| 1. |
- Aspegren, H., et al.
(author)
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The Urban Water System - a Future Swedish Perspective
- 1997
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In: Water Science and Technology. - 0273-1223. ; 35:9, s. 33-44
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Journal article (peer-reviewed)abstract
- It is argued, that the use of water can no longer be regarded as an almost free commodity. The idea to assess and value the environmental impact of the water use represents a true change of paradigm. The key issue is that any future wastewater treatment system has to be evaluated according to a quantitative criterion. This has to consider: •hygienic aspects: we believe that nobody will accept a lower hygienic standard than today. •environmental impact: the wastewater impact on the environment has steadily increased the need for better treatment. We need to be prepared for changes in the society by having a readiness manifested as continuing dynamic research environment in this area. Too often the knowledge build-up has been re-active instead of pro-active. •economising resources: wastewater treatment looks and probably should look quite different in densely populated urban areas and in rural areas. Considering resource handling one has to consider already invested capital costs, land use, water re-use, organic and nutrient use and re-use, as well as overall use of energy. •user aspects: technical functionality, economy and liability in different aspects require profound consideration. A sustainable wastewater treatment has to adapt to a local environment and the total resource demand has to be calculated, including a direct environmental impact on receiving waters, air and soil as well as energy consumption and nutrient recycling. Thus, there is an apparent need for. •quantitative performance index: the quest for sustainable development has to be based on objective reasons as well as subjective ones. An integrated performance index is part of a necessary decision making model for the design and operation of wastewater treatment systems. In this index, it is evident that a trade-off should be made between the pursued quality of the process outputs (liquid, solids, gas) and the associated efforts (investments, operation) required to achieve this considering the inputs (wastewater). In order to make this trade-off, however, a common framework is needed to quantitatively compare the different objectives. A metric to judge the sustainability of different options will facilitate a fruitful dialogue between e.g. politicians, ecologists, engineers and economists. Only a truly interdisciplinary approach can help to solve the challenges ahead.
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| 2. |
- Jeppsson, Ulf, et al.
(author)
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An evaluation of a dynamic model of the secondary clarifier
- 1996
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 19-26
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Journal article (peer-reviewed)abstract
- The main objective of the paper is to support and illustrate recent theoretical results on the mathematical modelling of the secondary clarifier. A new settler model is compared with a traditional layer model by means of numerical simulations. Emphasis is put on the numerical solution's ability to approximate the analytical solution of the conservation law written as a non-linear partial differential equation. The new settler model is consistent in this respect. Another important conclusion is that a layer model dividing the settler into only ten layers (normally used in settler models) is too crude an approximation to capture the detailed dynamic behaviour of the settler. All simulations presented are performed with the settler models coupled to the IAWQ Activated Sludge Model No. 1.
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| 3. |
- Jeppsson, Ulf, et al.
(author)
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On the modelling of the dynamic propagation of biological components in the secondary clarifier
- 1996
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 85-92
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Journal article (peer-reviewed)abstract
- When coupling a model of the biological reactor to a model of the settler, difficulties appear because of the different representations used for the particulate material. A combined model of the entire activated sludge process needs to include an algorithm for the dynamic propagation of the biological components of the particulate material through the secondary clarifier. In particular, this is of importance for an accurate description of the sludge that is recycled to the biological reactor. Two one-dimensional algorithms have been evaluated by means of numerical simulations. The first algorithm investigated is the one by Otterpohl and Freund in 1992 and some inherent problems of this method are discussed. For example, it will produce oscillating solutions as the number of layers in the settler model increases. Therefore, an alternative algorithm is proposed. It is based on a percentage vector that describes the different particulate biological components as fractions of the total suspended solids concentration. The vector is updated for every layer in the settler model by a robust numerical method. The algorithm is derived analytically, is computationally efficient and does not exhibit any oscillatory behaviour.
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| 4. |
- Jönsson, Karin, et al.
(author)
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Screening method for evaluation of inhibition of nitrification in Sweden
- 1999
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In: Water Science and Technology. - 0273-1223. ; 40:2, s. 175-178
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Journal article (peer-reviewed)abstract
- An investigation with respect to inhibition of nitrification of wastewater from 109 Swedish municipal wastewater treatment plants was performed. Flow proportional, 24-hour composite samples were collected during one week, and then analysed using the screening method. Inhibition of nitrification above 10% was found at only 20 plants. In general, the load of inhibiting substances is limited in Swedish municipal wastewater according to this study. The inhibition found is not connected to any special category of treatment plants with respect to the size of the plant. Neither was any general pattern of inhibition during the week found in this investigation. It was also shown that the screening method can be used for detecting small quantities of inhibiting substances if different dilutions of the same sample are analysed.
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| 5. |
- Olsson, Gustaf, et al.
(author)
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Operation and Control of Wastewater Treatment - A Scandinavian Perspective over 20 years
- 1998
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In: Water Science and Technology. - 0273-1223. ; 37:12, s. 1-13
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Journal article (peer-reviewed)abstract
- This paper aims to review the development of wastewater treatment operation and control over the last two decades. Due to the authors' background and experiences there is a special emphasis on the Scandinavian perspective. Since the developments in these countries have been in the forefront in the wastewater treatment area we believe that it may give a reasonable view of the progress also in other countries. The results of regulatory, technical and economical driving forces are discussed. A brief historical review of the progress of nutrient removal is made, and current methodologies for the operation and control of nutrient removal systems is reviewed.
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| 6. |
- Olsson, Gustaf, et al.
(author)
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Reviewing, assessing and speculating
- 1998
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In: Water Science and Technology. - 0273-1223. ; 37:12, s. 397-401
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Journal article (pop. science, debate, etc.)abstract
- A concise assessment is made of the scientific and technical programme of the 7th IAWQ Workshop on Instrumentation, Control and Automation of Water and Wastewater Treatment and Transport Systems. Although progress has been made in certain areas, others are identified as crucial targets for further research and development.
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| 7. |
- Rosén, Christian, et al.
(author)
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Disturbance detection in wastewater treatment plants
- 1998
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In: Water Science and Technology. - 0273-1223. ; 37:12, s. 197-205
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Journal article (peer-reviewed)abstract
- The development in sensor technology has made many wastewater treatment systems data rich but not necessarily information rich. To extract the adequate information from several sensors is not trivial, and it is not sufficient to consider only the time series. Different tools for detecting unusual on-line measurement data and deviating process behaviour are discussed. In this paper various dimension reduction as well as advanced filtering methods are considered in order to extract adequate information for fault detection and diagnosis. Both the operator and the process engineer can take advantage of such methods for proper monitoring of the plant, in particular extreme events and their causes.
