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The effect of enzyme pre-treatment on dewaterability of anaerobically digested biosolids was investigated at both laboratory and pilot scale. Similar to previously reported results, laboratory results revealed a significant increase in cake solid content (33% cake solids compared to 20% without enzyme pretreatment), using an enzyme dose of only 15 mg/L. In order to assess practical application, enzyme pre-treatment was applied at the Wilmington wastewater treatment plant, using a pilot-scale centrifuge. However, the dewatering efficiency reached in laboratory scale could not be obtained in pilot scale, where the final cake solids content reached only 20% with different enzyme doses. Possible factors that might cause the differences were tested by experimental and statistical comparisons. Results indicated that the higher shear applied in centrifugation is responsible for the lack of improved cake solids. The network strength of sludge determined by rheological measurements revealed that enzymatic treatment could weaken the gel structure of the sludge floc through the hydrolysis of extracellular polymeric substances; this allows improved dewatering by filtration processes, but leads to floc deterioration when subjected to high shear during centrifugation. Different polymers with different chemical structures were tested, however, only 2 pts increase in cake solids were observed in pilot centrifugation. Pilot or full scale testing with belt filter press devices is needed to verify the observed increase in cake solids with the Crown Press simulator.
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Document Type: Research Article

Publication date: 2007-01-01

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