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Wetland Curriculum Lesson #

Draft 2/8/04

Man’s Filters: Cleaning Up Wastewater


P
URPOSE
: This laboratory or classroom activity introduces students to
wastewater treatment and teaches the steps involved in basic
wastewater treatment.


S
UMMARY
: Students will learn the components of wastewater,
how
wastewater is treated at a treatment plants, and the basic steps in the
treatment process. They will then apply some of the steps to attempt to
purify a contaminated water sample.


B
ACKGROUND
: All the water that goes down the drain, whether in homes
or businesses, is considered wastewater. This includes water from
sinks, baths and showers, dish washing, washing machines, and toilets
and well as water used in manufacturing and industry. Some businesses
may collect and treat their own wastewater. Oth
ers will discharge the
wastewater into the municipal sewer system.


Wastewater from domestic and industrial uses contains a variety of
substances, including human wastes, kitchen debris, toxic chemicals,
and inorganic materials such as plastics. This wa
ter can be high in
nutrients, pathogens, and toxic chemicals, and poses a risk to both
drinking water and aquatic habitats.


For this reason, wastewater must be treated before it can be discharged
to rivers and lakes. In nature, water filtration occurs wh
en rainfall and
snowmelt seep into the ground, where the soil materials act as filters,
and microorganisms in the soil help degrade pollutants. Man’s
wastewater processing systems incorporate some of the same elements.


There are two main methods of waste
water treatment in use today. On
-
site septic systems, in which wastes enter a tank where settling and
biological breakdown occur before effluent is discharged to a leachfield
in the soil, are primarily used for single homes or small clusters of
homes. Mo
st cities and counties rely upon municipal wastewater
treatment plants. The effluent from these plants is considered a point
source discharge, and levels of pollutants are carefully monitored.


The Truckee Meadows Water Reclamation Facility (TMWRF) is the

primary wastewater treatment plant for the area. Another treatment plant
has been built in the South Meadows area. TMWRF has the capacity to
treat 40 million gallons per day (MGD), and on average, treats 30 MGD.


There are two basic phases to all munici
pal wastewater treatment:
primary treatment and secondary treatment. During primary treatment,
which is basically a physical process, the wastewater is screened to
remove large objects such as stones or sticks that could plug lines or
block tank inlets.
A grit chamber is used to allow sand, grit, and small
stones to settle to the bottom. The sewage than moves to a
sedimentation tank, where most of the solids settle to the bottom as raw
Grade Level:

6
-
8


Subject Areas:

Science


Natural Resources


Ecosystems


Process Skills


Duration:

30 minutes to teach
wastewater steps;

45
-
60 minutes for
laboratory exercise


Setting:

Classroom or
laborator
y


Link to Washoe County
School District
Standards:



4.8.2



15.8.4



15.8.2



15.8.4



16.8.1



16.8.2



16.8.3



16.8.4



16.8.5



19.8.1



19.8.4



23.8.6



24.8.4






Wetland Curriculum Lesson #

Draft 2/8/04

sludge, and oils and grease float to the top and are skimmed off. Su
bstances such as alum may be
used to help flocculate, or stick together particles, so they can be removed from the water. The raw
sludge is removed from the tank when necessary for further processing.


The wastewater resulting after primary treatment stil
l contains suspended and dissolved pollutants in
the form of organic matter. During secondary treatment, an activated sludge containing
microorganisms is used to break down organic material with aeration and agitation. Solids are then
able to settle out.

As much as 95% of wastewater pollutants can be removed during secondary
treatment. The resulting sludge mixture, which is full of millions of bacteria that feed on organic
wastewater pollutants, can be combined with new sewage in the presence of lots o
f fresh air to
continue the process. Secondary settling tanks are used to separate the water from organisms. After
these steps are complete, municipal wastewater is usually disinfected using chlorine or other
disinfecting compounds.


Tertiary treatment

may be used to remove nutrients such as nitrogen and phosphorus, and carbon
adsorption can be used to remove chemicals. The sludge byproduct can be treated and landfilled or
applied to land to improve soil properties, and the treated, clean effluent is d
ischarged to a local
waterbody.


TMWRF discharges its effluent into Steamboat Creek, which then flows into the Truckee River. By law,
since TMWRF is a point source of pollution, it must have a permit with limits on the amount of pollutants
that can enter
the river. For example, TMWRF is permitted to discharge up to 500 pounds per day of
nitrogen. The plant uses tertiary treatment to meet this requirement.


M
ATERIALS
: (one setup per group of students)


1.

Muddy water with added grass clippings or orange pee
ls, green food color and a few drops of
detergent (Prepare in advance and let it sit in the sun for a few days to “ripen”.)

2.

20 ounce clear plastic soda bottle cut in about ¼ of the way from the bottom (ask students to
collect the bottles)

3.

Alum (potassium a
luminum sulfate; available at a pharmacy)

4.

Flexible nylon screen (pantyhose works well)

5.

20 ounce large
-
mouth bottle with a lid

6.

2
-
3 plastic cups

7.

Washed fine sand

8.

Washed coarse sand

9.

Washed small pebbles

10.

Large beaker or jar

11.

Chlorine bleach

12.

Medicine dropper

13.

Tea
spoon

14.

Rubber band


P
ROCEDURE
: Students will build a filter and use it to clean “swampy” or muddy water.

1.

Pour about 1 cup of the muddy water into the 20 oz. large
-
mouth bottle with lid. Keep a sample
of water to use for comparison at the end of the exerci
se.

2.

Ask the students describe the appearance and smell of the water on their worksheet.

3.

