Created for SPICE by Jennifer Stokke, Bill White and Sara Charbonnet

plumbergamMechanics

Feb 22, 2014 (3 years and 5 months ago)

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WATER, WATER, EVERYWHERE

Created for
SPICE

by Jennifer Stokke, Bill White and Sara Charbonnet


Lesson 2

Clean Up That Water!
-

Coagulation and Sedimentation of Water
Contaminants


KEY QUESTION(S):

What is coagulation?

How can coagulation be used in wat
er treatment?

What conditions cause sedimentation of particles?


SCIENCE SUBJECT:
Middle school science


GRADE LEVEL:

6
-
8


SCIENCE CONCEPTS:

Water treatment, coagulation, sedimentation


OVERALL TIME ESTIMATE:

50
-
80 minutes


LEARNING STYLES:

kinesth
etic, visual, auditory


VOCABULARY:

potable, turbidity, colloid, flocculation, sedimentation,
Environmental Protection Agency (EPA), pathogen, coagulation, flocs,
coagulant


LESSON SUMMARY:

This lesson is a guided inquiry
-
based lab in which
students will
add various amounts of coagulant (aluminum sulfate, which is
commonly referred to as alum) to turbid water in order to cause the
particulates to settle. Students will discover that an optimal concentration
of alum is needed to cause settling of particles (
i.e. particles will not settle
with too much or too little coagulant). This lesson is based on an activity
presented by Dr. Paul Chadik, Associate Professor of Environmental
Engineering at the University of Florida.


STUDENT LEARNING OBJECTIVES:


The stude
nt will be able to…


1. Observe and measure the turbidity and pH of water.


2. Describe what forces (i.e. gravity) are involved in sedimentation.


3. Describe the need for protection of the natural systems on Earth.


4. Describe how to use scientific

processes to solve problems.


5. Describe how science, technology, and society are interwoven and
dependent.


MATERIALS:


ESSENTIAL:

1.

100 mL of turbid water per group

2.

25 mL of coagulant (10mg/L aluminum sulfate) per group

3.

1 eyedropper per group

4.

150 m
L (or larger) clear glass container or beaker per group

5.

1 popsicle stick per group

6.

2 pieces of litmus paper per person



SUPPLEMENTAL:

1.

Turbidimeter or spectrophotometer

2.

pH meter


BACKGROUND INFORMATION:

Drinking water can come from surface waters, such a
s lakes and rivers, or
ground water. In order for water to be
potable
, or safe to drink, the water
must meet the criteria set by the
Environmental Protection Agency (EPA)
under the Safe Drinking Water Act. The EPA sets maximum contaminant
levels (MCLs),
which are the highest level of a contaminant that is allowed in
drinking water, and secondary standards, which are non
-
enforceable
guidelines that help utilities ensure water does not have negative cosmetic
or aesthetic effects. The EPA sets MCLs for mircr
oorganisms, disinfection
by
-
products, disinfectants, inorganic chemicals, organic chemicals, and
radionuclides. Secondary standards are used to regulate pH, and
contaminants that cause skin or tooth discoloration, taste, odor, or color.
1



Water utilities

can use a variety of processes in order to treat their water.
The following is a list of processes that are commonly used to treat surface
water
2
:

1.

Rapid mix


A coagulant (such as aluminum sulfate) and powdered activated
carbon (optional) are added to th
e water and mixed together
thoroughly.

2.

Coagulation/Flocculation


The coagulant, which was added in the rapid mix section, causes fine
particles to agglomerate and form larger particles that can be
settled out or filtered. These larger particles are calle
d flocs.
Mixing during flocculation is constant and gentle to allow particles to
come together and not shear apart.

3.

Sedimentation


Solids are removed from water by settling due to gravity.

4.

Filtration


Suspended solids that are larger than the spaces b
etween the
filter

media are retained. Filters are commonly made out of sand or
activated carbon. Dual
-
media filters have sand on the bottom and
granular activated carbon on top.



