| 1. |
- Diehl, S., et al.
(författare)
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Steady-state analyses of activated sludge processes with plug-flow reactor
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437. ; 5:1, s. 795-809
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Tidskriftsartikel (refereegranskat)abstract
- Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analyzed in steady-state operation using a reduced model consisting of one soluble substrate and one particulate biomass component modelling the dominating biological process. Monod biomass growth rate is assumed. Two settler models are studied. One is the commonly used ideal settler, or point settler, which is assumed to never be overloaded and to have unlimited flux capacity. The other recently published steady-state settler model includes hindered and compressive settling, and models a realistic limiting flux capacity. Generally, the steady-state concentration profiles within the PFR and the settler are governed by nonlinear ordinary differential equations. It is shown that the steady-state behaviour of the ASP can, however, be captured by equations without derivatives. New theoretical results are given, such as conditions by means of inequalities on input variables and parameters for a steady-state solution to exist. Another novel finding is that, if the incoming substrate concentration is increased from a low or moderate stationary value and the solids residence time is kept fixed, then this results in a lower effluent concentration in the new steady state. The steady-state equations are solved numerically for different operating conditions. For common parameter values, numerical solutions reveal that an ASP having a PFR, instead of a continuously stirred tank reactor, is far more efficient in reducing the effluent substrate concentration and this can be obtained for much lower recycle ratios, which reduces the pumping energy considerably.
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| 2. |
- Jonfelt, Clara, et al.
(författare)
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Key parameters for modelling Anammox process with N2O emissions
- 2017
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Ingår i: French Federation of Biotechnology - Bioreactors Symposium 2017. - France.
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Konferensbidrag (refereegranskat)abstract
- In this paper, a sensitivity analysis and a calibration were applied to a recent published model used to replicate N2O emissions in an Anammox process of a moving-bed biofilm reactor (MBBR). The model used in this study was designed to replicate a one-stage nitrification-Anammox system in a MBBR at Hammarby-Sjöstad pilot plant (Stockholm, Sweden), whichtreats of anaerobic digestion liquor. The aeration was intermittently (45/15 minutes - on/off). During the aeration, a 1.5 mg/L DO set-point was set. Three main measurements wereobtained: NH4 in water, N2O in both water and gas phase.The sensitivity analysis was done via the one-at-a-time method, where one parameter at a timeis changed (in our case, 10%) from its nominal value and the model output is quantified. Next,the most sensitive parameters were used in the model calibration. Results indicate that the biofilm porosity (η [-]), biofilm density (ρ [gTS/m3]), maximum biofilmthickness (Lmax [mm]) and boundary layer thickness of the biofilm (L0 [μm]) were the mostsensitive parameters of the model. These parameters performed the model calibration.
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| 3. |
- Nookuea, Worrada, et al.
(författare)
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Comparison of Mass Transfer Models on Rate-Based Simulation of CO2 Absorption and Desorption Processes
- 2017
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Ingår i: Proceedings of the 9th International Conference on Applied Energy. - : Elsevier. ; 142, s. 3747-3752
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Konferensbidrag (refereegranskat)abstract
- The effective technology for capturing CO2 at the low concentration is chemical absorption, due to the high reactivity between CO2 and aqueous amine solutions. To capture CO2, the process involves complex reactive separations. The accurate calculation of hydrodynamic properties, and mass and energy transfer are of importance for the design of the absorber and desorber columns. This paper performs the rate-based simulations of CO2 absorption by Monoethanolamine in Aspen Plus. In the calculation of the mass transfer coefficients, different mass transfer models were implemented. In comparison with the desorber, the impacts of mass transfer models were more significant in the simulation of the absorber. For both columns, the impacts of the mass transfer models on the concentration profiles were more significant than those on the temperature profiles. For the absorber, the maximum deviations occur at the bottom of the column for both the concentration and the temperature profiles. Different from the absorber, for the desorber, the maximum deviations occur close to the top of the column.
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| 4. |
- Samuelsson, Oscar, et al.
(författare)
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Gaussian process regression for monitoring and fault detection of wastewater treatment processes
- 2017
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Ingår i: Water Science and Technology. - UK : IWA Publishing. - 0273-1223 .- 1996-9732. ; 75:12, s. 2952-2963
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Tidskriftsartikel (refereegranskat)abstract
- Monitoring and fault detection methods are increasingly important to achieve a robust and resource efficient operation of wastewater treatment plants (WWTPs). The purpose of this paper was to evaluate a promising machine learning method, Gaussian process regression (GPR), at WWTP monitoring applications. We evaluated GPR at two WWTP monitoring problems: estimate missing data in a flow rate signal (simulated data), and detect a drift in an ammonium sensor (real data). We showed that GPR with the standard estimation method, maximum likelihood estimation (GPR-MLE), suffered from local optima during estimation of kernel parameters, and did not give satisfactory results in a simulated case study. However, GPR with a state-of-the-art estimation method based on sequential Monte Carlo estimation (GPR-SMC) gave good predictions and did not suffer from local optima. Comparisons with simple standard methods revealed that GPR-SMC performed better than linear interpolation in estimating missing data in a noisy flow rate signal. We conclude that GPR-SMC is both a general and powerful method for monitoring full-scale WWTPs. However, this paper also shows that it does not always pay off to use more sophisticated methods. New methods should be critically compared against simpler methods, which might be good enough for some scenarios.
