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TI 01/2010

TECHNICAL INSTRUCTIONS

ON

DISINFECTION OF WATER SUPPLY

BY DTE OF WORKS

ENGINEER-IN-CHIEF’S BRANCH MILITARY ENGINEER SERVICES

INTEGRATED HQ OF MOD (ARMY)

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FOREWORD MES plays a vital role in providing portable water to the armed forces and its allied organizations. Disinfection is unquestionably the most important step in the treatment of water for drinking. The microbiological quality of drinking water is of paramount importance and must receive priority over any other considerations in relation to drinking water treatment. These technical instructions (TI) have been drafted to provide all inputs required for planning, execution and subsequent maintenance and operation of disinfected water supply. The main objective of this TI is not only to create technical awareness of various aspects but also to update the information and role of MES and users. Overall this TI is an informative compendium and will be helpful and useful to the planners and ground engineers to maintain the system in healthy state for 24x7 hours effectively and efficiently. I am confident that this TI will contribute to develop MES into a technology savvy, efficient and cost effective construction agency in creation of military infrastructure. It will also help to deliver drinking water and develop confidence level that a reasonable and informed person would feel safe while drinking water supplied by this organization I am sanguine that this TI will provide an effective tool for professionals in the field to evaluate the system and arrive at innovative and workable solution.

New Delhi (A K NANDA) Sep 10 Lt Gen

E-in-C

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PREFACE MES plays a vital role in providing portable water to the armed forces and its allied organizations. The link between water quality and health has been known since the early ages. Waterborne diseases were a major threat to public health prior to the introduction of disinfection treatment of drinking water in the early 20th century. Disinfection is unquestionably the most important step in the treatment of water for drinking-water supplies. The microbiological quality of drinking-water is of paramount importance and must receive priority over any other considerations in relation to drinking-water treatment. With various disinfection technologies, emerging contaminants, and new regulations to consider, choosing the right drinking water disinfection method can be an overwhelming task. Disinfection of drinking water continues to be important to the protection of troops health. Selection of the appropriate method of disinfection for a particular system should be based on site specific considerations, such as quality of the source water and economics of the project. TI 01/2010 has been drafted to provide all inputs required for planning, execution and subsequent maintenance and operation of disinfectant . The main objective of this TI is not only to create technical awareness of various aspects but also to update the information and role of MES and users. Overall this TI is informative compendium and will be helpful and useful to the planners and ground engineers to maintain the system in healthy state for 24x7 hours effectively and efficiently. I am sanguine that this TI will provide an effective tool for professionals in the field to evaluate the system and arrive at innovative and workable solution.

New Delhi (Brajesh Kumar) Sep 10 Maj Gen DG (Works)

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CONTENTS – DISINFECTION OF WATER SUPPLY

TOPIC PAGE NOs

1. INTRODUCTION 6

2. OBJECTIVE OF DISINFECTION 6-7

3. CRITERIA FOR A GOOD DISINFECTANT 7 4. MECHANISMS OF DISINFECTION 7 5. FACTORS AFFECTING EFFICIENCY 7 6. DESIRABLE LIMITS 8 7. RECOMMENDED TREATMENT 8-9

8. TESTING REQUIREMENT 9

9. METHODS OF DISINFECTION 9

10. CHLORINATION 9-23

A. GENERAL

B. CHLORINATION CHEMISTRY

C. EFFICIENCY

D. ESTIMATION OF CHLORINE

E.CHLORINATION PRACTICE

F. APPLICATION OF CHLORINE

G. HAZARDS ASSOCIATED

H. LEGISLATION FOR CHLORINE

J. SAFETY CONSIDERATION

K. PERSONNEL TRAINING

L. EMERGENCY MANAGEMENT

M. TESTING OF CHLORINE WATER

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11. IONIZATION 23-25

A. INTRODUCTION B. CHEMISTRY C. LIMITATIONS D. LEGISLATION E. ADVANTAGES F. DISADVANTAGES

12. OZONIZATION 25-27

A. INTRODUCTION B. : MECHANISMS C. ADVANTAGE

D.DISADVANTAGES

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1. INTRODUCTION

Many often think that the taste of the water determines its purity, not knowing that even the best tasting water could contain disease-causing organisms. The fact that disease could be spread through drinking water was not commonly known until the latter part of the 1800.With this knowledge came an awareness of the need to treat water. Water treatment process such as storage, coagulation, flocculation, sedimentation, filtration, aeration and water softening are specifically designed to produce water that is aesthetically acceptable and economical to use, but cannot be relied upon to provide safe water. For utmost safety of water for drinking purposes, disinfection of water has to be carried out for killing of disease producing organisms.

