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3.1: Filtering Solutions for Clean Water

Difficulty Level: At Grade Created by: CK-12
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Unit Overview

Contents

  • (Optional) Fine Filters: Pretest
  • (Optional) Fine Filters: Posttest

Name_______________

Date_______________

Period_______________

Fine Filters: Pretest

1. Which of the following types of contaminants can nanomembranes filter out of water? For which of these, would you typically use a nanomembrane for removal? Explain why or why not. (1 point each, total of 12 points)

Can a nanomembrane filter it out? Is a nanomembrane the best way to filter it out?
Bacteria Yes or No Yes or No
Why/why not:
Lead\begin{align*}(Pb^{2+})\end{align*} Yes or No Yes or No
Why/why not:
Salt (\begin{align*}Na^+\end{align*} and \begin{align*}Cl^-\end{align*}) Yes or No Yes or No
Why/why not:
Sand Yes or No Yes or No
Why/why not:

2. Name two benefits that nanomembranes bring to the filtration of water that help to address the world’s problem of a scarcity of clean drinking water. (1 point each, 2 points total)

3. Describe three ways in which nanofilters can operate differently than traditional filters to purify water: (2 points each, 6 points total)

Name_______________

Date_______________

Period_______________

Fine Filters: Posttest

1. Which of the following types of contaminants can nanomembranes filter out of water? For which of these, would you typically use a nanomembrane for removal? Explain why or why not. (1 point each, total of 12 points)

Can a nanomembrane filter it out? Is a nanomembrane the best way to filter it out?
Bacteria Yes or No Yes or No
Why/why not:
Lead\begin{align*}(Pb^{2+})\end{align*} Yes or No Yes or No
Why/why not:
Salt (\begin{align*}Na^+\end{align*} and \begin{align*}Cl^-\end{align*}) Yes or No Yes or No
Why/why not:
Sand Yes or No Yes or No
Why/why not:

2. Name two benefits that nanomembranes bring to the filtration of water that help to address the world’s problem of a scarcity of clean drinking water. (1 point each, 2 points total)

3. Describe three ways in which nanofilters can operate differently than traditional filters to purify water: (2 points each, 6 points total)

The Water Crisis

Contents

  • The Water Crisis: Student Data Worksheet
  • Fine Filters Initial Ideas: Student Worksheet
  • The Water Crisis: Student Quiz

Name_______________

Date_______________

Period_______________

Student Data Worksheet

Directions

Using the graphs and maps, answer the following questions. This activity will give you the opportunity to interpret some of the graphs and maps that you’ll see during the Water Crisis slide presentation during class.

Distribution of earth’s water.

Distribution of earth’s water.

1. According to the bar graphs in Figure 1, what percentage of the world’s water is fresh water?

2. What do these three divided bar graphs tell you about where the Earth’s fresh water resides?

Physical water scarcity refers to the lack of water to meet domestic, industrial, and agricultural needs. Areas of physical water scarcity are shown in red on the map in Figure 2 below. Economic water scarcity means that an area or country has insufficient financial resources to deliver safe, clean water to those areas that need it for drinking or agriculture. Areas of economic water scarcity are shown in orange in Figure 2.

Global map of water scarcity in 2006.

Global map of water scarcity in 2006.

Answer questions 3-8 based on information from the map in Figure 2.

2. Name the countries or global areas that are experiencing physical water scarcity.

3. What would you predict the climate to be in these areas and why?

4. Name the countries or global areas that are experiencing economic water scarcity.

5. Name the countries or global areas that are not experiencing any water scarcity.

6. What do you predict the difference in per capita income (average income per person) would be between regions with plenty of water and regions with economic water scarcity?

7. The southwestern United States is typically characterized as having a dry, arid climate. Why might this region be shown as having plenty of water even if it is dry and arid?

When water is taken from a natural source for human use, it is called “water withdrawal.” However, a country can never withdraw all of the fresh water that is theoretically available within its borders. Much of it is seasonal, or part of flood runoff, or rain that cannot possibly all be captured. Countries that withdraw a high percentage of their available fresh water are said to be under “freshwater stress” and are in danger of becoming considered “water scarce.” In the map in Figure 3, the light orange represents mild freshwater stress and the darker orange represents extreme fresh water stress. Blue areas are considered to be free from freshwater stress.

Global map of freshwater stress, 1995 and 2025 (predicted).

Global map of freshwater stress, 1995 and 2025 (predicted).

8. Compare the two maps above, showing freshwater stress from the year 1995 and projected to the year 2025. What are the changes that you see happening in which areas?

9. In Figure 4, what trend do you see in for the global population?

10. What would you predict the global population to be in 2060? Justify your prediction.

World population from 1950 to 2050 (predicted).

World population from 1950 to 2050 (predicted).

11. According to the graph in Figure 5, which sector uses the most water?

12. Which sector uses the least amount of water?

Global annual water withdrawal by sector, 1900-2000.

Global annual water withdrawal by sector, 1900-2000.

13. How does the trend in water consumption (Figure 5) compare to the trend in population (Figure 4) for the time period 1950-2000?

Average daily water use per person for selected countries, from 1998 to 2002.

14. According to Figure 6, which countries consume the most water?

15. Which countries consume the least water?

Average wealth for selected countries (purchasing power by person in 2005).

Answer questions 16-19 based on information from the graph in Figure 7.

16. How many countries have an average per person purchasing power of less than \begin{align*}\$ 10,000?\end{align*}

17. How many countries have an average per person purchasing power of more than \begin{align*}\$ 25,000?\end{align*}

18. How many countries have an average per person purchasing power of \begin{align*}\$ 10,000- \$ 25,000?\end{align*}

19. What is the difference between the average per person purchasing power in the highest wealth country and the lowest wealth country?

Average daily water use per person and wealth.

Average daily water use per person and wealth.

20. According to Figure 8, does there seem to be a relationship between a country’s wealth and their average daily water consumption? If so, what is the relationship?

Name_______________

Date_______________

Period_______________

Fine Filters Initial Ideas: Student Worksheet

Write down your initial ideas about each question below and then evaluate how confident you feel that each idea is true. At the end of the unit, we’ll revisit this sheet and you’ll get a chance to see if and how your ideas have changed.

1. Why are water’s unique properties so important for life as we know it?

How sure are you that this is true?

Not Sure

How sure are you that this is true?

kind-of Sure

How sure are you that this is true?

Very Sure

End of Unit Evaluation
2. How do we make water safe to drink?

How sure are you that this is true?

Not Sure

How sure are you that this is true?

kind-of Sure

How sure are you that this is true?

Very Sure

End of Unit Evaluation
3. How can nanotechnology help provide unique solutions to the water shortage?

How sure are you that this is true?

