MANUAL ON
Water ater Treatme Treatment nt Plant Plant Operation & Maintenance
The Project for Capacity Development of Water Su l Authorities in Lao
The fi first ed edition
March 20 2006
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 water 1.2 General treatment process based on classification of raw water 1) Definition of water treatment 2) Processes for surface water 3) Processes for groundwater and spring water 1.3 The explanation of unit process operation 1) Flocculation and sedimentation process 2) Slow sand filtration 3) Rapid sand filtration 4) Disinfection 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 2) In case of rapid sand filtration 3) In case of disinfection only 2.2 The explanation of items in process operation 1) Turbidity 2) Color 3) pH 4) Alkalinity 5) Ammonia nitrogen 6) Residual chlorine 2.3 Examination methods 2.4 The operation criteria of water treatment plant 3 Chemicals for water treatment 3.1 Coagulant 1) Roles of coagulant (1) Neutralization of electric charge 2) Conditions on the coagulant effectiveness (1) Temperature 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)Characteristics 4) High molecular coagulant
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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 water 1.2 General treatment process based on classification of raw water 1) Definition of water treatment 2) Processes for surface water 3) Processes for groundwater and spring water 1.3 The explanation of unit process operation 1) Flocculation and sedimentation process 2) Slow sand filtration 3) Rapid sand filtration 4) Disinfection 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 2) In case of rapid sand filtration 3) In case of disinfection only 2.2 The explanation of items in process operation 1) Turbidity 2) Color 3) pH 4) Alkalinity 5) Ammonia nitrogen 6) Residual chlorine 2.3 Examination methods 2.4 The operation criteria of water treatment plant 3 Chemicals for water treatment 3.1 Coagulant 1) Roles of coagulant (1) Neutralization of electric charge 2) Conditions on the coagulant effectiveness (1) Temperature 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)Characteristics 4) 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 adjustment 1) Roles of the chemicals 2) Alkali chemical 3) Acid chemical 3.3 Oxidant, disinfectant 1) Roles of oxidant 2) Calculation for feeding 3) Roles of disinfectant 4) 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 facilities 4.1 Maintenance 5 Receiving well 5.1 Functions 5.2 Maintenance 5.3 Feeding equipments of oxidant 1) Pre-chlorination equipment (1) Setup of equipment (2) Feeding point (3) Feeding rate (4) Note 6 Flocculation (coagulation) and sedimentation process 6.1 Rapid mixing basin 1) Functions 2) Maintenance 6.2 Feeding equipment of coagulant (1) Setup of equipment (2) Dissolving procedure of solid aluminum sulfate (3) Feeding point (4) Feeding rate 6.3 Flocculation basin 1) Functions 2) Operation of baffling type flocculation basin 3) Maintenance 6.4 Sedimentation basin 1) 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 plates 3) Settled sludge 4) Maintenance 7 Filtration process 7.1 Slow sand filter basin 1) Functions 2) Structure 3) Sand scraping 4) Note on operation 5) Maintenance 7.2 rapid sand filter basin 1) Functions 2) Structure 3) 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 washing 4) Note on operation 5) Maintenance 6) Abnormal phenomenon, causes and measures 8 Disinfection process 8.1 Mixing basin 1) Functions 2) Maintenance 8.2 Post-chlorination equipment 1) Setup of equipment 2) Dissolving procedure of calcium hypochlorite 3) Feeding point 4) Feeding rate 9 Clear water reservoir 1) Functions 2) Maintenance 10 Machinery 1) Pumps (1) Observation of operation state (2) Maintenance (2-1) Pumps (2-2) Submerged motor pumps 2) Valves 3) Chemical feeding facilities and equipments
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11 Electrical facilities 1) Motors 2) The others 12 Notes of daily inspection works 13 Regular inspection excluding daily inspection work 14 Recording and reporting 1) Recording 2) Daily operation report 3) Daily inspection and maintenance report 4) Other records and reports to be prepared 15 Prior provisions for accidents and emergency states 1) Necessity and causes of accidents 2) Preparation against accidents and disasters 3) Phone tree against an emergency 4) Measures against an emergency
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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.! ! ! ! !
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.
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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.
1.1 Classification and characteristics of raw water 1) Surface water (river, pond and rake water)
㋪To be susceptible to outer p ollutions and temperature. ㋪To be easy to be a breeding grounds of living thing. ㋪To contain much dissolved oxygen. ㋪River water is directly and strongly affected by rain.
2) Groundwater (shallow and deep well water and undercurrent water) ㋪To be little change of water temperature through all seasons. ㋪To be economically cheap. ㋪ 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. ㋪In case of undercurrent water, the quality is generally good because of natural filtration. ㋪But it depends on the quality of river water, the thickness of permeability of stratum and so on. ㋪In the season of flooding, there are some cases that the quality is directly affected by the nastiness of the river. 3) Spring water ㋪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 ㋪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 ㋪In general, we have the flocculation, sedimentation plus rapid sand filtration process. We usually add chlorine into water before flocculation and after filtration. ㋪Intermediate-chlorination is also introduced to prevent the formation of disinfection by-products. ㋪In case of good quality of raw water, we have the slow sand filtration process and add chlorine after filtration.
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3) Processes for groundwater and spring water ㋪In general, we have the disinfection process only. ㋪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)
1.3 The explanation of unit process operation 1) Flocculation and sedimentation process ㋪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. ㋪ According to Stokes equation, the settling velocity becomes faster as the density and diameter of the particle become bigger. ㋪Especially the enlargement of diameter is very effective to promote the settling velocity.
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V: settling velocity, g : gravity acceleration, Уp : density of the particle У: density of water, d: diameter of particle, О: viscosity coefficient of water Mainly settling velocity is in proportion to d 2.