2. OBJECTIVE OF DISINFECTION Disinfection is the process of selectively destroying or inactivating pathogenic organisms in water, usually by chemical means The objective of water treatment is to produce and store water that is hygienically safe, aesthetically attractive and palatable, in an economical manner. Though the treatment of water would achieve the desired quality, the evaluation of its quality should not be confined to the end of the treatment facilities but also be extended to the point of consumer use. The following are the main objectives of disinfection :- (a) Destruction of bacteria which cause water borne diseases.

(b) Control taste and odour.

(c) Prevents algal growth.

(d) To remove organic matter, iron and manganese from water for industrial use.

(e) To reduce Biological Oxygen Demand (B.O.D.) in waste water treatment.

(f) To control taste, odour and eliminate algal growth in the water.

The table below shows some common water related diseases –

Group Diseases Water borne Diseases transmitted by water where water

acts as a passive vehicle for infecting agent.

All these depend also on poor sanitation

Cholera, typhoid, bacillary dysentery, viral

hepatitis, leptospirosis, giardiasis, gastroenteritis

Water washed Diseases due to lack of water. Poor personal hugiene favours spread. Intestinal infections depend on lack of proper human waste disposal.

Scabies, skin sepsis & ulcers, yaws, leprosy, lice, typhus, trachoma, conjunctivitis, bacillary and amoebic dysentery, salmonellosis, worm infestations

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Water based Infecting agents spread by contact or ingestion water. An essential part of life cycle of agent takes place in aquatic animal.

Schistosomiasis, dracunculiasis

Water related Transmitted by insects living close to water.

Yellow fever, dengue, encephalitides, filariasis, malaria, onchocerciasis, sleeping sickness.

Faecal disposal s Caused by infecting agents- by eating uncooked fish and other food.

Clonorchiasis, diphyllobothriasis, fasciolopsiasis, paragonimiasis.

3. CRITERIA FOR A GOOD DISINFECTANT For a chemical or an agent to be potentially useful as a disinfectant in water supplies, it has to satisfy the following criteria: (a) Be capable of destroying the pathogenic organisms present, within the contact

time available and not unduly influenced by the range of physical and chemical properties of water encountered particularly temperature, pH and mineral constituents;

(b) Should not leave products of reaction which render the water toxic or impart colour or otherwise make it unpotable.

(c) Possess the property of leaving residual concentrations to deal with possible recontamination;

(d) Be amendable to detection by practical, rapid and simple analytical techniques in the small concentration ranges to permit the control of disinfection process.

(e) A disinfectant should function properly regardless of any fluctuations in the composition or condition of the water.

(f) A disinfectant should be safe and easy to handle

4. MECHANISMS OF DISINFECTION The mechanism of killing the pathogens depends largely on the nature of the disinfectant and on the type of micro-organisms. In general four mechanisms are proposed to explain the destruction or inactivation of organisms. (i) Damage to cell wall. (ii) Alteration of cell permeability. (iii) Changing the colloidal nature of the cell protoplasm. (iv) Inactivation of critical enzyme systems responsible for metabolic activities.

5. FACTORS AFFCTING EFFICIENCY OF DISINFECTION The efficiency of chemical disinfection is influenced by the following factors:- (a) Type, condition, concentration and distribution of organisms to be destroyed (b) Type and concentration of disinfectant. (c) Chemical and physical characteristics of water to be treated. (d) Contact time available for disinfection. (e) Temperature of water.

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6. DESIRABLE LIMITS FOR IMPORTANT PHYSICAL CHEMICAL AND BACTERIOLOGICAL PARAMETERS

Sl. No.

Characteristics IS:10500-1991- Drinking Water Specifications

Central Public Health Environmental Engineering Organisation (CPHEEO) Manual

WHO Guidelines

1. Turbidity (NTU) 5 1 0.1 2. pH 6.5to8.5 7.0 to 8.5 6.5 to 8.0

3. Total hardness (as CaCO3)((mg/l)

300 200 200

4. Sulphates (as SO4) (mg/l)

200 200 200

5.

Iron (as Fe) (mg/l) 0.3 0.1 0.3

6. Magnesium (as Mg) (mg/l)

30 30 30

7. E.coli or thermotolerant

coliform bacteria

Must not be detectable in

any 100-ml sample

Must not be detectable in any 100-ml sample

Must not be detectable in any 100-

ml sample

7. RECOMMENDED TREATMENT FOR DIFFERENT WATER

SOURCES

TYPE OF SOURCE RECOMMENDED TREATMENT

Protected, deep wells; essentially free of faecal

contamination

Disinfection

Unprotected, shallow wells; faecally contaminated Filtration and disinfection.

