Just as Philadelphia developed a drinking water system to ensure a healthy supply for keeping people healthy, it also had to design a system for collecting and disposing of wastewater– everything that we flush and send down the drain as “used” for public health. It is a big and complicated challenge to engineer a system of pipes and pumps to carry human and industrial waste away, but also to clean it up , decontaminate it and keep the clean water flowing. Philadelphia Water meets that challenge all day , every day at its three wastewater treatment facilities.

As cities grow, public utilities and all the people that make it work have to continually meet the challenges of keeping people healthy– a new way to look at the meaning of “out of sight, out mind”

As cities like Philadelphia burgeoned during industrialization,  polluted streams carrying unsanitary waste were encapsulated in a system of underground pipes. This complex system exists right under our streets and mostly unseen. From the perspective of individual use, We have learned how water is taken from the river, treated to make it potable (safe to drink) and distributed to our houses. We count on that water being available to us when we turn on the faucet. Now we will explore what happens to the water after it goes down the drain, or flushed down the toilet?

Slide 3 shows an image of a historic pipe plan for one of the oldest parts the city. The pipes are shown in blue and reveal what is  under our streets. NOTE: This is actually an old plan of center city showing drinking water pipe infrastructure but we are using it to help students  visualize the vast network of pipes under our streets.

Ask the students what they notice about the plan. This is intended to direct the students to think about what is underground, below their feet, and the beginnings of the system of pipes and sewers that move water through the city.

What does our underground system look like? If we dug a viewing hole in the street, what would we see? 

Slide 4: Exploring the term “unsanitary wastewater” ask students  what they think phrase means?

Have students brainstorm all of the types of unsanitary  of wastewater that might be generated at home or at school

• Kitchens – sinks, dishwashers
• Bathroom – toilets, sinks, tubs/showers
• Classroom/janitorial slop sinks

Slide 5: Where does all this unsanitary wastewater go after it goes down the drain or we flush it down the toilet ? Pipes and drains in buildings and houses are connected to what?

Why don’t we send this unsanitary wastewater directly  to the river anymore ? (Think back to our previous lessons and the Barber pollution data)

Slide 6: Introduce Wastewater Treatment

Have a brief discussion about the following terms Bacteria, density, and gravity and explain how they will learn how these things help to clean up our unsanitary wastewater.

Answers:

Bacteria: microscopic organisms, digest many organic materials found in the water

Density: mass, allows heavier impurities to sink and lighter ones to float, separating them in the water. This is called sedimentation or flotation.

Gravity: helps by pulling heavier contaminants to the bottom during sedimentation

Prepare the next part of the activity with a clear water bottle, water and clumps of debris (you can find clumps of soil, but  coffee grounds will work well too)

Slide 7:  Have a clear water bottle containing water with soil clumps or other debris that will settle after being shaken.

Sedimentation: This is the first major step in the treatment process

Shake up the water  bottle and allow the water to settle. While waiting for the water to settle, introduce the concept of density.

The material that was denser than water sank to the bottom. The material that was less dense than water floated to the top.

Note for the students that what we are observing is only the material that we can see in the water. There are other elements dissolved in the water that are removed in later stages of the treatment process.

Slide 8: Wastewater treatment – Video showing the water water treatment process in action

Slide 9: The diagram shows the wastewater treatment plant. A link to a pdf copy can be shown and enlarged on the screen.

There is a link to a graphic organizer that students can use to both draw and write their description of each step as you review the treatment process.

In describing the treatment process the students are accessing multiple scientific principles. Using the pdf as a presentation, have students complete the graphic organizer.

Vocabulary terms are listed in the right menu.

Slide 9: Summarize as a group the different processes at work. Use students definitions.

Slide 10-11: This is an opportunity to review microbiology and the role of bacteria in the wastewater treatment process, but also the role of bacteria in other contexts/environments. Discussing digestion, decomposition, fungus, or other related Life Science topics can be recalled.

The wastewater treatment process relies on natural biological processes as the central force in the process.

Slide 12: Asks the students to think about what might they might be able to do at the source (drains and toilets)  to help the treatment process ?  Check out flushable wipes mini-unit for ideas, thinking of other things that should be flushed down the toilet.

Here is an good activity to show why flushable wipes are not flushable!

Flushable wipes clog the sewer system and challenge the treatment of wastewater. This activity allows students to test the definition of flushable  and see the impact on the environment.  The activity takes one class period to complete. Materials needed:

• two small, clear plastic bottles (juice, water, gatorade, etc) [This can also be done using clear plastic cups or small cereal bowls. If you do not use bottles with caps, you will need a stirrer to agitate the water.
• toilet paper squares slightly smaller than a post-it  (Sample A)
• wet wipes squares – same size as toilet paper (Sample B)
  • wipes can be reused between sessions by air-drying if they are still in whole pieces
• small ziploc or other bags to separate the samples

View the activity here:  Is It Flushable?