a study on the performance of limestone roughing filter - ePrints@USM

2.4 Types of Roughing Filters
There are various types of roughing filters such as downflow roughing filters
(DRF), horizontal flow roughing filters (HRF) and upflow roughing filters (URF). The
layouts of different roughing filters are shown in Figure 2.2. The selection criteria for
types of roughing filtration are based upon raw water quality such as turbidity,
suspended solids, color, iron and fecal coliform levels (Wegelin, 1996; Wolter and
Mwiinga, 1997).
Figure 2.2: Types of Roughing Filters (Source: Wegelin, 1996)
Downflow roughing filter consists of 3 or 4 individual filter boxes, each box is
filled with filter media, with the coarsest media in the first compartment and the finest
media in the last compartment. Water flows downward through each media
compartment.
Horizontal flow roughing filtration consists of coarse gravel filter media arranged
in series from coarse to fine sizes in the direction of flow. It allows the treatment of
water with considerable contamination higher than the levels of slow sand filter. For this
reason roughing filters are often used before slow sand filters. Roughing filters have
turbidity removals ranging from 60 to 90%. Additionally it could achieve similar
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