Systems of Sanitation and the Modern sanitation system





The waste products of society including the human excreta had been collected, carried, and disposed of manually to a safe point of disposal, by the sweepers, since time immemorial. This primitive method of collecting and disposing of society's wastes has now been modernized and replaced by a system, in which these wastes are mixed with a sufficient quantity of water and carried through closed conduits under the conditions of gravity flow. This mixture of water and waste products, popularly called sewage, thus automatically flows up to a place, from where it is disposed of, after giving it suitable treatments; thus avoiding the carriage of wastes on heads or carts. The treated sewage effluents may be disposed of either in a running body of water, such as a stream or may be used for irrigating crops.

This modern water-carried sewerage system has completely replaced the old conservancy system of sanitation in the developed countries like the U.S.A. However, India being a developing country, still uses the old conservancy system at various places, particularly in her villages and smaller towns. The metropolitan cities and a few bigger towns of our country, no doubt, have generally been equipped with the facilities of this modern water carriage sewerage system, and attempts are being made to equip the remaining cities and towns with this system, as soon as funds become available.

The modern water-carried sewerage system is preferred to the old conservancy system, because of its following advantages:

(i) The water carriage system is more hygienic because, in this system, the society's wastes have not to be collected and carried in buckets or carts, as is required to be done in the conservancy system.

The free carriage of night soil in carts or as head load, which is required in the conservancy system, may pose health hazards to sweepers and other residents, because of the possibilities of flies and insects transmitting disease germs from these accessible carts to the resident's foods and eatables; whereas, in the modern sewerage system, no such danger exists, because the polluted sewage is carried in closed conduits, as soon as it is produced.

(ii) In the conservancy system, the waste products are generally buried underground, which may sometimes pollute the city's water supplies, if the water supply pipes happen to pass through such areas or the wells happen to draw water through such areas.

(iii) In the conservancy system of sanitation, the entire day's human feces are collected and then disposed of in the morning, once a day. Thus, from this type of latrines, pungent smells may continue to pollute the surroundings for the entire day. But since in the water carried system, the human excreta is washed away as soon as it is produced, no such bad smells are produced. Moreover, in the conservancy system of sanitation, the wastewaters from bathrooms, washbasins, kitchen sinks, etc.; are carried through open roadside drains, as this is supposed to be not so foul since it does not contain human excreta. But these roadside drains are generally abused by children or adults for passing their stools, particularly at night hours, thus creating foul and more unhygienic conditions. No such problems exist in the water carriage system.

(iv) In the water carriage system, the sewage is carried through underground pipes (popularly called sewers) which owing to their being underground, do not occupy floor area on roadsides or impair the beauty of the surroundings. The roadside drains carrying foul liquid in the conservancy system, will no doubt pose such problems.

(v) The water-carried system may allow the construction of latrines and bath-rooms together (popularly called water-closets (W.C.)], thus occupying lesser space with their compact designs. This system is also very helpful for multistoried buildings, where the toilets, one above the other, can be easily constructed, and connected to a single vertical pipe.

In spite of these advantages of the modern water-carried system, it has not been possible to completely replace the old conservancy system, mainly because huge capital funds (of the order of 10,000 to 15,000 per person) are required for the construction of such a system. Besides the huge initial investments, the RMO expenses are also high, which makes it difficult to replace the simpler and cheaper conservancy system. Moreover, for the functioning of the sewerage system, an ample amount of water must be made available to the people, and hence, a reliable and assured water supply system must, first, be installed, before installing the sewerage system.

Types of Sewage, and Types of Sewerage Systems

This modern water carriage sewerage system not only helps in removing domestic and industrial wastewaters, but also helps in removing water drainage. The runoff resulting from the storms is also sometimes carried through the sewers of the sewerage system, or more generally is carried through a separate set of drains (open or closed) directly discharging their drainage waters into a body of water, such as a lake or a river. Since the rain run-off is rot so foul as the sewage is, no treatment is generally required to be given to the drainage discharge. When the drainage is taken along with sewage, it is called a combined system, and when the drainage and sewage are taken independently of each other through two different sets of conduits, it is called a separate system. Sometimes, a part of the drainage water, especially that originating from the roofs or paved courtyards of buildings, is allowed to be admitted into the sewers and similarly sometimes, the domestic sewage coming out from the residences or institutions, etc., is allowed to be admitted into the drains, the resulting system is called a partially separate system.

Strictly speaking, it is generally advantageous and economical to construct a 'separate system' at least in the bigger cities and towns. But in practice, it is generally not possible to attain a 'truly separate system' because some rainwater may always find its way into the sewers either through wrong house sewer connections or through open manhole covers. Similarly, wherever the authorities find insufficient sewer capacities, they divert part of the sewage into the stormwater drains, thus making most of our existing systems partially separate' only.

In the modern days, a 'separate system' is generally preferred to a combined system', although each individual case should be decided separately on merits, keeping the following points into consideration:

(1) A separate system will require laying two sets of conduits, whereas, a combined system requires laying only one set of bigger sized conduits, thus making the former system costlier. Moreover, separate conduits cannot be laid in congested streets and localities, making it physically unfeasible.

(ii) The sewer pipes in the combined system are liable to frequent silting during the non-monsoon season (when the flows in them are quite less) unless they are laid at sufficiently steeper slopes, which, in turn, will make them deeper, requiring more excavation and pumping, thereby making them costlier.

(iii) In a combined system, the less-foul drainage water gets mixed with the highly foul sewage water, thus necessitating the treatment of the entire flow, needing more capacity for the treatment plant, thereby making it costlier. Whereas in the separate system, only the sewage discharge is treated, and the drainage discharge is disposed of without any treatment.

(iv) In case, flooding and backing up of sewers or drains occur due to excessive rains, more foul and insanitary conditions will prevail in the case of combined sewage than in the case of storm drainage alone.

(v) Since the sewer lines are generally laid deep and at steeper slopes, as compared to the stormwater surface drains, pumping of sewage and often no

pumping of drainage is required in a separate system. Whereas, the entire discharge will have to be pumped, if the sewage and drainage discharges are mixed together; thereby making the combined system more costly.

(vi) The economy of the two systems must be worked out for each individual project, and the economic system is adopted, if physically feasible.

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