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| 5. |
- Samuelsson, Oscar, et al.
(författare)
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Monitoring fouling on dissolved oxygen sensors in WRRFs with active fault detection
- 2017
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Konferensbidrag (refereegranskat)abstract
- Measurements of the dissolved oxygen (DO) concentration are central in aeration control strategies at Water Resource Recovery Facilities (WRRFs). Despite this, more research has been focused on DO-control strategies, see e.g. (Amand et al. 2013), than on fault detection (FD) methods to for DO-measurements. One FD-method was proposed in (Carlsson & Zambrano 2016), where the ratios between airflows at different aerated zones were monitored to detect bias in DO-sensors. However, this was argued to be inadequate to distinguish large process disturbances from sensor bias. It is a general problem that process disturbances are hard or impossible to separate from sensor faults.One approach that potentially could be used to distinguish between sensor and process fault is active fault detection, in contrast to traditional or passive fault detection. In active fault detection an auxiliary signal is designed exclusively for fault detection and injected into the system (Esna Ashari et al. 2012). In this paper, we used the impulse from an automatic air cleaning system of the DO-sensor as design signal, and monitored the impulse response, see Figure 1 for an example. A similar approach was suggested already in 1992 (Spanjers & Olsson 1992), where a changed time constant of the DO-sensor was shown to be a good indication of an artificially fouled DO-sensor. More recently, Andersson and Hallgren showed that the impulse response from an air-cleaning procedure could be used to detect a biologically fouled DO-sensor (Andersson S. & Hallgren F. 2015).However, none of the previous studies made repeated experiments of fouled versus cleaned sensors in order to characterize the variation between the impulse responses. This is needed to compare different FD-methods and their performance to distinguish fouled (faulty) from clean (normal) impulse responses.In this paper we made detailed experiments with artificial fouling and used the results to compare two fault detection methods, Rise time estimation (RTE), and Gaussian process regression (GPR) (Rasmussen & Williams 2005).
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| 6. |
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| 7. |
- Sylwan, Ida, et al.
(författare)
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Removal of metals for improvement of sludge quality, adsorption to primary sludge during primary settlement
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The primary and secondary sludge from a wastewater treatment plant are generally mixed and treated combined. Here we introduce an idea for a process concept where the sludge flows are separated and the treatment of primary sludge is modified, with the goal to concentrate micropollutants in primary sludge while nutrients are removed in the secondary (biological) treatment to produce a “bio-sludge” with low metal contents. The example is based on primary settlement and an activated sludge process. In contrast to a conventional process, the sludge flows are as mentioned separated. After anaerobic digestion and dewatering, primary sludge goes through pyrolysis. Biochar produced during pyrolysis is added in pulverized or granulated form to the primary settler. The hypothesis is that biochar will adsorb dissolved metals and thus enhance the metal removal in primary treatment. The biochar should settle with primary sludge, and pyrolysis is repeated. However, to remove metal content from the system some portion of the produced biochar will have to be removed in each cycle. A prerequisite for nutrients to end up in the bio-sludge is that chemical coagulants are not used in primary treatment and that there is no recirculation of sludge from secondary to primary treatment. To the best of the authors knowledge, biochar has not previously been tested as an adsorbent in primary treatment of wastewater. Efficient removal of metals has though been shown in several studies where wastewater was filtrated through biochar in granulated form (Huggins et al., 2016). Further, biochar has been shown to sorb pharmaceuticals from urine without removing nutrients (Solanki & Boyer, 2017). In this paper, results from experimental tests on addition of biochar in the primary settler will be presented. Experiments are made in lab-scale to test the adsorption and settling capacity depending on biochar properties, e.g. particle size, cation exchange capacity. The theoretical dosing requirement in a full scale application and possible biochar yields from pyrolysis of primary sludge are also investigated.
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| 8. |
- Zambrano, Jesús, et al.
(författare)
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Light and duty cycle optimization of a photo-bioreactor in batch mode
- 2017
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Ingår i: Energy Procedia. - : Elsevier. - 1876-6102. ; 105, s. 773-779
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Tidskriftsartikel (refereegranskat)abstract
- This paper is focused on optimizing the amount of light duty cycle of a photo-bioreactor operating in batch mode. The mathematical model used is confined to one dissolved substrate, one biomass (algae), one internal cell quota, and the irradiance for photo-acclimated culture. The model has been previously published and validated with experimental data. The following optimization problem is studied: minimize the effluent substrate concentration subject to: maximum and minimum amount of light to be used, the time of the light/dark illumination and the total time of the batch experiment. Analytical solution for this optimization problem seems difficult to obtain. However, numerical results obtained from simulations show that it is possible to find solutions which satisfy the problem requirements.
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| 9. |
- Zambrano, Jesús, et al.
(författare)
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Microalgae Activated Sludge : Process Modelling and Optimization
- 2017
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Konferensbidrag (refereegranskat)abstract
- This work deals with steady-state optimization of a process formed by an algae-bacteria photo-bioreactor (PBR) in an activated sludge configuration. The optimization is done by considering the total PBR volume as two volumes in series, and aiming for the minimal nitrogen concentration in the effluent, for a given external light and carbon dioxide (CO2) injection. Results suggest that it is possible to obtain an optimum volume distribution that gives a lower effluent substrate concentration compared to a single volume, and this optimum volume depends on the CO2 applied.
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