Protected, impounded upland water essentially free

of faecal contamination

Disinfection

Unprotected impounded water or upland river;

faecal contaminated

Filtration and disinfection.

Unprotected lowland rivers; faecal contamination Pre-disinfection or storage, filtration, disinfection

Unprotected watershed; heavy faecal contamination Pre-disinfection or storage, filtration,

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additional treatment and disinfection

Unprotected watershed; gross faecal contamination Not recommended for Drinking water supply

Water with dissolved solid/Brackish Reverse osmosis

8. TESTING REQUIREMENT

The goal of disinfection is to remove or inactivate all disease-causing organisms in water. However, testing for each type of pathogen individually would be costly and inefficient. Total coliform, is the most frequently used indicator of disinfection efficiency. It is relatively simple to test for the number of coliform bacteria found in water, and their presence indicates that other pathogenic bacteria are also likely to be present. If disinfection removes all of the coliforms from the water, then it can be safely assumed that the other disease-causing microorganisms have also been removed.

9. METHODS OF DISINFECTION

There are several different disinfectants, which either kill or deactivate pathogenic microorganisms. All disinfectants have benefits and drawbacks and can be used for water disinfection depending on the circumstances. For chemical disinfection of water, the following disinfectants are commonly used- - Chlorine (Cl2)

- Chlorine dioxide (ClO2) -Hypo chlorite (OCl-) -Ozone (O3) - Halogens: bromine(Br2), iodene (I) - Metals:copper(Cu2+),silver(Ag+)

10.CHLORINATION

A. GENERAL

Chlorination is the application of chlorine to water to accomplish some definite purpose.

Chlorination is currently the most frequently used form of disinfection in the water

treatment field. However, other disinfection processes have been developed. Chlorine is

only slightly soluble in water. Its maximum solubility is about 1% at 10oC. Below

10oC, it combines with water, forming crystalline chlorine hydrate (Cl2H2O), commonly

known as “Chlorine Ice”. In cold weather, this may cause blockage in pipe and pipe

fittings.

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B. CHLORINATION CHEMISTRY When chlorine is added to water, a variety of chemical processes take place. The chlorine reacts with compounds in the water and with the water itself. Some of the results of these reactions (known as the chlorine residual) are able to kill microorganisms in the water.

CHLORINE DEMAND

When chlorine enters water, it immediately begins to react with compounds found in the water. The chlorine will react with organic compounds and form trihalomethanes. It will also react with reducing agents such as hydrogen sulfide, ferrous ions, manganous ions, and nitrite ions.Two different reactions can occur:

H2S + Cl2 + O2- S + H2O + 2Cl-

H2S + 4Cl2 + 4 H2O H2SO4 + 8 HCl

In the first reaction, hydrogen sulfide reacts with chlorine and oxygen to create elemental sulfur, water, and chloride ions. The elemental sulfur precipitates out of the water and can cause odor problems. In the second reaction, hydrogen sulfide reacts with chlorine and water to create sulfuric acid and hydrochloric acid.

Each of these reactions uses up the chlorine in the water, producing chloride ions or hydrochloric acid which have no disinfecting properties. The total amount of chlorine which is used up in reactions with compounds in the water is known as the chlorine demand. A sufficient quantity of chlorine must be added to the water so that, after the chlorine demand is met, there is still some chlorine left to kill microorganisms in the water.

REACTION OF CHLORINE GAS WITH WATER

At the same time that chlorine is being used up by compounds in the water, some of the chlorine reacts with the water itself. The reaction depends on what type of chlorine is added to the water as well as on the the pH of the water itself. Chlorine may be added to water in the form of chlorine gas, hypochlorite, or chlorine dioxide. When chlorine gas enters the water, the following reaction occurs:

Cl2 + H2O HOCl + HCl

HOCl ↔ H+ + OCl-

The concentration of hypochlorous acid and hypochlorite ions in chlorinated water will depend on the water's pH. A higher pH facilitates the formation of more hypochlorite ions and results in less hypochlorous acid in the water. This is an important reaction to understand because hypochlorous acid is the most effective form of free chlorine

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residual, meaning that it is chlorine available to kill microorganisms in the water. Hypochlorite ions are much less efficient disinfectants. So disinfection is more efficient at a low pH.

C. EFFICIENCY

RESIDUAL AND DOSAGE

The chlorine residual in the clearwell should be at least 0.5 mg/L. This residual, consisting of hypochlorous acid and/or chloramines, must kill microorganisms already present in the water and must also kill any pathogens which may enter the distribution system through cross-connections or leakage. In order to ensure that the water is free of microorganisms when it reaches the customer, the chlorine residual should be about 0.2 mg/L at the extreme ends of the distribution system.

