Water filtration is a process for separating suspended or colloidal impurities from water by passage
through a porous medium, usually a bed of sand or other medium. Direct filtration is a water
treatment scheme that does not include separate in-plant sedimentation. It is not a new process but it
is becoming increasingly important because of the safe drinking water. Water treatment plants are
usually required to reduce filtered water turbidity down to 1 NTU. In this study, sand was used as a
filtration media under constant direct high rate filtration conditions and performance. Turbidity
removal performance and head loss were investigated as functions of filtration rate, bed depth,
influent turbidity and media size. The filtration materials used in a downflow filter were sand and
gravel. The sand bed thickness was changed from 60 cm to 120 cm with media size 1-2 mm, while
the gravel layer thickness was kept constant at 30 cm. The influent raw water turbidity was varied
from 10 to 30 NTU. The range of filtration rate was between 200 and 400 m3/m2/day. From analysis
and discussions of the experimental results, it was found that the depth of media has significant
effect on the water quality and head loss, with the increasing of sand depth in the filter, both the
water quality and the head loss increases. It was found that a sand depth of 120 cm is able to give a
constant filtration rate from 200 to 400 m3/m2/day with acceptable quality (≤ 1 NTU) for values of
influent turbidity ≤ 10 NTU.