Hygiene localities, its bioethics’ aspects.

Water hygiene and water supply. The impact of

drinking water quality in General and dental health.

The lectureThe lecture

Author: Lototska O.V.Author: Lototska O.V.

•Water covers 71% of the Water covers 71% of the Earth's surface; the oceans Earth's surface; the oceans contain 97.2% of the contain 97.2% of the Earth's water. Earth's water.

Water is a chemical substance with the chemical formula H2O. Its molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often coexists on Earth with its solid state, ice, and gaseous state (water vapor or steam).

Every organism consists mostly of Every organism consists mostly of water. The human body is usually water. The human body is usually made up of 50 to 75 made up of 50 to 75 %% water. All living water. All living things need a lot of water to carry out things need a lot of water to carry out their life processes.their life processes.

Body Water Lost And SymptomsBody Water Lost And Symptoms

% .....% ..... Few symptoms or signs of any thirst present;. Few symptoms or signs of any thirst present;. 2% ..... Beginning to feel thirsty; loss of endurance capacity and 2% ..... Beginning to feel thirsty; loss of endurance capacity and

appetite. appetite. 3% ..... Dry mouth; performance impaired. 3% ..... Dry mouth; performance impaired. 4% ..... Increased effort for exercise, impatience, apathy, vague 4% ..... Increased effort for exercise, impatience, apathy, vague

discomfort, loss of appetite. discomfort, loss of appetite. 5% ..... Difficulty concentrating, increased pulse and breathing, 5% ..... Difficulty concentrating, increased pulse and breathing,

slowing of pace. slowing of pace. 6-7% ..... Further impairment of temperature regulation, higher pulse 6-7% ..... Further impairment of temperature regulation, higher pulse

and breathing, flushed skin, sleepiness, tingling, stumbling, and breathing, flushed skin, sleepiness, tingling, stumbling, headache. headache.

8-9% ..... Dizziness, labored breathing, mental confusion, further 8-9% ..... Dizziness, labored breathing, mental confusion, further weakness. weakness.

10% ..... Muscle spasms, loss of balance, swelling of tongue. 10% ..... Muscle spasms, loss of balance, swelling of tongue. 2020% ..... Heat Exhaustion, delirium, stroke, difficulty swallowing; % ..... Heat Exhaustion, delirium, stroke, difficulty swallowing;

death can occur. death can occur.

Its main functions are that it:Its main functions are that it: Replaces loss of Replaces loss of

fluids from tissues.fluids from tissues. Maintains the fluidity Maintains the fluidity

of blood and lymph.of blood and lymph. Helps elimination of Helps elimination of

waste material of the waste material of the body.body.

Acts as a vehicle for Acts as a vehicle for dissolved food.dissolved food.

Helps in the Helps in the secretion of digestive secretion of digestive juices.juices.

Regulates body Regulates body temperature and acts temperature and acts as a distributor of as a distributor of body heat.body heat.

Domestic Use: 7 % of water

available is for domestic use i.e drinking, cooking, washing, bathing etc. Recommended need of water is 120 liters/day/person. It includes all aspects of life which a person has in his routine life i.e bathing, washing, drinking & for toilet use.

Uses of water

Public purpose: Water is required for public cleansing, maintenance of gardens, and swimming pools and other civic activities.

Industrial Use: 23 % of available water is used in industries.

Agricultural Use: 70 % of available water is used for growth of food and raw materials required.

Epidemiological and toxicological role of water

- as transfer factor of pathogens with the fecal-oral transfer mechanism: enteric infections of bacterial and viral origin (typhoid, paratyphoid А, В, cholera, dysentery, salmonellosis, coli-entheritis, tularaemia /deep-fly or rabbit fever/, viral and epidemic hepatitis А, or Botkin disease, viral hepatitis E, poliomyelitis and other enterovirus diseases, such as Coxsakie, EСНО etc.); geohelminthosis (ascaridiasis, trichocephaliasis, ankylostomiasis); biohelminthosis (echinococcosis, hymenolepiasis); of protozoal etiology (amebic dysentery (amebiasis), lambliasis); zooanthroponosis (tularemia, leptospirosis and brucellosis);

Water can participate in spread of infections in the following ways:

as a transfer factor of pathogens of the skin and mucous membrane diseases (when swimming or having another contact with water): trachoma, leprosy, anthrax, contagious molluscum, fungous diseases (i.e., epidermophytosis);

-as the habitat of disease carriers – anopheles mosquitoes, which transfer malarial haemamoeba malarial haemamoeba and others (open water reservoirs).

