Water treatment and Analysis

MD.AZMERI LATIF BEG
M. Sc in Textile Engineering
Specialized in Apparel Manufacturing, Processing and Designing

 INTRODUCTION
 The fresh water is rarely used directly for drinking purposes,
as the water gets contaminated with impurities during its
transportation to the city reservoir. Even, the water which is
to be used for industrial process also needs a pretreatment.
For instance water for textile industry should not contain too
much of iron, as it causes staining of fabric. Water for food
industry cannot afford to have manganese, as it causes
staining of containers and adversely affects the taste and
quality of material cooked in that water. The boiler feed water
should not contain excess of salts of calcium and
magnesium, as they consume more heat due to insulation of
containers and pipes by deposition of scales.

A substance that in its purest form is odorless, colorless and
tasteless and is needed for survival by every living being.
Classification of Water:
Water can be classified into three types according to the source:
 Surface water
 Subsoil water
 Deep well water
Surface water:
Rain inevitably finds its way into stream, rivers and lakes, all of
which are classified as surface water. As is passes over the surface
of the earth it carries with it or organic matter in various stages of
decomposition. Nitrifying bacteria will in the time convert the
organic substances into nitrous which are not objectionable in
dyeing and finishing.

Subsoil water:
When in this classification is collected from
shallow spring and wells which are about .15m
(50ft) or so deep. It is, therefore, surface water
which has percolated a short distance through
the soil or rock formation.
Deep well water:
The deep wells are those which are bored
through the subsoil into the water bearing strata
beneath.

 The treatment procedure also vary depending upon
its use. However, overall picture of water treatment,
irrespective of end use shall be considered. An
endeavor is made to comprehend the basic chemistry
involved in water treatment process. The important
stages involved in treatment are as follows:
coagulation or flocculation; sedimentation; filtration –
slow sand, rapid sand filtration; disinfection –
including chlorination and ozonolysis; removal of iron
and manganese; softening by lime-soda ash process
or deionization method; scale and corrosion control;
taste and odor removal; prophylaxiation treatment,
i.e., fluoridisation; and specialized treatment for a
specific purpose.

This is the first important step in the water treatment. The principal coagulants used in water
treatment consists of aluminum sulphate, ferric chloride, ferrous sulphate. The important
reactions involved in flock formation with alum are as follows:
Al2(SO4)3 + 3Ca(HCO3)2 → 3CaSO4 + 2Al(OH)3 + 6CO2
Al2(SO4)3 + 3Ca(OH)2 → 3CaSO4 + 2Al(OH)3
Al2(SO4)3 + 3Na2CO3 + 3H2O → 2Al(OH)3 + 3Na2SO4 + 3CO2
Al2(SO4)3 + 6NaOH → 2Al(OH)3 + 3Na2SO4

Figure: Water management
This flock of Al (OH)3 absorbs dirt and color during sedimentation. The reaction with ferric chloride
coagulation process is as follows:
2FeCl3 + 3Ca(HCO3)2 → 3CaCl2 + 2Fe(OH)3 + 6CO2
2FeCl3 + 3Ca(OH)2 → 3CaCl2 + 2Fe(OH)3
While with FeSO4 and chlorine,
Cl2 + 2FeSO4 + 3Ca(HCO3)2 → 2Fe(OH)2 + 2CaSO4 + 6CO2 + CaCl2
FeSO4 + Ca(OH)2 → Fe(OH)2 + CaSO4
FeSO4 + Ca(HCO3)2 → Fe(OH)2 + CaSO4 + 2CO2
2Fe(OH)2 + ½ O2 + H2O → 2Fe(OH)3
The last reaction in the presence of dissolved oxygen is critical. The effectiveness of a coagulant is
determined by the magnitude of zeta potential. The zeta potential is defined as the charge on ions
surrounding suspended particulate matter. The charges are usually negative and are expressed
in terms of mill volts.
Rejection
Accumulatinon
Circulation
Collection
Recycle
Water origin
Applications
Treatment

This treatment does not involve any chemical
process, nevertheless it is an important aspect of
water treatment. This is physical process of settling of
floc. Sedimentation may occur within 15 to 60 minutes
duration after vigorous stirring of water with baffles,
which in turn expedites the agglomeration process. In
this process the color of water is also removed, as
colored molecules form basic insoluble salts. The
settling tanks are of various sizes and shapes. They
have horizontal flow or circular flow or static settling
tanks. Sludge clarifier ensures proper circulation and
controls the turbulence, or excess of stirring during
process of settling. The large particles settle early in
comparison with small particles. The shallow depth
sedimentation is efficient.

