also shows that the effluent NO3–N concentration of the
bioreactor decreased when the C/N ratio was increased from 3 to
10. Nitrate accumulated considerably at low C/N ratios because
of the lack of organic carbon sources for denitrification. Denitrifiers
utilized nitrate as electron acceptors for respiration, and organic
carbon as electron donors [20]. However, the NO3–N concentration
in the effluent at high organic carbon level did not increase signif-
icantly when the C/N ratio was 12. At high organic carbon levels,
heterotrophic bacteria are dominant over nitrifiers in the uptake
of oxygen, which leads to inhibition of nitrifiers.