WATER AS A RESOURCE
Water is a transparent fluid which forms the world's streams, lakes, oceans and rain, and is the major
constituent of the fluids of living things.
As a chemical compound, a water molecule contains one oxygen and two hydrogen atoms that are connected
by covalent bonds.
Water (H2O) is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its
solid state, ice; and gaseous state, steam (water vapor).
The Water Molecule
HYDROGEN
OXYGEN
HYDROGEN
Water is the chemical substance with chemical formula H2O : one molecule of water has two hydrogen atoms
covalently bonded to a single oxygen atom.
Major chemical and physical properties of water
• Water is a liquid at standard temperature and pressure. It is tasteless and odorless.
• Since the water molecule is not linear and the oxygen atom has a higher electronegativity than hydrogen
atoms, the oxygen atom carries a slight negative charge, whereas the hydrogen atoms are slightly positive.
As a result, water is a polar molecule with an electrical dipole moment. Water also can form an unusually
large number of intermolecular hydrogen bonds (four) for a molecule of its size.
Hydrogen Bonds Exist Between Water Molecules
Formed between a highly Electronegative atom (like oxygen in a water molecule) of a polar molecule and a
hydrogen.
These factors lead to strong attractive forces between molecules of water, giving rise to water's high surface
tension and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube
against the force of gravity.
This property is relied upon by all vascular plants, such as trees.
PROPERTIES OF WATER
ADHESION: Attraction between two different substances. Water will make hydrogen bonds with
other surfaces such as glass, soil, plant tissues, and cotton. Capillary action-water molecules will
“tow” each other along when in a thin glass tube. Adhesion Causes Capillary Action: Which gives
water the ability to “climb” structures (Capillarity).
HIGH SPECIFIC HEAT: Amount of heat needed to raise or lower 1g of a substance by 1°C. Water resists
temperature change, both for heating and cooling. At 4181.3 J/(kg·K), water has a high specific heat
capacity, as well as a high heat of vaporization (40.65 kJ·mol−1), both of which are a result of the
extensive hydrogen bonding between its molecules. These two unusual properties allow water to
moderate Earth's climate by buffering large fluctuations in temperature.
HIGH HEAT OF VAPORIZATION. Water vapor forms a kind of global ‘‘blanket” which helps to keep
the Earth warm. Heat radiated from the sun warmed surface of the earth is absorbed and held by
the vapor.
The boiling point of water (and all other liquids) is dependent on the barometric pressure. For example,
on the top of Mount Everest water boils at 68 °C (154 °F), compared to 100 °C (212 °F) at sea level at a
similar latitude (since latitude modifies atmospheric pressure slightly). Conversely, water deep in the
ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.
Pure water has a low electrical conductivity, but this increases with the dissolution of a small amount of
ionic material such as sodium chloride.
WATER PHASE DIAGRAM
• DENSITY. The density of liquid water is 1,000 kg/m3 (62.43 lb/cu ft) at 4 °C. Ice has a density of 917 kg/m3
(57.25 lb/cu ft). Water is miscible with many liquids, such as ethanol, in all proportions, forming a single
homogeneous liquid. On the other hand, water and most oils are immiscible, usually forming layers with
the least dense liquid as the top layer, and the most dense layer at the bottom. The maximum density of
water occurs at 3.98 °C (39.16 °F). Most known pure substances become more dense as they cool,
however water has the anomalous property of becoming less dense when it is cooled to its solid form,
ice. During cooling water becomes more dense until reaching 3.98 °C. Below this temperature, the open
structure of ice is gradually formed in the low temperature water; the random orientations of the water
molecules in the liquid are maintained by the thermal motion, and below 3.98 °C there is not enough
thermal energy to maintain this randomness. As water is cooled there are two competing effects: 1)
decreasing volume, and 2) increase overall volume of the liquid as the molecules begin to orient into the
organized structure of ice. Between 3.98 °C and 0 °C, the second effect will cancel the first effect so the
net effect is an increase of volume with decreasing temperature. Water expands to occupy a 9% greater
volume as ice, which accounts for the fact that ice floats on liquid water, as in icebergs.
GOOD POLAR SOLVENT. Water is a good polar solvent and is often referred to as the universal solvent.
Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases – especially oxygen and
carbon dioxide (carbonation) – are known as hydrophilic (water-loving) substances, while those that are
immiscible with water (e.g., fats and oils), are known as hydrophobic (water-fearing) substances. All of the
components in cells (proteins, DNA and polysaccharides) are dissolved in water, deriving their structure and
activity from their interactions with the water.
Solutions & Suspensions
Water is usually part of a mixture
There are two types of mixtures:
◦
Solutions: substance dissolves in liquid
◦
Suspensions: substance suspends in liquid
Solution = Solute + Solvent
Water is the solvent, salt is the solute, salt water is the solution.
Aqueous solution contains hydrophilic compounds or Ionic compounds. Polar molecules (generally) are water
soluble. Hydrophobic or non-polar compounds are water insoluble.
