Mechinopedia For Mechanical Engineers

Soil pollution is defined as, " the contamination of soil by human and natural activities which may cause harmful effects on living beings". Types, Effects and Sources (Causes) Of Soil Pollution : Soil pollution mainly results from the following sources  1, Industrial wastes 2. Urban Wastes. 3. Agricultural Wastes. 4. Radioactive pollutants. 5. Biological agents. I) Industrial Wastes :  Disposal of  industrial wastes is the major problem for soil pollution.  Sources : The industrial pollutants are mainly discharged from the various origins such as pulp and paper mills., chemical industries, oil refineries, sugar factories, tanneries, textiles, steel, distilleries, fertilizers, pesticides, coal, and mineral mining industries, drugs, glass, cement, petroleum and engineering industries etc., Effect : These pollutants affect and alter the chemical and biological properties of soil.  As a result, hazardous chemicals can enter into human food chain from the soil and water and distu

 Objectives of waste water management :  The main objectives of waste water treatment are  i) To convert harmful compounds into harmless compounds. ii) To eliminate offensive smell. iii) To remove the solid content of the sewage.  iv) To destroy the disease producing micro-organisms. Treatment Process : The sewage (or) waste water treatment process involves the following steps. i). Preliminary Treatment : In this treatment, coarse solids and suspended impurities are removed by passing the waste water through bar and mesh screens.  ii). Primary Treatment (or) Settling Process : In this treatment, greater proportion of the suspended inorganic and organic solids are removed from the liquid sewage by settling. In order to facilitate quick settling coagulants like alum, ferrous sulphate are added. These produce large gelatinous precipitates, which entrap finely divided organic matter and settle rapidly. Al2(So4)3 + 6H2O --------------> 2 Al (OH)3  + 3H2SO4  iii) Secondary (or) Biological

 Water Pollution :   Water pollution may be defined as , " the alteration in physical, chemical, and biological  characteristics  of water which may cause harmful effects on humans and aquatic life."   The pollutants include sewage, industrial chemicals and effluents, oil and other wastes. Besides, chemicals from the air dissolved in rain waste, and fertilizers, pesticides and herbicides leached from   the  land  also pollute water. Types, Effects and Sources ( causes ) Of water Pollution : Water Pollution is any chemical, biological or physical change in water quality that has a harmful  effect  on living organisms or makes water unsuitable for desired uses.  1. Infectious Agents : Examples - Bacteria, Viruses, Protozoa  and Parasitic worms. Human Sources :  Human and Animals wastes.  Effects :  Variety of  diseases. 2. Oxygen Demanding Wastes ( Dissolved oxygen ) : Examples :   Organic wastes such as animal manure and plant debris that can be decomposed by  aerobic (oxygen

  As the ozone layer gets deteriorated the harmful UV rays will reach the ground and cause various adverse effects.  I. Effect On Human Health  i) The UV- Rays damage genetic material in the skin cells which cause skin cancer.  ii) For the fair skinned people life long exposure to the high level radiation of  UV rays increases the risk of non - melanin skin cancer. iii) Prolonged human exposure to Uv-rays may lead to slow blindness called actinic keratitis. Enhanced level of UV ray could lead to more people suffering from cataracts. iv) Human Exposure to UV- rays can suppress the Immune responses in humans and animals. It also reduces human resistivity leading to number of diseases such as cancer, allergies and some other infectious diseases.  II) Effect on Aquatic Systems    i) UV Rays  directly affect the aquatic forms such as phytoplankton, fish, larval crabs.  ii) The phytoplankton consumes large amount of CO2. Decrease in population of phytoplankton could have more amount of Co2 i

Ozone is a gas (O3) found through out the atmosphere, but most highly concentrated in the stratosphere between 10 and 50 km above sea level, where it is known as the ('ozone layer'). Importance of Ozone Layer : Without the ozone layer, life on the earth's surface would not be possible. It protects us from damaging ultraviolet radiation of the sun. In particular it filters out UV-B radiation.  Recent evidence has shown the certain parts of the ozone layer are becoming thinner and ozone 'Holes" have developed. The consequence of any thinning of the ozone layer is that more UV - B radiation reaches the earth's surface. UV - B radiation affects DNA molecules, Causing damage to the outer surface of the plants and animals. In humans it causes skin cancer, and eye disease.  Mechanism Of Ozone Layer Depletion (or ) Formation (or) Causes of ozone hole :  In 1970, it was found that the ozone layer was attacked by chlorofluorocarbons (CFCs) which are release into atmosphe

1. Improvement in technologies and switching to clean combustion technologies are highly essential in  order to monitor the air pollution.  2. Emissions of So2 and No2 from Industries and power plants should be reduced by using pollution  control equipment. 3. Coal with lower Sulphur content is desirable to use in thermal plants. Replacement of coal by natural  gas would also reduce the problem. 4. Liming the Lakes and soils should be done to correct the adverse effects of acid rain.  5. The real solution is to cut back on the use of fossil fuels by reducing our dependency on motor vehicles and unnecessary utility of motor vehicles. 

