chapter 2 saad hameed abid

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Chapter Two

Drinking Water Impurities and Treatment

2.1 Introduction

Many areas have water containing impurities from natural or

artificial sources. These impurities may cause health problems, damage

equipment or plumbing, or make the water undesirable due to taste, odor,

appearance or staining. Water related problems will be found primarily in

homes serviced by a private water supply, although occasionally, they

will be found in water from municipal water supplies. Those impurities

which cause health problems should be attended to immediately; other

problems caused by water impurities can be corrected if they are a

nuisance. Before beginning any treatment plan, have water tested by an

independent laboratory to determine the specific impurities and level of

contamination. This will help you select the most effective and

economical treatment method [1].

2.2 Source of Water [4]

The main sources of water are:

Surface water: It includes flowing water (streams and rivers) and

still water (lakes, ponds and reservoirs).

Underground water: It includes water from wells and springs.

Rain water

Sea water.



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2.3 Drinking-water supply agencies

Drinking-water supplies vary from very large urban systems

servicing populations with tens of millions to small community systems

providing water to very small populations. In most countries, they include

community sources as well as piped means of supply.

Drinking-water supply agencies are responsible for quality assurance and

quality control. Their key responsibilities are to rep are and implement

WSPs [6]

To provide water supplies to customers we abstract water from

lochs, reservoirs and boreholes and burns. source waters are treated to

remove impurities to provide safe drinking water. then distribute this high

quality treated water through an extensive network of pipes, pumping

stations and storage tanks for customers to use for drinking, cleaning,

recreation, gardening, or in business processes, as shown in figure (2.1)

[8].

(Figure 2.1) Drinking water supply agent

In many cases, the water supplier is not responsible for the

management of the catchment feeding sources of its supplies. The roles of

the water supplier with respect to catchments are to participate in

interagency water resource management activities; to understand the risks



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arising from potentially contaminating activities and incidents; and to use

this information in assessing risks to the drinking-water supply and

developing and applying appropriate management. Although drinking-

water suppliers may not undertake catchment surveys and pollution risk

assessment alone, their roles include recognizing the need for them and

initiating multiagency collaboration – for example, with health and

environmental authorities. Experience has shown that an association of

stakeholders in drinking- water supply (e.g., operators, managers and

specialist groups such as small suppliers, scientists, sociologists,

legislators, politicians, etc.) can provide a valuable non-threatening forum

for interchange of ideas. [6]

2.4 Community management

Community-managed drinking-water systems, with both piped andnon-piped distribution, are common worldwide in both developed and

developing countries. The precise definition of a community drinking-

water system will vary. While a definition based on population size or the

type of supply may be appropriate under many conditions, approaches to

administration and management provide a distinction between the

drinking-water systems of small communities and those of larger towns

and cities. This includes the increased reliance on often untrained and

sometimes unpaid community members in the administration and

operation of community drinking-water systems. Drinking-water systems

in per urban areas in developing countries – the communities surrounding

major towns and cities may also have the characteristics of community

systems [6].



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Effective and sustainable programmers for the management of

community drinking- water quality require the active support and

involvement of local communities. These communities should be

involved at all stages of such programmers, including initial surveys;

decisions on sitting of wells, sitting of off-takes or establishing protection

zones; monitoring and surveillance of drinking-water supplies; reporting

faults, carrying out maintenance and taking remedial action; and

supportive actions, including sanitation and hygiene practices [6].

A community may already be highly organized and taking action on

health or drinking- water supply issues. Alternatively, it may lack a well

developed drinking-water system; some sectors of the community, such

as women, may be poorly represented; and there may be disagreements or

factional conflicts. In this situation, achieving community participation

will take more time and effort to bring people together, resolve

differences, agree on common aims and take action. Visits, possibly over

several years, will often be needed to provide support and encouragementand to ensure that the structures created for safe drinking-water supply

continue to operate. This may involve setting up hygiene and health

educational programmers to ensure that the community:

