"Behold thy Landfill" © 2010 Justin Ritchie


A landfill is a big, deep hole. Items placed in a landfill sit there forever, producing methane gas, which contributes to global warming.  To prevent this, San Francisco aims to divert as much waste as possible to recycling and composting facilities. In just 2-3 months, a banana peel in the compost facility can become compost, rich in nitrogen and other nutrients directly benefiting plants, making a rich soil for farmers. In this lesson, students learn about decomposition and landfills, and learn how to sort their trash into the appropriate bin.

PLEASE NOTE: The content of this lesson is specific to the recycling and composting services and regulations in San Francisco County, however waste sorting is environmentally important wherever you live. Please research your municipality’s waste sorting guidelines to customize this lesson to your area.


Students will:

  1. learn to sort waste items into appropriate waste receptacles in San Francisco (Compost, Landfill, and Recycling).
  2. understand why it is important to reduce the amount of waste being sent to landfills.
  3. learn that compostable items decompose to become part of the soil.
  4. help San Francisco meet its waste-free goal.
  • A variety of clean, recyclable, compostable, and landfill waste items. Below are some recommended materials:
    • Compostable items: chop sticks, a pear, a waxed cardboard takeout food container, a spoon with the word "compostable" on it, a greasy paper plate, a napkin, a tissue, a pizza box, a paper bag
    • Recyclable items: a glass jar, an egg carton, a piece of junk mail with a plastic window, a soda can, burrito aluminum foil (best rolled in a ball), a coffee cup, plastic to-go drink cups, cardboard, paper, plastic to-go food containers (emptied of food), milk cartons, bubble tea cups
    • Landfill items: a Ziploc bag, a sponge, a twisty tie, a chip bag, a snack wrapper, a straw, a pen, a 3-ring binder
    • Teacher tip: Plan to do this activity after lunch, and task your students to save one thing from their lunch that otherwise would have been thrown out. Although it won’t be as clean, it will provide real examples and good variety.
  • A few examples of reusable items (reusable water bottle, cloth grocery bag, to-go coffee mug, reusable spoon & fork, reusable salsa dishes, reusable plates, etc.)
  • A box for landfill waste
  • A clean and empty compost bin
  • A clean and empty recycling bin
  • A bin of finished fully decomposed compost
  • Large Landfill, Composting, and Recycling signs, one for each bin
  • Landfill Photograph (projected digitally)
  • Map of where San Francisco sends waste (projected digitally)
  • Colors of Conservation coloring sheet (1 per student, for younger grades)
  • Student Sustainability Action Plan (1 per student, for older grades)
  • A computer and projector with internet access (optional)
Scientific Terms for Students
  • compost:
    • (Verb) The process of mixing food scraps and other quickly biodegrading waste materials together, and allowing them to decompose to become useable soil.
    • (Noun) A mixture of decayed or decaying organic matter used to fertilize soil.
  • compostable Materials: Food scraps, yard waste, and dirty paper products that can be composted to become soil.
  • recycling: The process of repurposing goods or materials so that they can be used to create new goods or materials.
  • recyclables: Goods and materials made of clean paper, glass, metal, or rigid plastic that can be used to create new goods and materials.
  • landfill: A location where waste that cannot be recycled or composted is buried in the ground.
  • decompose: To be broken down physically and chemically by bacterial or fungal action; to rot.
  1. Introduce the terms compost, recycling, and landfill. Ask students:
    • Raise your hand if you and your family compost. Raise your hand if you and your family recycle.
    • What do these words mean?
    • When you put something in that bin, what happens to it?
  2. If available, show videos of different foods decomposing. Ask students what they observe and why they think this is happening. Teacher tip: Prepare a YouTube playlist ahead of time with videos of decomposing food. Here are some to get started with, but there are MANY more to choose from:
  3. Pass around the bin of decomposed compost. Let students touch it and smell it. What do they notice? Is it gross? Remind them that this compost was rotting fruit and vegetables not that long ago. What do they think about that? Would this happen in a landfill? Tell them that living things like fungus and bacteria are responsible for decomposition, and this wouldn’t be possible in a landfill.
  1. Have students sit in groups of 3-4 students. Give each group a pile of “trash” – a mixture of items that can be recycled, composted, or must be thrown in the landfill. 4 or 5 objects will suffice for younger students; older students can have 10-12 objects.
  2. Instruct the students to sort their trash into three piles: recycleables, compostables, and landfill. Encourage them to work together and think about why these objects would go into those piles.
  3. When the groups are finished, have each group explain their choices. If they are correct, they will get to put it in that bin. If not, discuss why it would go into a different category and have a student place it in the correct bin. Teacher tip: Have other students politely give feedback on whether they think it was the correct choice.
  1. Once all the groups have gone, review the objects that were thrown in the landfill. Show students the Landfill Photograph and ask them the following questions:
    • Would you want to live near a landfill like this one?
    • What are some problems with landfills?
    • Do you see anything that could have gone into a different bin?
    • Would this be a good habitat for wildlife?
  2. (For older students) Provide students with some of the background on where San Francisco’s landfill waste goes, and show students the map of California showing where the landfills, composting facility, and vineyards are. Point out how much farther landfill waste must travel than compostable waste. Ask students:
    • What are the benefits to composting? (Less landfill, good soil for agriculture, less energy used in transport)
  3. Finally, introduce the reusable objects. Ask students:
    • What bin would this go in? (Solicit answers until someone says you can reuse it.)
    • What are some reusable items that you use?
    • What are the benefits of a reusable item?
  4. Pass out handouts to help students continue with reducing their landfill waste. Use the Recycling, Composting and Landfill signmaker to make a packet of signs for students that they can use at home with their family. Also:


