Vibratory shear enhanced processing membrane filtration applied for the removal of natural organic matter from surface waters

In this study, the performance of a vibratory shear enhanced unit (termed hereafter as VSEP) was evaluated for the removal of humic acids in the presence of inorganic particles (clays) from synthetic aqueous dispersions, simulating contaminated surface waters. For this purpose, several major parameters were examined, such as the specific membrane type, the feed quality (i.e. the concentration of main components in the feed, as well as the pH value) and the vibration amplitude. It was found that the permeate flux was stabilized after certain operation (filtration) time regardless of feed quality for each membrane process. The percentage recovery of liquid volume during the performed semi-batch laboratory-scale experiments exceeded 90%. The increase of pH value from 6 to 9, during microfiltration (MF), resulted in 30% decrease of permeate flux and 20% enhancement of HA rejection, indicating that the form of HA in solutions, as well as their interactions with ions and/or inorganic clay particles may play an important role in the filtration process. Although clay particles were removed almost completely during all the examined filtration processes, HA molecules removal exceeded 99% only during nanofiltration (NF), while for the other processes the removal did not exceed 95%. The permeate flux was affected by the respective feed quality and membranes' type (pore diameters), but also by the applied vibration amplitude as well, especially during ultrafiltration (UF), using the 10 kDa molecular weight cut-off (MWCO) membrane and NF processes. The permeate flux was found to be proportional to (gamma) over bar (0.21)(w) for UF and to (gamma) over bar (0.31)(w) for NF of humic acids solutions, where (gamma) over barw is the mean (induced) shear rate at the membrane surface. Finally, although the operating pressures, especially for MF and UF were relatively high, when compared with other commercially available membrane treatment systems, the examined VSEP unit presented rather stable hydrodynamic behavior, enabling the efficient treatment of surface waters. (c) 2005 Elsevier B.V. All rights reserved.