Hygiene of water and water-supply

HYGIENE OF WATER AND WATER-SUPPLY.

A METHOD OF SANITARY INSPECTION OF SOURCES OF WATER-SUPPLY AND SAMPLING WATER FOR BACTERIOLOGICAL AND SANITARY CHEMICAL RESEARCH. A METHOD OF ESTIMATION OF DRINKING-WATER AFTER THE RESULT OF LABORATORY ANALYSIS OF SAMPLES.

METHODS AND FACILITIES OF CLEANING AND DISINFECTING OF WATER AT THE CENTRALIZED AND DECENTRALIZED WATER-SUPPLY.

 

Water is vital to humans. It is needed for food preparation, drinking, washing, and irrigation. In addition, massive quantities are used daily in industrial processes. Yet, it is a limited resource that must be collected and distributed with increasing care. The most important source of water is rain, which may be collected directly in cisterns and reservoirs or indirectly through a watershed system or well. A watershed is the network of rivulets, streams, and rivers by which entire areas are watered. Ground water is rain that has trickled through rock layers, forming pools after many years. If it is under pressure, groundwater may bubble to the surface as a spring. Irrigation canals, reservoirs, wells, and water towers are man-made devices for diverting and collecting water from these natural sources. Because of contamination concerns, water from reservoirs, wells, and rivers is usually processed in a treatment plant before distribution.

http://www-sk.icrr.u-tokyo.ac.jp/sk/ykphd/chap3-4.html

Water is the main substance of biosphere, without which the existence of organic nature is impossible. Water is vital to humans. It is needed for food preparation, drinking, washing, and irrigation. In addition, massive quantities are used daily in industrial processes. Any vital process cannot be performed without water, and any cell cannot exist in anhydrous environment. Water has the importance not only for drinking and meal, and also for normal existence of the human. Yet, it is a limited resource that must be collected and distributed with increasing care.

The most important source of water is rain, which may be collected directly in cisterns and reservoirs or indirectly through a watershed system or well. A watershed is the network of rivulets, streams, and rivers by which entire areas are watered. Ground water is rain that has trickled through rock layers, forming pools after many years. If it is under pressure, groundwater may bubble to the surface as a spring. Irrigation canals, reservoirs, wells, and water towers are man-made devices for diverting and collecting water from these natural sources. Because of contamination concerns, water from reservoirs, wells, and rivers is usually processed in a treatment plant before distribution.

Because of enlargement of cities, villages, development of economy and raising of cultural inquiries of the population the consumption of water increases with each year. While choosing a water source for water supply its output and quality of water, and, also stability of parameters, which characterize its reliability that is determined by its origin and conditions of formation of water quality, and also character and intensity of its pollution are taken into consideration

The pollution of water sources represents the important ecological problem. Depending on type of pollution there are: chemical, physical (radioactive substances, hot water), bacterial, virus and biological. Industrial wastewater is characterized by considerable quantity of components.

It is a lot of chemical substances, which come at reservoir, worsen biological and organoleptic properties of water (smell, smack, color, turbidity, formation of a pellicle, foams etc) that not favorably influences on water usage and populations health.

The output of industries, agriculture, and urban communities generally exceeds the biologic capacities of aquatic systems, causing waters to become choked with an excess of organic substances and organisms to be poisoned by toxic materials. When organic matter exceeds the capacity of those microorganisms in water that break it down and recycle it. the excess of nutrients in such matter encourages rapid growth, or blooms, of algae. When they die, the remains of the dead algae add further to the organic wastes already in the water; eventually, the water becomes deficient in oxygen. Anaerobic organisms (those that do not require oxygen to live) then attack the organic wastes, releasing gases such as methane and hydrogen sulfide. which are harmful to the oxygen-requiring (aerobic) forms of life. The result is a foul-smelling, waste-filled body of water, a situation that has already occurred in such places as Lake Erie and the Baltic Sea and is a growing problem in freshwater lakes of Europe and North America. The process by which a lake or any other body of water changes from a clean, clear conditionwith a relatively low concentration of dissolved nutrients and a balanced aquatic community to a nutrient-rich, algae-filled body and thence to an oxygen-deficient, waste-filled condition is known as accelerated eutrophication.

 

 

The ultimate source of all natural potable water on the earth is rain, which is rarely used as a direct source except on islands in salt water, such as Bermuda, where the rain is collected and led into cisterns to serve as the only available water supply. When rain falls, it runs off into streams, in the case of heavy rains, or soaks into the ground, percolating through porous strata until it reaches an impervious stratum, upon which it collects, forming groundwater. Groundwater is the source of wells and of the springs that feed streams, rivers, and lakes. In its course, groundwater dissolves soluble mineral matter, and often the surface waters of rivers and lakes are polluted by the influx of sewage or industrial wastes (see Sewage Disposal; Water Pollution). In modern water-supply systems, an entire watershed is usually made into a reservation to control pollution. The waters are impounded by a system of dams, and flow by gravity, or are pumped, to the local distribution system.

Water is Essential for Life

It covers 71% of the earth's surface and makes up 65 % of our bodies. Everyone wants clean water-- to drink, for recreation, and just to enjoy looking at. If water becomes polluted, its loses its value to us economically and aesthetically, and can become a threat to our health and to the survival of the fish living in it and the wildlife that depends on it.

Water physiological functions:

-       flexibility about 65 % of body mass of adult person consists of water. 70 % of water is the intracellular water, 30 % - extracellular water (in blood), (7%) - lymph and 23 % - intertissue fluid. Water makes up 20 % of the bone mass, 75 %, of the muscle mass, 80% of the connective tissue mass, 20% of blood plasma mass, 99% of vitreous body of an eye. Major part of water is a component of macromolecular complexes of proteins, carbohydrates and fats, forming the jelly-like colloid cells and extracellular structures together with them. The smaller part of it is in a free state;

-       participation in metabolism and interchange of energy all assimilation and dissimilation processes in organism occur in water solutions;

-       role in support of osmotic pressure and acid-base balance;

-       participation in heat exchange and thermoregulation at evaporation of 1 g of moisture from lungs surface, mucous membranes and skin (latent heat of evaporation) organism loses 2.43 kJ (0.6 kcal) of heat;

-       transportation function delivery of nutrients to cells with blood and lymph, removal of waste products from the organism with urine and sweat;

-       as a component of dietary intake and a source of macro- and microelements supply to organism;

-       there are neuropsychic disorders that are resulted from impossibility to satisfy thirst if water is not available or if it is of bad organoleptic characteristics. According to I.P. Pavlovs doctrine on higher nervous activity, odour, taste, after-taste, water appearance, clarity (transparency) and colour are irritators that influence the whole organism through central nervous system. Worsening of organoleptic characteristics of water causes the reflex effect on water intake schedule and some physiological functions, for example it oppresses the secretory function of stomach. Drinking of such water causes the defence reaction in human organism the feeling of aversion, which makes a person to refuse such water irrespective of thirst.

 

Epidemiological and toxicological role of water

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

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

-       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 and others (open water reservoirs).

Symptoms of water epidemics:

-       simultaneous appearance of big number of enteric infected people, i.e. jump of population morbidity so-called epidemic outburst;

-       people who used the same water source, the same pipeline of water supply network, the same water-pump, shaft well etc. will suffer from diseases;

-       morbidity level will stay high for the long period of time to the extent of water contamination and consumption;

-       morbidity curve will have one, two, three, or more peaks. First of all those diseases that have short incubation period will be registered (coli-entheritis, salmonellosis - 1-3 days, cholera 1-5 days, typhoid 14-21 days and at last - those with the longest period: virus and epidemic hepatitis and 30 days and more);

-       after the taking of antiepidemic measures (liquidation of the contamination source, disinfection of water supply network, sanitation of wells) the outburst fades away and morbidity goes down drastically;

-       still, for some time morbidity remains above the sporadic level so-called epidemic tail. This is caused by the appearance of big amount of new potential sources of infection (sick people and infection carriers) during the epidemic outburst and activation of other ways of the pathogenic microorganisms spreading from these sources domestic contact (through dirty hands, dishes, children toys, personal hygiene articles), through food or by living carriers (flies) etc.

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 water

Sanitary-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.

Classification of water supply sources

Water supply sources are divided into ground and surface:

-      middle waters with pressure (artesian) and without pressure that lie in aquifers (water-bearing horizons,) (sandy, gravelled, cracked) between impermeable to water layers of soil (clay, granites), therefore safely protected from penetration of pollutants from the surface. Middle water replenishes in feeding zones places, where the auriferous stratum pinches out onto the surface, located considerably far away from the water take point. Middle waters are characterized by not very high, stable temperature (5-12), constant physical and chemical composition, steady level and considerable flow; they contain almost no microorganisms, especially pathogenic. Such waters are epidemically safe and dont require disinfection;

-      underground waters that are located in aquifers above the first impermeable layer of soil and therefore, in case of them lying not very deep, they are insufficiently protected from penetration of pollutants from the surface. They are characterized by seasonal fluctuations of chemical and bacteriological composition and level, flow that depends on frequency and number of precipitations, availability of open-air water reservoirs, depth and soil type. Getting filtrated through the 5-6 m or bigger layer of clean fine-grained soil ground waters become clear, colourless, contain almost no pathogenic microorganisms. Supplies of ground water are small, therefore, in order to use them as a source of centralized water supply, the artificial recharge (replenishment) of them using special technical facilities is required;

-      spring water, flowing out from aquifers that pinch out onto the surface due to descending relief, e. g. on the hill slope, in deep ravine.

- perched groundwater, lying next to the ground surface, is formed as a result of atmospheric precipitates filtration within a small area. Very small supplies and bad water quality do not allow recommending perched groundwater as the source of domestic and drinking water supply.

Surface waters are divided into flowing (running) waters (rivers, waterfalls, glaciers), stagnant (dead-water, still water) (lakes, ponds, artificial open water reservoirs). Their water composition depends much on the soil at the territory of water intake, hydrometeorological conditions, and varies sufficiently during the year depending on the season or even on the weather. Compared to ground waters, surface water sources are characterized by big amount of suspended substances, low clarity, higher colour due to humic substances that are washed away from the soil, higher content of organic compounds, presence of autochthonic microflora and dissolved oxygen. Open-air reservoirs can easily be polluted from outside, therefore, from epidemiological point of view they are potentially unsafe.

In some water-poor or arid areas, the imported and precipitation (atmospheric) water (rain, snow), which is stored in indoor water reservoirs or artificially filled wells, is used.

The best is the situation when quality of water in the source of water supply completely meets the contemporary criteria of the good water quality. Such water doesnt require any treatment and the only concern is not to spoil its quality at the stages of its take from the source and delivery to consumers. But disinfection of such water is the part of sanitary requirements anyway. Only some underground middle waters are like this, mostly artesian (pressure) waters. In all other cases water in the source, especially the surface water, requires quality improvement: lowering of suspended materials concentration (clearing) and colour (decolouration), getting rid of pathogenic and conditionally pathogenic microorganisms (disinfection), sometimes chemical composition improvement using special treatment techniques (desalination, softening, defluorination, fluorination, deferrization etc.). Hygienic requirements to water quality in sources of centralized water supply are given in appendix 4.

 

Sources of the surface water reservoirs pollution

The main source of pollution of surface water reservoirs are sewage waters (especially untreated or insufficiently treated water) that are created as the result of the water use in private life, industry, poultry and cattle factories etc. Partial pollution of water reservoirs occurs in the result of surface drainage of rain, storm waters and waters that appear during snow melting. Sewage waters and surface drainage add a big amount of suspended solids and organic compounds to water of reservoirs that results in more colour and water turbidity increase, clarity (transparency) lowering, oxidation and biochemical oxygen demand (BOD) increase, amount of dissolve oxygen lowers, concentration of nitrogen-containing substances and chlorides increases, bacterial insemination grows. Together with industrial wastewaters and sewage from farmlands, as it was mentioned before, various hazardous toxic chemical substances get into water reservoirs.

Water in open reservoirs may be polluted in the result of its use for transport purposes (passenger, freight shipping, timber floating), when working near river-beds (e.g., extraction of river sand), during watering animals, at sports competitions, recreation of population.

 

Self-purification (natural purification) of open-air water reservoirs

Self-purification (natural purification) of open air water reservoirs takes place in the result of various factors effect: ) hydraulic (mixing and dilution of pollutants by water of water reservoir); b) mechanical (precipitation/sedimentation of suspended solids); c) physical (solar radiation and temperature effect); d) biological (interaction of water plant organisms and microorganisms with sewage organisms that got into reservoir); e) chemical (elimination of contaminants as the result of hydrolysis); f) biochemical (conversion of some substances into other due to biological elimination, mineralization of organic substances as the result of biochemical oxidation caused by water autochthonic microflora). Natural purification with pathogenic microorganisms occurs due to their death as the result of antagonistic action of water saprophytic organisms, antibiotic substances, bacteriophages etc. In case of pollution of water reservoirs by domestic and industrial wastewaters, processes of natural purification may be stopped. Water in reservoirs becomes overgrown (vegetation burst of aquatic plants, plankton), putretaction of water.

 

Selection of the source of centralized domestic and drinking water-supply

It is based on two theses:

-       consumer supply with adequate amount of good quality drinking water (water quality in reservoir must be suitable for conversion using up-to-date water treatment methods into potable water of good quality that would meet all requirements of State Standard (2874-82, SSRandN 136/1940) currently in force);

-       control of the highest sanitary reliability of the source (selection of the source is based on assessment and prognosis of its possible pollution).

The source of centralized domestic and drinking water-supply is to be selected as follows: 1) middle water (artesian) aquifers; 2) middle water (not-artesian) aquifer; 3) underground waters, which are refilled artificially; 4) surface waters (rivers, water reservoirs, lakes, canals).

When selecting the source, water amount sufficiency for covering all needs of the built-up area is considered, water supply points (water intakes) are defined and organizational opportunities for sanitary protection zones are assessed.

Hygienic principles are assumed as the basis of selection of water- supply source; water quality requirements of ground and surface sources, selection procedure are represented in SS 2761-84 Centralized domestic and drinking water supply sources. Hygienic, technical requirements and selection guidelines.

Technique of sanitary inspection of water-supply sources

Sanitary inspection includes three main stages:

-         sanitary-topographic inspection of water source environment;

-         sanitary-technical inspection of condition of water source equipment;

-         sanitary-epidemiological inspection of area of water source location.

 

Main task of sanitary-topographic inspection of water source is to discover possible sources of water pollution (dumps, refuse pits, lavatories, livestock farms, cemeteries etc.), distances from them to water source, topography of the locality, (drain direction of rain and snow waters towards water source or in another direction, flow direction of ground waters, overflows). On the basis of sanitary-topographic inspection a map layout of positional relationship of water source and listed objects with marks of distances and direction of locality slope is created.