Background for Educators

The aim of this activity is to familiarize people with the process of composting, and clarify which bin waste items go in. While many San Francisco residents regularly recycle, fewer compost their food scraps at home. Additionally, regional variation in waste disposal policies and confusing packaging labels can often leave even the most well-intentioned person asking “which bin does this go in?”

According to a 2012 US EPA report, an average American generates 4.3 pounds of trash each day, and 65% of this is disposed in landfills or incinerators, which takes up large areas of land, and contributes to greenhouse gases. To mitigate this, the city of San Francisco is aiming to be “waste free” by 2020. Currently San Francisco recycles or composts an impressive 80% of its waste. In order to meet the zero-waste goal, the city has mandated recycling and composting programs to reduce landfill waste.

San Francisco is able to recycle and compost most household waste. Anything that comes from a plant or animal can be composted, including bones, waxed to-go containers and milk cartons. Items made of clean paper, rigid plastics, glass, or aluminum can be recycled. Items that are made of multiple materials or do not fit into the categories above go into the landfill.

While these basic rules are helpful, there are a few items that can be sorted into surprising locations. For example, disposable razors can be recycled, waxed paper can be composted, and small pieces of wood should go in the landfill. Also, items like plastic bags and batteries can be recycled, but should be separated from other items. It can be helpful to look at the Recology website and for the most up to date information.

Some of the items that are often incorrectly sorted in San Francisco are listed below, along with information about how to properly dispose of them.

  1. Soiled paper can go into a compost bin, but clean paper goes into the recycling bin.
  2. Plastic to-go containers should be put into a recycling bin after the leftover food is placed into a compost bin.
  3. When you put your recyclable items in the bin, either place them in loose or in a paper bag. Don't collect them in a plastic bag, as that will get stuck in the recycling equipment! Plus, plastic bags need to go to the landfill.
  4. If you have many clean plastic bags or lots of clean bubble wrap, bundle them in one bag no bigger than a soccer ball, tie up the bag, and place the full bag in the recycling bin. However, don't place single plastic bags in the recycling bin.

When we sort refuse correctly we help the environment in several ways. First, we conserve useful raw materials. Recyclable materials can be used to make new products, and compostable items can become useful fertilizer for agriculture. These materials go to waste if they are put into a landfill. Second, keeping landfills small saves space and energy. Landfills require significant energy, resources, and space to manage. There is significant infrastructure that has to be put in place to keep waste from leaking into the ground water or creating air pollution problems.

