What is a septic tank?
A Septic tank is a round, rectangular or square structure made up of concrete, plastic or other materials to collect waste materials from households and treat them for disposal.
There are different systems through which the waste materials reached the septic tank and are disposed of in a systematic way. The different septic system types are given below.
Septic system types
Septic system types may be classified as follows
- Separate System
- Combined System
- Partially Combined System
1) Separate System
The septic system in which two separate sewers or pipes are used to collect and carry sanitary sewage and stormwater respectively is known as a separate system.
The sewage from the first system of sewer can be led to treatment works and then treated sewage is disposed of in water bodies. The flow from another sewer is directly discharged to natural streams without any treatment.
Advantages of Separate System
- The cost of installation is low (older sewer can be used as storm sewer)
- The load on the treatment units will be lowered.
- Economical for lifting or pumping sewage.
- Sewage in a separate system is of a more uniform character.
- No need of providing an automatic flushing tank in dry weather.
- Sewers of smaller sizes can be easily ventilated.
- Rainwater can be discharged directly without any treatment.
Disadvantages of Separate System
- Cleaning is difficult due to the smaller size.
- They are likely to chock.
- Costly if older sewers are not available for stormwater.
- Skilled planning is required to avoid wrong connections.
- Storms sewer comes in use only during the rainy season.
- The anaerobic condition may develop due to the small size which may lead to a foul smell.
2) Combined System
Only one sewer is provided to carry both the sewage as well as stormwater. The sewage and stormwater are carried to the sewage treatment plant in one sewer before final disposal.
Advantages of Combined System
- Maintenance cost is low due to only one sewer.
- The chance of choking is less due to the larger size.
- The strength of the sewer is reduced by dilution.
- The chance of foul smell is less due large amount of air.
Disadvantages of Combined System
- The cost of construction is very high due to its large size.
- Handling and transportation of sewers is difficult
- Load on the treatment plant is increased
- The system is uneconomical in pumping large quantities of sewage.
- During heavy rain, sewers may overflow and create unhygienic conditions.
- Stormwater is unnecessarily polluted.
3) Partially Combined System
Only one set of underground sewers is laid. Sewage and stormwater are collected in the same sewer.
If the stormwater exceeds a certain limit, the stormwater overflows then the overflow water is located in an open drain and conveyed to natural streams.
Advantages of Partially Combined System
- The sewers are of reasonable size.
- Cleaning is not difficult as compared to a separate system.
- The chance of choking is less due to the inclusion of stormwater.
- Combines the advantages of both systems.
Disadvantages of Partially Combined System
- The velocity of flow is very low in dry weather.
- Stormwater increases the load on the treatment plant.
- The cost of pumping is also increased.
Different types of sewer
Soil pipe:- It is the pipe carrying sewage from a latrine in a house drainage system. It is a component of a house drainage system.
Waste Pipe:- It is the pipe carrying wastewater from bathrooms sinks and kitchens. It is one of the components of the house drainage system.
Lateral Sewer:- It is a sewer receiving domestic wastewater from the house sewer. It is a component of the sewerage system of a town or city.
Sub main/ Branch Sewer:- The sewer which receives water from laterals sewers is called a branch sewer. It is one of the components of the sewerage system of a city or town.
Main Sewer:- The main sewer is the sewer that receives wastewater from the branch sewer. It is one of the components of a sewerage system of a city or town.
Outfall sewer:- The sewer conveying wastewater from the treatment plant to the point of disposal is known as an outfall sewer.
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