Water AnalysisLecture # 3

1

Water AnalysisThe following goals may be formulated for the examination of water:

Determination of physical, chemical & biological characteristics of water.

Determination of pollution sources.Assessment of suitability of water for various

purposes e.g, drinking, industrial, irrigation etc.Establishment of size of various treatment

units.Determination of amount of chemicals

required for purification and conditioning of water for industrial usage.

2

General Water Analysis Parameters

3

ColorPure water is colorless. However color is contributed to natural water by many sources.

Sources:End products of organic matter degradationDivalent ions of iron & manganese in both ground & surface water. In surface water these ions may convert to Fe(OH)3 and MnO2 as a result of oxidation.

4

ColorColor caused by suspended matter is called apparent color.Color caused by dissolved solids that remains after removal of suspended solids is called true color.

Color Removal:Apparent color is removed by simple filtration or ultra filtration.True color causing organic compounds require chlorine demand.

5

pHpH is the method of expressing the concentration of ionized hydrogen.It is the logarithms to base 10, of the reciprocal of hydrogen ion conc. in g/L.Pure water has equal conc. Of hydrogen & hydroxyl ions and has pH of 7 (neutral).

6

pHpH of natural water lies in the range of 6.0 to 8.5.Most of natural water is alkaline due to the presence of carbonates.pH of natural water changes due to biological activity, photosynthesis, and industrial disposal.pH is one of the important parameter in water treatment.

11/10/11 7

Electrical ConductivityIt is the measure of the capacity of the substance or solution to carry an electric current.It is a parameter for dissolved solids.Its value depend on conc. Of ions, temperature and the migration velocity of the ions.

11/10/11 8

Electrical ConductivityIt helps in estimating the total dissolved solids by following empirical relation:TDS(mg/L) = C * Electrical ConductivityWhere C is empirical factor may vary from 0.55 to 0.9 depending on the soluble solids present in water.

9

Electrical ConductivityAlthough unionized species are the portion of total dissolved solids but they are not detected by conductivity meter e.g. silica.

10

TurbidityThe suspended solids interfering with the passage of light is called turbidity.

Sources:ClaySiltOrganic matter & metalsMicroscopic organisms

11

TurbidityTurbidity is measured by determining %age of light of a given intensity absorbed or scattered. Units are:

NTU (Nephlometric Turbidity Unit) based on light scatteringFNU (Formazin Nephelometric Unit) based on light scatteringFTU (Formazin Turbidity Unit) based on light absorptionJTU (Jackson Turbidity Unit) based on light absorption

12

SolidsOrganic Solids

Solids are about 50 percent organic. This fraction is generally of animal or vegetable life and synthetic organic compounds. Inorganic Solids

Inorganic solids are substances that are inert and not subject to decay. Inorganic solids include sand, gravel and silt as well as the mineral salts etc.

13

SolidsSolids can also be grouped depending on their physical state as suspended solids, colloidal solids and dissolved solids, each of which can include both organic and inorganic solids.Suspended Solids

Suspended solids are those which are visible and in suspension in the water. They are the solids which can be removed from the wastewater by physical or mechanical means, such as sedimentation or filtration e.g. sand, clay, paper, pieces of wood, particles of food and garbage, and similar materials.

14

SolidsSettleable Solids

Settleable solids are that portion of the suspended solids which are of sufficient size and weight to settle in a given period of time, usually one hour. Colloidal Solids

Colloidal suspended solids are solids that are not truly dissolved and yet do not settle readily. These are somewhat loosely defined as the differences between the suspended solids and the settleable solids

15

SolidsDissolved solidsDissolved solids are invisible and smaller in size

than suspended and colloidal solids. As used, the term means all of the solids which pass through the filter paper. Total SolidsTotal solids, as the term implies, includes all of the solid constituents of a wastewater. Total solids are the total of the organic and inorganic solids or the total of the suspended and dissolved solids.

16

ChloridesChlorides is present in all natural waters at greatly varying concentrations.Sources:Effluent from chemical industriesSewage disposalsIrrigation drainageSea water A man discharges 8 to 10 gm per day of NaCl through both urine & excreta

17

ChloridesWhen chlorides concentrations of 250 mg/L is present along with sodium ions, a salty taste can be observed.Chlorides can only be removed by reverse osmosis and distillation.

18

HardnessHardness is a measure of the ability of water to cause precipitation of insoluble calcium & magnesium from soap solutions.Principal hardness causing cations are calcium, magnesium, strontium, iron & manganese ions associated with carbonates, bicarbonates, chlorides & sulphates.

19

HardnessHardness is classified into two types:Temporary Hardness: It is due to the

presence of bicarbonates of calcium and magnesium. It can be easily removed by boiling.Permanent Hardness: This type of

hardness can not be removed by boiling. This is due to the presence of chlorides and sulphates of calcium and magnesium. The hardness can be removed by the addition of some agents.

20

SulphatesSulphates occur in natural water at conc. upto 50 mg/L.Sources:Rain water especially in areas of air pollution.Released during degradation of proteinsStandard for drinking water is 200 ppm.

21

Dissolved oxygen (DO)The presence of oxygen is essential for the survival of aquatic life.It plays an important role for the metabolic pathways of aerobic bacteria and other microorganisms which are responsible for the degradation and stabilization of organic constituents in waste water.

22

Dissolved oxygen (DO)A rapid fall of DO level in river waters is one of the first indication of organic pollution.DO level depends on physical, chemical & biological activities.Major inputs of dissolved oxygen to natural waters is from atmosphere & photosynthesis reaction.DO level in water should be 4-6 mg/L

23

Dissolved oxygen (DO)The solubility of oxygen in waters depends on temperature & chloride conc.The solubility of atmospheric oxygen decreases with increase in temperature.The solubility of oxygen is lesser in salt containing water than in clean water.

24

BODBiochemical oxygen demand is a measure of the oxygen utilized by microorganisms during biological oxidation of organic matter contained in the liquid waste under a specified conditions.

Organic matter + O2 CO2+H2O + energy

25

BODOn average basis, the demand for oxygen is directly proportional to the amount of biodegradable in waste water under aerobic conditions.BOD is a direct measure of oxygen requirement and indirect measure of biodegradable organic matter.

26

BODBiochemical is a slow process and theoretically takes an infinite time to go to completion.Within 20 days oxidation is 95 to 99% complete and within 5 days it is 60 to 70% complete.BOD is an empirical test in which water conditions such as temperature, oxygen conc. Or type of bacteria play a decisive role.

27

CODChemical oxygen demand is the oxygen required for chemical oxidation of organic matter by strong chemical oxidant (K2Cr2O7) under acidic conditions.Degree of oxidation depend upon the type of substance, pH value, temperature, rxn time & conc. Of oxidizing agent.

28

CODAdvantages:

Major advantage of the COD test is the short time required for evaluation. COD test is conducted in approximately 3 hours while BOD is conducted in 5 days.

COD test is much more useful for estimating strength of certain industrial wastes of both organic & inorganic which contained toxic chemicals.

29

CODDisadvantages:COD test does not differentiate b/w

biological oxidizable & biologically inert organic matter.

Some amino acids, ketones or saturated carboxylic acids, benzene, pyridine etc. are not oxidized by dichromate.

Some oxygen is consumed by inorganic substances such as nitrites, chlorides, sulphates, reduced metal ions, etc. So, test is a poor measure of strength of organic wastes unless these factors are considered.

30