Toxicological role of water consists in it containing chemical agents that may negatively influence people health causing different diseases. They are divided into chemical agents of natural origin, those, which are added to water as reagents and chemical agents, which come into the water as the result of industrial, agricultural and domestic pollution of water supply sources. Insufficient or non-effective treatment of such waters at waterworks procures the continuous toxic effect of small concentrations of chemical agents, or, rarely, in cases of accidents and other emergency situations – acute poisonings.

Balneal role of water

Water is used in medicinal purpose for rehabilitation of convalescents (drinking of mineral waters, medicinal baths), and also as tempering factor (bathing, swimming, rub-down).

Domestic and economic role of waterSanitary-hygienic and domestic functions of water

include:- water usage for cooking and as a part of dietary

intake;- usage of water as means of keeping body, clothes,

utensil, residential and public premises and industrial areas, settlements clean;

- watering of the green areas within settlements;

- sanitary-transport and disinfection functions of water – disposal of residential and industrial waste through sewer system, waste processing on plants, self-purification of water reservoirs;

fire fighting, atmospheric pollution clearing (rain, snow).

Economical functions of water:

-usage in agriculture (irrigation in crop and gardening, greenhouses, poultry and cattle breeding farms);

-industry (food, chemical, metallurgy etc.);

- as the route of passenger and cargo transportation.

http://www.epa.gov/seahome/groundwater/src/supply.htm

Sources of waterSources of water

RAINPrime source of all water.

Part of rain water sinks to form ground water, part of it evaporates and some runs in streams and rivers. These events are called "water - cycle".

Characteristics:Purest, bright & sparkling colour, soft water, only traces of dissolved solids, corrosive action on lead due to softness, in clean areas rain water is free of pathogens.

Impurities:Picks up local impurities such as dust, soot, micro-organisms, CO2, N2, O2, Ammonia & Sulphur. In areas where NO2 and SO2 are present in atmosphere, rain water becomes acidic and the rain is called acidic rain.

SURFACE WATER

Surface water mostly originates from rain water.It has highest chance of being polluted particularly river water because people near banks throw wastes in it.Sources of surface water are.a. Impounding reservoirsb. Rivers and streamsc. Tanks, ponds and lakes.

GROUND WATERIt is in form of:

a. Wells — Deep well, shallow well, Artesian well.

b. Springs — Seasonal springs, thermal springs, mineral spring, shallow springs, and deep springs.

The advantages of ground water are:a. It is usually free from pathogenic agents.b. It usually requires no treatment.c. Its supply is continuous.

The disadvantages of ground water are:a. It is high in mineral contentsb. It requires pumping or some arrangement

to lift the water.

A spring is ground water which finds its way to the surface because of topographical features. Cracks present in earth, water enters and comes out from other opening at a low level. So source may be quite far away such as 100-200 miles.

Springs:

WELLSWELLS

These are artificial holes These are artificial holes or pits dug into the earth or pits dug into the earth

to reach the to reach the underground water level. underground water level.

They constitute a very They constitute a very important source of important source of

water supply in villages. water supply in villages. There are four varieties There are four varieties

of wells:of wells:

There are four varieties of wells:There are four varieties of wells:

1. 1. Shallow WellsShallow Wells,,2. 2. Deep WellsDeep Wells

3. 3. Artesian WellsArtesian Wells are a variety of deep wells in which are a variety of deep wells in which water under great pressure comes out to the surface water under great pressure comes out to the surface

automaticallyautomatically 4. 4. Norton's Abyssinian Tube WellsNorton's Abyssinian Tube Wells are really shallow wells are really shallow wells which are bored by simply driving iron pipes 3.8 to 5 cm. which are bored by simply driving iron pipes 3.8 to 5 cm. in diameter and 6 to 7.62 metres deep to tap thein diameter and 6 to 7.62 metres deep to tap the ground ground

water. A pump is attached to the pipe to draw the water.water. A pump is attached to the pipe to draw the water.