Not Sure

How sure are you that this is true?

kind-of Sure

How sure are you that this is true?

Very Sure

End of Unit Evaluation
4. Can we solve our global water shortage problems? Why or why not?

How sure are you that this is true?

Not Sure

How sure are you that this is true?

kind-of Sure

How sure are you that this is true?

Very Sure

End of Unit Evaluation

Name_______________

Date_______________

Period_______________

Student Quiz

Write down your ideas about each question below.

1. What does it mean to have “clean fresh drinking water”?

2. Explain the term “water scarcity.”

3. Does water scarcity have an impact on human health? If so, what are some of the consequences?

4. Describe three reasons why some nations are experiencing a scarcity of clean drinking water.

5. Why is the water scarcity problem projected to increase?

6. Which sector––domestic, industrial, or agriculture––consumes the most water?

The Science of Water

Contents

  • The Science of Water Lab Activities: Student Directions
  • The Science of Water Lab Activities: Student Worksheets
  • The Science of Water: Student Quiz
  • Reflecting on the Guiding Questions: Student Worksheet

Lab Activities: Student Directions

Lab Station A: Surface Tension Lab

Purpose

The purpose of this lab is to investigate the property of the surface tension of water. This lab will look at the way that water sticks to itself to make a rounded shape, the way that water behaves as a “skin” at the surface, and a comparison of water’s surface tension with two other liquids, oil and soapy water.

Safety Precautions

  • Wearing goggles is dependent on your school’s safety criteria.
  • Caution needs to be exercised around hot plates and the alcohol burner.
  • Caution needs to be exercised around hot water and hot glassware.
  • Do not eat or drink anything in the lab.
  • Do not wear open-toed sandals in the lab.
  • Wear long hair tied back to prevent touching the substances at the lab stations.

Materials

  • 3 pennies
  • Available water
  • Small containers of water, oil, and soapy water
  • A dropper for each of the containers
  • A square, about \begin{align*}4'' \times 4''\end{align*}, of wax paper

Procedures

Counting Drops on a Penny

1. Check to make sure all of the materials needed are at your lab station.

2. Using a dropper bottle containing only water, count the number of drops of water that you can balance on top of a penny. When the water falls off of the penny, record the number of drops. Wipe the water off of the penny.

3. Repeat this procedure of counting and recording drops with oil and then with the soapy water.

Comparing the Shape of a Drop

4. Drop a small sample of each of the liquids––water, oil, and soapy water––on the wax paper. Draw the shape and label the shape of the drops made by each of the liquids on your worksheet. Wipe off the wax paper.

5. Answer the questions on your worksheet.

Lab Station B: Adhesion/Cohesion Lab

Purpose

The purpose of this lab is to investigate the property of cohesion and adhesion of water.

  • Cohesion is the molecular attraction exerted between molecules that are the same, such as water molecules.
  • Adhesion is the molecular attraction exerted between unlike substances in contact.

Cohesion causes water to form drops, surface tension causes them to be nearly spherical, and adhesion keeps the drops in place (http://en.wikipedia.org/wiki/Adhesion).

This lab will work with capillary tubing of various diameters to see the rate at which water is able to “climb” up the tubes. This is very similar to the way that water enters a plant and travels upward in the small tubes throughout the plant’s body. The “stickiness” of the water molecule allows the water to cling to the surface of the inside of the tubes.

You will see how the diameter of the tube correlates with the rate of traveling up the tube by measuring how high the dye-colored water column is at the end of the time intervals.

Safety Precautions

  • COOL GLASSWARE FOR A FEW MINUTES BEFORE PUTTING INTO THE COOLING BATH OR THE GLASSWARE WILL BREAK.
  • Wearing goggles is dependent on your school’s safety criterion.
  • Do not eat or drink anything in the lab.
  • Do not wear open-toed sandals in the lab.
  • Wear long hair tied back.

Materials

  • \begin{align*}4\end{align*} pieces of capillary tubing of varying small sized diameters (no greater than \begin{align*}7\;\mathrm{mm}\end{align*} in diameter), \begin{align*}8-24\;\mathrm{inches}\end{align*} in length
  • Metric ruler
  • Pan of dyed (with food coloring) water into which to set the capillary tubing
  • Clamps on ring stands to stabilize the tubing so that it remains upright in a straight position

Procedures

  1. Check to make sure all of the materials needed are at your lab station.
  2. Set the capillary tubing into the dye-colored water from the largest diameter tubing to the smallest. Make certain they are all upright and secure.
  3. Record the height of each of the tubes in the table on your worksheet every \begin{align*}2\;\mathrm{minutes.}\end{align*}
  4. After \begin{align*}10\;\mathrm{minutes,}\end{align*} release the capillary tubing, wrap the tubing in paper towels, and deposit them in an area designated by your teacher.
  5. Answer the questions about this experiment on your lab sheet.

Lab Station C: Can You Take the Heat?

Purpose

The purpose of this lab is to investigate the heat capacity of water. You will measure the temperature of water (specific heat of water is \begin{align*}4.19 \;\mathrm{kJ/kg.K}\end{align*}) and vegetable oil (specific heat of vegetable oil is \begin{align*}1.67 \;\mathrm{kJ/kg.K}\end{align*}) over equal intervals of time, and will record your data and findings on your lab sheet.

Specific heat is the amount of energy required to raise \begin{align*}1.0\;\mathrm{gram}\end{align*} of a substance \begin{align*}1.0^\circ C\end{align*}.

Safety Precautions

  • Cool hot glassware slowly. Wait a few minutes before placing in cold water or the glass will break.
  • Wearing goggles is dependent on your school’s safety criterion.
  • Do not eat or drink anything in the lab.
  • Do not wear open-toed sandals in the lab.
  • Wear long hair tied back.
  • Use caution when working with fire or heat. Do not touch hot glassware.

Materials

Assemble two Erlenmeyer flasks or beakers, each containing one of the liquids,with a thermometer suspended into each liquid, from a clasp attached to a stand, inserted about midway into the liquid.

  • 2 equal amounts, about \begin{align*}100 \;\mathrm{mL}\end{align*}, of water and vegetable oil
  • 2 \begin{align*}250-\;\mathrm{mL}\end{align*} Erlenmeyer flasks or 2 \begin{align*}250-\;\mathrm{mL}\end{align*} beakers
  • 2 thermometers
  • 2 Bunsen burners or 1-2 hot plates
  • 2 ring stands: each ring stand will have a clamp to hold the thermometer. Use a screen if using a Bunsen burner rather than hot plate(s).
  • Cold water bath for cooling the Erlenmeyer flasks or beakers

Procedures

1. Set the cooled flasks containing their solutions on the ring stands or hot plate.

2. Take the initial temperature reading of each of the liquids.

3. Turn on the hot plate to a medium temperature, or, if using Bunsen burners instead, light them, adjusting the flame of each to the same level.