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| 8. |
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| 9. |
- Adamsson, Marie, 1966, et al.
(author)
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Toxicity Identification Evaluation of ammonia, nitrite and heavy metals at the Stensund Wastewater Aquaculture plant, Sweden.
- 1998
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In: Water Science and Technology. - 0273-1223. ; 38:3, s. 151-157
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Journal article (peer-reviewed)abstract
- The Stensund Wastewater Aquaculture plant was built in 1989. The plant is contained in a greenhouse because of its northern location with a temperate climate; The plant receives wastewater from 40 persons and has a residence time of 30 days. The purification concept is to use a constructed aquatic food chain (algae, zooplankton and fish) combined with hydroponic culture of higher plants to further deplete the nutrients in the wastewater. However, the production of algae and zooplankton has not been working as expected from pilot studies. The purpose of this investigation was to study if toxic chemicals were limiting the production of zooplankton (Daphnia magna) in the aquaculture treatment system. Grab samples were taken at six sites and tested for acute toxicity to Daphnia magna and analyzed for BOD, COD, ammonium-, nitrite-, nitrate- and total nitrogen, total phosphorus and heavy metals (Cd, Ci, Cu, Ni, Pb, Zn). Toxicity to D. magna was also determined after addition of EDTA, sodium thiosulphate and pH adjustment of the,water to 6, 7 and 8, in order to assess if heavy metals and/or pH-dependent toxicants were present Potential toxicants, with concentrations high enough to intoxicate Daphnia magna, were Cu, ammonia and nitrite. Subsequent improvement of nitrification reduced the ammonia and nitrite concentrations as well as the toxicity. Furthermore, the improved production of algae and Daphnia at the Stensund Wastewater Aquaculture plant verified that the primary cause of toxicity was ammonia. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
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| 10. |
- Johansson, Lena, 1967-
(author)
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The use of LECA (Light Expanded Clay Aggregates) for the removal of phosphorus from wastewater
- 1997
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In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 35:5, s. 87-93
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Journal article (peer-reviewed)abstract
- Increasing attention is being focused on the phosphorus retention capacity of wetlands. Several attempts have been made to improve the reduction of phosphorus in wastewater by the use of constructed wetlands. One way of improving the phosphorus reduction capacity is to use efficient filter materials in the wetland. Leca(R) (Light Expanded Clay Aggregates) has been tested in Norway, where laboratory and field investigations gave promising results. To further study the chemical removal mechanism of Leca, an experiment utilising five columns was performed. A phosphate solution was applied to the columns intermittently and samples were taken twice a week. Parallel to this study, a P-fractionation experiment was conducted to find out how the phosphate was sorbed to various components of the material. Both experiments showed that only a small amount of the applied phosphate was sorbed by the Leca. The amount sorbed was primarily attached to Al-complexes. In a second column experiment Opoka, a reactive medium rich in CaCO3, was added to Leca and sand to investigate the P-sorption capacity. The results from this investigation showed a higher P-uptake than in the previous column experiment. The lime additive clearly increased the P-sorption and, in this study, Leca in its pure form could be considered as chemically non-reactive.
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| 11. |
- Karlsson, Susanne, 1967-, et al.
(author)
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Drinking water off-flavour caused by the formation of short-chain fatty acids in slow sand filters
- 1995
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In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 31:11, s. 49-54
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Journal article (peer-reviewed)abstract
- A case study carried out at a municipal drinking water treatment plant in southern Sweden showed that the formation of short-chain fatty acids in slow sand filters can result in severe off-flavour problems. When an extract of the headspace of the surface layer of a sand filter was subjected to gas chromatographic analysis with sensory detection (GC sniffing), several strong, rancid odours were detected. Mass spectrometric analysis of the same extract, before and after methylation, showed that substantial amounts of butyric acid, valeric acid and isovaleric acid were present in the analysed sample. The off-flavour caused by these compounds was removed by repeated shock chlorination of the malfunctioning slow sand filter. Analysis of fatty acid esters may provide an early warning of the described off-flavour problem.
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| 12. |
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| 13. |
- Mark, O., et al.
(author)
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Prediction of locations with sediment deposits in sewers
- 1996
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In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 33:9, s. 147-154
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Journal article (peer-reviewed)abstract
- The present paper presents an application of MOUSE ST, a general deterministic sediment transport model for sewer systems. MOUSE ST is used to predict the locations subjected to sedimentation in the sewer system of Ljubljana, Slovenia. The prediction is made by means of a sediment transport model with a movable bed. This model is run in parallel with the hydrodynamic MOUSE model. The results, in terms of locations with sediment deposits, are compared with field data from the sewer system in Ljubljana. Further, the model is used to predict the effect of the removal of the sediment deposits on the combined sewer overflows. The present paper presents an application of MOUSE ST, a general deterministic sediment transport model for sewer systems. MOUSE ST is used to predict the locations subjected to sedimentation in the sewer system of Ljubljana, Slovenia. The prediction is made by means of a sediment transport model with a movable bed. This model is run in parallel with the hydrodynamic MOUSE model. The results, in terms of locations with sediment deposits, are compared with field data from the sewer system in Ljubljana. Further, the model is used to predict the effect of the removal of the sediment deposits on the combined sewer overflows.
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| 14. |
- Perrusquía, Gustavo, 1954, et al.
(author)
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Influence of sewer sediments on flow friction and shear stress distribution
- 1995
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In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 31:7, s. 117-126
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Journal article (peer-reviewed)abstract
- Most sewers contain more or less deposited sediments. The paper discusses the distribution of the boundary shear stresses and the hydraulic resistance in part-full sewer pipes with such deposited sediments. The discussion is based on a series of numerical experiments using a validated numerical turbulence model. The results from the numerical model are compared with the sidewall elimination method. The validity of the sidewall elimination method is evaluated.
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| 15. |
- Rosen, B, et al.
(author)
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A systematic approach to optimal upgrading of water and waste water treatment plants
- 1998
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In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 37:9, s. 9-16
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Journal article (peer-reviewed)abstract
- Most of the future works in water and waste water treatment systems will involve the upgrading of existing facilities, for better performance and/or higher capacity. For the efficient implementation of any project, an upgrading strategy should be used, based on careful studies of the local conditions and the defined objectives to be reached. The paper presents a systematic approach to upgrading with emphasis on treatment plant extension, without investing in large volumes, by more efficient use of existing facilities, illustrated by some cases. The importance of real competition in obtaining a cost-effective implementation is stressed.