(Density Уp)
Water (DensityУ)
2) Slow sand filtration ㋪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. ㋪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. ㋪Coagulant for flocculation is not needed. A large area for filters, which means about ten several times to several ten times as much ㋪ area as that of rapid sand filter, is needed. ㋪Scraping off the sand of filter surface is needed every a certain period of time. ㋪Filtration is mainly due to the biological function. So chlorine obstructs this function. ㋪Standard filtration velocity is 2 to 10 day.
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.)
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This is the velocity of water passing thorough the filter vertically. This means the volume of water a day passing through 1m 2 sand area of filter ( a value which the volume of treated water a day divided by filter area ). Namely, Ч =Q/A(m/day) -------(1) Q: the volume of treated water a day (m3/day), A: sand area of filter ( m2 )
(m/day)
3) Rapid sand filtration ㋪Flocculation as a pre-treatment process is needed. ㋪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). ㋪This process is applicable to much higher turbidity on condition that there is flocculation and sedimentation process before this. ㋪Filtration velocity is 120 to 360m/day, but 120 to 150m/day is generally standard. ㋪The quality of rapidly filtrated water is generally less than that of slowly filtrated water. 4) Disinfection ㋪ After finishing processes mentioned above, we finally have to disinfect the water. ㋪In case of clean raw water like groundwater and spring water, we usually do not need flocculation, sedimentation and filtration. We can supply water treated by disinfection only.
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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 Observation items place or point Turbidity Color pH Alkalinity Others ♑ ♎ ♑ ♎ Raw water DO(☶) After sedimentation ------------♑ ♑ Filtrated water ------DO(☶),Note(1) ♑ ♎ ♑ Finished water ------R-Cⅲ(♑) ♑ ♑ ♎ Note1: Leaking living things, R-C ⅲ is free chlorine.
2) In case of rapid sand filtration Table 2 Observation items ( ♑: indispensable ♎: necessary ☶:desirable ) Observation Observation items place or point Turbidity Color pH Alkalinity Others Raw water Note2 ♑ ♎ ♑ ♎ After sedimentation -----------------R-Cⅲ(♑) ♑ Filtrated water ------R-Cⅲ(♑) ♑ ♎ ♑ Finished water ------R-Cⅲ(♑) ♑ ♑ ♎ Note2: Odor materials( ☶ ),Organic materials( ☶ ),Ammonia nitrogen( ☶ ), R-C ⅲ is free chlorine.
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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 ㋪Turbidity control is a fundamental work of water treatment process. ㋪Turbidity of raw water largely affects water treatment. So, turbidity is a main and critical indicator in controlling water treatment process. ㋪Turbidity spoils appearances of water and gives unpleasant feeling to consumers. ㋪Turbid materials sometimes wrap up bacteria. This prevents chlorine from reaching to those bacteria and weakens the effective of disinfection. ㋪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 ㋪The degree of yellowish or yellowish brown color by soluble and colloidal matters in water. ㋪This is due to humus, iron, manganese, copper, zinc and so on. ㋪Color spoils the quality of supplied water and is an index of humus (organic substances ) concentration. 3) pH ㋪ pH value of water is very important for flocculation (coagulation, to be exact) and disinfection in water treatment process ㋪Proper pH value is around 6 to 7 in flocculation coagulation, to be exact . ㋪If pH value of raw water largely run off this range, flocculation process will become difficult.
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㋪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 ㋪Coagulant makes flocks reacting to alkalinity in raw water. ㋪If the amount of alkalinity is poor, appropriate flocculation (coagulation) can not be done. ㋪More than 20mg/ ⅲof alkalinity in raw water is desirable. ㋪In case of poor alkalinity, we need add alkali chemical into raw water before flocculation. ㋪In case of excess, we add acids before flocculation. 5) Ammonia nitrogen ㋪ Ammonia nitrogen in raw water increases with the discharge of factory, sewage and human waste and so forth. ㋪ Ammonia nitrogen of 1mg/ⅲ consumes chlorine of around 10 mg/ⅲ. ㋪ You have to pay attention to pre-chlorination dosage since ammonia nitrogen concentration of raw water is changeable while raining. ㋪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 ㋪This value shows the effect of disinfection. ㋪It is necessary for the residual chlorine to be kept at the end of supply area. ㋪The minimum value of residual chlorine at the tap in s upply area is 0.1mg/ⅲ. 2.3 Examination methods See a manual of “Water quality examination ”. 2.4 The operation criteria of water treatment plant ㋪The general operation criteria, by which we can judge whether the operation is proper or not, is mentioned below. ㋪The case of flocculation, sedimentation plus filtration and disinfection(pre-disinfection and post-disinfection) is mentioned below as a standard type. ㋪In case of disinfection only, we judge the properness from finished water. ㋪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? ㋪Turbidity is 5 NTU or less? Exit of sedimentation basin ㋪If there is kicking up of flocks or not? (Supernatant) ㋪Residual chlorine is 0.5mg/ⅲ or more? Exit of filter basin ㋪Turbidity is 2 NTU or less? No color ? (filtrated water) ㋪Residual chlorine is around 0.5mg/ ⅲ? (Before disinfection) ㋪pH value is 6.5 to 8.5 or not? ㋪Turbidity is 2 NTU or less? No color ? Finished water (after disinfection) ℇ including the case of ㋪Residual chlorine is 0.8mg/ⅲ or more? disinfection only ㋪pH value is 6.5 to 8.5 or not? Tap water in supply area
㋪Turbidity is 2 NTU or less?
No color ? ㋪Residual chlorine is 0.1mg/ⅲ or more?
