Public Library

Suggestions for School Talks

Get the younger students involved as a "volunteer operator." Dress him or her up in gloves, safety glasses, and an apron... they love it.

Use the information on this web site for your own presentations. Change the presentations depending on your objectives and the age of the audience.

Some suggested areas to stress in your talk: Grease and oil, metals, and organic pollutants. Discuss how these materials cause problems in the collection system (as with oils and grease) or how they may pass through the treatment process, upset the process, or cause problems with solids disposal. Explain how properly treated sludge contains essential nutrients and is a valuable soil conditioner.

For older high school and college students, include handling of waste solids, costs of treatment, time needed to treat, and energy needed to treat the waste. Discuss MSDS, chemistry, biology, and how polymers and coagulants work on surface charges to bring solids together.

All the above are only suggestions, make your presentations fun and customize them to your needs.

Two of the demonstrations are geared more for operators working at wastewater facilities and have access to process sludge (Sludge Dewatering Demo and Activated Sludge Settling). The other demonstrations use common materials to illustrate the wastewater treatment process.

For free posters and additional information, check out the National Center for Environmental Publications and Information (NCEPI)  Then click "Search the Catalog" and enter the following suggested keywords for public education information... "School, Posters, Elementary, Video."

There are also copious quantities of information on various water and wastewater topics. The items offered change, so visit frequently. All information is provided free of charge. Some suggested books for younger students:

Water Source Book - From the Water Environment Association
Magic School Bus Goes to the Water Works
Good luck with your presentations.

Lettuce Seed Bioassay

A bioassay is a test for pollution in which plants or organisms are used to assess the toxicity of a sample. It would be nearly impossible and costly to analyze a sample of unknown quality for every known toxic substance. If plants and/or organisms can grow and survive in a sample it is assumed to be non-toxic. In a sense, a bioassay tests for multiple contaminants at the same time, however if the test shows toxicity, the contaminate is not identified.

Below is a brief explanation of a lettuce seed bioassay. It is a simple, low-cost experiment that demonstrates how water contaminated with metals can be treated. Additionally, it shows how high concentrations of metals can suppress the growth of plants. Just as a bioassay test is preformed on wastewater treatment effluent, a lettuce seed bioassay can be preformed on suspected contaminated soil or water to see if it will affect the germination and growth of the seeds.

The test is rather simple to perform and it's up the individual to decide how elaborate they wish to get. In addition to showing contamination and then treatment in this experiment, different concentrations of metals can be used to find the lethal concentration at which 50% of the seeds do not germinate. If you want more information on the procedures, use your favorite Internet search engine and input "Lettuce Seed Bioassay."

In this demonstration, a copper sulfate solution will be used as the contaminant to simulate metals pollution. The polluted water will then be treated by water softener resin. By comparing a control to the treated and untreated water, the students will be able to determine if the water has been cleaned.

Materials needed:

• Copper Sulfate
• Two small containers to prepare the solution and treat it
• Water softener resin - I was given some from our local water softer distributor
• Plastic ziploc bags or petri dishes
• Pipette
• Butter Crunch lettuce seeds
• Analytical Balance
• Brown hand drying paper towels or any non-bleached paper that will not affect seed germination or growth.

Procedure:

1. Prepare the Ziploc Bags.  Copper Sulfate, Resin.  Place two layers of brown hand drying paper cut to fit inside the bag. At least three bags will be needed for a control, treated, and untreated solution. Mark the bags respectively. 
   
2. Mix the Copper Sulfate Solution. Mix the copper sulfate solution by adding 1000mg to one liter of water. It's recommended using unsoftened tap water that has sat for a few hours to dissipate the chlorine. Use this same water for the control assay.
3. Clean the Softening Resin. The water softener resin will have a light brown color that will dissolve into the water. This can be removed by cleaning. Place a heaping tablespoon of resin into a 100ml container. Add 40 to 50 mls of water. Swirl to mix and carefully pour out the water. Place the remaining resin onto some paper to absorb the last bit of water. Then place the resin back into the cup.
4. Treat the Copper Sulfate Solution. Place 30 - 40 mls of the copper sulfate solution into the resin. (Make sure there is enough solution over the resin so a portion can be pipetted without resin.) Swirl gently for about 15 to 20 minutes allowing the resin to absorb the copper metal ions. Students will observe the blue color dissipate as the resin absorbs the copper metal cations.
5. Dose the Ziploc bags and Add Seeds. Pipette 8mls of the control, untreated, and treated into the respective labeled ziploc bags. Then carefully add 10 butter crunch lettuce seeds to each bag. Let the assays sit in a rather darkened area for 5 days.

