Depending upon the types of refuse or wastes following two systems are employed for collection and conveyance of refuse: 1. Conservancy System 2. Water Carriage System.
1. Conservancy System:
In this system different types of refuse or wastes such as night soil, garbage rubbish, etc., are collected separately and then each type is carried and suitably disposed off. This system is termed as conservancy system due to the fact that in this system different types of refuse or wastes are conserved and handled separately. The system is also known as dry system.
The methods of collection of various types of refuse or wastes in this system are indicated below:
i. Night Soil:
The night soil or human excreta is collected from lavatories in pans by labour (sweepers) and carried in carts, trucks, etc., to a place away from the town. It is usually buried into the ground and is thus converted into manure.
The garbage is collected in pans or baskets. It is then conveyed by carts, trucks, etc., to some suitable place and disposed off.
The rubbish is also collected in pans or baskets and conveyed by carts, trucks, etc., to some suitable place for its final disposal. The rubbish consists of two types of materials, namely – combustible and non-combustible.
The two types of materials are separated, and the combustible material is usually burnt in the incinerator and the non-combustible material is dumped into low lying areas of the locality or disposed off.
iv. Sullage and Storm Water:
The sullage and storm water are collected and conveyed separately in closed or open drains. These are discharged into natural streams or rivers.
The conservancy system is an old system which is out of date for modern cities. It is, however, adopted for small towns, villages and isolated areas where sufficient quantity of water is not available for providing water carriage system. The main advantage of conservancy system being that it is cheap because of very little quantity of water required for its working, but from the sanitary and the public health point of view, the conservancy system is not satisfactory.
Disadvantages of Conservancy System:
Various disadvantages of conservancy system are as indicated below:
(i) Unhygienic and Insanitary Conditions:
The conservancy system is highly unhygienic and develops insanitary conditions because the excreta starts decomposing within few hours of its production. Thus even if it is assumed that cleaning will take place twice in a day, the excreta remaining in the lavatories will emit bad smell and will give rise to fly nuisance.
(ii) Nuisance during Transportation of Night Soil:
In this system night soil is usually transported in open carts through streets and other crowded localities which causes a lot of nuisance. Moreover, the passing of night soil carts through busy streets is not desirable from the sanitary point of view.
(iii) Disruption in Working of System due to Labour Problem:
The working of this system depends entirely on the mercy of the labour (sweepers). Thus if they go on strike due to any reason, the refuse or wastes will not be removed due to which whole locality will start stinking (i.e., smell very badly) and the public will be put to a lot of inconvenience. Moreover, the accumulation of refuse or wastes will adversely affect the health of the public.
(iv) Compact Design of Buildings not Possible:
In this system lavatories are to be constructed separate from the main building. It, therefore, does not permit compact design of the buildings.
(v) Insanitary Conditions due to Open Drains:
If sullage is carried in open drains, it may result in insanitary conditions.
(vi) Risk of Outbreak of Epidemic:
Due to improper or careless disposal of refuse or wastes there are chances of outbreak of epidemic.
(vii) Pollution of Water:
There are chances of the liquid wastes from the lavatories to be soaked into the ground. In such a case the underground supply of water may be polluted.
(viii) Higher Operational Cost:
The initial cost involved for this system is less and hence it appears to be cheap in the beginning. However, its maintenance and establishment costs (i.e., operational costs or recurring expenditure) are relatively high.
(ix) Larger Requirement of Land for The Disposal of Refuse:
The system requires considerable land for the disposal of the different types of refuse or wastes.
(x) Humiliation and Social Injustice:
In this system the collection of night soil by human beings (sweepers) is obnoxious and a health hazard. Moreover, it is highly humiliating and socially unjust.
(xi) Necessity of Constant and Proper Supervision:
For satisfactory working of conservancy system constant and proper supervision is necessary.
2. Water Carriage System:
In this system, water is used as a medium to convey night soil from its point of production to the point of its treatment and/or final disposal. Sufficient quantity of water is mixed with solid matter (or night soil) so that the dilution ratio of solid matter with water is so great that the mixture may flow just like water.
For this purpose specially designed latrines called water closets (W.C.) are used which are flushed with 5 to 10 litres of water after its use by every person. The night soil is thus flushed away and led to suitably designed and maintained sewers. The sullage or wastewater from bath rooms, kitchens, wash basins, etc., is also led to the sewers.
The sewers are the underground closed conduits which are laid with suitable longitudinal slope so that flow takes place under gravity and proper velocity of flow is maintained to keep the sewer clean. The sewers lead the sewage so collected to a suitable site where it is treated and then disposed of.
The garbage, in this system, is collected and conveyed in the same manner as in the case of conservancy system. The storm water may be carried separately or may be allowed to flow along with the sewage in the same sewer.
The initial cost of installation of water carriage system is very high and also large quantity of water is required for efficient working of this system. As such it may be difficult to adopt this system if the financial condition of the area is poor and also if the required quantity of water is not available.
However, the water carriage system is the modern method of collection and conveyance of sewage, which has several advantages as indicated below, and hence it should be adopted wherever possible. Moreover, if sufficient funds are not available in the beginning then the system can be adopted in stages as the town develops.
Advantages of Water Carriage System:
Various advantages of water carriage system are as indicated below:
(i) Free from Unhygienic and Insanitary Conditions:
In water carriage system night soil and other wastewater are carried in closed conduits and these are not directly exposed to the atmosphere. Thus no bad smell is produced and no other nuisance is caused. The system is therefore free from unhygienic and insanitary conditions.
(ii) No Disruption in Working of System due to Labour Problem:
The working of this system is practically automatic. However, for operation and maintenance of the system some labour is required, but the requirement of labour for this purpose is extremely small. As such no disruption in the working of the system may be caused due to labour problem. Moreover, in the houses the latrines/lavatories can be conveniently cleaned by the occupants themselves.
(iii) Compact Design of Buildings Possible:
In this system since the latrines are flushed every time after use, excreta does not remain and there are no foul smells. The latrines can therefore be attached to the living and bed rooms and these can be accommodated in any part of the house. This permits a compact design of buildings.
(iv) No Risk of Outbreak of Epidemic:
In this system since flies, etc., do not have direct access to the sewage, there are no chances of outbreak of epidemic. Moreover, the risk of outbreak of epidemic is reduced to a minimum because of the treatment given to the sewage prior to its final disposal.
(v) No Pollution of Water:
In this system the liquid wastes from the latrines/lavatories are conveyed through the sewers, and therefore there are no chances of the wastewater being soaked in the ground and thus pollute the underground supply of water.
(vi) Use of Modern Methods of Sewage Treatment:
This system permits the use of modern methods of treatment of sewage collected and conveyed through sewers. The treated sewage can be safely disposed of without any risk. Moreover, the properly treated sewage may be reused for agriculture, aquaculture, etc., which would result in rendering the system economical.
(vii) Lesser Requirement of Land for the Disposal of Refuse:
The land required for the treatment plant and the disposal of the treated sewage in this system is smaller than that required in the case of conservancy system.
(viii) Lower Operational Cost:
Though the initial cost involved for the installation of this system is very high, the operational or running cost is low because of smaller requirement of labour for its operation and maintenance.
(ix) Free from Humiliation and Social Injustice:
In this system since night soil is not collected by human beings, it is free from humiliation and social injustice.