5
.
Disinfection


Chlorine is added to water to kill pathogens.


D
isease
-
causing microorganisms, called
pathogens
, can cause diarrhea,
cramps, nausea, headaches, or other symptoms.
Turbidity
, which is the
measure of the cloudiness of water, is used as a water quality indicator.
Water with a higher turbidity has a great
er chance of containing pathogens
such as viruses, parasites, and some bacteria. Turbidity is also used to
indicate the effectiveness of the filters in the water treatment plant.
1

Turbidity can be removed from water through various processes including
ra
pid mix, flocculation, sedimentation and filtration. Turbidity cannot be
removed through sedimentation alone because the fine particles suspended
in water that cause turbidity, called
colloids
, are too small to settle out of
solution. Colloidal particles

are negatively charged; since colloidal particles
experience repulsive forces from other colloids, they do not come together
to form large enough particles to settle out of water due to gravity. Thus,
by adding a positively
-
charged chemical to water, the
negative colloidal
particles will attach to the positively
-
charged chemical to form larger
particles, called
flocs
. These large flocs settle out of water due to the
force of gravity. The process of the colloidal particles coming together to
form larger pa
rticles is called
coagulation
. The positively
-
charged chemical
that is added to water to cause coagulation is called a
coagulant
. Aluminum
sulfate, often referred to as alum, is a common coagulant used in water
treatment. Alum can be found in the spice sec
tion of your local grocery
store.


Disinfection byproducts are formed when a disinfectant, such as chlorine,
interacts with organic material remaining in the water after treatment.
Disinfection by
-
products can increase cancer risk and cause nervous syste
m
effects. Activated carbon can be used to remove disinfection byproducts
from water.
1

Activated carbon is made from carbonaceous precursors, such
as wood, coal, coconut shells, etc. These carbon
-
containing materials are
heated in inert environments such
that the resultant material is very porous
and has a high surface area. A tablespoon of activated carbon has the
internal surface area of a football field. Contaminants adsorb onto the
internal surfaces of the activated carbon very well, and are thus, remo
ved
from the water.


Inorganic contaminants (such as arsenic, nitrate, and lead) and organic
contaminants (such as benzene) can occur naturally or be introduced into
water from corrosion of household plumbing, runoff, leaky septic or
underground storage
tanks or discharge from industrial sources. These
contaminants can cause a myriad of health problems including, but not
limited to, increased cancer risk, liver and kidney damage, death, and hair
and/or fingernail loss. Most organic contaminants can be r
emoved by
activated carbon. Inorganic contaminants are often harder to remove from
water.
1



Radionuclides (such as uranium) can be introduced into drinking water
sources from erosion of natural or man
-
made deposits. These contaminants
can cause increase
d cancer risk and/or kidney toxicity.
1



In addition to providing potable water, utilities also want their water to be
palatable
, which means that it tastes good. Many surface waters have bad
tastes and odors that water utilities have to remove to avoid
customer
complaints. MIB (2
-
methylisoborneol) and geosmin, which are chemicals
created by certain algae, impart earthy
-
musty tastes and odors in water
that are detectable by humans at very low levels (i.e. ng/L levels). Although
the taste and odors are n
ot harmful, removing them is a high priority for
water utilities. Activated carbon is effective at removing tastes and odors
from water. Water utilities sometimes prevent or decrease taste and odor
episodes by controlling the algae blooms (i.e. the cause
of tastes and odors)
by adding copper sulfate to the lake from which they take their water.
Copper sulfate bioaccumulates in the environment and is very toxic to fish.
3



In this lab, students will simulate the rapid mix, flocculation, and
sedimentation pr
ocesses used in water treatment. Students will add various
amounts of coagulant to water and stir rapidly for 30 seconds. This
simulates the rapid mix process. Then, they will gradually stir more and
more slowly for ten minutes. This simulates the floc
culation process. Then,
they will allow the water to sit undisturbed, which simulates sedimentation.
Students will add various amounts of alum to the water to see that there is
an optimal concentration of alum that causes good coagulation and settling
(i
.e. adding too much or too little alum results in poor coagulation and
settling). The students will also monitor the pH of the water since alum
addition causes the pH to change. It is important to monitor pH change
because the potable water drinking stand
ards indicate that the pH must be
between 6 and 9.