(Note: Residual chlorine means free chlorine)
3.1 Coagulant 1) Roles of coagulant (1)Neutralization of electric charge ㋪In general, suspended solids (colloidal particles) in turbid water carry a negative charge ! ! on the surface. ㋪So, they repel each other and are not easy to get together. The state of the water is called “stable”. ㋪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”. ㋪Coagulant in water brings about particles bearing positive electric charge. ㋪ And these particles neutralize the negative electric charge on the surface of suspended solids in turbid water. ㋪By neutralization of electric charge makes the suspended solids get together and makes them much larger. !
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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
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2) Conditions on the coagulant effectiveness (1)Temperature of water ㋪Coagulation is more effective at higher temperature of raw water. (2) H ㋪The H value of raw water should be kept in a certain range in order to make coagulant work well.
! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! Explanation of figure 10 ㋪This shows the relationship between alum(mg/ⅲ) required for 50% removal of materials
(kaolin and fulvic acid) in water and pH of the water. ㋪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. ㋪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. ㋪In any event, pH have a strong effect on coagulation process. (3)Alkalinity ㋪ 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) ㋪ As soon as feeding coagulant into raw water, coagulation instantaneously begins. ㋪Coagulant has to be mixed with water rapidly after feeding so that the chemical disperse rapidly and uniformly as much as possible in water. ㋪Coagulant must be fed continuously. (4-2)Slow mixing (for flocculation) ㋪ After reaction, relatively rapid mixing is needed to make larger flocks. ㋪ 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 ㋪Solid type aluminum oxide 15% or more and liquid type (aluminum oxide around 8%) ㋪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. ㋪Weak points are, Ⓓto make light flocks. Ⓔto be narrow range of pH for coagulation. ㋪The most suitable range of pH for coagulation is around 6 to 7. ㋪ This coagulant reacts to alkalinity in water and makes sodium sulfate(Na 2SO4), aluminum hydroxide(Al(OH)3) and carbon dioxide(CO2). ㋪Sodium sulfate dissolves into water, aluminum hydroxide settles out. ㋪Because of carbon dioxide, we can see bubbles in a flocculation basin.
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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. ㋪Solid aluminum sulfate is usually used in a solution with concentration of 3 to 30%
(weight volume). ㋪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=(QØ RsØ 100Ø 10⁼ 3) C ----------- (2) ! ! Vv feeding chemical volume (ⅲ/h)わQ treated water volume(m3/h), Rs aluminum sulfate feeding rate(mg/ⅲ) ! ! C solution concentration of solid aluminum sulfate(weight/volume%) ! = weight of solid aluminum sulfate(kg) (water volume(m3)Ø 1000) (Example 1) 1)Dissolution tank volume is 200ⅲわsolution concentration is 10%. Calculate the weight of solid aluminum sulfate needed. Since 0.1=W (0.2Ø 1000) ≹ W=20kg 2)Treated volume of water is 8,000m3/day(333m3/h), feeding rate is 20mg/ ⅲ. Calculate feeding volume of solution of aluminum sulfate. ≹ Vv=(333Ø 20Ø 100Ø 10⁼ 3) 10=66.6(ⅲ/h) In general, since solution concentration of solid aluminum is almost same in daily operation, feeding volume is expressed as blow. Vv=KaØ QØ R(ⅲ/h)---------(3) Q: m3/h, R: mg/ⅲ Ka: 1/(CØ 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.(ⅲ/h) according to treated water volume(m3/h),feeding rate(mg/ ⅲ) 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 ㋪High molecular liquid type coagulant (aluminum oxide around 10%). ㋪To be used in undiluted solution. ㋪The most suitable range of pH for coagulation is around 6 to 9. ㋪ A lowering of alkalinity of water is small. ㋪ A lowering of coagulability is hardly seen at lower temperature (less than 10±C) and alkalinity(less than 20mg/ⅲ). ㋪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 ㋪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.
㋪Types of high molecular coagulant is shown below.
Table 5 Types of high molecular coagulant Main suitable! Ion type Effects of treatment suspension Anionic type
Inorganic and organic colloidal suspension
Flocculation & sedimentation, Dehydration
Nonionic type Cationic type Organic colloidal suspension
Dehydration
Amphoteric type
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Characteristics Largely effective to flocculation & sedimentation Effective to acid waste water Effective to dehydration of sludge by machine Effective to sludge of difficult to dehydrate
㋪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 ㋪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. ㋪This coagulant gathers flocks by bridging. It looks like strings which entwine flocks together.