FILTRATION
The main role of filters is to retain the particles contained in a liquid
on the surface of filter media or in-depth. Surface filtration requires
supporting media, while in-depth filtration is performed through a
filter bed. The dissolved solids in the presence of chloride,
sulphates of magnesium and sodium increase bed penetration by
flock. The real filtration takes place in the first 3 to 4 cm in total
height of 80 cm filter bed. The slow sand filters involve filtration of
water without previous treatment, while rapid sand filters are used
for water which has been previously treated by coagulation or
sedimentation. Anthracite coals are used for filtering media along
with sand and gravel. The filter beds are usually cleaned by back
washing. In rapid filtration, water passes through bed. Washing of
filter bed leads to expansion of the filter bed. However,
simultaneous air and water washing proceeds without expansion of
filter bed.

REMOVAL OF IRONAND MANGANESE
From drinking water, Fe and Mn must be removed, as
they cause corrosion of pipes, affect appearance of
water, impart metallic taste and cause laundering
problems. The paper and textile mills also cannot
tolerate their presence in processing water. In
underground water, they are present in reduced form for
want of oxygen. The metal is present in complex form.
Zeolites are cheaper. Zeolites are complex alumina
silicates of alkali metals. The reaction with zeolites are-
Na2Z + Fe+3 → Fe-Z + 2Na+
Na2Z + Mn3+ → Mn-Z + 2Na+

The process of decreasing the hardness of water is
called softening. It involves decreasing the
concentration of calcium and magnesium salts in water.
The term softening is applied to the process whereby we
remove or reduce the hardness or water, irrespective of
whether it is temporary (or carbonate) or permanent (or
non-carbonate) hardness. We have seen that hardness in
water is objectionable because boiling a solution
containing Ca2+ and HCO3
- deposits CaCO3 just as in
cave formation. In industrial boilers the formation of
CaCO3 is an economic headache, because CaCO3 is a
poor heat conductor. Fuel efficiency is drastically cut
and boilers have been put completely out of action by
local overheating due to boiler scale.

Natural water containing large quantities of
dissolved salts of calcium and magnesium is called
hard water. The salts responsible for hardness are
not harmful to man, but when magnesium is present
in large quantities; it impairs the organoleptic
properties of water. The maximum permissible
quantity of magnesium oxide in water is 15 mg/liter .
Excess magnesium salts (over 50% of the total
volume of liquid) make water softening a difficult
problem.

Using hard water for domestic and industrial purposes is
undesirable for the following reasons:
A lot of soap is required for washing. The Ca2+ and Mg2+ ions
react with soaps, which are salts of fatty acids, to give
insoluble precipitates, (C15H31COO)2Ca and (C17H35COO)2Ca,
and similar salts of magnesium. Water with a hardness of 7.1
mg-eqiv will require the use of an extra 2.4 g per liter of soap.
The premature wearing out of fabric after laundering in hard
waters. The fibers adsorb calcium and magnesium salts and
this makes them brittle.
Meat and beans loss much of their nutritional value when
boiled in hard waters, the boiling time is increased, and
proteins extracted form meat pass into an insoluble form and
their assimilation becomes difficult.
The intense corrosion of boilers and hear exchangers
because of the hydrolysis of magnesium salts and the
increased connection of H+ ions in the solution.
Mg2+ +2H2O → Mg(OH)2 + 2H+

Scale deposits on the surfaces of heat exchangers (boilers,
condensers) reduce the efficiency of such equipment. Scale
has low heat conductivity and increases fuel consumption.
Metal under scale deposits overheats and becomes soft.
Boiler tubes begin to budge and crack. The scale should
therefore be removed periodically.
Scaling is connected with the thermal decomposition of
bicarbonates, hydrolysis of carbonates, and also decreased
solubility in hot water of calcium sulphate, magnesium
hydroxide, and silicates of Ca and Mg. The concentration of
these substances increases in boiler during water
evaporation. Moreover, additional quantities of silicates of
Mg and Ca can be formed at high temperatures.
CaSO4 + Na2SiO3 → CaSiO3 + Na2SO4
Salts of Fe, Mn, Al and suspended and colloidal particles are
also involved in scale formation. The scale deposit can
sometimes be so thick that it almost totally blocks the
passage.