ADVANCE PREPARATION:

The teacher needs to prepare a turbid water solution by mixing 10 mg of
kaolinite clay into every liter of water. The pH should be adjusted so that it
is between 8 and 9. The teache
r should use tap water or distilled water from
the grocery store. It is very important that the teacher test the solution to
make sure coagulation occurs since coagulation can be impacted by various
factors such as pH and alkalinity. If coagulation does
not occur, the teacher
can try adjusting various factors including: (1) pH and/or (2) the source of
water (i.e. use distilled water rather than tap water). The teacher should
also prepare a solution of alum by adding 20g of alum per liter of water.


If a

spectrophotometer or turbidimeter is available, students should
measure turbidity using either of these instruments. If these are not
available, the teacher should prepare vials containing various concentrations
of the turbid water. The highest concentrat
ion should be the initial
concentration given to students and the lowest concentration should be clean
water. For example, vials of turbid water containing 10, 8, 6, 4, 2, and 0 mg/L
of clay in water should be made. These standards should be placed on a
wh
ite sheet of paper and labeled so that students can compare their water
sample to the standards in order to estimate the concentration of clay in
their water.


PROCEDURE AND DISCUSSION QUESTIONS WITH TIME
ESTIMATES:

Pre
-
lab (5
-
15 minutes)

1.

Give brief le
cture to introduce/review vocabulary (i.e., turbidity,
colloids), how to measure pH and turbidity, and what makes a good
experiment (i.e., only change one variable at a time, include a control).


Lab (35
-
45 minutes)

1.

Students conduct the experiment and fil
l out student worksheet
(attached).

a.


Place 100mL of turbid water in the beaker.

b.

Measure the pH of the turbid water using litmus paper.

c.

Measure the initial turbidity of the water.

d.

Add drops of alum to the turbid water. Each group should add
the same num
ber of drops as their group number. For example,
lab group 3 should add 3 drops of alum to their water. Group 1
should also do the control.

e.

Rapidly stir the solution for 30 seconds with the popsicle stick.

f.

Stir the solution for 5 minutes, slowly decreasing

the speed of
stirring every minute. (During this time, the particles are
clumping together and forming larger particles. Thus, stirring
too rapidly will break them apart).

g.

Let the water sit for the rest of the period (about 20 minutes).

h.

Measure the final

turbidity of the water sitting on top.

i.

Measure the final pH of the water.

j.

Graph the results. Note: The students will see from the graph
that the addition of alum decreases the pH and that there is an
optimum number of alum drops that should be added to w
ater
(i.e., not too few or too many). With too few drops, not enough
alum is present for good coagulation. With too many drops, the
pH decreases below the optimum point for good coagulation.
Coagulation is pH dependent since the process depends on the
char
ges (positive for alum and negative for the colloids), which
change based on pH.






Whole
-
Class Discussion (10
-
20 minutes)

1.

Lead students in a whole
-
class discussion that addresses the following
questions (Time estimate: 10
-
20 minutes.):

a.

What happened to
the turbidity of the water after adding the
alum?

b.

In each group, what was the number of drops of alum that resulted
in the cleanest water? Was the greatest number of drops added?

c.

Why did the particles get bigger after adding alum and then
stirring?

d.

Why do
the particles not agglomerate (or stick together) if you
stir the water without the alum?

e.


What types of contaminants do the coagulation and settling
processes remove?

f.


Does the water need to be processed further to remove other
contaminants?