Determining the correct dosage of chlorine to add to water will depend on the quantity and type of substances in the water creating a chlorine demand. The chlorine dose is calculated as follows:

Chlorine Dose = Chlorine Demand + Chlorine Residual

CONTACT TIME

Contact time is the amount of time which the chlorine has to react with the microorganisms in the water, which will equal the time between the moment when chlorine is added to the water and the moment when that water is used by the customer. The longer the contact time, the more efficient the disinfection process is. When using chlorine for disinfection a minimum contact time of 30 minutes is required for adequate disinfection.

The CT value is used as a measurement of the degree of pathogen inactivation due to chlorination. The CT value is calculated as follows:

CT VALUE = (Chlorine residual, mg/L) (Contact time, minutes)

The CT is the Concentration multiplied by the Time. As the formula suggests, a reduced chlorine residual can still provide adequate kill of microorganisms if a long contact time is provided. The minimum CT value for the effective chlorination is 6.

OTHER INFLUENCING FACTORS

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Within the disinfection process, efficiency is influenced by the chlorine residual, the type of chemical used for chlorination, the contact time, the initial mixing of chlorine into the water, and the location of chlorination within the treatment process. The most efficient process will have a high chlorine residual, a long contact time, and thorough mixing.

Temperature influences chlorination just as it does any other chemical reaction. Warmer water can be treated more efficiently since the reactions occur more quickly. At a lower water temperature, longer contact times or higher concentrations of chemicals must be used to ensure adequate disinfection.

Turbidity of the water influences disinfection primarily through influencing the chlorine demand. Turbid water tends to contain particles which react with chlorine, reducing the concentration of chlorine residual which is formed. Finally, and most intuitively, the number and type of microorganisms in the water will influence chlorination efficiency.

D. ESTIMATION OF CHLORINE The usual tests practiced for estimating the residual chlorine in water are the orthotoulidine test (OT) and orthotoulidine arsenite test (OTA), the former used for total residual chlorine concentration and the later for free available chlorine. When orthotoulidine reagent is added to water containing chlorine; a greenish yellow colour develops, the intensity of which is proportional to the amount of residual chlorine present. The orthotoulidine test procedure does not overcome errors caused by the presence of nitrates, iron and manganese, all of which produce a yellow colour with orthotoulidine nor is it able to discriminate between “Free Chlorine” and “Combined Chlorine”. The O.T.A. reagent overcomes this drawback and hance gives better determination of free and combined chlorine separately. E. CHLORINATION PRACTICES (a) FREE AVAILABLE RESIDUAL CHLORINATION

The type of available chlorine residual required and the characteristics of the water being treated determine the process of disinfection to be employed (ai)PLAIN OR SIMPLE CHLORINATION This involves the application of chlorine to water as the only type of treatment to afford the necessary public health protection. Plain chlorination can be carried out in situation where:

(i) Turbidity and colour of the raw water is low, turbidty not exceeding 5 to 100 NTU;

(ii) Raw water is drawn from relatively unpolluted sources; (iii) Water contains little organic matter and iron and manganese do not exceed

0.3 mg/1; or (iv) Sufficient contact period between the point of chlorination and the

consumer end is available.

(aii) SUPER- CHLORINATION

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This is adopted in case of an emergency like a break down or in case of waters which are heavily polluted or fluctuate rapidly in quality. It can give excellent results in waters where:

(i) Plain chlorination produces taste and odour; (ii) The water is coloured; or (iii) Iron and manganese have to be oxidised.

(aiii) DECHLORINATION

When super chlorination is employed, the water usually contains excess of free available chlorine which must be removed before it becomes acceptable to consumers. Prolonged storage and absorption on charcoal, granulated carbon and activated carbon are effective. Also reducing compounds like sulphur dioxide, sodium thiosulphate and sodium bisulphate are frequently used as dechlorinating agents.

(aiv) BREAKPOINT CHLORINATION

The graph below shows what happens when chlorine (either chlorine gas or a hypochlorite) is added to water. First (between points 1 and 2), the chlorine reacts with reducing compounds in the water, such as hydrogen sulfide. These compounds use up the chlorine, producing no chlorine residual.

Next, between points 2 and 3, the chlorine reacts with organics and ammonia naturally found in the water. Some combined chlorine residual is formed - chloramines. The process would be stopped at point 3.

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Between points 3 and 4, the chlorine will break down most of the chloramines in the water, actually lowering the chlorine residual.

Finally, the water reaches the breakpoint, shown at point 4. The breakpoint is the point at which the chlorine demand has been totally satisfied. This process, known as breakpoint chlorination, is the most common form of chlorination, in which enough chlorine is added to the water to bring it past the breakpoint and to create some free chlorine residual.

