In every town, waste materials in solid and liquid shapes are required to be disposed off in such a way that it may effect the health of its inhabitants. The work of collection and disposal is administrated by the Administrative Authorities of the town. Generally the disposal of waste products of a town comprises of two systems i.e., collection works and disposal works.
The following two methods are generally employed for the collection of waste in a town or a city:
1. Conservancy System or Dry System
From the very ancient periods this system is being used. The waste of different types are collected separately and disposed off in a separate manner. This method now a days is out of date. It is only used in small towns and village and in the undeveloped portion of the big cities.
All the garbage or dry refuse is collected in the dust bins places at that sides of the road. From the dust bins it is collected in trucks or carts once or twice in a day is taken away for its disposal.
The non combustible materials are dumped into the pits are low lying areas and combustible materials like papers leaves etc., are the first burnt and then dumped. The peelings of vegetables and fruits and other such materials are first dried and then burnt and dumped.
In this system night soil or human excreta is collected separately through human agency and is taken outside the town in closed carts, trucks tractor trailers and is buried in trenches. This buried night soil is converted into manure in a period of about 2 years which can be used for the crops.
The sullage and storm water is carried by drains constructed outside the houses which may be open or closed. This sullage and storm water etc., is carried up to point of disposal where it is allowed to mix up with the stream, river or sea. The sullage may also be used for farming and gardening.
Merits and Demerits of conservancy System are as follows:
- It is a cheaper system. It is carried with low initial cost because latrines and open drains may be constructed economically.
- In this system the quantity of sewage to be carried at the treatment plant for disposal is low.
- The storm water is carried in open drains and the sewer section in this case shall be small and thus they will run full for the major portion of the year and thus sewer lines will be free from silting and other deposits.
- In this case the water level in rivers rises at the out falls due to floods, pumping of sewage for disposal may be done at a nominal cost.
- For burying night soil more space is required.
- There is every possibility that storm water may go in sewers which may cause heavy loads on the treatment plants.
- There is also every possibility of finding access in the sub soil of liquid refuse which may pollute underground water.
- As the latrines in the house are to be provided away from the inhabited rooms in a building, it creates inconvenience to use. If provided near the rooms, it emits foul smell.
- The excreta is not carried by the carts or trucks directly from the latrines, but it is first collected by human agency and placed at roadside for its further collection by carts etc. Which causes insanitary conditions dangerous to public health.
- In the presence of conservancy system, the aesthetic appearance of the city cannot be increased.
- The conservancy system completely depends upon the mercy of sweepers. So if they go on strike due to some reasons, there is every possibility of the spreading of diseases in the city due to decomposition of foul matters.
2. Water Carriage System
Due to development of engineering and technology it has become possible to collect the sullage and night soil etc., by the carriage system without taking the help of human agency. By experiments it was found that the water is the only cheapest material which can be used for collection of sullage and its conveyance. As the water is main substance in this system, hence it is called water carriage system. Human excreta from the water closets is mixed with water and became a semi-solid which is carried by properly designed under ground sewerage system to the treatment plants for its final disposal. In this system 99% of the sewerage is in liquid form and can easily be carried by properly designed sewer lines.
Merits and Demerits of the water carriage system are as follows:
- No human agency is employed in this method and the excremental matters are collected and carried by water in underground sewer system, hence this method is not unhygienic.
- Due to carriage of sewage in closed under ground sewers, the nuisance in towns is eliminated and hence risk of epidemics is reduced.
- In this system only one sewer is laid which require less space as compared to conservancy system in which two separate sewers are required.
- Compact design of building is possible in this case as toilet and WCs are attached to the bed room which do not emit any foul smell due to water seals provided for the closets and traps etc.
- As only one sewer is laid in this system, it carries large quantity of sewage due to which self cleaning velocity can be obtained even at smaller gradients.
- This system is not dependent fully on human agency except when sewers get blocked.
- No additional water supply is required because the usual supply of water is sufficient to cope with the needs of this system.
- Less land is required for disposal works in this system as compared to conservancy system in which more area is required to bury the excremental matter.
- The sewage after proper treatment can be used for various purposes like irrigation etc.
- Initial cost in this system is much more than conservancy system.
- Its maintenance cost is also high.
- During the rainy season large quantity of sewage is to be treated, but during the remaining period of year only small volume of sewage is carried for treatment.