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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Hydraulic analysis of gas pockets in wastewater rising mains
Hydraulic analysis of gas pockets in wastewater rising mains
Author : OSCAR POZOS-ESTRADA(1), OSCAR FUENTES(1), ALEJANDRO SANCHEZ(1), FAUSTINO DE LUNA(1) & EDUARDO RODAL(1)
ABSTRACT
Hydrogen sulfide corrosion can occur in wastewater rising mains in places where the sewage does not continuously
contact the top of the pipe. Corrosive gas pockets can accumulate at high points of rising mains when the hydraulic grade
line is below the pipe, or a gas pocket cannot be dragged downstream owing to the buoyancy of the pocket. Hydrogen
sulfide gases are generated within the anaerobic slime layer formed on the submerged pipe walls. Hydrogen sulfide gas
released from the slime layer rise into the airway portion of the sewer pipe and is oxidized by bacteria on the unsubmerged
portion of the pipe in the presence of moisture forming sulfuric acid. It is this sulfuric acid that corrodes ferrous
metals and concrete. This paper presents a methodology to locate the points where the pockets are likely to accumulate in
rising mains and subsequently compute the length of the pockets. The method can be used by the engineers to suggest
solutions during the design stage or for existing rising mains to replace or rehabilitate the line with inert pipe materials on
areas prone to corrosion attack. In addition, experimental investigations have been developed with the aim of
demonstrating that the flow under air pockets with a pressure greater than the atmospheric is similar to the flow in open
channels. From this investigation it was concluded that the gradually varied flow theory is applicable to compute the flow
profiles underneath gas pockets. A case study is analyzed by using the proposed methodology.
File Size : 1,426,904 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 19/08/2015
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