Water Treatment Plant OP&M

7/23/2019 Water Treatment Plant OP&M

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MMAANNUUAALL

OONN

Water Treatment Plant

Operation & Maintenance

The Project

for

Capacity Development

of

Water Su l Authorities in Lao

The first edition March 2006


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Table of Contents ( Basic Part )

Introduction

1 Unit processes of water treatment

1.1 Classification and characteristics of raw water

1) Surface water (river, pond and rake water)2) Groundwater (shallow and deep well water and undercurrent water)3) Spring water1.2 General treatment process based on classification of raw water1) Definition of water treatment2) Processes for surface water3) Processes for groundwater and spring water1.3 The explanation of unit process operation1) Flocculation and sedimentation process2) Slow sand filtration3) Rapid sand filtration4) Disinfection

2 Observation of water quality in the treatment process2.1 Observation items of water quality in each stage of the process

1) In case of slow sand filtration2) In case of rapid sand filtration3) In case of disinfection only2.2 The explanation of items in process operation1) Turbidity2) Color3) pH4) Alkalinity5) Ammonia nitrogen6) Residual chlorine2.3 Examination methods2.4 The operation criteria of water treatment plant

3 Chemicals for water treatment3.1 Coagulant1) Roles of coagulant(1) Neutralization of electric charge2) Conditions on the coagulant effectiveness(1) Temperature of water(2) pH(3) Alkalinity(4) Mixing with raw water(4-1) Rapid mixing (for coagulation)(4-2) Slow mixing (for flocculation)

3) Inorganic coagulant(1) Aluminum sulfate(1-1)Characteristics(1-2)Calculation for feeding(2)Poly aluminum chloride(2-1)Characteristics4) High molecular coagulant


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(1)Use in water treatment process(2)Characteristics(3)Concentration of polymer solution(4)Feeding rate(5)Calculation for feeding(6)Note of dissolving and use

3.2 Chemicals for pH adjustment1) Roles of the chemicals2) Alkali chemical3) Acid chemical3.3 Oxidant, disinfectant1) Roles of oxidant2) Calculation for feeding3) Roles of disinfectant4) Chlorine chemicals(1) Sodium hypochlorite(2)Calcium hypochlorite(3) Calculation for feeding and dissolving chemicals(4) Factors affecting on the disinfection effect of chlorine

(5) Weight of chemicals needed to make solution

4 Intake facilities4.1 Maintenance

5 Receiving well5.1 Functions5.2 Maintenance5.3 Feeding equipments of oxidant1) Pre-chlorination equipment(1) Setup of equipment(2) Feeding point

(3) Feeding rate(4) Note

6 Flocculation (coagulation) and sedimentation process6.1 Rapid mixing basin1) Functions2) Maintenance6.2 Feeding equipment of coagulant(1) Setup of equipment(2) Dissolving procedure of solid aluminum sulfate(3) Feeding point(4) Feeding rate

6.3 Flocculation basin1) Functions2) Operation of baffling type flocculation basin3) Maintenance6.4 Sedimentation basin1) Functions


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2) Types, etc(1) Horizontal-flow basin(without flocculation)(2) Horizontal-flow basin(with flocculation)(3)Horizontal-flow basin with inclined parallel plates3) Settled sludge4) Maintenance

7 Filtration process7.1 Slow sand filter basin1) Functions2) Structure3) Sand scraping4) Note on operation5) Maintenance7.2 rapid sand filter basin1) Functions2) Structure3) Washing of filter(1) Washing of rapid sand filter(2) Washing operation

(3) Washing criteria(3-1)Head loss of filter layer(3-2)Duration time(3-3)Surface washing(3-4)Backwashing(3-5)Air-blowing, air washing4) Note on operation5) Maintenance6) Abnormal phenomenon, causes and measures

8 Disinfection process8.1 Mixing basin

1) Functions2) Maintenance8.2 Post-chlorination equipment1) Setup of equipment2) Dissolving procedure of calcium hypochlorite3) Feeding point4) Feeding rate

9 Clear water reservoir1) Functions2) Maintenance

10 Machinery1) Pumps(1) Observation of operation state(2) Maintenance(2-1) Pumps(2-2) Submerged motor pumps2) Valves3) Chemical feeding facilities and equipments


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11 Electrical facilities1) Motors2) The others

12 Notes of daily inspection works

13 Regular inspection excluding daily inspection work

14 Recording and reporting1) Recording

2) Daily operation report3) Daily inspection and maintenance report4) Other records and reports to be prepared

15 Prior provisions for accidents and emergency states1) Necessity and causes of accidents2) Preparation against accidents and disasters3) Phone tree against an emergency4) Measures against an emergency


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Introduction

This manual describes basic and common matters on water treatment process and

facilities so that technicians who are responsible for the operation and maintenance of

water treatment plant can properly understand and do their daily work in their

workplaces. You may revise and correct this manual so that you can easily use this one

hereafter. The standard values in this manual are average values and should not be

always applied to all water treatment plants impartially.

If you want to precisely know about how to start or stop the machine and

equipments, you should refer to the other instruction manuals which are issued by

manufacturers.

A schematic drawing of water treatment plant is shown below.! ! ! ! !

Figure 1 A schematic drawing of water treatment plant

This schematic drawing shows that several kinds of thing, for example chemicals,

electric & mechanical energy, are inputted to water treatment process and then water

quality of finished water (Water quality out shown above) is finally outputted as well as

the volume of finished water as the result. The workers in WTP have to understand the

matters written below.

1) The fundamental water treatment process.

2) The characteristics of raw water.

Qin: Raw water Qout : Finished water

Machine & Electric facilities

Water treatment process

Chemicals Electric & Mechanical energy

Water quality in Water quality 1, 2 ,.

Water quality out


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3) The roles, functions and characteristics of chemicals.

4) The meanings of water quality items and standard values.

5) How to operate and maintain electric and mechanical facilities and equipments.

6) The measures corresponding to accidents, abnormal and emergency states.

And the recording and reporting these matters are very important to improve the

operation and maintenance of WTP.

1 Unit processes of water treatment

1.1 Classification and characteristics of raw water

1) Surface water (river, pond and rake water)

To be susceptible to outer pollutions and temperature.

To be easy to be a breeding grounds of living thing.

To contain much dissolved oxygen.

River water is directly and strongly affected by rain.

2) Groundwater (shallow and deep well water and undercurrent water)

To be little change of water temperature through all seasons.

To be economically cheap.

To be generally good quality. But there are some cases we need special treatment

processes due to the state of aquifer and stratum around the wells.

In case of undercurrent water, the quality is generally good because of natural filtration.

But it depends on the quality of river water, the thickness of permeability of stratum and

so on.

In the season of flooding, there are some cases that the quality is directly affected by the

nastiness of the river.

3) Spring water

To be much quantitatively affected by rain. The quality is almost the same as that of the

groundwater related.

1.2 General treatment process based on classifications of raw water

1) Definition of water treatment

Water treatment means Improving the quality of raw water so as to serve the purpose of

usage. In case of water supply services, that generally means making the safe and

hygienic water to be good for drinking.! !

2) Processes for surface water

In general, we have the flocculation, sedimentation plus rapid sand filtration process. We

usually add chlorine into water before flocculation and after filtration.

Intermediate-chlorination is also introduced to prevent the formation of disinfectionby-products.

In case of good quality of raw water, we have the slow sand filtration process and add

chlorine after filtration.


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Figure 2 Rapid filtration system

3) Processes for groundwater and spring water

In general, we have the disinfection process only.

In case of seasonally uprising of turbidity, we use the flocculation, sedimentation plus

filtration process or the filtration process only and add chlorine into water for

disinfection.

(Seasonally)

Figure 3 Disinfection only (usually)

1.3 The explanation of unit process operation1) Flocculation and sedimentation process

This process means that suspended solids in water get together and become bigger by

chemical (coagulant) and become easy to sink due to high settling velocity.

According to Stokes equation, the settling velocity becomes faster as the density and

diameter of the particle become bigger.

Especially the enlargement of diameter is very effective to promote the settling velocity.

Pre chlorination Post chlorination

Raw water

Coagulant

Flocculation

& Sedimentation

Filtration

Finished

water

Chlorination

Raw water

Finished

water

Chlorination, Flocculation,

Sedimentation & Filtration

Intermediate-chlorination


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(Reference 1)

Stokes equation : V= g (p ) d

2

18

V: settling velocity, g : gravity acceleration, p : density of the particle

: density of water, d: diameter of particle, : viscosity coefficient of water

Mainly settling velocity is in proportion to d2.

