Abstract
AbstractUnder the alkaline conditions expected in an intermediate-level waste repository, cellulosic material will undergo chemical hydrolysis. This will produce hydrolysis products, some of which can form soluble complexes with some radionuclides. Analyses of samples containing autoclaved tissue and cotton wool incubated in a saturated solution of Ca(OH)2 ( pH > 12) confirmed previous reports that isosaccharinic acid (ISA) is produced from these cellulose polymers at high pH. However, when inoculated with a sediment sample from a hyperalkaline site contaminated with lime-kiln waste, microbial activity was implicated in the enzymatic hydrolysis of cellulose and the subsequent production of acetate. This in turn led to acidification of the microcosms and a marked decrease in ISA production from the abiotic alkali hydrolysis of cellulose. DNA analyses of microbial communities present in the microcosms further support the hypothesis that bacterial activities can have a controlling influence on the formation of organic acids, including ISA, via an interplay between direct and indirect mechanisms. These and previous results imply that microorganisms could have a role in attenuating the mobility of some radionuclides in and around a geological disposal facility, via either the direct biodegradation of ISA or by catalysing cellulose fermentation and therefore preventing the formation of ISA.
Highlights
CELLULOSE is a polymer of 100–14,000 glucose units linked by β-1,4 glycosidic bonds and is the main component of plant cell walls
Studies have shown that the rate and extent of cellulose hydrolysis under alkaline conditions is dependent on a number of factors, including the starting pH, temperature and the degree of polymerization of the cellulose (Van Loon and Glaus, 1997; Van Loon et al, 1999; Pavasars et al, 2003; Glaus and Van Loon, 2008)
Previous work by our group has shown that alkaliphilic bacteria present in a sediment from a legacy lime-working site, were able to utilize isosaccharinic acid (ISA) as an electron donor for the reduction of a number of electron acceptors at pH 10 (Bassil et al, 2014). The aim of this present work is to test the ability of the bacteria present in a similar sediment to survive the initial hyperalkaline pH that is expected in an intermediate-level waste (ILW)-geological disposal facility (GDF) and to (1) study their ability to degrade cellulosic material at high pH, and (2) control the biogeochemical fate of cellulose degradation products under anaerobic conditions
Summary
CELLULOSE is a polymer of 100–14,000 glucose units linked by β-1,4 glycosidic bonds and is the main component of plant cell walls. Cellulose polymers are oriented in parallel and form highly ordered, insoluble crystalline domains interspersed by Previous studies have shown that hyperalkaline conditions ( pH 12–13) will dominate after resaturation of an ILW-GDF with groundwater, due to the extensive use of cement (Berner, 1992). Under these hyperalkaline conditions, abiotic hydrolysis of the cellulose present in ILW will. Take place, leading to the formation of watersoluble low molecular-weight compounds, in particular ISA (Glaus et al, 1999). Native cellulose (exemplified by cotton wool) has a greater degree of polymerization and a smaller fraction of reducing end groups than treated cellulose (e.g. tissue) and the rate and extent of hydrolysis of cotton wool is less than that of tissue
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