Module 1_water Impurities

8/11/2019 Module 1_water Impurities

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Module 1: Water Impurities

Course Teacher

Dr Muhammad Azizul HoqueAssociate Professor


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Sources of water/water quality

Water is a solvent

Source Quality

Rainwater natural distillation

Air quality + catchment

Surface water The above + pollutantsspecific to the catchment

Groundwater Rainwater characteristics+geological formation+minerals


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Potable Reuse (Unplanned)

Water Treatment

City A

Wastewater

Treatment

Water Treatment

City BWastewater

Treatment


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Important water-borne poisons

Toxic substances from mineral formations such as fluorine,selenium, arsenic, boron etc.

Phytotoxin produced by specific algae

Heavy metals from water-works structure, metallic pipes, industrialeffluents such as lead, copper, chromium, mercury, cadmium etc.

Poisonous compounds contained in industrial and householdwastes and wastewater discharged into water courses

Residues of pesticides and insecticides reaching water coursesfrom chemical dust and sprays applied to crops, land, and watersurfaces fro the control of pests,, nuisance insects, vectors ofdiseases, weeds etc.

Radioactive substances reaching water bodies


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Impurities of water

Impurities of mineral origin

Impurities organic origin

Living impurities

Radioactive impurities

Four categories:


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Effect of impurities present in water

Source: ITN-Bangladesh


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Water quality parameters

pH, Color, Turbidity, Total dissolved solids (TDS), Alkalinity,

Hardness, Chloride, Nitrate, Iron, Sodium, Total coliform and faecal

coliform, Arsenic, Boron, Chromium, Cadmium, Copper, Lead,

Nickel, Zinc

Go through: Source, Measuring unit and Significance of water

quality parameters

# Physical # Chemical # Bacteriological # Radiological


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Solids

SampleSettleable

solids TotalSolids

Filter

(glass fibre)

EvaporationEvaporation

Dissolved

SolidsSuspended

solids

Furnace (550C)

TS

Total

Fixed Solids

Total volatile

Solids

Fixed SSVolatileSuspended solids

VolatileDissolved Solids

Fixed filterablesolids

Furnace (550C)

Imhoff

cone Evaporation

Filtrate

SampleSettleable

solids TotalSolids

Filter

(glass fibre)

EvaporationEvaporation

Dissolved

SolidsSuspended

solids

Furnace (5500C)

TS

Total

Fixed Solids

Total volatile

Solids

Fixed SSVolatileSuspended solids

VolatileDissolved Solids

Fixed filterablesolids

Furnace (5500C)

Imhoff

cone Evaporation

Filtrate


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Total Dissolved Solids

Soluble inorganic salts

Cations of Ca, Na, Mg, K

Anions of Cl-, HCO3- and NO3

-

Need to filter using 0.45 micrometer

Drinking water can be treated Excellentwhen TDS < 300 mg/L

TDS >1200 mg/L is Unacceptable


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Hardness

Presence of polyvalent (but not singly charged)metallic cations.

Most polyvalent are divalent Ca and Mg

expressed as the sum of concentrations of these

elements (mg/L as CaCO3) Principal anions and cations indicating hardness

Cations Anions

Ca++ HCO3-

Mg++ SO42-

Sr++ Cl-

Fe++ NO3-

Mn++ SiO3-


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Total Hardness

Temporary hardness (Carbonate hardness)

Solution of Ca and Mg with bicarbonate in water

Removed by boiling water containing HCO3- can be

heated to precipitate (CO32-) as scale

Permanent hardness (Noncarbonate hardness)

Caused by Ca and Mg compounds of sulfates, chlorides

or silicates

Cannot be removed by boiling, but precipitation

softening process or ion exchange using selective ions


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Problems with hardness

Hard water (>200 mg/l as CaCO3)

Reduction in cleaning action of soap

Scale formation in boilers, water systems and heat

exchangers

Soft water (


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Alkalinity

Measure of the ability of a water to neutralize theacids. (absorb H+ ions without significant pHchange)

The principal alkaline ions are OH-, CO32- and

HCO3- and usually expressed in terms of CaCO3

Important during coagulation

Depending on pH, alkaline samples can containOH- alone, OH-+ CO3

2-, CO32-alone, CO3

2- andHCO3

- or HCO3- alone.

pH>10, OH- or OH- and CO32-(No significant OH- existbelow this pH)

pH>8.3 CO32- and HCO3

- (No significant CO32- exist

below this pH)


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Hardness and Alkalinity

Hardness by multi-positive ions and alkalinity by

negative ions

Alkaline water can be hard If hardness and alkalinity are same, then there

are no SO42-, Cl- or NO3

- (no non-carbonate

hardness)

If hardness > alkalinity, non carbonate hardnessis present and carbonate hardness = alkalinity

If hardness < alkalinity, all hardness is carbonate

hardness and extra HCO3- comes from other

sources such as NaHCO3


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Radiological (uranium and thorium ) Radioactivity

is the energy released from the breakdown ofradionuclides

Naturally occurring radioactive species in drinking water

sources

Contamination from concentration of natural levels such as

mining and processing of minerals

Artific ial radionuclides which may enter drinking water

supplies from medical and industrial use of radioactivematerials


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Pathogenic Bacteria and viruses

Bacterial water borne diseases (bacteria 0.5-5

micrometer)

Cholera, Typhoid fever, Gastro-enteritis

Viral diseases (Viruses 20 -100 nm)

Smallpox, influenza, diarrhoea, polio and hepatitis


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Indicator Microorganisms for Drinking

Water

Coliform group of microorganisms is present in large

numbers in animal and human excreta. Why is there a need

for such indicators?

Pathogenic microorganisms are small in numbers

Routine testing is not practicable and expensive

Involves skilled labour and specialist equipment

Time-consuming

Specific tests may not be available


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Indicator Microorganisms Properties

Always present when pathogens of like or igin are present

Present in large numbers, >> pathogens

Easy and quick to detect

Equal or greater survival time than pathogens

Absent from unpolluted waters

Similar sensitivity to disinfection as pathogens


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Basic requirements of Drinking water

Should be completely free of pathogenic micro-organisms that can

cause disease

Should contain no element or compound in concentrations that cancause acute or long-term adverse effect on human health

Should be fairly clear and aesthetically attractive, i.e. low turbidity

and color

Should not be saline to cause salty taste

Should contain no compounds that can cause an offensive taste

and odouor

Should not cause corrosion, scale formation, discoloration or

staining

Should not have a temperature unacceptable to the consumers


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Drinking water standardsSource: ITN-Bangladesh

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Module 1_water Impurities