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Waste-to-Resource Strategies in Agri-Food Systems

Transforming Agricultural Waste into Valuable Resources for a Sustainable Future

Module 2

Where Science Grows Solutions & Innovation Meets Sustainability

SLIDE 1 Spoken Dialogue:

“Welcome to Module 2. In this module, we’re going to shift the way we think about waste. Agriculture doesn’t just produce food—it also creates leftovers like crop residues, manure, and by-products from processing. Traditionally, these have been seen as a burden. But with science, technology, and creativity, they can become valuable resources—sources of energy, fertilizer, even new products. As we go through this unit, I want you to ask yourself: if waste isn’t really waste, but a resource, how can we design systems that capture its value? By the end, you’ll see how turning waste into resources helps the environment, the economy, and communities, and you’ll be challenged to think about what ‘waste’ in your own life could be transformed instead of thrown away.”

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Lesson A – Beyond the Trash: The Five Pathways of Food Waste

Identify: Five major waste-valorization pathways—landfill, aerobic composting, anaerobic fermentation / digestion (Bokashi & digesters), biochar pyrolysis, and insect bioconversion
Describe: Inputs, process conditions, and primary outputs of each waste pathway
Compare: Greenhouse-gas profiles of the five pathways and determine which emit or avoid the most CO₂-equivalent
Predict: Which pathway would deliver the greatest carbon reduction for a given food-waste scenario

Lesson B – Carbon Math

Understand: Recognize the ΔCO₂-equivalent for landfilling 1 kg of food waste versus treating it with alternative valorization options, using provided emission factors or data.
Create: Design an optimal valorization route for a specific real-world waste stream (e.g. cafeteria leftovers or farm waste), supporting the recommendation with evidence from carbon calculations and practical considerations.
Evaluate: Assess the trade-offs of each pathway – considering factors like cost, scalability, speed, and nutrient recovery – to justify which option might be preferable in a given context.
Rank: Categorize different waste-to-resource technologies by their net carbon impact (most to least climate-friendly) and also compare their energy requirements and useful co-products.

Lesson C - Measuring Waste & Calculating CO₂ Impact

Analyze: Quantify their campus’s waste-generation hotspots, estimating weekly amounts of food, yard, and paper waste at key locations and computing the associated CO₂-equivalent emissions for each.
Apply: Utilize the feasibility and projected carbon savings of their proposed solution in a brief presentation or “mini-pitch,” using data (emission reductions, etc.) and practical reasoning to persuade peers.
Create / Evaluate: Design a prototype waste-to-resource system for one selected hotspot or waste stream, specifying how the waste could be collected and processed (composted, fermented, fed to insects, etc.) to close the nutrient or energy loop.
Reflect: How can implementing multiple different valorization routes in parallel move the entire campus toward a circular economy, and identify challenges and next steps for making it happen.

Sustainable Agri-Food Systems and Circular Economy

Module 2: Waste-to-Resource Strategies in Agri-Food Systems

SLIDE 2 Spoken Dialogue:

“Here’s what you’ll be able to do by the end of Module 2. This module has three lessons, each with a different focus. First, you’ll learn the five main pathways for handling food waste—landfill, composting, Bokashi and anaerobic digestion, biochar, and insect bioconversion—and compare their greenhouse gas impacts. Then we’ll dive into something called ‘carbon math,’ which helps us put numbers on the emissions avoided or produced by each method, so we can make real evidence-based comparisons. Finally, you’ll learn how to measure waste and calculate its carbon footprint, applying those skills to school or community settings. By the end, you’ll not only understand the science but also be able to recommend solutions for real-world waste problems, balancing climate, economics, and practicality.”

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Which food waste pathway delivers the greatest climate benefit, and why?

Lesson A – Beyond the Trash: The Five Pathways of Food Waste

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Where Does the Peel Go?

Organic Waste has a lot of Nutrient Potential: Rich in carbon, nitrogen, and minerals that can be returned to soils or converted into valuable products.

Why It Matters: Managing organic waste sustainably can cut GHG emissions and support a circular economy.

Image: ChatGPT

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Landfill

Nutrient Cycling

Where Does the Peel Go?

Often this waste enters landfills and creates gasses that contribute to Greenhouse Gasses
Methane from rotting food warms the planet >25× faster than CO₂.
Instead we can divert that into the earth through nutrient cycling

Image: ChatGPT

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(EPA, 2021)

Food Waste by the Numbers

In the U.S., 40-50% of all food produced is never eaten (most losses in homes and restaurants!)
Drives ≈ 9% of national greenhouse-gas emissions
Food waste occupies ≈ 21% of landfill space
We’re throwing away land, water, energy, and labor that created these leftovers!

