Implications of enhancing critical flux of particulates by AC fields in RO desalination and reclamation

This paper discusses fouling in reverse osmosis in terms of the critical flux of foulants and the fouling mechanisms based on hydraulic resistance and loss of driving force due to cake-enhanced osmotic pressure (CEOP). In many cases CEOP is the dominant effect and this is exacerbated by the use of constant flux processing. The implications of increasing critical flux are described and the potential benefit of using AC field gradients to do this is illustrated for a model foulant.

Particulate fouling in RO can cause loss of performance by a fouling resistance and by loss of driving force due to CEOP. In many scenarios the contribution of CEOP dominates the loss of productivity. The critical flux of the particulate species directly affects the dynamics of fouling and efforts to enhance critical flux will see a reduction in fouling. Tests on a yeast suspension to measure critical flux by ‘direct observation’ (DOTM) have shown that AC field gradients can increase JCRIT by 25–50%. The mechanism is postulated to be an enhanced back transport provided by dielectrophoresis. The implications for practical RO of increasing the critical flux of foulants is that there could be a significant delay in cake layer development, fouling resistance and CEOP, which requires increased TMP and energy input.