Sewage for Water Supply: Detrimental Effects and Sewage Treatment!
Sewage is the spent water supply of the community which is liberated as a turbid dilute liquid to the water bodies. It contains a lot of organic matters, under composed biomolecules and minerals. It includes both biodegradable pollutants like human faceal matter, animal waste etc. and inorganic substances like soaps, detergents, ash, sewage sludge, atoms or ions of different toxic elements etc.
The inorganic substances may be nitrates, phosphates Na+, K+, Ca2+, Cl_, and HCO3_ etc. Latest reports suggest that trace amounts of metals such as Cu, Cr, Zn, Mn, Pb, Ni etc. are also present in sewage. Besides, sewage contains two important types of bacteria in very high quantity.
(i) Saprophytic bacteria (Which are harmless and feed upon dead organic substances);
(ii) Pathogenic bacteria (which cause diseases in man and animal), there are different types of wastes in sewage.
These may be municipal wastes, domestic waste, wastes of industries etc. Domestic waste includes waste water of bath room, lavatories, kitchens etc. When the quantity of organic waste is very high, it provides a good medium for the growth of aerobic bacteria. These bacteria decompose the waste and lead to depletion of oxygen in aquatic body. Under natural conditions, most of the biodegradable pollutants are decomposed by the decomposers.
The complex biomolecules like proteins, fatty acids, esters, amides, starch, amino sugars etc. are converted in to simple molecules first, then into simpler inorganic chemicals and finally into nutrients. When the rate of sewage disposal exceeds its rate of decomposition, it accumulates in large quantities. However, when the sewage contains large among of organic wastes and sufficient number of decomposers, the nutrient amount increases in water bodies.
The increased nutrient load enhances the productivity of aquatic bodies leading to algal blooms which makes water green. Such an excessive increase in the nutrient load in the water bodies is known as eutrophication.
When the sewage contains a lot of inorganic substances like soap, detergent, atoms and ions of toxic elements, the decomposers are killed. Such a lowering in number of decomposers reduces or stops the rate of decomposition.
Detrimental effects of Sewage:
The detrimental effects of sewage are as follows:
1. The presence in soaps, detergents etc. kill helpful saprophytic bacteria which help in decomposition.
2. Harmful pathogenic bacteria in sewage cause cholera, dysentery, typhoid etc.
3. Depletion of oxygen during the decomposition of organic wastes of sewage makes water bodies unfavorable for aquatic plants and animals.
4. A number of poisonous gases with foul odour come out of the sewage canal.
5. The turbidity of sewage decreases solar light penetration into the inner zones reducing photosynthetic ability of aquatic plants.
6. Due to enrichment of organic residues the system becomes eutrophicated. This disturbs the natural balance of the eco-system.
The level of pollution in sewage is characterized with a high BOD (Biological oxygen demand). Higher the value of BOD, higher will be the level of pollution in aquatic body.
The different objectives of sewage treatments are as follows:
1. To check destruction of aquatic plant and animal life.
2. To restore the self-balancing and self-regulating nature of the ecosystem.
3. To dispose the sewage which would not destroy the normal physio-chemical nature of water.
4. To kill all pathogenic bacteria in sewage.
5. To restore normal flora and fauna with essential microorganism.
6. To eliminate toxic metals and toxic chemicals from sewage system, which joins water bodies.
7. To make the water of the system more natural, usable and hygienic.
8. To render the sewage inoffensive.