Sewage conveyance and Sewer types

Sewage conveyance

Two systems are employed for collection, conveyance and disposal of waste:

1. Old conservancy system
2. Water carriage system

• In the old conservancy system the wastes (night soil and garbage) are collected separately in pools or pits and removed periodically atleast once in 24 hours
• This system is also known as the dry system
• Night soil refers to human excreta that is collected separately and carried on heads of sweepers to a central place from where it is transported in bullock carts to a place away from the town for final disposal.
• Normally it is buried in trenches to produce manure in one or two years.
• Garbage is collected separately and may consist of both combustible and non-combustible waste matter. It is disposed by dumping in the city outskirts
• Sullage and stormwater are collected and conveyed separately in closed or open gutters

DISADVANTAGES

• The conservancy system is highly unhygienic as the waste consists of organic matter that decomposes rapidly producing foul odour
• The conservancy system is undesirable as it involves transportation of night soil in open carts through streets and crowded localities
• The conservancy method operates entirely on the sweepers and any disruption of their work results in foul smell in the entire locality
• Compact design is not possible as the lavoratories should be located outside the house slightly away from the main residence
• Unhygienic conditions exist due to carriage of sullage through open drains laid in streets
• Improper disposal of night soil may cause the outbreak of an epidemic
• Liquid wastes from lavatories pose risk of contaminating the soil and groundwater
• The conservancy system may appear cheap but has high establishment and maintenance costs
• The system requires large amount of land for disposal of sewage

• In the new water carriage system, collection, conveyance and disposal of waste are carried out with the help of water
• Water is used as a medium to carry wastes from point of production to point of treatment or disposal

ADVANTAGES

• It is cheap in initial cost
• The quantity of sewage reaching the treatment plant before disposal is low
• There is no silting of deposits in the sewer line
• It is a hygienic method
• No nuisance on the streets due to offensive odours
• It requires less space
• Self-cleansing velocity can be obtained even at less gradients
• Buildings can be designed compact as a single unit
• Sewage after proper treatment can be used for other purposes

DISADVANTAGES

• This system is very expensive in initial cost
• Maintenance of this system is also expensive
• During monsoons, large volume of sewage is to be treated while very small volume is to be treated during the remaining part of the year

Patterns of collection system

1. Perpendicular pattern
2. Interceptor pattern
3. Radial pattern
4. Fan pattern
5. Zone pattern

Sewer types

According to the material that is used to form them, the types of sewers are classified as:

• Asbestos Cement (AC) Sewer
• Brick Sewer
• Cement Sewer
• Cast iron (CT) Sewer
• Steel Sewers and 
• Plastic Sewers
• Other types of sewers not in use nowadays are:
• Wooden sewers and
• Stoneware sewers