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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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- Persson, Frank, 1970, et al.
(författare)
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Removal of geosmin and MIB by biofiltration - An investigation discriminating between adsorption and biodegradation
- 2007
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Ingår i: Environmental Technology. - 0959-3330 .- 1479-487X. ; 28:1, s. 95-104
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Tidskriftsartikel (refereegranskat)abstract
- Geosmin and 2-methylisoborneol (MIB) are two substances causing earthy/musty odours that are difficult to remove by conventional chemical drinking water treatment. In this study removal of geosmin and MIB by biofiltration of untreated surface water was investigated using granular activated carbon (GAC) and crushed expanded clay (EC) as filter media. Biofiltration through both GAC and EC removed geosmin and MIB present at low (20 ng l(-1)) concentrations by at least 97% at an empty bed contact time of 30 minutes and a temperature of 15 degrees C. At lower temperature (6-12 degrees C) and simultaneously lower biomass concentrations, removal efficiency was similar in the GAC but considerably lower in the EC biofilter, pointing to a second mechanism different from biodegradation. Consequently, microbial activity was suppressed with azide to enable discrimination between biodegradation and adsorption. During azide dosage, the GAC biofilters still removed geosmin and MIB nearly unaffectedly. In the EC biofilter, however, removal of both odorants ceased completely. Methylene blue adsorption confirmed that the GAC, even after almost four years of operation receiving surface water, had capacity to remove geosmin and MlB by adsorption. Since odour episodes commonly occur during the warm season when microbiological activity is high, EC constitutes a viable option as carrier medium for direct biological filtration of surface water. The additional GAC adsorption capacity however adds robustness to the removal process.
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