Normal rain water is always slightly acidic because of the fact that CO2 present in the atmosphere gets   dissolved in it. Because of the presence of  SO2 and NO2 gases as pollutants in the atmosphere, the pH   of  the rain water  is further lowered. This type of precipitation of  water is called acid rain (or) acid deposition. Acid rains means the presence of  excessive acids in rain water. The thermal power plants, industries and vehicles release nitrous oxide and  Sulphur dioxide into atmosphere due to burning of coal and oil. When these gases react with water vapor in the atmosphere, they form acids and descend on the earth's "acid rain" through rain water.  SOx + H2O ------------->  H2SO4  NOx + H2O --------------> HNO3 Due to the drifting of these gases in the atmosphere by the wind, their presence are felt as far as 2,000 kilometers. The air pollution of one nation could cause acid rain for another nation. 

  Effects ( Impacts ) Of  Acid Rain :  Acid rain causes a number of harmful effects. Some of the adverse effects are as follows.  1. Effects of acid rain on human beings :  i)  Acidic rain has been found to be very dangerous to the living organisms as it can very dangerous to the living organisms as it can destroy life. Human nervous system, respiratory system and digestive system  are affected by acid rain. ii) It also causes the premature death from the heart and lung disorders such as asthma and bronchitis. 2. Effects of  acid rain on Buildings :  i) The Taj Mahal in Agra Suffering at present due to So2 and H2So4 acid fumes released from Mathura refinery. Crystals of CuSo4 & MgSo4 are formed as a result of corrosion caused by acid rain. ii) Acid Rai corrodes houses, monuments, statues, bridges and fences. British Parliament building also suffered damage due to H2So4 rains.  iii) Acid rain and dry deposition of acidic particles contribute to the corrosion of metals, and the deter

Peroxy Acetyl Nitrates is a secondary pollutant present in Photo chemical Smog. It is a lachrymatory substance. It is thermally unstable and decomposes into peroxy ethanoyl radicals and nitrogen dioxide gas. It is an oxidant and more stable than ozone. Health effect :   At lower Concentrations :  It is a powerful respiratory and eye irritants, toxic in nature.  At higher Concentrations : Cause extensive damage to vegetation, causing skin cancer.  Respiratory disease                                                                   Skin cancer Production Of  PAN :  They are formed by the photochemical reaction between hydrocarbons, nitrogen oxides and light. It occurs in two steps Step I :  Unburnt hydrocarbons undergo oxidation to give aldehydes, ketones and di carbonyl compounds, which creates peroxyacyl radicals.  Hydrocarbons + O2 + Light ----------------> Ch3 - C (=O) - O - O*  ie,  CH3CHO + OH-  ------------->  CH3CHO*  +  H2O  CH3CO* + O2 ----------------> CH3COOO* Step

  Formation of  Smog : Smog is a mixture of smoke and fog in suspended droplet form. The brownish smog like appearance that frequently forms on clear, sunny days over large cities with significant amounts of automobile traffic. Types Of Smog : There are two types of smog. 1. London Smog  2. Los Angles Smog (or) Photochemical Smog LONDON SMOG :   It is a coal smoke plus fog. Fog mainly consists of  mixture of SO2 + SO3 + humidity. It is bad in morning hours and becomes worse after sunrise. This is due to sunlight induced oxidation SO2 + SO3, Followed by reaction with humidity giving sulphuric acid and aerosd.  So2 + (O) -----------> SO3  SO3 + H2O -----------> H2SO4  LOSANGELS SMOG Or Photochemical SMOG :  It is not related to smoke (or) fog. It is formed by the combination of  NO, NO2, CO2, H2O, CO , SO2 and unburnt hydrocarbon particles. The important reaction is dissociation of  NO2 In sunlight. N2 + O2 --------> 2NO  2NO + O2 ----------> 2NO2  No2 ---------> NO + O  O

  1. The emission rates should be restricted to permissible levels by each and every industry.   2. Incorporation of Air pollution control equipment in the design of the plant layout must be made  mandatory.  3. Continuous monitoring of the atmosphere for the pollutants should be carried out to know the emission levels. Equipment used to control air pollution: Air pollution can be reduced by adopting the following approaches. i) To ensure sufficient supply of oxygen to the combustion chamber and adequate temperature so that the combustion is complete, eliminating much of the smoke consisting of party burnt ashes and dust.  ii)To use mechanical devices such as scrubbers, cyclones, bag houses and electro - static precipators, reducing particulate pollutants.  1) electrostatic precipitator  2)Baghouse filter   3.)Cyclone Separator  4.) Wet scrubber  The tools in pictures are commonly used control methods for removing particulates from the exhaust gases of electric power and industrial pla