| 1. |
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| 2. |
- Wilen, Britt-Marie, 1966, et al.
(författare)
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Impacts of structural characteristics on activated sludge floc stability
- 2003
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 37:15, s. 3632-3645
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Tidskriftsartikel (refereegranskat)abstract
- Activated sludge samples from seven full scale plants were investigated in order to determine the relationship between floc structure and floc stability. Floc stability was determined by shear sensitivity and floc strength. Floc structure was considered in terms of two size scales, the micro and macro-structure. The micro-structure refers to the organisation of the floc components, such as the individual microorganisms. The macro-structure refers to the overall floc. The floc macro-structure was characterized by filament index, sludge volume index (SVI), size, and fractal dimension. It had a significant impact on floc stability. Large and open flocs with low fractal dimensions, containing large numbers of filaments were more shear sensitive and had lower floc strength compared to small and dense flocs. Fluorescent in-situ hybridisation (FISH) analysis indicated that the organization of the bacterial cells might also have an affect on the floc stability.
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| 3. |
- Andersson, Anneli, et al.
(författare)
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Impact of temperature on nitrification in biological activated carbon (BAC) filters used for drinking water treatment
- 2001
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 35:12, s. 2923-2934
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Tidskriftsartikel (refereegranskat)abstract
- The impact of temperature on nitrification in biological granular activated carbon (GAC) filters was evaluated in order to improve the understanding of the nitrification process in drinking water treatment. The study was conducted in a northern climate where very cold water temperatures (below 2°C) prevail for extended periods and rapid shifts of temperature are frequent in the spring and fall. Ammonia removals were monitored and the fixed nitrifying biomass was measured using a method of potential nitrifying activity. The impact of temperature was evaluated on two different filter media: an opened superstructure wood-based activated carbon and a closed superstructure activated carbon-based on bituminous coal. The study was conducted at two levels: pilot scale (first-stage filters) and full-scale (second-stage filters) and the results indicate a strong temperature impact on nitrification activity. Ammonia removal capacities ranged from 40 to 90% in pilot filters, at temperatures above 10°C, while more than 90% ammonia was removed in the full-scale filters for the same temperature range. At moderate temperatures (4–10°C), the first stage pilot filters removed 10–40% of incoming ammonia for both media (opened and closed superstructure). In the full-scale filters, a difference between the two media in nitrification performances was observed at moderate temperatures: the ammonia removal rate in the opened superstructure support (more than 90%) was higher than in the closed superstructure support (45%). At low temperatures (below 4°C) both media performed poorly. Ammonia removal capacities were below 30% in both pilot- and full-scale filters.
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| 4. |
- Andersson, Per, et al.
(författare)
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A rapid preconcentration method for multielement analysis of natural freshwaters
- 1991
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 25:5, s. 617-620
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Tidskriftsartikel (refereegranskat)abstract
- This study describes an inexpensive and rapid preconcentration method which can be applied directly in the field. It is based on coprecipitation with magnesium hydroxide and has been applied for Al, Fe, Mn, Zn, Cu, Ni, V, Cr, Co, Cd, Be, Y, Sc and Yb in freshwaters. The method has been tested using inductively coupled plasma-atomic emission spectrometry (ICP-AES) by adding known amounts of metals to distilled water and natural freshwater. The detection limit for ICP-AES can be enhanced more than two orders of magnitude for Al, Y, Sc, Yb and approximately one order of magnitude for the other tested elements.
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| 5. |
- Du, Qing, et al.
(författare)
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Complexations in illite–fulvic acid–Cu2+ systems
- 1999
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 33:3, s. 693-706
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Tidskriftsartikel (refereegranskat)abstract
- As part of an extended project to illustrate how heavy metals are complexed by natural aquatic particles, we conducted various experiments to study the adsorption of fulvic acid (FA) at aqueous illite surfaces and the complexation of heavy metal copper(II) in illite-FA bi-complexant systems. By analyzing batch adsorption and potentiometric titration data, we found that (i) the adsorption of FA by illite decreases with increases in pH values and its pH adsorption edge resembles those of SiO2-FA and montmorillonite-FA systems described by other researchers, (ii) it is possible to effectively simulate the complexation of Cu2+ ions in illite-FA bi-complexant systems by taking it to be an additive complexation of two mono-complexant systems (FA-Cu2+ and illite-Cu2+) and (iii) FA can inhibit the retention of heavy metals at solid surfaces by forming soluble complexes with metal ions. The above results and conclusions are supported by FT-IR analysis of various illite-FA-Cu2+ systems.
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| 6. |
- Grunditz, C., et al.
(författare)
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Development of nitrification inhibition assays using pure cultures of Nitrosomonas and Nitrobacter
- 2001
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 35:2, s. 433-440
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Tidskriftsartikel (refereegranskat)abstract
- Restricted requirements for nitrogen reduction at wastewater treatment plants have increased the need for assays determining the inhibition of nitrification. In this paper, two new essays studying ammonia oxidation and nitrite oxidation, respectively, are presented. As test organisms, pure cultures of Nitrosomonas and Nitrobacter isolated from activated sludge are used. The assays are performed in test tubes where the bacteria are incubated with the compound or wastewater to be tested. The nitrification rate is measured during 4h and compared with reference samples. The test organisms were characterised with respect to temperature, pH and cell activity. Optimum temperature was 35 degreesC for Nitrosomonas and 38 degreesC for Nitrobacter; optimum pH was 8.1 for Nitrosomonas and 7.9 for Nitrobacter. There was a linear relationship between the nitrification rate and the cell concentration in the studied interval. The cell activity decreased slightly with storage time. A significant level of inhibition was calculated to 11% for the Nitrosomonas assay, and to 9% for the Nitrobacter assay. The assays are applicable to determination of nitrification inhibition in samples of industrial waste waters or influents of treatment plants, or chemical substances likely to be found in wastewater.
