(327d) Crossflow Filtration of Waste Simulants in Support of the Low Activity Waste Pretreatment System

Crossflow filtration (CFF) is a unit operation selected to perform separation of solids (expected to be < 0.8 wt% when fed) from the waste streams retrieved from the Hanford Tank Farms in the Low Activity Waste Pretreatment System (LAWPS) facility. Prediction of CFF performance for waste treatment (filter flux or flow rate) is complex as several factors need to be considered: solid particle size distribution and morphology, solution chemistry, operational parameters, and filter history. Historically, this has motivated experimental/empirical studies; however, the majority of data collected for crossflow filtration using actual waste or waste simulants have focused either on solids loadings greater than ~5 wt%, i.e. HLW streams, or CFF dewatering performance (where the solids loading changes with time). Experimental CFF work using actual waste or waste simulants with low solids (< 3 wt%) has been more limited. The primary concern with CFF of low solids slurries is the potential for more significant deep fouling, since there may not be enough solids present to form a protective cake on the filter/fluid interface. It is not well understood what parameters control the occurrence of deep fouling in these crossflow filtration systems and how filter performance is affected over longer periods of operation.

To address this gap in understanding, Pacific Northwest National Laboratoryâ??s bench-scale crossflow filtration system was used to examine performance at low solids loading in waste simulants developed to be representative of expected LAWPS feed. The bench-scale system was also modified to test a backflush cleaning approach proposed for use in the LAWPS facility. Resulting data from these tests, as well as comparisons with historical crossflow filtration data, will be presented and discussed.