Removal of Escherichia coli and total bacteria from water by granulated micelle-clay complexes: Filter regeneration and modeling of filtration kinetics

Abstract

Granulated micelle-clay composites (0.3 to 2mm) formed from Na-bentonite and the organic cations Octadecyltrimethylammonium (ODTMA), or Benzyldimethylhexadecylammonium (BDMHDA) were employed to remove from water by filtration (a) Escherichia coli S-17 and (b) total bacteria count (TBC). In (a) filters included 4g to 27g of complex mixed with sand, and bacteria numbers were 6.4·105 to 5·106/mL. A model which considered convection, adsorption, and desorption simulated the filtration results and yielded predictions. Bacteria capture by filtration was independent of the complex used, but BDMHDA complexes were superior in reducing numbers of emerging bacteria, due to a larger biocidal, or biostatic effect of released cations. Placing a layer of activated carbon after the micelle-clay filter reduced the released cations to 1μg/L. Regeneration was by: (i) passing a solution of 0.1% NaOCl, or 0.01M of HCl, or (ii) heating in a furnace at 105°C for 2.5h. Capacities for removal of bacteria after first and second regenerations by (i) were 86% and 57% of those with fresh granules, respectively. It is suggested that the technology can provide a safe and economical treatment for drinking water contaminated by pathogenic bacteria. In (b) the capacity of filters was smaller than in (a), but the technology enables to avoid using UV lamps in domestic filters.