2) Slow sand filtration

This process mainly depends on the function which is that a group of microorganism

formed on the surface of sand captures, oxidizes and decomposes fine particles and

soluble matter in water.

This process is subjected to treat relatively good quality of raw water, which means the

turbidity of raw water is less than around 10 NTU.

Coagulant for flocculation is not needed.

A large area for filters, which means about ten several times to several ten times as much

area as that of rapid sand filter, is needed.

Scraping off the sand of filter surface is needed every a certain period of time.Filtration is mainly due to the biological function. So chlorine obstructs this function.

Standard filtration velocity is 2 to 10 day.

(Reference 2)

NTU turbidity

In case that turbidity of water is the same as that of water which contains 1mg of

formazin per litter, the turbidity is defined as 1 NTU.

(Formazin: A chemical substance that makes the standard turbidity of water.)

d

V

Particle

(Density p)

Water

(Density)

Figure 4

A schematic

drawing of settling

velocity


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(Reference 3)

Filtration velocity (m/day)

This is the velocity of water passing thorough the filter vertically. This means the

volume of water a day passing through 1m2sand area of filter ( a value which the

volume of treated water a day divided by filter area ).

Namely, =Q/A(m/day) -------(1) Q: the volume of treated water a day

(m3

/day), A: sand area of filter ( m2

)

Figure 5 A schematic drawing of Filtration velocity

3) Rapid sand filtrationFlocculation as a pre-treatment process is needed.

The removal of turbidity is mainly depend on the adhesion to filter media(for example:

sand) and the sifting at filter layer(for example: sand filter).

This process is applicable to much higher turbidity on condition that there is flocculation

and sedimentation process before this.

Filtration velocity is 120 to 360m/day, but 120 to 150m/day is generally standard.

The quality of rapidly filtrated water is generally less than that of slowly filtrated water.

4) Disinfection

After finishing processes mentioned above, we finally have to disinfect the water.

In case of clean raw water like groundwater and spring water, we usually do not needflocculation, sedimentation and filtration. We can supply water treated by disinfection

only.

Sand layer

Q

A: Sand area of filter

=Q/A(m/day)

Under drain system

Q: Volume of treated water


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2 Observation of water quality in the treatment process

2.1 Observation items of water quality in each stage of the process

1) In case of slow sand filtration

Table 1 Observation items ( : indispensable : necessary :desirable )

Observation

place or point

Observation items

Turbidity Color pH Alkalinity Others

Raw water DO()After sedimentation ------- -------

Filtrated water ------- DO(),Note(1)

Finished water ------- R-C()

Note1: Leaking living things, R-C is free chlorine.

Figure 6 Observation items of slow sand filtration system

2) In case of rapid sand filtration

Table 2 Observation items ( : indispensable : necessary :desirable )

Observation

place or point

Observation items

Turbidity Color pH Alkalinity Others

Raw water Note2

After sedimentation ------- ------ ------- R-C()

Filtrated water ------- R-C()

Finished water ------- R-C()

Note2: Odor materials(),Organic materials(),Ammonia nitrogen(), R-C is freechlorine.

Raw water

Receiving

Well

SedimentationBasin

Filter

Basin

Finished water

Reservoir

Finished

water

Chlorine

Turbidity

Color

pH

Alkalinity

Turbidity

pH

Turbidity

Color

pH

Turbidity

pH

Alkalinity

R C


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Figure 7 Observation items of rapid sand filtration system

3) In case of disinfection only

Refer to raw water and finished water of each table shown above. In case of having

filters, see Table (2) shown above.

2.2 The explanation of items in process operation.

1) Turbidity

Turbidity control is a fundamental work of water treatment process.

Turbidity of raw water largely affects water treatment. So, turbidity is a main and

critical indicator in controlling water treatment process.

Turbidity spoils appearances of water and gives unpleasant feeling to consumers.

Turbid materials sometimes wrap up bacteria. This prevents chlorine from reaching to

those bacteria and weakens the effective of disinfection.

Turbid water in early stage of raining is relatively easy to treat, but turbid water

containing fine particles after raining continues for long time and is difficult to process.

2) Color

The degree of yellowish or yellowish brown color by soluble and colloidal matters in

water.

This is due to humus, iron, manganese, copper, zinc and so on.

Color spoils the quality of supplied water and is an index of humus (organic substances )

concentration.

3) pH

pH value of water is very important for flocculation (coagulation, to be exact) and

disinfection in water treatment process

Proper pH value is around 6 to 7 in flocculation coagulation, to be exact .

If pH value of raw water largely run off this range, flocculation process will become

difficult.

Receiving

Well

SedimentationBasin

Filter

Basin

Finished water

Reservoir

Flocculation

Basin

Turbidity

Color

pH

Alkalinity

Turbidity

R C

Turbidity

Color

pH

R C

Turbidity

pH

Alkalinity

R C

Coagulant

Pre-Chlorine

Post-Chlorine

Raw water

Finished

water


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The disinfection with chlorine is more effective along with the pH value of water goes

down. So, it is important to observe pH of water.

4) Alkalinity

Coagulant makes flocks reacting to alkalinity in raw water.

If the amount of alkalinity is poor, appropriate flocculation (coagulation) can not be done.

More than 20mg/of alkalinity in raw water is desirable.

In case of poor alkalinity, we need add alkali chemical into raw water before flocculation.In case of excess, we add acids before flocculation.

5) Ammonia nitrogen

Ammonia nitrogen in raw water increases with the discharge of factory, sewage and

human waste and so forth.

Ammonia nitrogen of 1mg/ consumes chlorine of around 10 mg/.

You have to pay attention to pre-chlorination dosage since ammonia nitrogen

concentration of raw water is changeable while raining.

If pre-chlorination feeding is not enough, residual chlorine disappears in a sedimentation

basin. It is not desirable from the point of view for removing iron and manganese and

disinfection.6) Residual chlorine

This value shows the effect of disinfection.

It is necessary for the residual chlorine to be kept at the end of supply area.

The minimum value of residual chlorine at the tap in supply area is 0.1mg/.

2.3 Examination methods

See a manual of Water quality examination .

2.4 The operation criteria of water treatment plant

The general operation criteria, by which we can judge whether the operation is proper or

not, is mentioned below.

The case of flocculation, sedimentation plus filtration and disinfection(pre-disinfection

and post-disinfection) is mentioned below as a standard type.

In case of disinfection only, we judge the properness from finished water.

The residual chlorine value of finished water should be adjusted by taking account of the

characteristics of supply area.


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Table 3 Operation criteria table (As a reference)

Judgment place or point Judgment criteria

Exit of flocculation basin If flocks are good or not?

Exit of sedimentation basin

(Supernatant)

Turbidity is 5 NTU or less?

If there is kicking up of flocks or not?

Residual chlorine is 0.5mg/or more?

Exit of filter basin(filtrated water)

(Before disinfection)

Turbidity is 2 NTU or less? No color ?Residual chlorine is around 0.5mg/?

pH value is 6.5 to 8.5 or not?

Finished water (after disinfection)

including the case of

disinfection only

Turbidity is 2 NTU or less? No color ?


pH value is 6.5 to 8.5 or not?

Tap water in supply area Turbidity is 2 NTU or less? No color ?


(Note: Residual chlorine means free chlorine)

3

Chemicals for water treatment

3.1 Coagulant

1) Roles of coagulant

(1)Neutralization of electric charge

In general, suspended solids (colloidal particles) in turbid water carry a negative charge ! !

on the surface.

So, they repel each other and are not easy to get together. The state of the water is called

stable.

Chemical that is added into the water to make unstable, which means neutralization of

electric charge on the surface of suspended solids, is called coagulant.

Coagulant in water brings about particles bearing positive electric charge.And these particles neutralize the negative electric charge on the surface of suspended

solids in turbid water.

By neutralization of electric charge makes the suspended solids get together and makes

them much larger. !


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Figure 8

Neutralization and Bridging by Coagulant

(Reference 4

Bridging

This means a phenomenon which is like building bridges across flocks with coagulant.

This function of coagulant makes flocculation more effective. High molecular coagulant

(polymer) has this function much more.