Currently, San Francisco’s landfill waste goes to a landfill in the Altamont Landfill in Alameda County. As of march 2013, there is 14-million tons of waste in the Altamont Landfill which has a 15 million ton capacity. At current rates of disposal, the Altamont Landfill will run out of space for San Francisco’s waste in January 2016 (Zero Waste FAQ). Once this landfill is full, San Francisco has proposed sending its waste to a landfill in Yuba County, over 100 miles away. When recyclable or compostable materials are sent to the landfill, it requires energy for transportation, and it takes up precious landfill space.

By contrast, there are significant benefits to composting. Composting generates revenue, and also provides farmers an effective fertilizer for their crops. San Francisco’s compost is sent to Jepson Prairie Organics in the central valley of California where it goes from food scraps to useable compost in approximately 60 days. This compost is then sold to vineyards in northern California.

Another way to reduce waste is to use reusable materials. Reusable grocery bags have become more common as plastic bags were banned from the city in 2012, and recent littering audits have noted a drop in the bags found (Media Matters 2015). By using reusable water bottles, utensils, and other objects, we can keep trash out of landfills by not creating any in the first place.

Below are web resources with more background information:

  • What Bin has information on how to properly sort confusing waste items.
  • SF Environment has information how San Francisco is addressing environmental issues including waste, transpiration, energy, and more.
  • Recology has information about waste collection, pricing, and the Waste Zero 2020 initiative.
  • Jepson Prairie Organics has information about San Francisco’s composting system and process.
Next Generation Science Standards

Science & Engineering Practices

  • Constructing Explanations and Designing Solutions: Use evidence to construct or support an explanation or design a solution to a problem.
  • Engaging in Argument from Evidence: Respectfully provide and receive critiques from peers about a proposed procedure, explanation or model.

Disciplinary Core Ideas

  • ESS3.C: Human Impacts on Earth Systems: Things that people do to live comfortable can affect the world around them. But they can make choices that reduce their impacts on the land, water, air, and other living things.

Cross-Cutting Concepts

  • Patterns: Similarities and differences in patterns can be used to sort and classify designed products.
  • Energy and Matter: Objects may break into smaller pieces and be put together into larger pieces, or change shapes.

Related Performance Expectations

  • 5-ESS3-1: Obtain and combine information about ways individual communities use science ideas to protect the Earth’s resources and environment.
  • MS-ESS3-3: Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.
  • MS-ESS3-4: Construct an argument supported by evidence for how increases in human population and per-capita consumption of natural resources impact Earth’s systems.
  • HS-LS2-7: Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.
  • HS-ESS3-4: Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

Jepson Prairie Organics, Compost Process. Retrieved May 9, 2014.

Jepson Prairie Organics, Compost Photo Gallery. Retrieved May 9, 2014.

SF Environment Recycling Signs. Retrieved November 14, 2017.

Media Matters. Retrieved May 14, 2015.

Solutions in Zero Waste. Retrieved May 9, 2014. San Francisco. Retrieved May 9, 2014.

Zero Waste FAQ. Retrieved May 9, 2014.

Make Your Own Compost, Recycle, and Landfill Signs, SF Environment. Retrieved May 9, 2014.

Tomponaut Timelapse. Rotting Watermelon Timelapse Footage. Retreived May 9, 2014.

Hirnduebel. Rotting Halloween Pumpkin Time Lapse. Retrieved May 9, 2014.

Jacob, Dan. Rotting Strawberries. Retrieved May 9, 2014.

Webiocosm. Fruit and Vegetable Decomposition, Time-Lapse. Retrieved May 9, 2014.

Image: "Behold thy Landfill" by Justin Ritchie, licensed and modified under CC BY-NC-SA 2.0; originally sourced from

Appropriate for: 1st Grade - 12th Grade
Standards for: 1st Grade, 6th Grade, 7th Grade, 8th Grade, 9th Grade, 10th Grade, 11th Grade, 12th Grade
Prep Time: 15 minutes
Activity Time: 30 minutes
Subjects: Energy & Matter