The Impact of Biofilms upon Surfaces Relevant to an Intermediate Level Radioactive Waste Geological Disposal Facility under Simulated Near-Field Conditions

Abstract

Abstract:The ability of biofilms to form on a range of materials (cementious backfill (Nirex Reference Vault Backfill (NRVB)), graphite, and stainless steel) relevant to potential UK intermediate level radioactive waste (ILW) disposal concepts was investigated by exposing these surfaces to alkaliphilic flocs generated by mature biofilm communities. Flocs are aggregates of biofilm material that are able to act as a transport vector for the propagation of biofilms. In systems where biofilm formation was observed there was also a decrease in the sorption of isosaccharinic acids to the NRVB. The biofilms were composed of cells, extracellular DNA (eDNA), proteins, and lipids with a smaller polysaccharide fraction, which was biased towards mannopyranosyl linked carbohydrates. The same trend was seen with the graphite and stainless steel surfaces at these pH values, but in this case the biofilms associated with the stainless steel surfaces had a distinct eDNA basal layer that anchored the biofilm to the surface. At pH 13, no structured biofilm was observed, rather all the surfaces accumulated an indistinct organic layer composed of biofilm materials. This was particularly the case for the stainless steel coupons which accumulated relatively large quantities of eDNA. The results demonstrate that there is the potential for biofilm formation in an ILW-GDF provided an initiation source for the microbial biofilm is present. They also suggest that even when conditions are too harsh for biofilm formation, exposed surfaces may accumulate organic material such as eDNA.

The Impact of Alkaliphilic Biofilm Formation on the Release and Retention of Carbon Isotopes from Nuclear Reactor Graphite

“…The generation of eDNA is often associated with biofilm formation, in which it provides both a scaffold material as well as a potential source of nutrients 29 , 30 . In this study the eDNA formed the basal layer of the biofilm at both pH values, as previously observed at alkaline pH on virgin graphite 21 . This suggests that the simulated surface deposits investigated here did not alter biofilm initiation.…”

“…showed that emplaced cotton cellulose within a highly alkaline site provided not only a substrate for CDP generation, but also a surface on which biofilm could form, allowing a flocculate-forming CDP-degrading community to be sub-cultured 16 . These flocs have been shown to provide protection against alkaline pH values by creating internal low pH environments 20 and be able to facilitate biofilm formation on cementitious backfill material and a range of surfaces relevant to potential UK ILW disposal concepts 21 .…”

The evolution of alkaliphilic biofilm communities in response to extreme alkaline pH values

“…Biofilm formation allows microorganisms to control their immediate environment by generating physical and chemical gradients at the micron scale. This control may lead to ecological advantages including protection against external stressors (Davey & O'Toole, 2000) such as antibiotics (Hall & Mah, 2017), disinfectants (Muazu et al, 2017), and pH (Charles, Rout, Laws, et al, 2017). Through global industrial activity and the prevalence of acid mine drainage, acidophiles and acidophilic biofilms have received considerable research focus (Aliaga Goltsman et al, 2015; Huang et al, 2016; Jiao et al, 2011).…”

“…Flocculants (flocs) are a type of biofilm that is typically a free‐floating composite of biofilm material and microbial cells. These flocs survived by using the extracellular polymeric substance (EPS) to attenuate the internal pH experienced by the resident microbial community (Charles, Rout, Laws, et al, 2017).…”

Enhanced microbial degradation of irradiated cellulose under hyperalkaline conditions

“…For example, studies showed that microbes can survive and even thrive under the hyperalkaline conditions that are expected in a cementitious GDF by forming flocks and biofilms that shield them from the high pH (Charles et al . 2015 , 2017a , b , 2019 ). Microbes have been found recently to bloom in high doses of ionising radiation in a high-pH outdoor spent nuclear fuel storage pond at Sellafield, UK (Foster et al .…”