Recent studies reported significant increases in indicator bacteria counts in anaerobically digested sludge samples during and shortly after centrifugal dewatering. The reasons behind the observed increases are not yet well-understood. This study investigated the effect of centrifuge
shear and polymer addition on the fecal coliform counts measured after centrifugation. Centrifuge shear and polymer dose may impact the attachment of bacteria to sludge solids, which in return may impact the enumeration procedure. In this study, the centrifugation speed and dose were varied,
and changes in the fecal coliform counts were monitored for two days after centrifugation. Fecal coliform counts were measured using EPA Method 1680 and Method 1681. The results indicate that centrifugation shear, polymer type and polymer dose do not cause a significant increase in the fecal
coliform counts measured after centrifuge dewatering.
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