AWWA JAW53029

Surface coating of hydrous iron aluminum oxide on Ottawa sand was investigated as a means of improving the removal of Cryptosporidium oocysts from water by filtration. Coating the sand increased the zeta potential from -40 to +45 mV at pH 7.0, increasing the potential for interaction with the negatively charged (-25 mV at pH 7.0) Cryptosporidium oocysts. Water seeded with Cryptosporidium oocysts was passed through parallel columns of uncoated and coated sand at superficial velocities of 200-800 m/d (3.5-14 gpm/sq ft) and column lengths of 100-400 mm (4-16 in.). In every trial, coated sand removed significantly more oocysts than uncoated sand. Filter coefficients of coated sand were 2.9 times as high as those of uncoated sand, indicating that coating can significantly improve the removal of Cryptosporidium by granular media filters. Includes 30 references, table, figures.