Activated Sludge Model No. 1 Research Articles

Effects of C/N ratio and dissolved oxygen on aerobic denitrification process: A mathematical modeling study

COD to ammonium nitrogen (C/N) ratio and dissolved oxygen (DO) concentration are the most important factors affecting aerobic denitrification process, however, the effects of those on the mix-cultured aerobic denitrification process are still ambiguous. A mathematical model based on the framework of activated sludge model No. 3 (ASM3) was proposed for simulating nitrogen removal in an aerobic denitrification SBR process via anoxic/aerobic denitrification. AQUASIM 2.1G was employed for parameter estimation, sensitivity analysis and model calibration, as well as model validation. Ultimately, the impacts of the C/N ratio and the DO concentration on the aerobic denitrification process were revealed by the validated model. The model proposed well described nitrogen removal in an aerobic denitrification SBR process. The total nitrogen (TN) removal efficiency of the process increased with the increasing of C/N ratio and the decreasing of DO concentration. C/N ratio impacted the synthesis of cell internal storage products (XSTO), and the effects of DO concentration on the process resulted from the competition with substrate between heterotrophs and aerobic denitrifiers. High C/N ratio was preferred, however, the DO concentration should be maintained at a relatively lower level under the premise of ensuring the aerobic condition.

Calibration and validation for a real-time membrane bioreactor: A sliding window approach

The paper presents a novel model calibration and validation strategy of membrane bioreactor (MBR) for wastewater treatment. The approach is based on a dynamic model of the activated sludge process and it consists simultaneously on estimating the model’s parameters and computing the dissolved oxygen control input. Activated sludge model No. 1 (ASM1) has been widely used to describe the biological process of activated sludge processes. However, most system states and parameters within ASM1 are not easily obtained, hence not applicable for model calibration and validation. In this work, a reduced-order model presented herein serves as a tool for predicting the dynamic behavior of the MBR plant. The model contains only 4 measurable states, where 13 parameters need to be identified. To reduce the complexity of the calibration, the static sensitivity analysis is performed to select the sensitive parameters. The selected parameters are identified based on directly measurable real-time data obtained from the plant. In addition, the dissolved oxygen is also maintained at a certain level to mimic the real-time control behavior. Model calibration is achieved based on a sliding window optimization problem, which searches for the optimal parameters set and control variables during each identification cycle. Different datasets sampled for the same MBR plant have been used for model validation. Both calibration and validation results are evaluated by several performance indexes, which indicates an acceptable correspondence with the experimental data. The developed model can be employed for process state estimation and control purpose as well as design issues for MBR systems.

Establishment of nitrous oxide (N2O) dynamics model based on ASM3 model during biological nitrogen removal via nitrification

ABSTRACT Nitrous oxide (N2O), as one of the six greenhouse gases, is mainly produced in the biological nitrogen removal process of wastewater treatment plants (WWTPs). Establishing the N2O kinetic model can provide insight into the N2O generation mechanism and regulate its production. This work uses Activated Sludge Model NO.3 (ASM3) as the basic framework, combines organic storage with endogenous respiration theory, and couples ammonia-oxidizing bacteria (AOB) denitrification pathway and the NH2OH/NOH model to establish a kinetic model. Meanwhile, the Sequencing Batch Reactor (SBR) process with artificial simulated urban domestic sewage was used as the carrier; MATLAB and EXCEL software were used as tools to establish a model calculation programme. The simulated values obtained by substituting the operating conditions of the SBR process into the model and the measured values of the SBR process were analysed. The correlation coefficient (R 2) between the experimental values and simulated values obtained for the 5 components of COD, ammonia, nitrite, nitrate and total N2O is 0.952, 0.996, 0.902, 0.991 and 0.956, respectively, which indicates that the N2O kinetic model has great consistency, this further shows that the established model modelling mechanism is clear and accurate, and provides a new method for the N2O dynamic model.

