| Nitrate accumulation in closed systems where water changes is challenging and expensive can cause toxicity problems to marine life. At the Montreal Biodome, a denitrification unit was installed in 1998 in a 3,25 million litres closed circuit seawater mesocosm (Saint-Laurent Marin, SLM) but never reached its expected performance because of hydraulic and operational problems.; To study seawater denitrification at the Biodome, a pilot scale moving bed biofilm reactor (MBBR) was installed in the mesocosm. It was designed to limit dead mixing zones and biofilm thickness, and to prevent sulfate reduction. The performance of the MBBR for seawater denitrification was investigated at various C/N ratios, using continuous influent flow and methanol as a carbon source. The use of the pilot reactors as sequencing batch reactors (SBR) solved the sludge accumulation problem. Real-time control of the SBRs was also achieved with the software detection of the nitrate knee, a bending point in the oxidation-reduction potential trend. Controlling the batch duration with this method was effective at preventing sulfate reduction from occurring as the nitrate knee occurred at a residual nitrate concentration of about 10 mg N l-1. (Abstract shortened by UMI.)... |
