Water treatment

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TYPES OF SEDIMENTATION TANKS1. Quiescent or fill and draw type: Rectangular in plan. Water is filled, allowed for retention period of 30 to 60 hrs (normally

24 hrs) then clear water is drawn from outlet Empty the tank and cleaning of sediment is done. Needs more detention period, labours and supervision, More than one tanks Not used nowadays.

2. Continuous type:A. Horizontal Flow Type

(a) Rectangular tanks with longitudinal flow

(b) Circular with radial flowi. Circular with central feed ii. Circular with peripheral feed

B. Vertical Flow Type

Surface loading or surface overflow rate (SOR) of sedimentationtank:

PROCESS OF SEDIMENTATION WITH COAGULATION

1. Feeding the coagulantDry feedingWet Fedding

2. Mixing of coagulanta. Mixing basin with baffle wallsb. Mixing basin with mechanical meansc. Mixing channelsd. Hydraulic jump methode. Compressed air methodf. Centrifugal pumping method

3. Flocculation4. Sedimentation

a. Mixing basin with baffle wallsi. Horizontal or round end type:

ii. Vertical or over and under type

b. Mixing basin with mechanical means

3. Flocculation

4. Sedimentation

FILTER AND THEIR CLASSIFICATION

1. Slow sand filter (SSF)

a. Enclosure tank: depth = 2.5 – 3.5 m surface area = 10 – 2000 m2

filtration rate = 100 – 200 lph/m2

cross slope = 1 in 100 – 1 in 200 towards central drainb. Filter media:• sand layer = 90 – 110 cm thick• effective size (D10) = 0.25 – 0.35 mm (0.3 mm is common)• coefficient of uniformity (Cu) = 3 – 5.c. Base material:• 30 to 75 cm thick gravel• four layers of each about 15 cm• 3 – 6 mm, 6 – 20 mm, 20 – 40 mm and 40 – 65 mm from the

tope. Appurtenances: vertical air pipes, depth controlling

devices,head loss measuring device, rate maintaining devicesetc

d. Under drainage system:

Efficiency of SSF: 98 – 99% bacteria removal removes turbidity up to 50 ppm Only 20 – 25 % of color removal not so efficient in removal of colloidal matters

2. Rapid sand filter (RSF)

a. Enclosure tank: depth = 2.5 – 3.5 m surface area = 10 – 50 m2

filtration rate = 3000 – 6000 lph/m2

Length width ratio = 1.25 – 1.35b. Filter media: sand layer = 60- 90 cm thick effective size (D10) = 0.35 – 0.60 mm coefficient of uniformity (Cu) = 1.3-1.7.c. Base material:• 45 to 60 cm thick gravel• four layers of each about 15 cm• 2 – 6 mm, 6 – 12 mm, 12 – 20 mm and 20 – 50 mm from the

d. Under drainage system:

e. Appurtenances:Wash water trough, aircompressor, ratecontrol device, headloss indicators meters,valves etc

Efficiency of RSF: 35-40 ppm turbidity removal removes colour below 3 ppm Less efficient in iron and manganese removal not efficient in odour removal Less efficient in bacteria removal (Only 80 – 90 %)

3. Pressure filter (PF)

water is passed under pressure of 3 – 7 kg/cm2 through pumping

Rate of filtration of PF is 6000 – 15000 lit/hr/m2 of filter area low efficient than RSF for the removal of color, turbidity and bacterial

load can be used for small colonies, industry and swimming pools etc.

Difference between

Criteria Slow sand filter Rapid sand filter

Filtration rate LPH/M2 100 – 200 3000-6000Filter Media :sand layer (cm) 90 – 110 60-90

effective size (D10) mm 0.25 – 0.35 0.35-0.6

coefficient of uniformity (Cu) 3 – 5. 1.3-1.7

Efficiency bacteria removal 98 – 99% Less efficient (Only 80 – 90 %)

DISINFECTION To kill pathogens Chemicals called disinfectants

Characteristics of a good disinfectants:1.Should be able to destroy all harmful bacteria

economically within the contact time and in the widerange of temperature and pH values.

2.It should not render the water toxic or impart colour andodour.

3.It should be easily available at reasonable cost.4.It should be safe to handle and method of application

should be simple.5.It should persist in residual concentrations as safeguard

recontamination.

