WATER TREATMENT

THOSHINA THOMASKEYI SAHIB TRAINING COLLEGE

TALIPARAMBA

What is meant by Environmental pollution ?

Environmental pollution is defined as the undesirable change in

physical, chemical and biological characteristics of our air, land and

water.

As a result of over-population, rapid industrializations, and other

human activities like agriculture and deforestation etc., earth became

loaded with diverse pollutants that were released as by-products.

Classification of Environmental Pollution

- Pollution can be broadly classified according to the components of

environment that are polluted. Major of these are:

Air pollution

Water pollution

Soil pollution

Noise pollution

RADIATION POLLUTION

THERMAL POLLUTION

Overview of main health effects on humans from some common types of pollution .

Earth- a blue planet

97% ocean

3% fresh water (2% locked in polae ice caps)

Sources of water:rain water, sea water, river water, lake water, spring water, well water etc.

Rain water is supposed to be the purest among all and dissolves only little amount of gases and suspended particles from the atmosphere

WATERPOLLUTION

Water pollution is the introduction into fresh or ocean waters of

chemical, physical, or biological material that degrades the quality of

the water and affects the organisms living in it.

This process ranges from simple addition of dissolved or

suspended solids to discharge of the most insidious and persistent toxic

pollutants (such as pesticides, heavy metals, and nondegradable,

bioaccumulative, chemical compounds).

impurities present in water

Dissolved gases:

Dissolved salts:

Suspended matter: They cause turbidity of water. They can be removed by filtration or settling.

Microscopic impurities: They may lead to water borne diseases.

Organic matter: These may include decayed plants and animals as impurities.

Parameters for checking water quality for domestic use

The parameters for checking water quality for domestic use are a follows

(i) Water should not contain hardness (not more than 300 ppm)

(ii) Turbidity should not be more than 10 ppm.

(iii) pH of domestic water should be around 7.5 — 8.0.

(iv) Coloured impurities should not be more than 20 ppm.

(v) Water should not contain dissolved solids more than 500 ppm.

(vi) Water should be free from disease producing micro organisms.

(vii) Water should be free from minerals like Pb, Arsenic, Chromium, Mn etc.

(viii) Water should be odourless and pleasant in taste.

The specifications of boiler feed water are as follows

(i)Water for boilers: Boiler feed water should be free from

soluble salts of Mg2+ and Ca2+ (ii) It should not contain any

organic matter.

(iii) Boiler feed water should be free from suspended

impurities.

(iv) Boiler feed water should not be acidic or alkaline.

Hardness of water: Hard water is one which does not produce lather with soap solution readily, but forms a white curd.

soft water gives lather easily on shaking it with soap solution.

Alternatively hard water contains dissolved calcium and magnesium salts; while soft water does not contain dissolved calcium and magnesium salts in it.

CaCl2 + C17H35COONa → (C17H35COO)2Ca + 2NaCl

Types of hardness:

1.Temporary hardness:

2.Permanent hardness:

Temporary hardness:

due to the presence of bicarbonates of calcium and magnesium and other heavy metals and the carbonate of iron.

removed by heating; because on boiling the bicarbonates of calcium and magnesium get decomposed to insoluble carbonates which get precipitated hence can be removed.

Therefore it is called Temporary hardness.

Permanent hardness:

due to the presence of chlorides and sulphates of Calcium and magnesium iron and other heavy metals.

It cannot be removed by heating but can be removed by only special chemical treatments.

Total hardness: temporary + permanent hardness.

Disadvantages of hard water in domestic and industrial use

Hardwater, when used for bathing and washing purposes, does not producing lather freely with soap. As a result cleansing quality of soap is decreased and a lot of water is wasted.

Hardwater reacts with soap it produces sticky insoluble precipitates of calcium and magnesium soaps (scum).

For cooking the boiling point of water is increased because of presence of salts. Hence more fuel and time are required. 

Hardwater lead to possibility of forming calciumoxalate crystals in urinary tracks is increased. 