Suspensions, when the substances don’t dissolve in water, but separate into tiny pieces.
Properties of aqueous solutions:
1. Concentration
2. pH
CONCENTRATION OF A SOLUTION
Definitions. Molecular weight = sum of the weights of all atoms in a molecule (daltons). Mole = amount of a
substance that has a mass in grams numerically equivalent to its molecular weight in daltons.
Avogadro’s number = 6.02 X 1023 of molecules form a mole.
A mole of one substance has the same number of molecules as a mole of any other substance.
Acids, Bases and pH
One water molecule is made of two ions (H+) and a Hydroxide Ion (OH-).
H2O
H+ (Hydrogen Ion Acid) + OH- (Hydroxide Ion Base)
Dissociation of Water Molecules: Occasionally, a hydrogen atom shared by two water molecules shifts from
one molecule to the other. The hydrogen atom leaves its electron behind and is transferred as a single proton
- a hydrogen ion (H+). The water molecule that lost a proton is now a hydroxide ion (OH-). The water molecule
with the extra proton is a hydronium ion (H3O+).
A simpler way to view this process is that a water molecule dissociates into a hydrogen ion and a hydroxide
ion:
H2O <=> H+ + OHThis reaction is reversible. At equilibrium the concentration of water molecules greatly exceeds that of H+
and OH-. In pure water only one water molecule in every 554 million is dissociated. At equilibrium, the
concentration of H+ or OH- is 10-7M (25°C).
Acid: A solution with lots of H+ ions has a pH between 0 and 7 is acid (ACIDIC SOLUTION)
Base: A solution with lots of OH- ions has a pH above 7 – 14 and is basic or (ALKALINE solution)
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Solutions with a pH less than
7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH very
close to 7.
The pH scale is a logarithmic scale, it means that each pH unit represents a factor of 10X change in
concentration.
The human blood has a pH of 7.35 – 7.45 (slightly basic). Balance is maintained by buffers in blood, breathing,
and urinating.
HYDROSPHERE: Introduction
Notice how of the world's total water supply of about 332.5 million cubic miles of water, over 96 percent is
saline. And, of the total freshwater, over 68 percent is locked up in ice and glaciers. Another 30 percent of
freshwater is in the ground. Fresh surface-water sources, such as rivers and lakes, only constitute about
22,300 cubic miles (93,100 cubic kilometers), which is about 1/150th of one percent of total water. Yet, rivers
and lakes are the sources of most of the water people use everyday.
Differences between seawater and a typical freshwater
FRESHWATER
SEAWATER
HYDROLOGIC CYCLE
The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water
within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.
Water moves perpetually through each of these regions in the water cycle consisting of following transfer
processes:
- evaporation from oceans and other water bodies into the air and transpiration from land plants and animals
into air.
- precipitation, from water vapor condensing from the air and falling to earth or ocean.
- runoff from the land usually reaching the sea.
Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same
rate as runoff into the sea, about 47 Tt per year. Over land, evaporation and transpiration contribute another
72 Tt per year. Precipitation, at a rate of 119 Tt per year over land, has several forms: most
commonly rain, snow, and hail, with some contribution from fog and dew. Dew is small drops of water that
are condensed when a high density of water vapor meets a cool surface. Dew usually forms in the morning
when the temperature is the lowest, just before sunrise and when the temperature of the earth's surface
starts to increase. Condensed water in the air may also refracts sunlight to produce rainbows.
Water runoff often collects over watersheds flowing into rivers. A mathematical model used to simulate river
or stream flow and calculate water quality parameters is a hydrological transport model. Some water is
diverted to irrigation for agriculture. Rivers and seas offer opportunity for travel and commerce.
Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and
level ground for the establishment of population centers. A flood occurs when an area of land, usually lowlying, is covered with water. It is when a river overflows its banks or flood comes from the sea. A drought is
an extended period of months or years when a region notes a deficiency in its water supply. This occurs when
a region receives consistently below average precipitation.
Human activities significantly affect the water cycle
Water pollution can get into oceans, rivers, lakes, streams, and ground water through human activities and
by natural means.
Here is where and pollution and water cycle are related: Rain water picks pollutants from the atmosphere
and then falls to the earth thus increasing the water pollution problems. Also when rain falls, street litter
(cigarette butts, plastic bottles, candy wraps, etc.) can be picked up by overland flows and can be released
into the sewer which ends up in rivers, streams, lakes, oceans. Fertilizers, chemical spills, septic tank, and
sanitary sewer overflows can contaminate ground water. All these sources are connected to water cycle.
WATER DESALINATION
Obtaining reliable fresh water supplies from challenging water sources.
The Water Cycle is a natural desalination process, composed by the following stages: 1. Evaporation, 2.
Condensation, 3. Precipitation and 4. Collection.
97% of the Earth’s water is in the ocean, where it maintains a salt content too high for human ingestion.
