| 1. |
- Feldman, Hannah, et al.
(författare)
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Model-based analysis and optimization of a full-scale industrial high-rate anaerobic bioreactor
- 2018
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; , s. 2726-2739
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to present the model-based optimization results of an anaerobic granular sludge internal circulation reactor. The International Water Association Anaerobic Digestion Model No. 1 extended with phosphorus (P), sulfur (S), and ethanol is used to describe the main biological and physico-chemical processes. The high-rate conditions within the reactor are simulated using a flow + reactor model comprised of a series of continuous stirred tank reactors followed by an ideal total suspended solids separation unit. Following parameter estimation by least squares on the measured data, the model had a relative mean error of 13 and 15% for data set #1 and data set #2, respectively. Response surfaces show that the reactor performance index (a metric combining energy recovery in the form of heat and electricity, as well as chemicals needed for pH control) could be improved by 45% when reactor pH is reduced down to 6.8. Model-based results reveal that influent S does not impose sufficient negative impacts on energy recovery (+5.7%, in MWh/day,+0.20 M€/year when influent S is removed) to warrant the cost of its removal (3.58 M€/year). In fact, the process could handle even higher S loads (ensuring the same degree of conversion) as long as the pH is maintained above 6.8. Nevertheless, a higher S load substantially increases the amount of added NaOH to maintain the desired operational pH (>25%) due to the acidic behavior of HS −. CO 2 stripping decreases the buffer capacity of the system and hence use of chemicals for pH control. Finally, the paper discusses the possibilities and limitations of the proposed approach, and how the results of this study will be put into practice.
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| 2. |
- Flores-Alsina, Xavier, et al.
(författare)
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A plant-wide aqueous phase chemistry module describing pH variations and ion speciation/pairing in wastewater treatment process models.
- 2015
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Ingår i: Water Research. - : Elsevier BV. - 1879-2448 .- 0043-1354. ; 85, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- There is a growing interest within the Wastewater Treatment Plant (WWTP) modelling community to correctly describe physico-chemical processes after many years of mainly focusing on biokinetics. Indeed, future modelling needs, such as a plant-wide phosphorus (P) description, require a major, but unavoidable, additional degree of complexity when representing cationic/anionic behaviour in Activated Sludge (AS)/Anaerobic Digestion (AD) systems. In this paper, a plant-wide aqueous phase chemistry module describing pH variations plus ion speciation/pairing is presented and interfaced with industry standard models. The module accounts for extensive consideration of non-ideality, including ion activities instead of molar concentrations and complex ion pairing. The general equilibria are formulated as a set of Differential Algebraic Equations (DAEs) instead of Ordinary Differential Equations (ODEs) in order to reduce the overall stiffness of the system, thereby enhancing simulation speed. Additionally, a multi-dimensional version of the Newton-Raphson algorithm is applied to handle the existing multiple algebraic inter-dependencies. The latter is reinforced with the Simulated Annealing method to increase the robustness of the solver making the system not so dependant of the initial conditions. Simulation results show pH predictions when describing Biological Nutrient Removal (BNR) by the activated sludge models (ASM) 1, 2d and 3 comparing the performance of a nitrogen removal (WWTP1) and a combined nitrogen and phosphorus removal (WWTP2) treatment plant configuration under different anaerobic/anoxic/aerobic conditions. The same framework is implemented in the Benchmark Simulation Model No. 2 (BSM2) version of the Anaerobic Digestion Model No. 1 (ADM1) (WWTP3) as well, predicting pH values at different cationic/anionic loads. In this way, the general applicability/flexibility of the proposed approach is demonstrated, by implementing the aqueous phase chemistry module in some of the most frequently used WWTP process simulation models. Finally, it is shown how traditional wastewater modelling studies can be complemented with a rigorous description of aqueous phase and ion chemistry (pH, speciation, complexation).
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| 3. |
- Flores-Alsina, Xavier, et al.