! ! Bridging by

! ! ! Synthetic polymer

Figure 9 A schematic drawing of Bridging by Synthetic polymer

Colloidal particles (negative charge) Coagulant particles (positive charge)

Colloidal particles electrically repel each

other (very stable)

Formation of coagulant particles by

addition of coagulant

Charge neutralization by coagulant

Flock making by bridging of coagulant

Synthetic polymer


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2) Conditions on the coagulant effectiveness

(1)Temperature of water

Coagulation is more effective at higher temperature of raw water.

(2) H

The H value of raw water should be kept in a certain range in order to make coagulant

work well.

! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! H

Figure 10 Optimum coagulation pH

Explanation of figure 10

This shows the relationship between alum(mg/) required for 50% removal of materials

(kaolin and fulvic acid) in water and pH of the water.

In a range of 6 to 8 pH, alum required for removing turbid material (shown as kaolin)

becomes the least. This means pH of this range is very effective in coagulation of

turbidity.

On the other hand, alum required for removing color and organic material (shown as

fulvic acid) becomes the least in a range of around 5 to 6 pH.In any event, pH have a strong effect on coagulation process.

(3)Alkalinity

Alkalinity is needed for coagulation. In case of poor alkalinity, coagulant does not work

well.

(4)Mixing with raw water

(4-1)Rapid mixing (for coagulation)

As soon as feeding coagulant into raw water, coagulation instantaneously begins.

Coagulant has to be mixed with water rapidly after feeding so that the chemical disperse

rapidly and uniformly as much as possible in water.

Coagulant must be fed continuously.(4-2)Slow mixing (for flocculation)

After reaction, relatively rapid mixing is needed to make larger flocks.

After then, relatively slow mixing is needed not to break up the flocks and to make the

flocks much larger.


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3) Inorganic coagulant

(1)Aluminum sulfate (Al2(SO4)3XH2O) (the most popular coagulant in Laos)

(1-1) Characteristics

Solid type aluminum oxide 15% or more and liquid type (aluminum oxide around 8%)

Good points are,

not to color treated water

to be effective to almost all the suspended solid like turbidity, color and so on.to be able to use in large quantities because of no toxicity.

Weak points are,

to make light flocks.

to be narrow range of pH for coagulation.

The most suitable range of pH for coagulation is around 6 to 7.

This coagulant reacts to alkalinity in water and makes sodium sulfate(Na2SO4),

aluminum hydroxide(Al(OH)3) and carbon dioxide(CO2).

Sodium sulfate dissolves into water, aluminum hydroxide settles out.

Because of carbon dioxide, we can see bubbles in a flocculation basin.

Picture Solid aluminum sulfate (Chimnaimo WTP)


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(Reference 5)

A reaction formula for coagulation is shown below.

Al2(SO4)3+6NaHCO3 2Al(HCO3)3+3Na2SO4(dissolved) ----------------

Al(HCO3)3+3H2O Al(OH)3 (precipitated)+3H2O+3CO2(gas) ---------

Namely, aluminum sulfate reacts to alkalinity in water, then sodium sulfate dissolves

into water, aluminum hydroxide is precipitated and carbon dioxide results as gas.

Solid aluminum sulfate is usually used in a solution with concentration of 3 to 30%

(weight volume).

Make sure not to mix with sodium hypochlorite and the solution of calcium hypochlorite

because the mixture gives off chlorine gas.

(1-2) Calculation for feeding and dissolving of solid aluminum sulfate.

Vv=(Q Rs 100 10 3) C ----------- (2)

! ! Vv feeding chemical volume (/h)Q treated water volume(m3/h),

Rs aluminum sulfate feeding rate(mg/)

! ! C solution concentration of solid aluminum sulfate(weight/volume%)! = weight of solid aluminum sulfate(kg) (water volume(m3) 1000)

(Example 1)

1)Dissolution tank volume is 200solution concentration is 10%.

Calculate the weight of solid aluminum sulfate needed.

Since 0.1=W (0.2 1000) W=20kg

2)Treated volume of water is 8,000m3/day(333m3/h), feeding rate is 20mg/.

Calculate feeding volume of solution of aluminum sulfate.

Vv=(333 20 100 10 3) 10=66.6(/h)

In general, since solution concentration of solid aluminum is almost same in dailyoperation, feeding volume is expressed as blow.

Vv=Ka Q R(/h)---------(3) Q: m3/h, R: mg/

Ka: 1/(C 10)

Table 4 Ka value with solution concentration(%) of aluminum sulfate

Alum.(%) 3 5 10

Ka 0.0333 0.020 0.01 0.0067 0.005 0.004 0.0033

Feeding Volume of Alum.(/h) according to treated water volume(m3/h),feeding rate(mg/

) at fixed solution concentration of Alum. are listed in the reference part.


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(2)Poly aluminum chloride (PAC) ({Al2(OH)nCl6n}m)

(2-1) Characteristics

High molecular liquid type coagulant (aluminum oxide around 10%).

To be used in undiluted solution.

The most suitable range of pH for coagulation is around 6 to 9.

A lowering of alkalinity of water is small.

A lowering of coagulability is hardly seen at lower temperature (less than 10C) andalkalinity(less than 20mg/).

Make sure not to mix with sodium hypochlorite and the solution of calcium hypochlorite

because the mixture gives off chlorine gas.

4) High molecular coagulant (Polymer)

(1) Use in water treatment process

Generally, in water treatment process, at first colloidal particles are coagulated and

flocculated through the neutralization of electric charge by inorganic coagulant like

aluminum sulfate. And then high molecular coagulant( polymer) is added in order to

make larger flocks.

Figure 11 A process of flock formation

Types of high molecular coagulant is shown below.

Table 5 Types of high molecular coagulant

Ion typeMain suitable!

suspensionEffects of treatment Characteristics

Anionic typeInorganic and

organic colloidalsuspension

Flocculation &sedimentation,Dehydration

Largely effective toflocculation &sedimentation

Nonionic type

Effective to acid

waste water

Cationic typeOrganic colloidal

suspensionDehydration

Effective todehydration of

sludge by machine

Amphoteric typeEffective to sludge of

difficult todehydrate

Colloidal particles

Micro flocks

Lager flocks

ine particles

Coagulation

Inorganic & organic

coagulant

Coagulation + Adsorption &

Bridging (Polymer)

Adsorption & Bridging

(Polymer)

Adsorption & Bridging

(Polymer)


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In water treatment process, high molecular coagulant of anion type ( molecular amount is

10 million to 20 million, poly-acryl amide type) is generally used.

(2) Characteristics

Even if the feeding amount is small, this coagulant shows an outstanding effect on

flocculation because the capacity of neutralization of electric charge is very large.

This coagulant gathers flocks by bridging. It looks like strings which entwine flocks

together.

! ! ! ! !

! ! ! ! ! Figure12 A schematic drawing of coagulation and flocculation

The larger the molecular amount is, the stronger the capacity of flocculation becomes.

The pH of water is not affected by adding polymer so much unlike an inorganic

coagulant.

(3) Concentration of polymer solution

It is very important for polymer to uniformly mix with colloidal particles in water.

Dilution over a certain limit is needed for that.

The lower concentration of solution is more effective because of the easiness of mixing

in flocculation process.

The concentration of 0.05 to 0.2 % in solution of anion and nonionic polymer type is

recommended. Namely, this means 0.5 to 2 kg of polymer is dissolved into 1 m3volume

of water.

(4) Feeding rate

Feeding rate is decided by jar testing. See details in a manual Water quality

examination.

(5) Feeding volume of polymer solution

Vv = Q R 10 (/h)! ---------(2)! Vv Feeding volume of polymer(/h)

Q Treated water volume(m3/h)

R Feeding rate of polymer(mg/)(By jar-testing)

Coagulation

Flocculation

Action of coagulant

Action of polymer


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(Example 2

Feeding rate is decided to 0.05mg/,Q=3,000m3/h

Feeding volume of polymer?

Vv = 3000 0.05/1000 = 0.15(/h)

(6) Note on dissolving and using

Water not contained impurities should be prepared to dissolve polymer.

Not to inhale the dust of polymer while dissolving.To dissolve polymer not so as to make lumps of polymer is required. The method is below.

Pour water into half of a solution tank and then polymer is added to the tank little by

little along with water as stirring as strong as possible at the same time.

Finish adding polymer before the tank is filled with water. And polymer particles

should be added so as to be dispersed over the water surface.

Around 1 hour for dissolving is needed. Rotation number for mixing is 200 to 400 rpm.

Avoid a mixing of long time.

Make a distance between a solution tank and feeding point as short as possible.