— is aware of the importance of drinking-water quality and its relation to

health and of the need for safe drinking-water in sufficient quantities for

domestic use for drinking, cooking and hygiene; — recognizes the importance of surveillance and the need for a

community response;

— understands and is prepared to play its role in the surveillance process;

— has the necessary skills to perform that role;

— is aware of requirements for the protection of drinking-water supplies

from pollution. [6]



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2.5 Chemicals from industrial sources and human dwellings

Chemicals from industrial sources can reach drinking-water directly

from discharges or indirectly from diffuse sources arising from the use

and disposal of materials and products containing the chemical. In some

cases, inappropriate handling and disposal may lead to contamination,

e.g., degreasing agents that are allowed to reach ground-water. Some of

these chemicals, particularly inorganic substances, may also be

encountered as a consequence of natural contamination, but this may also

be a byproduct of industrial activity, such as mining, that changes

drainage patterns. Many of these chemicals are used in small industrial

units within human settlements, and, particularly where such units are

found in groups of similar enterprises, they may be a significant source of

pollution. Petroleum oils are widely used in human settlements, and

improper handling or disposal can lead to significant pollution of surface

water and groundwater. Where plastic pipes are used, the smaller

aromatic molecules in petroleum oils can sometimes penetrate the pipes

where they are surrounded by earth soaked in the oil, with subsequent

pollution of the local water supply [6].

A number of chemicals can reach water as a consequence of disposal

of general household chemicals; in particular, a number of heavy metals

may be found in domestic wastewater. Where wastewater is treated, these

will usually partition out into the sludge. Some chemicals that are widelyused both in industry and in materials used in a domestic setting are

found widely in the environment, and these may be found in water

sources, although usually at low concentrations. Some chemicals that

reach drinking-water from industrial sources or human settlements have

other primary sources and are therefore discussed in other sections of this

chapter. Where latrines and septic tanks are poorly sited, these can lead tocontamination of drinking-water sources with nitrate [6].



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Identification of the potential for contamination by chemicals from

industrial activities and human dwellings requires assessment of activities

in the catchment and of the risk that particular contaminants may reach

water sources. The primary approach to addressing these contaminants is

prevention of contamination by encouraging good practices. However, if

contamination has occurred, then it may be necessary to consider the

introduction of treatment, Table (2.1) Guideline values for naturally

occurring inorganic chemicals that are of health significance in drinking

water [6].

Table (2.1) inorganic chemicals that are of health significance in drinking

water

2.6 Diseases

Sanitation and hygiene, approximately 2.4 million deaths globally

could be prevented each year if every person practiced good hygiene and

had clean drinking water. In developing countries water and sanitation

deficits contribute to almost half of all people’s suffering. This is largely

due to the many diseases that result from drinking unsanitary water.

Waterborne diseases constitute the majority of illnesses that cause



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suffering and death in developing countries. These are diseases that result

from contact or consumption of infected water. Some of these diseases

include malaria, typhoid, cholera, Guinea worm, E. coli, Giardia,

amoebas, and other parasites; but the greatest disease caused by unsafe

drinking water is diarrhea. In fact, diarrhea is currently one of the greatest

killers of children in the world. Pathogenic microorganisms, such as

protozoa or bacteria, in contaminated fresh water may be transferred to a

person through drinking the water, washing with the water, or eating

foods that have been prepared from the unclean water. The person then

becomes infected from the pathogenic microorganisms contained in the

water and develops a waterborne disease [3].

Not only are there waterborne diseases, there are also water-washed

diseases affecting millions of people. Water-washed diseases encompass

those diseases that are removed by merely washing with water. In regards

to health, water is vital to having proper hygiene. Simply washing one’s

hands with soap and water can reduce the risk of endemic diarrhea by upto almost 50% in addition to other respiratory or skin infections [3]

The quality of the water needs to be evaluated not only for

pathogens, but also for harmful chemicals that can contaminate the water

as well. For example, mercury is commonly found in water but is not

harmful in small amounts. However, in large quantities, mercury can be

very harmful to the human body and cause various forms of illness.Chemicals and pathogens immersed in water supplies also cause the

water to taste badly. The taste of the water influences how much of the

water a person drinks; humans need a lot of water and the poor taste of

the water available to a person should not be a factor determining how

much he receives. These issues of water quality are all part of the water

crisis that need to be solved.[3]



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2.7 Impurities of Water [4]

The impurities present in water may be categorized into following

categories:

(1) Dissolved Impurities

(a) Dissolved gases: O2, CO2, H2S etc.

