Lesson: Introduction to Water Chemistry

Contributed by: GK-12 Program, School of Engineering and Applied Science, Washington University in St. Louis

Photo shows a water dropped into a body of water and its surrounding nodal lines.
Improving water quality is an important aspect of environmental engineering.
copyright
Copyright © US Department of Agriculture http://www.ars.usda.gov/pandp//docs.htm?docid=18526

Summary

Students are presented with examples of the types of problems that environmental engineers solve, specifically focusing on water quality issues. Topics include the importance of clean water, the scarcity of fresh water, tap water contamination sources, and ways environmental engineers treat contaminated water.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

The environmental engineering topics concerning water quality are highly relevant issues facing engineers, as well as communities and ecosystems at large. Example issues include the impact of global warming on the Earth's fresh water supply, the sources of groundwater contamination, and the innovative technologies employed by environmental engineers to address groundwater contamination.

Learning Objectives

After this lesson, students should be able to:

  • Explain the importance of maintaining fresh, unpolluted drinking water supplies.
  • Describe sources and consequences of poor water quality.
  • List and describe new and existing water remediation technologies.

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Introduction/Motivation

(In advance, make copies of the Introduction to Water Chemistry Worksheet and prepare to show the class the attached 17-slide Introduction to Water Chemistry Presentation, a PowerPoint file.)

Water, or H2O, is a small yet complex molecule that can be linked to almost every organism and chemical process. Humans rely so heavily on water that it is essential that we maintain clean drinking water supplies. This presentation focuses on the importance of water, sources of water contamination, and ways environmental engineers help to clean contaminated water.

(Continue on to present students with the information found in the Lesson Background section.)

Lesson Background and Concepts for Teachers

(Hand out copies of the worksheet for students to complete during the PowerPoint presentation. The slides are "animated," so clicking the mouse or space bar brings up the next item.)

Slide 1: Introduction to Water Chemistry

Slide 2: Why Water? Clean water is essential to our lives! Review the interesting facts about water and U.S. water consumption. These are just some of the reasons why it is so important to maintain high water quality.

Slide 3: The Water Cycle: Thoroughly describe the water cycle if students are unfamiliar with it. Otherwise, just highlight the main processes, such as condensation, precipitation and evaporation. Water stored in oceans is extremely salty, making it undrinkable. When water evaporates and returns as rain or snow, it is clean because salts and other minerals are left behind during the process. A great amount of freshwater storage is in mountain ice caps. Global climate change (mentioned in the Introduction to Environmental Engineering lesson) is melting ice caps on mountaintops and at the poles, removing the Earth's last source of stored freshwater.

Slide 4: Key Terms: To continue the discussion on water quality, review with students the definitions for: contamination, purification and remediation.

Slide 5: How do we purify water? Larger-scale, industrial methods to clean large amounts of water include reverse osmosis, ultra-filtration and electro-deionization. Smaller-scale, household methods include filters and boiling. Often, these processes are combined in order to effectively remove contaminants. Details are covered in the next slides.

Slide 6: Reverse Osmosis: Reverse osmosis is one type of filtration method. The two left images show examples of reverse osmosis membrane layers. The two right images show example set-ups for the reverse osmosis process for large scale water purification. The system is composed of a series of membranes and pumps. What do the membranes do? (Answer: They separate things or keep things out.) As the water passes through the membrane, the larger contaminants are left behind, leaving cleaned water. (As necessary, show students two online diagrams on how reverse osmosis works; see the URLs in the Additional Multimedia Support section.) Note that government regulatory agencies permit some chemicals to be added to water, such as chlorine (for disinfection) and fluorine.

Slide 7: Filters: Sand filtration is a natural filtration process that occurs in groundwater systems, and is often used when treating natural water resources, such as rivers, to make them clean enough for drinking water. Water pitchers with activated carbon filters are used for small-scale water purification at home.

Slide 8: Activated Carbon: Activated carbon is an important component of many home water purification systems. Looking at the top left image, poultry manure pellets (top pile) are converted through a manufacturing process into activated carbon pellets (left pile), and then ground into either a granular (center pile) or powdered (right pile) form. A magnified image shows the tiny pores through which water flows through the activated carbon and out the filter. If desired, show students online illustrations of how activated carbon pores provide increased surface area for gas and chemical pollutants to adsorb; see the URLs in the Additional Multimedia Support section.) A system of water filtration includes many layers of materials through which water flows. In this one, the activated carbon layer is the fourth level from the bottom, and other layers include pebbles, palm fiber, alum, gravel, chlorine and sand.