! ! ! ! ! ! ! ! ! ! ㋪The larger the molecular amount is, the stronger the capacity of flo cculation becomes. ㋪ The pH of water is not affected by adding polymer so much unlike an inorganic
coagulant. (3) Concentration of polymer solution ㋪It is very important for polymer to uniformly mix with colloidal particles in water. ㋪Dilution over a certain limit is needed for that. ㋪The lower concentration of solution is more effective because of the easiness of mixing in flocculation process. ㋪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 m 3 volume of water. (4) Feeding rate ㋪ Feeding rate is decided by jar testing. See details in a manual “Water quality examination”. (5) Feeding volume of polymer solution (ⅲ/h)! ---------(2)! Vv Feeding volume of polymer(ⅲ/h) ㋪ Vv = Q Ø RØ 10 Q Treated water volume(m3/h) R Feeding rate of polymer(mg/ⅲ)(By jar-testing)
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(Example 2 Feeding rate is decided to 0.05mg/ ⅲ,Q=3,000m3/h Feeding volume of polymer? ≹ Vv = 3000Ø 0.05/1000 = 0.15( ⅲ/h) (6) Note on dissolving and using ㋪Water not contained impurities should be prepared to dissolve polymer. ㋪Not to inhale the dust of polymer while dissolving. ㋪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. ㋪Make a distance between a solution tank and feeding point as short as possible. ㋪Use the solution up as soon as possible because the solution is easy to degrade and the flocculation capacity deteriorates. ㋪The practical shelf life of anion polymer solution is around 7days. ㋪Over-feeding of polymer brings about reverse effects. ㋪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 ㋪For adjusting pH of water into the most suitable range for coagulation, anti-corrosion.. ㋪In case of running off the most suitable pH range for coagulation, alkali chemical or acid chemical is needed to adjust pH of water. ㋪In case of lowering of pH after treatment (around less than 6), alkali chemical is needed to prevent corrosion of pipes. 2) Alkali chemical ㋪To be used to increase pH of raw and finished water. ㋪The reasons of pH lowering are due to high turbidity, much usage of coagulant, mixing of waste water from factories and so on. ㋪Calcium hydroxide(Ca(OH)2) and sodium hydroxide(NaOH) are used as alkali chemical. ㋪ Alkali chemical is injected at the upstream of coagulant feeding point to raise pH of raw water( called pre-alkali). Fully agitation is needed. ㋪To raise pH of finished water, alkali is injected between sedimentation basin and finished water reservoir(called post-alkali). 3) Acid chemical ㋪To be used to decrease pH of raw and finished water. ㋪The reasons of pH uprising are due to assimilation of carbonic-acid gas by algae, mixing of waste water from factories and so on. ㋪Sulfuric acid(H2SO4) and hydrochloric acid(HCⅲ) are used as acid chemical. ㋪ Acid chemical is injected into raw water after measuring pH of raw water. 20
3.3 Oxidant, disinfectant 1) Roles of oxidant ㋪ To oxidize organic matter, iron, manganese, ammonia nitrogen, organic nitrogenous compounds and so on in water. ㋪The water that contains a lot of these matters consumes oxidant much more. ㋪In general, chlorine chemical is used as pre-chlorine which is injected to raw water and as intermediate- chlorine which is injected to the water after sedimentation. ㋪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. ㋪Oxidation effect of chlorine highly drops under the existence of turbidity. ㋪ Intermediate-chlorination is used to reduce disinfection by-products instead of pre-chlorination. ㋪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. ㋪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 ㋪ same time considering both merits.
This is a substance made by chlorine which is injected as oxidant or disinfectant reacts to organic matters in the water. The most popular one is THMs. On of them, chloroform, is recognized to be carcinogenic.
1mg of iron consumes 0.63mg of chlorine 1mg of manganese consumes 1.29mg of chlorine 1 mg of ammonia nitrogen consumes 7.6mg of chlorine The more water contained ammonia nitrogen, the more it consumes chlorine. 2) Calculation for feeding Chlorine weight fed into treated water. R=WØ 1000 Q -------- (3) R chlorine feeding rate(mg/ⅲ)わ 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 8,000m 3/day. Calculate the feeding rate of chlorine. ≹ R=4Ø 1000 8000=0.5 (mg/ⅲ) ! ! (Note This chlorine weight is the pure chlorine.) Inversely, W=RØ Q 1000 (kg/day) 21
3) Roles of disinfectant ㋪Disinfectant is injected to the water after filtration and the clear water like groundwater as the final process. ㋪In general, chlorine is used as post-chlorination after filtration. ㋪Post-chlorination feeding absolutely must not be stopped while processing the water to be supplied. ㋪Continuous feeding without any intermittent is indispensable to ensure safe supply water. 4) Chlorine chemical ㋪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. ㋪There are liquid chlorine, sodium hypochlorite(liquid),calcium hypochlorite(solid) and so forth as chlorine chemicals. (1) Sodium hypochlorite (NaOCl) ㋪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.). ㋪This chemical is corrosive and has strong alkalinity. ㋪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. ㋪This chemical is unstable and decomposes giving off the oxygen in normal temperature. ㋪ This reaction is facilitated by sunlight, ultraviolet rays, heavy metals, temperature raising and lowering of pH. ㋪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) ㋪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.). ㋪It slightly smells like chlorine and is readily soluble in water. ㋪It has good stability and is durable to keep for long time. ㋪To be used dissolving in water. In case of high concentration, be careful of scaling in pipes and lowering of effective chlorine. ㋪ To be kept in sealed up in a dry, cool and dark place keeping away from water, combustibles and explosive materials. ㋪In case of fire, the chemical gives off chlorine gas with decomposition. ㋪To be injected with solution of effective chlorine concentration 1 to 6 %. ㋪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. 22
㋪Make sure to put on glasses, a mask and outer wear to keep the dust away from while a
solution working.
(3) Calculation for feeding and dissolving chemicals ! Vv=(QØ RØ 100Ø 10 3) CØ ------------ (4) ! Vv feeding amount (ⅲ/h)わQ treated water volume(m3/h), R chlorine feeding rate(mg/ⅲ) わC effective concentration of chlorine(%) d density of solution with C%(kg/ⅲ) (Example 4) Treated water volume 8,000m3/day(333m3/h), chlorine feeding rate 0.5mg/ⅲ Effective concentration of chlorine 10%, Density 1.2 Calculate the feeding volume of chlorine solution. ≹ Vv=(333Ø 0.5Ø 100Ø 10 3) (10Ø 1.2)=1.39 (ⅲ/h) This means in case of feeding rate 0.5mg/ⅲ, around 139litters/hour of sodium hypochlorite is fed into the water.
