PNNL

Abstract

Treatment processes have been proposed that will utilize crossflow filtration to filter supernate and concentrated sludge waste streams at the Department of Energy’s Hanford Site in southeastern Washington state. Challenges associated with the solid-liquid separation of the waste streams pose a necessary evaluation of available Hanford high level waste filtration data. Limiting flux conditions during crossflow filtration are elucidated with the formation of a cake (gel) layer on the membrane surface. Before cake formation, the pressure drop on the boundary layer, as well as the permeate flux, increases with applied pressure. However, after the formation of the cake layer, the pressure drop on the boundary layer will not change with additional applied pressure. A mass transfer coefficient between the gel and bulk concentrations also plays a critical role in determining filter flux. A correlation between the gel concentration and mass transfer coefficient is made to assist in determining filter performance of select high level waste streams. As a process alternative to crossflow filtration, gravity settling of waste streams may be deployed as a solid-liquid separation technique. However, this results in a contrasting performance with the centrifuged solids concentration. A method was developed to estimate expected filtration and settling performance based on physical characterization data for Hanford tank waste samples.