The Water Pollution
Pollution is a major challenge of our times and is a serious threat to the very existence of mankind on this earth. The pollution of the environment has gone to such an extent that we are unable to breathe fresh air and drink fresh water. Pollution is an outcome of human civilization. When primitive man learnt to use fire, the air pollution began. The advancement of science and technology gave us comfort through automobiles, supersonic jets, space crafts, electrical appliances, better medicines and effective pesticides on one hand, but on the other has given us serious hazards to face namely, pollution. The rapid industrial progress has also added greatly to this serious problem.
Water pollution may be defined as “addition of excess of undesirable substances to water that makes it harmful to man and aquatic life, or otherwise causes significant departures from its normal activities of various living communities in or around water.” Water is said to be polluted if it has not been sufficiently high quality to be useful for man in present or future. In India the major rivers including the Ganga are facing acute water pollution problems. Many of our lakes have been severely polluted with foul odour, slit deposits, and excessive algal growth.
Sources of water pollution
Water pollution is mostly caused by uncontrolled rejection of waste. The following are the more important sources of pollution of water.
1. Domestic wastes and sewage: Discharge of untreated or partly treated sewage into rivers is one of the common sources of pollution. Rivers and water bodies also get polluted by human excreta, besides that of animals and birds. Disposal of sewage into rivers and lakes cause water pollution. Sewage provides nutrient for various decomposers like bacteria and fungi whose population increases in polluted water. The inorganic form of phosphorus and nitrates provide nutrient for algal growth and multiplication. These algal masses decay causing depletion of oxygen that is required by bacteria in decomposing the waste. The BOD test is the most important measure for assessing the polluting capacity of organic effluents. Chemical oxygen demand (COD) is more general measure for all oxygen consuming materials in a waste.
2. Industrial waste and effluents: the pollution of rivers and streams by industrial waste has been a problem from the time of industrial revolution. The trade waste effluents from various mills, factories and industrial organizations are generally discharged into the river or streams without considering their consequences. This cause pollution of water. The industries which play a major role in water pollution are paper and pulp, textiles, sugar, fertilizers, non-ferrous and ferrous metals, rubber, chemical works, vegetable oils, petrochemicals, distilleries and leather tanning industries. These wastes have diverse compositions which adversely affect aquatic life as well as man.
3. Asbestos: It is a fibrous mineral which is highly resistant to full disintegration. Asbestos is widely used as an insulating material. It occurs mainly in four forms: chrysotile, crocidolite, tremolite and amosite. The size of asbestos fibers in most water supplies is very small, generally less than 0.1 mm in diameter. Hence, it remains undetected by light microscopy. It causes cancer of lungs, stomach and intestine.
4. Slit: It is one of the components of soil with particles measuring around 0.002 mm in diameter. Loamy soils and sandy loamy soils contain slit is large quantities. The slit and sand particles are carried from land to water and cause serious pollution in water bodies. Slit particles can chock irrigation channels and rivers and affect the life of the aquatic biota. Fishes like Salmon unable to spawn on silted gravel beds.
5. Inorganic fertilizers: In developing country like ours, it is necessary to apply substantial doses of fertilizers to increase crop yield. But this practice of adding large amount of inorganic fertilizers has in some cases, been responsible for eutrophication of our rivers and streams. A significant fraction leaches off into the nearby water body encouraging algal growth. Nitrate in agricultural drainage contaminates water. Drinking of such water by cattle or human beings causes several health problems.
6. Detergents: Detergents have widespread household use. The materials pose a serious problem to our freshwater resources. A major ingredient of most detergents is phosphates. When discharged into water, they support luxuriant growth of algae. Excessive growth of algae causes depletion of dissolved oxygen. When the algae die, their decomposed inorganic and organic matters are released back into water and become pollutants by themselves.
7. Pesticides, herbicides and biocides: Man has been trying to increase agricultural production with the help of high yielding seeds, fertilizers better irrigation and above all by the use of pesticides, herbicides and biocides. These include chlorinated hydrocarbons, organophosphates, metallic salts, carbamates, thiocarbomates, acetic acid derivatives etc. Many pesticides are non degradable and their residue have a long life. These compounds are meant for various pests and harmful weeds. When spread in the field these poisonous substances percolate through soil and get dissolved in soil water, thereby polluting it. Some of these like DDT, BHC and other are washed down with the rain water and finally enter the sea through rivers and streams. It has been estimated that the concentration of DDT in the bodies of aquatic animals like fish is increasing day by day.
8. Thermal pollution: Power plants and nuclear power stations are the main sources of thermal pollution of water. In these plants water is used for cooling and therby becomes hot. This hot water is released into the rivers or the streams which increase the water temperature. As solubility of oxygen depends upon temperature, this reduces the dissolved oxygen content of water which adversely affects the aquatic life.
9. Radio active wastes: Man today is using various types of radio active elements and isotopes for heating his home, preserving food, powering industry and fuelling transport. Wastes from atomic reactors and plants containing various kinds of dangerous isotopes are discharged into the water bodies affecting aquatic life to a great extent.
10. Oils: Oils from oil spills and washing of automobiles are very often discharged into the river and pollute them. The wreck of oil tankers by accident in the ocean causes serious oil pollution which immediately affects living organism.
Effects of water pollution
Pollutants produce various physical, chemical and biological changes in wter.
