Theme: Our Water Environment
Learning and Teaching Activities
Simulation experiments on wastewater treatment
Teaching Tips
Experiments provide the opportunity for students to get the first-hand information and carry
out scientific investigation. Take precautions during practical and remind students to follow
instructions.
Objective: To master the basic principles (precipitation and neutralization) applied in
chemical wastewater treatment to remove pollutants.
Introduction
Water pollution includes industrial wastewater, domestic sewage, discharges from livestock
farms, runoffs from contaminated soil, etc. These discharges would bring along chemical
contaminants, such as heavy metals and nitrates from fertilizers, organic pollutants (e.g. oil
and grease), biological contaminants, such as toxins and disease causing agents; and physical
contaminants, such as heat to the water body. These pollutants would lower the water quality
and thus pose potential hazard to human health and aquatic life.
In order to improve water quality, wastewater needs to be collected and treated before
discharge.
A series of preliminary, chemical and biological treatment methods will be
applied to eliminate or reduce pollutants. This simulation experiment mimics wastewater
treatment methods used in sewage treatment works. Common chemical pollutants that exist
in wastewater include toxic heavy metal ions, such as Cu (copper), Pb (lead), Fe (iron).
Forming insoluble metal hydroxides through precipitation can reduce their concentrations and
facilitate removal from the aquatic medium.
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Exercise 1
Separation of Metal Ions by Precipitation
Toxic heavy metal ions may exist in wastewater in soluble state, such as copper ions in
copper (Ⅱ) sulphate (pose potential hazard to human health). Most of these metal ions form
insoluble complexes with hydroxide ion (OH-). This precipitation will result in precipitates
that can be separated from the aquatic system by filtration.
For example:
Metal Salt (aq) + NaOH (aq)  Metal Hydroxide (s) + Sodium Salt (aq)
However, a few metal ions do not form precipitate with hydroxide and therefore could not be
separated from the wastewater by precipitation method. Nitrate, phosphate and potassium are
common ingredients in fertilizers and may become water pollutants. Potassium ions do not
form precipitate with hydroxide ion and require other treatment methods to remove them
from the wastewater.
In this exercise, you are going to use sodium hydroxide solution (NaOH) to react with copper
(II) (Cu2+), iron (II) (Fe2+) and potassium (K+) ion from respective solutions. Observe if there
is any precipitate formed and describe any color change of the solution in the reaction. After
obtaining the metal precipitate, allow them to settle and transfer the clear solution to a clean
test tube by filtration.
You will be provided with:

5mL pipette

Test tube rack

A bottle of 0.2M NaOH (aq)

0.2M Cu (II) SO4

Filter paper

Test tube

Glass rod

Funnel
(aq), Fe
(II) SO4 (aq), K2SO4
(aq),
each 10 mL in separate test tubes
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Procedures
1. Observe and record the color of the copper (Ⅱ) sulphate solution.
2. Pour about 10mL NaOH into the test tube containing 2mL Cu (II) SO4 (aq).
3. Observe and describe any changes, compare the color of the mixture with copper (Ⅱ)
sulphate solution.
4. Allow the precipitate to settle for 10 mins.
5. Separate the clear solution by filtration using a funnel with a filter paper on it and an
empty test tube holding in a test tube rack.
6. Repeat Step 1-4 by replacing Cu (II) SO4 (aq) with Fe (II) SO4 (aq) and K2SO4
(aq).
7. Tabulate your observations.
Observations
Discussion

Explain the observations for the precipitation of copper(Ⅱ) hydroxide from the solution.

Which one of the three metal ions can be separated from wastewater by precipitation?
Explain your answers.
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Further Investigations

Most metal hydroxides are insoluble and can be separated from wastewater. However, the
precipitate itself could be another form of pollutant and further treatment should be done
to reduce its environmental impact. Search on the Internet for one treatment method to
deal with precipitates.

Suggest one contamination source each for iron and lead.

Search on the Internet to find one method to handle the metal ions that could not be
removed by precipitation.
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Suggested answers (Accept alternative and correct answers)
Discussion

Explain the observations for the precipitation of copper (Ⅱ) hydroxide from the solution.
Copper (Ⅱ) ion react with hydroxide ion to form blue precipitates.