Vv=(QØ RØ 100Ø 10 3) CØ d ------------- (5) Vv feeding chemical volume(ⅲ/h)わQ treated water volume(m3/h), R chlorine feeding rate(mg/ⅲ), C effective concentration of chlorine(%) (C=(weight(kg)Ø effective chlorine concentration in solid(%) water weight(kg)) d density of solution with C%(kg/ⅲ)
23
(Example 5) Tank volume is 190ⅲ. 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=WØ 0.7 190 ≹ W=(190Ø 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 5,000m3 to 0.5mg/ⅲ. Total chlorine weight needed to this water is, 5000Ø 1000Ø 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/ ⅲ in the water, we need 2,500/50=50 ⅲ of the solution. 1mg/ⅲ= 0.001g/ⅲ = 1g/m3 1% = 1g/100g = 10g/1kg = 10kg/1,000kg = 10,000mg/ ⅲ= 10g/ⅲ(in case of water) (Example 7) Treated water volume 8,000m3/day(333m3/h), chlorine feeding rate 0.5mg/ ⅲ , 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=WØ 0.7/1000 ≹ W=71.4kg 3 From Vv=(333Ø 0.5Ø 100Ø 10 ) (5Ø 1.01) ≹ Vv=3.3(ⅲ/h) In general, since effective chlorine concentration of solution is almost same in daily operation, feeding rate is expressed as below. Vv=KcØ QØ R (ⅲ/h)--------- (6) Q m3/h , R mg/ⅲ Kc 1/ 10Ø effective chlorine concentration of solutionØ density (= const.) A graph or tables between Q and R will be convenient for daily operation.
%
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( ⅲ/h) according to treated water volume(m 3/h), feeding rate(mg/ⅲ) at fixed effective chlorine concentration are listed in the reference part.
24
(4) Factors affecting on the disinfection effect of chlorine. ㋪The lower pH of water becomes, the larger the disinfection effect is. ㋪ Namely disinfection effect falls as an increase of pH value (See textbook “Water Purification “ p102 ). ㋪The higher temperature of water is, the larger the disinfection effect is. ㋪It is very important to mix chlorine with water and make it diffuse rapidly and uniformly for disinfection effect. (5) Weight of chemicals needed to make solution. ㋪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). ㋪If there is no suitable conditions, calculate the weight using adjacent value conditions. For example, ⒹIn case of Calcium Hypochlorite, concentration 3%, tank volume 3.3m 3 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 Ø 3 = 141.6kg ⒺIn case of Solid Aluminum Sulfate, W= concentrationØ water volumeØ 10,
In case that concentration is 12% and tank volume is 5.5m 3, then ≹ W=12Ø 5.5Ø 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%, 3m 3 and effective concentration of chlorine is 65%, the weight of calcium hypochlorite is 231kg ,then ≹ W=231Ø (65/60)=250.3kg (in 60% effective concentration of chlorine)
25
26
27
4.1Maintenance Table 9 Daily routine inspection cycle and items Cycle Items River state (Oil, Dead fish, Water level, A pile of earth Twice a daytime and sand around an intake point) River Once / 2hours Pump state (Current, Voltage, Pressure) Twice a daytime Well surrounding areas Once / 2hours Well pump state (Current, Voltage, Pressure) Wells Twice a daytime Well water level Twice a daytime Raw water quality(*) (Note(*): by water quality examination)
5.1 Functions ㋪To stabilize fluctuations of flow rate and water level of raw water flowing in. ㋪To measure and adjust the volume of raw water to carry out a series of treatment process correctly and easily. ㋪To be also used as a point of feeding of coagulant and chlorine. ㋪In case of effective use of law water’s 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 Twice a daytime
Items
Inflow states of raw water, water level
Once / 2 hours
Raw water quality(*) 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 ㋪It consists of solution tanks, mixers, feeding pumps, measuring devices, feeding pipelines and so on. ㋪They have many cases that the feeding is done by gravity from solution tanks in Lao. ㋪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 ㋪Feeding point is usually at receiving well. (3) Feeding rate ㋪To be decided based on the water quality of raw water, for example ammonia nitrogen, 28
iron, manganese and so on. ㋪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/ⅲof residual chlorine in filtrated water. (4) Note ㋪Since the decomposition of chlorine is facilitated by sunlight in fine weather, consider the differences of chlorine consumption in flocculation and sedimentation basin due to weather change.
6. Rapid mixing basin 1) Functions ㋪ A facilities for diffusing coagulant in water rapidly and uniformly. ㋪ As soon as coagulant is fed in this basin, rapid mixing is promptly needed so that coagulation disperses all over the basin. ㋪The time needed to diffuse and mix coagulant should be as short as possible. ㋪In case of baffling or weir typed mixing basin, mixing intensity depends on the volume of treated water. ㋪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 Inflow states of raw water Twice a daytime Mixing state Suspended dust and trash Once / 2 hours Coagulant feeding Once a daytime Leakage from outer surface of the basin 6.2 Feeding equipment of coagulant 1) Aluminum sulfate feeding equipment (1)Setup of equipment ㋪It consists of solution tanks, mixers, transferring pumps, feeding pumps, measuring devices, feeding pipelines. ㋪They have many cases that the feeding is done by gravity from solution tanks in Lao like chlorine feeding equipment. ㋪The solution tanks of aluminum sulfate must not be installed close to the tank of chlorine. (2) Dissolving procedure of solid aluminum sulfate. ㋪ An example of Chinaimo WTP is shown below. 29
! ! ! ! ! ! ! ! !
(3)Feeding point ㋪The chemical is fed at rapid mixing basin. It is very important to inject to the center of mixing. (4)Feeding rate ㋪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.
㋪See a manual “ Water quality examination”.
6.3 Flocculation basin 1) Functions ㋪By properly mixing, to get together fine coagulated flocks to make larger ones which are easy to precipitate. ㋪ 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. 30
! Take notice that the space of baffling wall gets wider as water f lows down.
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.)
31
2) Operation of baffling type flocculation basin ㋪Mixing intensity is in proportion to the power of 3 of velocity (P≢ Ч3). This means mixing intensity largely changes compared with the change of flow rate. ㋪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 Items Flocks growing Twice a daytime Suspended dust and trash Mixing state 6.4 Sedimentation basin 1)Functions ㋪ A basin that separates almost all the flocks, which are formed and grown up in flocculation basin, out of water by gravitational settling action. ㋪In this basin, organics, bacteria and organism can be also removed as well as particles of clay because the flocks has strong adsorption ability. ㋪The efficiency of sedimentation basin is defined as below. E=Ч0Ø A Q --------- (7) Ч0 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.
