Water Treatment Review

Collects and stores water prior to delivery to treatment plant

Removes large debris (fish, sticks, trash, etc.)

Controls algae and other taste and odor causing compounds

Mixes chemicals with raw water to begin coagulation process

Gathers fine particles together to allow for sedimentation and filtration

Settles out suspended particles

Filtration Filters suspended particles not settled out

Disinfection Kills bacteria and other disease causing organisms

Clear Well Provides disinfectant contact time and stores water for high demand

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Sedimentation

Vocabulary

Clarifier A large circular or rectangular tank or basin in which water is held for a period of time to allow the heavier suspended solids to settle to the bottom. Also called sedimentation basins.

Density A measure of how heavy a substance is for its size. Expressed as a weight per unit of volume.

Effluent Water flowing out of a reservoir, basin, tank, treatment process or treatment plant.

Influent Water flowing into a reservoir, basin, tank, treatment process or treatment plant.

Launders Sedimentation basin and filter discharge channels consisting of overflow weir plates and conveying troughs.

Overflow Rate One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if the settling basin is hydraulically overloaded. Also called surface loading. Overflow Rate = Flow, gal/day Surface Area,ft 2

Plug Flow A type of flow that occurs in tanks, basins or reactors when a slug of water moves through a tank without mixing with the other water flowing through the tank.

Sedimentation A water treatment process in which solid particles settle out of the water being treated in a large clarifier or sedimentation basin.

Short-Circuiting A condition that occurs in tanks and basins when some of the water flowing into a tank or basin flows in a direct path from inlet to outlet.

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Surface Loading One of the guidelines for the design of settling tanks and clarifiers in treatment plants. Used by operators to determine if the settling basin is hydraulically overloaded. Also called overflow rate. Surface Loading = Flow, gal/day Surface Area,ft 2

Viscosity A property of water which resists efforts to change its shape or flow. As water temperature lowers, the viscosity increases.

Typical Particle Size

Source Diameter (microns) Coarse Turbidity 1 – 1,000 Algae 3 – 1,000 Silt 10 Bacteria 0.3 – 10 Fine Turbidity 0.1 – 1 Viruses 0.02 – 0.26 Colloids 0.001 – 1

Sedimentation Zones

1. Inlet Zone

2. Settling Zone

3. Sludge Zone

4. Outlet Zone

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Types of Sedimentation Basins

1. Rectangular

2. Circular

3. Square

4. Double-Decker

5. High Rate Settlers (tube settlers)

6. Solids-Contact Units

Sedimentation Performance

1. Up to 95% removal of suspended solids

2. ~ 3 hour detention time

3. Max 2 NTU leaving basin

4. Not necessary in low turbidity waters (direct filtration)

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Source Water Quality Change Action Potential Process Change

Turbidity pH Alkalinity Temperature Color

Flocculation Process Quality Change

Turbidity Alkalinity pH

Sedimentation Basin Change

Floc Settling Rising or floating sludge

Sedimentation Effluent Quality Change

Turbidity Color

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