12587047 raw water intake screening and aeration in water supply project

7/28/2019 12587047 Raw Water Intake Screening and Aeration in Water Supply Project

1/22

Raw water intake,

screening, and aeration

1


2/22

Contents

Introduction

Raw water intakestructures

Types of intake

structures

Intake site selection

Intake-designconsideration

Screening Types of screening

Aeration

Purpose of aeration

Types of aerators 2


3/22

Introduction

Process flow chart in water supplyproject

3


4/22


5/22

Raw water intake structures

Control withdrawal of raw water froma surface water source.

Selectively withdraw the best quality

water while excluding fish, floatingdebris, coarse sediment, and otherobjectionable suspended matter.

Intake contains gates, screens,control valves, pumps, chemicalfeeders, flow meters, offices andmachine shop.

5


6/22

Types of intake structures

1. Floating intakes

6


7/22

2. Submergedintakes

7


8/22

3. Exposed or towerintakes

3.a. wet-intake

towers 3.b. dry intake tower

8


9/22

4. Shore-intake

structures 5. Pier intakes

9


10/22

Intake site selection

Water quality Water depth Stream or current velocities

Foundation stability Access Power availability Proximity to water treatment plant Environmental impact Hazard to navigate

10


11/22

Intake-design consideration

1. Intake velocities

High velocities headloss, entrain

suspended matter,trap fish, and otheraquatic animals.

Velocity below 8 cm/s

allows aquatic animalsto escape, andminimize thesuspended matter.

2. Intake-portlocation

Water quality in eachstratum may vary.

To achieve, multipleintake ports set atvarious levels aregenerally provided.

Top intake less than2 m below normallevel.

Bottom intake least

1 m above the bottom11


12/22

3. Gates

Usually sluice gates .

Large cast iron gates

that slide vertically ona guide track.

4. Control of ice

In cold regions, gatescovered with ice.

To avoid, intake portsare kept below watersurface below 8m .

Space heaters,

Compressed air isused to remove ice.

12


13/22

Screening

It is a unit operation that removessuspended matter from water.

Screens may be classified as coarse,fine, or microstrainer, depending onthe size of material removed.

Located at intake structure, rawwater pump station, or watertreatment plant.

13


14/22

1. Coarse screen or trashrack

To fprevent large objects rom enteringthe conveyance system.

Consists of vertical flat bars, or, in some

cases, round pipes spaced with 5 to 8cm of clear opening.

Installed outside of any sluice gate.

The velocity through the coarse screenis generally less than 8 cm/s.

14


15/22

2. Fine screen

To remove smaller objects that maydamage pumps or other equipment.

Screens consists of heavy wire meshwith 0.5 cm square opening.

The typical design velocity throughthe effective area is in the range of0.4 to 0.8 m/s.

There are two types:Travelingscreens and passive screen

installation. 15


16/22

Typical fine screens

Traveling screen Passive screen

16


17/22

3. Microstrainer

Mainly to remove plankton and algaefrom impounded waters.

Microstrainer is installed beforechemical coagulation will improve theperformance of clarifiers.

Consists of rotating cylindrical framecovered with fine wire mesh fabric.Water enters the cylinder and movesradially out.

Damaged by abrasive material metal ,sand.

Problem build up of slime on thefabric. 17


18/22

Aeration

Aeration involves bringing air orother gases in contact with water.

The purpose of aeration are

1. Reduce the conc. of taste and odor causingsubstance by volatilization

2. To oxidize iron and manganese, rendering theminsoluble.

3. To dissolve a gas in the water ( O2 and CO2)

4. To remove compounds for better watertreatment ( H2S removal before chlorination andCO2 removal before softening)

18


19/22

Types of aerators

1. Gravity aerators

Utilize weirs,waterfalls, cascades,

inclined planes withriffle plates,perforated tray towers

2. Spray aerators

This spray droplets ofwater into the air from

orifices or nozzles. To produce an

atomized jet, largepower required &

water must be free oflarge solids.

19


20/22

3. Diffused-airaerators

Aerated in tanks usingcompressed air .

Aeration period 10 to30 mins.

Air supply 0.1 to 1m3/min.

4. Mechanicalaerators

Motor driven impellersor combination of

impeller with airinjection device.

20


21/22

REFERENCE

Water works engineering planning,design, and operation

By syed R. QASIM, Edward M. Motley and

guang zhuPrentice-hall , india (2006)

And photos from internet.

21


22/22

22

12587047 raw water intake screening and aeration in water supply project

Documents