Polyelectrolyte Flocculation of Waste Activated Sludge in Decanter Centrifuge Applications: Lab Evaluation by a Centrifugal Compaction Test

Abstract

This article introduces a centrifugal compaction (spin tube) test to thoroughly evaluate polyelectrolyte conditioning on lab scale. In contrast to the well-known and widely applied existing tests (e.g., the beaker, the Jar settling, the free drainage, and the [sheared] capillary suction time test), the proposed spin tube test has a clear relation with the dewatering process taking place in a decanter centrifuge. First, based on the theory of centrifugal compaction, the solids stress of separate layers of sludge cake (obtained after spinning sludge in a lab centrifuge) is calculated. Next, the test was applied to assess in the lab the performance of three different polymers by evaluating the obtained sludge dryness. To verify and/or compare the results obtained with the spin tube tests, sheared capillary suction time tests were conducted and floc size distributions were analyzed. Finally, two of the three polymers evaluated in the lab were applied in the industrial sludge dewatering and drying system used at the wastewater treatment plant of Monsanto Antwerp in Belgium. Observed field performance was in perfect accordance with the spin tube tests.