Wastewater Treatment Plant: Modelling and Validation of an Activated Sludge Process

The aim of the present paper is to develop a reliable and accurate model of the wastewater biochemical treatment process and to explore the behaviour through a general dynamic simulation environment, namely the INtegrated Simulation Environment Language (INSEL), for the analysis of the energy demand of the whole wastewater treatment plant. In particular, the presented model pays special attention to the chemical kinetics involved in the activated sludge process for the reduction of nitrogen and carbon compounds. According to the best practices, the plant configuration considered in this work includes the denitrification-nitrification process, performed by completely mixed reactors. In particular, the process analysed in this paper is based on the Ludzak-Ettinger process. The biological process is simulated according to the well-known method widely used in the literature, namely the Activated Sludge Model No 1 (ASM1). The model includes a set of equations for the calculation of aerobic growth of heterotrophs, anoxic growth of heterotrophs, aerobic growth of autotrophs, decay of autotrophs, ammonification of soluble nitrogen, hydrolysis of entrapped organics, and hydrolysis of entrapped organic nitrogen. All these equations, along with energy and mass balances, are solved by the explicit Euler method. The developed model is validated using literature data, showing a great accuracy (deviation below 1%). As for the temperature, results show that, between 15 and 25 °C, in the initial part of the process, transport effects dominate the consumption ones. When the temperature is higher than 30 °C, nitrate consumption is so fast that biomass growth is limited by this effect. Conversely, in case of low temperatures (5–10 °C), biomass growth is not limited by nitrate availability. Finally, results also showed that temperature significantly affects the denitrification process, whereas the effect on the oxygen is lower.

Design of hierarchical control strategies for biological wastewater treatment plants to reduce operational costs

In this research, hierarchical control strategies are developed for biological wastewater treatment plants (WWTPs) to reduce the operational expenses. The benchmark simulation model no. 1 (BSM1) is used as the working platform which is developed based on activated sludge model no. 1 (ASM1) to control dissolved oxygen in aerobic reactors and nitrate levels in anoxic reactors. Fractional PI (FPI) controllers are designed at the lower level and model predictive control (MPC) and a fuzzy controller are designed at higher level in order to achieve enhanced set-point tracking. Initially, linear state space model is developed around the operating point using prediction-error method for lower level. For identification of the higher level model, the lower level control loop is closed in a feedback sense with the designed controller. Based on the identified model in the higher level, the controllers are designed. This paper presents two combinations of hierarchical control strategies: FPI-Fuzzy and FPI-MPC. It is observed that FPI controller at the lower level and MPC controller at the higher level results in better plant performance with better set-point tracking with reduced operational costs. It is observed that FPI-Fuzzy control strategy results in better EQI of 7041.7 for storm weather condition which also resulted in 48% reduction in total nitrogen violations and FPI-MPC results in better OCI of 17119.6 and this strategy resulted in nearly 38% reduction in total nitrogen violations. A significant improvement in the plant performance is observed for dry and rain weather conditions as well.

Electron transfer pathways and kinetic analysis of cathodic simultaneous nitrification and denitrification process in microbial fuel cell system

Microbial fuel cell (MFC) is an innovative bioconversion technology for wastewater treatment accompanied with electricity recovery. In this study, a kinetic model was developed base on Activated Sludge Model No.1 (ASM1) to describe electron transfer pathways during the simultaneous nitrification and denitrification (SND) process in the biocathode system of a dual-chamber MFC. The batch running of the dual-chamber MFC system showed that it produced a power density up to 2.96 W m−3 within 48 h, the achieved SND efficiency and autotrophic denitrification ratio in the cathodic denitrification process were up to 87.3 ± 0.8% and 69.5 ± 6.6%, respectively. Meanwhile, by integrating nitrification, autotrophic denitrification, heterotrophic denitrification, organic carbon oxidation, and oxygen reduction in the cathode, the model was able to precisely fit the concentration variations of NH3–N, dissolved oxygen (DO) and chemical oxygen demand (COD) during the cathodic SND process (R2 ≥ 0.9876). The cathode electrons tended to be completely utilized with the increase of autotrophic denitrification ratio in the cathodic denitrification process. When the nitrification rate was enhanced, the autotrophic denitrification would prevail in the competition with the heterotrophic denitrification. In summary, the developed model was confirmed to be effective and reliable for describing the electron transfer pathways and predicting the performance of the nitrogen removal reactions during the cathodic SND process in a double-chamber MFC.