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| 16. |
- Alexandersson, Tomas, et al.
(author)
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Biological treatment of whitewater in a laboratory process in order to determine kinetic parameters for model development
- 2004
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In: Water Science and Technology. - 0273-1223. ; 50:3, s. 195-206
-
Journal article (peer-reviewed)abstract
- Implementation of an in-mill biological treatment plant is one solution to the problems associated with closure of whitewater systems. It is, however, important to operate the treatment with low concentration of nutrients in the effluent. The effect on the COD reduction from decreased additions of NH4-N and PO4-P were investigated in three parallel aerobic suspended carrier reactors during treatment at 46 to 48degreesC of whitewater from a recycled paper mill producing liner and fluting. In the reference reactor, a COD reduction of 89% was achieved and 45.6 mg NH4-N/(g COD reduced) and 11.6 mg PO4-P/(g COD reduced) was consumed at an organic load around 20 kg COD/(m(3.)d). Reduced additions of NH4-N decreased the COD reduction. Addition of 56% of the consumption of NH4-N in the reference reactor resulted in a COD reduction of 80%. The response from decreased addition of PO4-P was different compared to NH4-N but it could not be determined if this is due to unsuitable experimental design or a different reaction mechanism. Reducing the addition of PO4-P to 26% of the consumption of PO4-P in the reference reactor, decreased the COD reduction to 83%. The main conclusion from the experiment is: biological treatment has the potential of treating whitewater from recycled paper mills with low effluent nutrient concentrations.
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| 17. |
- Alexandersson, Tomas, et al.
(author)
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Treatment of packaging board whitewater in anaerobic/aerobic biokidney
- 2005
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In: Water Science and Technology. - 0273-1223. ; 52:10-11, s. 289-298
-
Journal article (peer-reviewed)abstract
- Whitewater from production of packaging board was treated in a combined anaerobic/aerobic biokidney, both in laboratory scale and pilot plant experiments. Both the laboratory experiments and the pilot plant trial demonstrate that a combined anaerobic/aerobic process is suitable for treating whitewater from a packaging mill. It is also possible to operate the process at the prevailing whitewater temperature. In the laboratory under mesophilic conditions the maximal organic load was 12 kg COD/m(3)*d on the anaerobic reactor and 6.7 kg COD/m(3)*d on the aerobic reactor. This gave a hydraulic retention time, HRT, in the anaerobic reactor of 10 hours and 2 hours in the aerobic reactor. The reduction of COD was between 85 and 90% after the first stage and the total reduction was between 88 to 93%. Under thermophilic conditions in the laboratory the organic load was slightly lower than 9.6 COD/m(3)*d and between 10 and 16 COD/m(3)*d, respectively. The HRT was 16.5 and 3.4 hours and the removal was around 75% after the co anaerobic reactor and 87% after the total process. For the pilot plant experiment at a mill the HRT in the anaerobic step varied between 3 and 17 hours and the corresponding organic load between 4 and 44 kg COD/m(3)*d. The HRT in the aerobic step varied between 1 and 6 hours and the organic load between 1.5 and 26 kg COD/m(3)*d. The removal of soluble organic matter was 78% in the anaerobic step and 86% after the combined treatment at the lowest loading level. The removal efficiency at the highest loading level was about 65% in the anaerobic step and 77% after the aerobic step. In the pilot plant trial the removal efficiency was not markedly affected by the variations in whitewater composition that were caused b y change of production. The variations, however, made the manual control of the nutrient dosage inadequate co and resulted in large variations in effluent nutrient concentration. This demonstrates the need for an automatic nutrient dosage system. The first step towards such a system was to evaluate two different on-line instruments. Both had severe stability problems, which made them unsuitable as parts in a system for control of the nutrient dosage.
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| 18. |
- Alkan Olsson, Johanna, et al.
(author)
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How participatory can participatory modeling be? Degrees of influence of stakeholder and expert perspectives in six dimensions of participatory modeling
- 2007
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 56:1, s. 207-214
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Journal article (peer-reviewed)abstract
- The authors are involved in a project aiming at the development of a methodology for participatory modeling as a tool for public participation in water resource management. In this paper, some examples of different degrees of stakeholder influence in six key dimensions of participatory modeling are identified and discussed. Arnstein's (A ladder of citizen participation. Journal of the American Institute of Planners, 1969, 4, 216–224) critical discussion of different degrees of “real” decision-making power is taken as a point of departure to assess possible degrees of stakeholder influence. Can we as participatory modelers be sure that we are really inviting our research objects to an equal communicative relationship where local perspectives, knowledge and priorities are respected to the same extent as central and/or expert perspectives? This paper presents an approach that could be used as a tool for structured reflection to avoid unreflective tendencies towards expert knowledge dominance and low degree of stakeholders' real influence over the process.
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| 19. |
- Alpkvist, Erik, et al.
(author)
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A new mathematical model for chemotactic bacterial colony growth
- 2004
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In: Water Science and Technology. - : Biriwa Education Services. - 0273-1223 .- 1996-9732. ; 49:11-12, s. 187-192
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Journal article (peer-reviewed)abstract
- A new continuum model for the growth of a single species biofilm is proposed. The geometry of the biofilm is described by the interface between the biomass and the surrounding liquid. Nutrient transport is given by the solution of a semi-linear Poisson equation. In this model we study the morphology of a chemotactic bacterial colony, which grows in the direction of increasing nutrient concentration. Numerical simulations using the level set method and finite difference schemes are presented. The results show rich heterogeneous morphology.
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| 20. |
- Alpkvist, Erik, et al.
(author)
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Description of mechanical response including detachment using a novel particle model of biofilm/flow interaction
- 2007
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In: Water Science and Technology. - : Biriwa Education Services. - 0273-1223 .- 1996-9732. ; 55:8-9, s. 265-273
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Journal article (peer-reviewed)abstract
- Bacterial biofilms, while made up of microbial-scale objects, also function as meso- and macro-scale materials. In particular, macro-scale material properties determine how biofilms respond to large-scale mechanical stresses, e.g. fluid shear. Viscoelastic and other constitutive properties influence biomass structure (through growth and fluid shear stresses) by erosion and sloughing detachment. In this paper, using the immersed boundary method, biofilm is modelled by a system of viscoelastic, breakable springs embedded in a fluid flow, evolving according to the basic physical laws of conservation of mass and momentum. We demonstrate in the context of computer simulation biofilm deformation and detachment under fluid shear stress.