Use the solution up as soon as possible because the solution is easy to degrade and the

flocculation capacity deteriorates.The practical shelf life of anion polymer solution is around 7days.

Over-feeding of polymer brings about reverse effects.

Since polymer gets hard by moisture, be careful for keeping and handling. Keep them! in

a dry and cool dark place.

3.2 Chemicals for pH adjustment

1) Roles of the chemicals

For adjusting pH of water into the most suitable range for coagulation, anti-corrosion..

In case of running off the most suitable pH range for coagulation, alkali chemical or acid

chemical is needed to adjust pH of water.

In case of lowering of pH after treatment (around less than 6), alkali chemical is needed

to prevent corrosion of pipes.

2) Alkali chemical

To be used to increase pH of raw and finished water.

The reasons of pH lowering are due to high turbidity, much usage of coagulant, mixing of

waste water from factories and so on.

Calcium hydroxide(Ca(OH)2) and sodium hydroxide(NaOH) are used as alkali chemical.

Alkali chemical is injected at the upstream of coagulant feeding point to raise pH of raw

water( called pre-alkali). Fully agitation is needed.

To raise pH of finished water, alkali is injected between sedimentation basin and finished

water reservoir(called post-alkali).

3) Acid chemical

To be used to decrease pH of raw and finished water.

The reasons of pH uprising are due to assimilation of carbonic-acid gas by algae, mixing

of waste water from factories and so on.

Sulfuric acid(H2SO4) and hydrochloric acid(HC) are used as acid chemical.

Acid chemical is injected into raw water after measuring pH of raw water.


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3.3 Oxidant, disinfectant

1) Roles of oxidant

To oxidize organic matter, iron, manganese, ammonia nitrogen, organic nitrogenous

compounds and so on in water.

The water that contains a lot of these matters consumes oxidant much more.

In general, chlorine chemical is used as pre-chlorine which is injected to raw water andas intermediate- chlorine which is injected to the water after sedimentation.

Pre-chlorination is effective

to promote coagulation and to remove iron ion, manganese ion and odor by oxidation

to prevent the breeding of algae and fish

to prevent decay of sediment

to remove manganese ion on sand surface in filter basin

to prevent the breeding microorganism in filter layer.

Oxidation effect of chlorine highly drops under the existence of turbidity.

Intermediate-chlorination is used to reduce disinfection by-products instead of

pre-chlorination.Chlorine is added into settled water after suspended solids in raw water, which are cause

of disinfection by-products, are removed through flocculation and sedimentation.

In high turbidity, intermediate-chlorination is effective to save a consumption of chlorine.

As a practical matter, both pre-chlorination and intermediate-chlorination are used at the

same time considering both merits.

(Reference 6)

Disinfection by-products

This is a substance made by chlorine which is injected as oxidant or disinfectant reactsto organic matters in the water. The most popular one is THMs. On of them, chloroform,

is recognized to be carcinogenic.

(Reference 7)

The amount of chlorine consumption

1mg of iron consumes 0.63mg of chlorine1mg of manganese consumes 1.29mg of chlorine1 mg of ammonia nitrogen consumes 7.6mg of chlorineThe more water contained ammonia nitrogen, the more it consumes chlorine.

2) Calculation for feeding

Chlorine weight fed into treated water.

R=W 1000 Q -------- (3) R chlorine feeding rate(mg/)

Q volume of treated water(m3/day) ! W effective chlorine feeding weight(kg/day)

(Example 3

Consumption weight of chlorine a day is 4kg, treated water volume is 8,000m3/day.

Calculate the feeding rate of chlorine.

R=4 1000 8000=0.5 (mg/)

! ! (Note This chlorine weight is the pure chlorine.)

Inversely, W=R Q 1000 (kg/day)


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3) Roles of disinfectant

Disinfectant is injected to the water after filtration and the clear water like groundwater

as the final process.

In general, chlorine is used as post-chlorination after filtration.

Post-chlorination feeding absolutely must not be stopped while processing the water to be

supplied.Continuous feeding without any intermittent is indispensable to ensure safe supply

water.

4) Chlorine chemical

In general, chlorine chemical is used in the water supply services. The reasons are shown

below.

The effect of disinfection is perfect.

The disinfection to huge volume of water can be done easily

The effect of disinfection remains for long

The effect of disinfection can be easily checked and confirmed at the tap.

To be harmless for human beings and not to make the taste bad.There are liquid chlorine, sodium hypochlorite(liquid),calcium hypochlorite(solid) and so

forth as chlorine chemicals.

(1) Sodium hypochlorite (NaOCl)

Liquid of light yellow color with effective concentration of chlorine 5 to 12 % (It means

1kg of sodium hypochlorite contains 0.05 to 0.12 kg of pure chlorine.).

This chemical is corrosive and has strong alkalinity.

Tank and pipe made from corrosion-proof material should be used. Be careful to handle

not so as to get it to skin, mucous, especially to eyes.

This chemical is unstable and decomposes giving off the oxygen in normal temperature.

This reaction is facilitated by sunlight, ultraviolet rays, heavy metals, temperature

raising and lowering of pH.

This chemical is rapidly decomposed by acid and give off chlorine gas. Make sure not to

be mixed with acid materials, acid solutions like aluminum sulfate.

(2)Calcium hypochlorite (Ca(OCl)2) (the most popular disinfectant in Laos)

Powder, granule or tablet of white or silvery white color with effective concentration of

chlorine 60 to 70 % (It means 1kg of calcium hypochlorite contains 0.6 to 0.7 kg of pure

chlorine.).

It slightly smells like chlorine and is readily soluble in water.

It has good stability and is durable to keep for long time.

To be used dissolving in water. In case of high concentration, be careful of scaling in pipes

and lowering of effective chlorine.

To be kept in sealed up in a dry, cool and dark place keeping away from water,

combustibles and explosive materials.

In case of fire, the chemical gives off chlorine gas with decomposition.

To be injected with solution of effective chlorine concentration 1 to 6 %.

This chemical is rapidly decomposed by acid and give off chlorine gas. Make sure not to

be mixed with acid materials, acid solutions like aluminum sulfate.


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Make sure to put on glasses, a mask and outer wear to keep the dust away from while a

solution working.

Picture 2 Calcium hypochlorite

(3) Calculation for feeding and dissolving chemicals!

(Sodium hypochlorite)

Vv=(Q R 100 10 3) C ------------ (4)

! Vv feeding amount (/h)Q treated water volume(m3/h),

R chlorine feeding rate(mg/) C effective concentration of chlorine(%)

d density of solution with C%(kg/)

(Example 4)

Treated water volume 8,000m3/day(333m3/h), chlorine feeding rate 0.5mg/

Effective concentration of chlorine 10%, Density 1.2

Calculate the feeding volume of chlorine solution.

Vv=(333 0.5 100 10 3) (10 1.2)=1.39 (/h)

This means in case of feeding rate 0.5mg/, around 139litters/hour of sodium hypochlorite

is fed into the water.

(Calcium hypochlorite)

Vv=(Q R 100 10 3) C d ------------- (5)

Vv feeding chemical volume(/h)Q treated water volume(m3/h),

R chlorine feeding rate(mg/), C effective concentration of chlorine(%)

(C=(weight(kg) effective chlorine concentration in solid(%) water weight(kg))d density of solution with C%(kg/)


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(Example 5)

Tank volume is 190. Effective chlorine concentration of solution is 5%.

In case of calcium hypochlorite with effective chlorine concentration 70%, how much

weight of the chemical is needed?

0.05=W 0.7 190 W=(190 0.05)/0.7=13.57kg

(Example 6)How much volume of the chlorine solution mentioned above is needed to make the chlorine

concentration of water of 5,000m3to 0.5mg/.

Total chlorine weight needed to this water is,

5000 1000 0.5=2,500,000mg=2,500g

The 5% solution mentioned above contains 50g in one litter of the solution.

Then to keep the chlorine weight 0.5 mg/ in the water,

we need 2,500/50=50 of the solution.

(Reference 8

1mg/= 0.001g/= 1g/m3

1% = 1g/100g = 10g/1kg = 10kg/1,000kg = 10,000mg/

= 10g/

(in case of water)

(Example 7)

Treated water volume 8,000m3/day(333m3/h), chlorine feeding rate 0.5mg/, effective

chlorine concentration of calcium hypochlorite 70%, density 1.01, tank volume 1m3,

effective chlorine concentration of solution 5%, Calculate the weight of calcium

hypochlorite for solution and feeding rate.