(b) COMBINED AVAILABLE RESIDUAL CHLORINE This method involves the application of chlorine to water to produce with natural or added ammonia, a combined available chlorine residual and to maintain the residual through part or all of a water treatment plant or distribution system. They are less effective disinfectants and oxidants than free available chlorine forms. The residual, however, will persist much than free available chlorine which has a tendency to diffuse and be lost.

(c) POINT OF CHLORINATION

The use of chlorine at various stages of water supply system right from raw water collection to the distribution network is a common practice and terms like pre-post and rechlorination have come into common usage depending upon the points at which chlorine is applied.

(i) PRECHLORINATION

Prechlorination is the act of adding chlorine to the raw water. The residual chlorine is useful in several stages of the treatment process - aiding in coagulation, controlling algae problems in basins, reducing odor problems, and controlling mudball formation. In addition, the chlorine has a much longer contact time when added at the beginning of the treatment process, so prechlorination increases safety in disinfecting heavily contaminated water.

(ii) POSTCHLORINATION

Postchlorination is the application of chlorine after water has been treated but before the water reaches the distribution system. At this stage, chlorination is meant to kill pathogens and to provide a chlorine residual in the distribution system.

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F. APPLICATION OF CHLORINE

Chlorination can be carried out by using:-

(i) Gas chlorinator – pressure type

(ii) Gas chlorinator – All Vacuum Type.

(iii) Electrolytic Type.

(iv) Bleaching Powder Dozer

(i) GAS CHLORINATOR– PRESSURE TYPE

Working Principle – The chlorine gas is drawn from cylinder and connection is

made to the chlorinator through connecting valve screwed on to the nipple of the cylinder

and a connecting tube. The other end of tube is connected to the inlet nipple of the gas

filter.

From the filter unit, chlorine gas passes to the vacuum controller, to maintain

correct conditions for accurate and stable metering. The vacuum controller incorporates

a valve to shut off the gas supply, if the water supply to the injector assembly is

interrupted. Should the vacuum created by the injector falls below the required

minimum, the inlet valve on the regulator will close and thus prevents any further flow of

gas.

The gas next flows to the gas control valve. The rate of flow required to set by

the adjustment of control valve. The gas is then supplied to the injector and thus

entrained into the water system and discharged as aqueous solution to the point of

application. There are two types of system working on above principle:-

(a) GRAVITY FEED SYSTEM: - The aqueous solution of chlorine is directly

added to water supply sump.

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Fig-1

(b) PRESSURE FEED SYSTEM: - The chlorine solution is injected into the

rising mains, through a injector unit.

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Fig-2

(ii) GAS CHLORINATOR– ALL VACUUM TYPE

The most typical kind of chlorinator, a vacuum chlorinator, is shown below:

Fig-3

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Gas feeders are actuated by vacuum created by water or process fluid flowing

through the remote ejector. The ejector consists of a vacuum producing venturi

and a spring loaded diaphragm (or – diaphramless) check valve.

(iii) ELECTROLITE TYPE:

The chlorination is done by using either sodium or calcium hypochlorite.

Fig-4

The major advantage of this technique is the safety consideration as transportation, storage and application of chlorine gas involves major safety considerations to avoid hazards and fatal accidents.

(iv) BLEACHING POWER DOZER:

These are very simple in design and robust in construction. In the dozer a clear

solution of bleaching powder and soda ash is fed, which is dozed in pipe line

having flowing water by creating a differential pressure by incorporating an

orifice plate or ventury in the pipe line. This method of chlorine application has

the merits of simplicity, non requirement of electrical energy and relative safety

in operation and handling as available chlorine is either in powder or solution

form. However, the demerits include instability of bleaching powder, its

hygroscopic nature and relatively low percentage of available chlorine (25-33%).

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G. HAZARD ASSOCIATED WITH CHLORINE:

(a) Toxicity - Chlorine is not a poisonous gas, but is primarily a respiratory

irritant. The threshold limit value of chlorine accepted at present is 2.9 mg/m3 of

air. If the duration of exposure or the concentration of chlorine is excessive, it

will cause restlessness, throat irritation, sneezing and copious salivation.

(b) Fire And Explosion Hazards: - Through Fire hazard attributable to Cl2 is only moderate, it may react to cause fires or explosion upon contact with hydrocarbons, hydrogen, powered metals, phosphorous etc. (c) Volumetric Expansion: Liquid Chlorine has a high co-efficient of thermal expansion, resulting in rapid increase in volume, with rising temperature. This is why no chlorine container is filled completely. In practice, containers are filled only to the extent of about 80% of the designed capacity.

