(415a) Depth and Surface Fouling During Ultrafiltration

Crossflow filtration is to be a key process in the treatment and disposal of approximately 60,000 metric tons of hHigh- lLevel wWaste stored at the Hanford Site in the State of Washington. Pacific Northwest National Laboratory is assessing filter performance against waste simulant materials that mimic the chemical and physical properties of Hanford tank waste. Simulant studies indicate that waste filtration performance is limited by surface/depth fouling and filter cake formation. To limit the shutdown of waste treatment operations, the pre-treatment facility plans to recover filter flux loses as a cake formation and fouling by frequent back-flushing of the filter with collected permeate (hereafter referred to as backpulsing). The objective of the current paper is to propose a methodology for assessing backpulse optimization. The frequency of backpulsing is optimized by assessing the flux recovery against the volume of permeate returned during each backflush. To this end, a model characterizing the decline in filter flux as a function of both irreversible depth fouling and reversible cake formation is proposed. This model is then used to characterize the filtration behavior of Hanford waste simulants in both continuous and backpulsed operations. Finally, the model is applied to the backpulse optimization process.