(b) Inorganic salts:

(i) Cations: Ca++, Mg++, Na+, K +, Fe++, Al+++ etc.

(ii)Anions: CO3 – , Cl

– , SO4

– , NO3

– etc.

(c) Organic salts.

(2) Suspended Impurities

(a) Inorganic: Clay and sand.

(b) Organic: Oil globules, vegetables, and animal material.

(3) Colloidal Impurities

Finally divided clay and silica Al(OH)3, Fe(OH)3, organic waste products,

coloring matter, amino acids etc.

(4) Microscopic Matters

Bacteria, algae, fungi etc.

2.8 Sources of Impurities in Water [4]

Following are the sources of impurities in water:

Gases (O2, CO2 etc.) are picked up from the atmosphere by

rainwater.

Decomposition of plants and animals remains introduce organic

impurities in water.

Water dissolves impurities when it comes in contact with ground,

soil or rocks.



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Impurities are also introduced in water when it comes in contact

with sewage or industrial waste.

River water contains dissolved minerals like chlorides, sulphates,

bicarbonates of sodium, magnesium, calcium and iron. It also contains

suspended impurities of sand, rocks and organic matter. The composition

of river water is not constant. The amount of dissolved impurities in it

depends on its contacts of the soil. Greater the duration of contact, more

soluble is the minerals of soil in it. Lake water has high quantity of

organic matter present in it but lesser amount of dissolved minerals. Its

chemical composition is also constant. Rain water is obtaining as a result

of evaporation from the surface water. Probably it is the purest form of

natural water. But during its downward journey through the atmosphere it

dissolves organic and inorganic suspended particles and considerable

amount of industrial gases like (CO2, NO2, SO2 etc.). Rain water is

expensive to collect and is irregular in supply [4].

Underground water is free from organic impurities and is clearer in

appearance due to the filtering action of the soil. But it contains large

amount of dissolved salts. Sea water is very impure due to two reasons:

1. Continuous evaporation increases the dissolved impurities content,

which is further increased by the impurities thrown by rivers as they joinsea.

2. It is too saline for most industrial uses except cooling.



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2.9 Treatment Methods of Water [5]

A. Internal Treatment

B. External Treatment

A- Internal Treatment Method

1. Phosphate Conditioning:

- Small amount of phosphate ions are added to precipitate Ca ions.

- Chosen depending on the pH conditions of boiler.

2. Colloidal Conditioning:

-

Using kerosine, tannin, starch etc

-

Get coated over the scale forming particles

- Removed by Blow down Process

3. Carbonate conditioning:

- Na2CO3 is added to precipitate Ca salts as CaCO3

-

Removed by Blow down Process

-

Used in low pressure boilers

4. Calgon Conditioning:

-

Scale forming salts are converted into soluble complexes.

- E.g. Sodium Hexameta Phosphate (Na2PO3)6 is added…reacts with

Ca and forms Calcium Hexameta Phosphate (Ca2PO3)6

- Prevents Scale formation

5. Radioactive conditioning:



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-

Adding radioactive tablets

- Emits radiation energy which prevents Scale formation

6. Electrical Conditioning:

- Mercury bulbs placed in boiler

-

Emits electrical discharge

-

Prevents Scale formation

B- External Treatment Method (or) Water softening Method

• Removal of hardness causing substances from water

Methods:

1.

Zeolite process

2.

Ion Exchange Process

3.

Mixed Bed deionization

Zeolite (or Permutit) Process: are Hydrated sodium alumino Silicate

Na2O. Al2O3 X SiO2 Y H 2O (X= 2-10, Y= 2-6 )

Natural Zeolites:

1. Natrolite - Na2O. Al2O3 4SiO2 .2H 2O

2.