Have the students place the lid on the bottle and shake the water vigorously for 30 seconds.
This will aerate the water. Pour the water into a plastic cup, and pour

it back and forth at least
Wetland Curriculum Lesson #

Draft 2/8/04

10 times to continue aeration. Ask the students to describe any changes they note on the
worksheet.

4.

Next, have students add one heaping teaspoon of alum crystals to the aerated muddy water.
Explain that the alum will help glom

the particles together so they will settle out during
sedimentation. Slowly stir the mixture for 5 minutes.

5.

Allow the mixture to sit for 20 minutes so sedimentation can occur. Have students check the
solution every 5 minutes and write their observation
s of the changes in appearance on the
worksheet. While they are waiting, have them construct a filter as described in the next step.

6.

Have students build one filter per group.

a.

Use the cut part of the soda bottle that includes the capped end.

b.

Remove the

cap. Attach a nylon screen to the neck of the bottle using a rubber band.

c.

Turn the bottle upside down and place it in the beaker or jar to support it.

d.

Pour a layer of fine sand on top of the nylon screen in the inverted bottle.

e.

Pour a layer of coarse s
and on top of the fine sand.

f.

Pour a layer of pebbles on top of the coarse sand. The filter is complete. There should
be enough room above the pebble layer to pour in the 1
-
cup water sample.

g.

Pour clean tap water through the filter until it drains clean fr
om the bottom. Be careful
not to disturb the pebble layer too much. This step prepares the filter for use with the
sample.

7.

After the 20
-
minute settling period, carefully pour the top two
-
thirds of the water sample through
the filter. Be careful not to
disturb or pour out the sediment. It should stay in the jar. Let the
sample filter into a clean jar or beaker.

8.

Next, add one drop of the chlorine bleach to the filtered water and observe any changes.

9.

Compare the treated and untreated water, and have the
students complete their worksheet. Do
not allow them to drink the water!

Wetland Curriculum Lesson #

Draft 2/8/04

Steps in Wastewater Treatment


Step 1: Preliminary treatment



Screening


removes large objects and allows sand and dirt to settle out



Smaller objects are ground into even smaller

pieces, and sand and dirt are allowed to settle out

Step 2: Primary treatment



Primary settling


floating grease and scum are skimmed, and solids settle out.

Step 3: Secondary treatment



Aeration


aeration tanks add water and allow bacteria to digest or
ganic substances.



Final settling


sludge continues to settle out, and is removed to a solids treatment process for
stabilization. The final product, called biosolids, can be disposed on cropland, in landfills, or
used for compost or other soil additives.




Disinfection


additional chlorine is added to kill disease
-
causing organisms, or other methods
of disinfection such as ultraviolet radiation are used.

Step 4: Tertiary treatment



Carbon adsorption


used to remove chemicals



Other methods used to remove
nutrients such as nitrogen and phosphorus




Wetland Curriculum Lesson #

Draft 2/8/04



Truckee Meadows Water Reclamation Facility Schematic



Wetland Curriculum Lesson #

Draft 2/8/04

Student Worksheet


Wastewater Treatment


Record your observations during each step of the process.



What changes do you see? Describe appearance, co
lor, odor, clarity

Step 1: Aeration






Step 2: Sedimentation






Step 3: Filtration






Step 4: Chlorination







1.

What changes in the liquid did you observe after aeration?

2.

Did aeration remove any of the odor?

3.

What was removed by sedimentatio
n?

4.

What was removed by the filter?

5.

Do you think your purified water is safe to drink? Why or why not?

6.

What else would you need to do to make the water clean enough to drink?

Wetland Curriculum Lesson #

Draft 2/8/04

R
ESOURCES


Water Environment Federation,
www.w
ef.org


Truckee Meadows Water Reclamation Facility, www.tmwrf.com


V
OCABULARY
W
ORDS


Activated sludge

Sludge particles produced by the growth of microorganisms in aerated
tanks as a part of the activated sludge process to treat wastewater.


Aeration

Proc
ess of stirring or bubbling air through a liquid. This adds oxygen to the
wastewater and allows other trapped gasses to escape.


Chlorine

A chemical element, abbreviated Cl, that is used as a disinfectant in
drinking and wastewater treatment processes.


Contamination

The addition of any substance to water that makes it unfit for use.


Disinfection

Process by which most microorganisms in or on a substance are killed.


Filtration

A mechanical process which involves moving water through a material,
usuall
y sand, designed to catch and remove particles.


Flocculation

Process by which dirt and other suspended solid particles are chemically
stuck together to they can be removed from water by sedimentation.


Point source
pollution

Pollution that can be traced

to a single, identifiable source, such as a pipe
or culvert.


Pollutant

Something added to water that causes an undesirable change in the
physical, chemical, or biological characteristics of the air, water, or land that
may harm or affect humans or other

living organisms.


Primary treatment

The first stage of wastewater treatment in which settleable or floating solids
are removed.


Organic material

Material derived from living things and containing carbon compounds.


Secondary
treatment

A type of waste
water treatment in which biological treatment processes
such as activated sludge are used to convert dissolved and suspended
pollutants into a form that can be removed.


Settling

The process of a substance, such as heavy organic solids or sediment,
sinkin
g to the bottom.


Sludge

Any solid, semisolid, or liquid waste that settles to the bottom of
sedimentation tanks or septic tanks.


Surface water

All water on the surface of the earth, including lakes, rivers, streams, ponds,
oceans, and runoff.

Wetland Curriculum Lesson #

Draft 2/8/04


Tertiar
y treatment

Any level of treatment above secondary treatment, which could include
filtration, nutrient removal, and removal of toxic chemicals and metals.


Wastewater

Water that has been used for domestic or industrial purposes.