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- Routh, Joyanto, 1968-, et al.
(författare)
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Trace-element geochemistry of Onion Creek near Van Stone lead-zinc mine (Washington, USA) — Chemical analysis and geochemical modeling
- 1996
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 133:1, s. 211-224
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Tidskriftsartikel (refereegranskat)abstract
- Van Stone lead-zinc mine in Washington is a possible contamination source of Columbia River water. Breaching of an old tailings pond, seepage of contaminated water, and surficial transport of mine tailings have increased trace-element (TE) concentrations in the Onion Creek water and sediments. Chemical analyses of water and sediment samples indicate high TE levels near the breached tailings pond. TE contamination indices for sediments indicate high values of Pb, Zn, and other TE’s which decrease downstream. High Kd values (> 104) for several TE’s (e.g., Al, Cd, Fe, Mn, Pb, V, and Zn) suggest their enrichment in the solid phase. TE concentrations in Onion Creek water and sediment sharply attenuate downstream due to: (1) enhanced carbonate dissolution, thereby increasing pH and immobilizing TE’s; (2) sorption to oxides; and (3) change in lithology from carbonate to granite. Speciation model MINTEQA2 was used to study the effect on TE dispersion due to dissolution-precipitation reactions and adsorption to ferrihydrite. In addition to the field and chemical data, the model also supports the hypothesis that Onion Creek sediments are the major sink for TE’s at VSM. Model runs indicate precipitation of Al, Ba, Ca, Fe, Mg, and Mn minerals from oversaturation, whereas TE’s with low concentrations (Cr, Cu, Ni, Se) or geochemically more mobile (As, Mo, Sb) remain dissolved in water. Near the tailings ponds, high pH and abundance of sorption sites in sediments contribute to the complete adsorption of Pb and Zn species. Because ambient conditions result in the sorption of most Pb and Zn ions, Onion Creek water quality meets EPA regulatory standards. These species will persist in Onion Creek sediments as sorbed or insoluble complexes, and without drastic pH changes (< 4.0) they will remain immobilized. However, continued TE enrichment in sediments will prove hazardous to filter feeding and aquatic organisms.
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| 2. |
- Jeppsson, Ulf, et al.
(författare)
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On the modelling of the dynamic propagation of biological components in the secondary clarifier
- 1996
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 85-92
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Dave, Göran, 1945
(författare)
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Workshop 1: Aquacultures for wastewater treatment - Summary and conclusion by the chairperson
- 1996
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Ingår i: RECYCLING THE RESOURCE: PROCEEDINGS OF THE SECOND INTERNATIONAL CONFERENCE ON ECOLOGICAL ENGINEERING FOR WASTEWATER TREATMENT Book Series: ENVIRONMENTAL RESEARCH FORUM. - 1421-0274. - 0878497412 ; 5-6, s. 107-110
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Konferensbidrag (refereegranskat)abstract
- The primary objective of this paper is to address 6 questions on wastewater aquaculture. These are: 1. What is the state of the art of wastewater aquaculture? 2. Can aquaculture contribute to a sustainable use of wastewater? 3. Are there inherent dangers in this technology? 4. What should future research concentrate on? 5. What role can wastewater aquaculture play in wastewater treatment systems in the future? 6. What is the potential for wastewater treatment and food production in temperate climates? These questions were discussed at the 2nd International Conference on Ecological Engineering, and this paper is an attempt to provide very short answers to these very complex questions
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| 4. |
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| 5. |
- Jeppsson, Ulf, et al.