4. Record the temperature of the liquid in each flask every \begin{align*}2\;\mathrm{minutes}\end{align*} until \begin{align*}4\;\mathrm{minutes}\end{align*} after each liquid boils. Record the temperature in the table on your lab sheet.

5. After recording the final temperatures, move the Erlenmeyer flasks or beakers with tongs or a heat-resistant set of gloves into the cooling bath. Add small amounts of ice as needed to keep the water temperature cold.

DO NOT THRUST HOT GLASSWARE DIRECTLY INTO ICY WATER BEFORE COOLING BECAUSE THE GLASS WILL BREAK!

6. Answer the questions about this experiment on your lab sheet.

Lab Station D: Liquid at Room Temperature Data Activity

Purpose

The purpose of this activity is to discover how unusual it is, based on a substance’s molecular weight, that water is a liquid at room temperature.

Safety Precautions

None are needed, since this is a paper and pencil activity.

Materials

  • Water is Weird! Data Table
  • Lab worksheet for recording trends

Procedures

Data table 1 shows the physical properties of a variety of substances. This table is typical of one that a chemist would examine to look for trends in the data. For instance, is there any correlation with the color of the substance and its state of matter? Is there any correlation between the state-of-matter of a substance and its density? How does water compare to other substances?

  1. Examine the data table. Look for relationships between the physical properties of some of these substances. What do you notice that fits into any patterns? What is the opposite or is unusual to the most common pattern?
  2. Discuss the trends with your lab partner. Record your thoughts on your lab worksheet.
  3. Answer the questions about this experiment on your lab worksheet.

Water is Weird!

Data Analysis Activity

Water is Weird! How Do We Know?

We have been discussing the many ways that water is weird. Water seems pretty common to us. How do we know that it is unusual? Let’s compare water to some other substances and see what we can find, using the data table below.

Record the trends that you notice on your lab worksheet.

Physical Properties of Some Substances
Substance Formula Molar, mass, grams State of matter at normal room conditions Color Specific Heat \begin{align*}\;\mathrm{J/g \ K}\end{align*} Density of gas, liquid, or solid Boiling Temperature, \begin{align*}^\circ C\end{align*}
Water H2O 18.0 liquid colorless 4.19 0.997 g/cm3 100
Methane CH4 16.0 gas colorless 0.423-162 g/cm3 -161.5
Ammonia NH3 17.0 gas colorless 0.70 g/L -33
Propane C3H8 44.1 gas colorless 0.49325 g/cm3 -42.1
Oxygen O2 32.0 gas colorless 0.92 1.308 g/L -182.9
Carbon dioxide CO2 44.0 gas colorless 1.799 g/L -78.5
Bromine Br2 159.8 liquid red 0.47 4.04 58.8
Lithium Li 6.94 solid silvery, white metal 3.58 0.534 g/cm3 1342
Magnesium Mg 24.3 solid silvery, white metal 1.02 1.74 g/cm3 1090

Lab Station E: Now You See It, Now You Don’t A Dissolving Lab

Purpose

The purpose of this activity is to introduce the idea that different types of liquids may dissolve different substances.

Safety Precautions

  • Wearing goggles is dependent on your school’s safety criterion.
  • Do not eat or drink anything in the lab.
  • Do not wear open-toed shoes.
  • Tie long hair back.

Materials

  • 6 plastic cups
  • 6 plastic spoons
  • Water
  • Oil
  • Granulated salt
  • Granulated sugar
  • Iodine crystals

Procedures

  1. Fill 3 plastic cups \begin{align*}1/3\end{align*} to \begin{align*}1/2\end{align*} full with water.
  2. Fill 3 plastic cups \begin{align*}1/3\end{align*} to \begin{align*}1/2\end{align*} full with oil.
  3. Put about a half-teaspoon of salt into the water in one cup and another half-teaspoon of salt into the oil in one cup.
  4. Stir each for about \begin{align*}20\;\mathrm{seconds}\end{align*} or until dissolved.
  5. Record your observations in the table on your lab sheet.
  6. Repeat this procedure with sugar.
  7. Repeat this procedure using iodine crystals BUT only drop \begin{align*}2\end{align*} or \begin{align*}3\end{align*} crystals into the water and into the oil.
  8. Record your observations and answer the questions about this experiment on your lab sheet.

Lab Station F: Predict a New World! Inquiry Activity

Purpose

We all know that ice floats; we take it for granted. However, in nature, the solid form of a substance being less dense than the liquid form is extraordinary. What we don’t know or think about much is how our world would be affected if ice did not float in water. This “thought” activity is explores the worldly implications if ice had a greater density than water.

Safety Precautions

None are required because this is a paper and pencil activity.

Materials

  • A fish bowl with some fish and live plants

Procedures

1. Read the following. Look at the fish bowl. Think. Write your thoughts on your lab worksheet.

Assume that there will be one change in the way that nature behaves: On the day after tomorrow, worldwide, ice (the solid form of water) will now become denser than water, rather than its current state, which is less dense.

What will be the impact of this change?

Beautiful lake in early winter. [1]

Beautiful lake in early winter. [1]

2. Discuss this with your lab partner.

3. Answer the questions about this experiment on your lab worksheet.

Name_______________

Date_______________

Period_______________

Lab Activities: Student Worksheets

Directions: Go to the lab stations assigned by your teacher. Follow the directions for each lab that are posted at each of the lab stations. Conduct the lab activity and record your data on the lab write-up sheet. Answer the questions asked on the lab sheet. Be sure to pay special attention to the purpose of each lab before beginning the lab. You are encouraged to talk to your lab partners about the lab and to ask your teacher questions.

Lab Station A: Surface Tension Lab

Drops of Water

Fill in the table below with the number of drops you added to the penny of each substance before the liquid spilled over.

Water Oil Soapy Water
Number of Drops

Questions

1. What does a high surface tension do to the number of liquid molecules that can stay together?

2. Based on your evidence, compare the surface tension of these four substances.

3. After placing a few drops of each of the liquids on the wax paper, draw what the drops look like from the side view. Be sure to capture the relative height/flatness of the drop

Water

Oil

Soapy Water

Name_______________

Date_______________

Period_______________

Lab Station B: Adhesion/Cohesion Lab

Questions

1. Define adhesion

2. Define cohesion

3. Ask your teacher to provide you with the diameter of the capillary tubes if they are not labeled. In the table below, record the height of the liquid in capillary tubing of different diameters as you take your measurements.

