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Conventional systems for urban sanitation and wastewater management in middle- and high-income countries
Published in Thomas Bolognesi, Francisco Silva Pinto, Megan Farrelly, Routledge Handbook of Urban Water Governance, 2023
While little data are available regarding the type of sewers implemented, it may be assumed that a majority are gravity sewers. Gravity sewers are designed so that the wastewater flows via gravity downhill to a pumping station or treatment plant. Typically, the collection system is divided into branching networks that collect wastewater to the lowest local point, from which it is pumped to larger mains that cumulate at the wastewater treatment plant. Gravity sewers are designed with a minimum velocity in the pipes so that they are self-cleaning. Thus, they require a minimum amount of water and downhill gradient. In many cities, stormwater from urban runoff is also collected in the sewer network. A major advantage of the gravity sewers is that they can be designed to minimize the need for energy inputs for the transport of wastewater. However, to get the gravity flow, parts of the network may require deep excavation. Thus, construction costs for gravity sewers can be quite high. The gravity sewer system also requires large volumes of water to prevent deposition of solids and blockages. Depending on the terrain and expanse of the urban area being served by the sewer network, a number of pumping stations will be required, adding to operational costs.
Sewage Disposal Systems
Published in Herman Koren, Best Practices for Environmental Health, 2017
Where there are numerous problems of disposal of the effluent on-site, a small-diameter gravity sewer may be considered for collecting the effluent from several properties and allowing it to go to a central treatment location or pump station to be moved to a treatment facility. The pipes of the system are smaller in diameter than normal collection lines and are placed along the contours of the land always leading downward toward the collection station and pumping system. Most of the suspended solids have been removed by the septic tanks, thereby reducing clogging. Cleanouts and air release risers must be furnished and utilized. Odor control is a problem with the system. The advantages of this system are that: construction is rapid; unskilled people can operate and maintain the system; instead of manholes, cleanouts are used; there are reduced costs of excavation and materials (plastic pipes can be used); and final treatment is less because the organic load has been reduced. The disadvantages are that: these systems cannot handle commercial wastewater with lots of grit or settleable solids; the collected septage still has to go somewhere for treatment and disposal; and the system must be buried deep enough to keep from freezing.
General Information Concerning Pressure Sewer Systems
Published in David Thrasher, DESIGN and USE of PRESSURE SEWER SYSTEMS, 2020
No shoring is required during the construction of pressure sewers due to the fact that shallow trenches are used, and this creates less chance of construction accidents or fatalities. This can also result in major cost savings in cases where the alternative is an extremely deep gravity sewer since excavation costs tend to increase exponentially with greater depth. Service connections are easier due to the fact that watertight taps can be made with simple tools and that no precise vertical or horizontal alignment is required of service line connections to the pressure sewer main.
A Review of sewerage and drainage systems typologies with case study in Abidjan, Côte d'Ivoire: failures, policy and management techniques perspectives
Published in Cogent Engineering, 2023
Zié Adama Ouattara, Amos T. Kabo-Bah, Kouassi Dongo, Komlavi Akpoti
In Cote d’Ivoire, the gravity sewer system is the most used (BNETD, 2013). This method is based on using gravitational force to discharge the waste water to treatment plan. This method is preferred because it has the lowest cost and is suitable for most landscapes. Gravity sewer system delivers the waste water by utilizing the potential energy resulting from the difference in elevation (Koffi et al., 2012). The purpose of the flow from upstream to downstream is to maintain flow velocity, avoid backflow and minimize the head loss in the sewer pipe (Li et al., 2019). The pipe must be located on a slope to allow sewer discharge by velocity between 0.8 m/s to 4 m/s. If the velocity is less than required then the solid waste will block the pipe, necessitating repairs. Other than that, the minimum size of sewer diameter is 200 mm and the depth is 1.2 m from the manhole (SODECI, 2018). For rain water drainage networks, the most used material in Abidjan is concrete bricks (Ouattara et al., 2021).
A review on the durability of PVC sewer pipes: research vs. practice
Published in Structure and Infrastructure Engineering, 2020
Konstantinos F. Makris, Jeroen Langeveld, François H. L. R. Clemens
Plastics are used for a wide range of commercial and industrial piping applications. The most known are polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), acrylonitrile–butadiene–styrene (ABS), polybutylene (PB) and glass–fibre-reinforced polyester (GRP or FRP). Concerning piping systems for drinking water supply, gas distribution and sewage disposal, PVC, PE and PP are the most popular polymer materials (PlasticsEurope, 2017). Especially for gravity sewer pipes, PVC has been extensively used over the past decades and has become the dominant construction material. Cost efficiency, ease of installation, range of available diameters (40–630 mm) and its reputed chemical resistance favour its wide acceptance by decision makers in urban drainage (Davidovski, 2016).
Stationary leakage from a gravity sewer into horizontal unsaturated-saturated soil – a numerical benchmark for the verification of pipe leakage models
Published in Urban Water Journal, 2021
Pipe leakage out of and into defect subsurface gravity sewer (or stormwater) pipe networks in urban areas are related to a series of problems such as soil and groundwater contamination (Hornef 1983; Rutsch et al. 2008; Nguyen et al. 2021), decreasing groundwater levels (Wittenberg and Aksoy 2010; Peche et al. 2019) and sinkhole collapses (Hermosilla 2012). Numerical models may be used to contribute to understanding the pipe leakage process and solving above described problems.