Heterotrophic denitrification by mixed populations in nuclear waste repository context, effect of alkaline pH and high nitrate concentration

Author(s): Pierre Albina, Nadège Durban, Alexandra Bertron, Achim Albrecht, Jean-Charles Robinet and Benjamin Erable
Paper category: Proceedings
Book title: Proceedings of the Final Conference of RILEM 253-MCI Microorganisms-Cementitious Materials Interactions Volume I
Editor(s): Alexandra Bertron and Henk Jonkers
ISBN: 978-2-35158-207-7 (Set)
ISBN: 978-2-35158-209-1 (Volume1)
e-ISBN: 978-2-35158-206-0
Publisher: RILEM Publications SARL
Publication year: 2018
Pages: 267-276
Total Pages: 288
Language : English

Abstract: France envisages to dispose high and medium level long-lived radioactive wastes into a geological repository system constructed 500 meters deep into the clay-rich Callovo-Oxfordian rock formation [1]. After repository closure, water would percolate from the host rock, saturating the engineered zone and initiating lixiviation from repository structure and wastes. The structural material of the repository system, mainly concrete, will release hydroxide ions into the water, thus imposing an alkaline pH [2] [3]. The waste containers would release organic acids (such as acetate) and nitrate at different concentrations, into the water, after loss of waste container integrity. The comprehension of the fate of nitrate in the repository system is essential as nitrate could promote radionuclide mobility. Acetate and nitrate, the former released at low mM concentrations, the latter up to tens of mM, even molar concentrations depending on waste type [4][8][9], are potential substrates for heterotrophic denitrifying bacterial communities [5]. Examples of surviving bacterial communities have already been reported in a repository-comparable context [6]. Therefore, denitrifying bacteria have the potential to affect nitrate mass balance in the repository system.
The aim of this work was to assess bacteria capacity to survive and consume nitrate in a context applicable to a repository situation. It is known that, alkaline pH and high nitrate concentrations can severely inhibit bacterial denitrifying activity [7]. Therefore, two continuous flow reactors were used to acclimate bacteria to high pH or high nitrate concentrations. The culture medium was a cement leachate supplemented with 20 mM acetate and 10 mM nitrate. In the bioreactor acclimated to high nitrate concentration the concentration progressively increased to 780 mM. In the bioreactor acclimated to high pH, the maximal pH tested was pH 11.8. Results showed that bacteria were able to maintain denitrifying activity at nitrate concentrations of up to 200 mM or pH up to 10.9. Bacteria survival capacity has been demonstrated under conditions as extreme as 750 mM of nitrate or pH up to 11.8.

Online publication : 2018
Publication type : full_text
Public price (Euros) : 0.00

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