<!{|style="float: left;"|{{Language-box|english_link=Solids- table at top of page with logo, picture, Application level, Management level, and input-output tables -->free_Sewer|french_link=Réseau_d’égout_simplifié_sans_matières_solides|spanish_link=Alcantarillados_Libres_de_Solidos|hindi_link=coming soon|malayalam_link=coming soon|tamil_link=coming soon | korean_link=coming soon | chinese_link=Coming soon | indonesian_link=Coming soon | japanese_link=Coming soon}}|}{|width="100%"|style="width:50%;"|{{santablesantable_new|sys1=[[Blackwater Treatment System with SewerageEffluent Transport|67]]|
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'''A Solidssolids-Free Sewer free sewer is a network of small -diameter pipes that transports pre-treated and solids-free or pre-treated wastewater (such as [[Septic Tank]] or settling tank effluent) to . It can be installed at a shallow depth and does not require a treatment facility for further treatment minimum wastewater flow or slope 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 sewersfunction.'''
<br>Solids-free sewers are also referred to as settled, smallbore, variable-grade gravity, or septic tank effluent gravity sewers. A precondition for Solidssolids-Free Sewer networks free sewers is efficient pre-primary treatment at the household level. The An interceptor, septic or settling tank removes typically a single-chamber [[Septic Tank]] (S.9), captures settleable particles that could clog small pipes. A grease trap should The solids interceptor also be addedfunctions to attenuate peak discharges. Because there is little risk of depositions and clogging, the solids-free sewers do not have to be self-cleaning (cleansing, i.e. , no minimum flow velocity) and can therefore be laid at shallow depths, can have fewer or tractive tension is needed. They require few inspection points (manholes), can follow the topography more closely and have inflective gradients (i.e. , negative slopeslopes)and follow the topography. When the sewer roughly follows the ground contours, the flow in the sewer is allowed to vary between open channel flow and pressure (full-bore) flow. However, care should be taken with negative slopes as they may lead to surging above the ground level during peak flows. Inspection points should be provided at major connection points or when the size of the pipe changes.
Despite ===Design Considerations=== If the presence interceptors are correctly designed and operated, this type of sewer does not require self-cleansing velocities or minimum slopes. Even inflective gradientsare possible, as long as the downstream end of the sewer must be is lower than the upstream end. When choosing a pipe diameter (at least 75mm), the depth of water in the pipe during peak flow within each section must be less than the diameter of the pipe. In sections where there is pressure flow, the invert of water level in any interceptor tank outlet must be higher than the hydraulic head within the sewer just prior to the point of connection , otherwise the liquid will backflow flow back into the tank. If this condition is not metAt high points in sections with pressure flow, then either select the next larger pipe diameter for the sewer or increase the depth at which the sewer is laidpipes must be ventilated.
Solids-free sewers do not have to be installed on a uniform gradient with a straight alignment between inspection points. The alignment may curve to avoid obstacles, allowing for greater construction tolerance. A minimum diameter of 75 mm is required to facilitate cleaning. Expensive manholes are not needed because access for mechanical cleaning equipment is not necessary. Cleanouts or flushing points are sufficient and are installed at upstream ends, high points, intersections, or major changes in direction or pipe size. Compared to manholes, cleanouts can be more tightly sealed to prevent stormwater from entering.
Stormwater must be excluded as it could exceed pipe capacity and lead to blockages due to grit depositions. Ideally, there should not be any storm- and groundwater in the sewers, but, in practice, some imperfectly sealed pipe joints must be expected. Estimates of groundwater infiltration and stormwater inflow must, therefore, be made when designing the system. The use of PVC pipes can minimize the risk of leakages.
<br>{{procontable | pro=- Greywater can be managed at the same time. Does not require a minimum gradient or flow velocity <br> - Can be built and repaired with locally available materials. used where water supply is limited <br> - Construction can provide short-term employment to local labourers. <br> - Capital Lower capital costs are less than [[Conventional Gravity Sewer|Conventional Gravity Sewers]]conventional gravity sewers; low operating costs. <br> - Can be extended as a community changes and grows. <br>- Greywater can be managed concurrently| con=- Space for interceptors is required <br>- Interceptors require regular desludging to prevent clogging <br>- Requires expert design training and construction supervision. acceptance to be used correctly <br> - Requires repairs and removals of blockages more frequently than a Conventional Gravity Sewer. conventional gravity sewer <br> - Requires education expert design and acceptance to be used correctly. construction <br> - Effluent Leakages pose a risk of wastewater exfiltration and sludge (from interceptors) requires secondary treatment groundwater infiltration and/or appropriate discharge.are difficult to identify
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===Appropriateness===
This type of sewer is best suited to medium-density (peri-)urban areas and less appropriate in low-density or rural settings. It is most appropriate where there is no space for a [[Leach Field]] (D.8), or where effluents cannot otherwise be disposed of onsite (e.g., due to low infiltration capacity or high groundwater). It is also suitable where there is undulating terrain or rocky soil. A solids-free sewer can be connected to existing Septic Tanks where infiltration is no longer appropriate (e.g., due to increased housing density and/or water use).
