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Whole plant modeling and control has received increasing attention in recent years and as a result the Benchmark Simulation Model No 2 (BSM2) platform was developed to compare control strategies. The objective of this paper consists of evaluating whether MLSS concentration control (with changing set-points in summer and winter time to maintain nitr...
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... changes also caused a drop in the SRT of the anaerobic digester from 20 to 19 d. The final plant layout including these changes is depicted in Figure 1. The main simulation platforms in which BSM2 implementation is available to date are SIMBA®, WEST®, FORTRAN and MATLAB®/SIMULINK®. ...
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... A 1 uses a fixed set-point MLSS controller, A 2 includes a temperature-dependent MLSS controller and, finally, A 3 extends A 2 with a storage volume controller. The one-year simulation results depicted in Figure 1a clearly show that the MLSS=3300 g m -3 controller (strategy A 1 ) leads to important winter excursions of effluent ammonia concentrations ( Figure 1d). Strategy A 2 properly tackles this by applying its summer-winter switch controller. ...
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... A 1 uses a fixed set-point MLSS controller, A 2 includes a temperature-dependent MLSS controller and, finally, A 3 extends A 2 with a storage volume controller. The one-year simulation results depicted in Figure 1a clearly show that the MLSS=3300 g m -3 controller (strategy A 1 ) leads to important winter excursions of effluent ammonia concentrations ( Figure 1d). Strategy A 2 properly tackles this by applying its summer-winter switch controller. ...
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... the effect of the MLSS set-point change in the aerobic reactor did not have a drastic effect on the sludge treatment line. Figure 1b confirms that indeed a large overload is applied to the digester at the end of the winter period, but Figure 1c implies that the large retention time of the anaerobic digester sufficiently dampens this overload. Thus, neither incurs a step change in the return liquor nitrogen load to the water line, nor does it increase the effluent ammonia concentrations (Figure 1d). ...
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... the effect of the MLSS set-point change in the aerobic reactor did not have a drastic effect on the sludge treatment line. Figure 1b confirms that indeed a large overload is applied to the digester at the end of the winter period, but Figure 1c implies that the large retention time of the anaerobic digester sufficiently dampens this overload. Thus, neither incurs a step change in the return liquor nitrogen load to the water line, nor does it increase the effluent ammonia concentrations (Figure 1d). ...
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... 1b confirms that indeed a large overload is applied to the digester at the end of the winter period, but Figure 1c implies that the large retention time of the anaerobic digester sufficiently dampens this overload. Thus, neither incurs a step change in the return liquor nitrogen load to the water line, nor does it increase the effluent ammonia concentrations (Figure 1d). Next to the large retention time in the anaerobic digester, the absence of negative impacts can also be explained by the fact that the sludge mass that is still present at the time the wastage is increased provides sufficient nitrification capacity to handle the increased N peaks. ...
Citations
... The XTSS concentration is increased from 3 000 to 4 000 g TSS m -3 during winter conditions (i.e. T < 15 ºC) to establish a longer sludge retention time (SRT) and to maintain the nitrification capacity (Solon et al., 2017;Vanrolleghem et al., 2010). Table 2 shows that there is a reduction in N2O emissions due to the increase of the DO-setpoint, which decreases the nitrite concentration compared to A0 and leads to a reduction of N2O emissions through the ND pathway. ...
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.
... The S O2 concentration in AER2 is controlled by manipulating the air supply rate. The second controller regulates the total suspended solids (X TSS ) in AER3 by manipulating the wastage flow (Q w ) (Vanrolleghem et al., 2010). The set-point changes (set-point ¼ 3000 gTSS.m ...
