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- 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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- 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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- Westrell, Therese, et al.
(författare)
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A systems analysis comparing drinking water systems – central physical-chemical treatment and local membrane filtration
- 2002
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Ingår i: Water Science & Technology: Water Supply. - 0273-1223. ; 2:2, s. 11-18
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a first attempt at an integrated systems analysis of drinking water systems using Microbiological Risk Assessment (MRA) and Material Flow Analysis (MFA) with focus on the comparison of central physical-chemical treatment (conventional system) and local membrane filtration. The MFA shows that energy use is the most significant environmental impact of the three studied drinking water systems, but there are no considerable differences in energy use comparing central physical-chemical treatment and local membrane filtration. According to the MRA, the conventional system might not reduce the microbial risks sufficiently, but such a reduction can not confidently be achieved in a one-step ultrafiltration system either, since membrane filter integrity can hardly be guaranteed over the service life of the equipment. A quite costly two-step membrane filtration system, where water for all household purposes passes microfiltration and further reverse osmosis for drinking and cooking, seems to fulfil this criterion. On the other hand, this system does not reduce the microbial risks from ingestion of water from showers compared with the one-step ultrafiltration alternative. In order to achieve drinking water systems with sufficient microbial barriers and with reasonable costs for operation, a promising solution seems to be a combination of one-step membrane filtration and other methods e.g. biological treatment.
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