==Adequacy==As opposed to a [[Simplified Sewer]] (C.4) a solids-free sewer can also be used where domestic water consumptionis limited. This technology is a flexible option that can be easily extended as the population grows. Because of shallowexcavations and the use of fewer materials, it can be built at considerably lower cost than a [[Conventional Gravity Sewer | Conventional Sewer]] (C.6).
Solids-Free Sewers ===Health Aspects/Acceptance=== If well constructed and maintained, sewers are appropriate for both full a safe and partially filled flowshygienic means of transporting wastewater. Although a constant supply of water is required, less water is needed compared to Users must be well trained regarding the Simple Sewer because self-cleansing velocities are not requiredhealth risks associated with removing blockages and maintaining interceptor tanks.
[[Septic Tank|===Operation & Maintenance=== Trained and responsible users are essential to avoid clogging by trash and other solids. Regular desludging of the Septic Tanks]] is critical to ensure optimal performance of the sewer. Periodic flushing of the pipes is recommended to insure against blockages. Special precautions should be taken to prevent illegal connections, since it is likely that interceptors would not be installed and Solids-Free Sewers can solids would enter the system. The sewerage authority, a private contractor or users committee should be built responsible for new areasthe management of the system, particularly, or a Solids-Free Sewer can be connected to an existing primary treatment technology where local infiltration is inappropriate. A Solidsensure that the interceptorsare regularly de-Free Sewer can be built for 20% sludged and to 50% less than [[Conventional Gravity Sewer|Conventional Gravity Sewerage]]prevent illegal connections.
This technology must be connected to an appropriate [[(Semi===Upgrading===Solids-) Centralized Treatment System|(Semi-) Centralized Treatment technology]] that can receive the wastewater. It is appropriate Free Sewers are good upgrading options 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 Fields that have become clogged and less appropriate in low-density /or rural saturated with time as well as for rapidly growing areasthat would not accommodate more Septic Tanks with Leach Fields.
==Health Aspects/Acceptance=References===* Azevedo Netto, J. and Reid, R. (1992). [https://www.ircwash.org/sites/default/files/332-92IN-9897.pdf Innovative and Low- Cost Technologies Utilized in Sewerage]. Technical Series No. 29, Environmental Health Program, Pan American Health Organization, Washington, D.C., US. (A short summary and component diagrams – Chapter 5)
This technology requires regular maintenance on the part of the users * Crites, R. and is thereforeTchobanoglous, not as passive as [[Conventional Gravity Sewer|Conventional Gravity Sewers]]G. (1998). Users must assume some level of responsibility for the technology Small and accept that some potentially unpleasant maintenance may be requiredDecentralized Wastewater Management Systems. AlsoWCB/McGraw- Hill, users should be aware thatNew York, because the system is community based, they may have to work with and/or coordinate maintenance activities with other usersUS. pp. 355-364. The system will provide a high level (Book; A short summary of service design and may offer a significant improvement to non-functioning [[Leach Field|Leach Fields]].construction considerations)
==Upgrading==* Mara, D. D. (1996a). [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/2972 Low-Cost Sewerage]. Wiley, Chichester, UK. (Assessment of different low-cost systems and case studies)
Solids* Mara, D. D. (1996b). Low-Cost Urban Sanitation. Wiley, Chichester, UK. pp. 93-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 Fields108.(Book; Comprehensive summary including design examples)
==Maintenance==* Otis, R. J. and Mara, D. D. (1985). [https://www.ircwash.org/resources/design-small-bore-sewer-systems The Design of Small Bore Sewer Systems]. UNDP Interregional Project INT/81/047, The World Bank and UNDP, Washington, D.C., US. (Comprehensive summary of design, installation and 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=Acknowledgements=== * Elizabeth Tilley et.al (2008). [http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_high.pdf Compendium of Sanitation Systems and Technologies] ([http://www.eawag.ch/organisation/abteilungen/sandec/publikationen/publications_sesp/downloads_sesp/compendium_low.pdf low res version]). Department of Water and Sanitation in Development Countries ([http{{://www.sandec.ch/ Sandec]) at the Swiss Federal Institute of Aquatic Science and Technology (Eawag). (Provides a full overview of sanitation systems.) * 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.) * Crites, R. and Tchobanoglous, G. (1998). Small and Decentralized Wastewater Management Systems. WCB and McGraw-Hill, New York, USA. pp 355–364. (A short summary of design and construction considerations.) * Mara, DD. (1996). Low-Cost Sewerage. Wiley, Chicheser, UK. (Assessment of different low-cost systems and case studies.) * Mara, DD. (1996). Low-Cost Urban Acknowledgements Sanitation. Wiley, Chichester, UK. pp 93–108. (Comprehensive summary including design examples.) * 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.)}}