!
32
The index means a period of time which is needed for the water to pass through the sedimentation basin from entrance to exit. t=24Ø V Q ------- (8) t: detention time(h), Q: treated water volume(m3/day) V: volume of sedimentation basin(=LØ WØ D)(m3), L: length(m), W: width(m), D: depth(m)! of a sedimentation basin (Example 8) Treated water volume per basin 4,000m 3/day, depth 2.5m, width 5m, length 20m, Calculate detention time t. ≹ t = 24Ø (2.5Ø 5Ø 20)/4000=1.5(h)
The index means the effect of flock removal in sedimentation basins. u= Q A = QØ 1000 (LØ WØ 1440) -------- (9) u overflow rate(mm/min) Q treated water volume(m3/day), A plan area of a basin(=L Ø W) (Note: 1440= 24(h)Ø 60(min)) (Example 9) Treated water volume per basin 4,000m3/day, width 5m, length 20m, Calculate overflow rate. ≹ u=4000Ø 1000/(20Ø 5Ø 1440)=27.8(mm/min)
The index means the velocity of the stream of water in the basin. Ч= Q 24Ø 60Ø WØ D --------- (10) Ч 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. ≹ Ч= 4000/(24Ø 60Ø 5Ø 2.5)= 0.22(m/min) 2) Types, etc (1) Horizontal-flow basin (without flocculation) ㋪Suspended solids can be settled by flowing water slowly. This is the most basic one. ㋪Standard value of overflow rate is 5 to 10 mm/min. ㋪Standard value of mean velocity in a basin is 0.3m/min or les s. (2) Horizontal-flow basin (with flocculation) ㋪The same as mentioned above. ㋪Standard value of overflow rate is 15 to 30 mm/min. ㋪Standard value of mean velocity in a basin is 0.4 m/min or less.
(3) Horizontal-flow basin with inclined parallel plates ㋪Many inclined parallel plates are installed in the horizontal-flow basin to make the plan area larger for the improvement of settling efficiency. 33
㋪Standard value of overflow rate is 4 to 9 mm/min. ㋪Standard value of mean velocity in a basin is 0.6 m/min or less.
H
! ! ! ! Namely, settling time decreases to and the efficiency becomes H/h (>1). Note: Water flows perpendicularly to this figure.
! ! ! ! ! !
3) Settled sludge ㋪The more settled sludge is piled up in the bottom, the harder the sludge gets because of
compaction. ! ㋪That makes a cross section of basin narrower and velocity faster in the basin. ! ㋪In the end, that becomes to an obstacle to sedimentation of flocks. ㋪Settled sludge should be drained earlier. 4) Maintenance Table 13 Daily routine inspection items and cycle Cycle Items Flow states, sedimentations states of flocks States of inclined parallel plates Quality of settled water(*) Suspended dust and trash Collecting apparatus Once a daytime Leakage from outer surface of the basin Once a week Measurement of settled sludge amount (Note * : by water quality examination) Twice a daytime
34
7.1 Slow sand filter basin 1) Functions ㋪Generally, the facilities which treat relatively less turbid water and dose not need pretreatment process like flocculation, sedimentation and so on. ㋪There are some cases that have pre-filter basins which roughly f iltrate water. ! ㋪They are installed before slow sand filters to remove planktons, algae, turbidity and to reduce burden of slow sand filters. ㋪Standard value of filtration velocity is 2 to 10 m/day. ㋪This type of filter basin can remove turbidity and bacteria as well as an ordinary rapid sand filter basin. ㋪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. ㋪Filtration velocity Ч= Q A (m/day)-------(11) Q: treated water volume a filter basin (m 3/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 300m 2, Calculate filtration velocity. Q = 6000/4 = 1500m3/day ≹ Ч= 1500/300 = 5m/day 2) Structure ㋪This type of filter basin has the same structure as that of a rapid sand filter without washing equipments. ㋪It consists of under drain system, support gravel layer and sand filter layer from bottom to upward. ㋪Treated water flows down through sand and gravel layers to under drain system.
35
3) Sand scraping ㋪Slow sand filters do not need the washing operation like rapid sand filters because filtration of this filter is done by biotic filter membrane. ㋪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.
( 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 layer
decreases 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 operation ㋪The water depth above sand surface should be kept to be 0.9 to 1.2m. ㋪If possible, slow sand filters should be operated on fixed flow rate. The flow rate must not be changed so often according to demand. ㋪It takes much time to show the real capacity of filtration because the function is due to biological action. ㋪Immediately after scraping off or replenishing sand, observation of filtrated water quality is especially needed. 36
㋪The partial use of the slow sand filter surface is not desirable. ㋪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 Water level of filter basin Twice a daytime Inflow state of water Quality of filtrated water(*) Breeding algae and living things Once a daytime Surface state of sand Leakage from outer surface of the basin (Note (*): by water quality examination) 7.2 Rapid sand filter basin 1) Functions ㋪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. ㋪Standard value of filtration velocity for normal types is 120 to 150 m/day. ㋪Rapid sand filters is suitable for large volume of treated water. ㋪Substances which can be removed by rapid sand filters are limited because the function
of filter is based on physical actions. ! ㋪Turbidity is easy to be removed but ammonia, taste, odor and so on can not be removed at
all. ㋪Disinfection after filtration is indispensable. ㋪Iron and manganese can be removed on the surface of sand through contact oxidation by
residual chlorine in water. 2) Structure ㋪To be the same as that of slow sand filter ㋪While filtrating, treated water flows through sand layer down to under drain system. ㋪While backwashing, washing water flows through bottom to upward and into washing
trough. 3) Washing of filter (1)Washing of rapid sand filters ㋪ A certain time of use makes the function of rapid sand filter lower because turbid
substance is clogged in sand layer. ㋪The filters are needed to be washed to recover the function and to keep sand clean. ㋪In case of resuming filtration after suspension for a certain period of time, washing
should be needed to wash away flocks on filter layer. ㋪Normally finished water contained residual chlorine is used for washing.