The separation of salts from seawater remains energy intensive, however. Since the primary direct and
indirect energy source for desalination has been fossil fuels (where indirect energy is electricity produced
from fossil fuel power plants).
Desalination technology matches are very site-specific, and optimal technology combinations are selected
based on requirements and conditions, which include:
• geographic conditions
• topography of the site
• capacity requirements and plant size
• type and cost of fossil fuel energy available
• condition of local infrastructure, including ability to plug into the electricity grid
• feed water salinity and temperature
DISTILLATION (“GREENHOUSE PLANT”)
Consists in the separation of water from the salt to the different boiling point of the pure solvent (water)
with respect to its solutions. It works by SOLAR ENERGY.
Features of the plant:
1. Thermal Desalination Processes, Similar to the Earth’s natural water cycle: water is heated, evaporated
and collected using solar radiations.
2. Large industrial installations used in desert areas, small installations used in tourist facilities such as
camping.
DESALINATION WITH MEMBRANE PROCESSES
Reverse osmosis and electro-dialysis, using artificial membranes of which the first are permeable only to the
solvent, the second selective against ions of opposite charge.
REVERSE OSMOSIS (RO)
Saltwater is forced through a membrane at 600 to 1000 psi
Multiple layers of membranes remove as many of the salt ions as possible
Saltwater is forced through membrane sheets at high pressures
Membrane sheets are designed to catch salt ions
Process produces clean water and brine
Reverse Osmosis is the most dominant membrane desalination technology, at 88% of all membrane
production and 46% total world production capacity.
RO has four subsystems: 1) pre-treatment; 2) high pressure pump; 3) membrane modules; and 4) posttreatment.
-
Feed water pre-treatment involves filtration, sterilization, and addition of chemicals to prevent
scaling and biofouling. Pre-treatment is critical due to membrane sensitivity.
-
The desalination event happens when water is forced across a membrane surface at 17-27 bar for
brackish water and 55-82 bar for sea water.
The product, or permeate, water passes through the membrane, having the majority of its dissolved solids
removed.
Reverse osmosis removes bacteria, spores and viruses from water.
Water after being run through the reverse osmosis membrane is very, very clean. The water before the
membrane will have a built up of unwanted particles and must be cycled (flushed out) periodically.
WATER SALINITY
The water, depending on the quantity of salts, can be distinguished as:
1. SOFT contains limited amounts of dissolved salts, typically less than 1 g/L (rivers, lakes);
2. BRACKISH contains appreciable amounts of dissolved salts, but lower than that of seawater (lagoons,
coastal marshes)
3. SALTY or contains high amounts of salts, such as that of the sea which has about 37 g/L of salts, of
which almost 30 g are constituted by sodium chloride.
HARDNESS OF WATER
The presence of soluble salts of calcium and magnesium gives the water the characteristic defined as
HARDNESS. Hard water can not be used for domestic purposes or in civil and industrial heating systems
(boilers) because it has harmful effects to the pipes and to the electrical devices that use it. Hard water, in
addition to determining the problem of limestone is not suitable for washing with soap because it causes the
formation of insoluble compounds, the soap does not produce foam and therefore doesn't exert its cleaning
power.
There are three types of hardness:
TEMPORARY HARDNESS presence of bicarbonates of calcium and magnesium. It is defined as temporary
because by heating the water (70-80 ° C) these dissolved salts decompose to give the corresponding
carbonates which, being insoluble, are deposited on the walls of the vessel and form encrustations, with
considerable damages to the pipes.
PERMANENT presence of different salts of calcium and magnesium (chlorides, sulfates, nitrates, etc.) that
remains unchanged even in the hot water.
TOTAL given by the sum of the first two.
Water hardness is expressed as in French degrees units (°f). Water has the hardness of 1°f when it contains
dissolved salts of calcium and magnesium at a level equivalent to one gram of calcium carbonate in hundred
liters of water.
Classification according to the hardness of the water
Hardness
very soft
soft
intermediate hardness
hard enough
hard
very hard
°f
0-7
8-15
16-20
21-30
31-50
> 50
Hard drinking water is generally not harmful to one's health, but can pose serious problems in industrial
settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other
equipment that handles water. In domestic settings, hard water is often indicated by a lack of suds formation
when soap is agitated in water, and by the formation of limescale in kettles and water heaters. Wherever
water hardness is a concern, water softening is commonly used to reduce hard water's adverse effects.
ION EXCHANGE RESINS are synthetic molecules containing carboxyl (-COO- Na+) or sulfonic (-SO3- Na+) groups
salified with sodium.
These resins have the property to exchange and retains sodium cations with calcium and magnesium cations
present in hard water.
At the end of the process, the cylindrical purifiers filled of resin beads, can be regenerated by making leach
a concentrated solution of sodium chloride and removing the solution of CaCl2 and MgCl2 that comes out.