Photos below show the ziploc bag bioassay and a close up of germinated seeds from the 1000 mg/l copper sulfate solution. Notice the seeds germinated, but the roots didn't seem to grow with only a blackened tip on the end of the germinated shoot. (See the photo below under the "results" section to compare normal root growth and stunted growth.

Ziplock bio-assay. Closeup of seeds.

Results:
After 5 days, remove the assay from the darkened area. Take a sheet of graph paper and designate one line as a baseline. Remove all 10 spouts and any un-germinated seeds from the bag, then place the sprout-and-root division on the baseline. (If you look closely at the sprout you will be able to see a division between the root and the spout.) Also, place any un-germinated seeds on the baseline. By knowing the graph paper division spacing, it is easy to determine each root length. Results are recorded as root length and seed germination.

The results below show that 1000mg/l copper sulfate significantly affect root growth.

Treated seeds versus contaminated seeds.

Coagulation of Milk Proteins

Using common materials, demonstrate how milk colloids coagulate by adding an organic acid. In this demonstration, the ratio of milk, water, and acid is important. Your ratio may vary depending on your water's alkalinity, and the acid strength. Vinegar will give the most consistent results, but it's just a kick to squeeze a lemon at the demonstration for the younger students. For easier storage of metals use dry powdered milk. Just a suggestion, you may want to try this at home to make sure it works with your materials.

Materials:

• One beaker to hold 1 liter
• One of the following acids: 25 mils white vinegar, 50 mils lemon juice, or the juice of one lemon
• One stirring spoon
• Measuring utensils
• Milk (Either 120 mils 1% or 3 heaping teaspoons nonfat dry milk)
• Water

Procedure:
Measure 900 mils water and add your choice of 1% or dry milk. Stir the mixture and add the acid while stirring. Let settle. Some floc may settle and some may float.

The water will stay cloudy, but most of the milk proteins will coagulate under acid conditions. If there is too much milk, the proteins will not separate. Too little or too much acid and the milk won't coagulate.

It's my understanding that the milk proteins don't like the acid conditions. When the acid is added they come together and form a larger mass, which has less surface area exposed to the acid environment.

Metals Removal by pH Adjustment

This demonstration shows how dissolved metals are removed from wastewater by raising pH until the metal forms an insoluble complex. Two common metals are used in this demonstration; Aluminum (found in alum) and iron (found in ferric chloride). Alum and ferric chloride are used at wastewater treatment plants for phosphorus removal. Alum crystals can be easily found at grocery stores in the spice section. Ferric Chloride crystals can be obtained from laboratory chemical suppliers.

Materials:

• 500 ml beakers, jars, or other glassware
• Stir spoon
• A 10 to 20 ml pipette, or any other measuring device
• A base solution: Either household ammonia or 4% sodium hydroxide (20gms NaOH to 500mls water)
• A metal salt to precipitate: Either/or 1 level teaspoon crystals or 1 ml liquid FeCl3 or Alum

Procedure:
Label beakers for the metal salt. Add 500mls water to each beaker. Then add ferric chloride and/or alum to the respective beaker. Mix. Allow time for the crystals to dissolve. Add a base to raise pH allowing an insoluble precipitate to form. The amount will depend on your water's alkalinity and the acidity of the metal salt you use. (Eight to ten mls is what I used.) Be sure to stir the water while adding the base to mix completely. Use a circular motion, continuing for 5-10 sec. after the base addition. Slow the stirring, remove the spoon, and as the water slows on its own it provides the correct conditions to bring the metal precipitate together. Let stand and the metal precipitate will settle.

Additional Demonstration:
The treated water can be filtered through a coffee filter placed in its holder. If it plugs, try putting a half-inch sand in the filter first. Pour the mixture through.

Sludge Dewatering Demonstration

Demonstration Purpose: To show how polymer is used to thicken sludge and demonstrate liquid - solids separation.

Supplies needed:

• Polymer
• Isopropyl Alcohol (if making up dry polymer)
• Filtering device
• Belt press material cut to fit the filtering device
• Syringe or pipette
• Two mixing containers, 250 ml beakers
• Sludge container

Optional filter device:
The use of a buchner funnel is the more professional way to perform the test, but the Gatorade container explained below is inexpensive and transparent allowing students to see through. Make the filtering device by cutting the bottom from a Gatorade plastic container. Any container will do, as long as it has a design to hold the belt press material. One way to cut the belt press material is by using a gasket cutter. It leaves a small hole in the center, but by pushing the fibers back together you can't tell there was a hole. If you don't have access to either of the above, the sludge can be poured through a sample piece of belt press material, then capture the filtrate in a jar or pan below. Additionally, cheese cloth or nylons can be placed around one end of a PVC pipe to make a filter device.