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| 21. |
- Alpkvist, Erik, et al.
(author)
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Simulation of nitrification of municipal wastewater in moving-bed biofilm process : approach based on a 2D continuum model for growth and detachment
- 2007
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In: Water Science and Technology. - : Biriwa Education Services. - 0273-1223 .- 1996-9732. ; 55:8-9, s. 247-255
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Journal article (peer-reviewed)abstract
- This paper presents a complete mathematical model of a Moving Bed biofilm process for waste-water treatment, in particular for the nitrification process. The model is based on a bottom up approach adopting a multidimensional model for the biofilm growth and metabolism and a global mass balance model for the whole reactor. The model shows that oxygen is limiting the amount of biomass involved in the nitrification process. Furthermore, it suggests the existence of an optimal amount biomass for an optimal reactor turnover rate. Studies of two specific new suspended carriers show that the model output is dependable on the geometry of the carrier, and to a satisfactory extent agreeable with measurements.
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| 22. |
- Amaral, Andreia, et al.
(author)
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Modelling gas-liquid mass transfer in wastewater treatment : when current knowledge needs to encounter engineering practice and vice versa
- 2019
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In: Water Science and Technology. - : NLM (Medline). - 0273-1223 .- 1996-9732. ; 80:4, s. 607-619
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Journal article (peer-reviewed)abstract
- Gas-liquid mass transfer in wastewater treatment processes has received considerable attention over the last decades from both academia and industry. Indeed, improvements in modelling gas-liquid mass transfer can bring huge benefits in terms of reaction rates, plant energy expenditure, acid-base equilibria and greenhouse gas emissions. Despite these efforts, there is still no universally valid correlation between the design and operating parameters of a wastewater treatment plant and the gas-liquid mass transfer coefficients. That is why the current practice for oxygen mass transfer modelling is to apply overly simplified models, which come with multiple assumptions that are not valid for most applications. To deal with these complexities, correction factors were introduced over time. The most uncertain of them is the α-factor. To build fundamental gas-liquid mass transfer knowledge more advanced modelling paradigms have been applied more recently. Yet these come with a high level of complexity making them impractical for rapid process design and optimisation in an industrial setting. However, the knowledge gained from these more advanced models can help in improving the way the α-factor and thus gas-liquid mass transfer coefficient should be applied. That is why the presented work aims at clarifying the current state-of-the-art in gas-liquid mass transfer modelling of oxygen and other gases, but also to direct academic research efforts towards the needs of the industrial practitioners.
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| 23. |
- Amneklev, Jennie, et al.
(author)
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Upstream silver source mapping - a case study in Stockholm, Sweden
- 2014
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 69:2, s. 392-397
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Journal article (peer-reviewed)abstract
- Silver (Ag) can be a problem for wastewater treatment plants (WWTP) and their capability to use sewage sludge as a soil fertilizer. Due to a high accumulation rate in soils, the levels of Ag in the incoming water at the WWTP must be reduced. This study aims to identify major diffuse emission sources in the technosphere through a comprehensive substance flow analysis of Ag in Stockholm, Sweden. Large inflows and stocks of Ag were present in electrical and electronic goods and appliances as well as in jewellery and silverware. The total inflow was 3.2 tonnes (4.2 g/person), the total stock was 100 tonnes (140 g/person) and the total outflow was 330 kg (430 mg/person). Major identified Ag sources with emissions ending up in the WWTP (total 26 kg, 34 mg/person) were food, amalgam and beauty products (via urine and faeces, 12 mg/person or 11% of incoming amount), and textiles (via washing, 17 mg/person or 16% of incoming amount). This study explains approximately 35% of the total 80 kg Ag in the incoming water at Henriksdal WWTP in Stockholm. Plastic, photography and beauty products were identified as possible sources of Ag that need to be examined further.
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| 24. |
- Andersen, Henrik Rasmus, et al.
(author)
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Estrogenic personal care products in a greywater reuse system
- 2007
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 56:12, s. 45-49
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Journal article (peer-reviewed)abstract
- The occurrence and fate of parabens in a greywater system was assessed. The potential for removal of residual paraben concentrations in effluent greywater with chlorine dioxide was also investigated. The influent to the greywater plant was characterised by considerable variation, with concentrations from below the detection limit to 40 μg/L and the five commonly used parabens in consumer products were frequently detected. After the biological treatment only two paraben were detected with concentration from 65–120 ng/L. Chlorine dioxide treatment of the biologically treated effluent with dosages down to 0.75 mg/L resulted in more than 97% reduction of all parabens. Formation of the by-product chloroform was insignificant from the chlorine dioxide treatment.
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| 25. |
- Andersson, J., et al.
(author)
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Free water surface wetlands for wastewater treatment in Sweden : Nitrogen and phosphorus removal
- 2005
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In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 51:9, s. 39-46
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Journal article (peer-reviewed)abstract
- In South Sweden, free water surface wetlands have been built to treat wastewater from municipal wastewater treatment plants. Commonly, nitrogen removal has been the prime aim, though a significant removal of tot-P and BOD7 has been observed. In this study, performance data for 3-8 years from four large (20-28 ha) FWS wetlands have been evaluated. Two of them receive effluent from WWTP with only mechanical and chemical treatment. At the other two, the wastewater has also been treated biologically resulting in lower concentrations of BOD7 and NH4+-N. The wetlands performed satisfactorily and removed 0.7-1.5 ton N ha-1 yr-1 as an average for the time period investigated, with loads between 1.7 and 6.3 ton N ha-1 yr-1. Treatment capacity depended on the pre-treatment of the water, as reflected in the k20-values for N removal (first order area based mode). In the wetlands with no biological pre-treatment, the k20-values were 0.61 and 1.1 m month-1, whereas for the other two they were 1.7 and 2.5 m month-1. P removal varied between 10 and 41 kg ha-1 yr-1, and was related to differences in loads, P speciation and to the internal cycling of P in the wetlands. © IWA Publishing 2005.
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| 26. |
- Anh Nguyen, Viet, et al.
