Chapter: Environmental Engineering : Quality of water
Chemical Characteristics and Examination of Water
CHARACTERISTICS AND EXAMINATION OF WATER
OBJECTS OR ADVANTAGES OF ANALYSIS OF WATER
1. By knowing the results of analysis,
the outline of the treatment process may be framed.
2. Daily operation of the treatment
plant is based on this analysis report.
3. To ascertain the quality of raw
water to suggest the type of treatment to be given and the degree of treatment
necessary.
4. Water must also be analyzed at the
end of the treatment to find out the efficiency or performance of the treatment
plant.
CHEMICAL CHARACTERISTICS AND EXAMINATION OF WATER
Chemical
analysis involves test for determining total solids P? value hardness,
chronicle content, and nitrogen content, from and manganese, residual chlorine,
toxic metals, etc….
Total solids =these include the
solids in suspension, colloidal and dissolved state. The quantity of suspended
solids is determined by filtering the sample of water. Through a fine filter
and drying and weighing. The quantity of dissolved and colloidal solids is
determined by evaporating the filtered water and weighing the residue. The
total solids can be directly determined by evaporating the water sample and
weighing the residue. The amount of total solids should be less than
500milligram/Lit and should never exceed 1000 mg/Lit.
PH VALUE
PH
value of water indicates the log of
reciprocal of hydrogen ion concentration present in water. It is thus indicator of the acidic and alkaline nature of water.
Determination of PH
PH value may be determined by instrumental or colorimetric
method or PH paper method (narrow or wide ranged)
INSTRUMENTAL METHOD = this method is very quick and
automatic method of recording PH values. In this
potentiometer is used to measure electrical pressure exerted by positively
charged H ions. A meter is connected to the electric acquit which directly
indicates the PH value of
water.
COLORIMETRIC
METHOD = some
indicators or chemicals are added to the sample of water and the colour so obtained is compared with standard colours of
known PH value. The usual
indicators are benzol yellow, methyl
red, brown phenol etc… for PH range 0-7 and Thymol
blue, Tolylred and phenol red for PH values above 7.
HARDNESS
Definition:
Hardness is the property of water
which prevents the formation of lather or foam and needs large quantities of soap'. It forms scales in not water
pipes, heaters, boilers where the temperature of water is increased.
CAUSES
It is
caused by 'DIVALENT METALLIC CATIONS' the principal hardness causing cations
are calcium and magnesium there are two types of hardness temporary and
permanent hardness
TEMPORARY
HARDNESS Caused due
to presence of carbonates and bicarbonates of calcium and magnesium this can be removed by boiling or by adding
lime solution in water. Temporary hardness is also called carbonate hardness.
PERMENET
HARDNESS of water
is caused due to the presence of sulphates, chlorites and nitrates of calcium and magnesium. They cannot be removed by
simple boiling and require special treatment of water softening it is also
called as Non-=carbonate hardness.
DETERMINATION OF HARDNESS
Hardness
is generally defined as the caco3 equivalent of ca and Mg ions
present in water and expressed in mg/llitas caco3
Hardness can be determined by EDTA
titrometric method ( EthyleneDiamine Tetra acidic acid), Ferrochrome black - T
is used as indicator
Erichrome Black (Blue colour) + water
(Ca++,Mg++) = Less
stable ions(wine red colour)
EDTA+ Less stable ion = Erichrome
black T (Blue colour) + more stable lon
Colour change = Wine red to purple
to blue
Water are commonly classified
interms of degree of hardness.
Milligram /
Litre as CaCo3 Degree
of hardness
0 - 75 Soft
75 -150 Moderately
soft
150 - 300 Hard
300
and a bove Very hard
However the permissible Units of
hardness for potable water ranges between 75 - 115 mg/lit as CaCo3.
CHLORIDES
Chlorides
in combination with other elements are always found in water. Nacl is normally
found in water the presence of nacl may be due to water coming in contact with
saltish layer or sewage entering into it for potable water the amount of
chlorides is limited to 250mg/lit. Chlorides may be readily measured by means
of volumetric procedures employing indicator solution. For most purposes the
MOHR method employing silver nitrate as indicator solution (yellow - brick red)
is used.
NITROGEN CONTENT
The
presence of nitrogen in water is an indication of organic matter present in
water and they may occur in any of the following
a. Albuminoid Nitrogen
b. Free ammonia
c. Nitrate
d. Nitrate (stabilized end product of
nitrogen)
Presence of above indicate the
degree of pollution of water. Permissible limits of Nitrate is 45PPm
IRON AND MANGANESE
These metals at very low
concentrations are highly objectionable in water supplies for domestic or
industrial use. Fe and Mm in concentration greater than 0.3ppm and 0.05ppm
respectively stain plumbing fixtures and laundered clothes moreover they cause
incrustation of water main due to deposition of ferric hydroxide and Mno. Foul
taste and odours are produced by growth of fe bacteria in water distribution
mains. Fe and Mn may be determined either by precipitation Technique if they
are present in large amounts or by colorimeter or spectra photometer. In they
are present in small amounts (Phenol chlorine and per sulphate method
respectively)
Public water supplies should not
contain more than 0.3ppm of Iron and 0.05ppm of manganese. If they exceed the
above limits they can be oxidized by oxidizing agents like oxygen, chlorine and
potassium permanganate (KMno4) or by simple aerator Technique by adjusting PH 9-10 the
manganese gets precipitated.
RESIDUAL CHLORINE
The
important purpose of chlorinating public water supplies is to prevent the
spread of water borne diseases chlorine is used in water treatment for
disinfection, prevention and
destruction of odours, Iron and
colour remover. At optimum PH
and temperature of water its bactericidal efficiency is very high. In order to
ensure no bacterial growth even in the distribution, chlorination is necessary.
Therefore residual chlorine of 0.2ppm is required to be maintained in the
distribution system to ensure no further bacterial contamination. Residual
chlorine is determined by STARCH - IODIDE method or ORTHOTOLIDINE METHOD.
FLUORIDES
Excessive
fluoride ions in drinking water cause DENTAL FLUOROSIS or MOTLING OF TEETH. On
the other hand, communities whose drinking water contains no fluoride have a
high prevalence of dental caries optimum fluoride concentrations provided in
public water supplies generally in range of 1-1.5mg/lit reduce dental caries to
a minimum without causing noticeable dental fluorosis. Several fluoride
compounds are used in treating municipal water all of these dissociate readily
yielding fluoride ions (fluoridation).
Excessive
amounts of fluoride lons drinking water can be removed by defluoridation. The
two current treatment methods for defluoridation use either activated alumina
are bone char. In india
'NALAGONDA TECHNIQUE OF
DEFLUORIDATION' is most widely used as it is easier and convenient to use in
rural areas.
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