From 0.05=W 0.7/1000 W=71.4kg

From Vv=(333 0.5 100 10 3) (5 1.01) Vv=3.3(/h)

In general, since effective chlorine concentration of solution is almost same in dailyoperation, feeding rate is expressed as below.

Vv=Kc Q R (/h)--------- (6) Q m3/h , R mg/

Kc 1/ 10 effective chlorine concentration of solution density (= const.)

A graph or tables between Q and R will be convenient for daily operation.

Table 6 Kc value with effective chlorine concentration( ) of calcium hypochlorite

solution

% 1 2 3 4 5 6 7 8 9 10

Kc 0.099 0.0495 0.033 0.0248 0.0198 0.0165 0.0141 0.0124 0.01 0.0099

Note: density =1.01(fixed)Feeding Volume of Calcium hypochlorite(/h) according to treated water volume(m3/h),

feeding rate(mg/) at fixed effective chlorine concentration are listed in the reference

part.


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(4) Factors affecting on the disinfection effect of chlorine.

The lower pH of water becomes, the larger the disinfection effect is.

Namely disinfection effect falls as an increase of pH value (See textbook Water

Purification p102 ).

The higher temperature of water is, the larger the disinfection effect is.

It is very important to mix chlorine with water and make it diffuse rapidly and uniformlyfor disinfection effect.

(5) Weight of chemicals needed to make solution.

Next tables show weight of Calcium Hypochlorite and Solid Aluminum Sulfate which are

needed to make each solution according to a concentration of solution and a volume of

solvent (water).

If there is no suitable conditions, calculate the weight using adjacent value conditions.

For example,

In case of Calcium Hypochlorite, concentration 3%, tank volume 3.3m3

At concentration 3% from the table, in case of tank volume 3m3, weight is 129kg, in

case of 4m3

, weight is 171kg, then in case of 3.3m3

, W= 129+ (171-129)/10 3 = 141.6kg

In case of Solid Aluminum Sulfate, W= concentration water volume 10,

In case that concentration is 12% and tank volume is 5.5m3, then

W=12 5.5 10 = 660kg

In case of Calcium Hypochlorite, which effective concentration of chlorine is 60%,

Concentration of hypochlorite solution is 5%, water volume of solution tank is 3m3.

From table (2), at 5%, 3m3and effective concentration of chlorine is 65%, the weight of

calcium hypochlorite is 231kg ,then

W=231 (65/60)=250.3kg (in 60% effective concentration of chlorine)


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Table 7 Weight of chemicals needed to make solution


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Table 8 Weight of chemicals needed to make solution


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4 Intake facilities

4.1Maintenance

Table 9 Daily routine inspection cycle and items

Cycle Items

RiverTwice a daytime

River state (Oil, Dead fish, Water level, A pile of earthand sand around an intake point)

Once / 2hours Pump state (Current, Voltage, Pressure)

Wells

Twice a daytime Well surrounding areasOnce / 2hours Well pump state (Current, Voltage, Pressure)

Twice a daytime Well water level

Twice a daytime Raw water quality(*)

(Note(*): by water quality examination)

5 Receiving well

5.1 Functions

To stabilize fluctuations of flow rate and water level of raw water flowing in.

To measure and adjust the volume of raw water to carry out a series of treatment process

correctly and easily.To be also used as a point of feeding of coagulant and chlorine.

In case of effective use of law waters pressure and receiving conduit being enough large,!

a receiving well is not always provided.

5.2 Maintenance

Table 10 Daily routine inspection items and cycle

Cycle Items

Twice a daytimeInflow states of raw water, water level

Raw water quality(*)Once / 2 hours Pre-chlorine feeding

Operation state of instruments

(Note * by water quality examination)

5.3 Feeding equipments of oxidant

1) Pre-chlorination equipment

(1)Setup of equipment

It consists of solution tanks, mixers, feeding pumps, measuring devices, feeding pipelines

and so on.

They have many cases that the feeding is done by gravity from solution tanks in Lao.In this case, the control of feeding chemical is done by adjusting the overflow depth of

triangular weir or the opening degree of valves.

(2) Feeding point

Feeding point is usually at receiving well.

(3) Feeding rate

To be decided based on the water quality of raw water, for example ammonia nitrogen,


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iron, manganese and so on.

In general, the standard feeding rate is decided as ten times as much as concentration of

ammonia nitrogen in raw water and so as to keep around 0.5mg/of residual chlorine in

filtrated water.

(4) Note

Since the decomposition of chlorine is facilitated by sunlight in fine weather, consider the

differences of chlorine consumption in flocculation and sedimentation basin due toweather change.

6 Flocculation (coagulation) and sedimentation process

6. Rapid mixing basin

1) Functions

A facilities for diffusing coagulant in water rapidly and uniformly.

As soon as coagulant is fed in this basin, rapid mixing is promptly needed so that

coagulation disperses all over the basin.

The time needed to diffuse and mix coagulant should be as short as possible.

In case of baffling or weir typed mixing basin, mixing intensity depends on the volume oftreated water.

It is desirable to examine the mixing intensity at maximum volume of treated water and

at minimum one.

2)Maintenance


Cycle Items

Twice a daytimeInflow states of raw water

Mixing state

Suspended dust and trashOnce / 2 hours Coagulant feedingOnce a daytime Leakage from outer surface of the basin

6.2 Feeding equipment of coagulant

1) Aluminum sulfate feeding equipment

(1)Setup of equipment

It consists of solution tanks, mixers, transferring pumps, feeding pumps, measuring

devices, feeding pipelines.They have many cases that the feeding is done by gravity from solution tanks in Lao like

chlorine feeding equipment.

The solution tanks of aluminum sulfate must not be installed close to the tank of

chlorine.

(2) Dissolving procedure of solid aluminum sulfate.

An example of Chinaimo WTP is shown below.


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! ! ! ! ! ! !

Figure 13

Preparation of 20 Alum solution

! !

(3)Feeding point

The chemical is fed at rapid mixing basin. It is very important to inject to the center of

mixing.

(4)Feeding rate

To be decided by the jar test every day. To make a graph by the data of past turbidity and

coagulant feeding rate will be very useful for daily operation.

(Reference 9)

Jar test procedure

See a manual Water quality examination.

6.3 Flocculation basin

1) Functions

By properly mixing, to get together fine coagulated flocks to make larger ones which are

easy to precipitate.

A baffling type flocculation basin which uses energy of stream of water itself (very

popular in Lao) and a basin with rotating paddles which uses mechanical energy.

Empty tank

Close outlet valve

Aluminum Sulfate

36 bags = 1800kg

Water to full line

Start mixing

for 2 hours

Stop mixing

Ready to feed

Check

a specific gravity

Number of Alum tanks:4

Effective volume of a tank: 9.0m

3

Concentration of Alum

solution:20


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(1) Horizontal baffling type (2) Vertical baffling type

( plan view ) ( cross- sectional view )

Figure 14 Baffling type flocculation basin

! Take notice that the space of baffling wall gets wider as water flows down.

Picture 3 Baffling basin of Chinaimo WTP

Right: At an entrance of flocculation basin

Left: At an exit of flocculation basin (You can see flocks and water in upper

part of beaker becomes clear.)

Picture 4 A state of flocculation


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2) Operation of baffling type flocculation basin

Mixing intensity is in proportion to the power of 3 of velocity (P 3). This means mixing

intensity largely changes compared with the change of flow rate.

In general, it is desirable to operate this basin in a certain range of flow rate.

3) Maintenance

Table 12! Daily routine inspection item and cycle

Cycle ItemsTwice a daytime

Flocks growingSuspended dust and trash

Mixing state

6.4 Sedimentation basin

1)Functions

A basin that separates almost all the flocks, which are formed and grown up in

flocculation basin, out of water by gravitational settling action.

In this basin, organics, bacteria and organism can be also removed as well as particles of

clay because the flocks has strong adsorption ability.

The efficiency of sedimentation basin is defined as below.E=0 A Q --------- (7) 0 settling velocity,

A plan area of sedimentation basin,

Q treated water volume

Hence,

The faster settling velocity becomes,

The larger plan area of sedimentation basin becomes

The lesser treated volume of water becomes, the higher the efficiency becomes.

!