In Textile Industry, Hardwater causes wastage of soap. Scums adhere to the fabrics and cause problem. 

Similarly the dissolved salts in hardwater may reacts with costly dyes forming precipitates. 

Hard water if used in sugar refining, causes difficulties in the crystallization of sugar. (give de-liquescent sugar).

Hardwater may cause some undesirable products while preparation of pharmaceutical products and quality of the paper in paper industry. 

Water containing chlorides and sulphates, if used for concrete making, affects the hydration of cement and the final strength of the hardened concrete. 

If hardwater is fed directly to the boilers (For steam generation), there arise many troubles such as.. Scale and sludge formation, Hardwater may cause caustic embrittlement which is a type of boiler corrosion.

Lime scale furring of kettles and pipes. The fur is the insoluble carbonate formed The deposits of lime scale can build up on the inside of the piperestricting the flow of water or causing a blockage. Lime scale deposits can be removed using a weak acid (or water softner).

Permanent hardness: Unlike temporary hardness, permanent hardness is not

destroyed on boiling. It can be removed by following processes:

(i) Lime-soda process: In this method calculated quantity of chemicals are mixed with

water and these chemicals convert all the soluble hardness causing salts into insoluble

precipitates which may be removed by settling and filtration. For this purpose, Ca(OH)2 i.e.

lime, together with a calculated amount of sodium carbonate, Na2CO3 (soda) is added in

requisite amount.

 (ii) Zeolite process: Zeolites are naturally occurring hydrated sodium alumino

silicate minerals like (Na2O. Al2O3. xSiO2. yH2O) capable of exchanging reversibly its sodium

ions for hardness producing ions in water.

 

(iii) Ion-exchange process: It is a process by which ions held on a porous,

essentially insoluble solids are exchanged for ions in solution that is brought in contact with it; 

Water Softening Methods

The process of decreasing hardness of water is called softening.

Temporary hardness can be removed by boiling or by adding calculated amount of lime (calcium hydroxide) to the hard water (Clark’s method).

Similarly removal of permanent hardness can be achieved by the addition of washing soda (Na2CO3.10H2O).

Removal of both temporary and permanent hardness can be done by lime soda process and ion exchange process such as inorganic cation exchangers (Zeolites) or organic ion exchangers.

1. Lime-soda process

addition of calculated amounts of both lime [Ca(OH)2] and soda [Na2CO3] in to hard water followed by removal of the precipitates.

Lime soda process can be done in two different ways such as cold lime soda process (at room temperature) and hot lime soda process (at temperature 80-1500C).

2. Ion exchange method

Ion exchange devices reduce the hardness by replacing hardness ions (mainly Mg2+ and Ca2+) with Na+ and K+ ions in a crystal lattice or gel.

If the exchanged ions have +ve charge, the ion exchanger is called cationic and if they have –ve charge, it is called as anionic.

The ion exchanger may be natural or synthetic one.

a) Inorganic cation exchangers

Eg. Zeolite or permutits

Zeolites are hydrated sodium alumino silicates (Na2O.Al2O3.xSiO2.yH2O, where x = 2-10 and y = 2-6).

For convenience it is represented as Na2Z. Zeolites have empty channels with free holes thus are

capable of exchanging their Na+ ions for Ca2+ and Mg2+ ions of hard water.

The reaction can be represented as,

Ca(HCO3)2 + Na2Z CaZ + 2NaHCO3 CaCl2 + Na2Z CaZ + 2NaCl.

BOD (Biological Oxygen Demand):

It indicates the amount organic impurities present in water, which can be oxidized by micro-organisms.

It is defined as the amount of oxygen required by the micro-organisms, in presence of oxygen for the biological oxidation of organic matter in a sample water, when incubated for 5 days.

When more pollutants present more will be the, consumption of oxygen by the microbes. Hence the amount of dissolved oxygen present decreases.

BOD can be determined by Winklers method.

