Water Pollution
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Water Pollution |
water pollutants
About 80% of the earth’s surface is covered by water. It is estimated that 96% of this water is used for agriculture 3% for domestic zero and 1.1% for industrial; activity. The wasted polluted water is defined as water that does not meet over the minimum standards for any function and purposed for which it would be suitable in its natural state. Water pollution may be defined as “any change in the physical, Chemical and biological properties of water, as well as contamination with foreign, substance which results in the decrease in the utility of water or cause diseases. The main causes of water pollution are:
1. Industrial wastes: Water gets polluted by industrial effluents containing acid soaps, detergents, pesticides, insecticides, fungicides and metals like Cu, Zn, P, Hg etc.
2. Domestic sewage: The sewage contains human excreta urine, kitchen wastes, steel wastes and organic substances that provide nutrition for bacteria and fungi.
3. Suspended Particles: The surface water may contain a high concentration of suspended solid (organic as well as inorganic) bacteria algae etc. This makes water unfit for domestic as well as industrial purposes organic pollutants:
(a) Oxygen demanding wastes: These include domestic and animal sewage biodegradable organic compounds and industrial wastes from food processing plants meat packing plants, slaughter houses paper and pulp mills. All these wastes undergo degradation and decomposition by bacterial activity in presence of dissolved oxygen. The optimum DO in natural waters is 4.6 ppm is essential for supporting aquatic life.
(b) Disease causing water: These include pathogenic micro-organisms, which may enter the water along with sewage and other wastes and may cause tremendous damage to public health. These bacteria and viruses can cause dangerous water-borne diseases such as cholera, typhoid, dysentery, polio, hepatitis in human.
(c) Synthetic organic compounds: There are synthetic pesticides, detergents food additives insecticides pants synthetic fibbers elastomers plasticizes plastic and other industrial chemicals most of these Chemicals are toxic to plants animals and humans volatile substances such as alcohols, aldehydes, ethers and gasoline may cause an explosion.
(d) Sewage and agricultural runoff: Sewage and runoff from agricultural lands supply plant nutrients which may stimulate the growth of algae and other aquatic weeds. Due to growth of algae the concentration of oxygen in waterfalls. Due to lack of dissolved oxygen in water kills the fish.
(e) Inorganic Pollutants: It consists of mineral acid inorganic salts metal compounds finely divided metal complexes of metal, organometallic compounds, trace elements, polyphosphate in detergents. The mains source of phosphate in water are bodies acting as algae nutrients and is important as for as water pollutant is concerned numbering trace elements are found in polluted water. Out of that most dangerous are Hg, Cd, Pb, As, Se. The most toxic among the trace elements are the heavy metals such as Hg, Cd and Pb and metalloids such as As, Sb and Se. The heavy metals have a great affinity for sulphur and attack the --SH bonds in enzymes. Protein carboxylic acid group and amino groups may also be attacked by the heavy metal ions. As such Se enters to water bodies through pesticides. Excess amount of As and Se causes various disease such as skin cancer and bluing stager.
4. Sediments
Due to soil erosion agricultural development soil erosion by water wind and other natural sources are very significant. The organic matter contain sediments is generally higher than that in solids. Sediments and suspended particles exchange cations with the surrounding aquatic medium and act as repositories for trace metals such as Cu, Co, Ni, Mn Cr and Mo. Suspended solids such as salt and coal may injure the gills of the fish and cause asphyxiation.
5. Radioactive materials
The main sources of radioactive material for water pollutant are:
(a) Mining and processing ores eg. Uranium
(b) Increasing use of radioactive isotopes in research agricultural industrial and medical application I132, P32, Co45 and Cs137.
(c) Radioactive material from nuclear power plants and nuclear reactors eg. Sr90, Cs137.
These radioactive isotopes are toxic. This can be accumulates in bones and tooth and causes serious disorders in human beings.
Waste water treatment
1. Preliminary test
In preliminary treatment large floating and suspended solid matters, grit, oil and grease are removed. For removal of these materials, different types of screens are used.
