B Water Purification T

trextemperMechanics

Feb 22, 2014 (3 years and 7 months ago)

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Instructor Information





1

Water Purification

Objectives

Students will analyze the effectiveness of a set of treatments for improving water quality.

Procedural Overview

Students will gain experience conducting the following procedures:



Use the turbidity sensor, the pH sensor and the

conductivity sensor to investigate treatments
that will improve water quality.



Learn about basic processes used to treat polluted water.



Compare effectiveness of the various treatment processes.

Time
requirement



Preparation time




5 minutes



Pre
-
lab discu
ssion and activity

10
-
15 minutes



Lab activity





30
-
40 minutes

Materials and Equipment

For each student or group:



Electronic data collection and display device



1 Funnel



1 Turbidity sensor



1 pipet with bulb or Beral pipette



1 pH sensor



1 Conductivity sen
sor



Lens tissue



2, 250 mL beakers



250 mL Erlenmeyer flask




1 Wash bottle and waste container



1 stirring rod



5 mL egg whites



1 coffee filter



Polluted water
1


1
To formulate
polluted water
using

soil and tap water

refer to the Pre
-
lab Preparation section.




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2

Correlation to the
National Science Content Standards,
G
rades 9

12

1.

Content Standard A: Science as Inquiry

a.

Abilities necessary to do scientific inquiry

b.

Understanding about scientific inquiry


2.

Content Standard C: Life Science

a.

The Interdependen
ce of Organisms

i.

The atoms and molecules on the earth cycle among the living and nonliving
components of the biosphere.


3.

Content Standard D: Earth and Space Science

a.

Geochemical Cycles

i.

Each element on earth moves among reservoirs in the solid ear
th, oceans,
atmosphere, and organisms as part of geochemical cycles.


4.

Content Standard F: Science in Personal and Social Perspectives



a.

Environmental Quality

Note:

See the Introduction
section
,
About Correlations to
National Science
Standards
, for ad
ditional correlations
to the National Science Teaching and Content Standards as well as to the AAAS Science Literacy Benchmarks.

C
orrelation
to [(subject) Course Outline or Textbook]

(Style: Body Text)
Note to authors:

This is an optional section. If eithe
r correlation applies to
your lab, choose the appropriate heading, otherwise, delete this section. If the material is
correlated to a textbook, the heading should be "Correlation to Textbook." Then indicate the title,
edition, and author in the first parag
raph.

Concepts Students Should Already Know

Students should be familiar with the following concepts:



Turbidity



Conductivity



pH

Related Labs in this Manual

Labs conceptually related to this one include:




(Style: Bulleted Text)
Note to authors:

Include th
e names of the related labs.



Mirum est ut animus



Mirum est ut animus

Instructor Information




3

Technical Notes

The following technical procedures are used in this activity

and are

detailed in the Appendix. See
the section that pertains to your particular
data acquisition device/int
erface
.

You may want to
make copies of these available for the students.



(Style: Bulleted Text)
Connecting sensors to the
data
acquisition device

(
see
Tech Tip
___
)



Recording data

(see Tech Tip ___)



Identifying data points on a graph

(see Tech Tip ___)



Sav
ing data files

(see Tech Tip ___)

Background

Water purification involves several types of processes, with a goal of obtaining water that is safe
for a particular use, such as human consumption. It is necessary to remove mineral particles,
organic matter,
toxic chemicals and disease
-
causing microorganisms.

The basic methods for treating municipal waste water fall into three categories: primary
treatment, flocculation and sedimentation and secondary treatment. In the primary treatment
the water is passed th
rough coarse screens to remove sticks, leaves and other large objects. Sand
and grit settle out as well. During coagulation, a chemical is added that attaches to small
particles such as bacteria or other impurities. The water is then allowed to set and
the globs or
floc sink to the bottom. This is called flocculation. Next the water is pumped slowly across a
large basin where the remaining floc and solid material accumulates at the bottom in a process
called sedimentation. The water is then filtered b
y passing the water through layers or sand,
coal and other granular material to remove microorganisms. The water may then be treated
with disinfectants and the pH adjusted to neutral to prevent corrosion of water pipes or from
harming organisms in the bod
y of water that receives the treated water.

In this experiment, three sensors will be used to monitor the process of water purification: a
turbidity sensor, a pH sensor and a conductivity sensor. The turbidity sensor measures the
concentration of solids s
uspended in the water. The pH sensor measures the acidity of the water
while the conductivity sensor measures the level of dissolved salts in the water.

Pre
-
lab

Discussion and Activity


Prior to beginning the lab, overview the process of water purificatio
n and outline the procedure
students will be using in the lab. Also, discuss the three types of sensors.

1.