Image: ReFED, 2011

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(EPA, 2021)

Food Waste by the Numbers

In the U.S., 40-50% of all food produced is never eaten (most losses in homes and restaurants!)
Drives ≈ 9% of national greenhouse-gas emissions
Food waste occupies ≈ 21% of landfill space
We’re throwing away land, water, energy, and labor that created these leftovers!

Image: ReFED, 2011

SLIDE 7 Spoken Dialogue:

“Let’s look at the scale of the problem. About 40–50% of all food produced in the U.S. is never eaten. Almost half! And most of that waste happens in homes and restaurants. This waste is responsible for nearly 9% of U.S. greenhouse gas emissions, from the farm inputs used to grow the food all the way to landfill methane. In landfills, food waste fills about 21% of total space—making it the single largest category by weight. And remember, when we waste food, we’re also wasting the water, land, energy, and labor that went into producing it. To picture it another way: imagine buying two bags of groceries and throwing one straight into the trash—that’s basically what we’re doing at the national level. So the stakes are high. Cutting food waste is one of the biggest climate opportunities we have.”

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Food Waste by the Numbers

Video: Pagliaccia, 2022

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Optional Review: Linear VS. Circular Loop Pathway

We TAKE: We dig iron, pump oil, harvest timber
We MAKE: We turn those into phones, T-shirts, and fries
We WASTE: When we’re done, the leftovers hit the trash — end of story, and end of value

Linear Path

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Optional Review: Linear VS. Circular Loop Pathway

A circular system closes the loop by the 5 Rs, keeping nutrients and value cycling:

Refuse: Skip what we don’t need—say no to single-use forks
Reduce: Design lighter, smarter, longer-lasting products
Reuse: Pass gear along—swap, repair, thrift
Repurpose: Give items a second gig—turn jars into planters, orange peels into cleaners
Regenerate: Compost, biochar, or digest leftovers so nutrients cycle back to soil

Circular Alternative

Non-Regenerative Linear System

Regenerative System

Image: ChatGPT, 2025

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Linear VS. Circular (5 Rs)

Circular Alternative

What is a circular economy? | Sustainability 13 of 31 | Study Hall

Munjur et al., 2018

SLIDE 8 Spoken Dialogue:

“Before we dive into the pathways, let’s pause and think about systems. A linear system is the kind we’re used to: take, make, use, throw away. Food and resources flow in one direction, and waste piles up at the end. A circular system is different—it keeps materials cycling back into use. Waste is minimized, nutrients and energy are recovered, and the system regenerates itself. We often summarize this with the 5 Rs: Refuse, Reduce, Reuse, Repair, Recycle. Keep this in mind as we compare waste pathways: some are more linear, while others are more circular.”

“Here’s a video to illustrate the difference between linear and circular systems. As you watch, look for moments where waste is diverted back into use—those are the points where a circular economy is being created. After the video, I’ll ask you to share one example you saw of a circular solution in action.”

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Where Does the Peel Go?

Path 1: Landfill (Aerobic Decay)

Produces methane (CH₄), which has 28–36 times the global warming potential (GWP) of CO₂ over 100 years (EPA, 2021)
A typical ton of food waste in a landfill emits 0.25–0.75 metric tons of CO₂-equivalent methane over its lifetime.

Image: ChatGPT, 2025

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Where Does the Peel Go?

Path 2: Aerobic Compost

Emits mostly CO₂ (not methane) and at much lower overall greenhouse-gas (GHG) levels
One ton of food waste composted releases only ~0.05–0.15 t CO₂-eq—about 75–90 % less than landfilling (Pérez T., 2023)

Image: Google Gemini, 2025

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Where Does the Peel Go?

Path 3: Bokashi Fermentation (Anaerobic)

Able to process a wide variety of materials, from fruit and vegetable peel and trimmings to coffee grounds (pre and post-consumer waste)
Food composted through bokashi fermentation is often challenging to compost traditionally

Image: LabtoFarm, 2025

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Where Does the Peel Go?

Path 3: Bokashi Fermentation (Anaerobic)

Accepts meat, dairy, citrus, bones, and cooked food
Produces almost no greenhouse gases
Smells sour, not rotten
Liquid byproduct becomes fertilizer (dilute 1:100)
Fermented mash can be buried or composted
Soil microbes finish decomposition and retain nutrients

Image: ChatGPT, 2025

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Where Does the Peel Go?

Path 3: Bokashi Fermentation (Anaerobic)

Drawbacks of Bokashi Fermentation

Requires an airtight seal to function properly
Needs regular bran reloads to keep microbes active
Must be buried or composted afterward to fully break down

Image: LabtoFarm, 2025

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Where Does the Peel Go?