In most cases relationship between water source and source of pollution may be determined by research. For this purpose a saturated solution of sodium chloride or solution of fluoresceine is poured into the source of pollution (at least one bucket of mixture for every 10 m of distance towards water source), and every 3-4 hours during one or two days chlorides (or fluoresceines) are sampled in the water source.

The purpose of sanitary-technical inspection is to give a hygienic assessment of condition of technical equipment of hydraulic works at water source. Thus, in case of decentralized (local) water-supply, accuracy of allocation and exploitation of the mineshaft (availability and condition of log cabin, awning, riprap, devices for water lifting, loamy key trench); in case of centralized water-supply from ground middle water source accuracy of arrangement and condition of artesian well, water lifting pumps; in case of surface water source of diversion scoop and coastal sink. In case of centralized water-supply, sanitary-technical condition of main facilities of water-pipe, water supply network and constructions on it (namely, water-pumps).

It is of practical importance to determine the amount of water in the source of water and its discharge (output). E.g. amount of water in the well made of concrete rings with log cabin is determined by the formula:

V = π×R2×h,

where: V amount of water in the well, m3;

p - 3.14;

R radius of log cabin ring, m;

h water layer height, m.

Water height is determined by cord with weight, which is pulled down till the touch of the bottom and then a wet part of the cord is measured.

To find out discharge (output) of the well, 30-40 buckets of water are pumped out (scooped out) then the change in the level of water is marked and the time during which the previous level of water restores is fixed. Discharge (output) is calculated by formula:

D =

where: D discharge of the well, l/hour;

V volume of pumped out water, l;

t time, during which the level of water restores and time of water pumping, minutes.

River discharge is the amount or volume of water that flows through a given cross-section of a river in a given unit of time (m/sec)

Discharge (output) of a brook or a small river is calculated by formula:

D = 0.5×b×h×v,

where: D output (productivity), m3/sec;

b water flow width, m;

h water flow depth at the deepest point, m;

v flow velocity, m/sec (is determined using a float and stop-watch).

Sanitary-epidemiological inspection is aimed to discover and consider the following:

-       presence of intestinal infectious diseases (cholera, typhoid, paratyphoid , , dysenteries, virus hepatitis etc.) among population, which uses water from this source or lives close to it;

-         presence of epizootic diseases (tularemia, brucellosis, anthrax, murrain, mad cow disease (BSE) etc.) among rodents, domestic animals;

-       sanitary condition of the settlement (pollution of the territory, methods of collection and disinfection of liquid and solid domestic and industrial waste etc.).

During sanitary inspection water samples from open water reservoir, well or artesian well for further laboratory analysis are taken.

Technique of water sampling for laboratory analyses

During water sampling from open reservoir or a well the temperature of water is measured by a special thermometer (Fig. 16.1.) or by an ordinary chemical thermometer, the vessel of which is wrapped up with some layers of gauze bandage. Temperature is taken directly in the water source. Thermometer is put down into the water for 5-8 min., then it is quickly drawn up and temperature is read.

Fig. 1 Thermometer for taking temperature of water in reservoirs and wells (), bathometers for water sampling for analysis (b).

 

Water sampling from open reservoirs and wells is carried out using bathometers of different design and supplied by double cord for putting the instrument down to specified depth and for opening the cork of the vessel at that depth (Fig. 1-b).

For water sampling from flowing water reservoirs (river, brook) there is a design of bathometer with stabilizer that directs a neck of the vessel against the stream.

Water sampling from water tap or equipped catchment is carried out:

-      for bacteriological analysis. Sample is put into a sterile bottle of 0.5 l volume, with bulky cork, wrapped with paper cap from above after preliminary singeing of outlet port of the tap or catchment by spirit flame and letting water out from the tap during at least 10 min. In order to avoid bulky cork wetting, only three quarters of the bottle is filled with water to leave at least 5-6 cm of air space under the cork. The bottle with bulky cork is preliminary sterilized in drying box at 1600 during one hour;

-      for short sanitary-chemical analysis (organoleptic criteria, main indices of chemical compound and water pollution). About 1 liter of water is taken into a chemically clean glassware, which was preliminary rinsed with water to be sampled (for complete sanitary-chemical analysis 3-5 l of water are taken off).

During sampling a covering letter is written down. This letter indicates: type, name, location, address of the water source (surface water reservoir, artesian well, mineshaft, catchment, water tap, water-pump); its short specification, weather state during sampling and during last 10 days; reason and goal of sampling (regular inspection, adverse epidemic situation, population complaints about deterioration of water organoleptical properties); laboratory, to which the sample is sent; required extent of examinations (short, full sanitary-chemical analysis, bacteriological analysis, determination of pathogenic microorganisms); date and hour of sampling; research result received during sampling (temperature); who tested (surname, position, institution); signature of an official person, who took the sample.

Samples must be delivered to the laboratory as quickly as possible. Bacteriological analyses must be started during 2 hours since taking samples or in case of keeping samples in refrigerator at 1-8 at the latest 6 hours. Physical and chemical analysis is made during 4 hours after taking a sample or in case of keeping a sample in refrigerator at 1-8 at the latest 48 hours. In case of inability to perform the analysis during specified terms, sample must be preserved (except samples for physical-and-organoleptical and bacteriological analyses, and for BOD determination that must be necessarily made during terms specified above). Samples are preserved by 25% of H2SO4 - solution on the basis of 2 ml for 1 l of water or by another method depending on factors to be determined.

Taken sample comes with accompanying form, in which one indicates address details, kind of water source, where samples are directed, aim of the analysis, date and time of taking a sample, signature of an official person, which took this sample.

 

SOURCES OF WATER.

As a matter of fact all water is primarily derived from oceans. In tropical regions, evaporation of water into air is so great that it has been estimated that about 700 gallons (3182.20 litres) of water is evaporated every minute from each square mile (2.59 square kilometres) of ocean surface.

Water reaches earth in the form of rain, hail, snow, dew or mist, from water vapour in the atmosphere, derived mainly from evaporation of the sea, from lakes, rivers and other waters of the land. Sea water contains sodium chloride and land water contains lot of dissolved and suspended impurities, but it evaporates in the form of pure distilled water which reaches earth again in the form of rain, snow or hail. This condensed water from the air, which is the ultimate source of all our natural water supply, is pure except for a few impurities that are absorbed from the atmosphere.

A part of rain water on reaching earth is evaporated again into the atmosphere and a part of it percolates into the earth. Some part of it gets collected in the form of lakes, ponds etc. But a major portion of it runs away at once in the direction of natural slope of ground and gets collected in the form of small streams, which forms rivers and finally it runs again to the sea and thus the cycle goes on repeating. This phenomenon is known as Hydrolog-cal Cycle.

Sources of Water Supply.

The chief sources of water supply are:

(a)Rain water or snow water,

(b)Surface water i.e., streams, canals, rivers, lakes, tanks and ponds.

(c)Upland surface water and natural/artificial lakes.

(d)Ground water, i.e., wells and springs.

(e)Sea water.

 

Ground Water. It is superior to surface water, because the ground provides water an effective filtering medium. Water gets filtered and purified, while passing through it. Wells and springs constitute important sources of ground water.

Wells. These are artificial holes or pits dug into the earth to reach the underground water level. They constitute a very important source of water supply in Indian villages. There are four varieties of wells:

(1) Shallow Wells are those which do not penetrate an impermeable stratum. They simply tap the subsoil water, i.e., ground water lying between the surface and first impermeable stratum. The water of these wells gets pollut zd, cither from surface water or from contamination of subsoil water. Their water is moderately hard.

(2) Deep Wells are those which tap some water bearing layer below the first impermeable stratum. They may pass through one or more impermeable layers. They yield comparatively safer water for drinking purposes than shallow wells on account of efficient filtration, because their water travels a greater distance through the eai (h and also gets better protection from surface contamination by the impermeable strata above. They yield as a rule, more permanent supplies than shallow wells. The water is usually pure and germ free, but is often hard.

(3)Artesian Wells are a variety of deep wells in which water under great pressure comes out to the surface automatically. To accomplish this, the strata, which the well penetrates, must be cup shaped and the upper level of the ground water tapped between the two impervious strata must be higher than the surface of the earth, where the well lies. Thus in such a case the water shoots up. They are named after Artois province in France where they have been in use for a very long time.

Norton's Abyssinian Tube Wells are really shallow wells which are bored by simply driving iron pipes 1 1/2" to 2" (3.8 to 5 cm.) in diameter and 20-25 ft. (6.096 to 7.62 metres) deep to tap the ground water. A pump is attached to the pipe to draw the water. Chiefly they were used temporarily in the Abyssinian Campaign. Nowadays these are used where the ground water is not many feet deep below the surface of earth. These wells are of use only when a temporary water supply is required. Since water is drawn out by means of pumps, their water is free from most of the dangers manifested in open wells.

Requirements of a Sanitary Well.

Wells

A well is a hole in the earth from which a fluid is withdrawn. Water wells are the most common type. Oil and natural gas wells are also common. Mining companies also pump steam and hot water down wells to remove salt and sulphur from deep in the ground (Gunning.)

Water Wells

The underground water that flows into wells is called ground water. Most of this water comes from rain that soaks into the ground and slowly moves down to the ground water reservoir, an area of soil and rock saturated with water. The top of this zone is the water table, the level at which water stands in a well that is not being pumped (Taylor.)

In damp places, the water table may lie just below the surface. It is easily reached by digging. A dug well is usually lined with bricks, stone, or porous concrete to keep the sides from caving in. In drier places, the water table may be hundreds of feet or meters down. It may be necessary to drill the well and sink pipes. Power-driven pumps usually draw the water out of deep wells (Berger, Cossi, Taylor.)

In some areas, underground water moving down from the slopes of hills and mountains becomes trapped under watertight layers of clay or shale. Wells drilled through these layers in valleys and plains run into water under pressure. Such wells are called flowing artesian wells (Eliav, Weiss.)

Many people depend on wells for their water supply, especially in rural areas. Underground water is usually pure, because soil makes a good filter. This water generally contains dissolved minerals. A well that taps water with a high mineral content is called a mineral well (Taylor.)

Water wells should be located so that they do not collect poisons or disease germs. A well should be at least 100 feet (30 meters) from a cesspool and should never be located so that sewage drains toward it. Water from a well sunk through limestone may be dangerous because water runs through crevices and caves in limestone without being filtered. It is also important that surface water does not drain into a well.

(1) It should be tapped in a good soil and should be at least 50 ft. (15.24 metres) away from any possible source of contamination like a leaking cesspool, insanitary privy etc. The distance between the well and the houses of the users should be kept in view. If the well is situated far away, people may not use the well at all.

(2)The site should be sufficiently high to prevent entrance of water from outside into the well.

(3)It should be a deep well, i.e., sunk below the first impermeable stratum.

(4)It should be properly steined, i.e., built with bricks and lined with cement about 1 inch (2.54 cm.) thick or a watertight casting of concrete or bricks set in cement or having a metal wall, reaching below the water level, below which the joints are open to admit the water to the well. The water should only come from the bottom and not through the surface.

(5)Roots of trees should not be allowed to sprout from the linings of the wall.

(6)The space between the well wall and the lining should be sealed by cement grouting.

(7)It should be properly covered to prevent leaves and dust from blowing into it and also to prevent sparrows and pigeons making their nests in the crevices of the well wall.

(8)Around the top of the well, a parapet wall 3 ft. (0.91 metre) high should be provided, so as to prevent the surface water entering the well. The top of this well should be sloping and not horizontal to discourage people sitting on it for washing clothes thereupon and thus contaminating the well water.

(9)There should be a cemented area at least 6 feet (1.83 metres) with a fall away from the well, so that the surface washings may run away from it and not into it.

(10) It is best that no washing of clothes, utensils and bathing of persons be allowed near a well, as it is not uncommon for a well to get infected by washing clothes, etc., of patients suffering from cholera and other diseases. The best way to avoid this practice is to provide a proper washing and bathing place at a distance from the well to which water can be pumped by means of channels.

(11)All hollows, rat holes, foul tanks, cesspits etc. near the well should be filled up and useless trees and vegetation cut down.

(12)It is best to have a hand-pump or any other mechanical contrivance for drawing up the water in a sanitary manner, which should be discharged by a pipe ending at some distance from the well, so that no water after any possible contamination, can run back to the well. In the absence of any provision of such a mechanical contrivance, it is desirable that a bucket and a chain for public use should be attached to the well permanently.

Fig.. A properly protected well.

1. Cemented brick work.

2. Puddled clay.

3. Platform

4. Cover

5. Channelled drain.

 

 

 

Qualities of Well Water. For all intents and purposes it is an excellent water. The bacterial count is very low. It is generally free from pathogenic agents. It is cool and sparkling due to the dissolved carbon dioxide of the ground air.

Cleansing of Well. This is done at the close of hot weather, when the water is at its lowest level. The well must be dewatered.

The sides of the well are scraped and all mud, silt, stones or pieces of bricks, which block the pores of bottom of the well, are removed. Subsequently, the well is treated with a solution of 1 part of freshly prepared

slaked lime to 4 parts of water or bleaching powder, or potassium permanganate solution.

Examination of Wells.

The following points should be borne in mind while examining a well:

(1)Size and depth of the well.

(2)Depth of water in the well.

(3)Nature of soil in which the well is sunk.

(4)Any possible sources of pollution within 200 to 350 ft. (60.96 to 106.68 metres) of the well. Practical aspects are discussed subsequently.

(5)Average quantity of water which is daily drawn out.

(6)The way in which water is disposed off.

(7)Mechanical contrivance, with which water is drawn put, e.g., pump, rope and bucket etc.

(8)Whether there are cracks and fissures on the sides or not.

(9)Whether the mouth of the well is closed or open.

Detection of Sources of Pollution of a Well.

If a source of contamination is suspected in the neighbourhood of a well, it is detected by pouring certain chemicals which may be recognised on account of their characteristic smell, taste, colour and other chemical and physical properties into all the pools, drains etc., which may be regarded as possible, sources of pollution. The following methods of examination may be adopted:

(1)    By adding a strong solution of sodium chloride and detecting the increase in the amount of chlorides in well water by titrating with a standard solution of silver nitrate using potassium dichromate as an indicator.

(2)    By adding alkaline solution of fluorescein (1 lb.or 0.453 kgm. of fluorescein and 1 lb. or 0.453 kgm. of caustic soda) to 10 gallons (45.50 litres of water) and detecting the fluorescein in well water by means of a' fluoroscope.

(3)    Suspension of bacillus prodigiosus (viz., culture of chromo-bacterium prodigiosum) may be added and subsequently red colonies grown and ultimately isolated from the water.

(4) Kerosene oil may be poured and its smell and tinge detected in well water.

Yield of a Well. At first lower the level of the well water by pumping and notice the rise of water in it at intervals of 15-30 minutes.

The quantity of water in a well can be measured by the following formula:

Depth of water in feet X square of diameter of the well in feet x 5 = gallons of water.