Diameter of capillary tubing
\begin{align*}2 \;\mathrm{minutes}\end{align*}
\begin{align*}4 \;\mathrm{minutes}\end{align*}
\begin{align*}6 \;\mathrm{minutes}\end{align*}
\begin{align*}8 \;\mathrm{minutes}\end{align*}
\begin{align*}10 \;\mathrm{minutes}\end{align*}

4. Based on your evidence, what statement can you make about water’s speed of climbing a capillary tube relative to the diameter (size of the opening) of the capillary?

5. What does this mean about how fast water is able to “climb” tubes within plants?

Name_______________

Date_______________

Period_______________

Lab Station C: Can You Take the Heat? Student Lab Sheet

Specific heat is the amount of energy that it takes to raise \begin{align*}1.0 \;\mathrm{gram}\end{align*} of a substance \begin{align*}1.0^\circ C\end{align*}.

Fill out the table as you conduct your experiment.

Liquids Water Temperature Vegetable Oil Temperature
\begin{align*}2 \;\mathrm{minutes}\end{align*}
\begin{align*}4 \;\mathrm{minutes}\end{align*}
\begin{align*}6 \;\mathrm{minutes}\end{align*}
\begin{align*}8 \;\mathrm{minutes}\end{align*}
\begin{align*}10 \;\mathrm{minutes}\end{align*}
\begin{align*}14 \;\mathrm{minutes}\end{align*}

Questions

1. Based on your evidence, which substance has the highest specific heat? The lowest?

2. Think about and explain the relationship between high specific heat of a liquid and hydrogen bonding.

3. Compare the boiling temperatures of water and of oil. What is the relationship between hydrogen bonding and boiling temperature?

4. What happened to the temperature of the water and the oil after boiling? Explain why.

Name_______________

Date_______________

Period_______________

Lab Station D: Liquid at Room Temperature Data Activity

Questions

1. What trends do you notice in the data table? Explain.

2. What is unusual about the most common pattern? Explain.

3. How does water compare to other substances?

Name_______________

Date_______________

Period_______________

Lab Station E: Now You See It, Now You Don’t A Dissolving Lab

A solvent is the liquid that is doing the dissolving. A solute is the substance that will be dissolved in the liquid.

Record your observations about how quickly and thoroughly each of the solutes dissolves in water and oil in the table below.

SOLVENT SOLUTES SOLUTES SOLUTES
Salt Sugar Iodine Crystals
Water
Oil

Questions

1. Summarize what you found in your experiment, based on your recorded observations.

2. Why do you think that some substances dissolve easier in one type of liquid than in another?

Name_______________

Date_______________

Period_______________

Lab Station F: Predict a New World! Inquiry Activity

Questions

1. Summarize your thoughts about the impact on the world if ice were denser than water.

Name_______________

Date_______________

Period_______________

Student Quiz

Write down your ideas about each question below.

1. Why does all bonding occur between atoms, ions, and molecules?

2. Draw a water molecule. Label the atoms that make up the water molecule with their chemical symbol. If there is an electrical charge or a partial electrical charge on any of the atoms, indicate that by writing the symbols on the atoms:

\begin{align*}& + = \text{positive\ charge} && - = \text{negative\ charge} \\ & \delta^+ = \text{partial\ positive\ charge} && \delta^- = \text{partial\ negative\ charge} \end{align*}

3. Explain the term “polar” molecule.

4. Why does water have an increased surface tension compared to most other liquids?

5. What is “hydrogen bonding”? What makes these bonds unique?

6. a. Define or describe “specific heat.”

b. How does water’s specific heat have an impact on our climate?

7. Is water’s specific heat, compared to other liquids:

High \begin{align*}\Box\end{align*} or Average \begin{align*}\Box\end{align*} or Low \begin{align*}\Box\end{align*} ?

8. Are water’s melting and boiling temperatures, compared to other liquids:

High \begin{align*}\Box\end{align*} or Average \begin{align*}\Box\end{align*} or Low \begin{align*}\Box\end{align*} ?

9. a. What happens to the temperature of the water in a pot on a heated stove as it continues to boil?

b. Explain what the energy is being used for that is heating the water at the boiling temperature.

10. Explain how a spider can walk on water.

11. Fill out the following table: Name and explain five of water’s unique properties, and provide an example of the phenomenon in nature caused by each of these properties.

Property of Water Explanation of Property Phenomenon Property Causes

Name_______________

Date_______________

Period_______________

Reflecting on the Guiding Questions: Student Worksheet

Think about the activity you just completed. What did you learn that will help you answer the guiding questions? Jot down notes in the spaces below.

1. Why are water’s unique properties so important for life as we know it?

What I learned in these activities:

What I still want to know:

2. How do we make water safe to drink?

What I learned in these activities:

What I still want to know:

3. How can nanotechnology help provide unique solutions to the water shortage?

What I learned in these activities:

What I still want to know:

4. Can we solve our global water shortage problems? Why or why not?

What I learned in these activities:

What I still want to know:

Nanofiltration

Contents

  • The Filtration Spectrum: Student Handout
  • Types of Filtration Systems and Their Traits: Student Handout
  • Which Method is Best? Student Worksheet
  • Comparing Nanofilters to Conventional Filters Lab Activity:
Student Instructions & Worksheet
  • Cleaning Jarny’s Water: Student Instructions & Report
  • New Nanomembranes: Student Reading
  • Reflecting on the Guiding Questions: Student Worksheet

The Filtration Spectrum: Student Handout

Osmonics Filtration Spectrum

Osmonics Filtration Spectrum

Types of Filtration Systems and Their Traits: Student Handout

Types of Filtration Max Particle Size (meters) Characterization Example Particles Disadvantages Diagram
Microfiltration (MF) 10-5 to 10-7

Removal based on relatively large pore size, retains contaminants on surface.

Very low water pressure needed.

Often used as a pre-filter.

Sand, silt, clays, Giardia lamblia, Cryptospoidium, cysts, algae and some bacteria Removes little or no organic matter. Does not remove viruses.
Ultrafiltration (UF) 10-7 to 10-8

Removal based on smaller pore size, retains contaminants on surface.

Low water pressure needed.

Suspended organic solids

Partial removal of bacteria

Most viruses removed

Most problems are with fouling. Cannot remove iron or manganese ions (multivalent ions).
Nanofiltration (NF) 10-8 to 10-10 Removal based on very small pore size and shape and charge characteristics of membrane. Moderate pressure needed.

Suspended solids

Bacteria

Viruses

Some multivalent ions

Currently most are susceptible to high fouling.

Cost is relatively high (currently).

Reverse Osmosis (RO) 10-9 to 10-11 High pressure process that pushes water against the concentration gradient Different membranes have different pore sizes and different characteristics.

Suspended solids

Bacteria

Viruses

Most multivalent ions

Monovalent ions

Membranes are prone to fouling.

Cost is high.

