This PPT is based on techniques of Treatment of water from hardness, arsenic , fluoride

2. REMOVAL OF HARDNESS:

3. What is hard and soft water:
 Water which readily gives a lather
with 'soapy' soap (not detergents) is described as
SOFT water.
 Note: Detergents usually give a good lather with any
water.
 Some of these dissolved substances make the
water HARD.
 'Hard water' means the water does not readily give a
good lather with soap and so wastes soap as well
as causing a 'scum'! though the 'hardness' does not
affect soap less detergents.

4. Hard water come in two varieties
 Temporary hardness:
 Temporary hardness is a type of water hardness caused by the
presence of dissolved bicarbonate minerals (calcium bicarbonate and
magnesium bicarbonate). When dissolved, these minerals yield
calcium and magnesium cations (Ca2+, Mg2+) and carbonate and
bicarbonate anions (CO3
2−, HCO3
−).
 Temporary hard water can be softened by boiling the
water.
 Permanent hardness:
 Permanently hard water cannot be softened by boiling.
 Permanent hardness is caused by very soluble magnesium
sulfate (from salt deposits underground) and slightly soluble calcium
sulfate (from gypsum deposits).
 In order to soften water you must remove the calcium
ions (Ca2+) or magnesium ions (Mg2+) ions from it by
one means or another

5. Temporary hardness Removal:
 Chemical Process of Boiling Hard Water
 We can boil water to remove temporary hardness.
Temporary hardness in water can be easily removed by
boiling. On boiling, calcium/magnesium bicarbonate
decomposes to give
NOTE : calcium/magnesium carbonate, which is insoluble in
water. Therefore, it precipitates out.

6. Permanent hardness Removal:
 Adding Washing Soda:
 Calcium and magnesium ions present in hard water
react with sodium carbonate to produce insoluble
carbonates. The water now contains soluble and
harmless sodium salts.


7.  Calgon Process:
 Calgon is a trade name of a complex salt, sodium
hexametaphosphate (NaPO3)6. It is used for softening
hard water. Calgon ionizes to give a complex anion:
 The addition of Calgon to hard water causes the
calcium and magnesium ions of hard water to displace
sodium ions from the anion of Calgon.

8.  Using Ion ExchangeResins:
 Giant organic molecules having acidic or basic groups
are known as Ion-exchange resins. Acid resins contain
the acid group (- COOH).
 Acid resins exchange their H+ ions with other cations
such as Ca2+, Mg2+, etc., present in hard water. Acid
resins are, therefore known as base-exchange resins.

9.  Basic resins exchange their OH-ions with the other
anions such as HCO3
-, Cl-, SO4
2-, present in hard water.
Basic resins, therefore, are also known as acid
exchange resins.

10.  Fig: 11.5 - Ion-exchange process for water softening
 In the ion exchange process, hard water is passed through two tanks
 'A' and 'B'. Tank- A contains acid resin and tank- B is filled with basic resin. All
the cations present in hard water (except H+) are removed by the acid resin
present in Tank- A, and the basic resin present in Tank- B removes all the
anions (except OH-) present in hard water. Water obtained after passage
through both the tanks is free from all the cations and anions that make it
hard. The water obtained after passing through the ion-exchangers is called
deionised water or demineralised water. This is as good as distilled water. The
water becomes soft after this process.

11. REMOVAL OF ARSENIC:

12. Introduction:

Arsenic (As) is known to be a very toxic element and a carcinogen to human.
Even a trace amount of arsenic can be harmful to human health.
 The World Health Organizations (WHOs) current provisional guideline for
arsenic in drinking water is 10 ppb. In India, states like Uttar Pradesh, Bihar,
Jharkhand, West Bengal, Assam, Manipur, mainly in Ganga-Meghna-
Brahmaputra (GMB) plain covering an area of about 569749 sq km with a
population of over 500 million have reported serious illnesses due to presence
of arsenic.
 The arsenic removal from drinking water by physicochemical process provides
process for decontamination of water with respect to arsenic.
 BARC developed know how of ultra filtration (UF) based membrane
technology for water decontamination with respect to microbiological
contamination at both domestic and community scale is available for transfer
separately.
 The present technology is a novel Ultra filtration (UF) membrane assisted
physicochemical process for removal of arsenic from ground/surface water to
make the water safe for drinking.