Types of aquifers and wells.

In a water table well, the water table is at atmospheric pressure. In an artesian well, the water pressure is greater than atmospheric. In a flowing artesian well, the water pressure is such that it can flow freely above the ground surface

WatersWaters,, used for drink and everyday needs, used for drink and everyday needs, must correspond to the demands: must correspond to the demands:

good organoleptic properties: refreshing temperature, transparence, colorless, no smell and no taste . harmlessness of its chemical composition the absence of pathogenic microorganismssafety in the radiological attitude

The population should be provided not The population should be provided not only with enough of water, but also only with enough of water, but also with qualitative water. Water should with qualitative water. Water should not cause any pathological change in not cause any pathological change in the organism, should not cause of the organism, should not cause of spread of infectious diseases, and also spread of infectious diseases, and also not to cause unpleasant sensations.not to cause unpleasant sensations.

The pollution of water sources represents the The pollution of water sources represents the important ecological problem. Depending on important ecological problem. Depending on type of pollution there are:type of pollution there are:

chemical, chemical, physical (radioactive substances, hot water), physical (radioactive substances, hot water), bacterial, virus and biological. bacterial, virus and biological. Industrial wastewater is characterized by Industrial wastewater is characterized by

considerable quantity of components.considerable quantity of components.

Major categories of water pollutantMajor categories of water pollutant 1. Infections agents - Bacteria, viruses 2. Organic chemical - Pesticides, plastics,

detergents, oil, and gasoline 3. Inorganic chemicals - Acids, caustics, salts,

metals 4. Radioactive materials - Uranium, thorium,

cesium, iodine, radon

Fluoridation of drinking water as a hygienically problem.Fluoridation of drinking water as a hygienically problem.

Fluoridation of Fluoridation of drinking water as a drinking water as a hygienic problemhygienic problem

Fluoride is a naturally occurring mineral that is found in all water sources.  It is considered a beneficial nutrient and is present in trace amounts in the body. At low concentrations in drinking water, it helps strengthen teeth and bones.

Fluoride

The amount of fluoride present naturally in drinking water is highly variable, depending on the specific geological environment from which the water is obtained.

In non-fluoridated drinking water (i.e., drinking water to which fluoride has not been intentionally added for the prevention of dental caries) levels may reach up to about 2.0 mg/litre.

However, some places can have fluoride levels in drinking water of up to 20 mg/litre. In areas in which drinking water is fluoridated, the concentration of fluoride in drinking water generally ranges from 0.7 to 1.2 mg/litre.

An "optimum" level of fluoride in drinking water, associated with the maximum level of dental caries protection and minimum level of dental fluorosis, has been determined

0,7-1,5 mg/dm0,7-1,5 mg/dm33 of of fluoride is the fluoride is the optimal optimal concentration of concentration of fluoride in water.fluoride in water.

FluoridationFluoridation is addition of fluoride to public is addition of fluoride to public water supplies to reduce tooth decay. water supplies to reduce tooth decay.

Fluoride is a compound consisting of the Fluoride is a compound consisting of the element fluorine and a metallic element such as element fluorine and a metallic element such as sodiumsodium (forming sodium fluoride, used in water (forming sodium fluoride, used in water supplies) or supplies) or tin tin (forming stannous fluoride, used (forming stannous fluoride, used in toothpaste). in toothpaste).

Water fluoridation has been recognized as a Water fluoridation has been recognized as a significant method in preventing tooth decay significant method in preventing tooth decay since the 1930s.since the 1930s.

The maximum protection by fluoridation The maximum protection by fluoridation against tooth decay occurs when children against tooth decay occurs when children consume fluoridated water from birth through consume fluoridated water from birth through age 13. age 13.

