CE 326
Sand Filter Design
Filter Design (Due date Oct. 18)
Dr. S.K. Ong
A small community in Northern Iowa would like to install a filtration system for their drinking water
treatment plant. The temperature of the water ranging from 10 o C to 15o C. The following information is
available:
Current population
Projected growth in population
Projected demand
Design life of filters
= 15,000 people
= 1.5% per year
= 0.4 m3/day/person
= 20 years
Sand from a river will be modified and screened to provide a filter medium with a uniformity coefficient of
1.5 and an effective size of 0.4 mm. The bed porosity is expected to be 0.4, the shape factor of the sand is
0.8, and the specific gravity about 2.65. Based on the examples in your text book (Example 3-27 and 328), design a filter or filters to treat the water. Use P10, P30, P50, P70 and P90 sizes for the head loss
calculations and the guidelines provided in the textbook and lecture notes. Note that these sizes are
approximately equal to the average size of five equal fractions of the graded sand. For backwash flow rate
– suggest selecting a rate between 880 to 1,200 m/d or selecting the P 1 size that needs to be retained.
Specify the dimensions of the filter box (length and width of the filter beds or beds and depth of the box or
boxes), the amount of sand that will be needed, the location and size of the wash water troughs above the
sand bed.
Use Manning’s equation to design a rectangular wash water trough. Manning’s equation is given by:
v
where
Q R 2 / 3 S 1/ 2

A
n
v = average velocity in the trough (m/s)
Q = flow rate (m3/s)
A = cross sectional area of the trough
R = hydraulic radius (at the furthest end of the outlet of the trough) = A/P
where A = cross sectional area = H x B
P = wetted perimeter = 2H + B
S = slope = assume 0.001
n = Manning’s coefficient = 0.01
H
B
L
Side View of Trough
Front View
Provide a short report including a dimensioned sketch of your filter system showing the plan and elevation
views and your assumptions and calculations for the design.
Fill out the summary sheet. Use the summary sheet as the first page of your report.
CE 326 Principles of Environmental Engineering
Summary Sheet for Filter Design
GROUP MEMBERS: _________________________________________
1.
Design flow rate (m3/day):
_________________________
2.
Design Filtration rate (m3/m2-day)
_________________________
3.
Temperature of water used (o C)
_________________________
4.
No. of Filters:
_________________________
5.
Filtration area per filter (m2)
_________________________
6.
Length and Width per Filter (m x m)
_________________________
7.
Depth of Sand used (m)
_________________________
8.
Diameter of finest sand to
estimate backwash rate (mm)
_________________________
9.
Backwash rate (m3/m2 day)
_________________________
10.
Depth between the bottom of the backwash
trough and top of sand (under normal
filtration conditions) (m)
_________________________
11.
Size of trough (L x W x D) (m)
_________________________
12.
Total Depth of filter (from the bottom
of the sand to the top of the filter –
include a free board of 0.2 m above
the top of the water level) (m)
_________________________
Provide Plan and Side views of filters (attach drawings – must show all the dimensions clearly)
Attach all calculations.