Manuscript Click here to download Manuscript: KenneyBacteriaPaper16082017.docx Click here to view linked References

A pilot study on the effect of desferrioxamine B on uranium VI precipitation and dissolution in pH 11.5, 0.1 M NaCl solutions

“…We first conducted control experiments with no DFOB added to reproduce the U VI precipitation observed in previous research at pH 11.5 and ionic strength of 0.1 M [13,14,33]. At equilibrium, we observed that only 4 to 5% of U VI was present in the solution after it was filtered through 0.2, 0.45 and 1 μm nylon filter membranes (Fig.…”

“…The aim of this pilot study was to study whether DFOB, a siderophore typically found in the environment, prevents the U VI precipitation in alkaline NaCl solutions observed during previous studies [13,14,33] and to determine the possible controls of concentration and reaction time. Three types of experiments were conducted: a control experiment, a precipitation inhibition experiment, and a dissolution experiment.…”

“…Two types of long-term tests were conducted, firstly the DFOB was added at the same time as U VI to see if the siderophore could prevent U VI from precipitating, and secondly U VI was precipitated from solution before then adding DFOB to see if the siderophore could dissolve the U VI . Previous studies of our group demonstrated significant precipitations of U-Na minerals from these solutions [13,14,33]. Samples were filtered through 0.2, 0.45 and 1 μm Whatman nylon filter membranes to get a constrain on the particle size.…”

A Preliminary Sorption Study of Uranium on MnO2 (Pyrolusite) in the Presence of Siderophore Desferrioxamine B—The Mechanism of a Ternary System

“…Siderophores, in particular, are not limited to iron as they have been shown to form complexes with various other environmentally significant metals, including copper, nickel, zinc, americium, plutonium, and uranium [21,22]. Metal mobility has been altered by siderophores in the environment disproportionately to their concentration, making them an overlooked key component to the fate of contaminants in the environment [23]. Desferrioxamine B (DFOB) is naturally biosynthesized by fungi and bacteria in many ecosystems as a linear siderophore with three bidentate hydroxamic acid functional groups and a terminal amine that plays a key role during environmental sorption (Figure 1) [24][25][26][27].…”