Below is a suggested categorization of meal items. While multiple answers may be reasonable depending on local waste systems, this key represents the most accurate pathways based on national recycling and composting guidelines. Encourage students to justify and compare their reasoning to these suggestions.
| Meal Item | Best-Fit Energy Pathway Bin | Reasoning / Notes |
| Potato peels, pumpkin guts, corn husks | Compost/Biogas | Organic matter breaks down into compost or can produce biogas. |
| Onion skins and vegetable trimmings | Compost/Biogas | Fully biodegradable; ideal for composting or anaerobic digestion. |
| Eggshells and leftover popcorn kernels | Compost/Biogas | Adds calcium and organic material to compost. |
| Turkey bones | Compost/Biogas (optional) | Some composting systems accept bones; otherwise Landfill, if it is not industrial compostable. |
| Unopened cans of pumpkin/green beans | Food Donation | Shelf-stable, unopened; safe for donation. |
| Unopened box of instant mashed potatoes | Food Donation | Shelf-stable, non-perishable; donation appropriate. |
| Bag of dried beans or rice | Food Donation | Non-perishable, unopened food. |
| Clean cardboard packaging | Recycling | Recyclable if not contaminated by food residue. |
| Empty plastic beverage bottle | Recycling | PET plastic can be reprocessed efficiently. |
| Emptied metal food cans | Recycling | High energy recovery rate from aluminum or steel. |
| Emptied glass jars | Recycling | Recyclable if clean and free from food contamination. |
| Used cardboard takeout container | Compost/Biogas or Landfill | If clean/uncoated, compostable; if waxed or greasy, landfill. |
| Used paper napkins | Compost/Biogas | Compostable if free of synthetic dyes or coatings. |
| Plastic wrap and cling film | Landfill | Contaminated plastic films are not recyclable. |
| Plastic bags | Recycling (Store Drop-Off) | Often accepted at separate facilities but not in curbside bins. |
| Used Styrofoam plate/cup | Landfill | Non-recyclable and not biodegradable. |
Quantitative Reasoning: Estimation Questions Sample Student Responses
- Sample Student Response: Aluminum requires the most energy to produce at 372 MJ/kg and food waste requires the least amount of energy to produce at 7-8 MJ/kg. If the goal is to save the most energy per kilogram, prioritize capturing aluminum for recycling. Materials like food waste have far lower embedded energy, so energy savings per kg are smaller.
- Sample Student Response: At a 95% rate of energy recovery, about 353.4 MJ (0.95 x 372) per kilogram of recycled aluminum is saved.
- Sample Student Response: Some reasons for paper being recycled more than PET plastic could be the high volumes of paper in households, schools and offices, the established, simple collection and recycling systems in place, and often lower contamination and clearer sorting rules than mixed plastics. I would still target paper first because of its high volume and simpler recycling process, while continuing to improve PET plastic recycling where feasible to tap into its higher per kg savings.
- Sample Student Response: Source reduction avoids 100% of embedded energy, plus the extra energy used in collection and processing. For example, avoiding 1 kg of PET plastic avoids 60 MJ. Recycling 1 kg of PET saves ~45 MJ. The extra benefit from reduction vs. recycling would be around 15 MJ/kg.
- Sample Student Response: I think that the best balance would be achieved when systems for both are established and put in place. Aluminum needs to be targeted because of its high per kg savings, while paper and food also need to be targeted because of their higher usage.
Analyze and Reflect: Sample Student Responses
- Sample Student Response: I think that diverting food waste into compost and biogas has the greatest potential benefit locally. Our community generates a lot of organic waste that could be used to create compost for local gardens and, with digesters, be helpful to produce biogas for cooking. It addresses a large waste stream with meaningful environmental and energy benefits.
- Sample Student Response: We could plan portions and menus better to avoid overbuying. We could use reusable plates, cups and tablecloths instead of single-use plastics and paper. We could set up a compost bin for vegetable scraps, and choose items with minimal packaging.
- Sample Student Response: We could reuse glass jars as pantry containers and storage; clean and reuse trays for baking or potlucks; break down cardboard boxes for storage, repackaging and crafts; make stock from bones and vegetable scraps and compost the remainder.
- Sample Student Response: Barriers include lack of curbside service and the time it takes to transport to donation sites; confusing rules; limited space (e.g. apartments). Solutions include expansion of curbside programs; educational campaigns promoting clear guidelines; provision of compost kitchen caddies; place public drop-offs.
- Sample Student Response: My call to action would be “Plan Smart, Sort Right.” This holiday, prevent waste first, then carefully recycle and compost what’s left. Return cans, recycle clean packaging, and feed soil, not landfills, with food scraps.
Extension Challenge: CER Activity Sample Student Response
Claim: Sample Student Response: I think it’s better to conserve energy by reducing unnecessary or excessive energy use in the first place, rather than relying only on recovering energy from waste afterward.
Evidence: Sample Student Response: According to the data table, producing new aluminum requires about 372 MJ/kg and recycling saves about 90-95% of that (roughly 335-353 MJ/kg). While those savings are significant, if we can avoid making aluminum packaging that isn’t really needed (like single use cans when reusable containers would work) we save the entire 372 MJ/kg.
Reasoning: Sample Student Response: The evidence shows that recovery systems like recycling and composting are important, but they happen after energy has already been spent to make, transport, and sell those materials. If we focus on reducing unnecessary energy use, such as making disposable items that quickly become waste, we can prevent the largest energy losses in the system.
This doesn’t mean stopping energy use altogether. Energy is essential for modern life. But we can be more thoughtful about which energy adds real value and which is wasteful. For example reusing containers, buying durable goods, and planning meals to prevent food waste all conserve energy without reducing quality of life.
Because of this I can conclude that the most effective approach is to minimize unnecessary energy use first and then recover as much as possible from what remains.