(86a) Modeling Flux Decay In Cross-Flow Filtration

Recent work at Pacific Northwest National Laboratory has been concerned with understanding how cross-flow filter flux decays with time.  Understanding the cause(s) of flux decay is important for assessing long-term behavior of this separation technology, especially when used in challenging processing environments e.g. nuclear waste treatment.  Fouling in the filter is a complex issue which is affected by many parameters: the chemistry of the solution being filtered, particle size and morphology, operating conditions, and cleaning methods.  Based on filtration work performed at PNNL over the past several years, it is clear that a portion of the fouling can be “reversed” by back-pulsing the filter and another portion is irreversible (usually only rectified via cleaning protocols).  However, the sheer number of parameters requiring consideration complicates effective modeling of both the long-time behavior of the cross-flow filter and its response to back-pulses.  To combat this, a series of simple models were developed from first principles based on different suspected fouling mechanisms.  The models were tested against long-term data collected with PNNL’s bench-scale filtration system.  These models suggest some simple relationships between operating parameters and flux decay, provide a framework for predicting performance for other, similar filtration systems, and assist in determining a back-pulse strategy for cross-flow filters which will experience long-term decays in the filter flux.