DRINKINK WATER
Drinking water or potable water is water safe enough to be consumed by humans or used with low risk of
immediate or long term harm. In most developed countries, the water supplied to households, commerce
and industry meets drinking water standards, and it is actually consumed or used in food preparation. Typical
uses (for other than potable purposes) include toilet flushing, washing, and landscape irrigation. The word
potable came into English from the Late Latin potabilis, meaning drinkable.
POTABLE WATER: definition
⇒ Clear, colorless, odorless and pleasant taste
⇒ Defined chemical characteristics
⇒ Bacteriologically pure
From the qualitative point of view the anions allowed in good drinking water are bicarbonates, chlorides,
sulphates and nitrates, while the cations certainly allowed are lithium, sodium and potassium. Moderately
allowed are calcium and magnesium. They are also tolerated small doses of cations of aluminum, iron,
manganese and silica traces.
Absolutely absent must be heavy metals such as lead, mercury, copper and chromium. Finally judged drinking
waters must have at source temperatures between 7-15 °C.
Drinking water quality
The following parameters have to be checked:
organoleptic
chemical
physico-chemical
microbiological
WHO TABLES
NOEL: No Observed Effect Level
ADI: Acceptable Daily Intake
To calculate these values both the following considerations must be do:
intake of this substance through drinking water (which is never the only route of administration)
level of concentration in drinking water to ensure the non-exceedance of ADI
Drinking water production process
It’s a process by which water, usually groundwater or surface is treated to make it conform to the criteria of
their quality of water intended for human consumption. This process will adapt to the characteristics of the
water to be purified, which corresponds to a "raw material", and will be much more drastic as will be more
scarce its initial quality.
Law 152/99 classifies surface water intended for the abstraction of drinking water quality in three
categories, according to a series of chemical and microbiological parameters, and indicates which treatments
should be performed during the course of purification.
A1 Category - simple physical treatment (eg. Sand bed filtration) and disinfection (eg. With active
chlorine)
A2 Category - intermediate level, which provides a combination of normal physical and chemical
treatment and disinfection
A3 Category - more complex level that provides a physical and chemical treatment pushed, refining
and disinfection
Water Supplying
It can be done by or SURFACE WATER or GROUNDWATER
PROBLEMS:
INORGANIC pollutants: chlorides, manganese, iron, lead, arsenic, nitrates, sulfates, ammonium, cyanides
etc.
ORGANIC pollutants: halogenated aliphatic hydrocarbons, pesticides, benzene, vinyl chloride etc.
Massive use of inorganic fertilizers based on NITRATES: naturally present in water at levels 5-10 mg / L now
risen to values of 25-30 mg / L (the maximum accepted is 50 mg / L). Problem of METHEMOGLOBINEMIA IN
NEWBORNS.
Another problem of contamination is that of chemical pesticides such as atrazine, toxic and easily
biodegradable.
PRELIMINARY TREATMENTS TO OBTAIN PURE WATER
Removal of coarse solids through grids with a size and shape of the openings depending on the size of the
solids that are to be deleted.
Sedimentation (or settling), a physical phenomenon caused by the action of the force of gravity that deposits
on the bottom of the clarifier (tank), the material to be deleted.
Filtration is conducted on sand filters arranged in particle size increasing from the bottom upwards with the
addition of gravel and crushed stone. In cases where the filtration process would be too slow it is possible to
use a pressure filter (higher costs and maintenance).
Water Management Steps
Pre-chlorination
Treatment with Powdered Activated Carbon (PAC)
Clariflocculation
Sand filtration
Ozonization
Granular Activated Carbon
Final chlorination with chlorine dioxide (ClO2)
1. PRE-CHLORINATION
Its purpose is to inhibit the growth of algae and bacteria during the subsequent treatment cycles. The
current disinfection treatments provide the addition of chlorine in the forms of Cl2 (gas) or ClO-Na+ (sodium
hypochlorite or sodium hypochlorite), equivalent from a chemical point of view, or ClO2 (chlorine dioxide).
The addition of hypochlorite has the significant problem of the formation of unwanted side products, such
as trihalomethanes and chloramines (potentially carcinogenic). Benefits of ClO2: high disinfectant capacity
and much lower chlorinating activity. ClO2 not form compounds with the addition of chlorine, ie chlorinated
organic or trihalomethanes (chlorinated molecules of large size are blocked by carbon filters, but the small
ones, such as chloroform, have a period of life very low, with risk of release of them in water). ClO2 persists
in the distribution system, the water is safe at the time of collection (tap).
CHLORINE DIOXIDE: Benefits of ClO2: high disinfectant capacity and much lower chlorinating activity. ClO2
not form compounds with the addition of chlorine, ie chlorinated organic or trihalomethanes (chlorinated
molecules of large size are blocked by carbon filters, but the small ones, such as chloroform, have a period
of life very low, with risk of release of them in water). ClO2 persists in the distribution system, the water is
safe at the time of collection (tap). Disadvantages: formation of chlorate and chlorite.
