In discussing the reduction of pollution, it has to be emphasized that the pollutants shouldwhenever possible be removed at the source, where they are most concentrated. After they arereleased to the water and diluted, removal becomes much more difficult and may even beimpossible. Some of the methods of water pollution control are discussed below:
1. Dilution:
Dilution seems to be the most attractive method of waste disposal. Diluting thepolluted water mass to such an extent that the harmful effect of the pollutant is made ineffective.However, the disposal programme must be in coordination with a programme of environmentalmanagement to guarantee adequate supplies of fresh water for the dilution process.
2. Efficient use (Reuse):
One of the most important conservation activities is the use of freshwater in such a way that we get the very most for our efforts, without depleting it. Effortsshould also be directed to increase the usability of low grade or polluted water. Treatment of domestic sewage for industrial cooling is a good example of efficient use. Water reuse has aspecial significance in mining and similar industries where the resources are scarce.
3. Alternative use:
Where the waste material recovery is not economical, its alternative useshould be examined e.g. pulp, which cannot be easily recovered, is being trapped at the outfallarea of sulphite waste and is being used for the manufacture of cardboards. The uses of heatedwater for fish culture in many European countries and in North America have encouragingresults. In the temperate region, many species of fish and shellfish grow during only a brief partof the year because the water is too cold for growth during the winter. In U. K. water from powerplants has been used for the growing of Plaice and Sole in tanks and ponds and it has beendemonstrated that these fish can be brought to marketable size about two years earlier than if leftin their natural conditions. If the discharge of warm water in sea is closely regulated the warmerwater, being less dense than the receiving water, would entrain and carry the nutrient-rich watersto the surface and increase the fertility of the area.
4. Recovery of byproducts:products:products:products:
Recovery of by-products such as sodium hydroxide from sulphitewaste, calcium oxide from sulphite waste, oil from hydrogenated vegetable oil and soap, mercuryfrom chloro-alkali industry effluents and so on should be practiced.
5. Appropriate technology:
We should develop, import and adopt only appropriate technology,which is pollution free. As an example, the mercury cell in the chloro-alkali industry should bereplaced by diaphragm cell to avoid mercury pollution in the cell room itself and througheffluents in water bodies. Use of natural gas instead of coal as fuel along with pollution controlmeasures by industries and automobiles, will reduce the production of gases causing acid rain.
6.. Waste treatment/Purification:
There are many processes available for treatment and purification of waste beforedisposal.(A) Chemical treatment: Chemical treatment has long been used for industrial waste and fortreatment of water for human consumption. Recently it has come into use also for treatment of domestic sewage in order to remove phosphates, heavy metals and other pollutants. Forindustrial wastewater treatment, this treatment is desired if the colour of effluent is too intense.Normally colour removal is carried away by adsorption on clays and activated carbon,coagulation with lime, aluminum sulphite etc. but treatment costs are high and not suitable forremoving organic matter.
(B) Biological treatment:
In biological treatment optimum conditions are provided for naturalself-purification in lagoon with the help of trickling filters, activated sledge or waste stabilizingponds. Use of treated or partially treated sewage for fish culture is a traditional method of biological treatment of organic waste, in which organic matter is mineralized, nutrient contentconsiderably reduced and producing over one ton of fish per hectare per year without additionalfeeding. Under Indian conditions, water hyacinth (Eichhornia crassipes) can be used forpurifying municipal and industrial wastes on a large scale. Researches have shown that waterhyacinth grown in one-hectare water spread area can absorb the nitrogen and phosphorus wastesof over 600 persons. It also accumulates high rate of heavy metals and phenolic compounds fromindustrial effluents along with minerals.
(C) Biochemical treatment:
It is considered better than chemical treatment because it not onlyremoves colour, but also help in BOD reduction and removal or organic matters. Biochemicaloxidation is in fact a unit operation that conveys water-soluble organic compounds and eachcapable of converting 30-70% of soluble convertible carbonaceous materials having high BODto insoluble carbonaceous material, CO2, water and energy.
(D) Accelerated bio Accelerated bio----chemical process (ABC):chemical process (ABC):chemical process (ABC):chemical process (ABC):
It is recommended for high BOD removal upto 90% suspended solids and phosphorus removal as well as reduction in aeration time to asmuch as 30-45 minutes against 3-4 hours via conventional bio-chemical process and 20-30%lower construction costs. The process involves a two-stage biochemical system. The first stage isaerobic biological treatment, which receives raw effluents, deaerates, and converts the solubleand colloidal organic solids into a particulate insoluble form. It consists of a reaction vessel and aseparator. The influent residence time is 30-60 minutes; separator is a sedimentation vessel. Thesecond stage has a flocculator, clariflocculator aerator and a settler in sequence.
(7) Trapping:
Control of pollution from agricultural drainage and land erosion by conventionalmethods of treatment is not possible. In addition, the drainage from the agricultural land cannotbe checked. Therefore, the best way to check the agrochemicals and soil particles from enteringthe watercourses is to trap them on their land route. This can be achieved by adopting thefollowing practices;(a)
Provision of optimum soil cover (vegetation, crop residue) to dissipate raindrop impactand reduce runoff velocity.(b)
Provision for optimum soil infiltration and flow path to minimize erosion through soildetachment and transport, and reduce runoff volume through enhanced filtration.(c)
Minimization of soil solution concentration of pesticides, plant nutrients and otherchemicals at the soil surface or within the root zone during periods of high runoff,thereby minimizing the movement of such substances in runoff and percolate.(d)
Judicious application of pesticides and fert8ilizer to crops so that a potential pollutant isless available for detachment and transport.(e)
To replace use of chemical fertilizers and pesticides by biofertilizers and botanical & bio-pesticides.(8). Water pollution control legislations:i)
Water (prevention and control of pollution) Act-1974, first legislation towardspollution controls.ii)
The water (prevention and control of pollution) Cess Act, 1977.iii)
The Environment (protection) Act, 1986iv)
Ganga Action plan (1985). The central Ganga Authority was constituted inFeb.1985 to evolves and oversee the implementation of long term Ganga Actionplan for cleaning the river Ganga.
Conclusion:
The ultimate solution to pollution-The quatrain-“The solution