Long-term storage conditions for carriers with denitrifying biomass of the fluidized, methanol-fed denitrification reactor of the Montreal Biodome, and the impact on denitrifying activity and bacterial population

The Montreal Biodome has a denitrification system to stabilize the nitrate concentration in its 3 million liter seawater aquarium. However, this microbial process has failed periodically due to various technical problems. The system can take several weeks to recover its full denitrification capacity. In order to provide the denitrification system with a backup of active biomass, different freezing conditions for the denitrifying biomass were tested. The biomass was conserved for 1 week–17 months at −20 °C with and without glycerol or at −80 °C with and without glycerol, and the denitrifying activity was tested in batch culture for 140 h periods at various intervals. Our results showed that glycerol was required for fast recovery of the microbial communityʹs denitrifying activity. The −20 °C and −80 °C conservation temperatures with glycerol gave similar results although there was a short period of nitrite accumulation in the −20 °C sample. There were no substantial changes in the microbial community of any of the frozen samples after 17 months of conservation as monitored by denaturing gradient gel electrophoresis. This is the first report on the long-term conservation of a complex denitrifying population by freezing.