Methods of disinfection: Chlorination

• When Chlorine is used Cl2 + H2O ↔ HOCl + H+ + Cl –

[Called Hydrolysis reaction occurs at 49 - 212°C]The HOCl further dissociates (ionizes) as followsHOCl ↔ H+ + OCl – [Called Ionization reaction]HOCl and OCl – penetrate cell walls and reacts with the enzyme

system in the cell of micro-organism and results death of micro-organism

FORMS OF APPLICATION OF CHLORINE

(a) Bleaching powderCaOCl2 ↔ Ca++ + 2 OCl –

H+ + OCl – ↔ HOCl –

this process is called hypochlorination(b) Chloramines

H2O + Cl2↔ HOCl + H++ Cl –

NH3 + HOCl ↔ NH2Cl (monochloramine) + H2ONH2Cl + HOCl ↔ NHCl2 (dichloramine) + H2ONHCl2 + HOCl ↔ NCl3 (trichloramine) + H2O

(c) Chlorine gas or liquid chlorine(d) Chlorinedioxide

2NaClO2 + Cl2 ↔ 2NaCl + 2 ClO2↑

CHLORINE DEMAND AND DOSE

(a) Chlorine demandChlorine demand = Total amount of chlorine added – Amount ofresidual chlorine required after a specified contact periodReaction for combined available chlorine:Cl2 + H2O ↔ HOCl + H++ Cl –

NH3 + HOCl ↔ NH2Cl (monochloramine) + H2ONH2Cl + HOCl ↔ NHCl2 (dichloramine) + H2ONHCl2 + HOCl ↔ NCl3 (trichloramine) + H2O

(b) Chlorine doseQuantity of chlorine required to be added to water to leave 0.2 mg/lor ppm of freely available residual chlorine after 10 minutes ofcontact period

FORMS OF CHLORINATION

1. Plain chlorination or simple chlorination:To raw water

2. Pre-chlorination:Before treatment

3. Post chlorination:After treatment

4. Double or multiple chlorination:Two or more point

5. Super chlorination:Application beyond break point

6. De-chlorinationRemoving chlorine

7. Break point chlorination or free residual chlorination:

FACTORS AFFECTING BACTERIAL EFFICIENCY OF CHLORINE

1. Turbidity: low efficient2. Presence of metallic compound: Efficiency is

decreased.3. Ammonia compound: Efficiency is decreased4. pH value of water: If pH is high in water, efficiency is

low5. Temperature: If temperature decreased, efficiency

decreased.6. Time of contact: time of contact should be at least 30

minutes.7. Type, condition and concentration of micro-organism:

Efficiency low if the favorable condition for bacteria isavailable and concentration of bacteria is high.

WATER SOFTENING

• Process of removing hardness• Purpose: To remove HardnessA. Removal of temporary hardness:

(a) Boiling:It is costlier and not used in public water supply.Ca(HCO3)2 CaCO3↓ + CO2↑ + H2OMg(HCO3)2 MgCO3↓ + CO2 ↑+ H2O

(b) Adding lime:Ca(HCO3)2 + Ca(OH)2→ 2CaCO3↓ + 2H2OMg(HCO3)2 + Ca(OH)2→ CaCO3↓ + MgCO3↓ + 2H2O

A. Removal of permanent hardness:

a. Lime soda process:

CO2 + Ca(OH)2 = CaCO3↓ + H2OCa(HCO3)2 + Ca(OH)2 = 2CaCO3↓ + 2H2OMg(HCO3)2 + Ca(OH)2 = CaCO3↓ + MgCO3 + 2H2OMgCO3 + Ca(OH)2 = Mg(OH)2↓ + CaCO3↓MgSO4 + Ca(OH)2 = Mg(OH)2↓ + CaSO4CaSO4 + Na2CO3 = CaCO3↓ + Na2SO4MgCl2 + Ca(OH)2 = Mg(OH)2↓ + CaCl2CaCl2 + Na2CO3 = CaCO3↓ + 2NaClMgCl2 + Na2CO3 = MgCO3 + 2NaCl

2NaClSONa

2NaHCOZ

ZNa 42

b. Permutit Process:

C. Demineralization or deionization process:

Regeneration of zeolite:

22 Cl MgCa

ZNa2NaCl ZMgCa

2HClSOH

2COO2HR

Regeneration of hydrogen exchanger:

Cl/ClSO

2NaMgCa

NaMgCa

MISCELLANEOUS TREATMENT

A. Aeration:

(A) Aeration (B) Removal of iron and manganese (C) Removal of colour odour and taste

Purpose of aeration:1. To make water fresh by absorbing oxygen from air.2. To release dissolved gases (CO2, H2S etc) to

atmosphere.3. To remove bad taste and odour.4. To reduce corrosiveness of water.5. To precipitate Fe and Mn to some extent by oxidizing.6. To kill harmful bacteria to some extent.7. To mix mixing chemicals to water.

Methods of aeration:

Free fall or gravity aerators:

Methods of aeration:

Free fall or gravity aerators: Mechanical aerators:

Free fall or gravity aerators:

B. Removal of iron and manganese:

Effect:i. Produce taste, odour and brown red colour.ii. Stains on clothes, corrosion and clogging of pipes by

accumulation of precipates.iii.Causes difficult in various industrial process.

