In this study, the effects of organics removal efficiency, oxidant dose, and alum dose on aluminum hydroxide sludge characteristics were assessed. In order to maintain control over operating parameters, a continuous-flow laboratory-scale plant was operated in the laboratory with daily monitoring of pH, as well as influent and effluent turbidity, total organic carbon, and color.

Sludge thickening and dewatering characteristics were found to worsen when increasing amounts of organic matter were incorporated into the sludge floe matrix. Sludge properties improved with increases in oxidant dose and decreases in alum dose and alum/influent turbidity ratio. Changes in coagulation mechanism from sweep to charge neutralization were hypothesized to be partially responsible for changes in sludge properties caused by changing alum dose. Improvements in thickening and dewatering characteristics were found to be heavily dependent upon increases in sludge floe density, as well as decreases in aggregate water content.