Water fluoridation is the controlled addition of fluoride to a public water supply to reduce tooth decay. Fluoridated water has fluoride at a level that is effective for preventing cavities; this can occur naturally or by adding fluoride. Fluoridated water operates on tooth surfaces: in the mouth it creates low levels of fluoride in saliva, which reduces the rate at which tooth enamel demineralizes and increases the rate at which it remineralizes in the early stages of cavities.

Chronic (long term) exposure to Fluoride in water above 1.5 - 2 mg/liter can result in coloration of the teeth (fluorosis).  At higher levels, more severe impacts can result including alteration of bone density resulting in arthritis and tooth damage.The Maximum Contaminant Level (MCL) that has been established by the EPA for Fluoride is 1,5 mg/l. Boiling water with Fluoride will actually increase the concentration. Drinking water systems with source water containing Fluoride in excess of the MCL must treat the water to lower the concentration. 

Mild fluorosis looks like this:

  Even more disturbing than the cosmetic impact that fluoride can have on teeth, research is also linking fluoride to •increased risk of cancer (particularly bone cancer)•gene mutations•reproductive problems•neurotoxicity (hyper or depressed activity)•bone fluorosis (decreasing density)

Dental fluorosis is a health condition caused by an overdose of fluoride. In its severe form it is characterized by black and brown stains, as well as cracking and pitting of the teeth.

Skeletal Fluorosis:

Skeletal fluorosis is a bone disease exclusively caused by excessive consumption of fluoride. In advanced cases, skeletal fluorosis causes pain and damage to bones and joints.

Common causes of fluorosis include consumption of fluoride from drinking water, and consumption of fluoride from the drinking of tea. In India, the most common cause of fluorosis is fluoride-laden water derived from deep bore wells.

Geographical areas associated with groundwaterGeographical areas associated with groundwater having over having over 1.5 mg/L of naturally occurring fluoride, which is above 1.5 mg/L of naturally occurring fluoride, which is above recommended levelsrecommended levels. . A A 1994 World Health Organization expert 1994 World Health Organization expert committee suggested a level of fluoride from 0.5 to 1.0 mg/Lcommittee suggested a level of fluoride from 0.5 to 1.0 mg/L

Reverse Osmosis Filtration - This is used to purify several types of bottled water (not all), so some bottled waters are unfluoridated. Reverse osmosis systems are generally unaffordable for personal use.

Ways to Remove Fluoride from Water -

Defluoridation is needed when the naturally occurring fluoride level exceeds recommended limits.

Ways to Remove Fluoride from Water

 Activated Alumina Defluoridation Filter - These filters are used in locales where fluorosis is prevalent. They are relatively expensive and require frequent replacement, but do offer an option for home water filtration. 

Distillation Filtration - There are commercially available distillation filters that can be purchased to remove fluoride from water.

Hazards of Polluted Water:1. Biological HazardsThese are due to some specific agent that causes ill-

health.

Bacterial Typhoid, Bacillary dysentery, Typhoid, Bacillary dysentery, Cholera etc.Cholera etc.

Viral Viral hepatitis A & E, Viral hepatitis A & E, Poliomyelitis.Poliomyelitis.

Protozoal Amoebiasis, Giardiasis.Amoebiasis, Giardiasis.

Helminthic Round worm, whip worm, Round worm, whip worm, hydatid diseasehydatid disease

Leptospiral Weil's diseaseWeil's disease

Cyclops Guinea worm.Guinea worm.

2. Other Hazards

a. GIT disturbances due to Na ++, Mg ++ & Ca++ ions, e.g) increased MgSO4 lead to diarrhea.b. Lead poisoning c. Iodine deficiencyd. Fluorine deficiencye. Hardness of waterf. Infant methaemoglobinemia.

Impure water may be purified by either of the following methods:

A. NaturalA. Natural (a) Pounding or Storage.(a) Pounding or Storage. (b) Oxidation and Settlement.(b) Oxidation and Settlement.

B. ArtificialB. Artificial I. PhysicalI. Physical Distillation.Distillation. Boiling.Boiling.II. ChemicalII. Chemical Precipitation.Precipitation. Disinfection or Sterilization.Disinfection or Sterilization.III. FiltrationIII. Filtration "Biological" or "Slow Sand" Filtration."Biological" or "Slow Sand" Filtration. "Rapid Sand" or "Mechanical" Filtration."Rapid Sand" or "Mechanical" Filtration. Domestic Filtration.Domestic Filtration.

