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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 ?
Residual chlorine is 0.8mg/or more?
pH value is 6.5 to 8.5 or not?
Tap water in supply area Turbidity is 2 NTU or less? No color ?
Residual chlorine is 0.1mg/or more?
(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
Table 11 Daily routine inspection items and cycle
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 overflow rate is 15 to 30 mm/min.
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 overflow rate is 4 to 9 mm/min.
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
Table 13 Daily routine inspection items and cycle
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
Table 15 Daily routine inspection items and cycle
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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
(Note (*): by water quality examination)
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
Table 17 Daily routine inspection cycle and items
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(*)
(Note (*): by water quality examination)
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
Table 20 Daily routine inspection items and cycle
Machinery Cycle Items
The part which
can be observedby eyes
Twice
a daytime
Appearance, abnormal vibration, unusual sounds,
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
Table 21 Daily routine inspection cycle and items
Machinery Cycle Items
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
Table 22 Daily routine inspection cycle and items
Facilities Cycle Items
Solution and
storage tanks
Twice
a daytimeState of solution and mixing, storage amount
Feeding pumpsTwice
a daytime
Appearance, abnormal vibration, unusual sounds,
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
Facilities Cycle Items
Motors & Control
devices
Twice
a daytime
Appearance, abnormal vibration, unusual sounds,
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
Facilities Cycle Items
C/C board etcTwice
a daytime
Appearance, abnormal vibration, unusual sounds,
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
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