Molecular Digestion: From Elephant’s Toothpaste to a Plastic Cow

Infographic: Organic wastes to anaerobic digestion to product/use. Image description under Featured Image Description Heading.
Phenomena: Video of anaerobic respiration as an alternative to landfills

Share the video Anaerobic respiration as alternatives to landfills in Wales focus thinking about anaerobic respiration and what is a digester.

Essential Questions:

  1. What is a digester?
  2. How are molecules broken down during digestion?
Materials List

Classroom Supplies (for 45 students)

  • Yeast
  • 45 Graduated cylinders
  • Dish soap
  • Jars
  • Food coloring
  • Water heaters
  • Trays
  • Optional: 1-2 Blenders
  • Optional: Cafeteria waste

Important Links

Featured Image Description

Infographic: At the top are the inputs in 4 boxes. The left box “Manure (e.g. dairy, swine, beef, poultry) with an image farm animals from back to front – a red cow, a black and white spotted Holstein dairy cow, a pink pig, and a brown chicken. In the second box, Wastewater Biosolids (e.g. municipal sewage sludge) with a graphic of two brown lumps. In the third box, Food Waste (e.g. household, restaurant, cafeteria, grocery, food production) with an image of food scraps in a pile green leaves in three shades of green, an apple core, egg shells, and a banana peel. In the right most box, Other Organics (e.g., energy crops, fats, oils, grease, crop residue, winery/brewery waste) with an image of a mug of beer with foam on top, a cluster of stalk plants, like hemp, and a yellow jug with black lid like cooking oil comes in. These boxes have arrows pointing down and toward the center of the graphic with a black box of white text that reads “Feedstocks can be digested singularly or in a combination (co-digestion) below that is a bubble with two black pucks with domed tops with the label Anaerobic Digestion. Two arrow lead down from this bubble one to the left and one to the right. On the left the arrow leads to “Biogas” which is represented by two blue flames. Joined to the Biogas bubble are five squares. Bioproduct Feedstock (e.g. bioplastics) with an image of a white plastic chair and two different sized plastic bottles in white and blue. Below that is a box labeled Electricity with a yellow lightening bolt graphic. To the right is a box with two red flames labeled Heat. The next box is Vehicle Fuel with a graphic of a waste management collection truck. In the final box is Renewable Natural Gas with a graphic that shows white pipes connected to large white cylinders. The arrow from the Anaerobic Digestion that leads to the right is another domed puck in black with a gray area to the front with a brown pile in front of it labeled Digestate. It also has five boxes connected to it. The leftmost box is labeled Organic Fertilizer and has a dark brown pile next to a grey bag. To the right is a box labeled Animal Bedding it has an image of two dairy cows (Holsteins) laying in brown bedding. The next box has a graphic of a pile of lumber-like material and is labeled Other Products (e.g. building materials). The 4th box is Crop Irrigation and has a graphic of an aerial field sprinkler as seen from the end. The final box is Horticulture Products (e.g. soil amendments, peat moss replacement, plant pots) it shows a brown pile with a 4 square brown plant starter pot.

Lesson 2 of 10 / Time: 1-2 periods of 60 mins

This lesson presents the question “What is a digester?” to students. Students learn about chemical reactions and learn through observations of “elephant toothpaste” lab. As an optional extension, students can explore a Plastic Cow Digester (students put blender waste from the cafeteria into the Plastic Cow anaerobic digester) or Bacteria on a Petri Dish.

Waste to Power

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