PURIFICATION OF WATER ON SMALL SCALEPURIFICATION OF WATER ON SMALL SCALE•House hold purification of waterHouse hold purification of water•Disinfection of wellsDisinfection of wells

HOUSE HOLD HOUSE HOLD PURIFICATIONPURIFICATIONa.a. By Boiling:By Boiling:Water should be boiled for Water should be boiled for 5 -10 minutes.5 -10 minutes.It kills all bacteria, spores, It kills all bacteria, spores, cysts & ova.cysts & ova.It removes temporary It removes temporary hardnesshardnessTaste is altered but is Taste is altered but is harmlessharmless

b.b. Chemical disinfectionChemical disinfection

i) Bleaching Powder (CaOCIi) Bleaching Powder (CaOCI22))

Bleaching powder is a white amorphous powder.Bleaching powder is a white amorphous powder.Produced by action of chlorine on slaked lime.Produced by action of chlorine on slaked lime.When freshly made contains 33 % of available chlorine.When freshly made contains 33 % of available chlorine.

It must be stored at dark, cool, dry place in a closed It must be stored at dark, cool, dry place in a closed container that is resistant to corrosion.container that is resistant to corrosion.

In practise one cup (250 g) of laundry bleach is mixed with three In practise one cup (250 g) of laundry bleach is mixed with three cups (750 ml) of water to make a litre. Three drops of this cups (750 ml) of water to make a litre. Three drops of this solution are added to 1 litre water for disinfection. Contact solution are added to 1 litre water for disinfection. Contact period is 30 minutes to 60 minutes. period is 30 minutes to 60 minutes.

ii Chlorine SolutionChlorine solution may be prepared from bleaching powder.* If 4 kg of bleaching powder with 25 % available chlorine is mixed with 20 litres of water, it will give a 5% solution of chlorine.* This solution should be kept in dark, cool and dry place in closed container

v.Potassium Permanganate.It is a powerful oxidizing agent but not recommended as it alters colours, smell and taste of water.

iii. Chlorine tabletsAvailable under different trade name e.g. HalazoneOne tablet of 0.5 g is sufficient to disinfect 20 litres of water. Used in camps and during travel.

iv. Iodine:Two drops of 2 % ethanol solution of iodine is used. A contact period of 20 - 30 minute is sufficient for 1 litre water.

CHLORINATIONCHLORINATIONChlorination is the process in which chlorine is Chlorination is the process in which chlorine is

added to water for purification. Chlorination-is more added to water for purification. Chlorination-is more effective when pH of water is around 7.effective when pH of water is around 7.

Effects of Chlorine:Effects of Chlorine:

a.a. Chlorine kills pathogenic bacteria, it has no effect on Chlorine kills pathogenic bacteria, it has no effect on spores and certain viruses.spores and certain viruses.

b.b. It has germicidal effects.It has germicidal effects.

c.c. It oxidizes iron, manganese and Hydrogen sulphide It oxidizes iron, manganese and Hydrogen sulphide

d.d. If destroys some taste and odour producing If destroys some taste and odour producing constituents.constituents.

e. e. It controls algae and slim organismsIt controls algae and slim organisms

f.f. It aids coagulation It aids coagulation

Action of ChlorineAction of Chlorine

When Chlorine is added to water, there is formation of When Chlorine is added to water, there is formation of hypochlorous and hydrochloric acid. The hydrochloric acid is hypochlorous and hydrochloric acid. The hydrochloric acid is neutralised by alkalinity of the water. The hypochlorous acid neutralised by alkalinity of the water. The hypochlorous acid ionizes to form hydrogen ions and hypochlorite ions as follows.ionizes to form hydrogen ions and hypochlorite ions as follows.

HH22O + CIO + CI22 ► HCI► HCI- - + HOCI+ HOCI

HOCI HOCI ► H► H++ + OCI + OCI--

The disinfecting action ofchlorine is mainly due to hypochlorous The disinfecting action ofchlorine is mainly due to hypochlorous acid and to a small extent due to hypochloriteon.acid and to a small extent due to hypochloriteon.

