WATER
Water: is one of the environmental resources.
Public Water Supply: refers to same clean water for use in home, schools,
hospitals, workplaces, commercial and some industrial activities, street
cleaning, and fine protection.
Water
for dainty personal hygiene and sanitary purposes is of paramount importance to
in health and well –being of the society
WATER QUALITY STANDARDS
Water
contains a variety of chemical, physical and biological substances that are
either dissolved or suspended in it. From the moment it condenses as rain,
water dissolves the chemical components of its surrounding as it falls through
the atmosphere, runs over ground surface, and percolates through the soil.
Water also contends living organisms that react with its physical and chemical
elements. For this reasons, water must often be treated before it is suitable
for use.
Water quality requirement are
Est.
abolished in accordance with the intended use of the water quality is usually
judged as the degree to which water conforms to physical, chemical, and
biological standards set by the user. Water quality standards are also
essential in monitoring treatment processes.
Water
is evaluated for qualify in terms of its physical, chemical, and
microbiological properties.
Physical characteristics
Tastes, Odours, Co lour and turbidity are controlled
in public water supplies pertly because they make drinking water unpalatable, but
also because of the use of water in beverages, food processing and textiles
Tastes and odours are caused by the presence of volatile chemicals and
decomposing organic matter. Measurement for these are conduced on the basis of
the dilution needed to reduce them to level barely detectable by human
observation co lour in water is caused by minerals such as lion and manganese,
organic materials and co lour water form industries. Testy is done by
comparison with a standard set of concentrations of a chemical that produces a
co lour similar to that found in water. Turbidity, as well as being
aesthetically objectionable, is a health concern because the particles involved
could harbor pathogens water with enough suspended clay particles will be
visually turbid. Turbidity measurements are base on the optical properties of
the suspension that cause light to be scattered or absorbed rather than
transmitted in straight lines through the Samuel.
Chemical Characteristics
The May chemical compounds dissolved in water may be
of natural or industrial origin and may be beneficial or harmful depend on
their composition and concentration. For example, small amounts of lion and
manganese may not just cause co lour, they can also be oxidized to form deposits
of ferric hydroxide and manganese oxide in water mains and industrial equipment
these deposits reduce the capacity of pipes and are expensive to remove.
Hard Water are generally considered to be those water
that require considerable amounts. Of soap to produce a foam or lather and that
also produce scale in not water pipes, heaters, boilers, and other units in
which the temperature of water is increased materially.
Sources of Water
The quality and quantify of water form surface water
and ground water, the two main sources, are influenced by geography, chi male,
and human activities. Ground water can normally be used with life or no
treatment. Surface water, on the other hand, often needs extensive treatment,
particularly if it is polluted.
Ground water
Ground water: is water that has percolated down word from the
ground useful through the soil pores. For motions of soil and rock that have
become saturated with water are known as ground water reservoirs, or aquifers.
Soil pore size water viscosity and other factors combine to limit the speed at
which water can move through soil to replenish the well.
Ground water: is not as susceptible to pollution as
surface water, but once polluted its restoration, even if possible, is
difficult and long term. This is why municipalities even those located close to
surface water prefer wells for a municipal water supply much less treatment and
there for expense is needed to bring ground water standards. Ground water
quality is difficult to monitor when large number of well are in use.
Surface Water
Surface water is from rivers and levels are important
sources of public water supplies be cause of the light with darnel rates they
can normally sustain. One disadvantage of using surface water is that it is
open to pollution of all kinds. Contaminants are contributed to lakes and
rivers from diverse and intermittent sources, such as industrial and municipal
wastes, run off from urban and agricultural areas, and erosion of soil water
with variable turbidly and a variety of substance that contribute to the taste,
odour, and co lour of the water can necessitate extensive treatment.
Seawater
Seawater
available in almost unlimited quantities, can be converted into fresh water by
a number of processes
·
Desalination is
the general term used for the removal of dissolved salts from water.
Distillation, the oldest desalination techmvue depends
on the evaporation and condensation in water.
·
Energy intensive,
but using solar energy to evaporate water may make it practical in countries
with plentiful sunshine
·
Freezing lowers
the water temperature unit lice crystals free of salt can be separated from the
brine.
·
Electro dialysis
involves forced migration of charged ions through cat ion - permeable or anion
–permeable membrane by applying an electric Pont --- entail across a cell containing mineralized water.
Reclaimed waste water
Reclaimed waste water: is water that has been treated sufficiently
for direct reuse in loop operation may offer only alternative in areas that cannot
obtain enough fresh water. Suspended solids, boded addable organics, and
bacteria can be removed or degraded by normal waste water treatment processes,
but co lour, the inorganic salts or magnesium, sodium, and calcium, synthetic
organics like pesticides, and other taxi substance similar to those by
desalination.
