ESEL Paper Review_20130908
By Hong Guo
Mail: hongguo@gist.ac.kr
Phone: (+82) (0)10 82276568
1, Title and Author
Title: A modified Activated Sludge Model No.3 (ASM) with Two-step nitrification-denitrification
Journal: Environmental Modelling &Softwaere
Authors:
Ilenia Ilacopozzi, Valentian Innocenti, Stefano Marsili-Libelli, Elisa betta Giusti
Department of systems and computers, University of Florence, Via, S. Marata, 3-50139 Firenze, Italy
2. Summary of Paper
? 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 relevance process kinetics and adapting the stoichiometric matrix accordingly, the model implementation in the MATLAB/Simullink platform is described with reference to the benchmark setting.
? 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 f the bench mark plant volumes has been attempted in order to minimize.
?
3. Results
Model Structure
? Comparison with the ASM3 model in the simulation benchmark
? By compare the two forms of oxidized nitrogen produced by the ASM3_2N model with the corresponding Nox-N of the ASM3 model showing that nitrite represents a considerable fraction of the effluent nitrogen. Further ASM3 tends to under estimate effluent nitrogen during high-load periods.
? As expected, most of the denitrification occurs in the anoxic tanks, but due to insufficient aeration a slight amount of denitrification may develop in the aerobic tanks too, during the high-load period as a result of the dissolved oxygen shortage
? As to the fate of nitrogen, the emergence of nitrogen bubbles is a well-known shortcoming, which may cause rising sludge in the secondary settler. This occurs whenever the concentration of N2
exceeds its saturation in the liquid phase, according to the Henry’s law
? As long as denirogen remains below this concentration, it remains in the liquid phase and no gas is produce. This fact is important in view of an input-output nitrogen mass balance. In all the simulations the N2 concentration consistently remains below the saturation limit, thus its balance can be limited to the liquid phase.
Sensitivity analysis of the second-step nitrification rate.
? By compare the two forms of oxidized nitrogen produced by the ASM3_2N model with the corresponding Nox-N of the ASM3 model showing that nitrite represents a considerable fraction of the effluent nitrogen. Further ASM3 tends to under estimate effluent nitrogen during high-load periods.
? As expected, most of the denitrification occurs in the anoxic tanks, but due to insufficient aeration a slight amount of denitrification may develop in the aerobic tanks too,during the high-load period as a result of the dissolved oxygen shortage
? As to the fate of dinitrogen, the emergence of nitrogen bubbles is a well-known shortcoming, which may cause rising sludge in the secondary settler. This occurs whenever the concentration of N2 exceeds its saturation in the liquid phase, according to the Henry’s law
? As long as dinitrogen remains below this concentration, it remains in the liquid phase and no gas is produce. This fact is important in view of an input-output nitrogen mass balance. In all the simulations the N2 concentration consistently remains below the saturation limit, thus its balance can be limited to the liquid phase.
? Failure of model to satisfy the input ?output nitrogen mass balance, it has major influence on the output nitrites, with low values producing high concentrations because of the reduced activity of nitrite-oxidizing bacteria, whereas for high values the reverse is true
Overall performance index
? Process performance has been assessed with a global performance index including the effluent quality EQ with the violation Vx, as defined by Eq14, included as a penalty function
? In addition to third term has been introduced as the volume increase with respect to the benchmark design. This can be viewed as an additional cost and acts as a further penalty term
? If this term had not been introduced, the only factor controlling the size of the tanks would be the carbon limitation of denitrification for the anoxic compartments and the oxygen demand of the aerobic compartments. These limitations are in fact rather weak, leading to unrealistically large volumes.
Plant optimization
? The optimization variables are the volumes of the individual anoxic and aerobic tanks.
? From tables 4, it can be seen that the volume increase is highest for the rain situation, which is in fact the most demanding, requiring a 44% overall volume increase.
? The variations are not evenly distributed, with the maximum increase in anoxic volume occurring for the dry weather simulation, whereas the maximum aerated volume is required in the rating weather.
?
4. Contribution:
This research studies the behavior of activated sludge and the obtained profiles are very appropriate date for future studies.
5. Contact (Mail address): jd83@ufl.edu.