Comparison of Two Model Concepts for Simulation of Nitrogen Removal at a Full-Scale Biological Nutrient Removal Pilot Plant J. Makinia 1 ; K.-H. Rosenwinkel 2 ; and V. Spering 3 Abstract: The experimental studies conducted at the Hanover-Gümmerwald pilot wastewater treatment plant WWTP focused on minimizing nitrogen loads discharged during stormwater events. The data collected during the plant operation were used for a long-term process simulation. The aim of this study was to compare predictive capabilities of two different mechanistic models ASM2d and ASM3P in terms of nitrogen removal. The influent wastewater composition was generated using on-line measurements of only three parameters COD, N–NH 4 + , P–PO 4 3-  and the model predictions were primarily compared with on-line data concentrations of N – NH 4 + , N–NO 3 -  originating from the aerobic zone of the bioreactor. The simulation results confirmed the experimental data concerning the capabilities of the system for handling increased flows during stormwater events. The predicted peaks of N – NH 4 + at the line with the quadruple dry weather flow rate were normally exceeding 8 g N · m -3 similar to the observations, whereas no or minor peaks of N–NH 4 + were predicted for the line with the double dry weather flow rate. The relationships between ASM2d and ASM3P predictions for N–NH 4 + and N–NO 3 - were highly correlated r 2 =0.83–0.99 with the slopes remaining close to 1.0. Both models appear to be equally suitable for practical applications in common municipal WWTPs. DOI: 10.1061/ASCE0733-93722006132:4476 CE Database subject headings: Activated sludge; Calibration; Simulation; Nitrification; Stormwater management; Validation; Comparative studies. Introduction Mathematical modeling and computer simulation are considered to be valuable tools in various aspects of the wastewater treatment practice including optimization of the plant operation, planning and design of new facilities, as well as development of new treatment concepts. Currently, the most common approach to modeling biological nutrient removal activated sludge BNRAS systems is based on biokinetic mechanistic models, which are supposed to provide explanations for complex interactions occur- ring in the BNRAS systems. Different concepts can be formulated for the same processes. The classical examples are two activated sludge models: No. 1 ASM1 and No. 3 ASM3, developed by the Task Group of the International Water Association IWA; for- merly, IAWPRC and IAWQ and summarized by Henze et al. 2000. Although both models are capable of simulating the same biochemical transformations, such as carbon oxidation, nitrifica- tion, and denitrification, conceptual differences in the COD flow pattern exist between these two models. Due to a large number of applications in research and practice over the last 17 years, ASM1 is generally accepted as the state of the art Petersen et al. 2002, whereas ASM3 has not been extensively examined in full-scale wastewater treatment plants WWTPs so far Koch et al. 2000; Sahlstedt et al. 2003; Wichern et al. 2003. In spite of the con- ceptual differences between the two models, the writers of ASM3 claimed that these models might turn out to be equivalent Henze et al. 2000. In order to investigate this hypothesis, a comparative evaluation study was carried out using long-term operating data from a full-scale pilot plant located at the Gümmerwald WWTP in the city of Hanover Germany. The primary goal of experi- mental research conducted during the plant operation, described in detail by Seggelke 2002, was the examination of potential operating strategies for minimizing the nitrogen emission to meet the new German standards, i.e., N tot =13 gN·m -3 in a 2-h random sample. The pilot plant also performed enhanced biological phos- phorus removal EBPR and thus the use of “pure” ASM1 or “pure” ASM3 was not relevant in this case. Models describing the EBPR process had to be taken into account. For this purpose, ASM1 was extended to ASM2d Henze et al. 2000, whereas ASM3 was coupled with the EAWAG bio-P Module Rieger et al. 2001 and referred further to as ASM3P Gernaey et al. 2004. 1 Adjunct, Faculty of Civil and Environmental Engineering, Gdansk Univ. of Technology, ul. Narutowicza 11/12, 80-952 Gdansk, Poland. E-mail: jmakinia@pg.gda.pl 2 Professor and Head of the Institute, Institute for Sanitary Engineering and Waste Management, Univ. of Hanover, Welfengarten 1, D-30167 Hanover, Germany corresponding author. E-mail: rosenwinkel@ isah.uni-hannover.de 3 Research Assistant, Institute for Sanitary Engineering and Waste Management, Univ. of Hanover, Welfengarten 1, D-30167 Hanover, Germany. E-mail: spering@isah.uni-hannover.de Note. Discussion open until September 1, 2006. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and pos- sible publication on September 9, 2004; approved on August 16, 2005. This paper is part of the Journal of Environmental Engineering, Vol. 132, No. 4, April 1, 2006. ©ASCE, ISSN 0733-9372/2006/4-476–487/ $25.00.