Figure 15 A schematic drawing of sedimentation basin

D

W

L

Q

A=L

W

(m

2

)

V=L

W

D

(m

3

)


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Detention time

The index means a period of time which is needed for the water to pass through the

sedimentation basin from entrance to exit.

t=24 V Q ------- (8) t: detention time(h), Q: treated water volume(m3/day)

V: volume of sedimentation basin(=L W D)(m3),

L: length(m), W: width(m), D: depth(m)! of a sedimentation basin

(Example 8)Treated water volume per basin 4,000m3/day, depth 2.5m, width 5m, length 20m,

Calculate detention time t.

t = 24 (2.5 5 20)/4000=1.5(h)

Overflow rate

The index means the effect of flock removal in sedimentation basins.

u= QA = Q 1000 (L W 1440) -------- (9) u overflow rate(mm/min)

Q treated water volume(m3/day),

A plan area of a basin(=L W)

(Note: 1440= 24(h) 60(min))(Example 9)

Treated water volume per basin 4,000m3/day, width 5m, length 20m,

Calculate overflow rate.

u=4000 1000/(20 5 1440)=27.8(mm/min)

Mean velocity

The index means the velocity of the stream of water in the basin.

= Q 24 60 W D --------- (10) mean velocity(m/min),

Q treated water volume (m3/day),

D depth(m), W width(m)

(Example 10)

Treated amount of water per basin 4000m3/day, width 5m, depth 2.5m

Calculate mean velocity.

= 4000/(24 60 5 2.5)= 0.22(m/min)

2) Types, etc

(1) Horizontal-flow basin (without flocculation)

Suspended solids can be settled by flowing water slowly. This is the most basic one.

Standard value of overflow rate is 5 to 10 mm/min.

Standard value of mean velocity in a basin is 0.3m/min or less.

(2) Horizontal-flow basin (with flocculation)

The same as mentioned above.


Standard value of mean velocity in a basin is 0.4 m/min or less.

(3) Horizontal-flow basin with inclined parallel plates

Many inclined parallel plates are installed in the horizontal-flow basin to make the plan

area larger for the improvement of settling efficiency.


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Standard value of mean velocity in a basin is 0.6 m/min or less.

(Reference 10)

The basic principle of inclined parallel plates

! ! ! ! Namely, settling timeTdecreases to tand the efficiency becomes H/h (>1).

! ! ! ! ! Note: Water flows perpendicularly to this figure.

! Figure 16 Inclined parallel plates

3) Settled sludge

The more settled sludge is piled up in the bottom, the harder the sludge gets because of

compaction.

! That makes a cross section of basin narrower and velocity faster in the basin.

! In the end, that becomes to an obstacle to sedimentation of flocks.Settled sludge should be drained earlier.

4) Maintenance


Cycle Items

Twice a daytime

Flow states, sedimentations states of flocks

States of inclined parallel platesQuality of settled water(*)

Suspended dust and trashCollecting apparatusOnce a daytime Leakage from outer surface of the basin

Once a week Measurement of settled sludge amount

(Note * : by water quality examination)

H

T = H / v

t = h / v

Then, t < T

v : Settling velocity


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7 Filtration process

7.1 Slow sand filter basin

1) Functions

Generally, the facilities which treat relatively less turbid water and dose not need pre-

treatment process like flocculation, sedimentation and so on.

There are some cases that have pre-filter basins which roughly filtrate water.

! They are installed before slow sand filters to remove planktons, algae, turbidity and toreduce burden of slow sand filters.

Standard value of filtration velocity is 2 to 10 m/day.

This type of filter basin can remove turbidity and bacteria as well as an ordinary rapid

sand filter basin.

In addition to that, the organic oxidation action by biotic filter membrane which develops

on the sand surface can remove ammonia nitrogen, odor, taste, iron, manganese,

synthetic detergent, phenol and so on.

Filtration velocity = QA (m/day)-------(11)

Q: treated water volume a filter basin (m3/day)

A: the sand surface area a filter basin (m2

)(Example 11)

Treated water volume is 6,000m3/day, the number of filter basins is 4, and the sand

surface area a basin is 300m2, Calculate filtration velocity.

Q = 6000/4 = 1500m3/day = 1500/300 = 5m/day

2) Structure

This type of filter basin has the same structure as that of a rapid sand filter without

washing equipments.

It consists of under drain system, support gravel layer and sand filter layer from bottom

to upward.

Treated water flows down through sand and gravel layers to under drain system.

Figure 17 Schematic View of slow sand filter


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3) Sand scraping

Slow sand filters do not need the washing operation like rapid sand filters because

filtration of this filter is done by biotic filter membrane.

In case that the biotic filter membrane becomes too thick due to piling up of suspended

matters and breeding of microorganism by long time filtration, the capacity of filtration

decreases. So, scraping off the biotic membrane is needed to recover the capacity.

(Reference 11)

Scraping off the biotic membrane (sand) and replenishing of sand

( Extraction from The instruction manual of water treatment and quality control by

Kanagawa prefectural waterworks bureau

(1) Scraping off the biotic membrane (sand)

By confirming the head loss of filter once a day, in case that the head loss shows

500mm(this means the filtration becomes difficult.) or the duration time of filtration

runs up to 30days, the scraping of sand is needed.The thickness of sand scraped is around 1.5cm. This sand is washed and stored for

reuse.

Immediately after scraping off the sand, the filter can be put to use because the biotic

membrane is formed below the surface. But the examination of quality examination of

filtrated water, mainly turbidity, is needed before putting the filter to use in practice.

In case that there is a tendency of increasing head loss, scraping work is needed

earlier.

(2) Replenishing of sand

! ! The sand layer is needed to be replenished with sand when the thickness of layerdecreases to half through scraping

After replenishing, the filtrated water has to be drained until the formation of biotic

filter membrane is confirmed.

The confirmation of forming biotic membrane is done by examination of turbidity,

general bacteria and coliform group.

Two to four weeks is needed for recovering the capacity of filtration after replenishing.

The recovering of filtration capacity is facilitated by scattering the old sand, which has

been scraped but not washed, on the surface of new sand after replenishing.

4) Note on operationThe water depth above sand surface should be kept to be 0.9 to 1.2m.

If possible, slow sand filters should be operated on fixed flow rate. The flow rate must not

be changed so often according to demand.

It takes much time to show the real capacity of filtration because the function is due to

biological action.

Immediately after scraping off or replenishing sand, observation of filtrated water quality

is especially needed.


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The partial use of the slow sand filter surface is not desirable.

The use of chlorine to water flowing into slow sand filters must be avoided.

5) Maintenance

Table 14 Daily inspection items and cycle

Cycle Items

Twice a daytime Water level of filter basinInflow state of waterQuality of filtrated water(*)

Once a daytimeBreeding algae and living things

Surface state of sandLeakage from outer surface of the basin

(Note (*): by water quality examination)

7.2 Rapid sand filter basin

1) Functions

The rapid sand filter needs flocculation and sedimentation process by coagulant as the

pretreatment process to cope with higher turbidity and large volume of treated water.

Standard value of filtration velocity for normal types is 120 to 150 m/day.

Rapid sand filters is suitable for large volume of treated water.

Substances which can be removed by rapid sand filters are limited because the function

of filter is based on physical actions.

! Turbidity is easy to be removed but ammonia, taste, odor and so on can not be removed at

all.

Disinfection after filtration is indispensable.

Iron and manganese can be removed on the surface of sand through contact oxidation by

residual chlorine in water.

2) Structure

To be the same as that of slow sand filter

While filtrating, treated water flows through sand layer down to under drain system.

While backwashing, washing water flows through bottom to upward and into washing

trough.

3) Washing of filter

(1)Washing of rapid sand filters

A certain time of use makes the function of rapid sand filter lower because turbid

substance is clogged in sand layer.

The filters are needed to be washed to recover the function and to keep sand clean.

In case of resuming filtration after suspension for a certain period of time, washing

should be needed to wash away flocks on filter layer.

Normally finished water contained residual chlorine is used for washing.


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(2)Washing operation

Washing of filters is the operation that washing water washes away flocks clogged in

sand by loosening and fluidizationing sand layer and making sand particles collide each

other.

A combination of backwashing and surface washing is standard.

In addition to this, a combination of backwashing and air-blowing instead of surface

washing is also used.

Air-blowing is used to disturb and to inflate sand layer by air from the bottom.

(3)Washing criteria

Criteria for washing are written below.

Head loss of filter reaches a permissible limit,

Duration time period of filtration passes over certain time limit,

Turbidity of filtrated water is above certain limit,

The total amount of filtrated water reaches certain value.