Path 3: Anaerobic Digester

How Does Anaerobic Digestion Work? | US EPA

Anaerobic composting alternative

Image: The picture shows big tanks called anaerobic digesters. Food scraps & other waste go in, & the tanks make biogas for energy and fertilizer for plants. It shows how garbage can be turned into something useful instead of thrown away.

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Where Does the Peel Go?

Path 4: Biochar Pyrolysis

Heating dried biomass in low oxygen → biochar
Half of the original carbon is locked away for centuries, and the porous charcoal becomes a habitat and water sponge for soil microbes

Biochar in temperate soils: opportunities and challenges

Pacific Biochar

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Where Does the Peel Go?

Path 4: Biochar Pyrolysis

Benefits

Carbon vault: Locks away up to 50% of the peel’s carbon for centuries as a long-term climate sink
Soil super-sponge: Pores retain water and nutrients, reducing fertilizer runoff and increasing yields
Microbe mansion: Jagged surface gives beneficial microbes a perfect home, boosting soil health

Image: Google Gemini

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Where Does the Peel Go?

Path 4: Biochar Pyrolysis

Pyrolysis Trade-Offs

High heat needed: Pyrolysis requires significant energy to reach high temperatures
Loop closer: The process produces syngas, which can be burned to fuel the kiln itself
Setup cost: Kilns aren't cheap to build or maintain
Free fuel source: Campus yard waste could feed the system year-round

Image: Google Gemini

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What is Insect Bioconversion?

https://youtu.be/nEcuviqzXGA?f e ature=shared

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What is Insect Bioconversion?

Image: Pagliaccia, 2022

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Double Valorization

First Valorization

Converting the waste into a primary product

Second Valorization

Using the by-product of the first process to create valuable output

Image: ChatGPT, 2025

Image: Bethel, 2025

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More Valorization Streams

A) Crop residues → Oyster-mushroom substrate; spent mycelium becomes compost
B) Used cooking oil → Can be used to make Biodiesel that could power the school bus fleet
C) Fruit pulp → Bioplastic; pectin + starch = plastic that rot back into soil
D) Manure + food waste → Algae fertilizer pellets — slow-release nutrients, circular vibes

Image: Amhuru, 2023

A

B

C

D

Image: Fayah, 2024

Image: TradeKorea, 2000

Image: Jans, 2019

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Food-Waste Pathways at a Glance

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Upcycling Toolkit Comparison

Images generated by ChatGPT

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Where Does the Peel Go?

In Conclusion

Landfill, compost, bokashi, digesters, and biochar are not isolated options—they are all threads in a bigger circular system.
By thinking circularly, we see food scraps not as waste but as resources that can return energy, nutrients, and value to our communities.

The key takeaway: leftovers are opportunities, not trash.

Image: ChatGPT, 2025

SLIDE 23 Spoken Dialogue:

“So, what happens to our orange peel? We’ve seen that the answer depends entirely on the pathway. In a landfill, it becomes methane and wasted nutrients. In compost, it becomes fertilizer and avoids most emissions. In Bokashi or a digester, it’s transformed into a nutrient-rich product with very low emissions. In biochar, it’s locked away as stable carbon for centuries. And in insects, it becomes protein for animals and fertilizer for soil. No single pathway is perfect, but each has strengths. Often, the smartest systems combine multiple methods—compost plus Bokashi, or insects plus digesters—so that nothing goes to waste. The key message is: waste is a choice. And the choice of pathway determines whether that waste harms the climate or helps the food system.”

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Case Study: Circular Thinking in Action

Challenge: Citrus nurseries generate a lot organic waste. These would be sent to landfill, emitting potent greenhouse gas.
Intervention: Researchers at LabtoFarm at UCR tested two circular pathways together:

Bokashi fermentation turns citrus scraps into nutrient-rich soil material, helping farmers use less chemical fertilizer, reducing synthetic fertilizer use.
Biochar pyrolysis heats tree prunings to make charcoal-like material that stores carbon and helps soil hold water.

Transforming Citrus Waste in California

Results:

Bokashi boosted nursery tree growth and diverted waste from landfill.
Biochar achieved long-term carbon sequestration and reduced irrigation needs.

Image: Google Gemini, 2025

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Activity Corner: Dear Principal, Reimagining Waste

Group Writing Activity

Students will pick a pathway (compost, bokashi, digester, biochar, insects) and write a short letter to the principal asking for change in waste management
You will:

Write: 1 benefit, 1 challenge, 1 solution
Share ideas with a partner and plan a short pitch, then share it out to the class

Takeaway: Leftovers can be resources, not trash!