Which water treatment process do you think (sedimentation, sedimentation and
filtration, or coagulation, flocculation sedimentation and filtration)

will result in the
purest water?

Pre
-
lab Preparation

1.

To prepare the "Polluted Water", mix 1 cup of soil with 2 gallons of water. The turbidity
should be about 400 NTU. Adjust the amount of water or soil to achieve this turbidity level.



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4

2.

You may cho
ose to separate the egg whites or allow the students to do so. Using store
-
bought egg whites may alter the conductivity results due to the presence of added sodium.

Lab Safety



Emphasize the need to keep water away from any non
-
waterproof electronics.



Keep

water away from electrical outlets.



If students handle raw eggs they should wash their hands thoroughly.

Instructor Information




5

Sequencing Challenge

The steps below are part of the Procedure for this lab activity. They are not in the right order. Determine
the proper order an
d write numbers in the circles that put the steps in the correct sequence.

Procedure with Guided Inquiry

After you complete a step

(or answer a question)
, place a check mark in the box (

⤠湥x琠瑯⁴h
a琠
step
.

Set Up Equipment

1.



Connect the turbidity sen
sor to the data collection and display device and then calibrate
the sensor.

2.



Connect the pH sensor to the data collection and display device and then calibrate the
sensor.

3
.



Connect the conductivity sensor to the data collection and display device.

Note: Your instructor will assign you to one of the following three groups. Follow the instructions
for your group.

Collect Data

-

Sedimentation Only

4
.



Stir the polluted water thoroughly.

5
.



Pour 200 mL of the polluted water into a 250 mL beaker. In
sert the pH and conductivity
probes into the beaker.

Determine the pH
of the sample of
polluted water.

2

Determine the
turbidity of a
sample of
polluted water.

1

Depending on
your group's
assignment purify
the water and
determine the
change in
turbidity, pH and
conductivity of
the sample of
water.

5

Determine the
conductivity of

the sample of
polluted water.

3

Allow the sample
of polluted water
to settle for 20
minutes.

4



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6

6
.



Use the pipet to collect a sample of the polluted water from the beaker. Fill one of the
turbidity cuvettes with the water sample.

7
.



Wipe the sides of the cuvette clean with a piece of lens tiss
ue and insert the cuvette into
the turbidity sensor.

8
.



Select "Start" to begin collecting the data. Select "Keep" to record the turbidity, pH and
conductivity for the sample. When prompted, type in "before" to label this measurement
as the initial sam
ple before purification treatments are used. Record these values in
Table 1.

9
.



Remove the pH and conductivity sensors and carefully rinse each with distilled water.

10
.



Remove the cuvette from the turbidity sensor and rinse the cuvette thoroughly wit
h
distilled water.

11
.



Allow the beaker to sit undisturbed for 20 minutes.

12
.



Predict how the turbidity, pH and conductivity of the sample may change after settling.

Student predictions may vary. Students may accurately predict that the turbidity may

decrease slightly, but the
pH and conductivity will remain the same.

13
.



Using the pipet, carefully collect another sample of water and fill one of the turbidity
cuvettes with the sample. Insert the pH and the conductivity sensor into the beaker. Be
c
areful not to disturb the sample.

14
.



Select "Start" to begin collecting the data. Select "Keep" to record the turbidity, pH and
conductivity for the sample. When prompted, type in "after" to label this measurement
as the initial sample before purifica
tion treatments are used. Record these values in
Table 1.

15
.



How did the turbidity, pH and conductivity levels change after sedimentation?

The turbidity levels may have decreased slightly, but the pH and conductivity levels should have remained
constan
t.

Collect Data

-

Sedimentation and Filtration

16
.



Do steps 1
-
11.

17
.



Place a coffee filter into a funnel, and put the funnel in the Erlenmeyer flask.

18
.



Without disturbing the sediment at the bottom of the beaker, carefully pour 100 mL of
the settl
ed water from the beaker into the coffee filter.

19
.



Complete steps 13
-
14.

Instructor Information




7

20
.



How did the turbidity, pH and conductivity levels change after sedimentation and
filtration?

The turbidity levels may have decreased slightly, but the pH and conductivity le
vels should have remained
constant.

Collect Data

-

Coagulation, Sedimentation, Flocculation and
Filtration

21
.



Do steps 1
-
10.

22
.



Measure approximately 1 teaspoon (5 mL) of egg white and put it in the beaker with the
water. Use a stirring rod to vigor
ously mix the egg white into the water.

23
.



What is the purpose of adding the egg white?

The egg white is a coagulating agent.

24
.



Allow the beaker to sit undisturbed for 20 minutes.

25
.



Predict how the turbidity, pH and conductivity will change afte
r mixing the sample with
egg white, allowing the sample to settle and then filtering.

