Impact of polymer-sludge interaction on rheogram peaks and optimum dose determination.

Torque rheometry offers potential for in-line monitoring use, screening polymers, and on site optimization of polymer dose by treatment plant operators. This study investigates the peaks formed following direct polymer injection into sludge during rheological analysis. The peaks enable observation of both flocculation and deflocculation phases, and the highest point of the peaks indicates the point where network bonds rupture. The goal of this study was to test the method reported by Ormeci on anaerobically digested sludge samples with several polymers, covering a wide spectrum of molecular weights and cationic charges, to establish a better understanding of how polymer-sludge interaction affects torque-time rheograms and peaks observed after polymer injection. The results from this study indicate that peaks can potentially be used to select the best performing polymer and identify the optimum polymer dose. In the underdose region, the peaks increase in size with increasing polymer dose until the optimum dose is reached. Once the optimum dose is reached, the peaks may decrease in size and then increase again, or stay same size until the polymer dose is very high. In the overdose region, very large and erratic peaks are observed which can be explained by the presence of unmixed polymer in the sample.