Activated Sludge Model No. 1 Model Research Articles

A modified Activated Sludge Model No. 3 (ASM3) with two-step nitrification–denitrification

A common limitation of the Activated Sludge Models (ASM) [Henze, M., Gujer, W., Mino, T., van Loosdrecht, M.C.M., 2000. Activated Sludge Models ASM1, ASM2, ASM2d, and ASM3. IWA Scientific and Technical Report No. 9. IWA Publishing, London, UK] is the representation of the nitrification dynamics as a single-step process and the consequent denitrification on nitrate alone. This generally acknowledged simplification may represent a serious limitation in specific applications where nitrites become important, either as a target final product or an unwanted intermediate. This paper proposes an enhancement to the basic ASM3 model, introducing a two-step model for the process nitrification and, consequently, considering denitrification on both nitrite and nitrate. After introducing the relevant process kinetics and adapting the stoichiometric matrix accordingly, the model implementation in the Matlab/Simulink™ platform is described with reference to the benchmark setting. To obtain a fast implementation, the process units (reaction tanks and secondary settler) have been implemented as DLLs linked to the Simulink blocks, whereas the model parameters and stoichiometric matrix remain accessible to the user. The new model is compared with the standard ASM3 and checked for consistency and mass conservation. It is also shown that with the default kinetic parameters nitrite may represent a considerable fraction of the nitrified effluent, thus revealing a design limitation in the benchmark sizing. In the last part, an optimization of the benchmark plant volumes has been attempted in order to minimize such violations, resulting in a moderate increase of the overall reaction volume. The pertinent software is freely available for research purposes.

Significance of denitrifying enzyme dynamics in biological nitrogen removal processes: a simulation study

Activated Sludge Model No. 1 (ASM1) was extended to include the enzyme kinetics of denitrifying bacteria switching between oxygen and nitrate as electron acceptors. The extended ASM1 (eASM1) model was applied to two different periodic process configurations, fed-batch and Biodenipho, commonly used for nitrogen removal from wastewater. Predictions of optimal unaerated volume fraction (UVF) by eASM1 were similar to those by ASM1 for both the fed-batch and Biodenipho processes. However, eASM1 predicted substantially longer optimal cycle lengths than ASM1 for both processes. Predictions of optimal UVF and cycle length for the Biodenipho process by eASM1 were closer to current operational values for the University of Florida Biodenipho process than predictions by ASM1.

Linearization of the activated sludge model ASM1 for fast and reliable predictions

In this paper a strategy is proposed to reduce the complexity of the activated sludge model no. 1 (ASM1) which describes the biotransformation processes in a common activated sludge process with N-removal. The key feature of the obtained reduced model is that it combines high predictive value (all state variables keep their biological interpretation) with very low computation time. Therefore, this model is a valuable tool in a risk assessment environment (designed for the evaluation of wastewater treatment plants facing stricter effluent norms) as well as in on-line (MPC) control strategies. The complexity reduction procedure consists of four steps. In the first step representative input/output data sets are generated by simulating the full ASM1 model. In the second step the ASM1 model is rewritten in state space format with linear approximations of the nonlinear (kinetic) terms. In the third step the unknown parameters in the linear terms are identified based on the generated input/output data. To reduce the amount of parameter sets that have to be identified (to cover the full operation range of the plant), a Multi-Model interpolation procedure is introduced as a last step.

Control of an alternating aerobic–anoxic activated sludge system — Part 2: optimization using a linearized model

Complex models, such as activated sludge model No. 1 (ASM1), have rarely been used in practice for process control or optimization. One major reason for this is the computational effort demanded by these models for both parameter estimation and simulation. Therefore, a linearized version of the ASM1 model is developed and applied to the control and optimization of a bench-scale alternating aerobic/anoxic activated sludge system. The model prediction was used to optimize the aeration time by manipulating t c (total cycle time) and f a (fraction of aeration cycle time) while meeting the permit requirement of the effluent ammonia concentration. The linear nature of the model facilitates its use for on-line calculations, and error feedback is used to counteract problems of model inaccuracy. The model was applied to two cases in which the influent compositions were either known currently or only the previous day's information was available. The average optimized f a was found to be 0.30 for the first case and 0.37 for the second case, when the maximum effluent NH 4 +–N concentration was set at 1 mg/l. The efficiency of nitrogen removal was 76% for both test cases since nitrate could almost completely be removed through adequate anoxic cycle ratios resulting from the f a optimization.