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Chapter: Environmental Engineering - Quality of water

Chemical Characteristics and Examination of Water

Ph value, Hardness, Chlorides,Nitrogen, fluoride, Iron, Manganese, chlorine, fluoride, Iodine - 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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