Tube Wells. These are cheap in comparison to other sources of water supply and yield water, which is bacteriologically safe. These consist of lengths of iron tubing driven deep into ground up to the desired length. Firstly, a hole is made into the soil about 5-6 feet(1.52 to 1.83 metre) deep and first part of the tube having a perforated steel point at its lower end is hammered in. Subsequently, successive lengths of tubes are driven deep into the soil, one length being screwed into the other, till the sub-soil water is reached. In this case water is drawn by means of a pump. Tube wells form a rapid means of obtaining ground water and are comparatively more sanitary than dug wells.

Deep Tube Wells. These are largely used for municipal water supply and also for irrigation purposes. The average yield of a deep tube well of 1 to 1 1/2" (2.5 to 3.8 cm.) diameter is 200-300 gallons (909.20-1363.80 litres) and of 9" (22.86 cm.) diameter is 60,000 gallons (272,760 litres) of water per hour. The yield mainly depends upon the water bearing strata and a little on the diameter and depth on the tube well.

These are sunk through hard surfaces by boring through rocks with special machines. The depth is between 300-400 ft. (91.44 to 121.92 metres) and the characteristics of water are like deep well waters. In many towns, the water supply is now obtained from these tube wells.

The water obtained is free from bacteria. It does not show faecal bacilli in 60 c.c. The water is hard due to presence of calcium carbonate and sodium chloride in variable quantity, traces of iron, etc. The greater the depth from which the water is obtained, the more likely is the higher percentage of its mineral contents. While operating, limitation of their working speed must be kept in view, as they silt up if their rate of pumping exceeds the critical velocity.

Critical Velocity. The water flows through the filtering medium of sand outside the strainer of a tube well, without disturbing the sand bed. But if the rate of pumping is rapid or excessive, the water carries sand grains with it and the velocity at which this disturbance starts is called "Critical Velocity".

Cone of Influence. With the drawing of water the level in the well falls, resulting in a tendency, of the water flow into it from surrounding area. The area within which the level is appreciably lowered is called the "Circle or Cone of Influence".

Springs. These are natural outlets of ground water which is under pressure, due to the approach of the first impermeable stratum of the surface. These can therefore be considered as natural wells cropping up at places where the geological conditions are favourable.

Varieties of Springs.

(1)   Surface Springs or Shallow or Land Springs. These are outlets of limited collection of ground water resting on the superficial impervious strata. .They are of intermittent nature, supplying water when the level of subsoil water is high, as during rains, and ceasing to flow in summer season (May-June) and starting again in autumn on commencement of percolation. They are an unsatisfactory source of water supply.

(2)   Deep or Main Springs. They derive their water supply from extensive water bearing strata. The water of these springs is clear, sparkling and is generally safe, having been filtered in its passage through the earth, and the flow is also constant. The water is often hard. These springs have no surface outlets but issue through a fissure or a crack in the soil.

Ordinarily spring water is pure and less liable to contamination, since there is no mechanical means to draw out the water. It is generally cool and palatable, but is highly charged with carbonic acid gas, which it absorbs from the ground. Moreover, on account of passing under pressure, it dissolves out lime and various other mineral salts contained in the soil through which it passes. Consequently, it gets hard and becomes unsuitable for washing and cooking purposes, although it may be valuable from the medicinal point of view.

(3) Hot or Tliennal Springs. These result from continuance of high internal temperature after a volcanic eruption has ceased. They continue to maintain their heat even for centuries. These springs may arise in places even hundreds of miles away from the actual volcanic vent. As examples may be mentioned springs of Sitakoond (in Chittagong), Rajgir (in Bihar) Vajreswari (50 miles, i.e. 80.47 kilometres from Bombay) in India, springs of Bath and Buxton in England, and Yellowstone Park in U.S.A.

(4) Mineral Springs. The water of mineral springs is highly charged with minerafsalts and so used for medicinal or therapeutic purposes. There are also Sulphur Springs which contain sulphuretted hydrogen and various sulphides in solution. Water containing iron or magnesium in solution is known as Chalaybeate or Magnesia Water.

Yield of a Spring. It can be determined by:

(1)    Finding out the time, which it takes to fill a vessel of known capacity. The output of water in one hour can thus be determined.

(2)    By leading the entire flow of spring over a V or a rectangular notch and measuring the depth of flow over the side of notch. The yield of a spring can be calculated from charts and different formulae.

Safeguards against Pollution of Springs.

The sources of pollution such as leaking cesspits, insanitary privies, latrines and stables etc., should not be situated near the springs. The springs should be protected by a masonry structure, which should extend deep into the ground to protect against surface contamination.

(e) Sea Water.

Distilled sea water is used for drinking purposes, on board ships and in places like Aden, where wells happen to be brackish and rain does not fall even for several years. Distilled water is flat to taste as all gases are driven out of it by boiling and it is consequently unpalatable. So aeration of water should be done by allowing it to trickle down through a long column of wood charcoal, if it is required for drinking purposes. As sea water acts on lead, copper, zinc and iron, none of these metals should be exposed to its action in the condensing apparatus. Silver and tin linings are the best choice for pipes and vessels used for making distillation apparatus.

 

DETERMINATION OF HARDNESS OF WATER.

What is "Hard Water"?

Perhaps you have on occassion noticed mineral deposits on your cooking dishes, or rings of insoluble soap scum in your bathtub. These are not signs of poor housekeeping, but are rather signs of hard water from the municipal water supply. Hard water is water that contains cations with a charge of +2, especially Ca2+ and Mg2+. These ions do not pose any health threat, but they can engage in reactions that leave insoluble mineral deposits. These deposits can make hard water unsuitable for many uses, and so a variety of means have been developed to "soften" hard water; i.e.,remove the calcium and magnesium ions.

Problems with Hard Water

Mineral deposits are formed by ionic reactions resulting in the formation of an insoluble precipitate. For example, when hard water is heated, Ca2+ ions react with bicarbonate (HCO3-) ions to form insoluble calcium carbonate (CaCO3), as shown in Equation 1.

This precipitate, known as scale, coats the vessels in which the water is heated, producing the mineral deposits on your cooking dishes. In small quantities, these deposits are not harmful, but they may be frustrating to try to clean. As these deposits build up, however, they reduce the efficiency of heat transfer, so food may not cook as evenly or quickly in pans with large scale deposits. More serious is the situation in which industrial-sized water boilers become coated with scale: the cost in heat-transfer efficiency can have a dramatic effect on your power bill! Furthermore, scale can accumulate on the inside of appliances, such as dishwashers, and pipes. As scale builds up, water flow is impeded, and hence appliance parts and pipes must be replaced more often than if Ca2+ and Mg2+ ions were not present in the water.

Some Strategies to "Soften" Hard Water

For large-scale municipal operations, a process known as the "lime-soda process" is used to remove Ca2+ and Mg2+ from the water supply. Ion-exchange reactions, similar to those you performed in this experiment, which result in the formation of an insoluble precipitate, are the basis of this process. The water is treated with a combination of slaked lime, Ca(OH)2, and soda ash, Na2CO3. Calcium precipitates as CaCO3, and magnesium precipitates as Mg(OH)2. These solids can be collected, thus removing the scale-forming cations from the water supply.

To see this process in more detail, let us consider the reaction for the precipitation of Mg(OH)2. Consultation of the solubility guidelines in the experiment reveals that the Ca(OH)2 of slaked lime is moderately soluble in water. Hence, it can dissociate in water to give one Ca2+ ion and two OH- ions for each unit of Ca(OH)2 that dissolves. The OH- ions react with Mg2+ ions in the water to form the insoluble precipitate. The Ca2+ ions are unaffected by this reaction, and so we do not include them in the net ionic reaction. They are removed by the separate reaction with CO32- ions from the soda ash.

Household water softeners typically use a different process, known as ion exchange. Ion-exchange devices consist of a bed of plastic (polymer) beads covalently bound to anion groups, such as -COO-. The negative charge of these anions is balanced by Na+ cations attached to them. When water containing Ca2+ and Mg2+ is passed through the ion exchanger, the Ca2+ and Mg2+ ions are more attracted to the anion groups than the Na+ ions. Hence, they replace the Na+ ions on the beads, and so the Na+ ions (which do not form scale) go into the water in their place.

Unfortunately, many people with high blood pressure or other health problems must restrict their intake of sodium. Because water softened by this type of ion exchange contains many sodium ions, people with limited sodium intakes should avoid drinking water that has been softened this way. Several new techniques for softening water without introducing sodium ions are beginning to appear on the market.

Determination of hardness of water.

Salts of calcium and magnesium such as carbonates, bicarbonates, chlorides and sulphates condition total hardness.

Hardness in water is expressed in terms of milli-equivalents per liter (mEq/L). One mEq/L of hardness production is equal to 50 mg CaCO3 in one liter of water.

If the hardness is to 3,5 mEq/L so water is soft, from 3,5 -7,0 mEq/L water of middle hardness, more than 7,0 mEq/L hard and more than 14 mEq/L very hard. Very hard water is unsuitable for hygienic needs temporary dyspepsia can occur by the sharp change of soft water to hard one. The etiological role of hard water for the occurrence of urinary stones isn't proved but some authors consider that the use of hard water especially in hot countries can provoke the development and growth of urinary stones.

The epidemiological investigations in England, the USA, Japan and other countries show the opposite dependence on water hardness and the mortality from cardio-vascular diseases. The artificial increase of hardness in some regions had positive consequences as the artificial softening had negative results. The mechanism of protective action of hard water isn't known. It is a result of the presence of calcium, magnesium or some other microelements (fluorine) or the absence of some matters. Now, the scientists put down the protective role to calcium, which together with magnesium is a component of myocardium enzyme system and regulates electrolyte balance. If calcium level in blood decreases the changing of QT interval in ECG - it becomes longer, it's risky for the arrhythmia, and the risk of sudden death increases. The level of calcium is decreased in the blood serum of people, using soft water. Calcium of nutrient matters is assimilated only for 30 %; but calcium of drinking water - for 90 %.

According to IDWS-73 the recommended hardness of water is 2 mEq/L so the MAC is 10 mEq/L. However, nowadays, the optimum hardness should be 5-7 mEq/L, calcium content - 150 mg/l and magnesium can form a special taste and provoke the irritation of the intestines and the increase of peristalsis. If water contains to 250 mg/l of sulphates, the admissible magnesium concentration is to 150 mg/l. But, if the concentration of sulphates is higher, magnesium content mustn't exceed 30 mg/l.

Hardness of natural waters is caused largely by calcium and magnesium salts and to a small extent by iron, aluminum, and other metals.

Practically there are three kinds of hardness: general, permanent (or residual) and temporary.

http:// library.thinkquest.org/C0115522/article.php?q...

General hardness is the hardness of unboiled water, which is onditioned on all of the compounds of Calcium and Magnesium (sometimes Iron and Manganese), independently of what anions are linked with these cations.

Hardness resulting from the bicarbonates and carbonates of calcium and magnesium is called temporary hardness and can be removed by boiling, which also sterilizes the water.

Permanent (or residual) hardness is the hardness of water after the one-hour boiling, which depends on presence of different salts, which dont leave sediment during boiling. Mainly it is sulphates and chlorides of Calcium and Magnesium. The main technical meaning has the sulfuric Calcium, which leaves the sediment during the evaporation of great quantity of water in one and the same capacity (for example, steam-boiler) in the form of the thick layer of scale. These could bring to the explosion of the boiler.

The residual hardness is known as noncarbonate hardness. The methods of softening noncarbonate hardness include the addition of sodium carbonate and lime and filtration through natural or artificial zeolites, which absorb the hardness-producing metallic ions and release sodium ions to the water. Sequestering agents in detergents serve to inactivate the substances that make water hard. Residual hardness is the hardness of water, which is removed during boiling. This is explained by the destruction of bicarbonates of the Calcium salt Ca (HCO3)2 less Magnesium Mg (HCO3)2, and sometimes also Iron Fe (HCO3)2, their transformation in the insoluble carbonic salts (monocarbonates), which leave the sediment on the walls of capacity in the form of scale (CaCO3 , MgCO3 ). Thats why; disposable hardness is the part of the general hardness, which we could find by the difference between the general and the constant hardness.

Ca (HCO3)2 + Ca (OH)2 → 2CaCO3 + 2H2O

There is one more kind of hardness of water. It is the carbonate hardness, which is conditioned on the presence the bicarbonates of the Calcium, Magnesium, Potassium nd Sodium salts in water. It is usually coincided with the temporary hardness, but equate one to another impossible. While boiling removed part of carbonate hardness, which is depended on Calcium bicarbonate. In condition of great quantity of Magnesium carbonate in water the difference between the carbonate hardness and the temporary hardness may be great enough. General hardness is normable, but the practical interest has also the temporary hardness. For example when we choose the dose of the sulfuric Aluminium while coagulation of water.

www.sawater.com.au/SAWater/Education/OurWater...

Determination of water could be done by weight and volumetrical methods.

The general hardness of water calculate by formula

X = a x K x 0,1 x 1000 / V

Where: a-amount trylon B, which was used for titration

0,1 normality of solution of trylon B

K corrective coefficient of trylon B

V volume of water, which investigated, cm3

Advantages of hardness of water:

a. Low incidence of C.V.S. diseases.

b. Prevents lead poisoning.

Disadvantages of hardness of water

a. Domestic disadvantages such as consumption of more soaps and detergents. Unfit for washing clothes. Unfit for cooking.

b. Industrial hazards hard water unfit for certain processes.

c. Agricultural hazards hard water unfit for irrigation.

d. Fabrics washed in hard water do not have long life.

e. Hardness shortens the life of pipes and fixtures.

Removal of hardness

I Temporary Hardness

a. Boiling

b. Addition of lime

c. Addition of sodium carbonate

d. Permutit process

II. Permanent Hardness

a. Addition of sodium carbonate

b. Permutit process/ Base exchange process.

Boiling:

It removes temporary hardness by expelling carbon dioxide and precipitating the insoluble calcium carbonate.

Ca (HCO3)2 CaCO3 + CO2 + H2O

Addition of Lime:

It removes temporary hardness. Lime absorbs carbondioxide and precipitates the insoluble calcium carbonate.

Ca (OH)2 + Ca (HCO3)2 →2CaCO3 + 2H2O

Addition of Sodium Carbonate,

It removes both temporary and permanent hardness.

Na2CO3 + Ca (HCO3)2 2NaHCO3 + CaCOs

Na2CO3 + CaSO4 Na2SO4 + CaCO3

 

Base Exchange Method

In this method sodium permutit is used, which is a combination complex of Na, Al and Si (Na2 Al2 Si2OH2O)

Sodium permutit has property of exchanging the sodium cation for Ca++ and Mg++ ions in water.

Na2 Al Si2O + H2O = Mg++/Ca++

When hard water passed, sodium permutit exchanges Mg/ Ca and is converted into calcium and magnesium permutit.

