Dynamic responses of lactate-stimulated microbial communities in an excavated waste rock to water contents and oxic/anoxic conditions for biological Se immobilization
Excavated waste rocks generated during tunnel construction contain various minerals, metals and metalloids, such as As, Se, B, Pb, Cd, Cu and Zn, that are circumstantially mobile, due to the exposure of the rocks to water and the resulting solid-liquid interaction.  Indigenous microbial communities in the waste rocks were successfully activated to reduce Se with amendment of a substrate, lactate. When thinking of practical application, the redox condition control, for instance, by adjusting water content and air exposure is of importance. Employing the low water contents and atmospheric (oxic) conditions are desirable, because of the low environmental burden and low laboriousness for the immobilization treatment. However, very little is known about whether the lactate-stimulated microbial communities can adapt to reduce Se at the proper water contents and atmosphere compositions (i.e., oxic/anoxic phases) of the excavated waste rock slurries. The objective of this study was to investigate responses of the Se reduction activities and microbial communities to water contents of 40% and 50% and to oxic/anoxic conditions in batch incubations of the excavated waste rock slurries.