H. LEGISLATION FOR CHLORINE

IS:10500-1991

To be applicable only when water is chlorinated. Tested at consumer end. When protection against viral infection is required, it should be min 0.5 mg/l. WHO (World Health Organisation)

For effective disinfection, there should be a residual concentration of free chlorine of >_ mg/litre after at least 30 min contact time at pH <8.0.

USA The national drinking water standards state that the maximum residual amount of chlorine is 4 mg/L.

J. SAFETY CONSIDERATION (a) Only trained personnel should be permitted to handle chlorine cylinders and

chlorinating equipment. Rubber gloves, aprons and suitable gas masks should be provided. These should be housed in an easily accessible (unlocked) cupboard placed outside the chlorinator room.

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(b) When a chlorine leak occurs, the mechanical ventilation system should be opened immediately before any person enters the chlorine room. It must be made a point that chlorine container valves are closed first before any investigation is started.

(c) Cylinders containing chlorine should be handled gently. They should not be bumped, dropped or rolled on the ground and no object should be allowed to strike them with force. The protective hoods over the valve should always be kept in place except when the cylinders are in use. Flames should never be applied to chlorine cylinders or their valves.

(d) Cylinders should not be stored in the open or in damp places. Empty cylinders should be stored away from full cylinders so that they do not get mixed up.

(e) In case the valve is found to be stuck, the cylinder should be immediately returned to the supplier. No attempt should be made to a stuck valve by hammer, as this is very dangerous.

(f) Only the spanners prescribed for use should be used as it is important not to put too much leverage on the valves.

(g) Cylinders as well as the chlorinators must be tested at the start and end of every shift period, for leaks, first by trying to detect the sharp irritating smell of chlorine, then by passing over each cylinder and around each valve and pipe connections a rod with a small cotton-wool swab tied on the end, dipped in an aqueous solution of ammonia.

(h) Water should never be applied to a chlorine leak to stop it as it will only make it worse. If the leak is in the chlorinator, the cylinder should be immediately shut off until the pressure has reduced. The joint or gasket should be repaired replacing with new packing, if necessary.

(i) Solvents such as petroleum, hydrocarbons or alcohols should not be used for cleaning parts which come in contact with chlorine. The safe solvents are chloroform and carbon tetrachloride. Grease should never be used where it can come in contact with chlorine as it forms a voluminous frothy substance on reaction with chlorine.

(j) No direct flame should be applied to a chlorine cylinder, when heating becomes necessary, as this is hazardous. A water bath controlled not to exceed 27o C should be used.

(k) Before disconnecting the flexible lids from containers to gas headers, the cylinder valves should be closed first and then the gas under pressure should be drawn from the header and flexible lids before the header valve is closed.

K. PERSONNEL TRAINING Employee training should encompass the following: (i) Instruction and periodic drill or quiz regarding the locations, purpose and use of emergency fire-fighting equipment, alarms and emergency crash shut-down equipment such as valves and switches. (ii)Instruction and periodic drill or quiz regarding the locations, purpose and use of personnel protective equipment. (iii)Instruction and periodic drill or quiz regarding the locations, purpose and use of safety showers, eye baths, bubblier drinking fountains and the closest source of water for use in emergencies.

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(iv)Instruction and periodic drill or quiz of selected employees regarding the locations, purpose and use of respiratory first aid equipment. (v)Instruction to avoid inhalation of toxic vapours and all direct contacts with corrosive liquids. (vi)Instruction to report to the proper authority all leaks and equipment failures.

L. EMERGENCY MANAGEMENT Whenever chlorine is handled, a potential risk is involved, and a serious emergency may suddenly and unexpectedly crop-up. Such eventualities should be anticipated and proper schemes to meet them should be formulated in advance.The most common emergency that arises during chlorine handling is through leakage. GENERAL CUSES OF LEAKS

Leakage of chlorine gas can occur either from the cylinder or chloronomes plant. Main causes of leakage are as under:- (i) Defective cylinder valves & connecting valves. (ii) Mishandling of cylinders & chloronomes plant. (iii) Leakage from joints in the system (iv) Prolonged stoppage of chloronome plants without flushing the system for complete removal of chlorine gas and without plugging of the inlet & outlet ends.

IDENTIFYING LEAKS

Presence of chlorine in the atmosphere can be easily detected by its pungent smell, in order to ascertain the exact location of the leak, an “Ammonia Torch” is generally used.

NH4OH + Cl2 = NH4Cl + HOCl Chlorine even in traces, combines with ammonia to form ammonium chloride, which manifests as a white fume, pin pointing the exact location of the leaks. “All chlorine users must ensure that they have “Ammonia Torch” ready and handy”

PRELIMINARY MEASURES IN FACING LEAKAGES As soon as there is any indication of chlorine leakage immediate steps should be taken to meet the situation. It is to be realized that:- “A chlorine leak never gets corrected by itself”.It only gets worse, if not promptly attended to. The following action should immediately be taken: (a)Remove all persons not directly concerned.