(author)
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Design and performance of a coarse media, high hydraulic load polishing wetland for steel industry wastewater
- 2019
-
In: Water Science and Technology. - : IWA PUBLISHING. - 0273-1223 .- 1996-9732. ; 80:1, s. 59-66
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Journal article (peer-reviewed)abstract
- This paper presents the design of a constructed wetland (CW) system in an area with limited land availability, resulting in high hydraulic loads. The CW was constructed to act as a buffering/polishing step after stabilization ponds for steel industry wastewater post-treatment. A pilot test with two different filter media (50-100 mm vs 40-60 mm diameter) indicated that a flow rate increase from 49.5 m(3)/h to 122.4 m(3)/h would lead to a head loss increase from 2.9 cm to 8.7 cm, and more than double that for the finer gravel. This was substantially higher than the calculated theoretical values, though the relation with flow rate was similar. Four full scale wetland cells (CW1, CW2, CW3 and CW4) were constructed using the coarser gravel. A design value of total head loss of 1.01 m over the total system length, with a design flow of 36,000 m(3)/day, was expected based on pilot test results. During the first operation year (September 2017 to July 2018), the pond-CW system has received wastewater already meeting required discharge standards. The effluent from the CWs had consistently lower concentrations of all measured variables, and met the predicted values for biochemical oxygen demand (BOD5), total nitrogen (TN) and NH4+-N. Highest removal efficiencies were achieved for NH4+-N (amp;gt; 90%), Mn (amp;gt; 60%) and Fe (45%) with removal efficiencies for TN (14%), BOD5 and chemical oxygen demand (COD) (around 30%). Concentrations of phenol, CN- and Cr6+ were below 10, 4 and 3 mu g/l, respectively, in in- and outflows. An appreciated benefit of the wetland was the green element in the industrial landscape.
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| 27. |
- Arheimer, Berit, et al.
(author)
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Using catchment models to establish measure plans according to the Water Framework Directive
- 2007
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 56:1, s. 21-28
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Journal article (peer-reviewed)abstract
- A participatory modelling process (DEMO) has been developed and applied in a 350 km(2) catchment in southern Sweden. The overall goal is to improve the dialogues between experts and local stakeholders by using numerical models as a platform for discussions. The study is focused on reducing nutrient load and on the development of a locally established measure plan, which is requested by the European Water Framework Directive. The HBV-NP model was chosen as it can calculate effects and costs for different allocations of several combined measures in a catchment. This paper shows the impact of including local data in the modelling process vs. using more general data. It was found that modelled diffuse nutrient pollution was highly modified when including local know-how, soft information and more detailed field investigations. Leaching from arable land was found to be 35% higher using more detailed information on for instance, agricultural practices, crop and soil distribution. Moreover, the stakeholders' acceptance of model results and reliance on experts was increased by applying the participatory process and involving stakeholders in the modelling procedure.
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| 28. |
- Arnell, Magnus, et al.
(author)
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Plant-wide modelling and analysis of WWTP temperature dynamics for sustainable heat recovery from wastewater
- 2021
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In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 84:4, s. 1023-1036
-
Journal article (peer-reviewed)abstract
- Wastewater heat recovery upstream of wastewater treatment plants (WWTP) poses a risk to treatment performance, i.e. the biological processes. In order to perform a sustainability analysis, a detailed prediction of the temperature dynamics over the WWTP is needed. A comprehensive set of heat balance equations was included in a plant-wide process model and validated for the WWTP in Linköping, Sweden, to predict temperature variations over the whole year in a temperate climate. A detailed model for the excess heat generation of biological processes was developed. The annual average temperature change from influent to effluent was 0.78°C with clear seasonal variations, wherein 45% of the temperature change arose from processes other than the activated sludge unit. To address this, plant-wide energy modelling was necessary to predict in-tank temperature in the biological treatment steps. The energy processes with the largest energy gains were solar radiation and biological processes, while the largest losses were from conduction, convection, and atmospheric radiation. Tanks with large surface areas showed a significant impact on the heat balance regardless of biological processes. Simulating a 3°C lower influent temperature, the temperature in the activated sludge unit dropped by 2.8°C, which had a negative impact on nitrogen removal
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| 29. |
- Bakyayita Kizito, Grace, et al.
(author)
-
Kinetic studies of Cd (II) and Pb (II) ions biosorption from aqueous media using untreated and chemically treated biosorbents
- 2014
-
In: Water Science and Technology. - : IWA Publishing. - 1606-9749 .- 1607-0798 .- 0273-1223 .- 1996-9732. ; 69:11, s. 2230-2236
-
Journal article (peer-reviewed)abstract
- Untreated and chemically treated Albizia coriaria, Erythrina abyssinica and Musa spp were studied in batch for uptake of Cd2+ and Pb2+ ions at pH 2.0–9.0 and agitation time; 30–390 min. Optimum biosorption conditions were; pH 4 for Pb2+ ions and pH 5 for Cd2+ ions, contact time was 3.5 hours at 24 ± 1 °C for 10 mg/L biosorbent dosage and initial metal ions concentration of 20 mg/L. Chemical treatment had a 10–17% biosorption efficiency enhancement for Cd2+ ions and a 1.6–2.3% reduction effect for Pb2+ ions. The sorption capacities for Cd2+ and Pb2+ ions for treated biosorbents were between 1.760–1.738 mg g−1 compared to 1.415–1.539 mg g−1 for untreated materials. The pseudo second order model suitably fitted the Cd2+ and Pb2+ ions biosorption data with regression coefficients (R2) between 0.9784–0.9999. Fitting of the Ho model to the experimental data showed that the biosorption mechanism for both metal ions studied was mainly a chemisorption process. Therefore, treated A. coriaria, E. abyssinica and Musa spp were potential biosorbents for remediation of Cd2+ ions and the untreated materials suitable for removing Pb2+ ions from contaminated aqueous media.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Batstone, Damien, et al.
(author)
-
Industrial applications of the IWA anaerobic digestion model No. 1 (ADM1)
- 2003
-
In: Water Science and Technology. - 0273-1223. ; 47:12, s. 199-206
-
Journal article (peer-reviewed)abstract
- In this paper, the IWA anaerobic digestion model No. 1 (ADM1) is applied to two case studies from contract work on industrial treatment plants. The first was the assessment of acid addition for pH decrease and avoidance of calcium carbonate (CaCO3) precipitation in a paper mill fed UASB. The simulation work found, with a high degree of confidence, that acid dosing was neither economical for pH control, nor had any real effect on the CaCO3 levels present in the reactor. A specific calcium carbonate precipitation equation was added to the ADM1 to undertake this study. The second case study was an assessment of the benefits of thermophilic (as opposed to mesophilic operation) for reduced ammonia inhibition, improved stability and gas production in a solids digester at a gelatine production facility. Here, it was predicted that thermophilic operation could not attain either goal to a satisfactory extent. In addition to demonstrating the application of the ADM1 to the two systems, we have also assessed the predictions generated in the case studies in terms of quality and utility.