Slide 9: Boiling Water: Boiling water used to be the only way to purify water, but now is considered the "last resort" purification method. Boiling water destroys most bacteria and viruses, but can still leave behind harmful chemicals.

Slide 10: Contamination Sources: Common human-created water contamination sources include leaking sewage, leaking underground fuel storage tanks, agricultural chemical runoff, landfills and dumps, and industrial waste. As world population has increased over the years, the magnitude of freshwater contamination has generally increased as well. Increased population corresponds to increased demand for products and services, and many of which involve chemicals. Furthermore, new chemicals are often developed as part of technology advancement. Despite efforts to prevent chemical releases to the environment, the presence of chemical in the environment is inevitable, even with environmental regulations enacted in many countries. Details on contaminant sources are covered in the next slides.

Overall, the top water pollution sources are: pesticides; fertilizers/nutrient pollution; oil, gasoline and additives; mining; sediment, chemical and industrial processes; plastic; personal care products, household cleaning products and pharmaceuticals; sewage; air pollution (chemicals deposited out of air into water), carbon dioxide (absorbed into water, making it more acidic); heat (a water pollutant); noise pollution (human ships and sonars affect animal communication, navigation and hunting).

Slide 11: Sewage Spills: In the U.S., 850 billion gallons of raw sewage are dumped into rivers, lakes and oceans by leaking and overflowing sewer/storm systems. In developing countries, it is common for sewage to be discharged directly into bodies of water without treatment.

Slide 12: Underground Storage Tanks: Have you ever seen large trucks pumping gasoline underground at gas stations? In the U.S., most gasoline is stored underground in large storage tanks. To help gasoline burn better, we used to add chemicals that if ingested could cause birth defects and other illnesses in humans. The left image shows a newly installed underground storage tank. The right image shows an old, corroded, leaking tank that was polluting groundwater.

Slide 13: Pesticides and Herbicides: Pesticides and herbicides contain harmful chemicals with the purpose to kill insects and weeds. When it rains, the sprayed pesticides and herbicides on crops (and lawns!) are transported by runoff into groundwater and nearby bodies of water. If ingested in large amounts, these chemicals can cause birth defects in humans. Related to this, fertilizers also contain chemicals that enter groundwater through soil runoff. Excess nutrient levels overstimulate the growth of aquatic plants and algae and disturb organism balance.

Slide 14: Industrial Waste Spills: Hazardous liquid waste might include solvents, heavy metals and radioactive materials. In the U.S., 34 billion liters per year of hazardous waste is injected deep underground with the intent that it will be kept away from our water supplies for a long period of time; however, some of these pollutants have been detected in underground water supplies in many states. In developing countries, most wastewater from industrial plant chemical processes is added to sewage wastewater, which more often than not, is discharged directly into rivers and streams without treatment. Environmental engineers have developed various water remediation techniques to improve water quality at contaminated sites (see next three slides).

Slide 15: Pump-and-Treat: Several technologies have been developed to help treat groundwater contamination sources. In a pump-and-treat system, injection wells are placed near the start and end of an underground water source. Contaminated water is pumped up and sent to a treatment facility; once cleaned, it is pumped back underground. This process works well initially, but becomes less efficient over several years.

Slide 16: Permeable Reactive Barrier: Using permeable reactive barriers is another common method for purifying water at an underground water contamination source. The process is similar to reverse osmosis. The barrier is essentially a large membrane, made of some reactive material, such as activated carbon or iron (oxidation reaction), that lets clean water pass through and traps contaminants. Problems with this method include: it takes a long time for all the contaminated water to pass through, the reactive material must be replaced once the active sites for adsorption are saturated, and its use is limited to contamination sites at shallow depths.

