Effect of organic matter on nitrogen removal through the anammox process

In the anaerobic ammonium oxidation (anammox) process, the anammox bacterial activity is inhibited by high chemical oxygen demand (COD) contents. In this study, the effect of the COD/total nitrogen (TN) ratio and hydraulic retention time (HRT) on the efficiency of the anammox process in a fixed-bed reactor was assessed via experiments with increasing COD/TN ratios from 0 to 7.0 and different HRTs of 6, 9, and 12 hr. Felibendy cubes were used as the biomass carrier. The presence of organic compounds affects the performance of the treatment process, and the level of influence increases with the increase in influent COD. With COD greater than 300 mg/L, the anammox process was inhibited, TN efficiency was the lowest, and effluent water quality did not yield effluent standards. The kinetic parameters U_max (the maximum substrate removal rate constant) and K_B (the saturation constant) of the Stover-Kincannon model corresponding to the different COD/TN ratios were determined in this study. The kinetic parameter values of the ammonium removal process decreased gradually from U_max  = 0.685 g/L/day and K_B  = 0.846 g/L/day, for COD/TN = 0, to U_max  = 0.314 g/L/day and K_B  = 0.498 g/L/day, for COD/TN = 6. The kinetic parameter of the TN removal process also decreased gradually as the COD/TN ratio in wastewater increased gradually. This means that the anammox process was inhibited as much as high organic compounds. PRACTITIONER POINTS: The higher COD/TN ratios the more anammox activity is affected, especially COD/TN = 7.0 (COD = 350 mg/L). The tolerance threshold of anammox process about organic matter concentration is 300 mg/L as COD (COD/TN ratio <6). With the COD/TN ratios from 1.0 to 6.0, the values of U_max and K_B constants of Stover-Kincannon model for ammonium removal by Anammox process decrease gradually from 0.685 to 0.314 and from 0.846 to 0.498, respectively.