Sewer System Design

Topics: Sanitary sewer, Surface runoff, Water pollution Pages: 12 (2623 words) Published: August 9, 2012
Sewer system must be properly planned, designed and operated in order to protect the environment and people from serious diseases, as more than 50 diseases spread from sewage. Some of the important and relevant terms for sewer system are discussed below…. Sewage

It is Liquid Waste or Waste Water produce as a result of water use. Sewer
It is the pipe or conduit for carrying sewage. It is generally closed and flow takes place under gravity (Atmospheric Pressure). Sewerage
Sewerage is the system of collection of waste water and conveying it to a point of final disposal with or without treatment.

Following are the principal sources of waste water
It is the waste water from houses, offices, other buildings, hotels and institutions. Industrial
It is the liquid waste from the industrial places from their different industrial processes like dying, paper matting, tanneries, chemical industries, etc. Storm Water
It includes surface runoff generated from rainfall and the street wash.

Following are the types of sewerage.
Separate System
It is the system in which storm water is carried separately from domestic and industrial waste water. This system is preferred when
There is an immediate need for collection of sanitary sewage but not for storm water.
When sanitary sewage needs treatment but the storm water does not.

Combined System
It is the type of system in which sewer carries both the sanitary and storm water. Combined system is favored when
Combined sewage can be disposed off without treatment
Both sanitary and storm water need treatment
Streets are narrow and two separate sewers can not be laid1.5.3. Partially Combined System

Partially combined system:
If some portion of storm or surface run off is allowed to be carried along with sanitary sewage, the system is known as partially combined system. In urban areas of developing countries, mostly partially combined system is used. 3. TYPES OF SEWERS

Sanitary Sewers
It carries sanitary sewage i.e. waste water from municipality including Domestic and Industrial wastewaters. Storm Sewer
It carries storm sewage including Surface Runoff and Street Wash. Combined Sewer
It carries domestic, industrial and storm sewage.
House Sewer
It is the sewer conveying sewage from plumbing system of building to common/municipal sewers. Lateral sewer
This sewer carries discharge from two or more house sewers.
Sub-Main Sewer
This sewer carries discharge from two or more laterals.
Main/ Trunk Sewer
It receives discharge from two or more sub-mains.
Outfall Sewer
It receives discharge from all collecting system and conveys it to the point of final disposal.

It is flow derived from the sanitary and industrial sewage that is the raw water from these industries and houses, so it means it has direct relation with the amount of water consumed.
Generally 80 to 90 % of the water consumption is taken as sewage or waste water flow.

Variation In Sewage Flow
Like water supply, sewage flow varies from time to time. Since sewers must be able to accommodate Maximum Rate of Flow, the variation in the sewage flow must be studied. Generally Herman Formula is used to estimate the ratio of Maximum to Average FlowPeak Factor=M = (Q_max )/Q_avg =1+( 14/(4+√P)) Where, P is population in thousands .

WASA Lahore Design Considers the following relationship for sewer design Average Sewage Flow (m3 /day)Peak Factor
≤ 25004.0
2500 – 50003.4
5000 – 100003.1
10000 – 250002.7
25000 – 500002.5
50000 – 1000002.3
100000 – 2500002.15
250000 – 5000002.08
> 5000002.0

It is amount of water that enters into the sewers through poor joints, cracked pipes, walls and covers of manholes.
It is nonexistent during dry weather but increases during rainy season.
Water and Sanitation Agency (WASA) Lahore...
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