With time permutit loses effectiveness, it is regenerated by adding conc. sol of NaCI.

* By this process hardness of water is removed to zero. As zero hardness is corrosive, therefore a part of raw water is mixed with softened water.

 

The examination and sanitary estimation of water supply source.

At impossibility of their use it is necessary to use other sources of water in the next order:

        Artesian water or interlayer water with pressure;

        interlayer water without pressure;

                subsoil water;

                not regulated drainage, lakes;

        water from reservoirs with regulated drainage (rate, reservoirs etc).

Thus, it is considered, that the best source of drinking water is artesian water.

The underground and superficial waters can be used for water supplying. For installation of their suitability the sanitaryandtopographic and sanitary-and-technical examination must be conducted, we have to learn the epidemiological situation, to select assay, to make the laboratory analysis of water.

While using opened reservoir it is necessary to follow the rules:

1)      use bigger reservoir with constant flow of water;

2)      protect reservoir from the pollution by sewer and industrial waters and pesticides;

3)      disinfection the water. Often, except disinfection, it is necessary to purify the water from suspended particles and coloring and, in some cases, from toxic substances.

Lately opened reservoirs are used for the water supply with the usage of water pipe. It is explained by the development and modernization of techniques of clearing and disinfections of water and by increase of water consuming by big modern cities.

To summarize the said above, first of all use artesian waters as the source of water supply. In case of impossibility to use artesian waters, other sources should be found.

Because of enlargement of cities, villages, development of economy and raising of cultural inquiries of the population the consumption of water increases with each year. While choosing a water source for water supply its output and quality of water, and, also stability of parameters, which characterize its reliability that is determined by its origin and conditions of formation of water quality, and also character and intensity of its pollution are taken into consideration. Thus at the organization of the water supply, it is necessary seriously enough and competently to estimate all sources of water and opportunity of their use. For the decision of this task it is necessary: to reveal all local water resources and to determine how much water can they give to supply the population with drinking water according to the hygienic norms. It is necessary to take into consideration the prospects of development of the settlements and their conveniences. Quantity of water can have the main influence on a choice of a water source. Nevertheless at all variety of sources it is possible to point on their new debit. Debit of artesian boreholes is equal on the average 10 - 18 m3/h. Debit of water shafts, which are supplied by subsoil waters, is equal on the average 1,5 - 6,5 m3/day. The comparison of these sizes shows that opportunities of reception of great quantities of water from underground sources are limited.

The population should be provided not only with enough of water, but also with qualitative water. Water should not cause any pathological change in the organism, should not cause of spread of infectious diseases, and also not to cause unpleasant sensations.The estimation of quality of water is carried out under two standards: the demands to a source of water and demand to quality of drinking water at centralized water supply. But, not always it is possible to find out a source of water in which water meets the standard requirements on the drinking water and that is why frequently we have to use less qualitative source in the sanitary attitude, but they should satisfy next demands:

1) water must have such composition and such properties which can be improved by modern methods of processing;

2) intensity of pollution, that are subject to elimination, should correspond to efficiency of water processing methods;

3) natural and the local sanitary conditions should ensure reliability of a water source in the sanitary attitude.

While choosing a source it is necessary to prefer to subsoil water because (1) they in much or less degree are protected by layers of soil from pollution from a surface and (2) their positive physical properties and small content of bacteria are created by a natural way due to a filtration through layers of soil and more deeply placed layers, that deprives from necessity of difficult and expensive systems of clearing. Besides the water can be taken in borders of the settlement or near.

The most serious water pollutants of human health worldwide are pathogenic organisms. The main source of these pathogens is from untreated or improperly treated human wastes. Animal wastes from feedlots or fields near waterways and food processing factories with inadequate waste treatment facilities also are sources of disease causing organisms.

Detecting specific pathogens in water is difficult, time-consuming, and costly; thus, water quality control personnel usually analyze water for the presence of coliform bacteria, any of the many types that live in the colon or intestines of humans and other animals. If large numbers of these organisms are found in water sample, recent contamination by untreated feces is indicated.

Sanitary-and-topographic examination gives the analysis of the relief of terrain and features of soil, detection of possible sources of contamination of water, availability of the organized and random dumps, garbage.

Sanitary-and- technical examination set sanitary state of water sources and its possible influencing on quality of water (availability of the clay lock, the enclosure around the well, cover, lid, general bucket, place for cattle watering and its technical state).

Selection of assay of water for further laboratory research is carried out into clean glass or plastic carboys by volume 5 L (for integrated analysis) or 2 L (for the shortened analysis). Before selection of assay of water we must rinse the carboy not less two times with investigated water. The water is stuffed up to the top; we drain the upper layer so that the small interlayer of air was under the fuse. For each assay the accompanying document is made in which we indicate date of scooping of assay, the name of water source, the place of its presence, time and place of sampling, meteorological condition, temperature of water, manifesting sources of contamination, the aim of research, the profession and signature of face which one sampled.

The zone of sanitary preservation of water reservoir is a definite site of terrain around water source and main waterways. The special mode is established here with purpose of warning bad changes of quality of water. The zone of severe mode (the maiden belt) is the site of scooping of water and main facilities of aqueduct: water-bearing stations, water-cleaning stations, and reservoir of clean water. This terrain is an enclosure to protect the access is strictly forbidden.

The zone of limitation (second belt) includes terrain around water storage and its influx and is diffused upstream sometimes to tens km, downwards to tens meters. This zone depends from degree of contamination and ability to self- purification. The use of water sources is authorized only in retracted places.

The observation zone includes terrain on which one the overseeing of contagious infection. For closed underground sources of water facilities this zone is not implanted.

Hygienic standards of drinking water quality

Index

CIS ( 2874-82) of Ukraine

Highest desirable level

WHO (1986)

Highest desirable level

Transparency

30 cm and more for reading of Snellen's print

-

Smell and taste

< 2 number

1-2 number

Colourity

not more than 20 (35) degrees

15 units of the colority

General hardness

7 mg eq/l (to 10 mg eq/l for some cases)

2 mg-eq/l (100 mg/l Ca CO3)

(MAC is 10 mg-eq/1 (500 mg/l Ca CO3))

Turbidity

not more than 0,5 (1,5) nephelometrical units

5 nephelomeric units of turbidity

pH

6,0 9,0

7,0 to 8,5 (MAC 6,5 to 9,2)

Dry residuum

100 mg/dm3 to 1000 mg/dm3

1000 mg/l

Chloride (as Cl)

not more than 250 (300) mg/dm3

250 mg/l

Sulphates (as SO4 )

not more than 250 (500) mg/dm3

400 mg/l

Iron ( total as Fe)

0,3 mg/dm3

0,3 (1.0) mg/l

Fluorine F

0,7-1,5 mg/dm3

1,5 mg/l

Nitrates NO3-

45 mg/dm3

10 (by the nitrogen)

NH4

0,1 mg/dm3

 

NO2-

0,002 mg/dm3

-

Oxidizability

< 4 mg O2/dm3

-

Radioactivity:

General α-activity

General β-activity

 

0,1 Bq/l (Becquerel/dm3)

1,0 Bq/l

 

3 pCi/l

30 pCi/l

Index coliform bacteria

not more 3 CFU/dm3

 

General microbe index

Not more 100 CFU/ cm3

 

Number of stable to temperature intestinal rods

miss CFU/100cm3

 

Number of the pathogenic microorganism

miss CFU/dm3

 

Number of coliphages

miss CFU/dm3

 

 

Sampling of water

For physical and chemical examination, about 2 litres water is essential. It must be collected in a clean glass stoppered bottle made of neutral glass. Before collecting the sample rinse the bottle well three times with the water filling it each time, about 1/3 full. For bacteriological examination about 300 ml water is required. It must be collected in clean sterilized bottle made of neutral glass, provided with a ground glass stopper having an overlapping rim. If the water to be sampled contains or is likely to contain chlorine, a small quantity of sodium thiosulphate is added to bottle before sterilization.

A. Sampling from Tap

If sample is taken from a tap in regular use, the tap should be opened fully and the water run to waste at least for 2 minutes in order to flush the stagnant water in nozzle and pipe. If sample is taken from tap not in regular use, the tap should be sterilized by heating it till it is red hot. Then allow water to run to waste for one minute and then collect sample.

B. Sampling from a well:

Tie a sample bottle with a rope. Use a stone or piece of metal weighing about 500 gm as "the weight and attach the tube bottle just above it. After removing the cap aseptically, lower the bottle into the well into the well to a depth of 1m. When no more air bubbles rise to the surface, raise the bottle out of the well and carefully replace the cap.

C. Sampling from stream.

Water is taken from middle of a stream, with the mouth of the bottle facing upstream, lower the bottle into the stream and allow filling. Tilt bottle upwards to fill completely. The cap is carefully screwed back, taking care not to touch the screw thread at the top of the bottle.

After taking sample following information must be given with bottle.

a. Source of water supply

b. Date, place and time of sampling

c. Geological formation of soil, if available.

d. In case of well, its depth, diameter and how it is used.

e. Recent rainfall if there.

f. Any suspected source of pollution in vicinity

g. Whether any method of purification is used.

 

 

HYGIENIC ESTIMATION OF CHLORINATION OF WATER BY NORMAL DOZES .

METHODS OF WATER CLEARING, DECONTAMINATING OF WATER CENTRALIZE AND DECENTRALIZE OF WATER SUPPLY

Water pollution involves the release into lakes, streams, rivers, and oceans of substances that become dissolved or suspended in the water or deposited upon the bottom and accumulate to the extent that they interfere with the functioning of aquatic ecosystems. It may also include the release of energy in the form of radioactivity or heat, as in the case of thermal pollution. Any body of water has the capacity to absorb, break down, or recycle introduced materials. Under normal circumstances, inorganic substances are widely dispersed and have little or no effect on life within the bodies of water into which they are released; organic materials are broken down by bacteria or other organisms and converted into a form in which they are useful to aquatic life. But, if the capacity of a body of water to dissolve, disperse, or recycle is exceeded, all additional substances or forms of energy become pollutants. Thus, thermal pollution, which is usually caused by the discharge of water that has been used as a coolant in fossil-fueled or nuclear-power plants, can favour a diversity of aquatic life in waters that would otherwise be too cold. In a warmer body of water, however, the addition of heat changes its character and may make it less suited to species that are considered desirable. Pollution may begin as water moves through the air, if the air is polluted. Soil erosion adds silt as a pollutant. The use of chemical fertilizers, pesticides, or other materials on watershed lands is an additional factor contributing to water pollution. The run of from septic tanks and the outflow of manures from livestock feedlots along the watershed are sources of organic pollutants. Industries located along waterways downstream contribute a number of chemical pollutants, some of which are toxic if present in any concentration. Finally, cities and towns contribute their loads of sewage and other urban wastes. Thus, a community far upstream in a watershed may receive relatively clean water, whereas one farther downstream receives a partly diluted mixture of urban, industrial, and rural wastes. The cost of cleaning and purifying this water for' community use may be high, and the process may be only partially effective. To add to the problem, the cities and towns in the lower, or downstream, regions of the river basin contribute additional wastes that flow into estuaries, creating new pollution problems.

library.thinkquest.org/C0115522/article.php?q...

Natural settling is realized in the horizontal settling tanks the reservoirs with the depth about some meters. Water moves very slowly there, its speed doesn't exceed 0.15m/s. Water stays there for 4-8 hours, and previously coarse suspended particles are sedimented. The settling for 3-7 days is used in hot countries. During that time little particles, the significant part of absorbed matters and microorganisms are sedimented. If schistosomosis is widespread in this region, water must be in the settling tanks for about 3 - 4 days. This pathological agent dies in 48 hours, if it doesn't get into human or animal organism. So, the preservation of water for 2 days in the settling tank, free of mollusks, is a reliable method to prevent the spread of schistosomosis. The tank should contain the walls higher than the ground, and a screen made of galvanized net with the cells not more than 3mm to detain molluscs. These conditions are very important, as cercaria are stable for the disinfection by chlorine. After the settling water is passes through the slow filter to be lightened completely. It is a brick or concrete reservoir. There are drainages from concrete slabs or drainage tubes with the openings. The suspending layer of detritus and gravel of 0.7 m in the thickness is placed above the drainage. Above it there is one meter layer of sand, the diameter of its granules is 0,25 0,5 mm. Then, they pass water through it with the speed not more than 0,1 m/hour.

THE DISINFECTION OF WATER

The disinfection is one of the most usable methods of water improvement. Usually it is a concluding and very important stage. The most spread methods of disinfection are different methods of chlorination. Sometimes ozonization and UV-irradiation use also.

The chlorination of water is one of the most spread methods and it is of great importance for the prophylaxis of water epidemics. It is explained by the reliable disinfection, accessability and cheapness.

The principle of chlorination is based on the treatment by chlorine or the chemical compounds, containing active chlorine and able to oxidize and provoke bactericidal action. Chlorine is subjected to hydrolysis in water:

Cl2+HOH → HOCl+HCl, so hydrochloric and chloricious acids are formed. Chloricious acid takes the central place in the mechanisms of bactericidal action. It was thought earlier that the latter was destroyed in water and discharged out atomic oxygen (HOCl → HCl+O), which was the main bactericidal agent. Now, such explaination is considered insufficient. Chlorine in the structure of chloricious acid and hypochlorite-ion (HOCl→H +OCl ) free active chlorine, which determines bactericidal action in water. Not large molecules and electric neutrality let chloricious acid penetrate quickly through the bacterial membrane and influence upon the cellular enzymes, important for the metabolism and reproduction. It is assumed, that it reacts with SH-groups of enzymes, which become oxidized.

The reliable bactericidal effect of chlorine is achieved, if about 0,3 0,5 mg/l of free chlorine or 0,8 1,2 mg/l of connected chlorine are left in water after 30 - 60 min. of exposure.

There are 2 stages of chlorine action upon viruses: first, chloricious acid and hypochlorite-ion are absorbed in the viral membrane and penetrate through it, the second stage is an inactivation of viral RNA. Virocidal effect is the most expressed by the low pH.

Sanitary control of water pipes includes the determination of the remaining chlorine in water every hour, and the bacteriological investigation - not rare than once a day.

Long-term experience of using such method in almost all countries of the world is evidence of chlorinated water safety for use. However, lately, the safety of such water has been disputed owing to the following facts. There was found a trustworthy connection between the concentration of chloroform (carcinogenous matter) in the tap water and the level of mortality from cancer of people, who had used such water. Further studies showed, that different chlor-organic compounds (chloroform, tetrachlorethylene, etc) and polychlorinated biphenyls had often been met in the water of open reservoirs very polluted by sewers.

Nevertheless, chloroform and other chloroorganic compounds can be formed in small quantities during the chlorination of water. All these facts necessitate improvement of water treatment by the following methods: better purification of water before chlorination, the use of necessary doses in minimum quantities, the use of chlorination with the preceding preammonization, filtration of chlorinated water through the filtres with the activated coal, which absorbs chloro-organic compounds. It is admissible to aerate water in the small water-pipes. As a result 90% of chloroform and other volatile compounds are removed.

