Fluidized-bed pellet reactor technology was developed to remove water hardness with minimal sludge production. Operation procedures of this process include adding pellets into a column reactor and directing raw water and chemicals through the bottom of the column, keeping pellets fluidized to prevent them from being coagulated. In this study a process combining an ultrafiltration (UF) membrane with outside-in flow configuration and a fluidized-bed pellet reactor was proposed for hard water softening. The advantages of such a process include a compact reactor footprint, high treatment efficiency, and excellent effluent quality. Three different pellets of various sizes were used: quartz sand, beach sand, and heated iron oxide particles (HIOPs). Results show that with a removal efficiency of less than 16%, a UF membrane alone is not an effective process for removing hardness due to the slow reaction kinetic of calcium carbonate precipitation without the presence of pellets. When three types of pellets were added separately, the removal efficiency of the integrated UF/pellet process was more than 60% at a pH level of 9.0. Hardness removal efficiency improved with increasing pH and pellet surface area, and no significant membrane fouling was observed during the experiments.
Relation:
American Water Works Association. Journal 96(8), pp.151-158
