Page 52 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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1.7 Purification Works 15

Coagulants
disinfectant

Treated
Raw Mixing Flocculation Sedimentation Rapid granular water To distribution
water basin tank tank filters storage system
tank
(a) Surface water filtration plant

Lime Soda ash disinfectant

Treated
Raw Mixing Reaction Sedimentation Rapid granular water To distribution
water basin basin tank filters storage system
tank

(b) Groundwater softening plant
Figure 1.4 Common Types of Water Treatment Plants (Note: A sedimentation tank may be replaced by a dissolved
air flotation tank.)

The following normally applicable requirements provide the reader with a concept of the
sizing of principal structures:
1. Mixing basins hold a few minutes of flow.
2. Flocculating and reaction basins hold about half an hour’s flow.
3. Sedimentation basins hold an hour or more of flow and are rated at about 0.50 gpm/ft 2
2
(20 L/min/m ) of water surface area.
4. Slow sand filters pass water at rates of about 3 MGD/acre (28 MLD/ha) in surface
water filtration, stepping up to about 10 MGD/acre (94 MLD/ha) in groundwater treat-
ment for iron and manganese removal or when they are preceded by roughing filters.

Figure 1.5 Water Treatment Plant in Northern Portugal
Source: Wikipedia, http://en.wikipedia.org/wiki/Image:Bragan%C3%
A7a43.jpg