Chapter 3C: How is water treated?

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To the teacher

Purpose

To help students recognize there is a water cycle made by humans as well as the hydrologic cycle made by nature; and to examine the treatment of water before and after use.

Subject areas

Science, Environmental Studies, Social Studies, Art, Language Arts

Procedure

1. Review the concept of the hydrologic cycle and point out to the students that we have had to create our own water cycle so that we can treat water before and after we use it.
   
   
   • Remind them of the point made in the last chapter, "Pollution," that because of new chemicals and other substances being added to water, nature's purification cycle needs help from humans to keep water pure.
     
     
2. Depending on the area of Canada you live in, students may be served by individual septic tanks or water and wastewater treatment plants. Chances are they will not have had occasion to think too much about their water supply and how it is cleaned. Lead a discussion about the necessity of cleaning our water both before and after use.
   
   
3. The topic of wastewater treatment can generate a great deal of interest. If possible, arrange a visit to a plant or invite a guest speaker into the classroom. When students realize how much water is wasted by them, they may be more conscious of misuse.

Vocabulary aeration alum chlorine coagulation effluent filtration fluoride infrastructure purify reservoir sedimentation sewer

References

• Freshwater Series A-3: Clean Water – Life Depends on It!
• Freshwater Series A-4: Water Works!
• A Primer on Fresh Water: "Water – How good is it?"
• Water: No Time to Waste – A Consumer's Guide to Water Conservation

Student information

Can dirty water be cured?

If you are like most people, you have not given ten seconds of thought to how water got into your house or why it comes out of a tap ready to drink whenever you feel like it. And you probably never think that the wastewater you flush through your toilets or let run from your drain will turn up again in your drinking water supply. But it does. It's like the old saying, "what goes around, comes around."

Except for areas where people get their drinking water directly from a well, most water that comes into Canadian homes has been purified or treated at a water purification plant so that we can drink it safely. Your homes and your school make up one part of a community water cycle made by humans.

And, once the water goes down the drain, it travels through wastewater pipes or a sewer system to another treatment plant, this time a sewage treatment plant, where it gets treated again before it is released into nature's cycle.

Another water cycle

Water is collected in a reservoir or lake, piped to a water purification plant, treated for our use, and pumped through pipes or water mains to our houses. After we have used the water (or sometimes wasted it), it leaves our houses through sewer lines and heads to a sewage treatment plant. There it goes through another treatment before it is released to nature's water system to be recycled yet again. And on it goes.

A word of caution here – both treatment plants are very different; it wouldn't do to get them mixed up!

Look at the diagram that follows and trace the route that water can take.

Other areas of Canada rely on individual wells and septic tanks – but this is still part of another cycle – from your well, to the taps in your house, and out to the septic tank.

A closer look at where your water comes from

If you get a chance, try to visit a water purification plant and find out firsthand the treatment process water goes through before it begins its trip to the taps in your house or the water fountain at school. Remember, no matter how fresh water is, it usually picks up some impurities as it goes through the hydrologic cycle.

What happens in a water purification plant:

1. First there must be a source of water nearby. This could be a river or lake, or it could be a reservoir created by the building of a dam to hold the water back.
   
   
2. As this water is needed, it is carried by pipes into a purification plant where it is made safe for drinking by going through the following treatments:
   
   
   • First of all, water is sprayed into the air where it mixes with oxygen. This step is called aeration. The oxygen helps bacteria grow which in turn destroy some of the impurities.
     
     
   • The next step is coagulation where alum is added to the water. Alum forms sticky particles to which dirt and other particles cling.
     
     
   • In the next stage, sedimentation, these impurities settle to the bottom of a settling tank.
     
     
   • The water then goes to a filter tank where filtration occurs. Any impurities left in the water are filtered out through layers of sand, charcoal, and gravel.
     
     
   • In many communities, chlorine is added to the water to destroy any disease-causing germs that may remain; and in more and more communities, fluoride is added.
     
     
   When water has gone through these steps, it is ready for your use. The clean water is pumped to large storage tanks and from there it is pumped into pipes that carry it to your homes, schools, businesses and industries.

What happens next?

So, that's the first half of the community water cycle. What happens to the water after it has been used and leaves your house or school? This is where it gets the name "sewage" or "wastewater," and goes into another set of pipes to be taken to the sewage treatment plant. As the name tells you, this is where water gets another series of treatments before it is released back into the environment.

Let's hope that your community or city has a method to treat waste and that waste does not get dumped directly into the nearest body of water.