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| 34. |
- Bengtsson, Simon, et al.
(author)
-
Production of polyhydroxyalkanoates by glycogen accumulating organisms treating a paper mill wastewater.
- 2008
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 58:2, s. 323-330
-
Journal article (peer-reviewed)abstract
- A process for production of polyhydroxyalkanoates (PHA) by activated sludge treating a paper mill wastewater was investigated. The applied strategy was to select for glycogen accumulating organisms (GAOs) by alternating anaerobic/aerobic conditions. Acidogenic fermentation was used as pretreatment to convert various organic compounds to volatile fatty acids which are preferable substrates for PHA production. Enrichment resulted in a culture dominated by GAOs related to Defluviicoccus vanus (56%) and Candidatus Competibacter phosphatis (22%). Optimization of PHA accumulation by the enriched GAO culture was performed through batch experiments. Accumulation of PHA under anaerobic conditions was limited by the intracellular glycogen stored. Under aerobic conditions significant glycogen production (to 25% of sludge dry weight) was observed alongside PHA accumulation (to 22% of sludge dry weight). By applying a subsequent anaerobic period after an initial aerobic, the produced glycogen could be utilized for further PHA accumulation and by this strategy PHA content was increased to 42% of sludge dry weight. The PHA yield over the entire process was 0.10 kg per kg of influent COD treated which is similar to what has been achieved with a process applying feast/famine enrichment strategy with the same wastewater.
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| 35. |
- Biswas, AK, et al.
(author)
-
Workshop 3 (synthesis) : water, poverty alleviation and social programs
- 2003
-
In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 47:6, s. 129-132
-
Journal article (peer-reviewed)abstract
- Poverty is a complex issue, which must be understood in a holistic manner. Low and variable income is certainly a key element, but it is far from enough to portray poverty. The various characteristics of poverty and their relative strength are determined through contextually specific circumstances, in terms of history, environmental preconditions, socio-cultural traits, etc. Much of this context is made up of local and national circumstances. The consequences of globalisation must, however, increasingly to be taken into account. At a larger scale, it is also relevant to mention that climate change will have a negative, although largely unpredictable, impact for the people in some parts of the world. For those who are already living on marginal lands or who are exposed to water problems, climate change is likely to create considerable adverse effects.
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| 36. |
- Björklund, Karin, 1979, et al.
(author)
-
Screening of Organic Contaminants in Urban Snow
- 2011
-
In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 64:1, s. 206-213
-
Journal article (peer-reviewed)abstract
- Snowmelt is known to cause peak concentrations of pollutants, which may adversely affectreceiving water quality. High concentrations of metals and suspended solids in snow have beenreported, whereas studies on organic pollutants are rare. This study aims at investigating theoccurrence of anthropogenic organic compounds in urban snow in Gothenburg (Sweden). The mostfrequently detected organic pollutants in the collected snow samples were polycyclic aromatichydrocarbons (PAHs), high molecular-weight phthalates, 4-nonylphenol and 4-t-octylphenol.Brominated flame retardants and chlorinated paraffins were only sporadically detected. In severalsnow samples, the concentrations of specific PAHs, alkylphenols and phthalates were higher thanreported stormwater concentrations and European water quality standards. Pollutant sourceidentification and sustainable management of snow are important instruments for the mitigation oforganic contaminants in the urban environment.
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| 37. |
- Björklund, Karin, 1979, et al.
(author)
-
Simulating organic pollutant flows in urban stormwater: development and evaluation of a model for nonylphenols and phthalates
- 2011
-
In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 65:3, s. 508-515
-
Journal article (peer-reviewed)abstract
- Stormwater-quality models can be useful tools for predicting pollutant loads and identifying sources of contamination. Most models in current use handle pollutants such as metals, nutrients and suspended solids, whereas models including emerging organic contaminants are rare.This study aims at developing and evaluating a model for simulating stormwater flows of two groups of organic pollutants; nonylphenols and phthalates. Sources, emission patterns and environmental fate were examined to create a model framework for the organic contaminants. The model was calibrated using field data from three urban catchments. The results show that the simulated pollutant concentrations are overestimated compared to the measured concentrations, which are often close to or below the analytical detection limit. The high uncertainty and the lowpredictive power of the model may be explained by factors such as incorrect catchment data, lack of knowledge on buildup, washoff and other processes involved in substance fate, and an underreporting of pollutant concentrations in stormwater. More data on release patterns and sewer fate are needed to adequately simulate stormwater concentrations of nonylphenols and phthalates. A conventional substance flow analysis based on bookkeeping, evaluated in parallel to the computer model, has proven to be useful for calculating fluxes of nonylphenols and phthalates in urban catchments.
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| 38. |
- Björklund, Karin, 1979, et al.
(author)
-
Sorption of DOM and hydrophobic organic compounds onto sewage-based activated carbon
- 2016
-
In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 74:4, s. 852-860
-
Journal article (peer-reviewed)abstract
- Treatment of stormwater via sorption has the potential to remove both colloidal and dissolved pollutants. Previous research shows that activated carbon produced from sewage sludge is very efficient in sorbing hydrophobic organic compounds (HOCs), frequently detected in stormwater. The aim of this research was to determine whether the presence of dissolved organic matter (DOM) has a negative effect on the adsorption of HOCs onto sludge-based activated carbon (SBAC) in batch adsorption tests. Batch adsorption tests were used to investigate the influence of two types of DOM – soil organic matter and humic acid (HA) technical standard – on the sorption of HOCs onto SBAC, and whether preloading adsorbent and adsorbates with DOM affects HOC sorption. The results indicate that soil DOM and HAs do not have a significant negative effect on the adsorption of HOCs under tested experimental conditions, except for a highly hydrophobic compound. In addition, preloading SBAC or HOCs with DOM did not lead to lower adsorption of HOCs. Batch adsorption tests appear to be inefficient for investigating DOM effects on HOC adsorption, as saturating the carbon is difficult because of high SBAC adsorption capacity and low HOC solubility, so that limited competition occurs on the sorbent.
