DEVELOPMENT OF TWO-STAGE NITRIFICATION/DENITRIFICATION MODEL (TAIWAN EXTENSION ACTIVATED SLUDGE MODEL NO.1) FOR BNR PROCESS

In this study, an extended activated sludge model (or termed TaiWan Extended Activated sludge model, TWEA1) that considered the kinetics and stoichiometry of ammonia oxidizing bacteria (AOB, XAOB) and nitrite oxidizing bacteria (NOB, XNOB), denitrification of both nitrite (SNO2) and nitrate (SNO3) was established for biological nutrient removal process. Then the consistency between simulation and observed values of different soluble components in A 2 O process were compared to validate TWEA1. The success of modeling the two-stage nitrification/ denitrification behaviors was resulted from some extended kinetic equations considered in TWEA1: (1) the contribution and processes of heterotrophs (XH) which used different carbon sources to reduce SNO2 and SNO3 under aerobic or anoxic conditions, (2) the contribution and processes of phosphorus accumulating organism (XPAO) which reduce SNO2 and SNO3 under aerobic or anoxic condition, and (3) the contribution and two-stage nitrification processes of XAOB and XNOB which oxidized ammonia (SNH4) and SNO2 under aerobic condition. According to simulation, in anaerobic tank, SNO2 and SNO3 did vary significantly. XAOB and XNOB decreased due to lysis, their concentrations were 19.0 and 10.6 mg L -1 and their net growth rates (NGRs) were -2.4 and -1.8 mg L -1 d -1 , respectively. In anoxic tank, SNO2 and SNO3 decreased due to denitrification of XH and XPAO. XAOB and XNOB decreased due to lysis, their concentrations were 18.0 and 9.9 mg L -1 and their NGRs were -2.5 and -1.8 mg L -1 d -1 , respectively. In aerobic tank, SNO2 and SNO3 increased due to aerobic growth of XAOB and XNOB. XAOB and XNOB increased due to aerobic growth, their concentrations were 20.2 and 11.1 mg L -1 and their NGRs were 10.7 and 1.2 mg L -1 d -1 , respectively.