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Intermittent addition of external carbon to enhance denitrification in activated sludge

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Title: Intermittent addition of external carbon to enhance denitrification in activated sludge
Authors: Hallin, S., Hasselblad, S.
Source: Water Science & Technology. 1998, Vol. 37 Issue 9, p227. 0p.
Subjects: Sewage sludge, Wastewater treatment, Denitrification
Abstract: Efficient nitrogen removal in a pre-denitrifying activated sludge process strongly depends on the amount anil nature of the carbon sourcein the wastewater. If denitrification has to be supported at periods, the response to a supplemental carbon source should be immediate and substantial. The aim of this work was to study how intermittent addition of ethanol affects process performance and the denitrifying capacity of the biomass in a pre-denitrifying activated sludge process. The investigated intermissions simulated a possible operational situation with a short stop of ethanol addition or a strategy with addition only at weekends. The long-term effect of intermittent addition wasalso studied. Experiments were performed in a pilot-scale activated sludge plant. Effluent nitrate was measured on-line and potential denitrification rates were determined with the acetylene inhibition technique. Once the bacteria were adapted to the external carbon source, the studied intermission of 24 hours as well as an intermission of six days showed no severe effect on denitrification capacity of the sludge. In order to maintain process stability with intermittent addition, the denitrifying bacteria had to sustain a high capacity at each stop. Five weeks of intermittent addition of ethanol did not change the level of nitrate reduction in the system during periods of ethanol addition. Denitrification potential was, however, negatively affected. The results suggest that it is possible to use an intermittent strategy when adding ethanol as an external carbon source in a pre-denitrifying system and for instance only support the denitrifying bacteriaduring weekends. (c) 1998 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]
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Abstract:Efficient nitrogen removal in a pre-denitrifying activated sludge process strongly depends on the amount anil nature of the carbon sourcein the wastewater. If denitrification has to be supported at periods, the response to a supplemental carbon source should be immediate and substantial. The aim of this work was to study how intermittent addition of ethanol affects process performance and the denitrifying capacity of the biomass in a pre-denitrifying activated sludge process. The investigated intermissions simulated a possible operational situation with a short stop of ethanol addition or a strategy with addition only at weekends. The long-term effect of intermittent addition wasalso studied. Experiments were performed in a pilot-scale activated sludge plant. Effluent nitrate was measured on-line and potential denitrification rates were determined with the acetylene inhibition technique. Once the bacteria were adapted to the external carbon source, the studied intermission of 24 hours as well as an intermission of six days showed no severe effect on denitrification capacity of the sludge. In order to maintain process stability with intermittent addition, the denitrifying bacteria had to sustain a high capacity at each stop. Five weeks of intermittent addition of ethanol did not change the level of nitrate reduction in the system during periods of ethanol addition. Denitrification potential was, however, negatively affected. The results suggest that it is possible to use an intermittent strategy when adding ethanol as an external carbon source in a pre-denitrifying system and for instance only support the denitrifying bacteriaduring weekends. (c) 1998 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]
ISSN:02731223
DOI:10.1016/S0273-1223(98)00292-3