One way is to add sufficient quantities of soap. Thus
enough steerage ions are added to precipitate all the
objection-able Ca2+ ions, leaving the excess soap to
carry on the cleansing action.
Another way is to boil the water. The temporary
hardness, which is attributed to the presence of
bicarbonates of calcium and magnesium can be
removed simply by boiling the water or by adding
lime to the hard water. The soluble bicarbonates of
calcium and magnesium decompose on boiling and
are precipitated as insoluble carbonates which are
allowed to settle and water is filtered off.
Ca(HCO3)2 CaCO3 + CO2 + H2O Mg(HCO3)2
MgCO3 + CO2 + H2O

The reactions are reversible, but the forward reaction can be
made dominant by boiling off the CO2. Boiling, however, is not
practical for large scale softening.
In the Clark’s process, calculated amount of lime is added to the
hard water, whereby the bicarbonates are converted into
insoluble carbonates and are removed as above.
Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O
Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2 H2O
Permanent hardness is caused by the presence of sulphates and
chlorides of calcium and magnesium and can not be removed by
merely boiling or adding lime. Special methods are used for the
removal of permanent hardness. So the third way to soften water
is to precipitate Ca2+ by adding washing soda, Na2CO3. The
added CO3
2- ions react with Ca2+ ion to give insoluble CaCO3. If
bicarbonate ion is present, the water may by softened by adding
a base such as ammonia. The base de–protonates HCO3
- to give
CO3
2-, which then precipitates the Ca2+. A fourth way to soften
water is to tie up the Ca2+ ion so that it becomes harmless. One
way to do this is to form a complex containing Ca2+. Certain
phosphates, such as sodium phosphate (Na3PO4) act as
sequestering agents by forming complexes in which Ca2+ is
trapped by the phosphate.

The fifth and most clever method of softening water
is to replace the offending calcium ion by another
ion such as Na+. This is done by the process called
ion exchange. The ion exchangers originally used
for softening water were naturally occurring silicate
materials, called zeolites. The giant silicate network
of a zeolite is negatively charged and is composed
of covalently bound silicon, oxygen, and aluminium
atoms. Zeolites are very closely related in structure
to the clays, which also show ion exchange. The
mobile Na+ ions in the pores can be readily
exchanged for Ca2+ ions.

To understand the principle of cat-ion exchange, consider the
structure of a natural zeolite, NaAlSiO4. In it atoms of aluminium,
silicon and oxygen are bonded together to form a huge macro
anion similar in structure to a macromolecule such as quartz. The
negative charge of the anion is balanced by Na+ ions trapped in
holes in the anionic lattice. Nothing will happen when pure water is
passed through the zeolite because Na+ ions cannot leave the
crystal lattice because in that case there would be an unbalance of
charge. When hard water is passed, through the zeolite, some of
the Na+ ions migrate out of the lattice, being replaced by equivalent
number of Ca2+ ions.
Ca2+ (aq) + 2 NaZ (s) → CaZ2 (s) + 2 Na+ (aq)
Thus Ca2+ or Mg2+ ions responsible for hardness can be replaced
by two less objectionable Na+ ions. After a zeolite column has been
used for some time, more and more of the vacancies in the lattice
become filled with Ca2+ ions. Hence an equilibrium is reached
beyond which no further exchange of cat ions will occur. The
column is regenerated by flushing with a concentrated solution of
NaCl. As a result, above reaction is reversed and zeolite is ready for
use.

In this process, the lime treatment is followed
by the addition of soda ash (Na2CO3) as result
of which calcium ions in the hard water are
removed as CaCO3 and magnesium ions as
Mg(OH)2. This process is used for the removal
of temporary as well as permanent hardness
and has been divided into the cold lime
process and the hot lime process. The cold
lime process is used for partial softening of
water, say from 100 ppm to 35 ppm of
hardness. The hot lime soda process is
employed almost entirely for conditioning the
boiler feed water. The reactions involved are:

For Carbonate Hardness:
Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O
Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2H2O
Since MgCO3 is fairly soluble, it reacts further in the following manner.
MgCO3 + Ca(OH)2 → Mg(OH)2 + CaCO3
For Permanent Hardness:
MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2
CaCl2 + Na2CO3 → CaCO3 + 2NaCl
CaSO4 + Na2CO3 → CaCO3 + Na2SO4
MgSO4 + Na2CO3 + Ca(OH)2 → CaCO3 + Mg(OH)2 + Na2SO4

It is evident from the above reactions, that in case of temporary
hardness, each unit of calcium bicarbonate requires one mole of
lime, whereas for each unit of magnesium bicarbonate two moles
of lime are needed. In the case of permanent hardness, the
magnesium salts require one mole each of soda ash and lime,
whereas the calcium salts require one mole of sods ash. In other
words, for the removal of permanent hardness by Na2CO3, no
lime is necessary to remove permanent hardness caused by
calcium salts only, but some lime is necessary to remove such
hardness caused due to the presence of magnesium salts. If
there is excess of lime in the softened water, the water will be
made hard due to the presence of soluble Ca(OH)2. Hence it is
most essential to add requisite amounts of Ca(OH)2 and Na2CO3
to the hard water. For removing 10 ppm of hardness from one
million gallon of water, the following quantities have been
proposed.