The objective of this paper is to report the effects that control/operational strategies may have on plant-wide phosphorus (P) transformations in wastewater treatment plants (WWTP). The development of a new set of biological (activated sludge, anaerobic digestion), physico-chemical (aqueous phase, precipitation, mass transfer) process models and model interfaces (between water and sludge line) were required to describe the required tri-phasic (gas, liquid, solid) compound transformations and the close interlinks between the P and the sulfur (S) and iron (Fe) cycles. A modified version of the Benchmark Simulation Model No. 2 (BSM2) (open loop) is used as test platform upon which three different operational alternatives ( , , ) are evaluated. Rigorous sensor and actuator models are also included in order to reproduce realistic control actions. Model-based analysis shows that the combination of an ammonium ( ) and total suspended solids ( ) control strategy ( ) better adapts the system to influent dynamics, improves phosphate accumulation by phosphorus accumulating organisms (41%), increases nitrification/denitrification efficiency (18%) and reduces aeration energy ( ) (21%). The addition of iron ) for chemical P removal ( ) promotes the formation of ferric oxides ( , ), phosphate adsorption ( , ), co-precipitation ( , ) and consequently reduces the P levels in the effluent (from 2.8 to 0.9 g P.m⁻³). This also has an impact on the sludge line, with hydrogen sulfide production ( ) reduced (36%) due to iron sulfide ( ) precipitation. As a consequence, there is also a slightly higher energy production ( ) from biogas. Lastly, the inclusion of a stripping and crystallization unit ( ) for P recovery reduces the quantity of P in the anaerobic digester supernatant returning to the water line and allows potential struvite ( ) recovery ranging from 69 to 227 kg.day⁻¹ depending on: (1) airflow ( ); and, (2) magnesium ( ) addition. All the proposed alternatives are evaluated from an environmental and economical point of view using appropriate performance indices. Finally, some deficiencies and opportunities of the proposed approach when performing (plant-wide) wastewater treatment modelling/engineering projects are discussed.
... • V storage controller: control of the storage tank volume by manipulating the tank output flow rate (Q storage ) [17]. The controller works by storing the return flows during the day and releasing them during the night. ...
This paper presents the implementation and evaluation of control strategies for wastewater treatment plants. The study was carried out using the platform Benchmark Simulation Model No. 2 (BSM2) and is conceived plant wide by introducing as a distinctive feature the structuring of the plant on: a water line and a sludge line, the two operating lines being interdependent but at the same time influencing simultaneously the overall functioning of the plant. For the water line only one control strategy was implemented and this strategy was used together with the five control strategies proposed for the sludge line. In evaluating the obtained results special attention has been placed on the indicators related to the percentage of time when the pollutants in the effluent are violating the quality limits for total nitrogen and ammonium. However, the effect on the overall effluent quality and operation costs have also been considered by means of the usual aggregated cost indexes. The control strategy for the sludge line that offered the best results is the one that uses the control of the total suspended solids in the fifth tank by manipulating the wastage flow rate together with the control of the storage tank volume by manipulating its flow rate.
... Storage tank controller (V storage controller): this controls the storage tank volume (V storage ) by manipulating the tank's output flow rate (Q storage ). The controller works by storing nitrogen-rich return flows by day, when the nitrogen load in the influent is high, and releasing them at night, when the nitrogen load is low (Vanrolleghem et al., 2010). We therefore have four basic control loops. ...
The use of control engineering in the case of wastewater treatment processes can be an effective measure in the improvement of their performances. This paper presents the implementation and evaluation of control solutions for wastewater treatment plants taking into consideration the hypothesis that the plant can be structured as having two operating lines: a water line and a sludge line. For the water line there are proposed four control strategies and for the sludge line there are considered four control actions. After an initial evaluation of the control strategies used for the water line by comparison with a default closed loop strategy, the paper shows the influence of each control action of the sludge line over the considered evaluation indicators. The evaluation is presented for all the water line control strategies, trying to check the generality of the initial hypothesis. The results are validated using the Benchmark Simulation Model No. 2. The simulation results showed that the control strategies implemented for the water line act mainly on the global integral indicators and the control actions implemented for the sludge line act mainly on the acute effects.
This paper presents the application of different control strategies applied for wastewater treatment plants (WWTP). The main purpose is to evaluate its effectiveness/cost trade-off attending a set of criteria. The study has been performed by using the Benchmark Simulation Model No. 2 (BSM2) and the evaluation criteria have been selected taking into account the most relevant indicators provided by this benchmark scenario. More specifically, five strategies have been implemented and compared with the default closed loop control strategy (DCL) of BSM2 and between them. Results show that the control strategies that use the ammonia cascade controller provide better results in most of the evaluated criteria than the control strategies implemented by using only the oxygen controller. Ammonia controller improves the results in terms of effluent quality and operational costs due to the reported aeration energy savings. As a conclusion of this study the control strategy that uses the ammonia and carbon controllers has been selected as the most recommended for implementation.
