NEET Chemistry Notes Environmental Chemistry – Water Pollution
It is the degradation of quality of water due to addition of inorganic, organic, biological or radiological substances, factors (e.g. heat) makes it health hazard, unfit for human use and growth of aquatic biota.
Sources of Water Pollution
The sources from which the pollutants are obtained and released are given below:
- Natural Sources of Water Pollution
Leaching of minerals, slit from soil erosion and falling of organic matter from banks are the important natural sources of water pollution.
- Man Made Sources of Water Pollution
Sewage, domestic waste, soaps and detergents, fertilizers and pesticides, industrial wastes, heat, are the man made sources of water pollution.
Biochemical Oxygen Demand (BOD)
The amount of oxygen consumed by microorganism in decomposing the waste present in a certain volume of sample of water is called BOD.
To determine BOD, water sample is first saturated with oxygen and then incubated at constant temperature for five days.
Chemical Oxygen Demand (COD)
In COD determination, a known quantity of water sample is oxidised by acidified K2Cr207. The unused amount of dichromate is determined by back titration. The amount of oxygen used in oxidation is calculated from consumed concentration of K2Cr207
Effects of Water Pollution
- High concentration of fludBidtS are poisonous and are harmful to bones and t&rfh at levels over 10 ppm.
- Excessive sulphate (>500 ppm) have a laxative effect.
- Excess nitrate in drinking water can lead to blue baby syndrome (methemoglobinemia).
- Removal of large solids from waste water by filtration.
- Settlement of the filtered waste water to remove suspended solids, oily and greasy material which floats on the surface can be skimmed off.
- Degradation of organic content of waste water by microbial oxidation.
- Removal of phosphates, coagulation, filtration, and disinfection using chlorine for improving the quality of waste water.
Soil or Land Pollution
Soil pollution is the addition of such chemical substances (in an indefinite proportion) which decreases its productivity, quality of plants and ground water, to the soil system.
Causes of Soil Pollution
- Erosion of upper fertile layer and over use of the land.
- Pesticides like insecticides (e.g.DDT, BHC), herbicides (e.g..NaCl03,Na2As03), fungicides
(e.g. organomercury compounds) and fertilizers. Soil conditioners (e.g. compounds of As, Hg, Pb, etc.)
- Dumping of waste such as garbage, rubbish, industrial wastes, ash, sludge, broken cans and bottles, etc.
- Forestation to check the spread of desert.
- Chemicals like fertilizers, insecticides, polymers.
- Pesticides and herbicides should be used, only when necessary.
Strategies to Control Environmental Pollution
- Waste management and green chemistry are used to control environmental pollution. Waste management is done by recycling, digestion, incineration, dumping and sewage treatment.
- Recycling, i.e. conversion of waste into useful products.
It saves raw materials and reduces the cost of waste disposal, e.g. recycling glass bottles, scrap metal in the manufacture of steel, generation of energy by burning combustible waste.
- Incineration, i.e. reduction of many combustible wastes from households, hospitals etc., to ash by burning it at very high temperature (> 1000°C) in excess of oxygen. This is one of the best methods for disposal of polychlorinated biphenyls (PCBs) as high temperature breaks C—Cl bonds. The chief disadvantage of incineration is that it leads to air pollution.
- Green fuel, the plastic waste is being converted into fuel which has high octane number and doesn’t contain any lead.
- Digestion, i.e. conversion of the organic material (C,H,0) into carbon dioxide and methane by microorganisms (anaerobic digestion).
The invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazardous substance.