Removal of microorganisms from water by columns containing sand coated with ferric and aluminum hydroxides

Tap water seeded with different microorganisms or untreated waste water was passed through columns containing sand modified by the in situ precipitation of metallic hydroxides or unmodified sand. Columns (35.5×5.0 cm) packed with 1 kg of sand modified with a combination of ferric and aluminum hydroxide removed greater than 99% of Escherichia coli, Vibrio cholerae, poliovirus 1 and coliphage MS-2 from dechlorinated tap water. This removal efficiency was consistent throughout the passage of 120 l of water during a 30 day test. After the passage of 192 l of tap water, these columns were still able to remove 99.9% MS-2, 80% E. coli and 90% of poliovirus 1. Columns containing modified sand efficiently removed microorganism from water samples at the various pH and temperature values tested while columns containing unmodified sand did not. In addition, these modified sand filters were able to remove coliform bacteria and coliphage from raw sewage. More than a 4 log10 reduction in the numbers of these microorganisms was achieved at room temperature. The modified sand seems to better remove microorganisms due to increased electrostatic interactions. Neither E. coli nor MS-2 were inactivated by the modified sand column effluents. The metal used for coating the sand could not be detected in the column effluents, indicating that the coatings were stable.