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| 39. |
- Björklund, Karin, 1979
(author)
-
Substance flow analyses of phthalates and nonylphenols in stormwater
- 2010
-
In: Water Science and Technology. - : IWA Publishing. - 1996-9732 .- 0273-1223. ; 62:5, s. 1154-1160
-
Journal article (peer-reviewed)abstract
- The occurrence of nonylphenol and several phthalates in water environments is highly undesired because of their negative effects on aquatic organisms. The objectives of this study were to identify emission sources of phthalates, nonylphenol and its ethoxylates (NP/EOs) in urban stormwater, and to quantify the substance fluxes from the source to the stormwater system, using the methodology of substance flow analysis (SFA). The SFA, applied on an urban motorway area, showed that phthalates are mainly emitted from vehicles and coated roofing material, whereas the major NP/EOs sources are vehicles and concrete. It was estimated that approximately 4.1 kg of four selected phthalates and more than 400 g of NP/EOs are emitted annually to stormwater in the studied area. The SFA approach presented in this study, using factors that express the emission rate of a specific substance from a specific source, could be applied in urban catchments of various character to estimate fluxes of water contaminants.
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| 40. |
- Björn, Annika, et al.
(author)
-
Substrate and operational conditions as regulators of fluid properties in full-scale continuous stirred-tank biogas reactors - implications for rheology-driven power requirements
- 2018
-
In: Water Science and Technology. - : IWA PUBLISHING. - 0273-1223 .- 1996-9732. ; 78:4, s. 814-826
-
Journal article (peer-reviewed)abstract
- Understanding fluid rheology is important for optimal design and operation of continuous stirred-tank biogas reactors (CSTBRs) and is the basis for power requirement estimates. Conflicting results have been reported regarding the applicability of total solid (TS) and/or total volatile solid (TVS) contents of CSTBR fluids as proxies for rheological properties. Thus, the present study investigates relationships between rheological properties of 12 full-scale CSTBR fluids, their substrate profiles, and major operational conditions, including pH, TS and TVS contents, organic loading rate, hydraulic retention time, and temperature. Rheology-driven power requirements based on various fluid characteristics were evaluated for a general biogas reactor setup. The results revealed a significant correlation only between the rheological fluid properties and TS or TVS contents for sewage sludge digesters and thermophilic co-digesters (CD), but not for mesophilic CD. Furthermore, the calculated power requirements for pumping and mixing, based on the various fluid characteristics of the studied CSTBRs, varied broadly irrespective of TS and TVS contents. Thus, this study shows that the TS and/or TVS contents of digester fluid are not reliable estimators of the rheological properties in CSTBRs digesting substrates other than sewage sludge.
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| 41. |
- Blecken, Godecke-Tobias, et al.
(author)
-
The influence of temperature on nutrient treatment efficiency in stormwater biofilter systems
- 2007
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 56:10, s. 83-91
-
Journal article (peer-reviewed)abstract
- Nutrients can cause eutrophication of natural water bodies. Thus, urban stormwater which is an important nutrient source in urbanised areas has to be treated in order to reduce its nutrient loads. Biofilters which use soil filter media, biofilms and plants, are a good treatment option for nutrients. This paper presents the results of a biofilter column study in cold temperatures (+2 °C, +8 °C, control at +20 °C) which may cause special problems regarding biofilter performance. It was shown that particle-bound pollutants as TSS and a high fraction of phosphorus were reduced well without being negatively influenced by cold temperatures. Nitrogen, however, was not reduced; especially NOx was produced in the columns. This behaviour can be explained with both insufficient denitrification and high leaching from the columns
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| 42. |
- Bolmstedt, Jon, et al.
(author)
-
A benchmark study of controlled emptying of equalization basins
- 2005
-
In: Water Science and Technology. - 0273-1223. ; 52:12, s. 113-121
-
Journal article (peer-reviewed)abstract
- Storm tanks, or equalization basins, have been used for many years in sewer or wastewater treatment systems to reduce the amount of combined sewer overflows. In this paper, a systematic control of an equalization basin is used not only to dampen or reduce the hydraulic load, but also to systematically improve the effluent quality in a nitrogen removal plant. It is demonstrated that the effluent ammonia concentration is the key component. The Benchmark Simulation Model 1, implemented in MATLAB/Simulink, has been used to perform the evaluations. It has been extended with systematic rainfall generations. Intuitively, it is apparent that the equalization basin should be emptied before a rainfall. This requires a prediction capacity. It is shown that the choice of prediction time is by no means trivial and it is not true that a long prediction horizon is a,ways advantageous.
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| 43. |
- Borris, Matthias, et al.
(author)
-
An exploratory study of the effects of stormwater pipeline materials on transported stormwater quality
- 2017
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 76:2, s. 247-255
-
Journal article (peer-reviewed)abstract
- Implications of three sewer pipe materials (concrete, galvanized corrugated steel, and polyvinyl chloride (PVC)) for stormwater quality were explored in laboratory experiments, in which three types of stormwater, SW1-SW3, were circulated in 0.5 m long sewer pipe sections. SW1 and SW2 represented synthetic rainwater, without and with fine street sediment added (CTSS = 150 mg/L), respectively, and SW3 was actual stormwater with the same sediment addition as SW2. Following 20-min runs, with an equivalent distance of 500 m travelled by water particles, a number of statistically significant changes in the stormwater chemistry were observed: (i) pH of all the simulated stormwaters increased in the concrete pipe (from 7.0-7.3 to 8.1-9.3), (ii) turbidity decreased in two stormwaters with sediments (SW2 and SW3) in concrete and galvanized corrugated steel pipes (by 50 and 85%, respectively), (iii) the type of stormwater affected the observed copper (Cu) concentrations, with Cudiss concentrations as high as 25.3 μg/L noted in SW3 passing through the PVC pipe, and (iv) zinc (Zn) concentrations sharply increased (Zntot = 759-1,406 μg/L, Zndiss = 670-1,400 μg/L) due to Zn elution from the galvanized steel pipe by all three stormwaters. Such levels exceeded the applicable environmental guidelines.
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| 44. |
- Borris, Matthias, et al.
(author)
-
Simulating future trends in urban stormwater quality for changing climate, urban land use and environmental controls
- 2013
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 68:9, s. 2082-2089
-
Journal article (peer-reviewed)abstract
- The effects of climatic changes, progressing urbanization and improved environmental controls on the simulated urban stormwater quality in a northern Sweden community were studied. Future scenarios accounting for those changes were developed and their effects simulated with the Storm Water Management Model (SWMM). It was observed that the simulated stormwater quality was highly sensitive to the scenarios, mimicking progressing urbanization with varying catchment imperviousness and area. Thus, land use change was identified as one of the most influential factors and in some scenarios, urban growth caused changes in runoff quantity and quality exceeding those caused by a changing climate. Adaptation measures, including the reduction of directly connected impervious surfaces (DCIS) through the integration of more green spaces into the urban landscape, or disconnection of DCIS were effective in reducing runoff volume and pollutant loads. Furthermore, pollutant source control measures, including material substitution, were effective in reducing pollutant loads and significantly improving stormwater quality
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| 45. |
- Borzooei, Sina, et al.