DISINFECTION METHODS
Chlorination (hypochlorite 63%, 2% Cl2)
Chlorine dioxide (31%)
Ozone
Ultraviolet radiation
OZONE is a reactive gas that is formed from the oxygen via electrical discharge (10-20 kV). Also the OZONE
(O3), can be used in alternative to chlorine, either alone or coupled to the hydrogen peroxide H2O2
(PEROXON), but has the drawback of producing oxygenated organic compounds with considerable toxicity.
Furthermore, because of its remarkable reactivity, can not be used to ensure the disinfecting action during
the distribution of water in the water network.
Ultraviolet radiation is characterized by a wavelength between 100 nm and 400 nm of the electromagnetic
spectrum. The radiations with higher germicidal action are between 240 and 280 nm (UV-C). Disinfection
systems use UV mercury lamps in quartz tubes. The tubes are immersed in the flow of water or in the tank.
The disinfection mechanism of UV radiation differs considerably from the mechanisms of chemical
disinfectants (such as chlorine and ozone) that inactivate microorganisms by destroying or altering the
cellular structures, by interfering with the metabolism and preventing the biosynthesis and growth.
Ultraviolet light acts by altering the nucleic acids (DNA and RNA) of organisms and thus preventing
replication.
ADVANTAGES
Efficient inactivation of bacteria and viruses in drinking water. High doses are required for cysts of protozoa.
No known disinfection by-effect or chronic toxic (mutagenic / carcinogenic).
Prevents the formation of unpleasant odors and tastes.
Do not use toxic chemicals.
It requires a small space for the UV units.
DISADVANTAGES
Has no residual disinfectant action so you need to add a secondary disinfectant.
It is rather difficult to determine the optimal dose.
Lower disinfection in environments with high turbidity.
Requires maintenance and cleaning of the UV lamps.
2. TREATMENT WITH POWDERED ACTIVATED CARBON (PAC)
The treatment with Powdered Activated Carbon (PAC) has the purpose of breaking down the turbidity of the
water and removing by adsorption most of the organic compounds of the water (chemical-physical
treatment). The powdered activated carbon is eliminated by clariflocculation.
The activated carbon powder, in contrast to the granular, can not be regenerated and is then removed by a
flocculation process used both in the industrial field in which aqueducts to sediment solids and colloidal fine.
The physical-chemical treatment is accomplished by adding the water with aluminum chloride; this salt, for
pH below 8, originates a hydroxide gel which has the ability to drag with it both the suspended material, both
microorganisms.
The appropriate pH conditions are guaranteed by a system for blowing in CO2 upstream of the flocculation.
In this treatment, the water is located in suitable tanks equipped with a stirrer in order to disperse the
coagulant agent.
3. CLARI-FLOCCULATION
The powdered activated carbon, unlike the granular, can not be regenerated and is then subsequently
removed by flocculation, chemical-physical treatment made by adding the water with aluminum chloride.
This salt, for pH below 8, originates a hydroxide gel which has the ability to drag with it both the suspended
material, both microorganisms. The appropriate pH conditions are guaranteed by a system for blowing in
CO2 upstream of the flocculation.
In this phase the water is agitated so much lower than the coagulation, because one must prevent that the
flakes formats can break. The flakes thus formed can then precipitate in a special tank decanter, in which it
remains for 3 - 4 hours. Anconella aqueduct has 4 tanks of this type.
As already said, more coagulating agents used are polyelectrolytes, i.e. salts of Fe3+, Al3+, used for both
drinking water, and water for industrial uses. This phase is followed by a filtration on quartz filters (or sand
filters).
4. FILTRATION
The water, subsequently, undergoes a sand or quartz filtration, in open tanks, where the sand is placed in
layers of uniform particle size. The water enters the top of the filter bed, permeates and exits the bottom of
the drainage system. The filters are DISCONTINUOUS, after a certain period (1000 hours) must be
regenerated, with backwashing. Sand filters are equipped with a pressure sensor for controlling the
operation of the filter, in case of clogging the sensor records more pressure thus facing block the process.
For the cleaning process, is used to pass in countercurrent air first, then a mixture of air - water and finally
water that leads to the surface the material that blocks the passage.
5. OZONIZATION
After the filtration, the water subsequently is subjected to Ozonization with PEROXON (mixing H2O2
hydrogen peroxide and O3 ozone) or only OZONE (O3). The ozone generator is formed by two electrodes
separated by a space in which is placed a dielectric sheet with high conductance. A perfectly anhydrous
Oxygen, subjected to high voltage ionizes, discharges with ozone production. In the Anconella’s purification
cycle, the ozonation is after the filters. The use of ozone in water purification consists of the introduction of
ozonized air in water and the transfer of O3 from the gas phase to the liquid. The transfer rate of ozone
depends on the liquid, if it flows turbulently or less, the concentration of ozonized air, the operating pressure
and the solubility. The oxygenated organic compounds that are generated by ozone are then slaughtered by
a treatment with granular activated carbon (GAC).
