Dewaterability of unconditioned sludge digested in full scale and lab scale experiments using either extended aeration (EA) or anaerobic digestion were compared on full and lab scale sand drying beds. Sludge digested in EA plants resulted in improvement in sludge dewaterability compared to sludge digested anaerobically. This was demonstrated by comparing capillary suction time, time to filter a specific amount of water, the sludge volume index and the dry solids content. In addition, sieve analysis results from both types of sludge after drying in sand drying beds clearly shows that the grain portions in the fine range in case of anaerobically digested sludge are more than that in case of EA sludge. This was also clear in microscopic photos of samples. The microscopic photos of EA stabilized sludge are characterized by larger colonies of flocs and more open structure than anaerobically digested sludge.
Key words: Sludge, dewaterability, digestion, sand drying beds, particle size distribution.
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