A closer look at a sewage treatment plant

Wastes can be easily removed from the majority of our homes, just the turn of a handle or tap and whoosh! It's gone. Where does it go from there? To a sewage treatment plant where it goes through one or more of the following steps:

• Primary treatment – sand, grit, and other solids are separated from the liquids by screens and settling tanks.
  
  
• Secondary treatment – air is added (aeration) to stimulate the growth of bacteria to consume most of the remaining waste materials.
  
  
• Tertiary or advanced treatment – chemicals are added which remove nutrients that stimulate algae (tiny plants that use up oxygen needed by fish).

Sludge is what is left behind after wastewater is treated. When harmful microorganisms are removed, sludge is either burned, taken to landfills, or used to condition soil.

Processed wastewater is called effluent or "greywater." It is disinfected, tested, and returned to rivers and streams where the cycle begins again.

You would not want to drink this processed wastewater right away. But by the time it comes gushing out of your taps again it has been given one more thorough cleansing back at the water purification plant. Remember, don't get the two treatment plants mixed up!

As a human race, we haven't looked after water very well. You've seen how we have spoiled the pristine quality of many lakes and rivers, and you know we would not be very healthy if we had to drink water straight from the lakes or rivers on our doorsteps. Fortunately, this is not the case. Our own water cycle (water purification and sewage treatment plants) helps keep us free from diseases which trouble developing countries.

Learning activities

Activity 1 – Social Studies

One of the best field trips some of us have been on hasn't really been to a field. Quite the contrary. It has been to a sewage treatment plant. Ask your teacher if you can arrange a tour to such a plant or to a water purification plant.

• Plan your trip. Review any information you can find about these plants. Prepare questions in advance so that you can learn what it is you wish to know.
  
  
• For example, how many kilometres of sewer pipes or water mains service the area where you live? How much does it cost? Find out about the taxes charged to individual houses. How many people work in a plant? What do they do?
  
  
• In many cities the water mains or infrastructures are getting old and worn out. The costs are high to replace these pipes. Is this the case where you live?
  
  
• What about lead pipes? Are these being used where you live? Why? Why shouldn't they be used?
  
  
• Contact the proper authorities. If a field trip is not possible, invite a speaker to visit your class. You will probably find that most water supply agencies are very eager to talk about these issues as they are becoming serious problems in many areas in Canada.
  
  

Activity 2 – Environmental Studies

In Ocala, Florida, the municipality has a great use for its "greywater," which is water that has gone through a treatment but is not good enough for humans to drink. The city officials there just direct this water to their municipal golf course where it is used to water the greens and the fairways.

Is there a similar program where you live? Could there be? Is this a good use of processed water? Check to see if some industries reuse water within their complexes before releasing it to the sewage treatment plant.

Think about it. Do we really need to use "fresh water" from our water purification plants to water our lawns, wash our cars, and flush our toilets? Can't we use greywater? How much would this save in tax dollars?

Activity 3 – Language Arts

You would be surprised at the number of cities and communities in Canada which dump untreated wastewater straight into the harbour or nearest body of water. It's not a pretty sight. In Great Britain, for example, where many beaches on the ocean are becoming too polluted to swim in because of untreated waste, one solution was to build longer sewer pipes and dump the waste farther out at sea! What do you think of that solution?

Research to find out where in Canada untreated waste is dumped directly into the ocean or nearest body of water. Write about it. Find out why these places do not have sewage treatment plants. In one Canadian city, everybody wants such a plant but nobody wants it near them. This is called NIMBY, an acronym for "Not in my back yard," or GOOMBY, "Get out of my back yard."

Become a community activist. Write a letter to your municipality or newspaper about NIMBYs or GOOMBYs in your region.

Think up your own acronym for people who do not want to become good environmental citizens.

Option: Imagine that you are a river flowing through one of those communities. Write a short story or a couple of paragraphs describing how it feels to you to have all this junk dumped in the middle. Be imaginative!

Think about some questions you would like to ask those people who continue to allow the dumping of raw sewage into water bodies.

Activity 4 – Science

Research to discover why old-fashioned lead pipes are a problem. What damage have they caused? What can be done about them? What can they be replaced with? What kinds of pipes service your community?

Activity 5 – Environmental Studies, Art

Trace your own community water cycle. If you are like most people, you have no idea of the route water takes to get to your house and the route wastewater takes when it leaves your house and goes to the treatment plant.

Find out from your local water works department and draw your own diagram showing the class where water comes from and where wastes go.

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