Principles of Chlorination

a. First, water should be clear and free from turbidity.First, water should be clear and free from turbidity.b.b. Chlorine demand of water should be estimated.Chlorine demand of water should be estimated.c.c. At least one hour is essential as a contact period of At least one hour is essential as a contact period of free residual chlorine for killing bacterial and viruses.free residual chlorine for killing bacterial and viruses.d.d. Minimum recommended concentration of free Minimum recommended concentration of free chlorine is 0.5 mg/L for one hour.chlorine is 0.5 mg/L for one hour.e.e. The sum of the chlorine demand of the specific water The sum of the chlorine demand of the specific water plus the free residual chlorine of 0.5 mg/l constitutes the plus the free residual chlorine of 0.5 mg/l constitutes the correct dose of chlorine to be applied.correct dose of chlorine to be applied.

Methods of ChlorinationMethods of Chlorination

a.a. By means of chlorine gasBy means of chlorine gasIt is of first choice because it is cheap, quick in action, It is of first choice because it is cheap, quick in action, efficient and easy to apply. Chlorinating equipment is efficient and easy to apply. Chlorinating equipment is required to apply chlorine gas to water as chlorine gas is required to apply chlorine gas to water as chlorine gas is irritant to eyes.irritant to eyes.

b.b. By means of Chloramine:By means of Chloramine:Chloramines are loose compounds of chlorine and ammonia. Chloramines are loose compounds of chlorine and ammonia. They have slower action than chlorine. They give more They have slower action than chlorine. They give more persistent type of residual chlorine. They have a less tendency persistent type of residual chlorine. They have a less tendency to produce chlorinous taste.to produce chlorinous taste.

Chlorine Demand It is the difference between the amount of chlorine added to the water and the amount of residual chlorine remaining at the end of a specific period of contact (1 hour) at a given temperature and pH of water.

Residual Chlorine: Amount of untreated chlorine, remaining in the water after some time as an effective disinfecting agent i.e. 0.3 – 0.5 mg/liter

Break point chlorination:The point at which the chlorine demand of water is met and if further chlorine is added free chlorine begin to appear in water

Super Chlorination:It is addition of large doses of chlorine to the water and removal of excess of chlorine after disinfection.

Agents alternative to Agents alternative to ChlorinationChlorination

The ozonization of water The ozonization of water Ozone Ozone contains three oxygen atomscontains three oxygen atoms. It is destroyed in . It is destroyed in

water, forming atomic oxygen: O3 → O2 → O. ozonization is water, forming atomic oxygen: O3 → O2 → O. ozonization is one of the best methods of disinfection: water is well one of the best methods of disinfection: water is well disinfected, organic admixtures become destroyed, disinfected, organic admixtures become destroyed, organoleptic features are improved. Water becomes blue and organoleptic features are improved. Water becomes blue and it is equated with spring water.it is equated with spring water.

Ozone dose is 0,5 - 6 mg/l. Sometimes, higher doses Ozone dose is 0,5 - 6 mg/l. Sometimes, higher doses are necessary for the lighting of water and improving other are necessary for the lighting of water and improving other organoleptic features. The time of disinfection is 3-5 min. The organoleptic features. The time of disinfection is 3-5 min. The remaining ozone should make up 0,1 – 0,3 mg/l. The remaining ozone should make up 0,1 – 0,3 mg/l. The concentration of the remaining ozone 0.4 mg/l provides the concentration of the remaining ozone 0.4 mg/l provides the reliable inactivation of 99 % viruses for 5 min.reliable inactivation of 99 % viruses for 5 min.