The addition of the coagulating agent, the egg white, results in water that is less turbid but the water will also
have a higher conductivity and pH.

26
.



Complete steps

13
-
14.

Sample Data

Table 1. Turbidity, pH and conductivity for
the
polluted water

sample

before and after purification.

Treatment

Turbidity

Before After

pH

Before After

Conductivity

Before After

Sedimentation

309.6

292.4

7.0

6.5

610

439

Sedimentation
and filtration

309.6

206.6

7.0

6.7

610

146

Coagulation,
flocculation,
sedimentation
and filtration

309.6

62.1

7.0

8.1

610

1190





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Data Analysis

Table 1. Turbidity, pH and conductivity for
the
polluted water

sample

before and after purification.

Treatment

Turbidity

Before

After

pH

Before

After

Conductivity

Before After

Sedimentation







Sedimentation
and
filtration







Coagulation,
flocculation,
sedimentation
and filtration









Analysis Questions

1.

Which treatment resulted in the lowest turbidity?

Coagulation, flocculation, sedimentation and filtration resulted in the lowest turbidity.

2.

Which treatment resulted in the lowest conductivity?

Sedimentation and filtration resulted in the lowest conductivity.

3.

Which treatment resulted in the most neutral pH?

Sedimentation and filtration resulted in the most neutral pH.

4
.

Which treatment r
esults in the best water quality? Explain your answer.

Sedimentation and filtration resulted in the best water quality because it had the lowest conductivity and most
neutral pH. While coagulation, flocculation, sedimentation and filtration had lower tur
bidity measurements the
conductivity and pH readings are too high for the water to be potable.

5
.


Why do you think that the water treated with the egg white had the highest
conductivity?


The high salt content in the egg raises the conductivity level of t
he water.

Synthesis Questions

Answer the following ques
tions for each of the treatment methods used in the lab.

Instructor Information




9

1.

Does the conductivity exceed the limits for potable water?

Only the treatment using coagulation, flocculation, sedimentation and filtration h
ad conductivity levels that
exceeded the limits for potable water.

2.

Are the dissolved solids safe to consume?

Given that none of the techniques in this lab involved disinfection, it is not safe to assume that the dissolved
solids are safe for consumption
.

3.

Is the pH of the water acceptable?

The pH of the water is acceptable for either treatment involving sedimentation or sedimentation and filtration.

4.

What other methods are available to reduce turbidity?

Other methods of filtration such as reverse osm
osis or the use of carbon filters.

5.

Is the turbidity sufficiently reduced by this process?

Turbidity was sufficiently reduced only in the treatment using coagulation, flocculation, sedimentation and
filtration.

6.

Is the treatment economically feasible?

All of the treatments are economically feasible because they are simple and inexpensive.

Multiple Choice Questions

1.

A pH of 7 is considered

A.

Acidic


B.

Basic

C.

Neutral

2
.

Drinkable water has a conductivity of less than

A.


1 µS/cm

B.


500 µS/cm

C.

105
5 µS/cm

1.

Potable water should have a turbidity reading of less than

A.


0

B
.

1

C.

5

D.

10



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10


Key Term Challenge

Instructions:
Fill in the blanks from the list of randomly ordered words in the Key Term Challenge
Answers section.

1.
Purifying contaminated w
ater into
potable

water or into water that is safe to release back
into the environment involves a variety of treatments. First, grit and other large substances are
removed through screening and grinding. A
coagulating agent

is added to the water which
f
orms sticky globs that attach to small particles. The water is then kept in a settling tank where
the floc settles to the bottom. This is a much longer phase of purification called
flocculation
.
The water then undergoes
sedimentation

where the remaining

solid materials settle to the
bottom. Finally the water is filtered.

2.

Three measurements are used to monitor the process of water purification: turbidity,
conductivity and pH.
Turbidity

is the measure of the concentration of solids suspended in the
wa
ter. The units of measurement are
NTU
. When the water is turbid it is harder to sanitize.
Conductivity

refers to the level of dissolved salts in the water. When water has too many
dissolved solids, it is "hard", tastes bitter and leaves deposits on clo
thes and water pipes.
pH

is a
measure of the acidity of the water. Water must be adjusted to certain pH levels for treatments,
such as coagulation, to work properly. After treatment, the pH must be adjusted to neutral.

Key Term Challenge Word Bank

P
arag
raph 1

P
aragraph 2


activated sludge

clarification

coagulating agent

filtration

flocculation

potable

sedimentation


conductivity

NTU

pH

turbidity

[H+]

µ
S/cm






Instructor Information




11

Extended Inquiry Suggestions

Investigate other types of filters and coagulating agents on th
e effectiveness of water treatment.

Conduct an Internet search on water treatment and water quality standards. Write a report on
some aspect of interest.