DELIVERABLE 2.10 Microbial mobility in saturated bentonites of different density

Result code in IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F26722445%3A_____%2F18%3AN0000157" target="_blank" >RIV/26722445:_____/18:N0000157 - isvavai.cz</a>

Result on the web

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DOI - Digital Object Identifier

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Result language

angličtina

Original language name

DELIVERABLE 2.10 Microbial mobility in saturated bentonites of different density

Original language description

Indigenous bacteria are naturally present in bentonite materials to be used as an engineered barrier in deep geological repositories of nuclear waste. Their density is generally decreasing with the compactness of the bentonite, but they remain present even in densities above 2000 kg/m3 presumably in the form of spores characterized by unbelievable durability. Other factors, such as temperature or water availability do not limit the Gram-positive sporeforming bacteria predominating among indigenous bacteria as much as they do in the case of the non-spore-forming bacteria. Studies specifically focused on the spore-forming bacteria are thus highly needed. The second source of bacteria that may affect bentonite in deep geological repository is contamination from the surrounding environment, mostly pore water with predominating Gram-negative non-spore-forming bacteria. Moreover, bacteria will be inevitably introduced from the surface during construction and operation of the repository, before its final closure. The speed of penetration of allochthonous bacteria into the bentonite barrier is strongly dependent on the swelling pressure and composition of the clay material, on hydrogeological conditions and on the stability of the bentonite/host rock interface. Our study fulfilled two most important goals. First, we developed a reliable method for direct detection of bacterial presence (both viable and dead cells) in the bentonite, which has been missing. Our method is based on the extraction of bacteria from bentonite using density gradient centrifugation and their subsequent Live/Dead fluorescence staining. Although our method needs further optimization and testing of its general functionality on different bentonite types, we believe it will be very useful for future research of bacterial presence in various clay materials. Our second goal was to study microbial mobility within compacted BaM bentonite from Czechia of two different dry densities – 1400 kg/m3 and 1600 kg/m3. Fourteen sections of saturated bentonite samples differing in their distance from the source of natural bacterial community (Josef URL, Czechia) were inspected for the presence of bacteria. Viable cells were observed in each section of both bentonite densities tested. This finding indicates that bacteria are able to move through saturated bentonite of even higher dry density (1600 kg/m3) and thus higher swelling pressure of about 5 MPa. Czech BaM bentonite belongs to Ca-bentonites that might generally allow for better microbial mobility due to its physical properties, different from Na-bentonites. Based on previous studies, bacterial mobility in highly compacted Na-bentonite (≥ 1800 kg/m3) is very limited. Therefore, further tests are needed to reveal whether the surprisingly high bacterial mobility detected in our experiment was caused solely by the lower bentonite density used, or by the unique properties of BaM bentonite (or Ca-bentonites in general), or if our novel method is more sensitive than previously used methods.

Czech name

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Czech description

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Type

V_souhrn - Summary research report

CEP classification

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OECD FORD branch

20701 - Environmental and geological engineering, geotechnics

Project

Result was created during the realization of more than one project. More information in the Projects tab.

Continuities

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Publication year

2018

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Number of pages

47

Place of publication

Řež

Publisher/client name

Centrum výzkumu Řež, s.r.o.

Version

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