Purpose: Removal of iron and manganese

Methods:(a) By aeration(b) By adding lime(c) Passing over manganese zeolite

(a) By aeration: In this case aeration is done beforesedimentation.

Fe:4Fe + O2 + 10 H2O → 4Fe(OH)3 ↓ + 8HFe(HCO3)2 :Fe(HCO3)2 + 2H2O → FeO + 2CO2 + 3H2O4FeO + O2 → 2Fe2O3Fe2O3 + 3H2O → 2Fe(OH)3 ↓

Mn:6Mn + 3O2 + 6H2O → 6MnO2 ↓ + 12H

C. Removal of colour, odour, taste:

Purpose: Removal of colour, odour and taste

Methods:(a) By aeration(b) By activated carbon treatment

• Activated carbon is manufactured by heating sawdust, paper mill waste etc. at 500°C in a closed vesselin controlled condition of burning at 800°C.

• readily available in market in powder or granularform

• absorbs organic matters and removes colour, odourand taste.

(c) Using copper sulphate: in swimming pools

SODIS method is very easy to apply: A transparent PET bottle is cleaned with soap. Then, the bottle is filled with water and placed in full sunlight for at least 6 hours. The water has then been disinfected and can be drunk.

Membrane Filtration

Reverse Osmosis

BIO SAND FILTER• (BSF) is a point-of-use water treatment system adapted

from traditional slow sand filters. • Bio sand filters remove pathogens and suspended solids

from water using biological and physical processes that take place in a sand column covered with a bio film.

• BSFs have been shown to remove heavy metals, turbidity, bacteria, viruses and protozoa.

• BSFs also reduce discoloration, odor and unpleasant taste. • Studies have shown a correlation between use of BSFs and

a decrease in occurrence of diarrhea because of their effectiveness, ease of use, and lack of recurring costs, bio sand filters are often considered appropriate technology in developing countries.

How Well Does the Bio sand Filter Work? • Water naturally contains many living things. Some are harmless and

others can make people sick. Living things that cause disease are also known as pathogens. They are sometimes called other names, such as microorganisms, microbes or bugs, depending on the local language and country.

• There are four different categories of pathogens that are : bacteria, viruses, protozoa and helminths.

• Turbid water looks cloudy, dirty or muddy and is caused by sand, silt and clay that are floating in the water. Drinking turbid water will not make people sick by itself.

• However, viruses, parasites and some bacteria can sometimes attach themselves to the suspended solids in water.

• This means that turbid water usually has more pathogens so drinking it increases the chances of becoming sick

CHAPTER 7: INTRODUCTION TO CONVEYANCE

• Transportation of water to treatment plant or reservoir or distribution through conduits.

• Transmission: Source – TP – Reservoir• Distribution: Reservoir – Users Tap

• Conduits:A. Gravity: Open channel flow

Canals, aqueducts, tunnels

B. PressurePipes, pressure tunnels, pressure aqueducts etc.

PIPE, PIPE MATERIALS AND PIPE TYPES

Pipe: • Circular conduit where fluid flows under pressure• Designed to carry external and internal loads

Requirement of good pipe: • Withstand external, internal and temperature stresses • Smooth for minimum frictional losses • Durable• Light• Noncorrosive• Cheap • Easy joint

Pipe types as per materials:

(a) Cast Iron (CI) Pipe:

• Manufactured by sand molding or centrifugal method• Standard 1.8 m length but up to 3m for smaller diameter• 50 mm to 1.2 m dia.Advantages:Easy to join, can withstand high pressure, resistance tocorrosion, long life (> 100 yrs), durable, strong and moderatein cost, joined by flanged or Spigot and socket joint, lowmaintenance cost.

Disadvantages:Brittle and very heavy so difficult to transport and may beexpensive.

Suitability: Suitable for distribution system.

(b) Wrought Iron (WI) Pipe:

• Manufactured by rolling the flat plates of metal toproper diameter and welding to the edges

Advantages:Strong, light weight, can withstand high pressure (400m) and cheaper than CI pipesDisadvantages:It can’t withstand external load and when there is nowater inside, liable to corrosion and costly to maintain.It is costlier than CI pipesSuitability: Occasionally used for main lines where pressure is high

(c) Steel Pipe:

• Manufactured by WI or mild steel which are galvanized byproviding a protective coating of zinc on inner and outer surface

Advantages:It is cheap, light, easy in handling and transport, easy in joining withscrewed socket joints and 20 years of life, resistant to corrosionwhen exposed to atmosphere

Disadvantages:may get corroded by acidic and alkaline waters and liable toincrustation.

