Simplified sewerage is an important sanitation option in peri-urban areas of developing countries, especially as it is often the only technically feasible solution in these high-density areas.
Design of wastewater sewer system.
Repirt on storm sewer
we deal with planning and design of data communication systems. We look first in Section I at the larger issues of how the organizational strategy, culture and policies affect planning and design...
it is my work in semester 1
Supply Chain Management
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Design of Sanitary Sewer Networks CIVL 5995 Project I
Ahmad Sana Department of Civil and Architectural Engineering Sultan Qaboos University, Oman
Separate Sanitary and stormwater sewer systems
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Sanitary sewer system
Typical manholes
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Design of Sewer Network • A sewer system is a network of pipes used to convey storm runoff and/or wastewater in an area. • The design of sewer system involves the determination of diameters, slopes, and crown or invert elevations for each pipe in the system
Constraints and assumptions •
Free surface flow exits for the design discharges; that is, the sewer system is designed for “gravity flow”; pumping stations and pressurized sewers should be avoided as much as possible
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The sewers are of commercially available circular sizes
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The design diameter is the smallest commercially available pipe having flow capacity equal to or greater than the design discharge and satisfying all the appropriate constraints
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Constraints and assumptions •
Sewers must be placed at a depth such that they will not be susceptible to frost, will be able to drain basements, and will have sufficient cushioning to prevent breakage due to ground surface loading.
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To these ends, minimum cover depths must be specified. The sewers are joined at junctions such that the crown elevation of the upstream sewer is not lower than that of the downstream sewer
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Constraints and assumptions •
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To prevent or reduce excessive deposition of solid material in the sewers, a minimum permissible flow velocity at design discharge or at barely full‐pipe gravity flow is specified To prevent scour and other undesirable effects of high‐ velocity flow, a maximum permissible flow velocity is also specified At any junction or manhole, the downstream sewer cannot be smaller than any of the upstream sewers at that junction The sewer system is a dendritic, or branching, network converging in the downstream direction without closed loops
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Sewer hydraulics h
D 1 cos 2 2
P
2 sin
AD
8
D 2
A A Q n P
2/3
S 01/ 2
sin 5 / 3 20.16nQ 0 2/3
D 8 / 3 S 01/ 2
Main Specifications Minimum velocity (self‐cleansing velocity) = 0.6 m/s Maximum velocity = 3.5 m/s Minimum pipe diameter = 150 mm. Sanitary sewers up to 375 mm diameter should be designed to run half full. Larger pipes may run three‐fourths full.
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Sulfide generation Z 0.308
EBOD P S 00.5 Q 0.33 B
EBOD BOD 1.07T 20
B Top width of flow
BOD 5 - day BOD Q Discharge
S 0 Slope of the sewer
Z values Z < 5,000 5,000< Z < 10,000 Z > 10,000
P Wetted perimeter Sulfide Condition Sulfide rarely generated Marginal condition for sulfide generation Sulfide generation common
Design Steps Step 1 ‐ Topographical map • Obtain or develop a map of the contributing area • Add location and level of existing or proposed details such as: • Contours • Physical features (e.g. wadis) • Road layout • Buildings • Sewers and other services • Outfall point (e.g. near lowest point, next to receiving water body)
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Design Steps Step 2 ‐ Preliminary horizontal layout Sketch preliminary system layout (horizontal alignment): • locate pipes so that all potential users can readily connect into the system • try to locate pipes perpendicular to contours • try to follow natural drainage patterns • locate manholes in readily‐accessible positions
Design Steps Step 4 ‐ Preliminary vertical layout Draw preliminary longitudinal profiles (vertical alignment): • Ensure pipes are deep enough so all users can connect into the system • try to locate pipes parallel to the ground surface • ensure pipes arrive above outfall level • avoid pumping if possible
Step 5 ‐ Revise layout Revise the horizontal and/or vertical alignment to minimize system cost by reducing pipe: • Lengths • Sizes • depths
