Sanitation of a Town or City: 2 Methods | Sanitary Engineering

The sanitation of a town or city is done by two methods, which are: 1. Conservancy System 2. Water-Carriage System.

Method # 1. Conservancy System:

Sometimes this system is also called dry-system. This system is in practice from very ancient times. Actually this is out of date system even though it is prevailing in small towns, village and undeveloped portions of the large cities. Various types of refuse and storm water are collected, conveyed and disposed of separately by different methods in this system, therefore, it is called conservancy system.

Garbage or dry refuse of a town is collected in dust-bins placed along the roads and streets, from where it is conveyed by trucks or covered carts once or twice in a day to the point of disposal. All the non-combustible portions of the garbage such as sand, dust, clay, ashes etc. are used for filling the low level areas to reclaim land for the further development of the town.

The combustible portion of garbage such as dry leaves, waste paper, broken furniture etc. are burnt. The decaying fruits and vegetables, grass and other such things are first dried and then disposed of by burning or in the manufacture of manure.

Human Excreta or Night Soil is collected separately in privies or conservancy latrines. The liquid and semi-liquid wastes are collected in separate drains of the same latrine, from where they are removed through human agency. After removal night soil is taken outside the town in closed animal drawn carts, trucks or tanks mounted on the tractor trailors. The night-soil is buried in trenches.

After 2-3 years the buried night soil is converted into an excellent manure which can be used for growing crops. There are other methods also for the disposal of human excreta.

In conservancy system the Sullage and Storm waters are also carried separately in closed or open drains, up to the point of disposal, where they are allowed to mix up with streams, rivers or sea without any treatment. Sometimes sullage is used for individual gardening or farming on large scale.

Merits:

The following are the merits of conservancy system:

(i) It is cheaper in initial cost because storm water can pass in open drains and conservancy latrines are much economical.

(ii) The quantity of sewage reaching at the treatment plant before disposal is low.

(iii) As the storm water goes in open drains, the sewer section will be small and will run full for the major portion of the year, due to which there will be no silting and deposits in sewer-lines,

(iv) In floods if the water level of river rises at the out-fall, it will not be costly to pump the sewage for disposal.

Demerits:

The following are the demerits of conservancy system:

(i) It is possible that storm water may go in sewers causing heavy load on treatment plants, therefore it is to be watched.

(ii) In crowded lanes it is very difficult to lay two sewers or construct road-side drains, causing great inconvenience to the traffic.

(iii) For burying human excreta more space of land is required,

(iv) Buildings cannot be designed as one compact unit, because latrines are to be provided away from the living rooms due to foul smell, which are also inconvenient,

(v) There is every possibility that liquid refuse may get an access in the subsoil and pollute the underground water,

(vi) In the presence of conservancy system, the aesthetic appearance of the city cannot be increased.

(vii) Decomposition of sewage causes insanitary conditions which are dangerous to the public health.

(viii) This system completely depends on the mercy of sweepers at every time. If the sweepers go on strike, there is every possibility of the spreading of diseases in the town due to decomposition of foul matters.

Method # 2. Water-Carriage System:

With the development and advancement of the cities, urgent need was felt to replace conservancy system with some more improved type of system in which human agency should not be used for the collection and conveyance of the sewage. After large numbers of experiments, it was found that the water is the only cheapest substance, which can be easily used for the collection and conveyance of sewage.

As in this system water is the main substance, therefore it is called Water-Carriage System. In this system the excremental matters are mixed up in large quantity of water and are taken out from the city through properly designed sewerage systems, where they are disposed off after necessary treatment in a satisfactory manner.

The sewage so formed in water carriage system consists of 99.9 per cent of water and the remaining 0.1 per cent of solid matters. All these solids remain in suspension in the sewage and do not change the specific gravity of the water; therefore all the hydraulic formulae can be directly used in the designing of sewerage systems and the treatment plants.

Merits:

The following are the merits of water carriage system:

(i) It is hygienic method, because all the excremental matters are collected and conveyed by water only and no human agency is employed for it.

(ii) There is no nuisance in the streets of the towns due to offensive matters, because all the sewage goes in closed sewers under the ground. The risk of epidemics is reduced.

(iii) As only one sewer is laid, therefore it occupies less space in crowded lane,

(iv) Due to more quantity of sewage, self-cleansing velocity can be obtained even at less gradients.

(v) Buildings can be designed compact as one unit.

(vi) The land required for the disposal work is less as compared with conservancy system in which more area is required for burying the excremental matters.

(vii) The usual water supply is sufficient and no additional water is required in water carriage system.

(viii) This system does not depend on manual labour at every time except when sewers get choked.

(ix) Sewage after proper treatment can be used for various purposes.

Demerits:

The following are the demerits of water carriage system:

(i) This system is very costly in initial cost.

(ii) The maintenance of this system is also costly.

(iii) During monsoon large volume of sewage is to be treated whereas very small volume is to be treated in the remaining period of the year.

If both the merits and demerits of the water-carriage system are considered, we will reach at the result that this system is an essential amenity, which every city must have.