Suitability: main lines where pressure is high and when pipe is exposure in open atmosphere

(d) Galvanized iron (GI) pipes:

• Manufactured similar as WI pipes• 15,20,25,32,40,50,63,75,90,110,125,150, 200 mm inner dia

Advantages:Light in weight, easy in transport, handling, cutting, threading,working, joining, and gives neat appearance, joined couplings orscrewed socket joint.

Disadvantages:Costly, corrosive and less durable than CI pipes

Suitability: Inside plumbing in buildings but not used nowadays due to high cost.

(e) Concrete (GI) pipes:

• Made of cement concrete (precast or cast in site)

Advantages:Withstand 150 m head of water, resist corrosion and life is above75 years, maintenance cost is low, least thermal expansion, can belaid under water and resist normal traffic load

Disadvantages:Precast type is heavy to handle and transport, concrete pipes can’tresist high pressure and difficult to repair, it may be affected byacids and alkali and salty waters, difficult to join and liable to leakdue to porosity

Suitability:Where water does not flow under pressure (i.e. sewerage system)

(f) Asbestos cement (AC) pipes:

• Made of mixture of cement and asbestos fibers

Advantages:not affected by salt water and corrosive materials, smooth,light so easy in handling

Disadvantages:Affected by alkali and acid and also brittle so costlier intransport.

Suitability:Small size distribution pipes

(g) Wooden pipes:

• made of wood by making channels or boring at center and usedin ancient times

• not used in water supply nowadays

(h) Vitrified clay Pipes:

• made of vitrified clay so has smooth surface• not used in water supply nowadays

(i) Lead and copper Pipes:

• Copper pipe is made of copper and can resist corrosion even ifwater contains some acids and expensive so not used in watersupply nowadays

• Leads are soluble in water so lead pipe causes lead poisoninghence it is not used in water supply nowadays.

(f) Plastic Pipes: • Made of Plastic and common in nowadays• it is corrosion resistant, light in weight and economical

Advantages:Light, cheap, available in longer length, electrical insulation,corrosion free, life correspond to GI

Disadvantages:Less resistant to hot water, may impart smell to water, can be easilycut.

Suitability:All water sypply systems

Types:

1. Low density polyethylene (LDPE) pipes:

Used in electrical wiring

2. High density polyethylene (HDPE)pipes

3. Polyvinyl chloride (PVC) pipes:

4. Unplastisized Polyvinyl chloride (UPVC) pipes:

5. Poly Propylene Random (PPR) Pipes:

Plastic Pipes

LAYING OF PIPES1.Preparation of detailed maps:2.Locating proposed alignment of pipeline on the

ground:3.Location of pipes with respect to ground surface

during laying4.Excavation of trench:5.Dewatering of trench:6.Lowering the Pipes:7.Joining pipes:8.Testing of pipes:9.Back filling and disinfection before first use:

PIPE JOINTS

CHAPTER 8: VALVES AND FITTINGS

(a) Sluice or gate or cutoff valve

(b) Reflux or check or non-return valve

(c) Safety or pressure relief valve

(d) Air valve or air relief valve

(e) Drain or scour or blow off valve : Ordinary sluice valve to

remove silt deposit

(f) Butterfly valve and globe valve

Devices used to control the flow of water, regulate pressures,release air, prevent back flow etc

FIRE HYDRANT:

Devices used for tapping water from mains for thefire extinguishing, street washing, watering gardens,flushing sewer lines etc.

Provided at all road junctions & every 100 – 300 mapart.

For tapping water, the hose is connected to thehydrant and if necessary the engine is used toincrease head.

It should be cheap, easily connectable & detachableto the hose pipe and able to give sufficient water. Itmay be of post type or flush type.

FITTINGS

CHAPTER 9: PLANNING OF GRAVITY WATER SUPPLY

• Need identification of scheme• After need identification, mass meeting is called, prioritize is

done and then scheme acquisition form is filled up and submittedto VDC, DDC and divisional district water supply office

• With feasibility study report the schemes are forwarded fromdivisional office thru regional office to department of watersupply and sewerage (DWSS)

• After obtaining scheme acquisition form list from all 75 districts, budget ceiling is prepared for forthcoming fiscal year by DWSSand forward to ministry of concern.

• The ministry approves ceiling consulting with National planningcommission then distributed to DWSS and district offices forimplementation

• After obtaining approved budget ceiling, detailed surveyis carried out.

• Detail survey horizontal and vertical control and questionnaire

• Analysis based on detail survey, the design, drawing,estimating and costing is done and final report isprepared.

• Water Users Committee (WUS) is formed and trained inagreement with WUC or implementation agency

• After agreement, construction is carried out and it ishandover to the WUC.

• WUC are responsible for regular maintenance.

Water treatment

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