(3-1)Head loss of filter layer

The more the filter layer gets clogged while filtrating, the lower water pressure of

discharge becomes.

Head loss of filter layer is the difference of water levels between water level of filter basin

and that of discharge side (See figure 17).

! ! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! ! ! ! ! Figure 18 Head loss of filter

(Explanation of Figure 18)

The head loss means the difference of water level between A and B shown above.

It is due to the loss of filter media.

The larger the loss of filter media becomes, the bigger the difference of water level does.

The loss increase of filter media is caused by clogging of flocks, namely dirt.

(3-2)Duration time

This means operation period of time that is thought not to give bad effect to filtrated

water empirically.


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In case that head loss does not increase so much, washing is needed in a certain period of

time because filter media is firmly fixed with flocks by long-time filtration and the

function can not be recovered by normal washing operation.

(3-3) Surface washing

Flocks spreads on the surface of filter like a mat. Surface washing is done to break this

mat.

Pressurized water from the equipment installed above the surface of sand breaks the mat

of flocks.

(3-4) Backwashing

Pressurized water from the bottom of filter flows through sand layer, inflates it and

washes away turbid matters clogged in sand.

In general, inflating sand layer by 20 to 30% is needed. This pressurized water is

provided from an elevated tank or back washing pumps.

! ! ! !

Figure 19 Backwashing

(3-5) Air-blowing, air washing

Air from a blower is used instead of washing water.

This is used with back washing, in this case, surface washing is usually not used.

In case of back washing with air-blowing at same time, there is a possibility of outflow of

sand.

It is important for the air to be dispersed over the whole surface of filter.


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Picture 5 Air-blowing (Phanom WTP in Luangprabang)

(Reference 12)

Washing procedure

(1)Surface washing + backwashing

To lower the level of water to around 15 cm above the sand surface.

To start surface washing

After surface washing for 1 or 2 minutes, open the backwashing valve a certain extent

and then open full after several minutes.

Backwashing time with back washing velocity of 0.6 to 0.9 m/min is 5 to 15 minutes

according to the dirt condition of filter.

To stop surface washing before around 1 minute of finishing backwashing.

(2)Air-blowing + backwashing

(A design specification of Chinaimo WTP in Vientiane city)

Backwashing with air(1.0m3/min/m2) + water(0.36m3/min/m2) for 5 minutes.

Backwashing with water only (0.36m3/min/m2: 0.3 0.5m3/min/m2 is standard ) for

10minutes.

(An actual example of Chinaimo WTP )

To lower the level of water to around 20 to 30 cm below the normal water level.

To blow air for 2 or 3 minutes.

To stop air-blowing and leave still for 2 minutes. This is a step to keep sand from

flowing out of basin.

To start backwashing.

Backwashing lasts for 20 to 30 minutes according to the dirt condition of filter.

(An actual example of Phanom WTP in Luangprabang city)


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To lower the level of water to around 30 to 40 cm below the normal water level.

To blow air for 4 minutes. Backwashing is used together for last 1 minute of

air-blowing.

To stop air-blowing and continue backwashing for more than ten minutes.

Picture 6 Air-blowing only

Picture 7 Air-blowing + backwashing

Picture 8 Backwashing only


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Picture 9 Finishing of backwashing

(Reference 13)

Backwashing velocity ( Backwashing rate )

This means the amount of washing water per minute to be given to sand surface area of

1m2while backwashing.

= Q A (m/min) --------- (12)

Q is the volume of backwashing water, A is sand surface area,

= (m3/min) (m2) = m / min This has dimension of velocity.

(3-6) The volume of washing water

This means the water volume needed to wash a filter basin while backwashing.

Q = A t (m3/basin) ------------ (13)

Q is the volume of washing water(m3/basin), is backwashing velocity (m/min)

A is surface area of sand, t is back washing time (min)

(Example 12)

=0.6(m/min), A=30m2, t=10min, Calculate the volume of washing water.

Q = 0.6 30 10 = 180m3/basin

4) Note on operation

The water depth above sand surface should be kept to be 1 to 1.5m.

Filtration velocity must not be changed suddenly.

Coagulant always must be fed at pre-treatment process.

5) Maintenance



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Cycle Items

Twice a daytime

Water level of filter basinInflow state of water

Quality of filtrated water(*)

Once a daytimeSurface state of sand(while filtration)

Once a daytime Leakage from outer surface of the basin


6) Abnormal phenomenon, causes and measures

Table 16 Abnormal phenomenon, causes and measures

Phenomenon Causes Countermeasures

Becoming clouded

of inflow water

Excessive feeding of coagulant.

Unsuitable pH for flocculation.

Proper feeding of coagulant.

Lowering of filtration velocity

or Reducing volume of treated

water.

Leak of turbidity,color and

microorganism

Poor feeding of coagulant andchlorine.

Poor washing.

Increasing of coagulant andchlorine injection. Improving of

washing.

Abnormal head loss

Blockade of filter by algae.

Poor washing.

Sudden change of pH

(Note: pH greatly affects

flocculation).

Shortening of washing interval.

Improving of washing,

Introducing of pH control.

Abnormal partial

spouting of sandwhile washing

Inuniformity of gravel layers. Renewal of filter media.

Outflow of sand

Excessive washing velocity.

Excessive volume of air for

washing.

Adjustment of volume of

washing water and air. Stop

using them at the same time.

Cave-in of sand

surface

Abnormal state of under drain

system.

Checking of under drain

system.

Mud balls in sand

filter Poor washing.

Reconsideration of washing

conditions. Maintenance of

filter.

8 Disinfection process

8.1 Mixing basin (for post-chlorination)

1) Functions

A basin with buffering walls inside so that chlorine for disinfection is well mixed with

water.

Not always be installed because chlorine is mixed in a finished water reservoir or a water

main.


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2) Maintenance


Cycle ItemsOnce / 2 hours Post-chlorine feeding

Twice a daytime Solution and storage tanks, measuring devices, feeding pipe

8.2 Post-chlorination equipment

1) Setup of equipment

It consists of solution tanks or storage tanks, mixers, feeding pumps, measuring devices

and pipes.

The solution tanks of chlorine chemical must not be installed close to the tank of

coagulant.

2) Dissolving procedure of calcium hypochlorite

An example of Chinaimo WTP is shown below.

Figure 20 Preparation of Calcium Hypochlorite solution

3) Feeding point

To be injected at the entrance of mixing basin so as to be well mixed with treated water.

Drain & Clean tank

Close outlet valve

Calcium Hypochlorite

3 drums = 125Kg

Water to full line

Start mixing

for 30 minutes

Stop mixing

Leave for 30 minutes

Ready to feed

Number of Hypo tanks: 3

Effective volume of a tank:3.3m

3

Effective concentration of

Calcium Hypochlorite:70

Concentration of Hypo solution:2.65


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4) Feeding rate

Post-chlorination is done for disinfection of treated water.

Residual chlorine value at the exit of clear water reservoir must be decided so that

residual chlorine can be kept in a whole supply area taking the characteristics of the

area into account.

Feeding rate of post-chlorination must be decided by taking things shown below into

account.

the gap between the residual chlorine value at the exit of clear water reservoir and

that of filtrated water.

the detention time in a clear water reservoir.

In case of increasing turbidity and color of finished water because of overload, feed

chlorine more than as usual in order to prevent waterborne disease.

In case of flooding or an outbreak of infectious disease in supply area, feed chlorine more

than as usual in order to prevent waterborne disease.

!

(Example 13)

Residual chlorine value at the exit of WTP is 0.8mg/,which is a standard value. And that

of filtrated water is 0.5mg/,Detention time in a reservoir may be ignored here.! !

Feeding rate as post-chlorination is 0.8 0.5 = 0.3 mg/. Roughly 0.3mg/ is needed.!

9 Clear water reservoir

1) Functions

Alleviation and regulation of the difference between the volume of treated water and

supply water .

Storage function of finished water preparing for some accidents, troubles and

maintenance of facilities.

To be used for keeping the contact time with chlorine and mixing chlorine with filtrated

water.

2) Maintenance

Table 18! Daily routine inspection items and cycle

Cycle Items

Once a daytimeExterior and surrounding state of reservoirstate of

ventilatorsTwice a daytime Quality of finished water(*)


After newly constructing or repairing a clear water reservoir, it was washed and filled

with finished water with concentration of 10mg/chlorine and left for 2 to 4 hours.

(According to AWWA manual, For 6 hours left filling with water with 50mg/. )

Hereafter, washing and this disinfection process is repeated several times.


