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Types
of Screens in Waste Water Treatment Plants
By: Haseeb
Jamal
Screens can be classified on the basis of following
criteria:
1.
Opening size:
Coarse, Medium, Fine
2.
Cleaning Method:
Manual, Mechanical, Raked, Water jet
3.
Configuration:
Bar screens, Mesh screens
4.
Screen surface:
Fixed, Moving
Types of
Screens
Types of
Screens on the basis of Opening Size:
1. Coarse
Screens
o
Fixed Bar Screen
o
Band Bar Screen
2. Fine Screen
o
Fixed Screen
o
Band Screen
o
Disk Screen
o
Moving Screen
o
Drum Screen
3. Strainers
1. Coarse Screen
It is meant to protect pumps, valves, pipe lines,
impellers and other related equipment. It is installed at the intake of waste
water before pumping, primary settling or grit chamber and is made up of a grid
of rods or bars.
|
Sizes of Screen
Openings |
||
|
Coarse Screens |
Micro Screening |
Fine Screens |
|
6 to 150mm |
< 0.5 k |
less than 6mm |
2. Fine Screen
These screens are located behind coarse screens and
their openings range from 10 - 13mm. These screens are meant to prevent entry
of small debris such as sticks, barks, leaves, fishes etc.
Fixed
Screens
Fine Fixed screens are suitable when only small amount
of materials need to be removed and are often placed just after a bar screen.
The openings of these screens range from 1 - 25mm
Band or Belt
Screens
These are made up of flexible woven wire mesh screens
normally installed for a river supply. An adjoining bar screen made up of mild
steel is also attached to the flexible woven wire mesh.
The movement of these screens is either vertical or
horizontal in direction. Jets of water are used from the inside of the screens
to remove the debris that has accumulated/clogged on the outer side of the
screen.
Disc Screens
These screens operate in circular direction. The
diameter of these screens range from 2 - 5m and move at a speed of about
0.05m/s
Drum Screens
These screens are made up of hollow drums. The waste
water is passed through the inside/hollow portion of the drum. The solid is
retained inside the drum and the screenings are removed through gravitational
action. Jets of water from outside can also be used to clean the drums through
spraying.
Types of
Screens on the basis of Cleaning Methods
1.
Mechanically
cleaned bar screens
2.
Manually cleaned
bar screens
3.
Manually cleaned
fixed bar screens
3. Strainers
In waste water treatment plants strainers are
sometimes used to replace primary settling tanks to save higher construction
costs.
It can also reduce the burden of suspended solids in
consecutive treatment processes. Its largest application is that it can be used
as a sole treatment unit (except disinfection) for waters free of color and
colloidal turbidity.
The retained materials are transferred through pumps
to the digester for physical/chemical action.
Its working principle is same as a drum screen but its
mesh size ranges from 15-64 mm to remove very fine suspended matters (Algae in
Water Treatment Plant).
Jets of water are used for cleaning through spraying.
The diameter of strainers range from 0.8 m to 3 m,
having rotational speed of 0.075 - 0.75 m/s.
There are
two types of screening processes
1.
Manually Operated
2.
Automatically
Course screens (Bar Racks)
Fine screens
Micro screens
Haseeb
Jamal
I am a Civil Engineer, graduated from
University of Engineering and Technology, Peshawar, Pakistan in 2010. I also
have a PG-Diploma in Disaster Management and MS in Urban Infrastructure
Engineering (In Progress). My expertise include civil related softwares like
AutoCAD, SAP2000, MS Project, Primavera, MS Office and GIS. My technical skills
include project management, monitoring and evaluation, structural assessment,
disaster risk management, Quantity survey, land survey, material testing, site
management and technical writing. I am trained in writing project progress
reports as well as proposals and concept papers. I have also received advanced
training on surveying, proposal writing, Monitoring and Evaluation of projects
as well as organizations.
I have worked as Project Engineer at
National Research and Development Foundation, Peshawar and CENCON Associates. I
also worked with Spectra Engineering Solutions as Senior Civil Engineer in
monitoring of World Bank and UNDP funded projects all over Khyber Pakhtunkhwa
and FATA. Currently, I am working as Deputy Manager Development at NayaTel,
Peshawar.
https://www.aboutcivil.org/screen-types
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