6. GRANULAR ACTIVATED CARBON
The activated carbon are microporous adsorbent materials and are activated by high Temperatures (5001000 °C).
The characteristic porosity of the activated carbon depends on the total adsorbent surface, and the pore
diameter shape and average. The diameter of the pores is of Amstrong order (10exp-10m), and this
determines the surface structure and the adsorbing power (the property of adsorbing by a fluid substances
present in it).
With the use of GAC, an internal bacterial growth is almost inevitable. It 'is therefore important that the
water is thoroughly disinfected before and after this operation. A frequent use of GAC is for removing
oxidizing substances (mainly chlorine).
The oxygenated organic compounds that are generated in this process are killed by treatment with granular
activated carbon (GAC) and the water, after a 7. FINAL CHLORINATION with ClO2 can be introduced into the
town water supply.
The water coming out of the activated carbon filters is placed in a tank (volume about 20,000 m3) named
TANK STORAGE, thus further sterilized with a final chlorination with ClO2 is ready placing in the town water
supply (5 HOURS OF AUTONOMY IN CASE OF SYSTEM SHUTDOWN).
WATER FOR INDUSTRIAL USES
Water is essential for all industrial activities, so that its availability is among the factors that influence the
location.
FEATURES
•
•
•
steam generation
cooling
raw material for food processing
The water’s characteristics for industrial applications vary greatly according to the type of industry. In some
cases, only drinking water must be used, if water is in contact with food substances; in other cases, common
waters can also be used, or completely devoid of water hardness, distilled etc. In many industries (electrical,
oil, metals, etc.) more than 80% water is used as cooling medium.
This use only determines an increase of the water temperature that can, therefore, be recycled, after passage
in appropriate cooling towers. Often, the same water is repeatedly worked in the process cycle.
This measure should always be adopted, not only where there is a shortage of water, but also to avoid hot
water discharge in rivers, lakes or the sea, since the increase in temperature which results may alter the
balance of the receiving means, determining a form of thermal pollution.
Examples of industrial water requirements, which vary according to the use:
1. in the case of steam generation, the water must have an extremely low degree of hardness (eg. Power
boilers that produce steam at high pressure)
2. water intended for use in paper mills must not contain iron ions, calcium or manganese
3. Water for sugar must not contain ions sulfates, nitrates, carbonates
4. Water for textile must not contain organic substances, iron ions, manganese, etc.
WATER FOR AGRICULTURAL USE
(Agriculture is the sector that absorbs the higher freshwater consumption)
The use of these waters regards irrigation and livestock.
The source of supply of irrigation water is represented by 70% from runoff and the remainder mainly from
wells and underground aquifers and to a lesser extent, from rainwater tanks.
The water for irrigation must have a salt content not exceeding 2.5 g / L. Temperature must be ambient.
The water for breeding must:
•
•
•
have a salinity of no more than 5 g / L
be free of toxic substances
have suitable requirements from a bacteriological point of view
MINERAL WATER
Water is essential for life. It is possible to live without food than without water. Water makes up about 4575% of your body weight.
Why is water important?
Aids with transport
Mechanical functions
Helps to break substances down
Helps to maintain body temperature/pH
How much water do you need?
Adequate intake:
◦
For men: 125 oz / day
◦
For women: 91 oz / day
Ideally 80% of water should coming from drinking fluids; 20% of water intake should come from food.
Legislative decree n. 105, 1992 January 25:
Are considered as natural mineral waters those waters which, having originated from an aquifer or
underground reservoir, comes from one or more natural sources or perforated and which have particular
hygienic characteristics, and properties favorable to health.
Mineral waters are distinguished from the ordinary drinking water for their original purity, the minerals
content, trace elements and / or other constituents and their effects. They should be kept away from any
risk of pollution.
These characteristics shall be assessed from the following points of view:
a) geological and hydrological;
b) organoleptic, physical, physico-chemical and chemical;
c) microbiological;
d) pharmacological, clinical and physiological.
The current definition of mineral water is reported, HIGHLIGHTING the changes made by the Legislative
Decree 339/99:
Are considered as natural mineral waters those waters which, having originated from an aquifer or
underground reservoir, comes from one or more natural sources or perforated and which have particular
hygienic characteristics, and, POSSIBLY, properties favorable to health.
Mineral waters are distinguished from the ordinary drinking water for its original purity, for the content of
minerals, trace elements and / or other constituents and, EVENTUALLY, OF CERTAIN their effects.
They should be kept away from any risk of pollution.
These characteristics shall be assessed from the following points of view:
a) geological and hydrological;
b) organoleptic, physical, physico-chemical and chemical;
c) microbiological;
d) IF NECESSARY, pharmacological, clinical and physiological.
