Simplified Sewer

A simplified sewer describes a sewerage network that is constructed using smaller diameter pipes laid at a shallower depth and at a flatter gradient than conventional sewers. The simplified sewer allows for a more flexible design at lower costs.

Conceptually, simplified sewerage is the same as Conventional Gravity Sewerage, but without unnecessarily conservative design standards and with design features that are better adapted to the local situation. The pipes are usually laid within the property boundaries, through either the back or front yards, rather than beneath the central road, allowing for fewer and shorter pipes. Because simplified sewers are typically installed within the condominium, they are often referred to as condominial sewers. The pipes can also be routed in access ways, which are too narrow for heavy traffic, or underneath pavements (sidewalks). Since simplified sewers are installed where they are not subjected to heavy traffic loads, they can be laid at a shallow depth and little excavation is required.

Design Considerations

In contrast to conventional sewers that are designed to ensure a minimum self-cleansing velocity, the design of simplified sewers is based on a minimum tractive tension of 1 N/m2 (1 Pa) at peak flow. The minimum peak flow should be 1.5 L/s and a minimum sewer diameter of 100 mm is required. A gradient of 0.5% is usually sufficient. For example, a 100 mm sewer laid at a gradient of 1 m in 200 m will serve around 2,800 users with a wastewater flow of 60 L/person/day. PVC pipes are recommended to use. The depth at which they should be laid depends mainly on the amount of traffic. Below sidewalks, covers of 40 to 65 cm are typical. The simplified design can also be applied to sewer mains; they can also be laid at a shallow depth, provided that they are placed away from traffic.

Expensive manholes are normally not needed. At each junction or change in direction, simple inspection chambers (or cleanouts) are sufficient. Inspection boxes are also used at each house connection. Where kitchen greywater contains an appreciable amount of oil and grease, the installation of grease traps (see Pre-Treatment Technologies) is recommended to prevent clogging. Greywater should be discharged into the sewer to ensure adequate hydraulic loading, but stormwater connections should be discouraged. However, in practice it is difficult to exclude all stormwater flows, especially where there is no alternative for storm drainage. The design of the sewers (and treatment plant) should, therefore, take into account the extra flow that may result from stormwater inflow.

Appropriateness

Simplified sewers can be installed in almost all types of settlements and are especially appropriate for dense urban areas where space for onsite technologies is limited . They should be considered as an option where there is a sufficient population density (about 150 people per hectare) and a reliable water supply (at least 60 L/person/day).
Where the ground is rocky or the groundwater table high, excavation may be difficult. Under these circumstances, the cost of installing sewers is significantly higher than in favourable conditions. Regardless, simplified sewerage is between 20 and 50% less expensive than conventional sewerage.

Health Aspects/Acceptance

If well constructed and maintained, sewers are a safe and hygienic means of transporting wastewater. Users must be well trained regarding the health risks associated with removing blockages and maintaining inspection chambers.

Operation & Maintenance

Trained and responsible users are essential to ensure that the flow is undisturbed and to avoid clogging by trash and other solids. Occasional flushing of the pipes is recommended to insure against blockages. Blockages can usually be removed by opening the cleanouts and forcing a rigid wire through the pipe. Inspection chambers must be periodically emptied to prevent grit overflowing into the system. The operation of the system depends on clearly defined responsibilities between the sewerage authority and the community. Ideally, households will be responsible for the maintenance of pre-treatment units and the condominial part of the sewer. However, in practice this may not be feasible because users may not detect problems before they become severe and costly to repair. Alternatively, a private contractor or users committee can be hired to do the maintenance.

References

Further Readings

  • Cover image of a reference book or miscellany.

    TILLEY, E.; ULRICH, L.; LUETHI, C.; REYMOND, P.; SCHERTENLEIB, R.; ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies (Arabic). 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag). PDF

    This is the Arabic version of the Compendium of Sanitation Systems and Technologies. The Compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

  • Cover image of a reference book or miscellany.

    BRIKKE, F.; BREDERO, M. (2003): Linking Technology Choice with Operation and Maintenance in the context of community water supply and sanitation. A reference Document for Planners and Project Staff. Geneva: World Health Organization and IRC Water and Sanitation Centre. URL [Accessed: 30.03.2010]. PDF

    This document is addressed to planners and staff of water supply and sanitation projects on household and community level. The reader is guided through the main steps of informed choices regarding the main proven technologies for water supply, purification and water treatment at household and community level. Each technology is described in a small factsheet, regarding its functioning, actors and their roles, the main operation and maintenance (O&M) requirements and problems, which can occur.

  • Cover image of a reference book or miscellany.

    EAWAG/SANDEC (Editor) (2008): Sanitation Systems and Technologies. Lecture Notes . Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). PDF

    Lecture notes on technical and non-technical aspects of sanitation systems in developing countries.