Laumontite - CaO. Al2O3 4SiO2 .4H 2O

3.

Harmotome - (BaO.K 2O). Al2O3 5SiO2 .5H 2O

- Capable of exchanging its Na ions.



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As noted above, where a health-based guideline value cannot be

achieved by reasonably practicable treatment, then the guideline value is

designated as provisional and set at the concentration that can be

reasonably achieved through treatment. Collection, treatment, storage and

distribution of drinking-water involve deliberate additions of numerous

chemicals to improve the safety and quality of the finished drinking-water

for consumers (direct additives). In addition, water is in constant contact

with pipes, valves, taps and tank surfaces, all of which have the potential

to impart additional chemicals to the water (indirect additives) [7].

Water treatment transforms raw surface and groundwater into safe

drinking water. Water treatment involves two major processes: physical

removal of solids and chemical disinfection [7].

Water treatment must go through these steps:

1- Coagulation:

Coagulation removes dirt and other particles suspended in water.

Alum and other chemicals are added to water to form tiny sticky particles

called ―floc‖ which attract the dirt particles. The combined weight of the

dirt and the alums (floc) becomes heavy enough to sink to the bottom

during sedimentation, as shown in figure (2.2) [7].

Figure (2.2) Coagulation

Coagulation



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2- Sedimentation:

Coagulated particles fall, by gravity, through water in a settling tank

and accumulate at the bottom of the tank, clearing the water of much of

the solid debris and clear water moves to filtration, as shown in figure

(2.3) [7].

Figure (2.3) Sedimentation

3- Filtration, Disinfection & Storage:

Filtration: The water passes through filters, some made of layers of

sand, and charcoal that help remove smaller particles [7].



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Disinfection: A small amount of chlorine is added or some other

disinfection method is used to kill microorganisms that may be in the

water [7].

Storage: Water is placed in a closed tank or reservoir for disinfection

to take pace. The water then flows through pipes to home and business in

the community [7].

Figure (2.4) Filtration, Disinfection & Storage

Purpose of disinfection: To make Drinking water free of any disease

causing bacteria and microbes.



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Methods of disinfection :

There are 3 mainly used disinfection methods at large scale.

CHLORINATION

OZONATION

ULTRAVIOLET RADIATION

Chlorine is the most common cost-effective means of disinfecting

water. The addition of a small amount of chlorine is highly effective

against most bacteria, viruses, and protozoa. But cysts (durable seed-like

stages) formed by parasitic protozoa such as Cryptosporidium and

Giardia can survive chlorine [7].

Chlorine is applied to water in one of three forms: elemental

chlorine (chlorine gas), hypochlorite solution (bleach), or dry calcium

hypochlorite. All three forms produce free chlorine in water [7]

Ozonation: OZONE is Strongest oxidant/disinfectant available. More

effective against microbes than chlorination. But, costly and difficult to

monitor and control under different condition [7].

Ozonation process:

Ozone (o3) is generated on-site at water treatment facilities by

passing dry oxygen or air through a system of high voltage electrodes [7].



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Figure (2.5) Complete Cycle of Water Treatment

2.10 Hardness in Drinking Water

Hardness in drinking water is defined as those minerals that

dissolve in water having a positive electrical charge.

The primary components of hardness are calcium (Ca++) and magnesium

(Mg++) ions. Dissolved iron (Fe++) and manganese (Mn++) also satisfy

the definition of hardness, but typically make up only a very small

fraction of total hardness. Minerals are composed of either atoms or

molecules. An atom or molecule that has dissolved in water is called an

―ion.‖ Positively charged ions are called cations and are noted as (+). A

double sign would indicate a plus two electrical charge. Contaminants



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having a similar positive charge would be removed by a matching type of

ion exchange resin, i.e. water softening [9].

2.11 Health Effects of Hardness

The presence or absence of the hardness minerals in drinking water is not

known to pose a health risk to users. Hardness is normally considered an

aesthetic water quality factor. The presence of some dissolved mineral

material in drinking water is typically what gives the water its

characteristic and pleasant taste. At higher concentrations however,

hardness creates the following consumer problems [9].