The picture shows a Gatorade drink container filter device in use. The treated sludge is on the filter and the filtrate is in the beaker below.

Mixing up some polymer: 
If you don't have access to polymer already prepared, you'll need to mix and age some before the talk. Liquid polymer is not a problem to mix. However, dry can be hard to make up if your plant doesn't have any. For dry, make 100ml of 0.5% by putting a container on an analytical balance or top loader, taring the container, and weighing 0.5 grams of dry polymer. To dissolve the polymer, add 1 or 2 mls of isopropyl alcohol as a wetting agent. Next, quickly add 100 mls of water, cap, and shake. The solution will need some attention for the first 10 minutes or so. Just shake a few times to keep the polymer granules suspended. A few granules may stick to the bottom, but they always seem to dissolve. Now grab some sludge, and you are on your way to the talk.

Mix the Polymer and Sludge:
At the talk, measure 200mls of sludge in one of the premarked 250ml mixing beakers. Then draw the polymer in the syringe or pipette (our sludge took 11mls - there is 5mg per ml of polymer - for a dose of 275mg/l) and start pouring the sludge in the other beaker. As you pour, add the polymer as in the picture to the left. Then just mix back and forth (about 10 times). Students will see the polymer reacting with the sludge. Pour it in the filtering device to show separation. That's it.

Summary:
Weigh up the polymer in advance. The day of the talk, squirt in some alcohol and add 100mls of water. Get some sludge from the lab samples. Throw the stuff in the box, and you are on your way to give the talk.

Activated Sludge Settling Demonstration

A rather self-describing demonstration, but a good solid one. Simply take activated sludge and a settleometer (or any glass jar) to the talk. Show how zone settling "sweeps" the water clean as it settles.

Bring latex gloves, glasses, and a lab apron along to help demonstrate the potential hazards that wastewater plant employees are exposed to every day. Not to scare the students but to inform them.

Complete the demonstration by describing how the cleaned water is usually disinfected prior to discharge, and get some removal efficiency numbers to indicate how much cleaner it is leaving your plant than it was coming in.

Types of Solids in Wasterwater

This demonstration will show the types of solids found in wastewater; Grit, dissolved, colloidal, and settable, as will as grease and oil. It will be explained how their physical properties are used to remove them.

Materials needed:

• Sand
• Oatmeal
• Sugar
• Vegetable oil
• Milk (1% or dry)
• Five -500 ml beakers or any clear container such as pickle jars.
• Spoon to stir with.

Procedure:

1. Label the beakers; Sand, oil, oatmeal, milk, sugar
2. Add 500mls water to each beaker
3. For the dry materials (sand, oatmeal, sugar, and dry milk) place 1 to 2 teaspoons full of each material in their respective beaker. For liquid materials (milk and oil) place approximately 75 mls in their beakers.
4. Mix the milk and sugar. The oatmeal will wet on its own and slowly settle to the bottom. Note the speed the oatmeal settles compared to the sand.
5. Observe each beaker, note clarity and what happened to the material--settled, floated, or stayed suspended.
6. Provide discussion on each beaker.

Sand represents the material known as grit in wastewater (e.g., eggshells, sand, coffee grounds). This material is heavy and is removed by slowing the water to allow settling of heavy inorganic matter. If grit is not removed from wastewater it will settle in process tanks taking up space and its abrasive characteristics will wear pumps and equipment. Oil and oatmeal representing primary treatment After preliminary treatment, primary treatment removes the settleable and floatable matter. This is done by slowing the water to a still motionless state. In this undisturbed condition, floatable and settleable matter separates where it can be collected and removed from the top and bottom of a clarifer.

After preliminary treatment, primary treatment removes the settable and floatable matter. This is done by slowing the water to a still motionless state. In this undisturbed condition, floatable and settable matter separates where it can be collected and removed from the top and bottom of a clarifer.

Some solids are so small they stay suspend in water. Milk proteins are such solids. (You can coagulate the milk solids with 15 mls vinegar.) Other solids dissolve in water; Sugar, salt, and alum are some examples. Colloidal and dissolved solids are difficult to remove from water. Some can be removed by chemical addition, but it is preferred to use microorganisms, which use the solids as food. During secondary treatment, microorganisms are grown under optimum conditions. They eat the dissolved and colloidal solids and in turn multiply producing more microorganism mass. These microorganisms can be settled from the wastewater and removed. Thus, colloidal and dissolved solids are removed by converting them into settable microorganisms that can be removed from the water.

Summary:
Solids are removed during wastewater treatment by taking advantage of their physical properties (floating and settling). When the solid's physical properties make them difficult to remove, they are converted to a form that can be precipitated in biological secondary treatment.