Nitrogen removal from wastewater with a low COD/N ratio at a low oxygen concentration

In the SBR cycle alternating aerobic and anaerobic phases occurred; in the aeration phase the dissolved oxygen (DO) concentration was below 0.7 mg O2/L. The low DO concentration did not inhibit ammonia oxidation-nitrification and the efficiency was ca. 96-98%. However, a relatively high COD concentration in the effluent was detected. The values of Km and Vmax, calculated from the Michaelis-Menten equation, were 43 mg N-NH4/L and 15.64 mg N-NH4/L h, respectively. Activated sludge production was almost stable (0.62-0.66 g MLVSS/g COD). A high net biomass production resulted from a low specific biomass decay rate of 0.0015 d−1.