Reactor kinetics evaluation and performance investigation of a long-term operated UASB-anammox mixed culture process

To optimize the operation and know the relationships between operation and potential capability of UASB-anammox mixed culture process, reactor kinetic models were conducted and the potential nitrogen conversion rates were estimated. Total nitrogen (TN), NH4+-N and NO2--N removal efficiency were simulated and predicted by modified Stovere-Kincannon model, Monod model, First-order model and Grau second-order substrate removal models. The nitrogen gas production rate was also evaluated by Van der meer and heertjes model. During the process, the nitrogen loading rate (NLR) was increased from 0.93 to 7.34 g L^-1 d^-1 following the substrate increased from 280 to 462 mg N L^-1 and hydraulic residence times (HRT) decreased from 24 h to 1.5 h, the highest achieved removal efficiency of NH4+-N, NO2--N and TN were 99, 95 and 90%, respectively. Simulation results proved that the Modified Stover-Kincannon model and the Grau second-order model were the most appropriate models with prospected maximum TN removal rate U_max and saturation value constant K_B were 3.33 and 4.03 g N L^-1 d^-1, respectively. Validation of the linearity between the experimental data and predicted values of kinetics illustrated the two models appropriately described the kinetic behavior of UASB-anammox mixed culture. The reactor kinetic evaluation proved valuable information for guiding or optimizing the operation condition.