(författare)
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Benchmarking strategies to control GHG production and emissions
- 2022
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Ingår i: Quantification and Modelling of Fugitive Greenhouse Gas Emissions from Urban Water Systems : A report from the IWA Task Group on GHG - A report from the IWA Task Group on GHG. - : IWA Publishing. - 9781789060454 - 9781789060461 ; , s. 213-228
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Bokkapitel (refereegranskat)abstract
- Benchmarking has been a useful tool for unbiased comparison of control strategies in wastewater treatment plants (WWTPs) in terms of effluent quality, operational cost and risk of suffering microbiology-related total suspended solids (TSS) separation problems. This chapter presents the status of extending the original Benchmark Simulation Model No 2 (BSM2) towards including greenhouse gas (GHG) emissions. A mathematical approach based on a set of comprehensive models that estimate all potential on-site and off-site sources of COinf2/inf, CHinf4/inf and Ninf2/infO is presented and discussed in detail. Based upon the assumptions built into the model structures, simulation results highlight the potential undesirable effects on increased GHG emissions when carrying out local energy optimization in the activated sludge section and/or energy recovery in the anaerobic digester. Although off-site COinf2/inf emissions may decrease in such scenarios due to either lower aeration energy requirement or higher heat and electricity production, these effects may be counterbalanced by increased Ninf2/infO emissions, especially since Ninf2/infO has a 300-fold stronger greenhouse effect than COinf2/inf. The reported results emphasize the importance of using integrated approaches when comparing and evaluating (plant-wide) control strategies in WWTPs for more informed operational decision-making.
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| 4. |
- Flores-Alsina, Xavier, et al.
(författare)
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Benchmarking strategies to control GHG production and emissions : Chapter 9
- 2022
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Ingår i: Quantification and Modelling of Fugitive Greenhouse Gas Emissions from Urban Water Systems: A report from the IWA Task Group on GHG. - : IWA Publishing. - 9781789060461 - 9781789060454 ; , s. 213-228
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Benchmarking has been a useful tool for unbiased comparison of control strategies in wastewater treatment plants (WWTPs) in terms of effluent quality, operational cost and risk of suffering microbiology-related total suspended solids (TSS) separation problems. This chapter presents the status of extending the original Benchmark Simulation Model No 2 (BSM2) towards including greenhouse gas (GHG) emissions. A mathematical approach based on a set of comprehensive models that estimate all potential on-site and off-site sources of COinf2/inf, CHinf4/inf and Ninf2/infO is presented and discussed in detail. Based upon the assumptions built into the model structures, simulation results highlight the potential undesirable effects on increased GHG emissions when carrying out local energy optimization in the activated sludge section and/or energy recovery in the anaerobic digester. Although off-site COinf2/inf emissions may decrease in such scenarios due to either lower aeration energy requirement or higher heat and electricity production, these effects may be counterbalanced by increased Ninf2/infO emissions, especially since Ninf2/infO has a 300-fold stronger greenhouse effect than COinf2/inf. The reported results emphasize the importance of using integrated approaches when comparing and evaluating (plant-wide) control strategies in WWTPs for more informed operational decision-making.
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| 5. |
- Flores-Alsina, Xavier, et al.
(författare)
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Evaluation of plant-wide WWTP control strategies including the effects of filamentous bulking sludge
- 2009
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 60:8, s. 2093-2103
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Forskningsöversikt (refereegranskat)abstract
- The main objective of this paper is to evaluate the effect of filamentous bulking sludge on the predicted performance of simulated plant-wide WWTP control strategies. First, as a reference case, several control strategies are implemented, simulated and evaluated using the IWA Benchmark Simulation Model No. 2 (BSM2). In a second series of simulations the parameters of the secondary settler model in the BSM2 are automatically changed on the basis of an on-line calculated risk of filamentous bulking, in order to mimic the effect of growth of filamentous bacteria in the plant. The results are presented using multivariate analysis. Including the effects of filamentous bulking in the simulation model gives a-more realistic-deterioration of the plant performance during periods when the conditions for development of filamentous bulking sludge are favourable: compared to the reference case where bulking effects are not considered. Thus, there is a decrease of the overall settling velocity, an accumulation of the total suspended solids (TSS) in the middle layers of the settler with a consequent reduction of their degree of compaction in the bottom. As a consequence there is a lower TSS concentration in both return and waste flow, less biomass in the bioreactors and a reduction of the TSS removal efficiency. The control alternatives using a TSS controller substantially increase the food to microorganisms (F/M) ratio in the bioreactor, thereby reducing both risk and effects of bulking sludge. The effects of ammonium (NH4+), nitrate (NO3-) and reject water control strategies are rather poor when it comes to handling solids separation problems.