Heavy Metal Removal Investigation in Conventional Activated Sludge Systems

The combination of industrial and domestic wastewater in municipal WWTPs (waste water treatment plants) may be economically profitable, but it increases the difficulty of treatment, and also has some detrimental effects on the biomass and causes a low-quality final effluent. The present study evaluates the treatment process both in the presence and absence of heavy metals using ASM3 (activated sludge model no.3) so as to improve the model by means of incorporating other novel inhibitory kinetic and settler models. The results reveal that the presence of heavy metal, a case study for copper and cadmium at a concentration of 0.7 mgL−1 in a biological treatment system has a negative effect on heterotrophic bacteria concentration by 25.00 %, and 8.76 % respectively. Meanwhile, there are no important changes in COD (chemical oxygen demand), SS (total suspended solids) and TN (total nitrogen) in the final effluent in the conventional system. However, all these parameters are acceptable and consistent with EU Commission Directives. The results indicate that ASM3 can predict and provide an opportunity of the operation for an activated sludge wastewater treatment plant that receives the effluent from an industrial plant.

Extended Activated Sludge Model No.1 with Floc and Biofilm Diffusion for Organic and Nutrient Removal

AbstractThis paper presents a modified mathematical model for substrate degradation and nutrient removal by aerobic microorganisms. The modified model is based on Activated Sludge Model No.1 (ASM1)...

Reliability Analysis of Activated Sludge Process by Means of Biokinetic Modelling and Simulation Results

Analysis of wastewater treatment plant reliability is a difficult process, therefore it is often limited to selected aspects, e.g., mechanical reliability of equipment or technological availability of the process. The research presents a method of combining the above mentioned aspects in order to determine the complex operational availability index (CAVO). A hypothetical technological system with activated sludge (AS) in a typical layout (denitrification-nitrification) was selected for the studies. A number of operational scenarios have been developed, taking into account the possible mechanical failures of system components. Computer simulations with the use of Activated Sludge Model No.1 (ASM1), performed for selected scenarios allowed the determination of a complex operational availability of the system. Obtained results confirm high reliability of AS system in terms of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) removal (CAVO > 0.96) and indicate the necessity of further research in order to determine representative value of reliability of total nitrogen removal (from the study, CAVO-Ntot < 0.4) and to evaluate other technological solutions in terms of their complex reliability.

An improved ASM-GDA approach to evaluate the production kinetics of loosely bound and tightly bound extracellular polymeric substances in biological phosphorus removal process.

This study established an extended activated sludge model no. 2 (ASM2) for providing a new recognition of the contributions of both loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) into phosphorus (P) removal by incorporating their formation and degradation processes during the anaerobic–aerobic cycle. For determining the best-fit values for the new model parameters (kh,TB-EPS, kh,LB-EPS, fPP,TB-EPS, and fPP,LB-EPS) in this extended ASM2, a novel and convenient gradient descent algorithm (GDA) based ASM (ASM-GDA) method was developed. Sensitivity analysis of fPP,TB-EPS, fPP,LB-EPS, kh,TB-EPS, and kh,LB-EPS on the model target outputs of SPO4, XTB-EPS, XLB-EPS, and XPP proved the accuracy of the chosen parameters. Eight batch experiments conducted under different influential chemical oxygen demand (COD) and P conditions were quantitatively and qualitatively analyzed. Respectively, 9.37–9.64% and 4.17–4.29% of P removal by TB-EPS and LB-EPS were achieved. Self-Organizing Map (SOM) has shown its high performance for visualization and abstraction for exhibiting the high correlations of the influential COD/P concentrations and the P% removal by TB-EPS (and LB-EPS). Comprehensive analyses of the influences of influential COD and P concentration on the biological phosphorus removal process help us in successfully establishing the mechanism kinetics of production and degradation of P in a dynamic P biological-treatment model.