Think-Pair-Share

Image: Google Gemini, 2025

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Optional Extended Learning: Bokashi Microbial Diversity

Why Microbes Matter in Fertilizer

Healthy Plant VS. Stunted Plant

See the difference?

In order for plants to grow healthy and tall, they need more than fertilizer – they need nutrients:

But where do these nutrients come from?

Sources of Nutrients

Chemical fertilizers supply nutrients directly but can cause pollution
Microbes in soil recycle waste and release nutrients in forms plants can use

What if we could recycle waste AND let microbes supply nutrients? That’s what bokashi does!

Image: Google Gemini, 2025

Spoken Dialogue:

“Plants can’t thrive on sunshine and water alone—they need nutrients. Traditionally, we’ve given them chemical fertilizers, which supply nutrients quickly but can pollute soil and water if overused. Microbes in soil provide a different, more natural solution. They recycle organic matter and release nutrients in forms that plants can absorb. Bokashi is one system that relies heavily on microbes. Through fermentation, microbes transform food waste into nutrient-rich material that helps plants grow. Think of microbes as the hidden workforce in soil: they take what we think of as waste and turn it into food for plants. If you compare two plants—one grown with active soil microbes and one without—you’d see a big difference. The microbe-supported plant grows taller, stronger, and healthier. That’s why microbes matter.”

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Optional Extended Learning: Bokashi Microbial Diversity

Big Question: How Do Microbes Make Bokashi Effective?

Soil Microbiome: Diversity, Benefits and Interactions with Plants

Bokashi: Type of fertilizer made by fermenting organic waste (e.g. food scraps, manure, agricultural byproducts) with the help of microbes
Bacteria and fungi break down organic waste into nutrients that plants can more easily use

Because bokashi can recycle waste while enriching soils, scientists are interested in whether different ingredient combinations create different microbial communities, and how that changes the effectiveness of bokashi.

Image: Chauhan et al., 2023

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Scientists tested different bokashi recipes, and measured both nutrients (NH₄⁺, PO₄³⁻) and microbial diversity in bokashi as it matured.

Image: Abo-Sido et al., 2021

Optional Extended Learning: Bokashi Microbial Diversity

Big Question: How Do Microbes Make Bokashi Effective?

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Optional Extended Learning: Bokashi Microbial Diversity

Measuring Nutrients and Microbial Diversity

Why Measure Nutrients?

Ammonium (NH₄⁺): builds proteins & chlorophyll → key for plant growth
Phosphate (PO₄³⁻): used for energy (ATP) & root development
Their ratio tells us how microbes are transforming nutrients in bokashi

Image: Cai, 2025

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Optional Extended Learning: Bokashi Microbial Diversity

Measuring Nutrients and Microbial Diversity

Why Measure Microbial Diversity?

Microbial Diversity: Refers to the variety of different microbes (bacteria and fungi) living in a community, and how evenly they are represented

High Diversity = Healthier, more stable system, as many organisms are working together to recycle nutrients and support plants

Measuring diversity shows how microbial communities change over time, such as during bokashi maturation
Since microbes have different roles (decomposers, nitrogen fixers, disease suppressors), tracking diversity reveals which groups drive fertilizer effectiveness

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Optional Extended Learning: Bokashi Microbial Diversity

Measurement Methods

Measuring Microbial Diversity

To track which microbes were present, scientists collected DNA from bokashi samples:

Bacteria (16S rRNA gene)
Fungi (ITS region)

Two metrics used to describe microbial communities:

α-diversity
β-diversity

Image: Google Gemini, 2025

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Optional Extended Learning: Bokashi Microbial Diversity

α-diversity (Shannon Index)

α-diversity: Diversity within a single community
Shannon Index is a singular number that calculates α-diversity by combining:

Richness: How many species are present
Evenness: How evenly species are distributed

Shannon Index ranges from 0 up to 3-5 (higher = more diversity)

Depicted as a line graph / bar chart with x-axis = time, y-axis = Shannon Index

Image: Abo-Sido et al., 2021

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Optional Extended Learning: Bokashi Microbial Diversity

Why Use Both: Shannon Index & Bray-Curtis

Shannon Index (α-diversity): Tells us how diverse one community is; ↑ Number of species + ˃ Distance spread = healthier/more stable
Bray–Curtis (β-diversity): Shows us how different multiple microbe communities are → like changing over time (Day 0 vs. Day 12)
Together: Provides a complete story = how much diversity exists inside a community AND how that diversity shifts across time or treatments!