Note: Relative Pressure needed for operation: \begin{align*}RO > NF > UF > MF\end{align*} Relative Cost: \begin{align*}RO > NF > UF > MF [4]\end{align*}

References

(Accessed December 2007.)

Name_______________

Date_______________

Period_______________

Which Method is Best? Student Worksheet

Purpose

Use the Filtration Spectrum: Student Handout to determine which filtration method is best suited to filter a variety of particles.

Introduction and Example

If you had a filter that was made of paper, it would not let sand pass through but would allow water and dissolved sodium chloride pass through. To demonstrate this, you would draw the following arrows:

Refer to the Filtration Spectrum handout. Based on what you see in the handout, draw arrows that show which particles will pass through each membrane and which will not.

Comparing Nanofilters to Conventional Filters Lab Activity: Student Instructions

Overview

You are on a backpacking trip in the mountains with a friend. Each of you has brought \begin{align*}2 \;\mathrm{liters}\end{align*} of water with you and you are running very low. You had planned to stay at least for another day, but realize that if you don’t find a source of clean drinking water, you will need to turn back and end your trip early. You brought with you some water testing strips and a nanofilter that fits inside of a syringe, just in case you needed to drink the water from the river. Your job is to use your testing strips to find out what else, besides what you can see (such as leaves) is in the water. Once you find what is in the water, you will have to filter out any of the unwanted substances.

The pores of your nanofilter are so small that they will easily plug with large substances. You want to filter as much as you can using the gravel and the sand by the river in a funnel. You have also brought activated charcoal with you.

Can you make the river water clean enough to drink, or do you have to turn around and go home?

Materials: Filtration (Part I)

  • \begin{align*}1/2\end{align*} cup sand
  • \begin{align*}1/2\end{align*} cup gravel
  • About \begin{align*}50 \;\mathrm{mL}\end{align*} of activated charcoal
  • 1 \begin{align*}25 \;\mathrm{mm}\end{align*} NanoCeram® nanofilter disc
  • 1 Luer-Loc ceramic filter housing (to hold the nanofilter)
  • 2 \begin{align*}250 \;\mathrm{mL}\end{align*} beakers
  • 1 funnel
  • Paper towels
  • Syringe
  • Test strips for nitrate and nitrite ions
  • Test strips for chloride ions
  • Test strips for copper
  • Test strips or drops for iron(II) and iron(III) ions
  • \begin{align*}1/2\;\mathrm{liter}\end{align*} of “river water” in a bottle

Materials: Comparing Ultrafiltration with Nanofiltration (Part II)

  • 1 \begin{align*}25 \;\mathrm{mm}\end{align*} NanoCeram® nanofilter disc
  • 1 \begin{align*}25 \;\mathrm{mm}\end{align*} Millipore VS ultrafilter disc
  • 1 Luer-Loc ceramic filter housing (to hold the nanofilter and the ultrafilter)
  • Syringe
  • Bottle of water containing dissolved dye
  • (2) small effluent collectors
  • Paper towels

Procedures: Filtration (Part I)

Setup

  1. Put the charcoal in water to soak for at least \begin{align*}10\;\mathrm{minutes,}\end{align*} and proceed with the next step. After \begin{align*}10\;\mathrm{minutes,}\end{align*} take the charcoal out and rinse it thoroughly to prevent coloring the water.
  2. Arrange the ring on the ring stand and put the empty funnel inside of the ring, as shown in Figure 1. Put the \begin{align*}250 \;\mathrm{ml}\end{align*} beaker underneath the funnel so it will catch the effluent.
  3. Look at the river water in the bottle. Record your observations of the river water on your lab sheet. Be sure to notice texture, colors, and anything else that stands out.
  4. Follow the instructions in the Ion Testing box below to test the river water for the presence of the ions.

Funnel supported by ring with beaker underneath to catch effluent [1].

Ion Testing

1. Label a paper towel with each of the symbols of the ions you will test:

\begin{align*}Fe^{2+}& & Fe^{3+}& & CI^-& & NO_3{^-}& & NO_2{^-}& & Cu^{2+}&\end{align*}

2. Dip the appropriate strips in the river water to test for these ions.

3. Put the wet strips on a paper towel under their appropriate symbols so you don’t forget which strip represents a test for which ion.

4. Match the color of your strip with the color chart on the side of the relevant test strip bottle. The amount of the ion in your river water sample will be listed underneath the matching color square on the bottle.

5. Record on your lab sheet the color of the strip and the amount of each ion indicated by the test strip.

You will repeat this “ion testing” step after each filtration to find out if the ions are still present in the water.

Table 1 summarizes the consequences of the presence of these ions in drinking water.

Ions and Consequences in Drinking Water
Ions Consequences in Drinking Water
\begin{align*}Fe^{2+}\end{align*} and \begin{align*}Fe^{3+}\end{align*} These ions indicate that rust from pipes has gotten into the water. While rust is not dangerous, it makes the water taste bad and leaves mineral deposits in sinks and bathtubs.
\begin{align*}NO_3{^-}\end{align*} and \begin{align*}NO_2{^-}\end{align*} These ions are an indication that pesticides from agriculture have gotten into the water.
\begin{align*}Cl^-\end{align*} This ion indicates that salt has intruded into the water. People cannot use salty water for drinking. Salty water usually cannot be used for agriculture either, although there are a few exceptions.
\begin{align*}Cu^{2+}\end{align*} Copper is normally found in water from natural sources as well as from corrosion of the copper pipes used for water. Copper is not harmful in quantities less than \begin{align*}1000- \mu \mathrm{m}\end{align*}.

Gravel Filtration

1. Put \begin{align*}1/2\end{align*} cup of gravel into the funnel.

2. Put a clean \begin{align*}250 \;\mathrm{mL}\end{align*} beaker underneath the funnel.

3. Pour the river water supplied by your teacher over the gravel. Notice if the gravel stopped any of the substances that you saw in the water from going into the beaker below.

4. Record your observations on your lab sheets.

Gravel and Sand Filtration

5. Put \begin{align*}1/2\end{align*} cup of sand on top of the gravel in the funnel.

6. Put a clean \begin{align*}250 \;\mathrm{mL}\end{align*} beaker under the funnel.

7. Pour the contents of the first beaker, the effluent, into the funnel on top of the sand. Notice if the sand and gravel stop any of the substances in the water from going into the beaker below.

8. Record your observations on your lab sheet.

9. Rinse the empty \begin{align*}250 \;\mathrm{mL}\end{align*} beaker and place it underneath the funnel.

Gravel, Sand, and Activated Charcoal Filtration

10. Put the activated charcoal into the funnel on top of the sand and the gravel.

11. Pour the remaining water (the effluent) left from the sand filtration step into the funnel on top of the charcoal. Notice if the charcoal removes anything else.