Gaseous chlorine, preserved in the steel containers, is used to chlorinate water in the large water pipes. A special apparatus chlorator, which measures chlorine input to water, is added to the container.

Chloric lime (3Ca(ClO)2*CaO*H2O) is used for the small water-pipes and other reservoirs. Its bactericidal effect is determined by OCl-group, which forms chloricious acid in water. Chloride of lime contains up to 33% of active chlorine.

Chlorine dioxide (ClO2), calcium hypochlorite - Ca (OCl)2, containing 60-70% of active chlorine, and different chloramins (organic and inorganic) are also used for the disinfection. Calcium hypochlorite is more stable than chloride of lime and that's why it is recommended for hot countries. However, during the storage in the tropical sun, there were some explosions of containers. Oxidizing and bactericidal features of chloramins are inferior to that of chlorine and chloric lime.

Simple chlorination (by chlorine request). Right choice of the dose is of great importance for the reliable disinfection. Only about 1 2 % active chlorine are spent on the bactericidal action during the disinfection. The rest part is spent on oxidation of organic and inorganic matters in water. All these connected forms of chlorine form such a notion as "chlorine-absorbability of water". Different natural waters have different chlorine-absorbability. To disinfect water by such a method, they introduce such amount of chlorine, that the remaining free chlorine should be 0,3 - 0,5 mg/l and the remaining chlorammoniac chlorine 0,8 - 1,0 mg/l. In such a case the organoleptic features of water do not become worse.

The number of active chlorine (mg), necessary for the disinfection of 1 liter of water, is called chlorines need of water (chlorine-request). It is determined by the experimental chlorination of certain volume of water, subjected to disinfection.

Besides the correct dose, good mixture and sufficient contact of chlorine with water are necessary for the effective disinfection.

The presence of suspended matters, gumines and other organic compounds in water lowers the action of chlorine. That's why it is necessary to light and decolourize turbid and colored waters before disinfection.

The chlorination of water by chlorine-request reliably disinfects water from the intestinal infections (typhoid fever, dysentery, cholera, patogenous strains of E.coli, salmonellas), brucellosis, tularemia, leptospirosis. There are some disputes about the polio virus. Many scientists consider, that this virus is inactivated by the chlorination for an hour. Water, containing Berket's rikketsia, amoebic cysts, worm eggs and the spores of some types of anthrax, cannot be disinfected by this method.

 

The definition of the contents of active chlorine in the chlorine combinations.

The method is based on the ability of active chlorine to supersede the equivalent quantity of iodine from a solution of potassium iodide. Ousted iodine is being titrated by hyposulfite.

For the analysis prepare average test of the lime chloride by careful hashing of several tests taken from different places of a vessel with lime chloride. Then 3,55 g of average test of the chloride of lime is being pounded with small quantity of distilled water, and then leads up in measuring flask by distilled water up to 1L, where it is being left up to the enlightenment.

In measuring flask to 50 ml of distilled water add 10 ml of the clarified solution of the lime chloride, 5 ml of 10% solution of potassium iodide and 5 ml of a solution of a hydrochloric acid (1 : 5). In 5 minutes ousted iodine is being titration by 0,01normal solution of hyposulphite before occurrence of pale yellow coloring, then add 1 ml of 0,5% solution of starch and continue to titration till the disappearance of dark blue coloring. 1 ml of 0,01normal solution of hyposulphite connects 1,269 mg of iodine, which corresponds to 0,355 mg of chlorine. The quantity of 0,01normal solution of hyposulphite Na (ml), spent on titration, corresponds to the percentage contents of active chlorine in a researched sample of the lime chloride.

It is inexpedient to use lime chloride with the contents of active chlorine less than 20% for the decontamination of water.

 

Definition of the chlorines need of water in chlorinate.

In the field conditions the choice of the doze of chlorine will be carried out by a three-glass test. 2 drops, 4 drops, 6 drops of 1 % solution of the lime chloride bring by a special pipette (1 ml = 25 drops) to three glasses with 200 ml of water accordingly. After that mix and leave for 30 minutes. Then to each glass add 5 ml of 10 % solution of potassium iodide, 5 ml of a solution of hydrochloric acid (1:5) and 1ml of 0,5 % solution of starch. The occurrence of light-blue coloring testifies to presence of residual chlorine at the researched water.

For definition of quantity of residual chlorine the researched water is being titrated by 0,01normal solution of hyposulfite till the disappearance of colouring. The content of residual chlorine (mg/l) in researched water one can define by using this formula:

= 0,355 x x x 5,

Where a - the quantity of 0,01normal solution of hypo sulfite spent on titration of 200 ml of water, ml;

- correction factor to a titer of hyposulfite (0,96).

The need of water in chlorine is equal to that doze of chlorine, after the addition of which the residual chlorine in the researched water makes 0,3-0,5mg/l.

METHODS OF MAKING WATER QUALITY BETTER

www.montecitowater.com/how_is_water_treated.htm

There are many methods of making water quality better. They give possibility to free the water from: hanging fractions, guminous substances, salt hyperincluding, gases with disagreeble small, toxic and radioactive substances, dangerous microorganisms.

Desinfection is the most useful method of making water quality better. As a rule, it is the final and very important stage of water desinfection. There are physical (boiling, influence of ultra-violet radiation, ozonization of water) and chemical methods of water desinfection. Chlorination with normal doses and overchlorination belong to chemical methods.

The chlorination by the post-break doses. By the results of some investigations the water can be disinfected by 2 doses of chlorine: 1mg/l (before-break dose) and 5,2 mg/l (post-break doses), as the concentration of the rest chlorine makes 0,5 mg/l in both cases.

However, by before-break dose the remaining chlorine is determined as chloramin, and by post-break doses - as free chlorine. The bactericidal action of such method is very effective. At the same time we improve water organoleptic features at the expense of oxidation of organic substances with the bad smell. It is necessary to use this method in hot countries widely.

The chlorination with the preammonization (chlorammination).

First, they introduse ammoniac solution and than, in 0.5-1 min, chlorine to the water. As a result chloramins are formed in water: NH2Cl - monochloramin and NHCl2 - dichloramin. The last one has the most expressed bactericidal action. The effectiveness of such method depends on the ratio NH3:Cl. That's why they use the doses of reagents in the following ratios: 1:3, 1:4, 1:6, 1:8. The ratio should be chosen for certain reservoirs individually.

This method prevents bad smells, which can appear by the chlorination of water, containing phenol and the matters from its group (as chlorphenols are formed). Chlorphenols impart medicinal smell and smack to the water even in the small quantities.

The speed of disinfection by this method is lower than that by chlorine. The exposure time should be not less than 2 hours.

If the water of reservoirs contains ammonium salts, chloramines are also formed. This fact decelerates disinfection. So, it is necessary to define free and connected chlorine separately to determine the reliability of disinfection. Obviously, the presence of only free chlorine is evidence of reliable disinfection.

Double chlorination. In many river water-pipes chlorine is given before the settling and than after the filtration as usual. The introduction of chlorine before the settling improves the coagulation and decolorization of water, inhibits the development of microorganisms in the settling tanks, increases the reliability of disinfection. However, the possibility of chlororganic compounds formation increases too.

The ozonization of water. It is widespread in the industrial countries. Ozone is destroyed in water, forming atomic oxygen: O3 → O2 → O. Now, it is proved, that this mechanism is more complicated: there are many intermediate reactions with the formation of free radicals (for example, HO2), which also have oxidizing features. Ozone oxidizing potential (+1.9) is higher than that one of chlorine (+1.36). From the hygienic point of view, ozonization is one of the best methods of disinfection: water is well disinfected, organic admixtures become destroyed, organoleptic features are improved. Water becomes blue and it is equated with spring water.

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

UV-irradiation. The maximal bactericidal effect is achieved by the waves 250-260 nm, which pass even through the 25 cm layer of transparent and decolorized water.

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

There are some advantages of UV-irradiation over the chlorination: bactericidal rays don't denaturate the water and don't change its organoleptic features, they have wider biological action. Their bactericidal action is spread over the spores, viruses and worm eggs, resistant to chlorine. Many investigators consider this method the best for the disinfection.

Advantages:
  -   UV does not alter taste, odour, colour or pH of the water
  -   UV does not require the addition of chemicals
  -   UV does not impart toxic by-products into the water
  -   UV systems are compact and easy to install
  -   UV systems require very little maintenance
  -   Running costs are often lower than those of a household lightbulb

The boiling. It is the simplest method of disinfection. Vegetative forms of pathogenous microorganisms die in 20-40 sec. at the temperature - 80 C. The water is almost disinfected until it begins to boil. 5 minutes of boiling provides reliable safety even in the very strong pollution by suspended matters, viruses and other pathological agents. During 30 min. of boiling most of spores die too. The spores of anthrax, worm eggs and larvae are inactivated. Protozoa die too. This method is often used in the everyday life, in hospitals, child welfare institutions, in the manufactures, railway stations. It is necessary to clean tanks before filling them with the boiled water and change water every day, as the microorganisms multiply here very quickly.

When there is much water and the use of boiling is unreal, the following methods are used:1)the coagulation by aluminium sulphate (100-150mg/l); 2)the settling for an hour; 3) the filtration through the sand filter; 4) the chlorination for 30 min. to the concentration of the remaining chlorine 1 mg/l.

Bacterial filters. Earlier it was said, that worm eggs and amoebic cysts didn't die during the chlorination. That's why portable bacterial filters are widely used in many tropic countries. Here, the water is filtered through the special filters - candles (by Backfield, Chamberlains models) under pressure. The candle is an empty cylinder, made of porous ceramic material (for example, porcelain). Water is filtrated through the external surface of the candle to the inside part. It is liberated from the suspended particles, worm eggs, bacteria and even viruses, depending on the size of pores. The candles are cleaned and boiled for 5-10 min. once a week. The series of firms make the candles of 3 models. Model "V"- these filters are intended to the removing of suspended matters. They can be used at the first stage of cleaning. Model "N" - middle- porous, they are intended to clean water from worm eggs, cysts and cercaria. Model "W" - small-porous filters, they keep even viruses.

Chemical tablet methods. The use of tablets and solutions are widely used for the disinfection in the expeditions and hikes. Tablets "Halazone" contain chloramin, stable during the storage. The tablet is introduced to a certain volume of water (usually it is 1 liter), water and stirred every 3-5 min. It can be used in 30 min. But this tablet cannot be enough for the very contaminated water.

In these cases we can use tablets "Chlor-dechlor", which contain more chlorine and dechlorinated agent in the middle of the tablet (sodium hyposulphite). They introduce one tablet to the water and stir it every 2-3 min. thoroughly. After dissolving of the external part of the tablet its central part inactivates the surplus chlorine. If the water is very shady introduce 2-3 tablets at once. In Ukraine, we use tablets "Aquasept" and "Aquacide", which contain steady chlorine-containing preparations. One tablet (3,5 mg of active chlorine) is introduced to the 1 liter of water. Water becomes desinfected in 30 min.

Iodine-containing preparations are widespread in tropical countries. They disinfect water from bacteria, many viruses and cysts. The simplest method is the disinfection by 10% solution of iodine: 2 drops of such solution are introduced in 1 liter of very contaminated water. The water is usable in 20-30 min. Tablets "Globaline", "Potable", containing sodium tetraglycerate triiodate, disinfect water from bacteria, amoebic cysts, many viruses. They are the best disinfectant matters for the torrid zinc. They are safe for humans. Large tanks for the preservation of water must have sturdy cover and a tap.

The cleaning and disinfection of wells.

It is necessary to clean and chlorinate the wells periodically. Remove water from the wells, clean the walls, remove the upper layer of silt and put the layer of coarse sand or small gravel to the bottom. The walls of the well are treated by 3-5% solution of chloride of lime. When the well is filled with water introduce one backet of 3-5% solution of chloric lime for every 1 m3 of water. Then the water is stirred and left for 10-12 hours. The water is ladled out until the chlorine smell disappears. Some samples of water are kept for the analysis. The chlorination of the well is carried on after its repair, if the data of analysis are unfavourable for the presence of infectious agents.

DISINFECTION OF WELL

Wells are main source of water in rural area. The most effective and cheapest method of disinfecting wells is by bleaching powder. Disinfection of well is required in normal days and during epidemics.

Steps:

1. Find volume of water in well.

Measure depth of water column (h) metres

Measure the diameter of well (d) metres

Substitute (h) & (d) in:

Volume (litres) = π x d2 x h x 1000 π= 3.14

* One cubic metre - 1,000 litres of water

2. Find amount of bleaching powder required

Measures by Horrock's apparatus.

Roughly 2.5 gm of good quality bleaching powder would be required to disinfect 1,000 litres of water.

3. Dissolve bleaching powder in water

The calculated amount of bleaching powder is placed in a bucket (not more than 100 g in one bucket) and made into a thin paste. More water added till bucket is 3/4 full. The contents are stirred and allowed to stand for 5 - 10 minutes. When lime settles down, the supernatant solution which is chlorine solution is transferred to another bucket.

4. Delivery of Chlorine solution into the well.

The bucket containing the supernatant chlorine solution is lowered some distance below surface water. The well water is agitated by moving the bucket violently both vertically and laterally. Note: The precipitate or lime is never entered in well because it increases the hardness of water.

5. Contact period - 1 hour contact period is required.

6. Ortho-Tolidine test: It is done to list for residual chlorine at the end of one hour. If "free" residual chlorine level is less than 0.5 mg/ litre, then procedure should be repeated, before water is drawn.

The chlorination is ineffective if there is a contamination of subsoil waters. It is necessary to remove the source of pollution. In this case notify people about the necessity to boil the water or carry out the chlorination of water in wells for general use. The chlorination in the wells is inferior to chlorination of reservoirs. But it still lowers the epidemic danger.

OVERCHLORINATION

By this method large doses of chlorine are used in to the water, for example 10-20 mg/l and more. As a result the reliable bactericidal effect is achieved even after the exposure for 15 min. By the 30-60 min. of exposure even the turbid waters are disinfected reliably. Such agents, stable for the chlorine, as Berket's rikketsia, amoebic cysts, Kochs bacillus, viruses become dead. But even such doses of chlorine cannont destroy spores of anthrax and helminthes eggs. A lot of residual chlorine remains after the overchlorination. Water is dechlorinated by the filtration through the layers of activated coal or by the addition of sodium hyposulphite (Na2S2O3*5H2O) in the concentration of 3.5 mg per 1mg of chlorine.

Overchlorination of water in comparison with chlorination by normal doses has some advantages - we don't need: to determination chlorine's need of water, calculate the dose of chloric lime, time of water's disinfection is decreasing to 15-20 min. in summer and to 30-60 min. in winter. Disinfection of turbid water is very well too. During this, unpleasant smell and smack are eliminated better.

