Water pollution is the contamination of water bodies (e.g. lakes, rivers, oceans and groundwater). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds.
Water pollutants come from point and non-point sources. Their effects on aquatic systems largely depend on whether polluted waters are standing (lakes and ponds) or flowing (rivers). Standing systems are generally more susceptible because of slow turnover. The major water pollutants are organic nutrients, inorganic nutrients, infectious agents, toxic organics, toxic inorganics, sediment and heat. Organic nutrients come from feedlots, municipal sewage treatment plants, and industry. They promote growth of natural populations of aquatic bacteria. Bacterial decomposition of organic materials results in declines in dissolved oxygen, with dire effects on other oxygen-requiring organisms.
Two inorganic plant nutrients of major concern are nitrogen and phosphorus. They come primarily from septic tanks, barnyards, heavily fertilized crops, and sewage treatment plants, and cause excessive plant growth that clogs navigable waterways. Bacterial decay of plants in the fall result in a drop in dissolved oxygen, which may suffocate fish and other organisms.
water is the important consistent of life-support system, Water is the most important natural resource. 80% f the earth area is occupies by water. However, hardly 2.5% makes up the total world’s supply of fresh water including the frozen water in the polar ice caps and glaciers. Water is needed for irrigation, industry, domestic needs shipping and for sanitation and disposal of waste. The conservation and keeping up of a good supply of water is thus very essential. main, has however, polluted much of this limited supply of water by industrial wasters sewage and a number of synthetic chemicals, many rivers of the world receive heavy flux of sewage, domestic waste, industrial effluents, agricultural wastes, etc, which contain substances varying from simple nutrients to highly toxic materials, In our counter, all the major reverse has been polluted. These have actually becomes an unending sewer fit only to carry urban liquid waste half burnt dead bodies, pesticides and other wastes. many of our laks have become dark with foul smell. Moreover, the rainfall on its way down to the earth brings down the air pollutants. Polluted water is the water which has more negative qualities than it has positive ones, i.e. it is no longer fit for any use
| Pollutant | Source |
| Micro-organisms | Domestic sewage |
| Organic wastes | Domestic sewage, animal excreta and waste, decaying animals and plants, discharge from food processing factories. |
| Plant nutrients | Chemical fertilizers |
| Toxic heavy metals | Industries and chemical factories |
| Sediments | Erosion of soil by agriculture and strip mining |
| Pesticides | Chemicals used for killing insects, fungi and weeds |
| Radioactive substances | Mining of uranium containing minerals |
| Heat | Water used for cooling in industries |
Chemical Oxygen Demand is another important water quality parameter. It is an index of the waste (organic inorganic) of water which cab be oxidized by a strong oxidized by a strong oxidising agent usually acidified potassium dichromate, K2Cr2O7. This reagent oxidizes most of the substances present in water including those which are not oxidized by microorganisms. The water sample is treated with a known amount of acidic potassium dichromate solution. The unrated potassium dichromate is determined by back titration with a suitable reducing net like Mohr’s salt.Form the amount of K2Cr2O7 consumed, the amount of oxygen utilized in the oxidation of water sample can be calculated. With the help of following oxygen.
How to Control water pollution ?
(i) Septic tanks should be used for each house. This will reduces the flow of municipal sewage and human excreta towards river, lake or pool
(ii) Rivers, lakes, etc. should to be used for bathing and washing purpose. In this way, water sources are not polluted with detergents and germs.
(iii) Too much use of pesticides with are not degradable should be avoided. These are highly toxic substance.
(iv) Efforts should be made to increase the use of low grade or polluted water. Treatment of domestic sewage for industrial cooling is a good example of efficient use. Water reuse has a special significance in mining an similar industries where the water availability is less These efforts will save fresh water from being polluted.
COD is also expressed in ppm. COD values do not necessarily match the BOD values. Textile wastes, paper mill wastes, paper mill wastes, etc., with high cellulose content have COD values considerably higher than BOD values as cellulose is not radily attached by dissolved oxygen.
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