1. The water polluted with domestic sewage spread a number of epidemic diseases like cholera, typhoid, dysentery, infectious hepatitis and jaundice. Due to addition of domestic sewage containing phosphates and nitrates, the water bodies become very rich in nutrients. This is called eutrophication. The rich nutrients stimulate the growth of blue green algae which form algal blooms. These algal blooms cause depletion of oxygen and release some toxic chemicals which kill fish and other animals. Thus the clean water body is turned into sinking drain.
2. Due to accumulation of industrial effluents there is oxygen depletion in water bodies causing death of fishes and other aquatic animals. The industrial effluents impair the taste of water and give an unpleasant odour to water.
3. The poisonous substances released through various industrial wastes kill bacteria and other aquatic organisms responsible for bio-purification of water.
4. Pollution by mercury causes brain damage and even death in man. The main source of mercury pollution is fungicides, used for treating seeds. Some other sources are cosmetics, medicines, paper and pulp industries. Mercury discharged into the rivers, lakes and seas are directly absorbed by fish. Consumption os such contaminated fish was responsible for Minamata epidemic that caused several death in Japan and Sweden.
5. Nitrate fertilizers used on soil enter our wells and ponds. This water becomes very rich in nitrates. This water when taken by us, the nitrates are converted into nitrites by microbial flora of our intestine. These nitrite combine with haemoglobin of blood to form methaemoglobin which reduces the oxygen carrying capacity of blood. The disease produced is called methaemoglobinaemia which causes damage to respiratory and vascular system, blue colouration of skin and even cancer.
6. Radio active waste accumulation in the body of fish, thus harming the animals and men who eat them.
7. Lead impairs metabolism and brings about congential deformities, defective gums, anaemia and loss of apetite. Cadmium damages kidneys and liver.
8. Phosphates promote growth of oxygen consuming algae causing oxygen depletion, thereby killing fish and other animals.
9. Fine suspended particles or colloidal substances make the water turbid.
10. The pesticides and biocides used to kill pests and insects in the crop field find their way into the ponds, rivers and lakes. These are absorbed by the lower organisms and enter various food chains. At each trophic level the concentration of pesticide increases. This increase in the concentration of pesticide and other toxic substances at each trophic level of the food chain is known as bio-magnification. For example, DDT after reaching a stream or river is absorbed by microorganisms on which small fishes feed. Finally it reaches into the body of carnivorous fishes, since bigger fishes consume more food. So more and more DDT accumulated in their body and the fish becomes unfit for human consumption.
11. Above all, due to pollution the self-purifying ability of water is lost and water becomes unfit for drinking and other domestic uses.
Control of water pollution
The various ways and techniques suggested for control of water pollution as follows:
1. Waste treatment: In this method the domestic sewage and industrial wastes are properly treated before release into natural streams and rivers.
Sewage treatment - It involves three steps. In the first step, the large and suspended particles are removed. In the second step aeration is supplied to promote bacterial decomposition of organic compounds, followed by chlorination to eliminate the bacteria and in the third step, nitrates and phosphates are removed. The treated water is then released.
Treatment of industrial effluents - Industrial effluents should also be treated to eliminate the pollutants. The treatment involves neutralization of acids and alkalines, removal of toxic compounds, coagulation of colloidal impurities, precipitation of metallic compounds and reducing the temperature of waste water to decrease thermal pollution.
2. Recycling and reutilization of waste: The conventional method of sewage and industrial waste treatment are expensive which involve sophisticated equipments. The inexpensive as well as efficient methods of sewage treatment can be adopted where sufficient land, plentiful sunshine and hot climate exist. Under these conditions sewage water can be treated in the so called oxidation or stabilization ponds. Domestic or industrial wastes are stored in a large shallow pond and kept in it for a few days. In the presence of sufficient sunlight and organic nutrients healthy blooms of algal develop along with colonies of bacteria. The bacteria speedily digest the organic waste and rendering it harmless. These effluents then can be released for irrigation. In West Bengal, Fish farms have been developed using well treated sewage.
In developed countries, the waste water consisting of industrial effluents, municipal and domestic sewage are recycled and reused to generate cheaper fuel, gas and electricity.
3. Removal of Pollutants: Various pollutants (radio active, chemical, and biological) present in water body can be removed by appropriate methods such as adsorption, electrodialysis, ion exchange, reverse osmosis etc. Reverse osmosis is commonly used to desalinate the blackish water and purifying water from sewage. In Norway organic sewage is mixed with sea water and subjected to electolysis to remove phosphorus from the sewage, which enhances eutrofication in lakes and rivers.
4. Composting: Composting is an effective method of waste disposal. It minimizes the risk of environmental pollution. Health hazard is eliminated during composting since the pathogenic organisms are destroyed during the process.
5. Use of water hyacinth: Water hyacinth and duck-weeds species can be used for treatment of wastes. Water hyacinth can control the water pollution by reducing the pollutants up to 80 to 90%. These weeds act as natural filters and absorb toxic effluents.
6. Using solar power: Very recently scientists have claimed to use solar power for purifying the polluted waste water cheaply. According to them, a combination of sunlight and a catalyst such as titanium dioxide can dissociate chemical toxicants of water. Such photolytic reaction can kill pesticides, foul smelling bacteria and other toxic substances.
7. Legislation: The water (Prevention and Control of Pollution) Act of 1974 as amended in 1988 should be strictly enforced.
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