(författare)
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An evaluation of a dynamic model of the secondary clarifier
- 1996
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223. ; 34:5, s. 19-26
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Wik, Torsten, 1968
(författare)
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An investigation of the fast dynamics in a nitrifying trickling filter
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The fast dynamics of a large pilot scale nitrifying trickling filter (NTF) using effluent waste water from Rya Waste Water Treatment Plant in Göteborg, Sweden, has been investigated experimentally and by simulations. The plant is 7.2 m high, have a diameter of 2.7 m, and was filled with a cross-flow media with a specific surface area of 226 m^2/m^3. Continuous ammonium meters connected to the NTF measured influent and effluent ammonium concentrations.Two different phenomena may affect the fast dynamics in this type of biofilm reactors: The mixing in the bulk flow and the dynamics within the biofilm, i.e. the mixing in the biofilm and the response time for the bacteria to changes in substrate concentrations.Pulse response experiments conducted at two different flows (7.3 l/s and 14.5 l/s), where dissolved LiCl was used as trace substance, showed that the flow through the NTF could not be characterized as laminar, but significant mixing occurs inside the plant. The residence time distributions are well approximated by four identical continuously stirred tanks in series, and from the mean residence time the liquid film thickness was estimated to be 0.5 mm.Two experiments, where the influent ammonium concentration was rapidly increased while the flow was held constant at 14 l/s, were also conducted as well as an experiment where the flow was stochastically varied around 12 l/s. Comparisons are made between the measured effluent concentrations in these experiments and simulations of a model of the plant, where the NTF is divided into a series of continuously stirred tank reactors (CSTRs) having the total volume estimated from the pulse response experiments. The nitrification rate in each CSTR is modelled as a first order dynamic system driven by a physically derived expression of the stationary nitrification rate. Simulations for different values of the time constant of this dynamic system, and comparisons with the experimental data, shows that the dynamics within the biofilm are much faster than the dynamics of the mixing in the bulk. Implicitly, this means that the response times for the nitrifying bacteria to changes in ammonium bulk concentration were less than a few minutes. Hence, the fast dynamics in the biofilm can in many cases be neglected, which greatly facilitates simulations of many nitrifying biofilm reactors when more complex biofilm models are used.
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| 7. |
- Wik, Torsten, 1968
(författare)
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Experiment utförda på en nitrifierande biobädd 1995
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A number of experiments was conducted on a pilot scale nitrifying trickling filter during 1995. The experiments aimed for better knowledge of the flow-dependent fast dynamics, and the slow bacterial dynamics.The residence time distribution was investigated by a number of impulse response experiments where dissolved LiCl was added to the influent. The experiments showed that the amount of water in the trickling filter is almost independent of the flow through the plant, and corresponds to a liquid film thickness of approximately 0.5 mm. The residence time distribution can be approximated by a model with four or five identical and ideally continuously stirred tanks.Based on the results of the impulse response experiments the plant is modelled by four continuously stirred tank reactors in series, where the nitrification in each tank is described by a physically derived nonlinear expression.Data from a few step response experiments, where the ammonium concentration in the influent was raised from a low constant level to a high constant level at a constant flow through the plant, was compared to model simulations. The comparisons showed that the fast dynamics in the biofilm can be neglected in comparison to the dynamics caused by the mixing in the bulk and the residence time distribution. Implicitly, this means that the response time for the active nitrifying bacteria to changes in ammonium concentration is less than a few minutes, also when the ammonium load has been very low for a long time.An experiment, where the flow was stochastically varied around an operating point during one day, showed that the simple model derived sufficiently well describe the fast dynamics of nitrifying trickling filter also when the flow changes. When the ammonium concentration in the effluent is low, a model where the nitrification rate is assumed constant is not sufficient.The slow dynamics that depend on the growth and decay of the active nitrifying bacteria was investigated by a three months long step response experiment, where the ammonium concentration in the influent first was held at a high level (not full nitrification) for approximately one month and then at a low level (approximately 50% of the nitrifying capacity) for one month, and finally at the same high level as before for one more month. In spite of several practical problems, the experiment indicated that it takes one to two weeks for the concentration of active bacteria in the biofilm to increase to a new higher concentration after the raise in influent ammonium concentration. The corresponding increase in nitrification rate is approximately 20%.The two periods of the same high influent ammonium concentration was during periods with different water temperature. Comparisons of the nitrification rate between the two periods indicated a stronger dependency on the temperature than has earlier been observed. The standard temperature dependency of the maximum growth rate for nitrifying bacteria that are used for laboratory scale experiments may well apply also for this large scale process.During periods of the experiment the ammonium sensors were not working. Therefore the possibility to determine the influent ammonium concentration based on the flow into the plant was investigated. Both black box models and a physically based model was fitted to data. The investigation showed that with a good model of the influent flow to the plant it may be possible to predict the ammonium concentration with quite good accuracy.The trickling filter was flooded weekly for a couple of hours for predator control. An investigation of the nitrification rate before and after the floodings showed no short term effects of the flooding.When the pilot plant was taken out of operation at the end of the year the uppermost meter of the plant was investigated. It was observed that the biofilm thickness was approximately 0.5mm and no bare surfaces without biofilm could be observed.
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