Control of nitratation in an oxygen-limited autotrophic nitrification/denitrification rotating biological contactor through disc immersion level variation

• Nitratation in an OLAND RBC could be controlled through the immersion level.
• 85–89% of the O2 input was directly absorbed during the air exposure of the discs.
• Process control strategies solely based on DO level did not seem to be effective.

With oxygen supply playing a crucial role in an oxygen-limited autotrophic nitrification/denitrification (OLAND) rotating biological contactor (RBC), its controlling factors were investigated in this study. Disc rotation speeds (1.8 and 3.6 rpm) showed no influence on the process performance of a lab-scale RBC, although abiotic experiments showed a significant effect on the oxygenation capacity. Estimations of the biological oxygen uptake rate revealed that 85–89% of the oxygen was absorbed by the microorganisms during the air exposure of the discs. Indeed, increasing the disc immersion (50 to 75–80%) could significantly suppress undesired nitratation, on the short and long term. The presented results demonstrated that nitratation could be controlled by the immersion level and revealed that oxygen control in an OLAND RBC should be predominantly based on the atmospheric exposure percentage of the discs.