13. Application:
 � Removal of arsenic from ground/surface water to
provide safe drinking water free from primary
contaminant like arsenic as well as secondary
contaminants like iron and microorganisms.
�
 Technology can be adopted at both domestic and
community level

14. Process:
 UF membrane assisted physicochemical process/device is
capable of removing arsenic contamination from ground/surface
water for drinking purposes from a feed concentration of 500
ppb or more to less than 10 ppb (which is the desirable limit set
by BIS).
 The entire process involves two steps:
 1) Absorption of arsenic species on the in situ generated
absorbent by simple addition of two reagents.
2) Filtration of arsenic containing sludge using UF membrane
device based on the technology developed by BARC. The two
reagents required for the first step are to be prepared using the
procedure given in the technology transfer document. The details
of the device required for the second step is available in the form
of technology with BARC and can be taken separately. These
devices are also available with several licensees of BARC in the
form of commercial products.

16. Second Method:
 Arsenic removal from water requires special adsorption
media. Granular ferric oxide, titanium and hybrid media
that contain iron-impregnated resin are all highly effective,
but there are differences in media life.
 Before choosing a treatment technology, homeowners
should ask water treatment providers to estimate the
number of days that media can remove arsenic based on
their water usage and water test results.
 The media are either contained in tanks for whole-house
treatment or in cartridges for point-of-use (POU) treatment.
Whole-house treatment is intended to treat all water for the
house.
 The POU treatment system is installed at one location, such
as a kitchen faucet, that provides water for drinking and
cooking.

18. Installation:
 A typical whole-house adsorption system installed by a
water treatment professional is shown in Figure 1.
 The system consists of a flow control module, an incoming
water pressure gauge, an untreated water sampling port, a
tank containing two cubic feet or more (depending on the
size of the household and water test results) of adsorption
media with backwash control valves, a shut-off valve and a
sampling port for treated water.
 The system should be thoroughly backwashed before being
placed into service. The system requires backwashing every
28 days or after treatment of every 8,000 gallons of water.
 Most systems have an automatic backwash option based on
the volume of water treated or the time since the last
backwash.
 This periodic backwash helps to “fluff” the bed to eliminate
channelling and to remove sediment and minerals that
increase the pressure and reduce water flow.

19. REMOVAL OF FLUORIDE:

20. Introduction:
 Fluoride is a normal constituent of natural water samples.
Its concentration, though, varies significantly depending
on the water source.
 Although both geological and manmade sources contribute
to the occurrence of fluoride in water, the major
contribution comes from geological resources.
 Except in isolated cases, surface waters seldom have
fluoride levels exceeding 0.3 mg/l. Examples are streams
flowing over granite rich in fluoride minerals and rivers
that receive untreated fluoride-rich industrial wastewater.
 There are several fluoride bearing minerals in the earth's
crust. They occur in sedimentary (limestone and
sandstone) and igneous (granite) rocks.
Weathering of these minerals along with volcanic
and fumaroles processes lead to higher fluoride levels in
groundwater. Dissolution of these barely soluble minerals
depends on the water composition and the time of contact
between the source minerals and the water.

21. Guidelines And Standards:
 Taking health effects into consideration, the World
Health Organization (1996) has set a guideline value of
1.5 mg/1 as the maximum permissible level of
fluoride in drinking waters.
 However, it is important to consider climatic
conditions, volume of water intake, diet and other
factors in setting national standards for fluoride.
 As the fluoride intake determines health effects,
standards are bound to be different for countries with
temperate climates and for tropical countries, where
significantly more water is consumed.

