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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.
Design of Intercepting Sewers
Published in Syed R. Qasim, Wastewater Treatment Plants, 2017
Sewers are underground conduits for conveying wastewater to the treatment facilities or to the point of disposal. There are three types of sewers: sanitary, storm, and combined. Sanitary sewers are designed to carry wastewater from residential, commercial, and industrial areas and a certain amount of infiltration/inflow that may enter the system because of deteriorated conditions of the sewers and manholes and roof conditions. Storm sewers are exclusively designed to carry the surface runoff. Combined sewers are designed to carry both the sanitary and storm flows. Combined sewers are undesirable because heavy precipitation may cause flows far exceeding the designed capacity of the treatment facilities. These days, combined sewers are seldom designed and constructed in the United States. A discussion on stormwater runoff and combined sewer overflow is given in Chapter 26.
Sanitary Engineering
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
The separate system provides two separate systems of sewer—the one intended for the conveyance of foul sewage only such as fecal matter, domestic wastewaters, the washings, and draining of places such as slaughter houses, laundries, stables, and the wastewaters derived from the manufacturing processes and the other for the rainwater including the surface washing from certain streets, overflow from public baths, and foundations, etc. The sewage from the principal arrangement of sewers can be directed to the treatment works, while the spillout of the second arrangement of sewers can be released specifically to common streams and so forth with no treatment.
Temporal global sensitivity analysis of concrete sewer pipes under compounding corrosion and heavy traffic loads
Published in Structure and Infrastructure Engineering, 2023
Soroush Zamanian, Abdollah Shafieezadeh
Sewer systems are recognized as a critical infrastructure as any disruption in their services can damage the environment, significantly impact public health, and incur economic loss. In many countries worldwide, the sewer systems are in poor conditions due to aging and corrosion effects (ASCE, 2017; Saegrov, 2006). For instance, the overall condition of sewer systems in the US is below standard as they received Grade D+ (on a scale from A to F, where A is exceptional, and F refers to the failing/critical state) according to the latest infrastructure report card released by the American Society of Civil Engineering (ASCE) (ASCE, 2017). Underground sewer pipelines that collect, transport, and dispose sanitary and industrial sewage are one of the primary components of sewer systems (Zamanian, 2016). The underground sewer pipelines are exposed to continuous aging and corrosion. Such degradations in pipes have led to severe consequences such as overflow of 23,000 to 75,000 sanitary sewers per year in the US (US EPA, 2004). One of the main problems with underground sewer pipelines is the frequent occurrence of infiltration and exfiltration (Zamanian, Rahimi, & Shafieezadeh, 2020).
Vulnerability hotspot mapping (VHM) of sewer pipes based on deterioration factors
Published in Urban Water Journal, 2023
Afshin Sadeghikhah, Ehtesham Ahmed, Sohini Chakraborty, Stefan Trülzsch, Peter Krebs
Sewer pipes, based on their functionality, can be categorised into separated sanitary, separated stormwater, and combined sewer systems. Despite the continuous flow in combined and sanitary sewer systems due to their base flow patterns, separated stormwater pipes only transport flow when there is a rainfall or a local urban runoff happening. The continuous presence of the base flow with organic compounds in combined and sanitary pipes will form a biofilm which will gradually deposits on the pipe surface and forms a colmation layer. A combined sewer system is often called ‘self-sealing’ due to the colmation layer above any rough surfaces such as defects or cracks which will even reach to 50 mm in some cases and can effectively but temporarily cover the cracks and stop the leakages (Ellis et al. 2009).
Developing a new methodology for wastewater pipes cleaning prioritization using integrating Induced Ordered Weighted Averaging and fuzzy logic methods
Published in Urban Water Journal, 2023
Mojtaba Barzegar Hamzekolae, Mohammadreza Jalili Ghazizadeh, Mohammadreza Majdzadeh Tabatabai, Iman Moslehi, Ehsan Yousefi-Khoshqalb
There are two different types of sewer pipe failures: structural and hydraulic. Hydraulic failure is characterized by a continuous process involving a reduction in cross-sectional area and an increase in pipe roughness, which reduces discharge capacity (Tran, Perera, and Ng 2007). The sewer systems blockage, as an important hydraulic failure, occurs for several reasons, including (1) poor network design (ignoring the design limitations), (2) grease and oil injected into the system, (3) tree roots that penetrate the system, and (4) particles that enter the system (Butler and Davis 2011). Achieving optimal hydraulic conditions in sewer pipes begins with proactive O&M functions, such as cleaning. Therefore, prioritizing pipes cleaning will ensure success. That is why this study focuses on pipes, considering each pipe’s operating conditions as an ‘option’.