  • Cover image of a reference book or miscellany.

    MARA, D.; SLEIGH, A. (2001): PC Based Simplified Sewer Design. Leeds: University of Leeds. URL [Accessed: 13.01.2011]. PDF

    The purpose of this document is to disseminate the simplified sewer technology more widely in the developing world, so that it can be used in peri-urban sanitation programmes and projects to improve health of poor communities. The document contains chapters on theory, planning and also practical advice.

  • Cover image of a reference book or miscellany.

    MARA, D. (1996): Low-cost Sewerage. Leeds: University of Leeds. URL [Accessed: 10.01.2011]. PDF

    This article reviews low-cost sewerage options, their potential and their limitations. It also provides guidance on how to choose the most appropriate option, and gives examples of their successful application.

  • Cover image of a reference book or miscellany.

    OTIS, R.; MARA, D. (1985): The Design of Small Bore Sewer Systems. Washington, DC: The International Bank for Reconstruction and Development/The World Bank. PDF

    This technical document contains information about small bore sewer systems.

  • Cover image of a reference book or miscellany.

    WAaF (Editor) (2002): Sanitation Technology Options. Pretoria: Department of Water Affairs and Forestry (WAaF). PDF

    In this document, you will find more information on the various technical options that meet the requirements for basic sanitation. These need to be considered within all the sustainability requirements, e.g. affordability, operation and maintenance. The options are divided into two categories: Dry non-water reliant on-site systems and wet systems (that do require water for operation).

  • Cover image of a reference book or miscellany.

    MONVOIS, J.; GABERT, J.; FRENOUX, C.; GUILLAUME, M. (2010): How to Select Appropriate Technical Solutions for Sanitation. Cotonou and Paris: Partenariat pour le Développement Municipal (PDM) and Programme Solidarité Eau (pS-Eau). URL [Accessed: 19.10.2011]. PDF

    The purpose of this guide is to assist local contracting authorities and their partners in identifying those sanitation technologies best suited to the different contexts that exist within their town. The first part of the guide contains a planning process and a set of criteria to be completed; these assist you in characterizing each area of intervention so that you are then in a position to identify the most appropriate technical solutions. The second part of the guide consists of technical factsheets which give a practical overview of the technical and economic characteristics, the operating principle and the pros and cons of the 29 sanitation technology options most commonly used in sub-Saharan Africa.

Case Studies

  • Cover image of a reference book or miscellany.

    MARA, D. (1996): Low-cost Sewerage. Leeds: University of Leeds. URL [Accessed: 10.01.2011]. PDF

    This article reviews low-cost sewerage options, their potential and their limitations. It also provides guidance on how to choose the most appropriate option, and gives examples of their successful application.

  • Cover image of a reference book or miscellany.

    MELO, J.C. (2005): The Experience of Condominial Water and Sewerage Systems in Brazil. Case Studies from Brasilia, Salvador and Parauapebas. World Bank, Bank-Netherlands Water Partnership (BNWP), Water and Sanitation Program (WSP). URL [Accessed: 13.01.2011]. PDF

    This study presents the experience of applying the condominial approach to expand water and sewerage networks in three contrasting Brazilian cities. It is based on the findings of a Study Tour to Brazil organised in December 2003 for utility managers and public officials from the Peruvian water sector, who were in the process of applying large-scale condominial systems in Lima for the first time. The goal of the visit was to permit the Peruvian delegation to see mature and functioning condominial systems on the ground, and to interact with local policymakers, utility managers, residents and specialists, to obtain a better idea of the challenges and potential advantages and disadvantages of implementing this system.

Awareness Material

  • Cover image of a reference book or miscellany.

    EAWAG/SANDEC (Editor) (2008): Sanitation Systems and Technologies. Presentation. Duebendorf: Swiss Federal Institute of Aquatic Science (Eawag), Department of Water and Sanitation in Developing Countries (Sandec). PDF

    PDF presentation on the technical and non-technical aspects of sanitation systems in developing countries.

  • Cover image of a reference book or miscellany.

    PEARCE-OROZ, G. (Editor) (2011): Rural Water Supply and Sanitation Challenges in Latin America for the Next Decade. Lima: Water and Sanitation Program (WSP). URL [Accessed: 14.05.2012]. PDF

    Based on market research, this new WSP technical paper analyzes the main features of the fecal sludge collection businesses in each city, including the marketing mix, potential demand, supply capacity, and legal frameworks. In addition, the paper spotlights major challenges and opportunities in fecal sludge management, describing the current and potential market for fecal sludge removal, collection, and disposal in peri-urban areas—which typically struggle with high population density, limited land planning, high citizen insecurity, and low coverage of basic services.

Important Weblinks

  • http://www.efm.leeds.ac.uk/ [Accessed: 13.01.2011]

    This website contains a short description of simplified sewerage and several links publications.