12. Record your observations on your lab sheet.

Conduct Ion Test

13. Using the test strips, test for the presence of the ions in the filtered water by following the instructions in the Ion Testing box above.

14. Record the results of your ion tests on your lab sheet and answer the questions.

Nanofiltration

15. Get a \begin{align*}25 \;\mathrm{mm}\end{align*} NanoCeram® nanofilter disc and a Luer-Loc ceramic filter housing.

16. Open the filter housing and carefully place the disc into the filter housing, place the O-ring on top of the disc, and close securely, making sure the disc is centered in the housing to prevent leakage around the edges of the disc.

17. Rinse the empty \begin{align*}250 \;\mathrm{mL}\end{align*} beaker and place it underneath the filter.

18. Fill the syringe with the effluent collected after filtering with the charcoal, sand, and gravel.

19. Screw the filter housing onto the syringe, taking care not to depress the plunger of the syringe during this operation.

20. Push the effluent through the nanofilter using even, steady pressure.

21. Record your observations of the solution after it has gone through the nanofilter on your lab sheet.

Conduct Ion Test

22. Using the test strips, test for the presence of the ions in the filtered water by following the instructions in the Ion Testing box above.

23. Record the results of your ion tests on your lab sheet and answer the questions.

Procedures: Comparing Ultrafiltration with Nanofiltration (Part II)

You have just used a new nanofilter (the NanoCeram filter) that has recently come to market. An older ultrafilter, called the Millipore VS filter is also available. The NanoCeram® filter is a multilevel woven membrane with various nanoparticles embedded into the layers of membranes. The Millipore VS membrane is a nonwoven, matte-like paper.

The purpose of this part of the lab activity is to compare the nanofilter with the ultrafilter based upon the following two criteria:

  • Completeness of filtration
  • The relative amount of pressure needed to push the water through each filter

The completeness of filtration will be measured by filtering dissolved dye through each of the filters and looking at the color of the filter and the effluent. The relative pressure needed for filtration will be measured by how hard you have to push the syringe to get the water to pass through the filters.

Compare Millipore VS and NanoCeram® Filtration

  1. Open the bottle containing the dissolved dye and draw \begin{align*}2-3 \;\mathrm{mL}\end{align*} into the syringe.
  2. Open the Luer-Loc filter housing and carefully place a single \begin{align*}25\;\mathrm{mm}\end{align*} disc of Millipore VS membrane material into it. Place the O-ring on top of the disc and close securely, making sure the disc is centered in the housing to prevent leakage around the edges of the disc.
  3. Screw the filter housing onto the syringe, taking care not to depress the plunger of the syringe during this operation.
  4. Depress plunger of the syringe while holding the syringe over an effluent collector to capture the fluid as it exits the syringe through the filter housing.
  5. Apply enough pressure to ensure that the dissolved dye is passing through the filter media. Typical results for this stage using the Millipore VS membrane material show only several drops coming out of the syringe due to the extreme amount of pressure required to force the dissolved dye through the filter.
  6. Once this is completed, carefully remove and open the filter housing, and remove the filter membrane.
  7. Place the membrane aside, next to the effluent collector containing the effluent from this test.
  8. Rinse the syringe and repeat the sequence of steps 1-7 above, but with the NanoCeram® filter. Push the dissolved dye through gently and steadily; avoid pushing fast.
  9. Compare the color of the effluent from the two filters, the color of the filters, and how easy or hard it was to push the dissolved dye through the filters with the syringe.
  10. Record your observations on your lab sheet.
  11. Answer the questions on your lab sheet.
  12. Clean your lab station.

References

(Accessed January 2008.)

Name_______________

Date_______________

Period_______________

Comparing Nanofilters to Conventional Filters Lab Activity: Student Worksheet

Part 1: Filtration

1. DRAW and DESCRIBE the contents and appearance of your river water. After looking carefully, write down everything that you see that is in the river water. Be sure to include any identifiable substances, and any colors.

2. Record the color of the test strip and amount of each ion indicated by the test strip.

Substance Tested Color Presence or Absence
\begin{align*}Fe^{2+}\end{align*} and \begin{align*}Fe^3\end{align*}
\begin{align*}NO_3{^-}\end{align*} and \begin{align*}NO_2{^{-}}\end{align*}
\begin{align*}Cl^-\end{align*}
\begin{align*}Cu^{2+}\end{align*}

Gravel Filtration

3. Describe the appearance of the effluent after it was poured through the gravel.

4. Based on your observations, what was removed from the river water after filtering with the gravel?

5. Based on your observations, what remained in the river water after filtering with the gravel?

Gravel and Sand FIltration

6. Describe the appearance of the effluent after it was poured through the gravel and sand.

7. Based on your observations, what was removed from the river water after filtering with the gravel and sand?

8. Based on your observations, what remained in the river water after filtering with the gravel and sand?

Gravel, Sand, and Activated Charcoal Filtration

9. Describe the appearance of the effluent after it was poured through the gravel, sand, and charcoal.

10. Record the color of the test strip and amount of each ion indicated by the test strip.

Substance Tested Color Presence or Absence
\begin{align*}Fe^{2+}\end{align*} and \begin{align*}Fe^3\end{align*}
\begin{align*}NO_3{^-}\end{align*} and \begin{align*}NO_2{^{-}}\end{align*}
\begin{align*}Cl^-\end{align*}
\begin{align*}Cu^{2+}\end{align*}

11. Based on your evidence (observations and strip tests), what was removed from the river water after filtering with the gravel, sand, and charcoal?

12. Based on your evidence (observations and strip tests), what remained in the river water after filtering with the gravel, sand, and charcoal?

Nanofiltration

13. Describe the appearance of the effluent after it was pushed through the NanoCeram® nanofilter.

14. Record the color of the test strip and amount of each ion indicated by the test strip.

Substance Tested Color Presence or Absence
\begin{align*}Fe^{2+}\end{align*} and \begin{align*}Fe^3\end{align*}
\begin{align*}NO_3{^-}\end{align*} and \begin{align*}NO_2{^-}\end{align*}
\begin{align*}Cl^-\end{align*}
\begin{align*}Cu^{2+}\end{align*}

15. Based on your evidence (observations and strip tests), what was removed from the river water after filtering through the nanofilter?

16. Based on your evidence (observations and strip tests), what remained in the river water after filtering through the nanofilter?

Part II: Comparing Ultrafiltration with Nanofiltration

After following the lab directions for putting the effluent through the two filters, fill out the following table.

Filter Type Color of Effluent Color of Filter Relative Pressure Required to Push the Solution Through the Filter
Millipore VS ultrafilter
NanoCeram® nanofilter

17. Which filter removed the dye the best? How do you know?

18. Which filter required less pressure to push the water through?

19. Based on your results about pressure, which filter would cost less overall?

20. Based on the evidence from your experiments, can you stay and camp another day or do you have to go home to get clean, drinkable water?