A Methodology for Global Sensitivity Analysis of Activated Sludge Models: Case Study with Activated Sludge Model No. 3 (ASM3).

The main objective of this study was to demonstrate a computational approach of global sensitivity analysis (GSA) integrated with functional principal component analysis (fPCA) for activated sludge models through aggregation of time-dependent model response patterns into time-independent coefficients of functional principal components (PCs). This proposed approach addresses the main issue of time-varying character of GSA indices when calculated solely on the time-dependent model outputs. The GSA-fPCA methodology was implemented using the rigorous model Activated Sludge Model No. 3 (ASM3) as case study. The approach transforms the time-dependent model outputs into functional PCs prior to calculation of GSA indices to remove the time-varying character of the calculated GSA indices. This work focused on the evaluation of the following key computational factors that may significantly influence the performance of the GSA-fPCA methodology: (a) model parameter sampling range, (b) model simulation period, (c) basis functions system, and (d) state of the system being modeled-batch or continuous activated sludge process. Results show that first few functional PCs capture up to 100% of the curve patterns in the time-dependent model outputs. The sensitivity indices calculated from the PC scores via Morris' GSA technique elucidated parameter sensitivity patterns inherent to the complex mathematical structure of ASM3. PRACTITIONER POINTS: Functional principal components-mediated GSA technique to remove time-varying character of sensitivity indices derived from time-dependent dynamical models. Technique amenable to improving efficiency of capturing response patterns into few functional principal components through various basis functions. Identifying priority parameters for ASM3 model calibration requires specification of target model outputs to which parameter sensitivities are calculated. GSA-fPCA offers a comprehensive numerical approach to manipulating models depending on the intended applications: simple fast-responding models to complex models.

Modelling the simultaneous effects of organic carbon and ammonium on two-step nitrification within a downward flow biofilm reactor

Process modelling is an approximated description of the reality, and choosing appropriate kinetics forms is crucial for model accuracy. It has been long observed that the inhibition effect from organic carbon on nitrification does not change gradually as the organic carbon level changes, which is not capable to be adequately reflected by traditional Monod type kinetics. Therefore, with a purpose to address this issue from modelling perspectives, this study combines the inhibition effects from organic carbon and ammonium on two-step nitrification and incorporates them into a modified ASM1 (Activated Sludge Model No.1) based two-step nitrification framework using two different forms: one in traditional Monod type and one in Logistic type. The two modified models demonstrate improvements in model prediction from both temporal and spatial perspectives, with the Logistic type model even better than the Monod type model. Simulated bacterial depth profiles of the biofilm reactor correspond to lab observations in that heterotrophs dominate the upstream layers where nitrification is inhibited, while ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) dominate the downstream layers where the inhibition on nitrification is relieved. A direct implication for process control is that higher media porosity and longer biofilm length can work in favor of nitrification, but higher hydraulic loadings and higher ratio of organic carbon over ammonium in the influent will be undesirable for nitrification. Overall, a necessity is proven in this study to use appropriate numerical forms to describe the combined inhibition effects of organic carbon and ammonium on two-step nitrification.

Operational performance and biofoulants in a dynamic membrane bioreactor

In this study, a mathematical model was developed to have a better understanding of the process and be used in future reactor scale models to predict its process performance. This model utilizes the Activated Sludge Model NO.1 (ASM1) framework and incorporates bioprocesses of formation and degradation of soluble microbial products (SMP) and extracellular polymeric substances (EPS). Simulation result shows the model could very well predict the bioreactor performance. The average error of COD, BOD and NH3-N removal efficiency was 0.48, 0.28 and 1.18%, respectively.

