Shots Notes on Pollutant

POLLUTANT :
A pollutant is substance or energy introduced into the environment that has undesired effects, or adversly affects the usefulness of a resource. The pollutants may be inorganic, biological or radiological in nature.

There are many types of Pollutant :
1.Primary Pollutants :
(Eg: H₂S  , SO₂ , CO, NO, HF, NH Smoke, Dust, Fumes)

2. Secondary Pollutants :
(Eg : SO3 , NO2 , CH4 , Aldehydes, Ketones, Nitrates, Sulphates)

3.Bio-degradable Pollutants :
(Eg : Domestic Waste)

4.Non-Biodegradable Pollutants :
(Eg : Mercuric salt, Lead,compounds, Pesticides.etc.)

AIR POLLUTION :
Major Air Pollutants :

• Carbon monoxide (CO)
• Sulphur dioxide (SO₂) 
• Oxides of nitrogen (NO₂ and NO )
• Smoke, dust
• Ammonia
• Chlorine and hydrogen chloride
• Chlorinated hydrocarbons
• Mercaptans
• Zn and Cd
• Freon

Photochemical pollutants : The nitrogen dioxide by absorbing sunlight in blue and U. V. region decomposes into nitric oxide and atomic oxygen followed by a series of other reactions producing
O3, formaldehyde, acrolein and peroxy acylnitrates.

SMOG : It is a mixture of smoke and fog in suspended droplet form. 
It is two types :
(a) London smog or classical smog : It is coal smoke plus fog.
(b) Photochemical smog or Los Angeles smog : The oxidised hydrocarbons and ozone in presence of humidity cause photochemical smog.

ACID RAIN : 
The oxides of C, N and S present in the atmosphere, dissolve in water and produce acids which lowers the pH of water below 5.5.The acids are toxic to vegetation, react with marble and damage buildings.
GREEN HOUSE EFFECT :
The retention of heat by the earth and atmosphere from the sun and its prevention to escape into the outer space is known as Green House Effect. Global warming refers to an increase in average global temperature.
(i) Global warming would result in rise in sea level due to increased rate of melting of glaciers and floods.
(ii) Increase in infectious diseases like Malaria, Dengue etc.

OZONE LAYER AND ITS DEPLETION :
The ozone layer, existing between 20 to 35 km above the earth’s surface, shield the earth from the harmful U. V. radiations from the sun. The U. V. radiations cause skin cancer, cataract of eye, and
are harmful to vegetation. Depletion of ozone is caused by oxides of nitrogen The presence of chlorofluorocarbons also increase the decomposition of O3 .

WATER POLLUTION :
The contamination of water by foreign substances which would constitute a health hazard and make it harmful for all purposes (domestic, industrial or agriculture etc.) is known as water pollution.

Sources of Water Pollution :

• Domestic sewage
•  Industrial waters
•  Suspended particles
•  Wastes from fertilizer 

Control of Water Pollution :

• Recycling of waste water
• Special techniques
• Waste-water reclamation

Aerobic and Anaerobic Oxidation :
The oxidation of organic compounds present in sewage in presence of good amount of dissolved or free oxygen (approx.8.5 ml/l) by aerobic bacteria is called aerobic oxidation.
When dissolved or free oxygen is below a certain value the sewage is called stale anaerobic bacteria bring out purification producing H₂S, NH3, CH4, (NH4)2S etc. This type of oxidation is called anaerobic oxidation.
The optimum value of D.O. for good quality of water is 4-6 ppm (4-6 mg/l). The lower the concentration of D.O., the more polluted is the water.

Biological Oxygen Demand (BOD) :
It is defined as the amount of free oxygen required for biological oxidation of the organic matter by aerobic conditions at 20°C for a period of five days. Its unit is mg/l or ppm. An average sewage
has BOD of 100 to 150 mg/l.

Chemical Oxygen Demand (COD) :
It is a measure of all types of oxidisable impurities (biologically oxidisable and biologically inert organic matter such as cellulose) present in the sewage. COD values are higher than BOD values.

SOIL OR LAND POLLUTION :
The addition of substances in an indefinite proportion changing the productivity of the soil is known as soil or land pollution.

Sources of Soil Pollution :

• Agricultural pollutants 
• Domestic refuge
• Radioactive wastes 
• Farm wastes