It's A Gas

It's A Gas
Adapted from Recycle Reuse, by Cornell Cooperative Extension of Rockland County

Back to Trash Goes to School

GRADE LEVELS: 9-12

SUBJECT AREAS: physical science and earth science

CONCEPT: Gases are produced when waste degrades.

OBJECTIVE: To build an organic waste methane generator. To learn by running a scientific experiment, and to see what happens when people alter nature's way of recycling.

MATERIALS:

Copies of attached data recording sheet and graph for each member
Measuring cup
Wax pencil
3 one-gallon jugs, glass or plastic (1 painted black or dark-colored)
1 rubber stopper with one hole
1 rubber stopper with two holes
2 three-inch long pieces of glass or copper tubing
2 18-inch lengths of rubber tubing that will fit over the glass or copper tubes
1/2 gallon of vegetable food wastes, chopped fine
graph paper for charting
handout: Data Sheet: Methane Generation

KEYWORDS: methane, landfill

BACKGROUND:
The teacher should:

1. Collect materials necessary to build a model digester.
2. Paint one of the jugs before the meeting.
3. Involve members in discussing what methane gas is, how it is generated and how it can be used.
4. Assign tasks independently or plan to do together as a group.
5. Discuss where the digester should be kept once it is built
The students should:

1. Discuss how methane gas is produced and how it can be either a hazardous or valuable by-product of landfills.
2. Discuss how to build a model methane digester.
3. Follow the steps to build the digester.
4. During the next 12 weeks, keep track of the water level in the third jug. Record your findings on the data recording sheet.
5. Use the data you gather from the experiment to draw a line or bar graph on graph paper. (Graph the gas generated vs. time). What factors influence the speed, amount and concentration of gas generation?

PROCEDURE:
1. Fill the painted jug at least half full of vegetable material. Finish filling to the top with water.

2. Fill the second gallon jug with water.

3. The third jug should be clear enough to see the water level. Use the measuring cup to fill this jug with water one cup at a time. After each cup, mark the water level on the outside of the jug with a wax pencil. When the jug is filled and marked, pour the water out. Number the cup markings from bottom to top. (The experiment begins with this jug empty).

4. Fit the glass or copper tubing into the stoppers:
The first stopper has one hole, and the tubing extends through the hole into the gas layer at the top of the jug. The second stopper has two holes: one for the tube coming from the first jug, and the other for the tube connecting the second and third jugs. The tube from the first jug extends into the gas layer at the top of the second jug. The tube leading to the third jug extends down into the water of the second jug, reaching almost to the bottom of the jug. The third stopper has just one hole, for the tube coming from the second jug.

5. Insert the stoppers and connect the bottles.

6. Place the entire apparatus where it will not be disturbed or moved for 12 weeks, but where it can be examined regularly by the group.

7. At the end of the 12th week use a methane gas meter to measure the methane concentration in the second bottle.

8. Hints:

A methane gas meter is helpful but not necessary to measure the amount of gas generated at the end of 12 weeks. Check to see if you can borrow one from a local gas company.
The amount of gas can be measured without a meter. Note that the methane generated in the dark jug moves as a gas to the second jug where it displaces water. That water flows into the third jug. Each cup of water that collects in the third jug represents 14 cubic inches of methane gas.
Factors that influence the amount of methane produced include:

FOLLOW-UP:
Find out if your community landfill is collecting methane for use, or venting it to prevent explosions.
Repeat the experiment, varying environmental conditions to see how they affect methane generation.

- Change the composition of the waste used.
- Place the model generator in a location where the temperature is different.
- Don't add water to the waste.
- Replace the painted jug with a clear one, and put the generator in a well-lit spot.
- Compost some wastes before putting them into the generator.

A model digester, accompanied by copies of the data sheet, could be used as a fair project.

Data Sheet: Methane Generation

Date of Measurement
# Days Since Experiment Started
Water Collected This Day
Total Water Collected
Gas Displaced (1 Cup water = 14 in. ³ methane

Date of Measurement	# Days Since Experiment Started	Water Collected This Day	Total Water Collected	Gas Displaced (1 Cup water = 14 in. ³ methane