Steady-state modeling of the biodegradation performance of a multistage moving bed biofilm reactor (MBBR) used for on-site greywater treatment

In this study, the Activated Sludge Model No. 3 (ASM3) was applied for the simulation of the removal of organics and nitrogen in a multistage moving bed biofilm reactor (MBBR) used for biological greywater treatment. The data related to the characterization of the greywater were collected over a period of 5months to be investigated in the model. The reactor showed a high performance for the removal of chemical oxygen demand (COD), dissolved organic carbon (DOC), biological oxygen demand (BOD5), ammonia (NH4-N), and total nitrogen (TN) with a removal efficiency of 93%, 80.7%, 99%, 89%, and 77%, respectively. The results of modeling showed a good correlation between simulated and experimental concentrations of COD issued from different reactors of the MBBR system. The adaptability of the ASM3 model to fit other parameters such as TN, NH4-N, total suspended solids (TSS), and the dissolved oxygen (DO) was also investigated for two selected reactors: reactor (R1) and the reactor (R5). The simulation results showed an acceptable correlation regarding the evolution of the investigated parameters in R1 and R5 and in the effluent except for total nitrogen TN. The adjustment of the stoichiometric parameters led to a satisfactory simulation of TN concentrations.

WWTP MODEL CALIBRATION BASED ON DIFFERENT OPTIMIZATION APPROACHES

There is a significant interest in modelling the wastewater treatment plants (WWTP) because with a calibrated model a large variety of operational strategies can be evaluated, the control system design may be improved and enhanced constructive alternatives may be proposed. The Activated Sludge Model No. 1 (ASM1) has the potential of describing the biochemical processes taking place in WWTPs, in association with the Benchmark Simulation Model No. 1 (BSM1) which adds the description of the involved physical processes. An important challenge for reliable simulators development is the dynamically changing composition of the influent wastewater, also varying from one WWTP to another. Due to this reason, it is necessary to fit the model for each WWTP. This paper proposes a new methodology for the dynamic simulator calibration of a municipal WWTP. Different optimization methods are used for the simulator calibration and results of the different approaches are comparatively presented. Based on WWTP measurements a set of influent variables, bioreactor parameters and settler parameters are calibrated. Optimization was carried out based on classical, genetic, hybrid and Pareto multiobjective algorithms and their performance is discussed, revealing their strengths and limitations.

Mathematical Simulation and Validation of a Wastewater Treatment Plant in Northern Italy

Abstract The aim of this study was to calibrate and validate activated sludge model No. 3 (ASM3) for an Italian municipal wastewater treatment plant (WWTP) located in Friuli Venezia Giulia region. ...

Effect of operating parameters on the performance of wastewater treatment plant (Case study: The south of Tehran wastewater treatment)

Despite the fact that there are wastewater treatment plants (WWTPs) currently operational across Iran and great advances have been made in this area, there are still problems in the design, construction, and operation of WWTPs with large nonlinear systems, varying flow rates, and pollution charges. The objective of this study was to investigate the effect of operating parameters including the return activated sludge (RAS) ratio, internal recycle (IR) ratio and dissolved oxygen (DO) concentration in an activated sludge system for the Modules 5&6 of the Southern Tehran WWTP. This study designed and simulated a plant based on the activated sludge model No.1 (ASM1) to determine the factors affecting wastewater treatment systems; then, the kinetic parameters were measured. The kinetic parameters such as the yield coefficient (Y), decay coefficient (Kd), maximum specific growth rate (K), and saturation constant (Ks) were in the range of 0.303-0.331g/g, 0.030-0.033d-1, 1.65-1.93d-1 and 37.6-44.92mg/l, respectively. The RAS ratios, IR ratios, and DO concentration varied from 0.2 to 2, 1 to 3.5, and 0.27 to 3.54 mg/l, respectively. The amount of RAS had the greatest impact on the effluent. The amounts of IR and DO concentration had no significant effect on the concentration of the five-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and total suspended solids (TSS) in the effluent. After the RAS, the amount of IR had the most direct effect on reducing the effluent total nitrogen (TN) concentration. As a result, the overall removal efficiency increased up to 75% when the IR rate was 200% of the influent flow rate, the RAS rate was 90% of the influent flow rate, and the DO concentration in the first aeration unit was 2 mg/l considering the aeration cost. Therefore, proper operating parameters can provide the best quality of effluent that meets environmental standards.

