Removal of thermophilic spores from gum Arabic streams using ceramic alumina microfiltration membranes

The microfiltration (MF) of high solids content gum Arabic solutions (15 wt%) inoculated with Bacillus mycoides spores (10⁵ CFU ml^-1) was carried out using Membralox tubular ceramic membranes with a nominal pore size of 0.8 μm. Consistent permeate fluxes were achievable over multiple fouling and cleaning cycles, while giving low rejection of solids and high rejection of spores (after ten cycles, a permeate flux of 42.9 L m^-2 h^-1, a solids retention of 19.8%, and a spore rejection of 5.0 log orders were achieved). Although fouling during filtration was severe, permeate fluxes could be restored to a satisfactory condition after cleaning with 0.5 wt% NaOH solution containing 200 ppm NaOCl. Results were described by a two species first order removal model, whereby one species was removed quickly by cleaning and the other was more difficult to remove. The optimum cleaning time for NaOH + NaOCl solutions at 60 °C was found to be ca. 20 min. Subsequent citric acid cleans had a negative effect upon restoring permeate flux.