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| 6. |
- Ramin, Pedram, et al.
(författare)
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Fault detection in a benchmark simulation model for wastewater treatment plants
- 2022
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Ingår i: 14th International Symposium on Process Systems Engineering. - 1570-7946. - 9780323851596 ; , s. 1363-1368
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Bokkapitel (refereegranskat)abstract
- The International Water Association (IWA) Benchmark Simulation Models (BSM1 and BSM2) have been successfully used in both industry and academia to test and verify control strategies in wastewater treatment plants (WWTPs). In this study, a new (plant- wide) benchmark simulation model, the BSM2-LT, is developed to evaluate monitoring algorithms. This platform provides opportunities to generate various sensor/actuator and process faults. To make this realistically, different Markov-chain models are used to re- create the alternation of sensor/actuator states based on predefined occurrence probability. The same principle is used to describe the occurrence of toxic/inhibitory compounds. Using this platform, one can test the performance of a monitoring algorithm such as a fault detection method. To demonstrate this in an example, a multivariate method based on adaptive dynamic principal component analysis (dPCA) was used to detect faulty events. The performance of the monitoring algorithm is evaluated with a penalization index, scoring from 0 to 100. While the tested method had a good false alarm score, it resulted in a low false acceptance. While the results could be certainly improved, the main focus of this study is the benchmark simulation model and not presenting a well optimized monitoring algorithm. The software which will be produced and freely distributed in the near future, will allow an objective evaluation of monitoring algorithms for WWTPs for any user.
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| 7. |
- Saagi, Ramesh, et al.
(författare)
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Catchment & sewer network simulation model to benchmark control strategies within urban wastewater systems
- 2016
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Ingår i: Environmental Modelling and Software. - : Elsevier BV. - 1364-8152. ; 78:April, s. 16-30
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims at developing a benchmark simulation model to evaluate control strategies for the urban catchment and sewer network. Various modules describing wastewater generation in the catchment, its subsequent transport and storage in the sewer system are presented. Global/local overflow based evaluation criteria describing the cumulative and acute effects are presented. Simulation results show that the proposed set of models is capable of generating daily, weekly and seasonal variations as well as describing the effect of rain events on wastewater characteristics. Two sets of case studies explaining possible applications of the proposed model for evaluation of: 1) Control strategies; and, 2) System modifications, are provided. The proposed framework is specifically designed to allow for easy development and comparison of multiple control possibilities and integration with existing/standard wastewater treatment models (Activated Sludge Models) to finally promote integrated assessment of urban wastewater systems.
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| 8. |
- Saagi, Ramesh, et al.
(författare)
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Key control handles in integrated urban wastewater systems for improving receiving water quality
- 2018
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Ingår i: Urban Water Journal. - 1573-062X. ; 15:8, s. 790-800
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in modelling and control of integrated urban wastewater systems (UWS). Nevertheless, given the multiple interactions between the sub-systems–catchment, sewer system, wastewater treatment plant (WWTP) and receiving water system–the selection of effective control handles for improving receiving water quality is a major challenge. In this paper, a systematic study to identify the most important control handles in an UWS is presented. The Benchmark Simulation Model for Urban Wastewater Systems (BSM-UWS) is selected as a virtual case-study. Morris screening is used to perform global sensitivity analysis. Results indicate that, for the BSM-UWS layout, while river dissolved oxygen quality (Texc,DO) is influenced by multiple control handles both in the sewer system and WWTP, river un-ionized ammonia quality (Texc,NH3) is mainly influenced by WWTP control handles. The study highlights the need to perform simulations for at least 1 year when determining key control handles for UWS.