• Produces soap scum most noticeable on tubs and showers.

• Produces white mineral deposits on dishes more noticeable on

clear glassware.

• Reduces the efficiency of devices that heat water. As hardness

deposits build in thickness, they act like insulation, reducing the

efficiency of heat transfer.

It has also been observed that areas of higher hardness in drinking water

maybe associated with lower incidents of heart disease. This possible

relationship is being investigated [9].

2.12 Water Softening

Water softening uses an ion exchange process. Sodium typically is

put into the water while hardness and certain other minerals are

proportionally removed. A private home water softener typically has two

tanks. The taller tank contains the purifying media called a cation ion



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exchange resin, while the smaller tank contains the sodium or potassium

salt used to regenerate the exchange resin. During normal operations, raw

water passes through the ion exchange resin media in the tall tank. The

calcium (Ca++), magnesium (Mn++), iron (Fe++), or manganese (Mn++)

ions and other ions in the water are ―exchanged‖ for sodium (Na+) or

potassium (K+) ions which have been temporarily stored in the pores of

the exchange resin. A recent improvement in softeners is the introduction

of an equipment configuration that backwashes when needed rather then

by time clock.

As the softener removes hardness minerals from the water supply,

sodium or potassium will be given back to the water proportionally.

Shown below is the concentration of either sodium or potassium that

would be added to the existing raw water concentration, if 10 mg/L of

hardness is removed. To determine the increase for your situation, divide

your total hardness by 10 and then multiply that result by the appropriate

number to the right of the equal sign [9].

Eventually the removal capacity of the resin media becomes

exhausted and the resin will need to be regenerated. The regeneration

process begins by a rapid backwashing of the resin to remove any fine

particulate material that may originate in the well. The process then

continues at a slower rate by ―brining‖ which is the adding of salt

solution to the resin. During this process the sodium or potassium from

the brine enters the resin pores and displaces the previously removed

hardness ions or iron/manganese. After approximately 20 minutes, the



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remaining brine, along with the concentrated displaced hardness ions and

other ions are flushed out of the device and disposed of into an approved

dry well, septic tank, or sewer [9].

Some owners of water softeners have expressed concerns relative to

the affect of the waste brine on their leach fields. Studies by the Water

Quality Association (WQA) indicate that concentrated waste brine and

purged contaminants do not injure leach fields or septic tanks. The WQA

is the professional association of the small water treatment device

industry. Additional studies are now underway [9].

Sodium and chloride do not disappear when disposed into the

ground. Sometimes this disposal can contaminant wells downhill of the

party using the softener. Thus, reducing salt usage as much as possible is

desirable [9].

2.13 Advantages of Water Softening [9]

• Softener resin can be regenerated and re-used.

• Ion exchange can consistently remove hardness from water to

extremely low levels.

• Softening removes dissolved iron and manganese (ie colorless).

Other water quality factors, such as pH and alkalinity, are notcritical to removing iron and manganese.

• Conventional softening can also remove other health related

contaminants.



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2.14 Disadvantages of Water Softening [9]

• Adds sodium or potassium to your drinking water depending on

which ―salt‖ you use. For those concerned with elevated sodium

levels in their drinking water, potassium chloride (KCl) can be

substituted in place of sodium chloride (NaCl). The process is

equally as efficient, however the cost of potassium chloride is

higher than sodium chloride.

• Softening will not operate satisfactorily if particulates such as

iron bacteria, clay particles, rusty colored water exists, even

occasionally. If any solids are present, a particle (sediment)

filter must be installed before the media tank.

• Water softeners require a location to dispose of waste brine. If

you do not have sewer service, disposal of the waste brine will

likely be into the ground. This creates the potential of

contaminating the groundwater, and subsequently your own

well or those wells of your neighbors down hill. When

potassium chloride is used, the potassium should be recognized

as a soil nutrient, being one of the three components of typical

manmade fertilizer.

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