| 1. |
- Heinicke, G., et al.
(författare)
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The effect of biological pre-filtration on the performance of conventional surface water treatment
- 2006
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Ingår i: Journal of Water Supply: Research and Technology - Aqua. - 0003-7214. ; 55:2, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Many waterworks that apply conventional treatment of surface water, by flocculation and filtration, have to deal with seasonal changes of the raw water quality, increasing concentrations of natural organic matter (NOM), and the necessity to improve particle removal. A pilot plant was operated to closely resemble the full-scale treatment at a surface water treatment plant in Göteborg, Sweden. Treatment consisted of flocculation, sedimentation and rapid granular activated carbon (GAC) filtration. To assess the effects of biological pre-filtration, the feed water to the pilot plant was switched weekly between surface water and biofiltered water which had passed through adsorptively exhausted GAC at an empty bed contact time (EBCT) of 34 minutes. The processes were investigated with regard to NOM, the bacterial re-growth potential, as well as their function as a barrier for suspended particles that originate from the raw water. Biological pre-filtration improved particle removal and made it less dependent on the post-sedimentation GAC rapid filter, thereby improving robustness. Episodically elevated concentrations of earthy-musty odour compounds, which are not reliably removed by flocculation and filtration, were reduced by the biofilters. The process combination may be of particular interest for waterworks with variable raw water quality.
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| 2. |
- Persson, Frank, 1970, et al.
(författare)
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Characterisation of the behaviour of particles in biofilters for pre-treatment of drinking water
- 2005
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Ingår i: Water Research. - : Elsevier BV. - 0043-1354 .- 1879-2448. ; 39:16, s. 3791-3800
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Tidskriftsartikel (refereegranskat)abstract
- Biofiltration of surface water was examined using granular activated carbon (GAC) and expanded clay (EC). Particle removal was 60-90%, measured by flow cytometry, which enabled discrimination between total- and autofluorescent particles (microalgae) in size ranges of 0.4-1 and 1-15 mu m, and measured by on-line particle counting. Total particles were removed at a higher degree than autofluorescent particles. The biofilters were also challenged with 1 mu m fluorescent microspheres with hydrophobic and hydrophilic surface characteristics and bacteriophages (Salmonella typhimurium 2813). Added microspheres were removed at 97-99% (hydrophobic) and 85-89% (hydrophilic) after 5 hydraulic residence times (HRT) and microspheres retained in the biofilter media were slowly detaching into the filtrate for a long time after the addition. Removal of bacteriophages (5 HRT) was considerably lower at 40-59%, and no long-lasting detachment was observed. A comparison of experimental data with theoretical predictions for removal of particles in clean granular media filters revealed a similar or higher removal of particles around 1 mu m in size than predicted, while bacteriophages were removed at a similar or lesser extent than predicted. The results highlight the selectivity and dynamic behaviour of the particle removal processes and have implications for operation and microbial risk assessment of a treatment train with biofilters as pre-treatment. (c) 2005 Elsevier Ltd. All rights reserved.
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| 3. |
- Persson, Frank, 1970, et al.
(författare)
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Performance of direct biofiltration of surface water for reduction of biodegradable organic matter and biofilm formation potential
- 2006
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Ingår i: Environmental Technology. - 0959-3330 .- 1479-487X. ; 27:9, s. 1037-1045
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Tidskriftsartikel (refereegranskat)abstract
- Direct biofiltration of surface water may be considered as pre-treatment for membrane filtration, in order to reduce fouling. The biofiltration process was investigated with regard to biodegradable organic matter and biofilm formation, covering the annual variations under moderately cold climate conditions. Granular activated carbon (GAC) and two types of crushed expanded clay (EC) were compared as filter media. To assess the biological properties of the biofilters, viable biomass and respiratory activity was examined. Biofiltration removed assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) by about 30% and also reduced the bacterial concentration in the water phase. Also, biofilm formation in the treated water was reduced by 80-90% during summer and winter conditions. The reductions in the investigated parameters were similar in the biofilters with GAC and EC. Likewise, a similar amount and development of biomass was found in the GAC and EC biofilters of comparable grain size with a pronounced stratification from top to bottom of the filter bed. The specific respiratory activity of the biofilter biomass was dependent on raw water temperature. Even though slight correlations between BDOC removal and temperature or respiratory activity were observed, AOC and BDOC removals were mainly dependent on the feed water concentrations of these compounds. The results indicate that direct biofiltration of surface water, by reducing AOC, BDOC and biofilm formation in the water, may be an advantageous pre-treatment for membrane filtration processes.
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