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| 9. |
- Solís, Borja, et al.
(författare)
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A plant-wide model describing GHG emissions and nutrient recovery options for water resource recovery facilities
- 2022
-
Ingår i: Water Research. - : Elsevier BV. - 0043-1354. ; 215
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Tidskriftsartikel (refereegranskat)abstract
- In this study, a plant-wide model describing the fate of C, N and P compounds, upgraded to account for (on-site/off-site) greenhouse gas (GHG) emissions, was implemented within the International Water Association (IWA) Benchmarking Simulation Model No. 2 (BSM2) framework. The proposed approach includes the main biological N2O production pathways and mechanistically describes CO2 (biogenic/non-biogenic) emissions in the activated sludge reactors as well as the biogas production (CO2/CH4) from the anaerobic digester. Indirect GHG emissions for power generation, chemical usage, effluent disposal and sludge storage and reuse are also included using static factors for CO2, CH4 and N2O. Global and individual mass balances were quantified to investigate the fluxes of the different components. Novel strategies, such as the combination of different cascade controllers in the biological reactors and struvite precipitation in the sludge line, were proposed in order to obtain high plant performance as well as nutrient recovery and mitigation of the GHG emissions in a plant-wide context. The implemented control strategies led to an overall more sustainable and efficient plant performance in terms of better effluent quality, reduced operational cost and lower GHG emissions. The lowest N2O and overall GHG emissions were achieved when ammonium and soluble nitrous oxide in the aerobic reactors were controlled and struvite was recovered in the reject water stream, achieving a reduction of 27% for N2O and 9% for total GHG, compared to the open loop configuration.
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| 10. |
- Solon, Kimberly, et al.
(författare)
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Effects of ionic strength and ion pairing on (plant-wide) modelling of anaerobic digestion.
- 2015
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Ingår i: Water Research. - : Elsevier BV. - 1879-2448 .- 0043-1354. ; 70:March, s. 235-245
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Tidskriftsartikel (refereegranskat)abstract
- Plant-wide models of wastewater treatment (such as the Benchmark Simulation Model No. 2 or BSM2) are gaining popularity for use in holistic virtual studies of treatment plant control and operations. The objective of this study is to show the influence of ionic strength (as activity corrections) and ion pairing on modelling of anaerobic digestion processes in such plant-wide models of wastewater treatment. Using the BSM2 as a case study with a number of model variants and cationic load scenarios, this paper presents the effects of an improved physico-chemical description on model predictions and overall plant performance indicators, namely effluent quality index (EQI) and operational cost index (OCI). The acid-base equilibria implemented in the Anaerobic Digestion Model No. 1 (ADM1) are modified to account for non-ideal aqueous-phase chemistry. The model corrects for ionic strength via the Davies approach to consider chemical activities instead of molar concentrations. A speciation sub-routine based on a multi-dimensional Newton-Raphson (NR) iteration method is developed to address algebraic interdependencies. The model also includes ion pairs that play an important role in wastewater treatment. The paper describes: 1) how the anaerobic digester performance is affected by physico-chemical corrections; 2) the effect on pH and the anaerobic digestion products (CO2, CH4 and H2); and, 3) how these variations are propagated from the sludge treatment to the water line. Results at high ionic strength demonstrate that corrections to account for non-ideal conditions lead to significant differences in predicted process performance (up to 18% for effluent quality and 7% for operational cost) but that for pH prediction, activity corrections are more important than ion pairing effects. Both are likely to be required when precipitation is to be modelled.
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