Effect of dissolved oxygen on denitrification using polycaprolactone as both the organic carbon source and the biofilm carrier

• Aeration with 6 mg/L DO did not inhibit PCL-denitrifying process while 10 mg/L DO inhibit a little.
• Pre-treatment of excluding DO in wastewater could be avoided in PCL-denitrification.
• Aeration could accelerate the bio-degradation of PCL under denitrification environment.

Dissolved oxygen (DO) can inhibit the denitrifying process. Using polycaprolactone (PCL) as an organic carbon source and biofilm carrier (PCL-denitrifying process), an anoxic environment can be created to minimize the inhibition. This study investigates the effect of DO on the PCL-denitrifying process. Four DO conditions are established, ananoxic condition (group A, 0.44 ± 0.01 mg/L DO), a low DO condition (group B, 3.83 ± 0.22 mg/L DO), a moderate DO condition (group C, 6.12 ± 0.50 mg/L DO), and a high DO condition (group D, 10.45 ± 0.65 mg/L DO). This study demonstrates that the amount of released dissolved organic carbon is greater in the presence of DO compared to the anoxic condition. However, the amount of dissolved organic carbon released from PCL does not increase with an increase in DO. No significant differences in the nitrate nitrogen (NO3−–N) and total nitrogen (TN) removal efficiencies were between groups B and C. The NO3−–N and TN removal efficiencies in the group B and C were higher than those of group A and group D. The lowest NO3−–N and TN removal efficiencies were in the group D. These results indicate that the use of PCL as an organic carbon source and biofilm carrier can effectively minimize the inhibition of DO on the denitrifying process, although more than 10 mg/L DO in the water phase still inhibits this process to a certain degree.