Size-dependent anaerobic digestion rates of flocculated activated sludge: Role of intrafloc mass transfer resistance
Resource
Journal of Environmental Management 76 (3): 239-244
Journal
Journal of Environmental Management
Journal Volume
76
Journal Issue
3
Pages
239-244
Date Issued
2005
Date
2005
Author(s)
Abstract
The anaerobic digestion rate for flocculated sludge has been considered to be lower than that of original sludge, particularly in the later stages of digestion; attributed this relatively slower rate to the increased mass transfer resistance for reactants through the large flocs after flocculation. This study confirmed that methane production was retarded by flocculation. The structure of the floc was identified with fluorescence in situ hybridization (FISH) and a confocal laser scanning microscope (CLSM) technique. To verify the mass transfer resistance induced by flocculation, microsensors were applied to assess the response of oxygen concentration distribution inside the flocs that are subjected to sudden changes in ambient oxygen levels. Response time for the electrode at a floc's center was five times greater than the response time in original sludge flocs. Although the effective diffusivity of oxygen in the floc increased by 2.3 times after flocculation, the increased size of the flocculated floc was the major contributor to the total mass transfer resistance to oxygen.
Type
journal article
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