21. What do you think might have been the sources of the pollutants in your river water?

Cleaning Jarny’s Water: Student Instructions & Report

There’s a Problem with Our Water...

In the Eastern part of France, in the city of Jarny (see Figure 1), the local people have a serious problem with their drinking water. Their main source of drinking water comes from the ground water table located near an old iron mine. (See Figure 2 for an explanation of ground water.)

The water has always been pumped out of the mine and filtered before being used for drinking water. When the mine was active, this system worked fine. But since closing, the water has flooded up into the mine, creating a pool of standing water that seeps into the ground water used for drinking.

Jarny, France (green arrow) [1].

Jarny, France (green arrow) [1].

Over time, the water sitting in the mine reacted with the debris left in the abandoned mine, leaving much of the water contaminated. A local water-monitoring agency has watched the rising contamination levels and determined that the current water cleaning system is not good enough to make the water safe to drink. Even before the water flooded up into the mine, a few substances were slightly above safety limits, but now their levels are even higher.

Ground water [2].

Ground water [2].

Water that comes from rain (precipitation) trickles through the ground (infiltration) until it flows to an area that it can’t pass through, such as bedrock. Fresh water accumulates in these places and is referred to as ground water. The top of the ground water is the water table. When this underground water is large enough, it is called an aquifer. Aquifers are a commonly used source of fresh drinking water for people all over the world.

Now that you have some background on the water problem facing Jarny, your team’s job is to design a system to clean the water to make it drinkable by the local residents. To do this you will need to do the following:

1. Analyze the data in Table 1 to identify what harmful substances are present in the water. This table provides raw water measurements on a set of substances, selected due to their change in concentration before and after the flooding.

2. Complete question 1 in the Student Report. Record the following information for each substance:

  • The name of the substance identified to be filtered out of the water
  • The amount the substance is over the acceptable limit
  • The ranking of substances by size \begin{align*}(1 = \;\mathrm{largest})\end{align*}
  • The least expensive filter needed to filter the substance identified

3. Analyze the data on the current water cleaning system (Table 2), your reading handouts, and relevant charts to help inform your design of a system to clean the water to make it drinkable. Assume that your design will be added on to the system currently in place: a flocculation procedure, a sand filter, and a \begin{align*}1.0\end{align*} micron microfilter. Remember that the town is poor and your design needs to provide a cost-effective solution. Your design may involve single-step or multiple-step methods.

4. Complete questions 2 and 3 in the Student Report.

Water Measurements Before and After Flooding
Substance Before flooding \begin{align*}(\;\mathrm{mg/L})\end{align*} After flooding \begin{align*}(\;\mathrm{mg/L})\end{align*} “Safe” levels \begin{align*}(\;\mathrm{mg/L})\end{align*} Health hazard or water-taste quality
\begin{align*}Ca^{2+}\end{align*} \begin{align*}168\end{align*} \begin{align*}296\end{align*} \begin{align*}160\end{align*} Contributes to water “hardness”
\begin{align*}Mg^{2+}\end{align*} \begin{align*}31\end{align*} \begin{align*}185\end{align*} \begin{align*}15\end{align*} Contributes to water “hardness”
\begin{align*}Na^+\end{align*} \begin{align*}50\end{align*} \begin{align*}260\end{align*} \begin{align*}350\end{align*} Dehydration
\begin{align*}CO_3{^{2-}}\end{align*} \begin{align*}367\end{align*} \begin{align*}500\end{align*} \begin{align*}100\end{align*} Taste or alkalinity
\begin{align*}SO_4{^{2-}}\end{align*} \begin{align*}192\end{align*} \begin{align*}1794\end{align*} \begin{align*}300\end{align*} Water taste
\begin{align*}Cd^{2+}\end{align*} \begin{align*}.002\end{align*} \begin{align*}.018\end{align*} \begin{align*}.005\end{align*} Kidney damage
Bacteria (E. coli) \begin{align*}0\end{align*} \begin{align*}24\end{align*} \begin{align*}0\end{align*} Diarrhea, cramps, nausea, or headaches
Asbestos (million fibers/L) from rotting pipes \begin{align*}2\end{align*} \begin{align*}12\end{align*} \begin{align*}7\end{align*} Increased risk of developing intestinal polyps
Human hair (million hairs/L) \begin{align*}16\end{align*} \begin{align*}48\end{align*} \begin{align*}3\end{align*} None known, just disgusting

Jarny’s Current Water Cleaning System

Jarny’s current water cleaning system involves treating the water with a flocculent (a material that combines with large-sized particles in the water) and then letting the flocculent (with the large particle combinations) sink to the bottom so it can be removed. The remaining water is filtered through two filters: 1) sand, and then 2) a membrane with \begin{align*}1.0 \;\mathrm{micrometer}\end{align*} diameter holes.

References

Student Report

1. Use the water quality information in Table 1 to fill in Table 3 below.

Substances Present at Unacceptable Levels
Substance Amount over acceptable limit Rank substances by size \begin{align*}(1=\mathrm{largest})\end{align*} If there is a range, choose the size at the smallest end of the range Particles of similar size can have the same ranking Least expensive filter necessary
\begin{align*}Ca^{2+}\end{align*}
\begin{align*}Mg^{2+}\end{align*}
\begin{align*}CO_3{^{2-}}\end{align*}
\begin{align*}SO_4{^{2-}}\end{align*}
\begin{align*}Cd^{2+}\end{align*}
Bacteria (E coli)
Asbestos
Human hair

2. The best filter or combination of filters to add to Jarny’s water system are the following, in order:

3. Draw your design showing the water and its contents before and after passing through each filter in your design.

New Nanomembranes: Student Reading

The Desalination Problem

In the early1960’s, the United States government challenged the scientific community to discover an inexpensive yet effective method for removing salt from water (desalination) on a large scale. Desalination offered the potential to make water from the oceans drinkable, but at the time, desalination methods tended to be expensive and inefficient.

Accepting this challenge, Samuel Yuster and two of his graduate students at the University of California, Los Angeles created a porous material that simulated the movement of water through a living cell’s membrane. This material, a type of cellulose polymer, was called a reverse osmosis (RO) membrane.

Within a living cell, water travels across the cell membrane from an area of higher concentration of solute to an area of lower concentration. This natural process, called osmosis, continues until the concentration of solute on the inside and outside of the cell are equal. In reverse osmosis, water is transported through an artificial membrane from an area of lower concentration to one of higher concentration––the opposite of osmosis. The water goes against the “concentration gradient.”