The composition, temperature and other essential characteristics of natural mineral water shall remain
stable within the source of natural variations, even in the case of any change in flow.
The Legislative Decree 105/92 has subsequently been amended by Legislative Decree 4 August 1999 n. 339
and by the law of 1 March 2002, n. 39. The amendments also involved the definition of mineral water taking
into account the judgment of 17 July 1997 Case C 17/96, the First Chamber of the Court of Justice of the
European Communities. The ruling provides that a Member State can not demand that water has healthy
properties to be able to recognize such water as a mineral water.
This means that can coexist mineral water and source water, both free of healthy properties, and with the
only difference of the assessment of chemical and chemical-physical parameters (DM 542/92 for mineral
water, Legislative Decree 31/2001 for source water).
Mineral waters must be chemically and bacteriologically pure at the source; this characteristic is
guaranteed, since they come from springs located in prime locations, often in the mountains.
They should not be subjected to treatments of filtration or purification but, if necessary, made effervescent
by the addition of carbon dioxide.
Sparkling waters are divided into three categories:
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naturally carbonated sparkling mineral water;
natural mineral water fortified with gas from the source;
natural mineral water with added carbon dioxide.
Mineral waters can be used as a beverage, for therapeutic purposes, directly in the spas, often built close to
the source. Mineral water can also be placed on the market, in tightly closed containers, with a label of
“mineral water” or “still water” or simply “water”. By law, bottling plants must be located close to the source,
with inevitable higher costs for the distribution.
The commercial success of the mineral waters is strongly influenced by the packaging.
In the past, the classic and most popular container was the returnable glass, start of the commercial success
of the mineral after the II world war.
The rapid spread of consumption of the mineral water is greatly increased thanks to the use of plastic
containers (PVC and PET) and composite material.
The mineral waters are marketed in bottles of glass or plastic, sterilized, closed with pressure caps or screw
and bearing a label, where it must be indicated:
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bacteriological examination, for the absence of pathogenic microorganisms
chemical and physical examination
brand, classification of water content, name, authorization to sell, bottling date, barcode
LABELING OF MINERAL WATERS
Analytical parameters that must be reported on the label:
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elements characterizing the mineral water (concentrations as mg/L)
conductivity
residue
pH and free CO2 at the source
Legislative Decree 105/92 states that on the labels may not indicate the date of bottling but the batch number
and the date of minimum durability.
Production batch
Amount of a foodstuff produced in almost identical circumstances.
Allows you to identify any contaminated or altered consignments.
The lot number is often printed on the cap or on the neck of the bottle.
Minimum term of Conservation
Is the date by which the product, when properly maintained, retains its specific properties.
For bottled water this term is not established by law, but by the manufacturer.
From "brand to brand" varies from 12 to 24 months (after this time water can modify the organoleptic
characteristics and the concentration of carbon dioxide).
On the label must be present:
pH
The term "pH of the water temperature of the source," gives us an estimate of the acidity of the mineral
water. The pH of natural mineral waters is generally between 6.5 and 8.0. The higher the content of carbon
dioxide and sulfates and the lower the pH.
Electrical conductivity
This data is provided on the mineral water with the term "specific electric conductivity at 20°C" .This value
increases with the increase of the mineral substances dissolved in it. Therefore, the greater the electrical
conductivity and the higher the mineral content. Most of the mineral waters marketed electrical conductivity
of between 100 e 700 µS/cm.
Hardness
The hardness of a mineral water is expressed in French degrees (° F) and gives us an estimate of the presence
of calcium and magnesium. The higher this value, the water is considered limestone. There is not a limit value
for the hardness of the mineral water.
COMPOSITION OF MINERAL WATER
The composition of a mineral water is determined by the presence of macro-elements and micro-elements.
The macro-elements can be divided in turn into cations and anions and are represented by Ca, Mg, Na, K and
Bicarbonates, Chlorides and Sulfates.
The main elements characterize more than 90% of the chemical composition of water.
Another important component present in the mineral waters as a non-ionic form is silica (SiO2) that reaches
high concentrations in the thermal waters or those coming from volcanic rocks.
The micro-elements or trace elements are substances in concentrations lower than or equal to mg / L.
Frequent trace elements found in mineral waters are lithium, strontium, fluorine.
In mineral waters constant residue is an important parameter which allows to classify them; subdivided in
accordance with the 25/01/1992 n. 105 Decree, as the following:
Slightly mineralized: residue after evaporation at 180°C ≤ 50 mg/L.
OLIGOMINERAL: 50 mg/L ≤ residue after evaporation at 180 °C ≤ 500 mg/L
MEDIUM-MINERAL: 500 mg/L ≤ residue after evaporation at 180 °C ≤ 1000 mg/L
MINERAL: residue after evaporation at 180 °C > 1000 mg/L
In practice, for the determination of CONSTANT RESIDUE 1 L of water is evaporated at T = 180 ° C in a
platinum vessel.
