Surface coating of hydrous iron aluminum oxide on Ottawa sand was investiga
ted as a means of improving the removal of Cryptosporidium oocysts from wat
er 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 negati
vely 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) an
d column lengths of 100-400 mm (4-16 in.). In every trial, coated sand remo
ved significantly more oocysts than uncoated sand. Filter coefficients of c
oated sand were 2.9 times as high as those of uncoated sand, indicating tha
t coating can significantly improve the removal of Cryptosporidium by granu
lar media filters.