23. Ways to fight against fluoride:
Chemical Additive method:
 These methods involve the addition of soluble chemicals to the water.
Fluoride is removed either by precipitation, co-precipitation, or
adsorption onto the formed precipitate.
 Chemicals include lime used alone or with magnesium or aluminium
salts along with coagulant aids. Treatment with lime and magnesium
makes the water unsuitable for drinking because of the high pH after
treatment.
 The use of alum and a small amount of lime has been extensively studied
for defluoridation of drinking water. The method is popularly known as
the Nalgonda technique (RENDWM, 1993), named after the town in
India where it was first used at water works level.
It involves adding lime (5% of alum), bleaching powder (optional)
and alum (Al2(SO4)3.18H2O) in sequence to the water, followed by
coagulation, sedimentation and filtration. A much larger dose of alum is required
for fluoride removal (150 mg/mg F-), compared with the doses used in routine water treatment.

24.  As hydrolysis of alum to aluminium hydroxide releases H+ ions, lime
is added to maintain the neutral pH in the treated water. Excess lime
is used to hasten sludge settling.

25.  The Nalgonda technique has been successfully used at
both individual and community levels in India and other
developing countries like China and Tanzania.
 Domestic defluoridation units are designed for the
treatment of 40 litres of water.

26. Contact Process:
 Contact Precipitation:
 Contact precipitation is a recently reported technique
in which fluoride is removed from water through the
addition of calcium and phosphate compounds.
 The presence of a saturated bone charcoal medium
acts as a catalyst for the precipitation of fluoride either
as CaF2, and/or fluorapatite (Fig. 22.3).
 Tests at community level in Tanzania have shown
promising results of high efficiency. Reliability, good
water quality and low cost are reported advantages of
this method (Chilton, et al., 1999).

28. Bone char as Defluorinating
material:
 Bone char consists of ground animal bones that have been
charred to remove all organic matter.
 Major components of bone charcoal are calcium
phosphate, calcium carbonate and activated carbon.
 The fluoride removal mechanism involves the replacement
of carbonate of bone char by fluoride ion.
 The method of preparation of bone charcoal is crucial for
its fluoride uptake capacity and the treated water quality.
Poor quality bone char can impart bad taste and odour to
water.
 Exhausted bone char is regenerated using caustic soda.
Since acid dissolves bone char, extreme care has to taken
for neutralising caustic soda.
Presence of arsenic in water interferes with fluoride
removal.

30. Calcined Clay:
 Freshly fired brick pieces are used in Sri Lanka for the
removal of fluoride in domestic defluoridation units
 The brick bed in the unit is layered on the top with charred
coconut shells and pebbles. Water is passed through the
unit in an upflow mode. The performance of domestic
units has been evaluated in rural areas of Sri Lanka
(Priyanta & Padamsiri 1997).
 It is reported that efficiency depends on the quality of the
freshly burnt bricks.
 The unit could be used for 25-40 days, when withdrawal of
defluoridated water per day was around 8 litres and raw
water fluoride concentration was 5 mg/l.

32. Activated Alumina as a
defluorinating material:
 Activated alumina or calcined alumina, is aluminium oxide,
Al2O3.
 It is prepared by low temperature dehydration (300-600°C) of
aluminium hydroxides.
 Activated alumina has been used for defluoridation of drinking
water since 1934, just after excess fluoride in water was identified
as the cause of fluorosis.
 The fluoride uptake capacity of activated alumina depends on
the specific grade of activated alumina, the particle size and the
water chemistry (pH, alkalinity and fluoride concentrations).
 In large community plants the pH of the raw water is brought
down to 5.5 before defluoridation, as this pH has been found to
be optimum and it eliminates bicarbonate interference.

33.  Activated alumina has been the method of choice for
defluoridation of drinking water in developed
countries.
 Generally it is implemented on a large scale in point of
source community plants.
 A few point of use defluoridation units have been
developed which can be directly attached to the tap.
 During recent years this technology is gaining wide
attention even in developing countries.
 Domestic defluoridation units have been developed in
India using indigenously manufactured activated
alumina, which is commercially available in bulk
quantities.