Mineral waters can also be classified according to:
a) DISSOLVED SUBSTANCES
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salted, if chloride ion prevails
sulfur, if hydrogen sulfide prevails
bicarbonate (or alkaline) if bicarbonate ion prevails
sulphate, if sulfate ion prevails
arsenical, if containing arsenic salts
ferruginous, if containing iron salts
acidic, if containing CO2.
b) WATER TEMPERATURE AT THE SOURCE
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cold, if the temperature is less than 20 °C;
hypothermal, if the temperature is between 20 and 30°C;
thermal, if the temperature is between 30 and 40 °C;
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hyperthermal, if the temperature exceeds 40 °C.
According to their daily needs, the minerals can divided into:
Macroelements (needs >100 mg/die) - Ca, P, Na, K, Cl, Mg, S
Microelements (needs 1-100 mg/die) - Fe, Cu, Zn, Mn, I, Mo, Se, F, Br, Cr, Co, Si, B
Oligoelements (needs of some mg/die) - As, Ni, Ge, V, W
Mineral waters, as required by Legislative Decree no. 105/92, are classified according to the main type of
ionic species:
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SULPHATE waters if the sulfate anion is dominant, reported on label as SO42- greater than 200 mg / L.
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CHLORIDE waters if the chloride is the dominant anion or if the chlorides are greater than 200 mg / L.
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BICARBONATE waters if the bicarbonate anion is dominant, the label as HCO3-, is greater than 600 mg /
L.
(for practical purposes, however, a water bicarbonate, sulphate, chlorinated is defined as such even if the ion
that characterizes it does not reach the concentration established by law: it is sufficient that it is the dominant
element in the ionic formula)
- CALCIUM Water if calcium is the dominant cation and is greater than 150 mg / L.
- MAGNESIUM Water if the magnesium is the dominant cation, and is greater than 50 mg / L.
- SODIUM Water if the sodium is the dominant cation and is greater than 200 mg / L. (The words "suitable
for low sodium diets" is used for water in which the sodium content is less than 20 mg / L)
- FLUORINATED water if the fluoride is greater than 1 mg / L. If you exceed the value of 1.5 mg / L must be
indicated on the label the downside of using the product for infants and children under 7 years.
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FERRUGINOUS waters if the iron expressed as Fe (II) is greater than 1 mg / L.
NITRATE and NITRITE in drinking water are among the parameters most closely supervised.
In particular, if for NITRATES a slight variation can be admitted (however, it is recommended that they do not
exceed never the value of 25 mg / L, although the current legislation provides up to 45 mg / L and, for water
intended to 'childhood, 10 mg / L), NITRITES, more dangerous to health, must be completely absent
(maximum extent permitted by law 0.02 mg / L).
RULES AND CONTROLS ON MINERAL WATER
The parameters to be checked, the methods and frequencies of analysis of mineral waters are defined by
various regulatory measures the last of which, the Decree 29/12/2003, transposed the provisions of the EU
Directive 2003/40 / EC, requiring manufacturers more restrictive limits to some components of mineral
especially with regard to those substances that may be hazardous to health.
From 1 January 2006, natural mineral waters must comply, at the time of packaging, with the maximum
concentration limits established by the Directive, Annex I, which lists 16 components naturally present in
natural mineral waters and maximum limits which, if exceeded may present a health risk; between these
components are cited, for example, barium, arsenic, cyanide, boron etc.
Table 2, section A- Comparison of the limit values in the mineral waters for undesirable substances and
contaminants of inorganic nature (Art. 6 Decree 542/92 and changes Decree 29/12/2003). Bold numbers
show the changed parameters.
In accordance with the Decree 29/12/2003, for undesirable substances or contaminants listed in Article 6 of
the DM 542, together with the reduction of the limit values for some elements (arsenic, barium, boron,
cadmium, lead, nitrites), is scheduled their determination by referring to methods published in the latest
edition of the Standard methods for the examination of water and wastewater of “American Public Health
Association”.
Table 3, section B - Comparison of the limit values in the mineral waters for undesirable substances and
contaminants of organic nature (Art. 6 Decree 542/92 and changes Decree 29/12/2003) - Concentrations as
μg/L
Directive 2003/40 / EC of 16 May 2003 establishing the list, concentration limits and labeling requirements
for the constituents of natural mineral waters and the conditions for using ozone-enriched air for the
treatment of natural mineral waters and spring waters.
This directive provides for the use of treatments using ozone-enriched air to eliminate residues of heavy
metals and arsenic; the operation should be mentioned on the label in close proximity to the analytical
composition with the words “water subjected to an oxidation technique authorized ozone-enriched air”.
It is also provided that, in the case of fluoride concentration greater than 1.5 mg / L, the label should explain,
in immediate proximity to the trade name and in clearly visible characters, the following indication: “contains
more than 1.5 mg / L of fluoride: not is suitable for regular consumption by infants and children under the
age of seven years”.