Overchlorination of water by method of weight doses consists of the following stages: determination of active chlorine (in percents) in chloric lime, calculation of quantity of chloric lime which is necessary for disinfection all quantity of water, preparation solution of chloric lime and addition it to reservoir with water. After interaction we must determine the residual chlorine in water, calculate quantity of hyposulfite, which is necessary for dechlorination of water.

With the aim of disinfection water in field conditions may use more simple method of standart doses. With the help of experimental method is determining that when we add 100 mg/l of coagulant and 50 mg/l of chloric lime to water of any quality we will have its disinfection and purification. The residual chlorine is removed by filtration of the water through the filter with activated coal.

In field conditions it is possible to use weight doses method" too. The reason of this method is: that to every 1 l of water (that we need to desinfect) we add 1 ml of 5 % solution of chloric lime, mix, add 1 ml of 10 % solution of coagulant, mix during 2-3 min. and leave it on 30 min. Then we make the filtration of water through the filter. If water has a little temporary hardness (less than 2 mgEq/ l), it has bad coagulation too. So, in such case before coagulation we must to determine temporary hardness adds it, if it is necessary to make alkalinization. For that reason we should take 2.5 % solution of hydrocarbosodium.

The quantity of coagulant solution, chloride lime and soda are in table

Quantity of water for desinfection

10 % solution

of coagulant

5 % solution of chloride lime

2,5% solution of soda

1L

1 ml

1 ml

0,5 ml

10L

10 ml

10 ml

5 ml

100L

100 ml

100 ml

50 ml

 

Method of determination of water temporary hardness

To 100 ml of water add 2 drops of methylene orange and titrate with 0,1 n solution of HCl to colour changing. Quantity (ml) of HCl used for titration is equal to temporary hardness in mg/equ/L.

Method of determination of chlorine residue in rechlorinated water.

Put into retort 200 ml of investigated water. Then with the help of glass stick add 10-15 crystals of potassium iodide, 0,5 ml (10-12 drops) of HCl which are dissolved 1:3 and water, mix. Add 1 ml of starch solution and mix. Drop bu drop add 0,7% solution of sodium tiosulphate, 1 drop of which connects 0,04 mg of chlorine residue. If on colouring of 200 ml of water we need 10 drops, then on 1 l = 10 x 5 = 50 drops. So, one liter of water includes: 0,04 mg x 50 = 2 mg of chlorine.

It is possible to use more simple method of chlorine residue determionation. Pour into test tube such quantity of water that its height is equal to 10 cm3, then add 5-10 drops of iodide potassium, 0,5 ml of HCl which are dissolved 1:3 and 10-12 drops of 1% solution of starch. Content must be mixed and using tables determine the quantity of chlorine residue in investigated water.

Determination of chlorine residue contents in rechlorinated water

Colour of water looking downwards

Chlorine residue

Very little blue

0.05

A little blue

0.1

Light blue

0.2

Blue

0.3

Dark blue

0.5

Black blue (bottom is not seen)

1.0 and more

 

There are many methods of water improvement. They make it possible to purify water from dangerous microorganisms, suspended matters, gumines, surplus salts, stinking gases, toxic and radioactive matters.

1. Disinfection (overchlorinating) of water with different degree of contamination by method of weight doses.

We must disinfect two samples of water; each is 1 dm3 of water. 1st sample is almost clear water, second is not clear. Make water desinfection by next scheme:

Names of reactives

Sample of clear water

(1 dm3)

Sample of not clear water

(1 dm3)

Chloride lime

25 mg

50 mg

Mix, contact during 15 min.

Sodium hyposulphite

12 mg

24 mg

 

2. Determination of chlorine residue in water.

For determination residue chlorine we take 100 cm3 of chlorinated water, add some drops of HCl, 5 - 6 crystals of KI, and 0,5 cm3 of 1% solution of starch. Then titrate by drop method with 0,75 % solution of sodium hyposulphite to uncolouring. 1 drop of sodium hyposulphite is equal to 0,04 mg of free chlorine. Make recalculation on 1 dm3 of water.

3. Calculation necessary quantity of sodium hyposulphite for water dechlorination.

When in water is residue chlorine more than 0,5 mg on 1 dm3, the last is neutralized by addition of sodium hyposulphite at the rate of 3,5 mg on 1 mg of residue chlorine. After dichlorination we filtrate this not clear water through filter. Overchlorination of water by weight method in any case gives guarantee effect of disinfection.

Except this method of weight doses overchlorination of water may be made by method of standard doses. Independently from cleanliness of water we add 50 mg of chloride lime to 1 dm3 of water. Then, after 10 minutes, we add 100 mg of coagulant and filtrate through any filter.

 

Water can play a major role in the transmission of enteric infections, and virtually all of the agents that cause travellers' diarrhea may be present in contaminated water. Anywhere that trekkers are able to travel these days, people live or travel higher up; all ground water should be assumed to be contaminated. I feel strongly that travellers wishing to avoid diarrhea should not consume untreated water. Various water treatment methods are reviewed below.

Bottled Water

Bottled water is only as safe as the source. There are recorded instances of contaminated bottled water contributing to cholera epidemics. In an unpublished study performed in Kathmandu, randomly purchased bottles of various brands of water were cultured, and a significant percentage grew enteric pathogens (diarrhea-causing organisms). Carbonated water is acidic enough (due to the dissolved carbon dioxide) to kill contaminating bacteria. Bottled water has the disadvantage of being an additional expense, and is not always available. I also discourage trekkers from relying on bottled water for the simple reason that all of these plastic bottles are carried into the mountains, and none are ever carried out, producing a tremendous and completely unnecessary waste disposal problem.

Heat

Heat kills microorganisms, and virtually all enteropathogens are readily killed at temperatures well below the boiling point. The process of heating water to a boil makes it hot enough long enough to disinfect it, even at elevations as high as Everest Base Camp. There is no need to boil water for 5 minutes, 10 minutes, or 20 minutes, as some guide books recommend! Bringing water to a boil is adequate for disinfection.

Chemical Treatments

Chemical disinfection of water depends on the killing of bacteria, Giardia and amoeba cysts, and viruses by the chemical. Halogens (chlorine and iodine) are most commonly used. The important points are that the killing effectiveness of the chemical is dependant on concentration of the chemical, temperature of the water, and contact time. Decreased concentration (better flavor) or decreased temperature (inevitably the case in the mountains) requires a longer contact time for disinfection. Sediment (cloudy water) increases the need for halogen. Bear in mind that adding flavor crystals to your water will use up the halogen and should only be done AFTER the recommended contact time for disinfection. Remember: "Add Flavor Later."

Chlorine

Chlorine has been used for several centuries for water disinfection. The most common objection to it is the flavor, though there have been some suggestions that it is unreliable in killing Giardia cysts in the commonly used concentrations.Halazone tablets

 These are convenient and inexpensive, but have several disadvantages. Due to its chemical formulation, reliable disinfection in all conditions requires 6 tablets per liter for 1 hour contact, resulting in poor flavor (Backer 1995). The tablets rapidly lose effectiveness when exposed to warm, humid air.

 Superchlorination-dechlorination

 This two-step method is somewhat inconvenient, and the chemicals needed are destructive to clothing and gear if spilled, but it is highly effective and results in nearly flavorless water. High concentrations of chlorine are initially developed, and then in a second step removed by the addition of peroxide.

Iodine

 Iodine has been used to disinfect water for nearly a century. It has advantages over chlorine in convenience and probably efficacy; many travellers find the taste less offensive as well. It appears safe for short and intermediate length use (3-6 months), but questions remain about its safety in long-term usage. It should not be used by persons with allergy to iodine, persons with active thyroid disease, or pregnant women.

Note that Iodine and other halogens appear to be relatively ineffective at killing cyclospora, a troublesome diarrhea-causing bacteria seen in Nepal only in the late Spring and Summer months. At these times it may be reasonable to pre-filter water to remove the large cyclospora (about the size of Giardia cysts), and then treating with iodine. Iodine is available in numerous forms, which can be confusing to the traveller. A simplified table is presented below; for more complete information refer to (Backer 1995).

Iodine Preparations

Preparation

Iodine

Amount/Liter

Iodine Topical Solution

2%

8 drops

Iodine Tincture

2%

8 drops

Lugol's Solution

5%

4 drops

Povidone-Iodine (Betadine)

10%

4 drops

Tetraglycine hydroperiodide
(Globaline, Potable Aqua, EDWGT)

8 mg

1 tablet

 

NOTES: final drinking concentrations calculated at 8 mg iodine/liter measure with a tuberculin syringe or dropper: 1 drop = 0.05 ml.

In general, if you are in a hurry double the chemical dose and halve the contact time; if you want better flavor halve the dose and double the contact time.If you believe the water may be heavily contaminated, double the chemical dose or double the contact time.

Iodine Topical Solution and Iodine Tincture also contain 2.4% sodium iodide, Lugol's Solution also contains 10% potassium iodide, increasing the dose of iodine ingested.

Povidone is a non-toxic polymer that binds the iodine and allows higher concentrations in a water-based solution. This complex system provides a sustained-release reservoir of free iodine, and makes calculation of the "strength" of the solution difficult.

  A system comprising iodine crystals in plain water is available, and works well. It lasts an extremely long time. I have not shown it here because the amount of iodine dissolved in the water is highly temperature-dependent, and this is problematic in the universally cold environment of the Himalaya.

Addition of a small amount of vitamin C (50 mg) to your water after the contact time with the iodine will render the water nearly flavorless!

Filtration

Filters work by physically removing infectious agents from the water. The organisms vary tremendously in size, from large parasitic cysts (Giardia and Entamoeba histolytica 5-30 m), to smaller bacteria (E. coli 0.5 x 3 m, Campylobacter 0.2 x 2 m), to the smallest viruses (0.03 m). Thus, how well filters work depends to a great extent on the physical size of the pores in the filter medium.

Filters have the advantage of providing immediate access to drinking water without adding an unpleasant taste. However, they suffer from several disadvantages: micro cracks or eroded channels within the filter may allow passage of unfiltered water, they can become contaminated, and no filters sold for field use are fine enough to remove virus particles (Hepatitis A, rotavirus, Norwalk virus, poliovirus, and others). In addition, they are expensive and bulky compared to iodine. Alas, many travel filters are inadequate even to reliably remove E. coli, the most common infectious contaminant.

Some filter manufacturers have added an iodine resin layer to the filter in order to kill any agents passing through the filter stage. Data on effectiveness is limited, but some models have still been shown to provide incomplete disinfection of contaminated water.

...for foreign travel and for surface waters with heavy levels of fecal or sewage contamination, filters should not be used as the sole means of disinfection. One rational use of filtration is to clear the water of sediment and organic debris, allowing more accurate, lower doses of halogens. Filters are also useful as a first step to remove parasitic and Cryptosporidium organisms that have high resistance to halogens (Backer 1995).

PURIFICATION OF WATER

Three main steps in purification of water on large scale:

Storage, Filtration, Chlorination

1. Storage:

Water is drawn out from source and impounded in natural or artificial reservoirs. Storage provides a reserve of water from which further pollution is excluded.

Advantages
a. Physical About 90% of suspended impurities settle down in 24 hours by gravity.

b Chemical The aerobic bacteria oxidize the organic matter present in water with the aid of dissolved oxygen. As a result the content of free ammonia is reduced and a rise in nitrates occur.

c. Biological 90% of total bacterial count drops in first 5 - 7 days.

2. Filtration

Filtration is important because 98 - 99% of bacteria are removed by filtration, a part from other impurities. Two types of filters are in use, they are:

a. Slow sand filters (biological filters)

b. Rapid sand filters (Mechanical filters)

a. Slow Sand Filter.

ADVANTAGES OF filter.doc

Following are the elements of a slow sand filter.

* Supernatant (raw) water:

Supernatant water is present above sand bed, its depth varies from (1 1,5 m). It serves 2 important functions.

i. It serves as a constant supply of water,

ii. It provides waiting period of some hours and there is partial purification by sedimentation & oxidation

* Sand bed:

It is most important part of the filter; its thickness is about (1,2 m). The sand grains are of diameter between (0,15 0,35 mm). Sand bed is supported by a layer of graded gravel. Water percolates through the sand bed very slowly and during this it is subjected to number of purification processes mechanical straining, sedimentation, adsorption, oxidation and bacterial action.

Vital Layer

Few days (3 to 5 days) after laying the filter, surface of sand bed gets covered with a slimy, green coloured growth made of fungi, algae, bacteria, diatoms and plankton. The formation of vital is known as "ripening of the filter". The growth present on sand bed is called as "Schmutzdecke". It removes organic matter, holds bacteria and oxidizes ammoniacal nitrogen into nitrates and helps in yielding a bacteria - free water.

Under - drainage system

It consists of porous or perforated pipes lying at the bottom of the filter bed and provides an outlet for filtered water and also provides support to the filter medium above.

Slow filters clear water well only after theyre "ripening": the diameter of pores in the sand decreases, owing to the keeping of suspended matters in the highest layer. So, small particles, worm eggs and larvae and to 99.9% of bacteria can be detained. The clean sand does not absorb viruses. But after the "ripening", about 50-99% viruses are kept in the slow filters. If such filters are used correctly they free water from cercaria. At the same time the series of biological processes proceed in the ripped highest layer - biological film: the mineralization of organic matters and the death of bacteria. The contaminated highest layer of the sand is changed in 30-60 days.Slow filters are used when water turbidity doesn't exceed 200 mg/l in the small country water-pipes. They are always used after the preceding aeration to remove surplus iron and manganese.

 

Filter control valves:

The filter is equipped with certain valves and devices which are incorporated in the outlet pipe system maintaining a steady rate of filtration.

When the vital layer becomes dense and resistance to the passage of water is increased the supernatant water is drained off Sand bed is cleaned by scrapping of the top portion of the sand layer to a depth of 1 - 2 cms. Scrapping is done 20 - 30 times. The process is known as Filter Cleaning.

b. Rapid Sand Filter

Rapid sand filters are of two types, the gravity type and the pressure type. Both the types are in use. The following steps are involved in the purification of water by rapid sand filters.

i. Coagulation:

Raw water is treated with a chemical coagulant such as alum. The dose required is usually 5 - 40 mg/liter.

ii. Rapid mixing:

The treated water is subjected to rapid mixing for few minutes. This allows a quick and thorough dissemination of alum throughout the bulk of water.

iii. Flocculation:

Treated water is gently stirred in a "flocculation chamber" for about 30 minutes. In chamber there are paddles which act as flocculator. They rotate at speed of 2 to 4 rate per minute. This slow and gentle stirring results in the formation of a thick, copious, white flocculent precipitate of aluminum hydroxide. The thicker the precipitate or flock diameter, the greater the settling velocity.

iv. Sedimentation:

The coagulated water is now led into sedimentation tanks where it is detained for periods varying from 2 - 6 hours.

v. Filtration:

The partly clarified water now subjected to rapid and filtration.