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(2)Washing operation ㋪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. ㋪ A combination of backwashing and surface washing is standard. ㋪In addition to this, a combination of backwashing and air-blowing instead of surface
washing is also used. ㋪ Air-blowing is used to disturb and to inflate sand layer by air from the bottom.
(3)Washing criteria ㋪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 ㋪The more the filter layer gets clogged while filtrating, the lower water pressure of
discharge becomes. ㋪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).
! !
! ! ! ! ! ! ! !
! ! ! ! ! ! ! ! ! ! ! ! !
(Explanation of Figure 18) ㋪The head loss means the difference of water level between A and B shown above. ㋪It is due to the loss of filter media. ㋪The larger the loss of filter media becomes, the bigger the difference of water level does. ㋪The loss increase of filter media is caused by clogging of flocks, namely dirt.
(3-2)Duration time ㋪This means operation period of time that is thought not to give bad effect to filtrated
water empirically. 38
㋪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 ㋪Flocks spreads on the surface of filter like a mat. Surface washing is done to break this
mat. ㋪Pressurized water from the equipment installed above the surface of s and breaks the mat
of flocks. (3-4) Backwashing ㋪Pressurized water from the bottom of filter flows through sand layer, inflates it and
washes away turbid matters clogged in sand. ㋪In general, inflating sand layer by 20 to 30% is needed. This pressurized water is
provided from an elevated tank or back washing pumps.
! ! ! !
(3-5) Air-blowing, air washing ㋪ Air from a blower is used instead of washing water. ㋪This is used with back washing, in this case, surface washing is usually not used. ㋪In case of back washing with air-blowing at same time, there is a possibility of outflow of
sand. ㋪It is important for the air to be dispersed over the whole surface of filter.
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(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(1.0m 3/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 leve l. Ⓔ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) 40
ⒹTo lower the level of water to around 30 to 40 cm below the normal water leve l. Ⓔ 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.
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This means the amount of washing water per minute to be given to sand surface area of 1m2 while backwashing. Ч= Q A (m/min) --------- (12)
Q is the volume of backwashing water, A is sand surface area, Ч= (m3/min) (m2) = m / min
This has dimension of velocity.
(3-6) The volume of washing water ㋪This means the water volume needed to wash a filter basin while backwashing.
Q = ЧØ A Ø t (m3/basin) ------------ (13) Q is the volume of washing water(m3/basin), Чis backwashing velocity (m/min) A is surface area of sand, t is back washing time (min) (Example 12) Ч=0.6(m/min), A=30m2, t=10min, Calculate the volume of washing water. ≹ Q = 0.6Ø 30Ø 10 = 180m3/basin
4) Note on operation ㋪The water depth above sand surface should be kept to be 1 to 1.5m. ㋪Filtration velocity must not be changed suddenly. ㋪Coagulant always must be fed at pre-treatment process.
5) Maintenance Table 15 Daily routine inspection items and cycle 42
Cycle
Items Water level of filter basin Inflow state of water
Twice a daytime
Quality of filtrated water(*) Once a daytime
Surface 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 Becoming clouded of inflow water
Excessive feeding of coagulant. Unsuitable pH for flocculation.
Leak of turbidity, color and microorganism
Poor feeding of coagulant and chlorine. Poor washing. Blockade of filter by algae. Poor washing. Sudden change of pH (Note: pH greatly affects flocculation).
Abnormal head loss
Abnormal partial spouting of sand while washing Outflow of sand Cave-in of sand surface Mud balls in sand filter
Countermeasures Proper feeding of coagulant. Lowering of filtration velocity or Reducing volume of treated water. Increasing of coagulant and chlorine injection. Improving of washing. Shortening of washing interval. Improving of washing, Introducing of pH control.
Inuniformity of gravel layers.
Renewal of filter media.
Excessive washing velocity. Excessive volume of air for washing. Abnormal state of under drain system.
Adjustment of volume of washing water and air. Stop using them at the same time. Checking of under drain system. Reconsideration of washing conditions. Maintenance of filter.
Poor washing.
8.1 Mixing basin (for post-chlorination) 1) Functions ㋪ A basin with buffering walls inside so that chlorine for disinfection is well mixed with water. ㋪Not always be installed because chlorine is mixed in a finished water reservoir or a water main. 43
2) Maintenance Table 17 Daily routine inspection cycle and items Cycle Items Once / 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 ㋪It consists of solution tanks or storage tanks, mixers, feeding pumps, measuring devices
and pipes. ㋪ The solution tanks of chlorine chemical must not be installed close to the tank of coagulant. 2) Dissolving procedure of calcium hypochlorite ㋪ An example of Chinaimo WTP is shown below.
3) Feeding point ㋪To be injected at the entrance of mixing basin so as to be well mixed with treated water.
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4) Feeding rate ㋪Post-chlorination is done for disinfection of treated water. ㋪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. ㋪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. ㋪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. ㋪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/ⅲ,which is a standard value. And that of filtrated water is 0.5mg/ⅲ,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/ ⅲ is needed.!
1) Functions ㋪ Alleviation and regulation of the difference between the volume of treated water and
supply water . ㋪ Storage function of finished water preparing for some accidents, troubles and
maintenance of facilities. ㋪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 Exterior and surrounding state of reservoir わstate of Once a daytime ventilators Twice a daytime Quality of finished water(*) (Note (*): by water quality examination) ㋪ After newly constructing or repairing a clear water reservoir, it was washed and filled
with finished water with concentration of 10mg/ ⅲchlorine and left for 2 to 4 hours. (According to AWWA manual, For 6 hours left filling with water with 50mg/ⅲ. ) ㋪Hereafter, washing and this disinfection process is repeated several times.