Asaka Water Purification Plant 

  Ozone has been used in water treatment since 1903. It is more Ozone has been used in water treatment since 1903. It is more effective against bacteria and viruses than chlorine and adds no effective against bacteria and viruses than chlorine and adds no chemicals to the water. Ozone cannot be stored and requires an chemicals to the water. Ozone cannot be stored and requires an on-site ozone generator. In general, ozonation equipment and on-site ozone generator. In general, ozonation equipment and operating costs are higher than other treatment proceduresoperating costs are higher than other treatment procedures

 Advanced Water Purification System

                                                                      

Ultraviolet LightUltraviolet Light       Ultraviolet irradiation will kill bacteria by creating Ultraviolet irradiation will kill bacteria by creating photochemical changes in its DNA. No chemicals are added to photochemical changes in its DNA. No chemicals are added to the water by this process. Most ultraviolet water treatment the water by this process. Most ultraviolet water treatment units consist of one or more ultraviolet lamps usually units consist of one or more ultraviolet lamps usually enclosed in a quartz sleeve, around which the water flows. enclosed in a quartz sleeve, around which the water flows. The UV lamps are similar to fluorescent lamps and the quartz The UV lamps are similar to fluorescent lamps and the quartz sleeve surrounding each lamp protects the lamp from the sleeve surrounding each lamp protects the lamp from the cooling action of water. The killing effect of the lamp is cooling action of water. The killing effect of the lamp is reduced when the lamp temperature is lowered. Ground reduced when the lamp temperature is lowered. Ground water is usually a constant temperature year round and so it water is usually a constant temperature year round and so it is possible to set a flow rate that will not lead to excess is possible to set a flow rate that will not lead to excess cooling. cooling.

The effectiveness of UV irradiation depends onThe effectiveness of UV irradiation depends on• the intensity of the light, the intensity of the light, • depth of exposure and depth of exposure and • contact time.contact time.                 

Water passes in a relatively thin layer around the lamp; Water passes in a relatively thin layer around the lamp; therefore, water flow must be regulated to ensure that all therefore, water flow must be regulated to ensure that all organisms receive adequate exposure. If the water is at all organisms receive adequate exposure. If the water is at all turbid, or if it contains traces of iron, the effectiveness of UV is turbid, or if it contains traces of iron, the effectiveness of UV is greatly reduced. In such cases, the water needs to be filtered greatly reduced. In such cases, the water needs to be filtered before it reaches the UV system. before it reaches the UV system.        The maximal bactericidal effect is achieved by the waves The maximal bactericidal effect is achieved by the waves 250-260 nm, which pass even through the 25 cm layer of 250-260 nm, which pass even through the 25 cm layer of transparent and decolorized water.transparent and decolorized water.

The disinfection proceeds very quickly: vegetative forms The disinfection proceeds very quickly: vegetative forms of microorganisms die in 1-2 min. The turbidity, colour and iron of microorganisms die in 1-2 min. The turbidity, colour and iron salts decelerate the disinfection, decreasing the transparence salts decelerate the disinfection, decreasing the transparence of water. Consequently, it is necessary to light and decolorize of water. Consequently, it is necessary to light and decolorize water beforewater before the disinfection.the disinfection.

There are some advantages of UV-There are some advantages of UV-irradiation over the chlorination:irradiation over the chlorination:

bactericidal rays don't denaturate the bactericidal rays don't denaturate the water and don't change its organoleptic water and don't change its organoleptic features, features,

they have wider biological action.they have wider biological action. Their bactericidal action is spread over the Their bactericidal action is spread over the

spores, viruses and worm eggs, resistant to spores, viruses and worm eggs, resistant to chlorine. chlorine.

Many investigators consider this Many investigators consider this method the best for the disinfection.method the best for the disinfection.

The following steps are involved in the The following steps are involved in the purification of water by rapid sand filters.purification of water by rapid sand filters.

i. Coagulation:i. Coagulation:ii. Rapid mixing:ii. Rapid mixing:iii. Flocculation:iii. Flocculation:iv. Sedimentation:iv. Sedimentation:v. Filtration:v. Filtration:

Coagulation:  Alum and other chemicals are added to water to form tiny sticky particles called "floc" which attract the dirt particles.

How is water treated?

Sedimentation:  The heavy particles (floc) settle to the bottom

and clear water moves to filtration.

 

Filtration:  The water passes through filters that help to remove smaller particles.

      Disinfection:  A small amount of chlorine is added to kill any bacteria or microorganisms that may be in the water.

Storage:  Water is placed in a closed tank or reservoir where it flows through pipes to homes and businesses in the community.