Slide 17: Nanoparticle Injection: This newer water remediation technique involves nanotechnology. Have you ever seen an old, rusted piece of metal? Rust is produced when water reacts at the iron surface. The same chemical reaction happens when iron nanoparticles make contact with contaminated groundwater. (Nanoparticles are so tiny we cannot see them. A billion nanometers are in one meter.) Instead of rust forming at the surface of the iron nanoparticles, the reaction breaks down contaminants into smaller, less harmful species. Researchers are still figuring out issues with this method, such as how to stabilize the nanoparticles so they can travel underground easily.

Vocabulary/Definitions

adsorption: The binding of atoms, ions or molecules from a gas, liquid or dissolved substance to a surface, such as on the surfaces of pores of activated carbon.

contamination: The presence of a minor component in another chemical or mixture.

groundwater: The water under the Earth's surface, consisting largely of surface water that has seeped down and is stored within saturated soil and rock. (In this usage, saturated means full of water.) The source of water in springs and wells.

purification: To make something pure or to cleanse.

remediation: To correct something that has gone bad or defective; to provide a remedy.

Associated Activities

  • Chromatography Lab - To increase students' awareness of possible invisible pollutants in drinking water sources, they investigate the chromatography process using the ink from markers. This concept helps them understand the environmental engineering water remediation process by which pollutants can be removed if they can be separated from a water source.

    Watch this activity on YouTube

  • Water Remediation Lab - Students collect data on how well activated carbon filters purify chlorine-contaminated water. Groups prepare chlorinated water samples, pass the samples through Brita® water filters, and measure chlorine concentrations over time. After gathering and graphing data, students evaluate the effectiveness of this engineer-designed household water remediation method.
  • Red Cabbage Chemistry - Like environmental engineers working on water remediation or water treatment projects, students learn about pH—an extremely important chemical property—and how to measure the pH of some common household liquids using red cabbage juice, a natural pH indicator.

Attachments

Assessment

Worksheet: Have students complete the Introduction to Water Chemistry Worksheet by writing definitions and answering questions while the teacher presents the PowerPoint presentation. Collect, review and grade the worksheets to assess student engagement and comprehension of the material.

Additional Multimedia Support

Show students two online diagrams that illustrate the concept of osmosis through semi-permeable membranes and why these membranes are able to filter out impurities in water, under the Osmotic Balance and Free Water Passing Through Membrane Pores sections at the at the Equistat (Isle of Man) Limited website: http://www.equistat.co.uk/science/understanding_fluid_comp.php.

Show students online illustrations of how activated carbon pores provide increased surface area for chemical pollutants to adsorb at: http://innofresh.wordpress.com/2011/01/04/carbon-vs-activated-carbon-for-use-as-an-odor-absorber/ and http://www.capitalcarbon.in/process.html.

References

Jeantheau, Mark. A List of Water Pollution Causes. Published September 6, 2005. Grinning Planet: Saving the Planet One Joke at a Time. Issue No. 141. Accessed October 24, 2012. (Comprehensive list and description of the top point and nonpoint water pollution sources.) http://www.grinningplanet.com/2005/09-06/water-pollution-causes-article.htm

Reddy, Krishna R. Physical and Chemical Groundwater Remediation Technologies. Chapter 12 in Overexploitation and Contamination of Shared Groundwater Resources: Management, (Bio)Technological, and Political Approaches to Avoid Conflict. Editor: Christophe J.G. Darnault. Netherlands: Springer, 200; pp 257. http://link.springer.com/content/pdf/10.1007%2F978-1-4020-6985-7_12

The Water Cycle – Water Science for Schools. Last updated October 15, 2012. U.S. Geological Survey, U.S. Department of the Interior. Accessed October 24, 2012. (Water cycle diagram and information on the distribution of the Earth's water) http://ga.water.usgs.gov/edu/watercycle.html

What You Should Know about Water. Read, Learn, and Know about Water, AllAboutWater.org. Accessed October 24, 2012. http://allaboutwater.org/

Contributors

Jessica Ray; Carleigh Samson

Copyright

© 2013 by Regents of the University of Colorado; original © 2010 Washington University in St. Louis

Supporting Program

GK-12 Program, School of Engineering and Applied Science, Washington University in St. Louis

Acknowledgements

This curriculum was developed with support from National Science Foundation GK-12 grant number DGE 0538541. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: June 3, 2017

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