Using Algae for Phytoremediation (Part 2/3)
Lesson 6 of 11
Objective: Students will test algae's ability to remove pollutants from waste water to better understand phytoremediation.
Students will continue to test the ability of a mixture of plant-like protists (commonly known as algae) to clean up wastewater. We will finish collecting data today and start our data analysis. Student will plot data to determine an uptake kinetics curve and determine if the algal mat still has the ability to remove pollutant from the waste water. This is the second day of a three day lab. You can find yesterday's lesson at this link. The final lesson in the series is located at this link. Here is an overview of what students will learn today.
Using their notes from yesterday's web quest, have students draw a simple schematic of how a waste water treatment plant works.
Student Data Collection
Using the student handout from yesterday, have students remove a 5 mL from the algal/wastewater culture and determine the absorbance of the pollutant using a Spectrovis spectrophotometer. Have students record the absorbance in the data table.
Disposal instructions: Students should clean up their lab areas with lysol solution. Algal cultures should be sterilized in an autoclave at 15 lbs pressure for 15 minutes. Excessive waste water should be filtered and placed in the waste water disposal container. Dispose of container by follow your state's disposal guidelines. Algal mat should be disposed in the chemical disposal bucket.
For this section students should complete the following steps:
- Determine the concentration on the unknowns based on absorption.
- Locate the absorbance of the unknown on the vertical axis of the graph; the corresponding concentration will be found on the horizontal axis. (Note: The concentration of the unknown can also be found using the slope of the Beer’s law curve.)
- Determine the copper concentration of the simulated wastewater by displaying a graph of absorbance vs. concentration with a linear regression curve.
- Move the cursor along the regression line until the absorbance value is approximately the same as the absorbance value they recorded yesterday. The corresponding concentration value is the concentration of the unknown solution, in mol/L.
- Record the concentration in their data table.
- Print a graph of absorbance vs. concentration, with a regression line and interpolate the unknown concentration.
- Place the graph in their lab notebook.
Explain to students how to determine the uptake kinetic curve. Students should open LoggerPro and graph the pollutant concentration data and time that data was collected. First have students graph the concentrations of the wastewater on the y axis and the time on the x axis. Demonstrate to students how to use the analyze tools in LoggerPro.
Next, have students select analyze and curve fit. Demonstrate several possible functions that might fit the data points. Determine the function that best fits the data points collected and select OK. Explain why it is important not to assume that the function is always linear.
Next have students select Analyze and Statistics. Select Ok to display the statistics. Briefly explain to students the meaning of this mathematical test.
Have students print a copy of their graph and place it in their lab notebook.
Ask student to consider the following:
- Predict if they think the algae would be able to remove more of the copper from the wastewater or if they have reached the maximum amount of copper that can be removed.
(Possible student answers: Students are typically split on this. Half of the students think that algae will be able to remove more, probably infinite amounts of copper. The other half think that no more copper will be removed.)
- Ask student to explain their thinking.
(Possible student answers: Students who think that the algae can remove more copper have predicted that the function of the graph is linear. Students who think that the algae are done removing copper think that the algae have predicted that the function of the graph is 1/x.)
(Note: It actually takes the algae two weeks before the algae plateaus in its removal of copper from the simulated wastewater. Tomorrow, students graph data from a two week study and compare it to the graphs that they made in this lesson.)
- How they might test this hypothesis?
(Possible student answers: When we did this exercise in class, one lab group decided to add more copper once a plateau was reached and see if the algae would remove the additional copper from simulated wastewater. This was compared to a flask that did not have additional copper added to it, but still had the same algae. The other group decided to remove the algae that was no longer removing copper from the flask. That algae was weighed. Then they added the same amount of "fresh" algae to determine if the copper could continue to be removed if simulated wastewater was added.)
- What might engineers do to continue to remove copper if the algae in the wastewater can no longer remove anymore copper?
(Possible student answers: Engineers can calculate the total amount of copper an algal mat will remove. They can continually sample the wastewater. When the amount of residual copper left is showing that the algae have reached a plateau in their ability to remove copper,then the algal mat can be replaced.)
Have students record their responses in their lab notebook and turn them in for evaluation at the end of the period.