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Sewer System Essentials

This document discusses sewer appurtenances and sewage pumping stations. It defines appurtenances as devices other than sewers that are essential for sewer system operation, such as manholes, drop manholes, inlets, catch basins, oil and grease traps, and flush tanks. It provides details on the purpose and design of these appurtenances. It also discusses the components, design considerations, and wet well sizing methodology for sewage pumping stations, which are used to elevate and transport wastewater when gravity flow is no longer feasible.

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Ashhad Shafique
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156 views17 pages

Sewer System Essentials

This document discusses sewer appurtenances and sewage pumping stations. It defines appurtenances as devices other than sewers that are essential for sewer system operation, such as manholes, drop manholes, inlets, catch basins, oil and grease traps, and flush tanks. It provides details on the purpose and design of these appurtenances. It also discusses the components, design considerations, and wet well sizing methodology for sewage pumping stations, which are used to elevate and transport wastewater when gravity flow is no longer feasible.

Uploaded by

Ashhad Shafique
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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ENVIRONMENTAL

ENGINEERING II
(CE 4803)
Slide Credits:
PROF.DR ZULFIQAR ALI KHAN

LECTURE NO : 4
SEWER APPURTENENCE
SEWER APPURTENENCES
Appurtenances are those devices, other than
sewers, which are essential for the operation
of sewer systems. These include;
 Manholes, Drop manholes

 Inlets, Catch basins

 Oil and grease traps

 Flush tanks

 Inverted siphons

 Pumping station
SEWER APPURTENENCES
MANHOLES:
Purpose, spacing, locations have already been discussed. A
standard brick manhole sketch is shown in fig below.
SEWER APPURTENENCES
DROP MANHOLE:

When lateral or sub-mains join in a deeper sewer,


excavation will be saved by keeping the upper sewer
at a reasonable grade and making a vertical drop at
the manhole. This is known as “Drop Manhole”.

Fig: Drop Manhole


SEWER APPURTENENCES
INLETS:
An inlet is an opening into a storm or combined
sewer for entrance of storm sewage.
i. Curb Opening Inlet
SEWER APPURTENENCES

INLETS:

ii. Grate Inlet:


SEWER APPURTENENCES
INLETS:
iii. Catch Basins:
These are same as inlets but deeper enough
to store the settled grit which is then removed
periodically.
SEWAGE PUMPING STATION
Objectives:
To elevate and transport wastewater when;
 Continuation of gravity flow is no longer feasible.

 Basements of buildings are below the grade of the


sewer
 Any obstacle lies in the path of sewer

 Receiving stream is higher than the sewer

 Sewage is to be delivered to an above ground


treatment plant.
COMPONENTS OF SEWAGE PUMPING STATION

1. Screens

2. Dry Well For installation of pumps

3. Wet Well For receiving wastewater

4. Pumps along with valves, pipes, motor,


control panel etc.
SEWAGE PUMPING STATION
DESIGN CONSIDRATIONS:
 Pump suctions are usually larger than the discharge
(force main)
 The smallest discharge pipe: 75 mm
 The smallest suction pipe: 100 mm
 Capacity of Pumps: Max Sewage Flow
 No. of Pumps: Minimum two
 Screens should be provided to remove particles
larger than 50 mm size.
 Sump pump should be provided in dry well to pump
leakage water.
SEWAGE PUMPING STATION
Selection of Pumps for Sewage:
 Centrifugal, Vertical, Non-clog Type

 Impeller having 2 - 3 vanes

 Speed 200 – 1200 RPM

Operating Conditions:

 Pumps should be self-priming type or should


operate under positive suction head.

 Each pump should have an individual intake.


SEWAGE PUMPING STATION
Operating Conditions: (cont…)
 The pump must run for at least 2 minutes.

 Cycle time must not be less than 5 minutes.

Cycle Time:

“It is the time between successive start-ups of the


motor pump”

 The detention time in the wet well should,


preferably, be not more than 30 minutes.
SEWAGE PUMPING STATION
Design of Wet Well:
Design of wet well refers to the calculation of
operating volume of wet well. It is designed on
the basis of minimum cycle time.
Cycle Time = Time on + Time off
= Time to empty + Time to fill
Let V be the volume of wet well;
Cycle Time = V/(P – Q) + V/Q ………(1)
Where;
P = Pumping rate (constant)
Q = Sewage inflow (Variable)
SEWAGE PUMPING STATION
Design of Wet Well (Cont….)
To find minimum cycle time, differentiate eq-1
w.r.t. Q

dt/dQ = V/(P-Q)2 + V/Q2

for min. cycle time, dt/dQ = 0

0 = V/(P-Q)2 + V/Q2

Q = P/2
NOTE: Minimum cycle time will be reached when sewage folw rate is half of the
pumping rate.
SEWAGE PUMPING STATION
Design of Wet Well (Cont….)
Putting Q=P/2 in eqn-1 gives

tmin = V/(P-P/2) + V/(P/2)


tmin = 4V/P
V = (tmin x P )/4

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