EXTENSION A
CTIVITIES:

Environmental Protection Agency. Drinking Water for Kids


Activities and
Experiments. Last Updated Feb 14, 2005.
http://www.epa.gov/safewater/kids/exper.html




RESOURCES/REFERENCE
S:

1.

Environmental Protection Agency. EPA Ground Water and Drinking
Water> Current Drinking Water Standards. Last Updated Feb 23,
2005.
http://www.epa.gov/safewater/mcl.html#rads


2.

City of Greensbor
o, NC. Water Treatment Process.
http://www.greensboro
-
nc.gov/water/Supply/treatment.htm


3.

Copper Sulfate.
http://pmep.cce.cornell.edu/profiles/extoxnet/carbaryl
-
dicrotophos/copper
-
sulfate
-
ext.html











SUNSHINE STATE STANDARDS (Science Grades 6
-
8):

SC.A.1.

The student understands that all matter has observable,
measurable
pro
perties.

SC.C.2.

The student understands that the type of force that act on an
object and the effect of that force can be described, measured and
predicted.

SC.D.2
. The students understands the need for protection of the natural
systems on Earth.

SC.G.2.

The student understands the consequences of using limited natural
resources

SC.H.1.

The student uses scientific processes and habits of mind to solve
problems.

SC.H.3
. The students understands that science, technology and society are
interwoven and inter
dependent.




Provided by



Names__________________________

Date_______________ Period_____


COAGULATION and SEDIMENTATION

Introduction

Drinking water can come from surface waters, such as lakes and rivers, or
ground water. In order for water to be
po
table
, or safe to drink, the water
must meet the criteria set by the Environmental Protection Agency (EPA).
Treating dirty water is just one thing that environmental engineers work on
every day! Colloids are fine particles suspended in water that make wa
ter
look dirty, or
turbid
. In this lab, you will attempt to remove the turbidity
from water by adding a chemical called aluminum sulfate (alum for short) to
the water.

Purpose

The purpose of this experiment is to find the optimum amount of alum
needed t
o remove turbidity from water.

Hypothesis

If

0,1,2,3,4,5,6 and 7 drops of alum are added to turbid water, mixed, and
then allowed to settle
then

the turbidity will be the lowest in the water
where _________ drops were added
because

_______________________
_____________________.

Materials

100 mL of turbid water per group

25 mL of alum solution per lab station

1 eyedropper per group

150 mL (or larger) clear glass container per group

1 popsicle stick per group

2 pieces of litmus paper per group

Turbidimeter o
r spectrophotometer (optional)


Procedure

1.

Place 100mL of turbid water in the beaker.

2.

Measure the pH of the turbid water using litmus paper.

3.

Measure the initial turbidity of the water.

4.

Add drops of alum to the turbid water. Each group should add the
same
number of drops as their group number. For example, lab group 3
should add 3 drops of alum to their water. Group 1 should also do the
control.

5.

Rapidly stir the solution for 30 seconds with the popsicle stick.

6.

Stir the solution for 5 minutes, slowly decreas
ing the speed of
stirring every minute.

7.

Let the water sit for the rest of the period.

8.

Measure the final turbidity of the water sitting on top.

9.

Measure the final pH of the water.

10.

Graph the results.

Data

Group
Number

Initial
Turbidity of
Water

Initial pH
of Water

Number of
drops of
Alum Added

Final
Turbidity
of Water

Final pH of
Water

Control






1






2






3






4






5






6






7







Results

Title ________________________________
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0
1
2
3
4
5
6
7
8
9
10
Drops of Alum Added
pH


Title ________________________________
0
10
20
30
40
50
60
70
80
90
100
0
1
2
3
4
5
6
7
8
9
10
Drops of Alum Added
Turbidity (NTU)

Conclusion




Questions

Describe the control in this experiment.






What were the indep
endent and dependent variables?






If colloidal particles are negatively charged, what charge do you think the
alum has?






Why does the addition of alum cause larger particles to form?







Do you think that adding more and more alum causes better se
ttling of
particles? Why or why not?