Influence of Temperature on Activated Sludge Systems

The present study aims to determine the influence of temperature in the treatment efficiency of the activated sludge systems. To reach this aim, a simulation study is performed using Matlab® programming language. A biological tank is modelled by the ASM3 (activated sludge model No. 3) and a settling tank is modelled by Takács settling velocity model. For a defined inflow rate and inlet waste water characteristics with the predefined design and operational parameters, the treatment model is simulated. The changes in the kinetic parameters by temperature are estimated from the values given in ASM3 and the dissolved oxygen saturation concentration in water is also concerned as a function of temperature. All the other design and the operational conditions are kept constant during simulations. The simulation algorithm is executed for the temperatures 0°C, 10°C, 20°C, and 30°C. The results show that chemical oxygen demand and total suspended solids reduce slightly with increasing temperature, however, the total nitrogen content in the effluent is changing, first increases for the temperatures 10°C, 20°C, and then decreases for 30°C when it is compared to that of at 0°C. The change in temperature affects mostly the ammonium concentration in the waste water treatment systems.

A Modified Activated Sludge Model No.3 (ASM3) for Membrane Bioreactor (MBR) with an Emphasis for Solids Hydrolysis

The previously assumed “inert” organics measured by respirometric method has been reported to be hydrolysable under long sludge retention time (SRT) configuration such as membrane bioreactor(MBR). The sludge production under long SRT has also shown to be lower than the standard activated sludge model (ASM) prediction. The hydrolysis of “inert” organics can provide the extra carbon source for denitrification. The current modeling approach has not yet included this aspect. In this study, a modified ASM3 was developed to account for the hydrolysis of “inert” organics and subsequent effect on the denitrification process under long SRT.

Design and Comparison of Wastewater Treatment Plant Types (Activated Sludge and Membrane Bioreactor), Using GPS-X Simulation Program: Case Study of Tikrit WWTP (Middle Iraq)

Mathematical models and simulation are considered a powerful tool in engineering practice. Those tools are becoming increasingly used for the improvement of wastewater treatment plants design because the conceptual design is complex and ill-defined. In this paper, three alternatives: 1) complete mix activated sludge without nitrogen removal (CAS); 2) complete mix activated sludge with nitrogen removal (CAS-N) and; 3) membrane bioreactor (MBR) processes were designed into two steps: first concept design to calculate the size of process units, then second implement modeling and simulation to improve the accuracy of the conceptual design. In brief, the treatment process design has been verified by using the activated sludge model No. 1 (ASM1) in GPS-X (v.7) simulation software. This application helps not only in sizing the treatment units but also in understanding the plant’s capacity. In the same time, it can assist in studying the future expansion works required for increased hydraulic and organic loadings. For this purpose, Tikrit WWTP was selected as a case study. The used model was validated by comparing the designed values of the plant and the modeling data. The verification of the obtained results from both hand calculations and the results of the program showed a good agreement. A significant difference in the volume of secondary treatment was obtained from design calculations, where the CAS without denitrification system was 9244 m3 (aerobic and secondary tanks), CAS with denitrification system was 11,324 m3 (anoxic, aerobic and secondary tanks) and for MBR system was 7468 m3 (anoxic, aerobic and immersed membrane tanks). From the obtained results point of view, it can be concluded that mathematical models can be considered as worthy tools to complement the established wastewater treatment plant design procedures.