(b)Put on the gas mask, rubber gloves and apron.

(c) Close the cylinder valve.

(d)Disconnect the cylinder from the plant.

(e)In case of leakage from the cylinder valve, shift the cylinder to horizontal position.

(f)Place a wet empty jute bag dipped in lime slurry over the cylinder valve.

(g)Place lot of lime over the jute bag.

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(h)Report the mater to AGE (E/M)/Supdt incharge installation by telephone or through

messenger.

(j)Water should never by used on a chlorine leak.

CONTROLLING LEAK

Most Chlorine leakages can be controlled by trained personnel, suitably equipped with

safety appliances and emergency kits. However, after controlling the leakage, it should

be the endeavour to use up the chlorine inside the container with the least possible delay.

If it is not possible to utilize the chlorine in the process itself, it should be neutralized.

“All chlorine consumers, irrespective of quantity consumed, should have emergency kits

handy and in proper working-condition, at all times. Appropriate facilities for chlorine

neutralization, if need arises should also be established and maintained.”

EMERGENCY KITS

An emergency kit consists of various appliances and tools such as gaskets, yokes, hoods,

clamps, studs, the rods, mild steel channels, spanners, screws, chains, pins wooden pegs

etc of standard sizes, to fit chlorine cylinders.

It is very essential that these kits are always maintained properly and kept ready for use.

Only authorized and trained persons should use these kits. After every use these kits

should by thoroughly cleaned with alkaline solution and dried.

ACTION BY EXECUTIVE STAFF

Following action should be taken by Supdt incharge installations/AGE (E/M):-

(a)On getting the report of leakage of gas, rush to the location and personally supervise

the operation till 100% gas has been discharged. The GE should also be informed at the

earliest.

(b)Ensure the 100% serviceability state of all safety devices i.e. gas mask, rubber gloves,

apron, lime solution tank, first aid box etc. A record of the same should be maintained at

each installation.

M. TESTING OF CHLORINE WATER:-

Water after chlorination should be tested for “Free residual Chlorine”. Potable water

should invariably have some “Free residual Chlorine” to ensure the complete oxidation of

impurities which require longer contact time. Too little of “Free residual Chlorine”

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makes the water unsafe for drinking and too much of it can cause throat irritation, bad

taste and odour etc. Therefore the question arises how such chlorine should be added to

the water, the answer lies in the para 862 of RMES which states ---

“ The MES will be responsible for all sedimentation, filtration and chlorinate plant

including the provision of reagents. The medical authorities will test the water

periodically and notify the MES when they consider that the water not being

adequately treated. They will also lay down the proportion of the reagents to be

used.

Where water is supplied in small service tanks, from which the water is drawn

direct by units, the medical authorities will be entirely responsible for providing the

reagents and treating the water.”

Thus medical authorities after carrying out all tests should advise MES authorities about

the amount of reagents to be added. To ensure that adequate chlorination is done,

testing should be done jointly by MES rep & medical rep and the report be submitted to

higher authorities duly signed by both the reps.

11. SILVER IONIZATION A. INTRODUCTION Nomads used silver coins to improve drinking water quality. Well water containing copper and silver coins is very bright, due to the biocidal affect of these metals. The Egyptians kept their water in silver containers to prevent contamination. The ancient Greeks were the first to discover the sanitizing power of copper.The early American pioneers put silver coins in large wooden water casks to provide them with safe drinking water on their long voyage. During the plague-ridden middle ages, mothers knew that to place a silver spoon in an infant’s mouth was a way of warding off disease. Silver has been used as an Ayurvedic Medicine in India for well over 2500 years. It was NASA that harnessed what nature already knew and designed an ionization system for their Apollo flights. B. CHEMISTRY Silver Ions Ag2+ are produced from pure Silver Electrodes by passing a calculated

amount of current.Silver ions bond to various parts of the cell, such as the DNA and

RNA, celular proteins and respiratory enzymes, causing all life support systems in the

cell to be immobilized. As a result, there is no more cellular growth or cell division,

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causing bacteria to no longer multiply and eventually die out. The ions remain active

until they are absorbed by a microorganism.

C. LIMITATIONS OF SILVER IONS AS DISINFECTANTS

Hardness: When the hardness is high i.e., above 800mg/lit, it may tend

to scale up on the electrode surface or inside the chamber and will

hamper the ionization process.