(author)
-
Application of unsupervised learning and process simulation for energy optimization of a WWTP under various weather conditions
- 2020
-
In: Water Science and Technology. - : IWA PUBLISHING. - 0273-1223 .- 1996-9732. ; 81:8, s. 1541-1551
-
Journal article (peer-reviewed)abstract
- This paper outlines a hybrid modeling approach to facilitate weather-based operation and energy optimization for the largest Italian wastewater treatment plant (WWTP). Two clustering methods,K-means algorithm and Gaussian mixture model (GMM) based on the expectation-maximization (EM) algorithm, were applied to an extensive dataset of historical and meteorological records. This study addresses the problem of determining the intrinsic structure of clustered data when no information other than the observed values is available. Two quantitative indexes, namely the Bayesian information criterion (BIC) and the Silhouette coefficient using Euclidean distance, as well as two general criteria, were implemented to assess the clustering quality. Furthermore, seven weather-based influent scenarios were introduced to the process simulation model, and sets of aeration strategies are proposed. The results indicate that incorporating weather-based aeration strategies in the operation of the WWTP improves plant energy efficiency.
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| 46. |
- Brion, G, et al.
(author)
-
Probing Norwalk-like virus presence in shellfish, using artificial neural networks.
- 2004
-
In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 50:1, s. 125-9
-
Journal article (peer-reviewed)abstract
- A database was examined using artificial neural network (ANN) models to investigate the efficacy of predicting PCR-identified Norwalk-like virus presence and absence in shellfish. The relative importance of variables in the model and the predictive power obtained by application of ANN modelling methods were compared with previously developed logistic regression models. In addition, two country-specific datasets were analysed separately with ANN models to determine if the relative importance of the input variables was similar for geographically diverse regions. The results of this analysis found that ANN models predicted Norwalk-like virus presence and absence in shellfish with equivalent, and better, precision than logistic regression models. For overall classification performance, ANN modelling had a rate of 93%, vs 75% for the logistic regression. ANN models were able to illuminate the site-specific relationships between indicators and pathogens.
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| 47. |
- Buhl-Mortensen, Lene, et al.
(author)
-
Carbon sequestration, the precautionary approach and the responsibility of scientists
- 2005
-
In: Water Science and Technology. - 0273-1223 .- 1996-9732. ; 52:6, s. 205-212
-
Journal article (peer-reviewed)abstract
- This paper reviews problems connected to the use of the deep-sea and sub-sea geological formations for carbon sequestration. We will focus on the risks and dangers involved in using this kind of large-scale engineering approach, which is not yet fully tested, to combat global warming. We will not provide a complete discussion on the technologies involved, but concentrate on a few principal questions, such as the responsibility of environmental scientists involved in this research. We will also discuss carbon sequestration in relation to the precautionary approach. We argue that there may be a place for large-scale engineering attempts, but this should be the last rather than the first option. © IWA Publishing 2005.
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| 48. |
- Bürger, Raimund, et al.
(author)
-
A consistent modelling methodology for secondary settling tanks: A reliable numerical method.
- 2013
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 68:1, s. 192-208
-
Journal article (peer-reviewed)abstract
- The consistent modelling methodology for secondary settling tanks (SSTs) leads to a partial differential equation (PDE) of nonlinear convection–diffusion type as a one-dimensional model for the solids concentration as a function of depth and time. This PDE includes a flux that depends discontinuously on spatial position modelling hindered settling and bulk flows, a singular source term describing the feed mechanism, a degenerating term accounting for sediment compressibility, and a dispersion term for turbulence. In addition, the solution itself is discontinuous. A consistent, reliable and robust numerical method that properly handles these difficulties is presented. Many constitutive relations for hindered settling, compression and dispersion can be used within the model, allowing the user to switch on and off effects of interest depending on the modelling goal as well as investigate the suitability of certain constitutive expressions. Simulations show the effect of the dispersion term on effluent suspended solids and total sludge mass in the SST. The focus is on correct implementation whereas calibration and validation are not pursued.
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| 49. |
- Bürger, R., et al.
(author)
-
A review of flux identification methods for models of sedimentation
- 2020
-
In: Water science and technology : a journal of the International Association on Water Pollution Research. - : IWA Publishing. - 0273-1223. ; 81:8, s. 1715-1722
-
Journal article (peer-reviewed)abstract
- Most models of sedimentation contain the nonlinear hindered-settling flux function. If one assumes ideal conditions and no compression, then there exist several theoretically possible ways of identifying a large portion of the flux function from only one experiment by means of formulas derived from the theory of solutions of partial differential equations. Previously used identification methods and recently published such, which are based on utilizing conical vessels or centrifuges, are reviewed and compared with synthetic data (simulated experiments). This means that the identification methods are evaluated from a theoretical viewpoint without experimental errors or difficulties. The main contribution of the recent methods reviewed is that they, in theory, can identify a large portion of the flux function from a single experiment, in contrast to the traditional method that provides one point on the flux curve from each test. The new methods lay the foundation of rapid flux identification; however, experimental procedures need to be elaborated.
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| 50. |
- Bürger, Raimund, et al.
(author)
-
On time discretizations for the batch simulation of the settling-compression process in one dimension
- 2016
-
In: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 73:5, s. 1010-1017
-
Journal article (peer-reviewed)abstract
- The main purpose of the recently introduced Bürger-Diehl simulation model for secondary settling tanks was to resolve spatial discretization problems when both hindered settling and the phenomena of compression and dispersion are included. Straightforward time integration unfortunately means long computational times. The next step in the development is to introduce and investigate time-integration methods for more efficient simulations, but where other aspects such as implementation complexity and robustness are equally considered. This is done for batch settling simulations. The key findings are partly a new time-discretization method and partly its comparison with other specially tailored and standard methods. Several advantages and disadvantages for each method are given. One conclusion is that the new linearly implicit method is easier to implement than another one (semi-implicit method), but less efficient based on two types of batch sedimentation tests.
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