Dewatering characteristics of polymer conditioning alum sludge under low compressive pressure by a constant-rate strain compression test

In this study, the constant-rate strain compression test (CRSC test) was proposed to evaluate the dewatering characteristics of coagulated sludges, such as alum sludges and polymer conditioned sludges, under low compressive pressure below 50 kPa. In CRSC test, a uniform compressive cake is formed when the initial thickness of a sample and rate of constant strain are 2 cm and 0.03 mm/min, respectively. Dewatering characteristics of alum sludge from the results of CRSC test have a good agreement with a conventional compression-permeability test. From these results, CRSC test have a merit to evaluate dewatering characteristics continuously and quantitatively under low compressive pressure. From the results of CRSC test, the equilibrium porosity of conditioned alum sludge with cationic polymer is not so different from that of unconditioned sludge at the same compressive pressure. On the other hand, kS₀² of conditioned sludge remarkably decreases as compared with that of unconditioned sludge, and it is clear that polymer conditioning affects the floc structure of alum sludge under low compressive pressure. Although the improvement of dewaterability by polymer conditioning is remarkable in low compressive pressure range, local specific resistance of conditioned sludges is close to that of unconditioned sludge with the increase of compressive pressure over 100 kPa. From these results, it is necessary to develop a solid-liquid separation process fitting to the dewatering characteristics of coagulated sludge under each dewatering pressure range.