Chloride: When the concentration of chloride is found to be more than

about 300mg/lit, it may form silver chloride and precipitate. Hence the

action of silver ions are disturbed.

pH: Ideal pH for Water disinfection is 5-9 . Anything below and above

this limit will slow down the disinfection.

Turbidity: Turbidity definitely decreases the efficiency when it is more

than 10 NTU. More the turbidity more the contact time.

D.LEGISLATION

EU

Permissible limit is 100 ppb (micro grams/lit for drinking water as per EPA

and 90 ppb(micro grams/lit) as per European Union Standard.

WHO World Health Organization (WHO) has suggested a maximum limit of silver that may be consumed by a human being is 10gms.. USA The United States dictates a maximum value of 0.1 mg/L of silver. E. ADVANTAGES Silver ionization affectively deactivates Legionella bacteria and bio film and it

improves water quality. Silver ionization has a larger residual effect than most other disinfectants. Silver

ions remain in the water for a long period of time. Silver is effective throughout the entire water system, even in dead-end points and

parts of the system that contain slow-running water.

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Silver use affectivity does not depend on water temperature. Less maintenance to the water system is required. Silver is non-corrosive; it causes less strain on the distribution system. There are no transport and storage difficulties.

F. DISADVANTAGES

Silver affectivity depends on the pH value of the water. At a pH value of 9, only one tenth of all Legionella bacteria are removed.

When dissolved solid concentrations are high, silver will precipitate. This means silver ions are no longer available for disinfection.

Silver ions easily react with chlorines and nitrates that are present in the water, causing them to no longer be effective.

Some species of microorganisms can become resistant to silver ions. They can remove metal from their systems or convert it to a less toxic product. These microorganisms can become resistant to silver ionization

12. OZONIZATION A. INTRODUCTION

Ozone might be called an “orphan” disinfectant since it has worldwide a very low use in water treatment plants. Yet it has been known for over a hundred years .A disinfectant which is strong and does produce only low levels of byproducts is the ideal choice. When compared to other disinfectants like chlorine, chloramine and chlorine dioxide, ozone is the strongest disinfectant and also the fastest acting. Oxygen in the air (O2) is composed of two oxygen atoms. Under certain conditions, three oxygen atoms can be bound together instead, forming ozone (O3).

Ozone is produced when oxygen (O2) molecules are dissociated by an energy source into

oxygen atoms and subsequently collide with an oxygen molecule to form an unstable gas, ozone (O3), which is used to disinfect water.

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It is a faintly blue gas of pungent odour. Being unstable it breaks down to normal oxygen and nascent oxygen. This nascent oxygen is a powerful oxidizing and germicidal agent. Ozone is produced by the corona discharge of high voltage electricity into dry air. Ozone, being unstable, has to be produced onsite.

B. MECHANISMS : The mechanisms of disinfection using ozone include: • Direct oxidation/destruction of the cell wall with leakage of cellular constituents outside of the cell. • Reactions with radical by-products of ozone decomposition. • Damage to the constituents of the nucleic acids (purines and pyrimidines). • Breakage of carbon-nitrogen bonds leading to depolymerization.

C.ADVANTAGES Ozone is more effective than chlorine in destroying viruses and bacteria. The ozonation process utilizes a short contact time (approximately 10 to 30 minutes). There are no harmful residuals that need to be removed after ozonation because ozone

decomposes rapidly. After ozonation, there is no regrowth of microorganisms, except for those protected

by the particulates in the wastewater stream. Ozone is generated onsite, and thus, there are fewer safety problems associated with

shipping and handling. Ozonation elevates the dissolved oxygen (DO) concentration of the effluent. The

increase in DO can eliminate the need for reaeration and also raise the level of DO in the receiving stream.

It kills all pathogenic organisms by a direct effect on their DNA. Disinfection with ozone occurs 30,000 times faster than with chlorine, so a prolonged

contact time is unnecessary.

D.DISADVANTAGES • Low dosage may not effectively inactivate some viruses, spores, and cysts. • Ozonation is a more complex technology than chlorine or ionization, requiring complicated equipment and efficient contacting systems. • Ozone is very reactive and corrosive, thus requiring corrosion-resistant material such as stainless steel. • Ozonation is not economical for wastewater with high levels of suspended solids (SS),biochemical oxygen demand (BOD), chemical oxygen demand, or total organic carbon. • Ozone is extremely irritating and possibly toxic, so off-gases from the contactor must be destroyed to prevent worker exposure.

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• The cost of treatment can be relatively high in capital and in power intensiveness •Ozone treatment can create undesirable byproducts that can be harmful to health if they

are not controlled (e.g., formaldehyde and bromate). •Ozone is not effective at removing dissolved minerals and salts.