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4 KSU - Filtration

Here are the steps to solve this problem: 1. Flow rate = 100,000 m3/day = 100,000,000 L/day 2. Rate of each filter = 18 m3/m2-hr 3. Area of each filter = Flow rate / Rate of each filter = 100,000,000 L/day / (18 m3/m2-hr x 24 hr/day) = 277.78 m2 4. Area of each filter unit = 5 m x 8 m = 40 m2 5. Number of filter units required = Total filter area / Area of each unit = 277.78 m2 / 40 m2 = 7 filter

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105 views15 pages

4 KSU - Filtration

Here are the steps to solve this problem: 1. Flow rate = 100,000 m3/day = 100,000,000 L/day 2. Rate of each filter = 18 m3/m2-hr 3. Area of each filter = Flow rate / Rate of each filter = 100,000,000 L/day / (18 m3/m2-hr x 24 hr/day) = 277.78 m2 4. Area of each filter unit = 5 m x 8 m = 40 m2 5. Number of filter units required = Total filter area / Area of each unit = 277.78 m2 / 40 m2 = 7 filter

Uploaded by

meita
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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5.

7 Filtration
Objective

In this lesson we will answer the following questions:


How does filtration fit into the water treatment process?
How does filtration clean water?
What types of filters are used for water treatment?
How are filters cleaned?
What media are used in filters?
The purpose of filtration is to remove suspended particles
from water by passing the water through a medium such
as sand. As the water passes through the filter, floc and
impurities get stuck in the sand and the clean water goes
through. The filtered water collects in the clearwell,
where it is disinfected and then sent to the customers.
Mechanism of Filtration

Straining
- passing the water through a filter in which the pores are
smaller than the particles to be removed.
- the picture below shows an example of straining in a filter.
As you can see, the floc cannot fit through the gaps between
the sand particles, so the floc are captured. The water is able
to flow through the sand, leaving the floc particles behind.
Adsorption
- in many cases the most important mechanism of
filtration.
- Adsorption is the gathering of gas, liquid, or
dissolved solids onto the surface of another
material, as shown below:
Absorption
- the soaking up of one substance into the body of another
substance.
- in a filter, absorption involves liquids being soaked up
into the sand grains, as shown :
Types of Filter
Filters can be categorized in a variety of
ways.
1. Gravity Filter System
- commonly used
- there are 2 general categories:
Slow Sand Filter (SSF)
Rapid Sand Filter (RSF)

2. Pressure Filter System


The characteristics of three types of filters which can be used
in water treatment:
Filter cleaning
Filters

Pressure Filters
Filter Gallery

Rapid Gravity Filter


Filter Bed Below
Example

Determine the percentage of filtered water required


for wash water based on the following criteria:

Flow, Qf = 250 L/s


Rate of filtration, of = 150 m3/m2.day
Time of washing = 10 min/24 hr
Rate of washing, oBW = 15 mm/s
Solution

Quantity of filtered water every 24 hrs operation:

 = Qt

f = 250 L/s x 24 hr x 60 s/min x 60 min/hr x m3/103


L

= 21600 m3
2. Filter area , As

As = Qf/of
= (250 L/s)/(150 m/day) = 144 m2

3. Quantity of wash water

QBW = As x oBW = 144 m2 x 15 mm/s = 129.6 m3/min


BW = 129.6 m3/min x 10 min = 1296 m3
4. The percentage of filtered water required for wash
water

 BW 1296
 x100  6%
f 21600
Example :

Design a set of rapid sand filters for treating a


flow of 100 000 m3/day. The filters are rated to
work 18 m/hour. Assuming a surface is 5 m x 8 m,
how many filter units will be required?

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