Which one of the three metal ions can be separated from wastewater by precipitation?
Explain your answers.
Copper (Ⅱ) and iron (Ⅱ) ions. They react with hydroxides to form insoluble complexes
that can be separated out from the solutions.
Further Investigation:

Most metal hydroxides are insoluble and can be separated from wastewater. However, the
precipitate itself could be another form of pollutant and further treatment should be done
to reduce its environmental impact. Search on the Internet for one treatment method to
deal with precipitates.
Convert the precipitates to useful substances such as calcium carbonate that can be used
in construction, or regenerate the metals by electrolysis, reduction and oxidation

Suggest one contamination source each for iron and lead.
Contamination source for iron: rusting / leakage from industries (e.g. electroplating
industries or electrolysis processes)
Contamination source for lead: leaded petrol, paint contains lead

Search on the Internet to find one method to handle the metal ions that could not be
removed by precipitation.
Iron exchange filtration to remove ions such as potassium ion
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Theme: Our Water Environment
Learning and Teaching Activities
Simulation experiments on wastewater treatment
Exercise 2
Neutralization
Wastewater discharges, especially from industrial sources, may have extreme pH due to the
application of acids, alkalis and other chemicals in production processes. These chemicals
will affect water quality if not treated and therefore should be neutralized to acceptable range
to meet safety standard. Neutralization could serve as a means to control pH of wastewater,
involving the reaction between acid and alkali. This could convert extreme pH to a level
similar to natural water, which is pH 7.
Consider the following reaction:
Na2CO3 (aq) + H2SO4 (aq)  Na2SO4 (aq) + CO2 (g) + H2O (l)
In this exercise, you will carry out a neutralization reaction. pH paper with range 1.0 –11.0
are used as indicator, as the reactants and products are colorless. A pH paper will give a
color change, and thus is used.
You will be provided with:

0.05M Na2CO3 (aq)

0.05M H2SO4 (aq)

1 set of pH paper 5.0 to 9.0

10 ml measuring cylinder

1ml pipette

Test tube

Test tube rack
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Procedures
1. Rinse the test tube with 5mL Na2CO3 solution and discard the solution. Repeat the step.
2. Transfer 10 mL Na2CO3 solution to the test tube by a measuring cylinder.
3. Determine the pH of the solution by pH paper.
4. Using 1mL pipette to transfer 1 mL H2SO4 solution into the test tube.
5. Mix the solutions in the test tube by shaking continuously. Determine the pH of the
mixture.
6. Repeat step 4 and 5 until pH reaches neutrality.
Observations
Discussion

List two industrial applications of sulphuric acid (H2SO4).

Do the presence of heavy metal ions cause environmental problems? If yes, state the
problems. Propose one method to solve the problems.
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
This experiment simulates the operations in wastewater treatment works. However, the
process involved will be much more complicated in real case. Suggest two limitations of
this simulation experiment. (Hint: State the possible contaminants in sewage)
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Suggested answers (Accept alternative and correct answers)

List two industrial applications of sulphuric acid (H2SO4).
Production of explosives or fertilizers / artificial fibre production / oil industry / textile

Do the presence of heavy metal ions cause environmental problems? If yes, state the
problems. Propose one method to solve the problems.
Yes, organisms absorb toxic heavy metal ions will affect the biochemical reactions in
their bodies, such as reduce the kidney’s ability to remove wastes or even induce cancers
(such as cadmium ion). The biological accumulations of them in the food chain even
make the problem worse.
Ban / restrict the use of heavy metals in industrial processes, or treat and reduce their
concentration in industrials wastes, etc.

This experiment simulates the operations in wastewater treatment works. However, the
process involved will be much more complicated in real case. Suggest two limitations of
this simulation experiment. (Hint: State the possible contaminants in sewage)
The wastewater may contain lots of waste such as dye or toxic biological wastes / the
processes are more complicated that utilize lots of energy and divided into many steps /
the wastes and products need further treatments before dumping
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