2. Primary treatments
In primary treatment the sedimentation of suspended particles is taken place. Water is allowed to stand in big tanks where particles are settled down at bottom under gravity. To settle down the lighter colloidal particles certain chemicals are used called coagulants.
3. Secondary treatment
In this treatment the dissolved and colloidal organic matter present in waste water is removed by biological process involving bacteria and micro-organism. These processes may be aerobic or anaerobic.
The effluent from primary sedimentation tanks is first subjected to aerobic oxidation in system, such as aerated lagoons, trickling filters, activated sludge unit and oxidation plants. Then it subjected to anaerobic digestion in the sludge digesters. Certain micro-organism, in presence of dissolved oxygen utilizes organic waste as their food, and converts into simpler compounds such as CO2, H2O, nitrites and sulphates, which are non-pollutants.
Anaerobic micro-organisms eat organic matter and transfer complex organic compound in low molecular weight products such as acids and alcohols. These compounds then turn into CO2 and CH4.
4. Tertiary treatment
Tertiary is the final treatment which improves the quality of water obtained from secondary treatment. The major objectives of tertiary treatment are:
a. Removal fine suspended solids
b. Removal of bacteria.
c. Removal of dissolved inorganic solids.
d. Removal of final traces of organics, if it is felt necessary.
Removal of finely divided suspended solids can be achieved with the help of micro strainers and sand filters.
Removal of bacteria can be achieved by retaining the effluents from secondary biological treatment plants in maturation ponds or lagoons for specified periods of time. Three or Four lagoons arranged in series give an excellent final effluent with very low BOD and low suspended solids. The Final effluent is chlorinated if necessary.
Removal of the dissolved inorganic solid is a major problem with waste from industries such as fertilizer, textile processing, tannery, and electroplating. Depending upon the required quality of final effluent and cost of treatment that can be afforded in a given situation, any of the following treatment methods can be employed.
1. Nutrient Removal
2. Removal of nitrogen
3. Removal phosphorus
4. Evaporation
5. Ion-exchange
6. Adsorption
7. Reverse osmosis
8. Chemical precipitation
Solid waste management
The objectives of solid waste management
- To control, collect, treat, utilize and dispose of the solid waste in an economical manner.
- To protect the public health with the appropriate management of solid waste.
The major considerations in the solid waste management
- Public health
- Judicially use of waste for energy generation
- Classification of waste for the recycling process
- Appropriate disposal of hazardous solid waste
Public health
Under warm and humid conditions organic waste is an ideal breeding place for pathogenic organisms like rodents, mosquitoes, and flies. Further solid waste management aimed to improve ground water quality. Due unhygienic land-filling led to contamination of ground water by chemicals, biodisposals and active micro-organism.
Separation of solid waste for recycling
Separation of domestic solid waste is possible, but it is difficult job to separate industrial waste. Domestic solids separation based on a biodegradable property of solids. Biodegradable solids are directly converted into fertilizers and generation of biogas. Undegradable wastes (plastics, rubber, fiber articles) require specifically designed plants. It is mandatory to recycle industrial waste before disposing it. It is quite expensive.
Energy recovery
Solid is not fully utilized before it disposed of as a waste. Sold waste has great potential for generation of energy with lower cost. Bio-solid is used for generation of fertilizers and biogases. To recover energy solid waste is first burnt in incinerators or converted to more efficient refuse derived fuel (RDF). Reuse of the recovered materials from the solid waste is the other principal mode of energy conservation. Obviously, mining and manufacture of ferrous and non-ferrous metals starting from mining ores have tremendous energy. Reuse of this energy will be justified from the standpoint of energy conservation.
Disposal of hazardous solid waste
Today the disposal of wastes by landfilling or landspreading is the ultimate fate of all solid wastes, whether they are residential wastes collected and transported directly to a landfill site, residual materials from materials recovery facilities (MRFs), residue from the combustion of solid waste, compost or other substances from various solid waste processing facilities. A modern sanitary land is not a dump; it is an engineered facility used for disposing of solid wastes on land without creating nuisances or hazards to public health or safety, such as the breeding of rats and insects and the contamination of groundwater.
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