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Since the drain water after disinfection has high concentration of chlorine and pH, the

water has to be discharged through dechlorination or neutralization in order to prevent

harmful influence to aquatic life.

1 Machinery

1) Pumps

(1)Observation of operation state

It is very important to observe the operation states of pumps and motors from the point

of view of confirmation of pump capacity.

The delivery amount, the relationship of suction pressure and delivery pressure, electric

current value, abnormal vibration or wobbling and so on should be confirmed.

The leak state of axial sealing, which can not be observed by equipments, should be

inspected while a patrol and adjusted if needed. Generally it is standard that liquid

from a gland packing runs down continuously.

In case of plural pumps, running time a pump should be grasped in order to average the

accumulated running time of each.

! That leads to extend the useful life of pumps through the deliberate parts change.

(2)Maintenance

(2-1) Pumps

Table 19 Daily routine inspection items and cycle on pumps

Machinery Cycle Items

Pumps

Twice

a daytime

Appearance, abnormal vibration, unusual sounds,

nasty smell, temperature at bearings, leak water

from axial sealing, oil amount and pressure,(Note) Delivery pressure, electric current, voltage

and rotation number are recorded every two hours.

(2-2) Submerged motor pumps



The part which

can be observedby eyes

Twice

a daytime


leak from valves and pipes

(Note)Delivery pressure, electric current, voltage

and rotation number are recorded every two hours.


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2) Valves



The part which

can be observed

by eyes

Twice

a daytime

Appearance, leak from flange, abnormal vibration,

unusual sounds, deformation, damage, rust,

corrosion

3) Chemical feeding facilities and equipments


Facilities Cycle Items

Solution and

storage tanks

Twice

a daytimeState of solution and mixing, storage amount

Feeding pumpsTwice

a daytime


leak, pressure, temperature

Measuring

devicesOnce / 2 hours

Adhesion and stuffing of deposition at measuring

point! (in case of weir)

Pipes and valvesTwice

a daytimeAdhesion and stuffing of deposition inside, leak

In case of measuring feeding rate by triangular weir, adhesion of deposition prevents

accurate measuring. Removing the substance is needed soon.

! ! ! ! ! ! !

Picture 10 Measuring device of feeding chlorine solution

!


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To confirm feeding volume of chemical, you should check actual feeding volume per min(

/min) at feeding point.

In case that feeding volume is set up at 66.6(/h), if feeding volume per minute(/min)

is around 1, feeding condition will be practically no problem.!

11 Electrical facilities

1) Motors

(1) Table 23! Daily routine inspection cycle and items on motors


Motors & Control

devices

Twice

a daytime


oil pressure, temperature at bearings, damage, nasty

smells,

indicator lamps, electric current and voltage value

2) The others

(2) Table 24 Daily routine inspection cycle and items on other electrical facilities


C/C board etcTwice

a daytime


nasty smells, indoor temperature of board and room,

smoke, indicator lamps, electric current and voltage

value

1 Notes of daily inspection works

Use your Five senses for the inspection at first.

The daily routine inspection route for the facilities and equipments should be decided

beforehand.

It is desirable to take simple tools on a inspection tour.

The results of inspection should be recorded on a daily inspection report form.

In case of any abnormality, record and report it to the person in charge of the plant.

1 Regular inspections excluding daily inspection work

Regular inspection works based on a weekly, monthly and yearly plan are desirable and

important.

See instruction manuals about detailed items to be inspected (Attached in Reference

Part).


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1 Recording and reporting

Recording

It is desirable to record operation and maintenance items in certain cycle shown below.

! Table 25 Operation and maintenance cycle and items

Recording cycle Operation and maintenance items

Once/ 2 hours

The volume of raw water, filtrated water and supply water.

Chemical feeding rate or volume. Clear water reservoir and

distribution water reservoir level

Voltage and current of machine. Pressure. Revolution No and

so on (operational conditions).

Twice a daytimeWater quality of raw water, filtrated water and finished water

(turbidity, pH, color, alkalinity, residual chlorine and so on).

Once a daytime Chemical (coagulant, chlorine) storage in solution tanks

Once a week Sludge accumulation in sedimentation basins.

(Note: Examples of recording form are attached in reference part of this manual.)

) Daily operation report

The volume of treated water, the amount of chemicals and power consumed, water

quality and so on should be recorded on a report in a certain time interval a day.

! Several kinds of report form are attached in the reference part of this manual.

The report should be signed by the person in charge and submitted to a administrator for

approval every day.

The reports should be kept for a certain period of time.

) Daily inspection and maintenance report

The inspection results and data should be recorded on a report in a certain time interval

a day. Several kinds of report form are attached in the reference part of this manual.!

The report should be signed by the person in charge and submitted to a administrator for

approval every day.

The reports should be kept for a certain period of time.

) Other records and reports to be prepared

A facilities register in which the spec, the date of manufacture, the history of repairs and

the place installed on machinery are written should be prepared.

Completion documents, testing reports and instruction manuals of machinery.

15 Prior provisions against accidents and disasters.

1) Necessity and causes of accidents

In accidents and disasters, a rapid and large change of treated water amount and quality

will consequently happen.!

Prior provisions have to be prepared beforehand to properly cope with accidents and

disasters and to ensure the safety operation.


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In water treatment plant, natural and human causes could be thought as the causes of

accidents and disasters.

! The sorts of accidents and disasters and the consequences are shown below.

Table 26 Anticipated influences that accidents and disasters affect

Causes of

accidents &

disasters

Classification of facilities

Intake &

ConveyanceTreatment

Transmission

& DistributionSupply

Natural

Drought

Intakerestriction

Increase ofturbidity

Fluctuation ofsupply

volume(decreaseof pressure, etc)/Colored water

Poor supply/Water

suspension

Flood

Downpou

r

Scouring,/Inflow of

driftwoods,earth and sand

/Clogging ofscreen/Damage of pipes and

conduits

Increase ofturbidity

/Inflow of foul

water into pipesand conduits

Inflow of foulwater into basins

and manholes/Damage of

pipeline by mudslides andcave-ins

Damage ofservice

installations

by mud slidesand cave-ins

Earthquake

Damage ofpipelines,

conduits andbuildings/Leakage

Damage ofbasins,

tanks, pipes andconduits,

/Secession ofpipes /Leakage/Outflow of filtersand /Chemical

leak

Damage ofpipelines andappurtenants

/Leakage

Damage ofservice

installations/Leakage

Human

Water

quality

Intakesuspension

/Chemical use(Activated

carbon, etc)

Change oftreatment/ Odor

Supplyrestriction

Poor supply/Water

suspension

Power

failure

Pumpsuspension Pump suspension

Pump suspension/Colored water

Decrease ofpressure/Water

suspension

Fire

Pump

suspension

Pump suspension/Chemical feeding

suspension

/Chemical leak/Explosion

Pump suspension

Indoor

leakage

Damage

of

facilities

Intake orconveyancesuspension

Decrease offinished water

volume

Decrease ofpressure /Water

suspension/Decrease of

supply /Coloredwater

Decrease ofpressure/Water

suspension


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2) Preparation against accidents and disasters

Preparation of reference materials like specifications and drawings of facilities and

machines.

Preparation of emergency measures which is described about the procedures to cope with

the situation, the person in charge, the roles of person and so on.

3) A phone tree against an emergency

A phone tree against an emergency has to be prepared beforehand in order to take

measure corresponding to the situation.

The phone tree has to be put up on the place where everyone can see easily.

An example of phone tree is shown below.

4) Measures against an emergency

Grasp of the state of damage and accident.

Reporting to persons concerned on the state through a phone tree.

Securing water supply at the minimum.

Taking measures corresponding to the situation, for example suspending water supply.

Informing customers in supply area of the situation before suspending.


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( Note: shows the stream of reports and instructions )

Figure 21 An example of phone tree against an emergency

Director

Tel:020-///////

( Deputy director)

Tel:020-///////

HQs

WTPoperation

room

Tel: 020-///////

Supervisor

Tel:020-///////

Manager

Tel:020-///////

The headquarters

(Administrative section)

Tel:021-///////

Police department

Tel:020-///////

Fire department

Tel:020-///////

The others

Tel:020-///////

Government

administrative bodies

A: Tel:021-///////

B:Tel:021-///////

C:Tel:021-///////

Discoverer

WTP

Report

Discoverers

Discoverers

Report

Report

Documents

Water Treatment Plant OP&M