Flocculating activity of cross-linked poly-γ-glutamic acid against bentonite and Escherichia coli suspension pretreated with FeCl3 and its interaction with Fe3+

Cross-linked poly-γ-glutamic acid (C-L γ-PGA) at 5 μg/ml flocculated bentonite suspension pretreated with polyaluminum chloride (PAC) at 2 μg/ml Al 3+ -PAC to a transparency of approximately 30% after 30 min and more than 90% after 4 h, while Al 3+ concentration in the upper phase of the suspension decreased with incubation time. When pretreated with FeCl 3 at 16 μg/ml Fe 3+ -FeCl 3 , similar results were obtained. In the case of Escherichia coli suspension, the combination of C-L γ-PGA and FeCl 3 demonstrated a more marked flocculating activity with a satisfactory transparency occurring after 30 min of treatment, accompanied by a decrease in residual Fe 3+ concentration. In the above two suspensions pretreated with FeCl 3 , small visible floats appeared in the early stage of incubation. These floats were found to be due to the direct interaction between FeCl 3 and C-L γ-PGA, indicating the formation of a water-insoluble complex. After allowing the suspension to stand for a long time, elemental analysis and inductively coupled plasma spectroscopy of the precipitates produced suggested that not only the complex was formed due to the interaction between Fe 3+ in FeCl 3 and COO − in the C-L γ-PGA molecule, but also Fe 2 O 3 and Fe(OH) 3 might be entrapped in this complex. This could be applied to scavenge metal ions including Fe 3+ from polluted water.