WATER TREATMENT PROCESSES
Water treatment
plant: one of the great achievements of modern technology has been to
drastically reduces the incidence of water borne diseases such as cholera and
typhoid ever these diseases are no longer the great risks to public health that
they once were.
Today’s water treatment plans are designed
to provide water continuously that meets drinking water standards at the top
there are four main consideration involved in accomplishing this:
·
source selection
·
protection of
water quality
·
treatment methods
to be used
·
prevention of
recontamination
Common precaution to prevent ground water and surface
water pollution include.
·
Prohibiting the
discharge of sanitary and storm sewers close to the water reservoir.
·
Installing fences
to prevent pollution from recreational uses of water
·
Restriction on
the application of fertilizers and pesticides in areas that drain to the
reservoir.
Screening, Coagulation / Flocculation,
Sedimentation, filtration, and disinfection are the
main unit operations involved in the treatment of surface water.
Water treatment operation fulfills one or more of
three key tasks:
·
Removal of particulate substance such as send and
clay, organic matter, bacterial and algae.
·
Removal of
dissolved substances such as those
causing co lour and hardness.
·
Removal of
destruction of pathogenic bacteria and viruses. The actual selection of
treatment processes depends on the type of water source and the desired water
quality.
In a form, water flows by gratuity through
intake structure and pipe, screens remove larger items, such as fish sticks,
and leaves, and low ---lift pumps raise incoming water to the level of the
treatment plant. From this point on, water moves through the plant by gravity.
Occasionally raw water with low turbidity can be plain sedimentation to remove larger
par tickles and then filtration to remove the few prentices that failed to
settle out. Usually, however, particles in the raw water are two small to be
removed in a reasonably and simple filtration alone to remedy this a chemical
is added to coagulate / flocculate the small particles, called Colloids, into larger ones, which can
then be settled out in sedimentation tanks or removed directly in filters where
sedimentation proceeds filtration, filters can operate for longer periods, or
at higher rates before they have to be backwashed. Filtration of chemically coagulated
/flocculate water with no prior sedimentation (called direct filtration) is
effective for water with low to moderate turbidity and is in fact the practice
in many of the newer water treatment plants. Following filtration and before it
flows into the storage reservoir, the water is disinfected; usually with
chlorine fluoride may also be added because of its ability to retard tooth decay.
Treated water is then pumped by the high-lit pumps into the distribution system
to serve customers and to maintain water levels in storage reservoirs if
required. It is impotent to recognize that water treatment still remains some
what of an at despite many scientific advances in understanding the physical
and chemical principles involved.
Removal of particulate matter
The unit operations employed for the removal of
particulate matter for water include: screening, sedimentation,
coagulation,
Screening: to remove large solids such as logs, branches, rags,
and small fish is the first stage in the treatment of water. Water intake is
located below the surface of the lake to exclude floating object and minimize
physical damage from lce.
Sedimentation the oldest and most widely used form of water and waste water treatment, uses
gravity settling to remove particles from water. It is relatively simple and inexpensive and
can be implemented in basin that are round, square, or rectangular- water
containing particulate matter flows slowly through a sedimentation tank and is
thus detained long enough for tank over a weir at the outlet end.
Coagulation/
flocculation: is a chemical physical predate
where by particles too small for practical removal by clustered together for
faster settling.
Coagulation is a chemical process used to destabilize colloidal particles.
The exact mechanism is not well understood, but the general idea is to add a
chemical that provides positively charged ions to water containing negatively
charged colloids.
Removal of
Dissolved Substance several of the
unit operations discussed so far are partially effective in removing objection
able dissolved substances. For example, co lour in water caused by coagulation
flocculation. If these are a problem, several other unit operations are
available:
Aeration: is used to remove excessive amounts of iron and
manganese from ground water. These substance cause taste and co
lour problems, inter fare with laundering, stain plumbing fixtures, and promote
the growth of iron bacteria in water mains.
Softening of
water is a process that removes
hardness, caused by the presence of divalent metallic irons, principally Ca+2 and Mg+2. Hardness, in water is
the result of contact with soil and rock, particularly limestone, in the
presence of CO2.
Activated Carbon: is an extremely adsorbent
material used in water treatment to remove organic contaminants.
Reverse Osmosis (RO), fresh water is forced through a semi permeable
membrane in the direction opposite to the occurring in natural Osmosis. Because
the membrane removes dissolved salts, the main application for Ro has been in
desalination.
STORAGE
Storage: is necessary in
any municipal water supply system to meet variable demand, to provide fire protection, and for emergency needs.
Types
of water storage
Equalizing storage: also called operating storage, is used to meet
variable water demands while maintaining adequate pressure on the system.
*
Fire Storage: is calculated
by taking the product of fire flow and fire duration. Fire flow duration times
suggested by the national fire protection Association (NFPA).
* Emergency storage: of up to five time the
maximum daily demand is suggested by the insurance Advisory Organization, to provide water during
shutdowns for maintenance or repaint to the system.