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'''A Solids-Free Sewer is a network of small diameter pipes that transports solids-free or pre-treated wastewater (such as [[Septic Tank]] or settling tank effluent) to a treatment facility for further treatment or to a discharge point. Solids-Free Sewers are also referred to as settled, small-bore, small-diameter, variable-grade gravity, or septic tank effluent gravity sewers.'''
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===Adequacy===
Solids-Free Sewers are appropriate for both full and partially filled flows. Although a constant supply of water is required, less water is needed compared to the Simple Sewer because self-cleansing velocities are not required.
This technology must be connected to an appropriate [[(Semi-) Centralized Treatment System|(Semi-) Centralized Treatment technology]] that can receive the wastewater. It is appropriate for densely populated areas where there is no space for a [[Soak Pit]] or [[Leach Field]]. This type of sewer is best suited to urban and less appropriate in low-density or rural areas.
===Health Aspects/Acceptance===
This technology requires regular maintenance on the part of the users and is therefore, not as passive as [[Conventional Gravity Sewer|Conventional Gravity Sewers]]. Users must assume some level of responsibility for the technology and accept that some potentially unpleasant maintenance may be required. Also, users should be aware that, because the system is community based, they may have to work with and/or coordinate maintenance activities with other users. The system will provide a high level of service and may offer a significant improvement to non-functioning [[Leach Field|Leach Fields]].
===Upgrading===
Solids-Free Sewers are good upgrading options for [[Leach Field|Leach Fields]] that have become clogged and/or saturated with time as well as for rapidly growing areas that would not accommodate more [[Septic Tank|Septic Tanks]] with Leach Fields.
===Maintenance===
The septic/interceptor tank must be regularly maintained and desludged to insure optimal performance of the Solids-Free Sewer network. If the pre-treatment is efficient, the risk of clogging in the pipes is low, but some maintenance will be required periodically. The sewers should be flushed once a year as part of the regular maintenance regardless of their performance.
===References===
* Azevedo Netto, MM. and Reid, R. (1992). Innovative and Low Cost Technologies Utilized in Sewerage. Environmental Health Program, Technical Series No. 29. Pan American Health Organization, Washington DC. (A Short summary and component diagrams-Chapter 5.)
* Otis, RJ. and Mara, DD. (1985). The Design of Small Bore Sewer Systems (UNDP Interreg. Project INT/81/047). TAG Technical Note No.14. United Nations Development Programme + World Bank, Washington. Available: www.wds.worldbank.org (Comprehensive summary of design, installation and maintenance.)
===Acknowledgements===
{{:Acknowledgements Sanitation}}