Filter Beds:

Each unit of filter bed has a surface of about 80 - 90 m2. Sand is filtering medium. The effective size of sand particles is between 0.6 - 2.0 mm. The depth of sand bed is usually about 1 m. Below the sand bed is a layer of graded gravel 30 - 40 cm. The gravel supports the sand bed and the filtered water to move freely towards the under drains. The rate of filtration is 5 - 15 m3/ m2/hour.

Back - Washing:

Rapid sand filters need frequent washing daily or weekly. Washing is accomplished by reversing the flow of water through the sand bed, which is called "back-washing". Back - washing dislodges the impurities and cleans up the sand bed.

 

Comparison of Rapid & Slow Sand Filters.

 

Slow Sand Filter

Rapid Sand Filter

Space

Occupies large space

Occupies very little area

Rate of filtration

0.1 -0.4m3/m2/h

5- 15m3/m2/h

Effective size of sand

0.15-0.35 mm

0.6 - 2.0 mm

Preliminary treatment

Plain sedimentation

Chemical coagulation

Washing

By Scraping the sand bed

By back-washing

Operations

Less skilled

Highly skilled

Removal of turbidity

Good

Good

Removal of colour

fair

Good

Removal of bacteria

99.9-99.99 per cent

98 - 99 per cent

 

Advantages of Slow Sand Filter

Advantages of Rapid Sand filter

1. Simple to construct and operate

1. It deals with raw water directly. No. preliminary storage is needed

2. Cost of construction is cheaper

2. Occupies less space.

3. Physical, Biological and Chemical quality ' of filtered water is very high

3. Filtration rate is high.

 

4. Washing of filter is easy

 

5. More flexibility in operation.

 

The disinfection is one of the most usable methods of water improvement. Usually it is a concluding and very important stage. The most spread methods of disinfection are different methods of chlorination. Sometimes ozonization and UV-irradiation use also.

3. CHLORINATION

Chlorination is the process in which chlorine is added to water for purification. Chlorination-is more effective when pH of water is around 7.

Effects of Chlorine:

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

b. It has germicidal effects.

c. It oxidizes iron, manganese and Hydrogen sulphide

d. If destroys some taste and odour producing constituents.

e. It controls algae and slim organisms

f. It aids coagulation

Action of Chlorine.

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

H2O + CI2 HCI--+HOCI

HOCI H++OCI"

The disinfecting action of-chlorine is mainly due to hypochlorous acid and to a small extent due to hypochloriteon.

The chlorination of water is one of the most spread methods and it is of great importance for the prophylaxis of water epidemics. It is explained by the reliable disinfection, accessability and cheapness.

The principle of chlorination is based on the treatment by chlorine or the chemical compounds, containing active chlorine and able to oxidize and provoke bactericidal action. Chlorine is subjected to hydrolysis in water:

Cl2+HOH → HOCl+HCl, so hydrochloric and chloricious acids are formed. Chloricious acid takes the central place in the mechanisms of bactericidal action. It was thought earlier that the latter was destroyed in water and discharged out atomic oxygen (HOCl → HCl+O), which was the main bactericidal agent. Now, such explaination is considered insufficient. Chlorine in the structure of chloricious acid and hypochlorite-ion (HOCl→H +OCl ) free active chlorine, which determines bactericidal action in water. Not large molecules and electric neutrality let chloricious acid penetrate quickly through the bacterial membrane and influence upon the cellular enzymes, important for the metabolism and reproduction. It is assumed, that it reacts with SH-groups of enzymes, which become oxidized.

The reliable bactericidal effect of chlorine is achieved, if about 0,3 0,5 mg/l of free chlorine or 0,8 1,2 mg/l of connected chlorine are left in water after 30 - 60 min. of exposure.

Sanitary control of water pipes includes the determination of the remaining chlorine in water every hour, and the bacteriological investigation - not rare than once a day. Long-term experience of using such method in almost all countries of the world is evidence of chlorinated water safety for use.

Disinfectants such as chlorine, chloramines, ozone and chlorine dioxide are very important to protect drinking water against germs and fight disease transmitted through water. However, they can also react with natural material in the water to form unwanted by-products, which can be of concern to public health.

The formation of by-products depends on the disinfectant used, the chemical and physical characteristics of water and the treatment conditions.

While all disinfectants form by-products, different disinfectants form different by-products, for instance:

                     Chlorine can form halogenated by-products (i.e. that have chlorine or bromine incorporated into their structure) such as trihalomethanes and haloacetic acids.

                     Ozone can form bromate.

                     Chlorine dioxide can form chlorite and chlorate.

All disinfectants form a variety of oxidation products that have not been well characterized. There are several options to reduce the amount of disinfectant by-products in drinking water.

What happens to disinfectants and their by-products when ingested or inhaled?

Disinfectants still present in drinking water will react with saliva and stomach content to form disinfectant by-products similar to those produced in water.

The way disinfectant by-products are metabolised and eliminated depends on the by-product. Some will change to a harmless form but some can be converted into a form that can affect health.

How can disinfectants and their by-products affect health?

Disinfectants in drinking-water do not raise health concerns themselves at the levels used but some of their by-products do:

      Some chlorine by-products can harm the liver and kidney of laboratory animals given high doses and may even cause tumours. They do not appear to affect reproduction except at very high doses.

      Chlorine dioxide by-products can affect the red blood cells.

      Ozonation by-products can cause tumours in animals at high dose.

Have disinfectants and their by-products affected human health?

- Some studies in human populations seem to indicate that chlorinated and chloraminated drinking-water may cause cancers of the bladder, colon and rectum, but the studies are not conclusive.

- There is no convincing evidence that water chlorination can harm pregnancies or cause reproductive problems.

What are the risks posed by disinfectants and their by-products?

The World Health Organization (WHO) has set intake limits for most disinfectants and by-products. These are used for developing the WHO drinking water guidelines that are, in turn, used by many countries as a basis for their drinking water standards.

Several milligrams of disinfectant per litre of water are typically employed in treatment plants, but what arrives at the tap is generally considerably less and well below the WHO guidelines. The concentration of disinfectant by-products varies according to the properties of the water and the amount of natural organic matter it contains.

Potential human health effects would depend on both the concentration of disinfectant by-products and the length and timing of exposure. However, it is difficult to measure actual exposure levels and to take into account all possible risk factors.

Studies on human populations are useful but those on disinfectant by-products in particular have been difficult to interpret. Available studies are insufficient to establish that water disinfectants and their by-products affect health.

Since disinfection is a very important barrier to waterborne disease, it should never be compromised in attempting to control disinfection by-products. Studies to date do not provide sufficient evidence to say that exposure to disinfectant by-products actually causes cancer or affects reproduction.

However, it is prudent to take steps to limit the exposure to disinfectant by-products where this can be achieved without compromising disinfection effectiveness

Simple chlorination (by chlorine request). Right choice of the dose is of great importance for the reliable disinfection. Only about 1 2 % active chlorine are spent on the bactericidal action during the disinfection. The rest part is spent on oxidation of organic and inorganic matters in water. All these connected forms of chlorine form such a notion as "chlorine-absorbability of water". Different natural waters have different chlorine-absorbability. To disinfect water by such a method, they introduce such amount of chlorine, that the remaining free chlorine should be 0,3 - 0,5 mg/l and the remaining chlorammoniac chlorine 0,8 - 1,0 mg/l. In such a case the organoleptic features of water do not become worse.

The number of active chlorine (mg), necessary for the disinfection of 1 liter of water, is called chlorines need of water (chlorine-request). It is determined by the experimental chlorination of certain volume of water, subjected to disinfection.

Besides the correct dose, good mixture and sufficient contact of chlorine with water are necessary for the effective disinfection.

The presence of suspended matters, gumines and other organic compounds in water lowers the action of chlorine. That's why it is necessary to light and decolourize turbid and colored waters before disinfection.

The chlorination of water by chlorine-request reliably disinfects water from the intestinal infections (typhoid fever, dysentery, cholera, patogenous strains of E.coli, salmonellas), brucellosis, tularemia, leptospirosis. There are some disputes about the polio virus. Many scientists consider, that this virus is inactivated by the chlorination for an hour. Water, containing Berket's rikketsia, amoebic cysts, worm eggs and the spores of some types of anthrax, cannot be disinfected by this method.

At chlorination of water under action of active chlorine oxidize the microorganisms, organic and inorganic substances, which are in water; the part of chlorine is absorbed by the substances, which have hanged in water, that is denoted as the chlorine absorption of water.

For reliable decontamination of water its contact with chlorine must be last: in summer - not less than 30 minutes, and in winter - not less than 1 hour. The residual chlorine (chlorine, which has remained in water after its decontamination) is the criterion of complete satisfaction of the chlorine absorption of water and also of the epidemic safety of water. Water which was correctly chlorinated must contain 0,3-0,5 mg/l of residual chlorine, as water, which contains more than 0,5 mg/l of residual chlorine, has specific unpleasant taste and smell. The sum of the chlorine absorption of water and the quantity of residual chlorine (0,3-0,5 mg/l) makes the chlorines need of water for chlorinate.

The chlorination by the post-break doses. By the results of some investigations the water can be disinfected by 2 doses of chlorine: 1mg/l (before-break dose) and 5,2 mg/l (post-break doses), as the concentration of the rest chlorine makes 0,5 mg/l in both cases.

However, by before-break dose the remaining chlorine is determined as chloramin, and by post-break doses - as free chlorine. The bactericidal action of such method is very effective. At the same time we improve water organoleptic features at the expense of oxidation of organic substances with the bad smell. It is necessary to use this method in hot countries widely.

The chlorination with the preammonization (chlorammination).

First, they introduse ammoniac solution and than, in 0.5-1 min, chlorine to the water. As a result chloramins are formed in water: NH2Cl - monochloramin and NHCl2 - dichloramin. The last one has the most expressed bactericidal action. The effectiveness of such method depends on the ratio NH3:Cl. That's why they use the doses of reagents in the following ratios: 1:3, 1:4, 1:6, 1:8. The ratio should be chosen for certain reservoirs individually.

This method prevents bad smells, which can appear by the chlorination of water, containing phenol and the matters from its group (as chlorphenols are formed). Chlorphenols impart medicinal smell and smack to the water even in the small quantities.

The speed of disinfection by this method is lower than that by chlorine. The exposure time should be not less than 2 hours.

If the water of reservoirs contains ammonium salts, chloramines are also formed. This fact decelerates disinfection. So, it is necessary to define free and connected chlorine separately to determine the reliability of disinfection. Obviously, the presence of only free chlorine is evidence of reliable disinfection.

Double chlorination. In many river water-pipes chlorine is given before the settling and than after the filtration as usual. The introduction of chlorine before the settling improves the coagulation and decolorization of water, inhibits the development of microorganisms in the settling tanks, increases the reliability of disinfection. However, the possibility of chlororganic compounds formation increases too.

The ozonization of water. It is widespread in the industrial countries. Ozone is destroyed in water, forming atomic oxygen: O3 → O2 → O. Now, it is proved, that this mechanism is more complicated: there are many intermediate reactions with the formation of free radicals (for example, HO2), which also have oxidizing features. Ozone oxidizing potential (+1.9) is higher than that one of chlorine (+1.36). From the hygienic point of view, ozonization is one of the best methods of disinfection: water is well disinfected, organic admixtures become destroyed, organoleptic features are improved. Water becomes blue and it is equated with spring water.

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

Advanced Water Purification System

UV-irradiation.

The maximal bactericidal effect is achieved by the waves 250-260 nm, which pass even through the 25 cm layer of transparent and decolorized water.

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

There are some advantages of UV-irradiation over the chlorination: bactericidal rays don't denaturate the water and don't change its organoleptic features, they have wider biological action. Their bactericidal action is spread over the spores, viruses and worm eggs, resistant to chlorine. Many investigators consider this method the best for the disinfection.

PURIFICATION OF WATER ON SMALL SCALE

The boiling.

It is the simplest method of disinfection. Vegetative forms of pathogenous microorganisms die in 20-40 sec. at the temperature - 80 C. The water is almost disinfected until it begins to boil. 5 minutes of boiling provides reliable safety even in the very strong pollution by suspended matters, viruses and other pathological agents. During 30 min. of boiling most of spores die too. The spores of anthrax, worm eggs and larvae are inactivated. Protozoa die too. This method is often used in the everyday life, in hospitals, child welfare institutions, in the manufactures, railway stations. It is necessary to clean tanks before filling them with the boiled water and change water every day, as the microorganisms multiply here very quickly.

Chemical tablet methods. The use of tablets and solutions are widely used for the disinfection in the expeditions and hikes. Tablets "Halazone" contain chloramin, stable during the storage. The tablet is introduced to a certain volume of water (usually it is 1 liter), water and stirred every 3-5 min. It can be used in 30 min. But this tablet cannot be enough for the very contaminated water.

In these cases we can use tablets "Chlor-dechlor", which contain more chlorine and dechlorinated agent in the middle of the tablet (sodium hyposulphite). They introduce one tablet to the water and stir it every 2-3 min. thoroughly. After dissolving of the external part of the tablet its central part inactivates the surplus chlorine. If the water is very shady introduce 2-3 tablets at once. In Ukraine, we use tablets "Aquasept" and "Aquacide", which contain steady chlorine-containing preparations. One tablet (3,5 mg of active chlorine) is introduced to the 1 liter of water. Water becomes desinfected in 30 min.

Iodine-containing preparations are widespread in tropical countries. They disinfect water from bacteria, many viruses and cysts. The simplest method is the disinfection by 10 % solution of iodine: 2 drops of such solution are introduced in 1 liter of very contaminated water. The water is usable in 20-30 min. Tablets "Globaline", "Potable", containing sodium tetraglycerate triiodate, disinfect water from bacteria, amoebic cysts, many viruses. They are the best disinfectant matters for the torrid zinc. They are safe for humans. Large tanks for the preservation of water must have sturdy cover and a tap.

The cleaning and disinfection of wells.

It is necessary to clean and chlorinate the wells periodically. Remove water from the wells, clean the walls, remove the upper layer of silt and put the layer of coarse sand or small gravel to the bottom. The walls of the well are treated by 3-5% solution of chloride of lime. When the well is filled with water introduce one backet of 3-5% solution of chloric lime for every 1 m3 of water. Then the water is stirred and left for 10-12 hours. The water is ladled out until the chlorine smell disappears. Some samples of water are kept for the analysis. The chlorination of the well is carried on after its repair, if the data of analysis are unfavourable for the presence of infectious agents.

The chlorination is ineffective if there is a contamination of subsoil waters. It is necessary to remove the source of pollution. In this case notify people about the necessity to boil the water or carry out the chlorination of water in wells for general use. The chlorination in the wells is inferior to chlorination of reservoirs. But it still lowers the epidemic danger.

