Module 3 - POLLUTION
57. Water Pollution
The various causes or sources of water pollution are:
Contamination of waterbodies like ocean, river, lake, pond and underground water with undesirable substances are called water pollution
1. Oxygen demanding wastes
2. Pathogens
3. Nutrients
4. Salt
5. Thermal pollution
6. Heavy metals
7. Pesticides and fertilizers
58. Causes of water pollution
1. Oxygen demanding wastes
Municipal waste water and industrial effluents reduce the dissolved oxygen in water. When the amount of dissolved oxygen reduces and the following effects are occurred:
a) fishes and other aquatic life are threatened and in the extreme cases killed.
b) Undesirable odour, taste and colour make the water useless.
a) fishes and other aquatic life are threatened and in the extreme cases killed.
b) Undesirable odour, taste and colour make the water useless.
2. Pathogens
They are disease producing organisms that grow and multiply within the host. E.g. Bacteria, Fungi
3. Nutrients
The nutrients like nitrogen, phosphorous, potassium etc. are considered as pollutants when their concentration are large to allow excess growth of aquatic plants and causes eutrophication effect.
4. Salt
Salt concentration in water reduces its acceptability for domestic,industrial and agricultural purposes.
5. Heavy metals
Heavy metals like mercury, cadmium, lead etc. are considered as pollutants, as these metals adversely affect the human health.
6. Other pollutants
The various other materials that causes water pollution are, plastic,chemicals, marine oil, radio active wastes etc.
59. Sources of water pollution
1. Point sources like industries and municipal sewage treatment plants.
2. Diffused sources like agricultural land, mine, construction sites etc.
60. Effects of water pollution
- Oxygen demanding wastes like municipal waste water reduces the acceptability of water for domestic use and aquatic lie is threatened.
- Excess quantity of nutrients like nitrogen, phosphorous etc. causes eutrophication effect thereby make the water bodies dead.
- Heavy metals like mercury, cadmium, lead etc. cause diseases like nervous and kidney failure in human being.
- Excess salt in water makes it not suitable for domestic use and irrigation purposes.
- Disease causing pathogens like viruses spread viral diseases.
- Hot water discharge from the power plants to the nearby waterbodies adversely effect the aquatic life.
61. Control measures of water pollution
1. Enforcement of laws to prevent water pollution.
2. Citizen should be aware and strictly follow all the laws regarding water pollution.
3. Industries should behave more responsibly.
- Waste should be disposed properly.
- Make changes in the processes to avoid water pollution.
- Effluents must be treated and cooled before running out to waterbodies.
4. Clean drainage and sewage canals regularly.
5. Develop technology to keep the drainages away from water resources.
6. To reduce the chemical fertilizers and pesticides, adopt organic farming.
7. Treat the sewage water from plants before it is disposed into waterbodies.
62. Water treatment methods
1. Screening
Screening is done to remove relatively large floating and suspended debris.
2. Coagulation
Chemicals like iron salts, lime and alum are added to neutralize the negative charges on the particles, so that they can stick together to form large particles and can be easily removed.
3. Flocculation
Coagulated water flows into a tank with paddle type mixer in which small particles stick together to form large particles called flocs.
4. Sedimentation
In sedimentation, water flow is slowed enough so that the flocs will settle by gravity.
5. Filtration
Small impurities are removed by percolating the water downward through a layer or a bed of porous granular material such as sand.
6. Disinfection
Filtered water is disinfected by adding chlorine and bleaching powder.