Regular articleUse of a continuous-flow bioreactor to evaluate nitrate reduction rate of Halomonas desiderata in cementitious environment relevant to nuclear waste deep repository

- Possible microbial denitrification at pH 10 in a cementitious environment.
- Cement leachate can provide some nutrients for sustaining H. desiderata activity.
- H. desiderata can colonise cementitious material.
- H. desiderata biofilms can promote the apparent microbial rate of denitrification.

The redox level of repositories can influence the mobility of the waste components stored in them (i.e. radionuclides) and thus the related safety assessments. Microbial activity is known to impact the control of redox reactions, the mechanisms and kinetics of which must be evaluated. This study investigates the denitrification rates of a model bacterium Halomonas desiderata (Hd) in cementitious environment with alkaline and anoxic conditions comparable to those found in radioactive waste repository cells. The growth and the total oxidized nitrogen (TON) reduction rates of Hd was determined in a continuous bioreactor with several feeding solutions with or without solid cement paste. Temporary nitrite accumulation and reduced denitrification rates are correlated with diminished bacterial growth. When the system was fed by optimal culture medium supplemented with acetate and nitrate, the TON reduction rates varied between 0.082 mM TON/h and 0.063 mM TON/h, depending on whether solid cement paste was present in the reactor or not. When the culture medium was replaced with pure cement leachate, the reaction rates increased to 0.137 mM TON/h with solid cement paste and dropped to 0.023 mM TON/h without. In these conditions at pH 10, solid cement paste had no negative influence on Hd activity.