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| 7. |
- Johansson, Lena, 1967-, et al.
(författare)
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Phosphate removal using blast furnace slags and opoka-mechanisms
- 2000
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 34:1, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- The abiotic sorption efficiency of on-site wastewater treatment systems can be improved by using a strongly sorbing filter material that, if it retains phosphorus (P) in a plant available way, can be used as fertiliser when P saturation is achieved. Two materials, blast furnace slag and the siliceous sedimentary rock opoka, have shown a high P sorption capacity and were included in a set of experiments to investigate the P retention mechanisms from model P-solution. Experiments focusing on the P sorption, capacity and calcium (Ca) and PO4 determination were carried out. The pH was also measured. The P sorption experiment showed that some slags were efficient P retainers, while the opoka was the least efficient P retainer. The pH decreased in all samples as a function of P addition. In the slag samples, the Ca concentration also decreased as a function of P addition, suggesting Ca-P precipitation as the major P removal mechanism for the slag. The Ca and PO4 speciation data ruled out the formation of amorphous calcium phosphates and/or octacalcium phosphate as the major P removal mechanism. However, the calculated ion activity products displayed clear evidence that hydroxyapatite had precipitated above a certain critical supersaturation limit. This would explain the poor P retention efficiency of the opoka samples in this study as the ion activity products were too low. The finding that direct hydroxyapatite formation is the predominant P removal mechanism might have important implications for their possible use as fertiliser due to the poor solubility of hydroxyapatite.
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| 8. |
- Jonsson, K., et al.
(författare)
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Occurrence of nitrification inhibition in Swedish municipal wastewaters
- 2000
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 34:9, s. 2455-2462
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of substances inhibiting nitrification in Swedish municipal wastewaters was investigated using three methods: a screening method based on activated sludge and two pure culture methods based on Nitrosomonas and Nitrobacter. Influent samples from 109 wastewater treatment plants collected every day during one specific week were investigated. The three test methods were also compared. The results of the screening method showed that about 60% of the plants received wastewater containing inhibitory substances, although only 4% had considerable inhibition (>20%). With the two pure culture methods, inhibition was found at about 45% of the plants investigated, with considerable inhibition found at 13% and 20% of the plants with the Nitrosomonas and the Nitrobacter methods, respectively. The limit of detection was determined to be 5% inhibition for the screening method, 11% inhibition for the Nitrosomonas method and 13% inhibition for the Nitrobacter method. The pure culture methods found more samples strongly inhibitory or stimulating than the screening method. The highest correlation between the inhibition results from the three methods was found between the screening method and the Nitrosomonas method. It was also shown for sludge from several activated sludge treatment plants, that they were adapted to the toxic compounds present in the influent. At high inhibition this acclimatisation was less pronounced. No correlation was found for any of the methods between the inhibition and parameters such as the size of the plant, the geographic location, the content of ammonia, COD or conductivity in the influent, the presence of leachate or the percentage of industrial wastewater in the influent, or types of industries in the catchment area. However, the constantly highest inhibition was found at a plant with a large number of different industries connected. Any clear pattern for the variation of inhibition during the week was not found.
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| 9. |
- Jonsson, Susanne, 1965-, et al.
(författare)
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Mono- and diesters from o-phthalic acid in leachates from different European landfills
- 2003
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Ingår i: Water Research. - 0043-1354 .- 1879-2448. ; 37:3, s. 609-617
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Tidskriftsartikel (refereegranskat)abstract
- Leachates from 17 different landfills in Europe were analysed with respect to phthalates, i.e. phthalic acid diesters (PAEs) and their degradation products phthalic acid monoesters (PMEs) and ortho-phthalic acid (PA). Diesters are ubiquitous and the human possible exposure and potential to human health and environment has put them in focus. The aim of this study was to elucidate whether monoesters and phthalic acid could be traced in landfill leachates and in what concentrations they may be found. The results showed that phthalates were present in the majority of the leachates investigated. The monoesters appeared from 1 to 20 μg/L and phthalic acid 2–880 μg/L (one divergent value of 19 mg phthalic acid/L). Their parental diesters were observed from 1 to 460 μg/L. These observed occurrences of degradation products, of all diesters studied, support that they are degraded under the landfill conditions covered by this study. Thus, we have presented strong evidences to conclude that microorganisms in landfills degrade diesters released from formulations in a variety of products, including polyvinyl chloride (PVC) species.
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| 10. |
- Larsson, Per, et al.
(författare)
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Microbial mineralization of chlorinated phenols and biphenyls in sediment/water systems humic and clear-water lakes
- 1989
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 23:9, s. 1081-1085
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Tidskriftsartikel (refereegranskat)abstract
- The microbial mineralization of three chlorophenols and a PCB mixture was studied using natural bacterial assemblages in laboratory model systems. The systems consisted of water and surface sediment from two lake types: one with a high content of humic substances and the other with a low content. Aerobic mineralization of the 14C-ring-labelled compounds was determined as production of 14CO2 in the systems. The mineralization rates of 3,4-dichlorophenol and 2,4,5-trichlorophenol were higher in humic cultures whereas pentachlorophenol showed higher rates in clear-water cultures. Mineralization of PCBs in the systems was low. Compared with microbial mineralization rates in cultures containing only lake water, the addition of sediment resulted in a decrease in DCP and TCP mineralization. Pentachlorophenol was mineralized at considerably higher rates in the presence of sediment.
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