The performance of the bioreactor for TN removal at various DO
concentrations were also studied (Fig. 3); a maximum TN removal
efficiency of 78% was observed when the DO concentration was
2.5 mg/L. DO concentration of 3.5 mg/L was also acceptable when
a TN removal of 74% was achieved. DO concentration is the most
important factor for the extent of the denitrification process, the
dominant mechanism for TN removal [16]. Denitrification rates
rapidly dropped at high DO concentrations. An anoxic environment
was needed for denitrification [20]. DO concentrations higher than
0.5 mg/L could inhibit denitrification [21]. However, nitrification
could be enhanced when a high DO concentration generates
nitrates which are electron acceptors necessary for nitrogen
removal, and therefore DO concentrations that are below or exceed
the optimal may hinder TN removal.