 Ca(HCO3)2 hardness (expressed CaCO3) – 521 lbs of lime.
 Mg(HCO3)2 hardness (expressed as CaCO3) – 1040 lbs of lime.
 Calcium non-carbonate hardness (expressed as CaCO3) – 900 lbs
of soda ash.
 Magnesium non-carbonate hardness (expressed as CaCO3) – 900
lbs of soda ash, 520 lbs of lime.

The cat ion exchange resin in H+ form, is used while
anion exchange resin is used in OH- hydroxyl form.
A strongly acidic resin (like vinyl styrene DVB
copolymer with sulphonation) is used as cat ion
exchanger, while basic anion exchanger (also vinyl
styrene base with labile OH – group) is used for
removal of anions. The important reactions are:
H2R + CaCl2 → CaR + 2HCl
H2R + MgCl2 → Mg-R + 2HCl
H2R + CaSO4 → CaR + H2SO4
H2R + MgSO4 → MgR + H2SO4
Then water is passed on anion exchanger RNH3OH

WTP contains three filter these are given below:
1) Multimedia filter : Only stone remaining in this filter of
tank.
2) Activated Carbon filter : Activated carbon in upper side &
stone in lower side.
3) Resin filter (Softener vessel) adjusted with NaCl vessel: Resin
in upper side & stone in lower side.

Procedure :
At first water come inside the multimedia filter by input pipe.
Then water pass to second tank means carbon tank. Here
polluted water must be purified and pass to the next tank or
Resin tank. It is very important tank for wtp. In this tank,
Resin must be given for washing water. Wastage of other
tank and polluted water wastage are remove in this tank by
extra pressure. Resin hold the ca, mg in attach with it. After
that it hold clean water supplied. Next supply to clean
water(hardness of water must be 5 above). Incase of Resin
damage, then it can not hold ca, mg, at this time supply of
water to dyeing must be stopped. At this moment additional
tank is used with the resin tank. Here used (NaCl - 550 kg +
Water 1500 Lt). It is used to clean the resin tank. It is also
used to increase the activity of resin tank.

After this treatment, all Salty water should be drained by
pressure. Then water is used to dyeing section supply
again. This system is also called back wash. Water
treatment plant is used for the removal of Water
hardness, creosote and pesticides from the liquid phase
in a timber treatment facility. A storage tank is used for
smoothing the flow, from where the water is pumped into
a chemical dosing system for pH adjustment. At this
stage, ferric sulphate is added to form a precipitate with
suspended solids, which is subsequently flocculated by
the addition of polyelectrolyte.

Water is then pumped through series operated
sand filters, which provide the final stage of
suspended solids removal and protect the
granular activated carbon (GAC) filters from
particulate contamination. Series operated GAC
filters are then used to remove the dissolved
creosote and pesticides from the water. To
ensure compliance with specification levels, the
water is sampled and analyzed after the first
GAC filter. The second GAC filter acts as a guard
bed.

The key features of these products are :
•Range of activity levels and pore size distributions provide a
flexible approach to adsorption
•Excellent product hardness to resist mechanical attrition
•Spent material can be thermally reactivated
Water Hardness Test : Equipments :
•Solution (TH-C)
•Indicator (TH-B)
•Buffer soln (TH-A)

Test :
•Water : 10 ml
•Buffer : 3 drop
Indicator : something
Soln making
Details are given below:

Test Procedure : At first water should be taken. After
that Buffer must be added only 3 drops. Next add
something indicator. If in this time color will appear blue
means hardness zero. On the other hand if color will
appear in violet means hardness is present. At this time
solution TH-C added in according to drop. Per drop
grading of this solution is 5. If the blue color come by
adding TH-C 1 drop then this water hardness is 5. So
much added this solution then hardness is also more.

First of all, take 5ml water in a bottle than added 5
drop of buffer solution and 1 drop of indicator.
Then add EDTA (Ethylene di amine Tetra Acetic Acid)
by injection. Injection is pointed 0.01 to 1.
Finally calculate by giving result how many EDTA are
needed to change the color.
5 ml water+5 drop of
buffer solution+1
drop indicator

 if we use 10 ml water
then multiply 500.
If we use 5 ml water
Then multiply 300.

Water Treatment Process Flow diagram :

Water treatment and Analysis

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Water treatment and Analysis