EXPRESS METHODS OF WATER QUALITY IMPROVING.

Deodorization - elimination of smack and odour of water by aeration, usage of oxidants (ozonization, dioxide of chlorine, large doses of chlorine, potassium permanganate), filtrating through a layer of absorbent coal, by introduction in water to sedimentation of absorbent coal.

Deironation is carried out by spraying water with the purpose of aeration in graduation towers. Thus, bivalent iron is oxydated in ferric hydroxide, which sediments in settling tank, or delays on the filter.

Softening. By an aged method of water softening is soda calcareous, at which calcium and magnesium settle in a settling tank as unsolvable salts. Today is used filtrating water through filters, which are completed by ion exchangers. Ion exchangers are firm, unsolvable, acinose stuffs, which have property to exchange their ions on ions of salts, which are solved in water.

Desalting - the sequential filtrating of water through kationite, and then through anion exchanger permits to liberate it from solvable salts and consequently use with the purpose of desalting. For desalting water on water pipes, sea courts thermal method is used which bases on evaporation of water with the following condensation of steams. Also is used electro dialysis with usage of selective diaphragms, freezing and other methods.

Decontamination - at coagulation, settling and filtrating of water on waterpipes contents of radioactive substances in it is reduced only on 70-80%. For more penetrating decontamination water is filtrated through ionic exchanger of resin.

Fluoridation of water - synthetic adding of fluorine bonds with the purpose of decrease of its rate by caries of teeth.

The protective effect of fluoride occurs primarily during infancy and early childhood when the teeth are developing, but its caries-preventive action is carried over into adulthood as long as one has access to fluoridated water.

The main source of fluoride for humans is the water they drink. If water contains about 1 part per million (ppm) of fluoride, it will supply adequate amounts of this mineral nutrient. Many waters contain quantities of fluoride much less than that, and the addition of fluoride (fluoridation) to raise its level in water to what is considered optimal is an important public health measure. Fluoridation has been shown to reduce the incidence of dental caries by 60% to 70%.

Requirements: An intake of about 1 to 2 mg per day is considered adequate. A water supply containing 1 part per million of fluoride will supply 1 to 2 mg per day, depending on the consumption of water and other beverages made with that water, such as coffee, tea, soft drinks, and those reconstituted from frozen fruit drinks.

A deficiency of fluoride during infancy and childhood leaves the teeth relatively unprotected from dental caries. Tooth decay is a major public health problem that has important economic implications. Increasing evidence indicates that there is less osteoporosis in areas where the fluoride content of the water is high than in comparable areas where the fluoride content of the water is low. There are good data to show that osteoporosis improves if large doses of fluoride are administered therapeutically. Recent evidence suggests that arterial calcification may be less marked in high-luoride than in low-fluoride areas.

An excessively high intake of fluoride during childhood causes a condition known as dental fluorosis, in which the teeth become mottled and somewhat discolored. Very large intakes of fluoride cause bone changes with increased bone density, calcification of muscle insertions, and exostoses. The condition can be diagnosed most easily by radiographic means. The most likely places to find these changes is in roentgenograms of the forearm. Dental and skeletal fluorosis do not occur in communities with properly controlled fluoridated water supplies. Fluorosis is found in certain defined areas of India.

WATER PURIFICATION

Suspended and dissolved impurities present in naturally occurring water make it unsuitable for many purposes. Objectionable organic and inorganic materials are removed by such methods as screening and sedimentation to eliminate suspended materials; treatment with such compounds as activated carbon to remove tastes and odors; filtration; and chlorination or irradiation to kill infective microorganisms.

In aeration, or the saturation of water with air, water is brought into contact with air in such a manner as to produce maximum diffusion, usually by spraying water into the air in fountains. Aeration removes odors and taste caused by decomposing organic matter, and also industrial wastes such as phenols and volatile gases such as chlorine. It also converts dissolved iron and manganese compounds into insoluble hydrated oxides of the metals, which may then be readily settled out.

Hardness of natural waters is caused largely by calcium and magnesium salts and to a small extent by iron, aluminum, and other metals. Hardness resulting from the bicarbonates and carbonates of calcium and magnesium is called temporary hardness and can be removed by boiling, which also sterilizes the water. The residual hardness is known as noncarbonate, or permanent, hardness. The methods of softening noncarbonate hardness include the addition of sodium carbonate and lime and filtration through natural or artificial zeolites, which absorb the hardness-producing metallic ions and release sodium ions to the water. Sequestering agents in detergents serve to inactivate the substances that make water hard.

Iron, which causes an unpleasant taste in drinking water, may be removed by aeration and sedimentation or by passing the water through iron-removing zeolite filters, or the iron may be stabilized by addition of such salts as polyphosphates. For use in laboratory applications, water is either distilled or demineralized by passing it through ion-absorbing compounds.

WATER DESALINIZATION

Water Desalinization Technique Flash evaporation is the most widely used method of water desalinization. The seawater is heated and then pumped into a low-pressure tank, where the water is partially vaporized. The water vapor is then condensed and removed as pure water. This process is repeated many times (three stages are shown). The remaining liquid, called brine, contains a large amount of salt and is removed and often processed for minerals. Note that the incoming seawater is used to cool the condensers in each evaporator. This design conserves energy since the heat released when the vapor condenses is used to heat the next batch of seawater.

To meet the ever-increasing demands for fresh water, especially in arid and semiarid areas, much research has gone into finding efficient methods of removing salt from seawater and brackish waters. Several processes are being developed to produce fresh water cheaply.

Three of the processes involve evaporation followed by condensation of the resultant steam and are known as multiple-effect evaporation, vapor-compression distillation, and flash evaporation. The last-named method, the most widely used, involves heating seawater and pumping it into lower-pressure tanks, where the water abruptly vaporizes (flashes) into steam. The steam then condenses and is drawn off as pure water.

Freezing is an alternate method, based on the different freezing points of fresh and salt water. The ice crystals are separated from the brine, washed free of salt, and melted into fresh water. In another process, called reverse osmosis, pressure is used to force fresh water through a thin membrane that does not allow the minerals to pass. Reverse osmosis is still undergoing intensive development. Electrodialysis is being used to desalt brackish waters. When salt dissolves in water, it splits into positive and negative ions, which are then removed by electric current through anion and cation membranes, thus depleting the salt in the product water. Although developmental work on electrodialysis is continuing, a number of commercial plants are in operation.

library.thinkquest.org/C0115522/article.php?q...

COAGULATION

The coagulation is used to accelerate the sedimentation of suspended matters, filtration and lightening of water. They add the following coagulators to water: Al2(SO4)3, FeCl3, FeSO4 and so on. They form unsoluble compounds with the dissolved electrolytes, which are quickly sedimented as flocks. These flocks have a large active surface and positive electric charge. That's why they absorb even the smallest negative microbe particles and colloidal gumines, taking them to the bottom of the settling tank. The transparent and uncolored filtrate is formed after the sedimentation of flocks and the next filtration of water. The use of coagulators allows decolorizing water, to shorten the time of settling to 2-3 hours and to use fast filters. 95% worm eggs, 90% and more bacteria and viruses are left water after the coagulation and settling. Coagulation belongs to the most effective methods of water clearing from viruses. The best cleaning is realized by the combined coagulator (Al2(SO4)3 and iron salts).

Aluminium sulpfate Al2(SO4)3*18H2O is often used as a coagulator. It reacts with the calcium bicarbonate and forms Al(OH)3, which is bad-dissoluble and sediments as flocks. The dose of coagulators is 30-200mg/l, it depends on the color, turbidity, pH of water and many other conditions. It is determined by the experi ment for the certain water. Lately they have been used large-molecular matters - flocculators (activated silicic acid), which are active in very small doses (0,2 2,0 mg/l), to accelerate coagulation and economize the coagulator. 5% solution of coagulator is given to the mixer with the help of special dosator, where it is quickly mixed with water. Then, the water enters the reaction chamber, where the formation of flocks completes in 10-20 min. Such water passes to the settling tank, where the flocks are sedimented. The size of settling tank corresponds to the settling for 2 3 hours.

Then the water is given to the fast filters, where the layer of sand is 0,8 1,2 m and the granules - from 0,5 - 1 mm. The speed of filtration is 5 - 8 m/h (it is automatically regulated). Soon after the beginning of the work, the filtrating film, consisting of the flocks of coagulator and unsedimented particles, is formed in the highest layer. It improves the detain of microorganisms and admixtures. In 8-12 hours the film becomes denser and the speed of filtration decreases. That's why the work is stopped and the filter is cleaned for 10-15 min. by the stream of clean water, directed upwards, to remove the film.

A complete system of water supply


The water becomes transparent, uncolored, and free of worm eggs and 70 98 % microorganisms after the coagulation, settling and filtration. However, water, passed through the fast filters, must be subjected to disinfection.

For acceleration of sedimentation of small particles coagulation of the water is carried out.

Its essence is in the next: substances, which are in water in colloid condition, are curtailed with making flakes and sediment.

In practice coagulation of the water is achieved with adding of chemical reagents - coagulum, that: 1) has a charge opposite to a charge of colloid particles, which are in the water and 2) forms colloid solution itself, that coagulate fast with formation of the flakes, which drop out into deposit. As coagulum chloric iron, iron vitriol, aluminium sulfide are used.

Sulfide aluminium hydrolyzes in the water; also react with bicarbonate potassium and magnium salts (bicarbonates), which frame so-called temporary hardness of the water. The presence of these salts predetermines and so-called alkalinity of the water.

Aluminium-oxide hydrate forms in water colloid solution, that gives to the water an opalescence shade. Further aluminium hydrate is coagulated, the external attributes of that is formation of the flakes in whole water volume.

The dose of a coagulum depends on turbidity of water.

Quantity of the colloid particles

100

200

600

1400

1800

Dose of aluminium sulfide or chloric Ferri

25-35

30-45

45-75

65-105

80-125

Synchronously with an enlightenment of water clarifying is held out (absorption of the humines), the quantity of bacteria decreases.

A necessary condition of coagulation is the size of temporary hardness of water should not less then 2. If it is smaller - than the slaked lime (Ca(OH)2) is added to the water at 1 of hardness it is necessary 10 mg/l of CaO. Besides, some influence have pH, temperature; presence of humine substances, so-called "protective colloids ", characteristics of colloid particles.

Average dose of a coagulum for river water of low turbidity is 40 - 60 mg/l.

The organization of coagulation on waterpipes is made with following operations:

1)           the dissolution of coagulum,

2)           dosing,

3)           mixing with water that is a subject of processing,

4)           creations of favorable conditions for formation of flakes and their sedimentation.

Successes of chemistry in creation of high-molecular structures have opened new opportunities for improvement of coagulation process. With this purpose the new synthesized chemical substances are used, as, for example, polyacrylamid, that allow to speed up process of enlightenment and clarifying of water. The flocculants added in small doses to water considerably improve formation of flakes, their clarifying and filtration.

Recently in water-supply practice the new type of the clarifying agent with previous coagulation of the colloid particles is used, in which water passes through a layer colloid deposit. As a result, flakes of coagulum are enlarging and detain particles, which frame turbidity. Thus layer of colloid flakes is of the sort filter through which water passes. The process of clearing of water passes much more quickly and with less expense to a coagulum, than usually.

1. Decontamination of water by a method of perichlorination by standard doses (with participation of coagulant). In hallmark of water, independing on degree of its purity, the lime chloride at the rate of 50 mg on 1 dm3 adds. Mixed water. After 10 - minute contact in water ads coagulant in amount 100 mg and mixed water again. After 10-15 minutes water nesessary filtrates through any filter.

2. Determination of a necessary dose of coagulant for water cleaning.

With the purpose of an acceleration of water settling clearing from hand particles, chemical substances coagulants are used. After adding to water the coagulants react with hydrocarbonates, organizing hydroxides which settling absorb on themselves hanging particles in water. In those cases, if contents of hydrocarbonates in water are small (the total base level smaller 2 mEq/dm3), water is necessary to alkaline with 1 % of soda solution in amounts, which are equal to half of dose of coagulant. Last years are used high molecular weight materials - flocculants that in small amounts facilitate and accelerate coagulation. For example, polyacrylamide promotes action of silicon acid.

The sum of bicarbonates, which are in water, carbonates, and salts of other weak acids, which react with hydrochloric acid, predetermine the total base level of water. Alkalinity expresses in ml 1,0 n of hydrochloric acid used for binding of bicarbonates, which are in 1 dm3 of water, which is equal to1 mEq/ dm3.

For determination general hardness of water to 100 3 of examined water add 2-3 drops of 0,05 % solution of methyl orange and titrate by 0,1n solution of Ѳ to appearance of orange-pink color. Total base number -B (mEq/dm3) calculate according to the formula:

B = a 1000 / 10 V ,

Where: a - amount of 0,1n solution of Ѳ that was used for titration (sm3),

V - volume of examined water, sm3,

- correction factor of titre to 0,1n solution of Ѳ,

The maximum dose of coagulant can be calculated by the formula:

= B - 0,5 / 0,0052

Where: B - general hardness of water (in mEq/dm3);

0,5 - advisable surpluses of alkalinity, which ensures completeness of a response

(mEq/dm3);

0,0052- quotients of equivalence.

Alkalinity after coagulation 0,3 - 0,5 mEq/ dm3.

3. Definition of a dose of a coagulant by trial coagulating.

In 4 glasses put 250 3 of examined water add in anyone accordingly: 1 sm3, 2 sm3, 3 sm3 and 4 sm3 of 1 % aluminum sulphate, mix by glass rod and let it stay for 30 minutes. Dose of coagulant is considered optimal after adding of which quickly are received large flakes.

If the reaction of coagulation of water in beaker with the least dose of coagulant takes place very quickly (faster than 5 minutes), the trial coagulating is necessary to repeat with smaller doses of coagulants. If in one from beakers the effective coagulation is not reached, retry experiment with usage of higher doses of coagulant. Lowering colority of examined water up to 200, augmentation of transparence more than 30 cm3, alkalinity not smaller than 0,5 mEq/dm3 testifies about effectiveness of coagulation.

REFERENCES:

Principal:

1.                      Hygiene and human ecology. Manual for the students of higher medical institutions/ Under the general editorship of V.G. Bardov. K., 2009.  PP. 14-34, 71-106.

2.                      Datsenko I.I., Gabovich R.D .Preventive medicine. - K.: Health, 2004, pp. 14-74.

3.                      Lecture on hygiene.

additional:

1.                      Kozak D.V., Sopel O.N., Lototska O.V. General Hygiene and Ecology. Ternopil: TSMU, 2008. 248 p.

2.                      Dacenko I.I., Denisuk O.B., Doloshickiy S.L. General hygiene: Manual for practical studies. -Lviv: Svit, 2001. - P. 6-23.

3.                      A hand book of Preventive and Social Medicine. Yash Pal Bedi / Sixteenth Edition, 2003   p. 26-36, 92-97.