COD (Chemical Oxygen Demand):

It accounts for the organic matter that is not oxidized by microbes.

It is defined as the amount of oxygen required organic matter in a sample water for it’s oxidation by strong chemical oxidizing agents like potassium dichromate.

Different Kinds of Water

Fresh Water : Only 2.75 percent of the water on Earth is fresh water, about two-thirds of it is frozen in glaciers, a quarter is groundwater and only 0.005 percent of it is surface water. Fresh water may be either ‘hard’ or ‘soft’.

Brackish Water: Brackish water is the type of water that has salinity between that of fresh water and seawater.

Seawater: Seawater typically contains about 3.5% sodium chloride.

Distilled/ Demineralized Water: water that is ripped of its impurities through the process of distillation.

Potable Water: Potable water is fresh water that is sanitized with oxidizing biocides such as chlorine or ozone to kill bacteria and make it safe for drinking purposes.

Potable waterThe water used for drinking purpose is called potable water. The water

should be free from organic matter, suspended impurities, and pathogenic bacteria. The water should be safe and pleasant. The potable Water should be

clear, colourless, odourlessShould have good tasteShould be free from pathogenic microbesShould be free from minerals like lead, arsenic, chromium etc. pH should be between 6.5-8.5.

DESALINATION

It is method to remove dissolved salt from saline water to get pure water. By

1. Electrodialysis:

2. Reverse osmosis:

Electrodialysis:Principle: charged ions move towards oppositely charged electrodes through ion selective membrane, in the presence of electric field.

Reverse osmosis:

When a semi-permeable membrane is placed between brackish water (brine) and pure water, solvent (pure water) has a natural tendency to flow into brine which is called osmosis. But when pressure is applied to brine, the water from brine will flow into water, which is called reverse osmosis.

cellulose acetate

Too high pressure cannot be applied, which would result in the rupture of the membrane

Sewage treatment

The sewage water contains various minerals, organic matters, suspended impurities, pathogenic bacteria etc. Therefore water has to be treated before letting into sea.

The principal objectives in Municipal water treatment are removal of suspended paticles, removal of colour and removal of disease causing bacteria.

Generally it consists of following methods.

1. Primary treatment (physical and chemical treatment): It removes all the settled impurities.

Screening; The sewage water is passed through metallic screens or bar screens.Slit or grit removal: remove sand and broken pieces of glass.

Oil and gas removalSedimentation: coagulating agent like alum is added, to remove suspended particles

2. Secondary treaetment of sewage (Biological treatment):

This involves the removal of organic matter present in the water.

1). Trickling filtration: Water is passed through trickling filters during which some of the organic maters are oxidized by the micro-organisms.2). Activated sludge process:The organic impurities get oxidized to carbon dioxide, nitrogen is converted to ammonium and then to nitrites and nitrates.

Tertiary treatment:

Sedimentation: Sewage water is taken in sedimentation tank and treated with coagulant like alum to remove suspended impurities in the form of precipitates.

Filtration: The traces of suspended impurities are are removed by filtering through sand filters.

Degasification: removes gases like hydrogen sulphide , ammonia etc.

Disinfection: It is treated with chlorine in acid medium to remove pathogenic bacteria by forming hypochlorous acid.

The Winkler Fixing Mn2+ + 2 OH- + ½ O2 → MnO2

(s) + H2O

MnO2 (s) + 2 I- + 4 H+ → Mn2+ + I2 + 2 H2O

Do you see the brilliance of this two-step sequence?

The first step converts O2 to MnO2 under basic conditions. The second step converts MnO2 to I2 under acidic conditions. When you acidify the solution – you prevent the first reaction!!! Any oxygen that dissolves later can’t react!

We’ve seen it before:

The Residual chlorine determination converted Cl2 to I2, then analyzed the I2 by titration with sodium thosulfate!

I2 + 2 S2O32- → S4O6

2- + 2 I-

THANK YOU……………………