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㋪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) Pumps (1)Observation of operation state ㋪It is very important to observe the operation states of pumps and motors from the point
of view of confirmation of pump capacity. ㋪The delivery amount, the relationship of suction pressure and delivery pressure, electric
current value, abnormal vibration or wobbling and so on should be confirmed. ㋪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. ㋪In case of plural pumps, running time a pump should be grasped in order to average the
accumulated running time of each. ! ㋪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 Appearance, abnormal vibration, unusual sounds, Pumps
Twice a daytime
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 The part which can be observed by eyes
Items
Appearance, abnormal vibration, unusual sounds, 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 Table 21 Daily routine inspection cycle and items Machinery Cycle The part which can be observed by eyes
Twice a daytime
Items
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 Solution and
Twice
storage tanks
a daytime
Feeding pumps Measuring devices Pipes and valves
Items
State of solution and mixing, storage amount
Twice
Appearance, abnormal vibration, unusual sounds,
a daytime
leak, pressure, temperature
Once / 2 hours Twice a daytime
Adhesion and stuffing of deposition at measuring point! (in case of weir) Adhesion and stuffing of deposition inside, leak
㋪In case of measuring feeding rate by triangular weir, adhesion of deposition prevents
accurate measuring. Removing the substance is needed soon.
! ! ! ! ! ! !
!
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㋪To confirm feeding volume of chemical, you should check actual feeding volume per min( ⅲ
/min) at feeding point. In case that feeding volume is set up at 66.6( ⅲ/h), if feeding volume per minute(ⅲ/min) is around 1ⅲ, feeding condition will be practically no problem. !
1) Motors (1) Table 23! Daily routine inspection cycle and items on motors Facilities Cycle Items Appearance, abnormal vibration, unusual sounds, Motors & Control
Twice
oil pressure, temperature at bearings, damage, nasty
devices
a daytime
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 Appearance, abnormal vibration, unusual sounds, C/C board etc
Twice a daytime
nasty smells, indoor temperature of board and room, smoke, indicator lamps, electric current and voltage value
㋪Use your “ Five senses” for the inspection at first. ㋪The daily routine inspection route for the facilities and equipments should be decided
beforehand. ㋪It is desirable to take simple tools on a inspection tour. ㋪The results of inspection should be recorded on a daily inspection report form. ㋪In case of any abnormality, record and report it to the person in charge of the plant.
㋪Regular inspection works based on a weekly, monthly and yearly plan are desirable and
important. ㋪See instruction manuals about detailed items to be inspected (Attached in Reference
Part).
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Recording ㋪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 The volume of raw water, filtrated water and supply water. Once/ 2 hours
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 daytime
Water 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 ㋪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. ! ㋪Several kinds of report form are attached in the reference part of this manual. ㋪The report should be signed by the person in charge and submitted to a administrator for
approval every day. ㋪The reports should be kept for a certain period of time. ) Daily inspection and maintenance report ㋪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.! ㋪The report should be signed by the person in charge and submitted to a administrator for
approval every day. ㋪The reports should be kept for a certain period of time. ) Other records and reports to be prepared ㋪ 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. ㋪Completion documents, testing reports and instruction manuals of machinery.
1) Necessity and causes of accidents ㋪In accidents and disasters, a rapid and large change of treated water amount and quality
will consequently happen.! ㋪Prior provisions have to be prepared beforehand to properly cope with accidents and
disasters and to ensure the safety operation. 49
㋪In water treatment plant, natural and human causes could be thought as the causes of
accidents and disasters. ! ㋪The sorts of accidents and disasters and the consequences are shown below.
Table 26
Anticipated influences that accidents and disasters affect
Intake restriction Scouring, /Inflow of driftwoods, earth and sand /Clogging of screen/Damag e of pipes and conduits Damage of pipelines, conduits and buildings /Leakage
Intake suspension /Chemical use (Activated carbon, etc) Pump suspension
Pump suspension
Intake or conveyance suspension
Increase of turbidity
Fluctuation of supply volume(decrease of pressure, etc) /Colored water
Poor supply /Water suspension
Increase of turbidity /Inflow of foul water into pipes and conduits
Inflow of foul water into basins and manholes /Damage of pipeline by mud slides and cave-ins
Damage of service installations by mud slides and cave-ins
Damage of basins, tanks, pipes and conduits, /Secession of pipes /Leakage/ Outflow of filter sand /Chemical leak
Damage of pipelines and appurtenants /Leakage
Damage of service installations /Leakage
Change of treatment/ Odor
Supply restriction
Poor supply /Water suspension
Pump suspension /Colored water
Decrease of pressure /Water suspension
Pump suspension
Pump suspension /Chemical feeding suspension Pump suspension /Chemical leak /Explosion
Decrease of finished water volume
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Decrease of pressure /Water suspension /Decrease of supply /Colored water
Indoor leakage
Decrease of pressure /Water suspension
2) Preparation against accidents and disasters ㋪ Preparation of reference materials like specifications and drawings of facilities and
machines. ㋪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 ㋪ A phone tree against an emergency has to be prepared beforehand in order to take
measure corresponding to the situation. ㋪The phone tree has to be put up on the place where everyone can see easily. ㋪ An example of phone tree is shown below.
4) Measures against an emergency ㋪Grasp of the state of damage and accident. ㋪Reporting to persons concerned on the state through a phone tree. ㋪Securing water supply at the minimum. ㋪Taking measures corresponding to the situation, for example suspending water supply. ㋪Informing customers in supply area of the situation before suspending.
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