Nitrate and nitrite reduction at high pH in a cementitious environment by a microbial microcosm

Abstract

The possible release of oxyanions, such as nitrate, from radioactive waste repositories may influence redoxconditions of the near field environment and thus promote mobility of some redox sensitive radionuclides. The fate of dissolved oxyanions will be significantly conditioned by microbial activities, if present in the aqueous interstitial phase of a waste cell. This study investigates microbial nitrate reduction in a cementitious environment. A consortium of microorganisms was used, an inoculum prepared with sediments collected from a former lime works site, characterized by a pH of pore water of 11-12. The biomass was acclimated to cement leachate supplemented with nitrate, acetate and yeast extract. According to experiments performed in closed and in dynamic systems, the microbial consortium was adapted to reduce nitrate and nitrite in a cementitious, anaerobic environment (pH 11, with and without hardened cement paste and leachate). Although, nitrite accumulation was observed in close system and temporally in dynamic system. The rate of nitrate reduction was between 0.12 and 0.75 mM/h with incoming nitrate concentrations between 6 and 48 mM, respectively. The microorganism diversity and the biofilm present on the hardened cement paste helped maintain microbial activity in all of the conditions simulating cementitious environments.

Influence of Hydrogen Electron Donor, Alkaline pH, and High Nitrate Concentrations on Microbial Denitrification: A Review

“…Therefore, during the denitrification with acetate, the pH may acidify or alkalinize depending on whether the initial pH is higher or lower than 10. This pattern is reported in the literature as “self-acidification” at alkaline pH [23,57,104] and “self-alkalinization” at acidic pH [58,109].…”

Nitrate and nitrite reduction activity of activated sludge microcosm in a highly alkaline environment with solid cementitious material

“…the bio mass undergoes cell decay leading to residual dead cells (Laspidou and Rittmann, 2002). The nitrate reduction into nitrite without acetate oxidation has been observed in previous work in the presence of cement paste (Rafrafi et al, 2017;Durban et al, 2018).…”

“…The nitrate reduction to nitrite can produce a drop of pH by producing protons (reaction 2), while nitrite reduction would tend to consume protons (reaction 3). Nitrate reduction leads to a pH decrease (reaction 1) due to "self acidification" phenomenon controlled by carbonate equilibrium (Rafrafi et al, 2017;Durban et al, 2018;Albina et al, 2019):…”

Microbial Degradation of Citric Acid in Low Level Radioactive Waste Disposal: Impact on Biomineralization Reactions

“…Research regarding anaerobic microbial metabolism at high pH has been gaining momentum in recent years, especially in context of cementitious repositories where the impacts of microbial colonization are considered significant ( Williamson et al, 2013 , 2014 , 2015 ; Bassil et al, 2015a , b ; Charles et al, 2015 ; Rout et al, 2015a , b ; Durban et al, 2018 ; Nixon et al, 2018 ; Mijnendonckx et al, 2020 ). Previous work has confirmed anaerobes will colonize wastes; metabolizing the waste components by fermentation or a cascade of terminal electron accepting processes ( Rizoulis et al, 2012 ).…”