Simultaneous effect of organic carbon and ammonium on two-step nitrification within sequential batch reactor (SBR)

Abstract

Nitrification in biological wastewater treatment is a two-step process: first from ammonium to nitrite and then from nitrite to nitrate. This two-step nitrification process has been incorporated into different versions of International Water Association (IWA) activated sludge models (ASM), but numerical simulation on the combined inhibitory effect from organic carbon and nitrogen on the two-step nitrification process still seem not thoroughly enough, especially from process operation standpoint. In this study, the combined inhibitory effect from organic carbon and ammonium on two-step nitrification is simulated within a modified ASM1-based two-step nitrification framework. Specifically, the combined inhibitory effects from organic carbon and ammonium are comparably presented in two different mathematic forms: a traditional Monod type and a Logistic type. The two types of modified models are evaluated under two different SBR scenarios. The simulation results proved that both of the two mathematical forms show improvements in model prediction, with the Logistic-type inhibition form offers an even better model performance. This outcome suggests it is necessary to use appropriate model forms to reflect the combined inhibitory effects from organic carbon and ammonium on two-step nitrification modeling. However, the results of this study should not be interpreted as a holistic modeling approach, but an attempt to attract more in-depth studies on the two-step nitrification process from both mechanical and numerical perspectives so as to offer more accurate predictions and controls on nitrogen removals for the wastewater industry.