Water Pollution

Water Pollution

Water is one of the most precious resources.It is more abundant than anything else.It is the most wonderful natural resource.Water is very essential for the survival of all biotic substances on the earth.It is the major constituent of protoplasm and is necessary for life activities.Water is the soul of nature,its pollution will destroy the world.Water is used for diverse purposes in the country which can be conveniently grouped into the five sectors namely domestic,industrial,transportation,power generation and irrigation.But due to industrial growth,urbanisation and domestic uses many unwanted substances are introduced in water and is polluted.Today clean and potable water has become a precious commodity as its quality is very often adversely affected by numerous sources of pollution.Polluted waters are turbid,bad smelling,unpleasant and unfit for drinking,bath and other purposes.They cause many diseases and are harmful to human beings.The water in the rivers,lakes,ponds and streams may be contaminated with various water pollutants mostly originating from human activities.The following are the possible sources of water pollutants.

1.Sewage and Waste

All homes,restaurants and hotels produce sewage and waste.These domestic sewage and waste and large quantities of other organic waste coming out from the food processing plants,slaughter houses etc. are sometimes directly drained or dumped in the river,lakes and streams.The organic matter in these waste decomposes by bacterial action in the presence of the dissolved oxygen(D.O).This results in the rapid depletion of the dissolved oxygen in the water,which is very harmful to aquatic organisms.

These wastes may also carry various pathogenic microorganisms which may sometimes enter even the drinking water and cause serious damage to the public health.

It is very fortunate that even the dumping of solid waste and plastic materials at various places in the streets and roads of Kathmandu has been occasional scenes at Kathmandu.

2.Pesticides and Chemical Fertilizers

These days lots of pesticides and fertilizers are used for the cultivation of plants and crops.Some of the pesticides and fertilizers are washed by the rainwater to the ponds,lakes, and streams.The widely used pesticides like D.D.T are not biodegradable and have accumulaDissolve oxygen potash fertilizers like potassium nitrate,washed down by the rainwater to the ponds and lakes cause the overgrowth of unnecessary algae which depletes the dissolved oxygen in the water and kill the aquatic life.

3.Soap and Detergents

The synthetic detergents or washing powder in the market containing phosphates are also water pollutants.Phosphates are water nutrients.They also cause the population growth of the undesirable algae and weeds in the water and consume dissolved oxygen.The lowering of the dissolved oxygen in the water retards the growth of aquatic animals such as fish.

4.Oil

Large scale oil pollution may take place in oceans and seas because of oil spills from cargo oil tankers,leaks and losses during off shore exploration of oil wells.Oil pollution leads to hazardous conditions,which are detrimental to marine life and sea food.

5.Inorganic pollutants

Some of the inorganic water pollutants may be mineral acid,inorganic salt,finely divided metal or metal compounds.Water pollution by heavy metal occurs due to street dust and industrial effluent(waste liquids).

Heavy metal such as Zn,Cd,Sg,Pb,Ni and Cr and metalloids such as As,Sb and Se may be present in industrial effluents.This metal are toxic and cumulative and their side effects.Cadmium causes damage mercury impairs hearing and eyesight and causes paralysis and Minamata disease.

Lead adversely effects the functioning of the organs of muscular ,circulatory and nervous system, and damages kidney and liver.

Dissolved Oxygen(DO)

Oxygen is vitally important spices in water.It is consumed by oxidation of organic metal\reducing agents.It is an important water polluting parameter.The optimum value for good water quality is 4 to 6 mg\l of dissolve oxygen,which ensures healthy aquatic life in water body.Lower DO values indicate water pollution.The primary cause of water deoxygenation has been the presence of substances collectively called oxygen demanding wastage.The available dissolved has been consumed by bacterial activity,and thus,the presence such materilas quickly gives rise to depletion of dissolve oxygen.

Biochemical oxygen demand(BOD)

Biochemical Oxygen Demand (BOD) has been a standarized measurement of the amount of oxygen that would be required by microorganism to cause the decomposition of certain organic and inorganic matter in the water. Hence the amount of oxygen required by micro organism to oxidise organic wastage aerobically is called the biochemical oxygen demand.The measurement is done under standarized condition(example at 20°c and five days to allow the decomposition to take place).The result is called the five day BOD and is expressed in miligram of oxygen per litre of water.BOD is not pollutant but an indicator.

Bod value of several hundred miligram\litre charactarize strong sewage.For excellant drinking water the five BOD,on a monthly average should be in the range of 0.75 to 1.5 miligrams per litre.BOD values are important when they signify that the oxygen supply dissolve in water will be so greatly reduced that disirable fish no longer can survive or when they signify that condition for propagation of dangerous bacteria exist.

Chemical oxygen demand(COD)

Chemical oxygen demand (COD) is an index of an organic content of water.(Oxygen demanding substances in water) and is an important water quality parameter .The COD has been a measure of concentration of substances in water that can get attacked by the string chemical oxidizing agent in a standarized analysis.COD value do not get necessarily co releted with BOD value.

Diffences between BOD and COD

Alkanity of Water

Alkanity of water is a measure of the water' ability to absorb hydrogen ions without significant pH change.Hence,alkanity is a measure of the buffering capacity of water.Alkalinity is related to the pH of a solution but measures a different property. Roughly, the pH of a solution is a measure of how "strong" the bases are in a solution, whereas the Alkalinity measures the "amount" of chemical bases. A good example is a buffer solution which can have many available bases (high alkalinity) despite having only a moderate pH level.

References

Poudel, Bhoj Raj Poudel and Dr.Megh Raj. A Text Book Of Inorganic Chemistry. Kathmandu: National Book Centre, 2012.

Sons, John Wiley and. J.D Lee Concise Inorganic Chemistry. 2007.