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- Comas, J, et al.
(author)
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Demonstration of a tool for automatic learning and reuse of knowledge in the activated sludge process
- 2006
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 53:4-5, s. 303-311
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Journal article (peer-reviewed)abstract
- Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance.
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- Comas, J, et al.
(author)
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Extension of the IWA/COST simulation benchmark to include expert reasoning for system performance evaluation
- 2006
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 53:4-5, s. 331-339
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Journal article (peer-reviewed)abstract
- In this paper the development of an extension module to the IWA/COST simulation benchmark to include expert reasoning is presented. This module enables the detection of suitable conditions for the development of settling problems of biological origin (filamentous bulking, foaming and rising sludge) when applying activated sludge control strategies to the simulation benchmark. Firstly, a flow diagram is proposed for each settling problem, and secondly, the outcome of its application is shown. Results of the benchmark for two evaluated control strategies illustrate that, once applied to the simulation outputs, this module provides supplementary criteria for plant performance assessment. Therefore, simulated control strategies can be evaluated in a more realistic framework, and results can be recognised as more realistic and satisfactory from the point of view of operators and real facilities.
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- Comas, J., et al.
(author)
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Risk assessment modelling of microbiology-related solids separation problems in activated sludge systems
- 2008
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In: Environmental Modelling & Software. - : Elsevier BV. - 1364-8152. ; 23:10-11, s. 1250-1261
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Journal article (peer-reviewed)abstract
- This paper proposes a risk assessment model for settling problems of microbiological origin in activated sludge systems (filamentous bulking, foaming and rising sludge). The aim of the model is not to diagnose microbiology-related solids separation problems with absolute certainty but to quantify in dynamic scenarios whether simulated operational procedures and control strategies lead to favourable conditions for them to arise or not. The rationale behind the model (which integrates the mechanisms of standard activated sludge models with empirical knowledge), its implementation in a fuzzy rule-based system and the details of its operation are illustrated in the different sections of the paper. The performance of the risk assessment model is illustrated by evaluating a number of control strategies facing different short-term influent conditions as well as long-term variability using the IWA/COST simulation benchmark. The results demonstrate that some control strategies, although performing better regarding operating costs and effluent quality, induce a higher risk for solids separation problems. In view of these results, it is suggested to integrate empirical knowledge into mechanistic models to increase reliability and to allow assessment of potential side-effects when simulating complex processes. (c) 2008 Elsevier Ltd. All rights reserved.
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- Isaksson, Björn, et al.
(author)
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Hepatic encephalopathy verified by psychometric testing and EEG in cirrhotic patients : Effects of mesocaval interposition shunt or sclerotherapy
- 2005
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In: HPB. - : Elsevier BV. - 1365-182X .- 1477-2574. ; 7:1, s. 65-72
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Journal article (peer-reviewed)abstract
- Background. The aim of this randomised prospective study was to evaluate hepatic encephalopathy after mesocaval interposition shunt operation and after repeated endoscopic sclerotherapy. Methods. Forty-five patients with bleeding oesophageal varices due to liver cirrhosis were randomised to the two treatment groups, 24 to the shunt group and 21 to the sclerotherapy group. The patients were evaluated preoperatively regarding blood tests, hepatic encephalopathy as measured by electroencephalogram with spectral analysis and by a battery of psychometric tests. The direction of portal flow in the shunt group was investigated by shunt phlebography and ultrasonography with Doppler. During follow-up the same investigations were performed twice at median 6.7 and 14.7 months after operation. Results. No statistically significant difference was found during follow-up regarding blood tests and electroencephalography with spectral analysis. Although the preoperative psychometric tests showed that the shunt group performed significantly better than the sclerotherapy group, the first follow-up showed that the shunt group performed statistically worse than the sclerotherapy group in seven of the tests: Synonyms (measuring verbal ability), Block Design Test (measuring visuo-spatial ability), Memory for Design Test, Error Score (measuring memory function), Revised Visual Retention Test, correct answers and the same test error answers (measuring visuo-spatial memory, ability and immediate memory), Digit Symbol Test (measuring perceptual ability) and Trial Making Test B (measuring cognitive motor abilities). Conclusions. Patients treated by mesocaval interposition shunt showed a progressive general reduction in psychometric performance compared with patients treated with repeated sclerotherapy, in whom a general intellectual improvement was observed. This finding corresponds to the reverse direction of the preoperative portal flow to a hepatofugal pattern at first follow-up and at 12 months among two-thirds of the patients. © 2005 Taylor & Francis Group Ltd.
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- Jeppsson, Ulf, et al.
(author)
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Benchmark simulation model no 2: general protocol and exploratory case studies
- 2007
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 56:8, s. 67-78
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Journal article (peer-reviewed)abstract
- Over a decade ago, the concept of objectively evaluating the performance of control strategies by simulating them using a standard model implementation was introduced for activated sludge wastewater treatment plants. The resulting Benchmark Simulation Model No 1 (BSM1) has been the basis for a significant new development that is reported on here: Rather than only evaluating control strategies at the level of the activated sludge unit (bioreactors and secondary clarifier) the new BSM2 now allows the evaluation of control strategies at the level of the whole plant, including primary clarifier and sludge treatment with anaerobic sludge digestion. In this contribution, the decisions that have been made over the past three years regarding the models used within the BSM2 are presented and argued, with particular emphasis on the ADM1 description of the digester, the interfaces between activated sludge and digester models, the included temperature dependencies and the reject water storage. BSM2-implementations are now available in a wide range of simulation platforms and a ring test has verified their proper implementation, consistent with the BSM2 definition. This guarantees that users can focus on the control strategy evaluation rather than on modelling issues. Finally, for illustration, twelve simple operational strategies have been implemented in BSM2 and their performance evaluated. Results show that it is an interesting control engineering challenge to further improve the performance of the BSM2 plant (which is the whole idea behind benchmarking) and that integrated control (i.e. acting at different places in the whole plant) is certainly worthwhile to achieve overall improvement.
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| 10. |
- Karlsson, B, et al.
(author)
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Calculation of isoeffective doses and the alpha/beta value by comparing results following radiosurgery and radiotherapy for arteriovenous malformations of the brain
- 2006
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In: Journal of neurosurgery. - : Journal of Neurosurgery Publishing Group (JNSPG). - 0022-3085 .- 1933-0693. ; 105105 Suppl, s. 183-189
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Journal article (peer-reviewed)abstract
- The authors sought to assess the relationship between obliteration rate and different dose parameters following fractionated radiotherapy for arteriovenous malformations (AVMs). A comparison of the results of radiosurgery and radiotherapy for AVMs was made to calculate the best fit α/β value, which would then be used as a model for predicting the treatment outcome, independent of the number of fractions applied.MethodsData from 1453 patients were analyzed: 1154 treated with radiosurgery and 300 with fractionated radiotherapy. The relationships between dose and obliteration rate after 3 years were calculated, and the best fit curve to the empirical results was defined. The higher the dose per fraction, biologically effective dose, and the lower the total dose, the higher the obliteration rate. The isoeffective doses when comparing radiotherapy and radiosurgery independent of the α/β value could not be defined. The dose per fraction had the best predictive value, independent of the number of fractions.Conclusions Dose per fraction seems to be the decisive parameter for the treatment response following both radiotherapy and radiosurgery. A larger number of fractions did not increase the obliteration rate. The data indicate that higher doses per fraction should be used when irradiating AVMs.
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