Because this does not happen naturally, pressure (e.g. from a pump) is required to push the water through the membrane. By pushing water through this membrane, which salt and other ions can’t pass through, the water is filtered, leaving it pure and safe to drink. Reverse osmosis is the most expensive type of water filtration due to the constant energy required to pump water through the membrane at high pressure. Thus, even though we have a technique to make ocean water drinkable, the cost still prevents wide scale use.

Desalination technology has not changed much over the last fifty years…until now. Currently, there is a considerable amount of active research going into the creation of a variety of nanotechnology membranes, all with the goal of finding an inexpensive, but highly efficient method of removing salt from water.

Meet Eric Hoek

Eric Hoek, a researcher at the University of California, Los Angeles, has been making the news lately. Dr. Hoek is an assistant professor of civil and environmental engineering and is working with a company to patent a nanofiltration membrane that shows promise as an efficient and cost effective way to remove salt from water.

Dr. Hoek is working to create membranes with pore sizes of one nanometer. Because of the small pore size, the membrane blocks substances that are only a few nanometers in size.

Dr. Eric Hoek, Assistant Professor at the University of California in Los Angeles (UCLA) [1].

However, the membrane not only filters based on size but also based on charge. In other words, the membrane can stop particles of a particular size and of a particular electrostatic charge while allowing water through. He explains that one-nanometer pores are an optimal size because an electric field is generated that covers the entire pore. This electric field is adjustable in strength so that it can be “tuned” to reject charged items in solutes.

In addition, Dr. Hoek has figured out how to embed noxious substances in his nanomembranes––substances that will kill bacteria on contact! Dr. Hoek explains that at the nanoscale level, you can build substances into the membrane to give it certain properties. For example, by implanting into the membrane substances that are toxic to bacteria, you can effectively kill bacteria in water.

Dr. Hoek’s nanomembranes provide all of these new filtration benefits, but equally importantly, they filter water at much less pressure and cost than traditional reverse osmosis techniques. How does this happen? Dr. Hoek explains that channels can be built into the membranes that are surprisingly hydrophilic (attractive to water molecules). The hydrophilic channels attract water to pass it through the membrane, thus reducing the pressure needed to push the water through it.

Dr. Hoek plans to continue working on the development of smaller, “adaptive” membranes that can be adjusted through the combination of pressure-driven and electric/charge driven filtration. In other words, the membrane will allow you to have much greater control over the types of particles that can be filtered out. He also envisions creating membranes that are self-cleaning, which would reduce both maintenance and operating expenses. As Dr. Hoek tells his students, “Work on important problems, and your work will be appreciated. You'll do incremental work along the way to the goal, but you need the important problem to steer your work.”

Fred Tepper and His Company Argonide

Fred Tepper, founder of the company Argonide, invented a new type of water filtering membrane with pores containing nanosized ceramic fibers. What is the advantage of this type of filter?

Because the filter has such a large quantity of nanofibers, it contains a tremendous surface area. The larger the surface area in a filter, the greater amount of “dirt” the filter can trap and remove from the water. This type of filter can hold many times more dirt than an ultrafiltration (UF) membrane can. And it is highly efficient in capturing very small particles in a water stream. Ultrafilters are often used as prefilters for reverse osmosis (RO) membrane systems, taking out particles that can clog, or foul, RO membranes.

Fred Tepper, founder of Argonide [2]

Fred Tepper, founder of Argonide [2]

How Does Argonide’s Nanofiltration Membrane Work?

The nanoceramic filter is composed of several different filter materials. In effect, each filter contains multiple layers of pores, which makes it very efficient at trapping a wide variety of particle sizes through a nanoscale adhesion process (nanoadhesion). The filter is completely lined with an alumina-based material which, when reduced to nano-sized fibers, gives the fiber surfaces a very strong positive charge. Negatively-charged particles, like salts or ions that need to be removed from water, are attracted to the positively-charged fiber surfaces and are effectively removed from the water.

Nanoceramic filters can sustain high water-flow rates, and are very good at capturing small particles. In traditional filtration, to capture smaller particles, you need smaller pores in the filter. However, with the electroadhesive properties of nanoceramic filters, particles are attracted to and captured by the positive charges on the filter surfaces. For standard filters to approach the efficiency of nanoceramic filters, they must typically use a smaller pore size. This smaller pore size leads to increased clogging (fouling) of the pores and a lower flow rate of water compared to the nanoceramic filters.

Nanoceramic filters act as prefilters to reverse osmosis membranes since they are able to filter out particles that would typically harm or foul RO membranes. This allows the RO membrane to do what it does best: remove salt ions from water. The RO membrane will last much longer if it doesn’t have to trap bigger particles, and it will need fewer maintenance/cleaning cycles, which can extend its lifetime. Thus even though the nanoceramic filter does not perform reverse osmosis, it contributes to a larger technology solution that makes RO less expensive.

References

Glossary

alumina
A synthetically produced aluminum oxide \begin{align*}(Al_2O_3)\end{align*}
desalination
The process by which salt is removed from salt water (e.g. sea water) to make it drinkable.
electroadhesive
Two substances adhere to each other by the attraction of opposite charges.
electroconductor
A material that conducts electricity.
foul (fouling)
The process in which the substance(s) being filtered out block the pores of a filter, making that filter unable to transport water.
nanoadhesion
A process in which charged particles are (electrostatically) attracted to nanofibers that have been coated with a thin metallic film.
nanoceramic
A ceramic (inorganic, nonmetallic material) that is synthesized from nano-sized powders.
nanofibers
Fibers with diameters less than \begin{align*}100\;\mathrm{nanometers.}\end{align*}
osmosis
The passage of water through a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration until equilibrium is reached.
polymer
A long molecule that is made up of a chain of many small repeated units.
prefilter
A filter that cleans small particles out of the water, thereby increasing the efficiency of the next, smaller filter.
reverse osmosis
A method of producing pure water by forcing saline or impure water through a semi-permeable (selectively permeable) membrane across which salts or impurities cannot pass.
solute
A substance that is dissolved in another substance (called the solvent) in a homogeneous mixture. For example in salt water the salt ions are the solute and the water is the solvent.
ultrafiltration
Method for removing particles from water via a membrane filter. By applying pressure, water passes through this membrane.

Name_______________

Date_______________

Period_______________

Reflecting on the Guiding Questions: Student Worksheet

Think about the activities you just completed. What did you learn that will help you answer the guiding questions? Jot down notes in the spaces below.

1. Why are water’s unique properties so important for life as we know it?

What I learned in these activities:

What I still want to know:

2. How do we make water safe to drink?

What I learned in these activities:

What I still want to know:

3. How can nanotechnology help provide unique solutions to the water shortage?

What I learned in these activities:

What I still want to know:

4. Can we solve our global water shortage problems? Why or why not?

What I learned in these activities:

What I still want to know:

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