Image: Abo-Sido et al., 2021

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Optional Extended Learning: Bokashi Microbial Diversity

Different Bokashi Recipes Tested

Control: Rice hulls
Charcoal: Rice hulls burned into charcoal

Control: Rice hulls + yeast and molasses (starter microbes & sugar for growth)
IMO: Rice hulls + local soil microbes collected from the environment + molasses

Experiment 1

Experiment 2

Common to All Treatments:

Base mix of cow manure, soil, and corn flour
All piles matured for 12 days, sampled at multiple timepoints

Image: Google Gemini, 2025

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Optional Extended Learning: Bokashi Microbial Diversity

How To Read a Shannon Index Graph

Step 1: Identify the Variables

Note: Shannon Index graph = Shannon Diversity graph

Look at the y-axis: Shannon Diversity (how rich and balanced the community is)
Look at the x-axis: Day of bokashi maturation
The colors/legend show the 4 bokashi treatments

Experiment 1: Control, Charcoal
Experiment 2: Control + Yeast, IMO

Image: Abo-Sido et al., 2021

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Optional Extended Learning: Bokashi Microbial Diversity

How To Read a Shannon Index Graph

Step 2: Look for Highs and Lows

The highest line = the treatment with the most diverse microbial community
The lowest line = the treatment with the least diversity

Step 3: Compare Treatments

Which treatments increased in diversity faster?
Do they all end up at similar diversity by Day 12, or do some stay higher/lower?

Image: Abo-Sido et al., 2021

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Optional Extended Learning: Bokashi Microbial Diversity

How To Read a Shannon Index Graph

Step 4: Interpret the Meaning

Higher diversity = more types of microbes working together
A more diverse community makes bokashi a stronger fertilizer: Healthier soil, better nutrient supply, stronger plants

Image: Abo-Sido et al., 2021

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Optional Extended Learning: Bokashi Microbial Diversity

Shannon Index (α-diversity):

Diversity increased as bokashi matured
IMO & Biochar recipes = highest diversity → most active, balanced microbes
Control = lowest diversity → fewer microbes working together

Bray–Curtis (β-diversity):

Early (Day 0) vs. late (Day 12) samples = very different communities
All treatments shift over time → microbes reorganize during fermentation
Recipes overlap somewhat → time had bigger effect than recipe

Interpreted Results for Microbial Diversity

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Optional Extended Learning Activity Corner: Reading a Graph – Soil Microbial Diversity & Bokashi

Group Analysis Activity

Students will read a graph showing Shannon Index across treatments
You will:

Identify the highest and lowest diversity values
Discuss what this means for soil health
Predict how adding Bokashi would change the graph

Image: ChatGPT, 2025

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Review Questions

List the major waste-valorization pathways we discussed in class.
Which pathway avoids the most CO₂-e emissions per kilogram of food waste, and why?
Given a scenario where you must process food scraps quickly with minimal equipment, which pathway would you recommend and what trade-offs would you accept?

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Review Answer

Landfill, Aerobic composting, Anaerobic fermentation/digestion (Bokashi & digesters), Biochar pyrolysis, and Insect bioconversion
Biochar pyrolysis (about –450 g CO₂-e/kg orange peel in the example) because it locks carbon into a stable form for centuries and displaces some fossil energy use.
Bokashi fermentation — fast and low-tech, handles wide range of food scraps; trade-offs include needing airtight containers, consistent bran addition, and post-processing.

SLIDE 26 Spoken Dialogue:

“Here are the answers. The five pathways are landfill, composting, Bokashi and anaerobic digestion, biochar, and insect bioconversion. Of these, biochar avoids the most emissions—around minus 450 grams of CO₂-equivalent per kilogram of food waste—because it locks carbon into a stable form that stays in soil for centuries, and it can even displace fossil fuel use. For the fast and simple option, Bokashi is usually best. It works in about two weeks, requires only a sealed container and bran, and can handle a wide range of food scraps. The trade-offs? You need airtight containers, consistent additions of bran, and you still need a post-processing step like burying the mash or mixing it into compost. So each pathway has strengths, and the right choice depends on your situation.”

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What are the environmental (carbon) impacts of different waste management strategies, and how can we quantify and compare them?

Lesson B: Carbon Math

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Why Each Path Works

1 kg of Orange Peel

Pathway*	Why It Matters
Landfill 🔴 ~ +500 g	Methane from rot = worst-case emissions
Compost 🟢 ~ –100 g	Aerobic; avoids methane, stores a bit of carbon
Bokashi 🟢 ~ –200 g	Fermentation acids curb GHGs; adds carbon to soil
Biochar 🟢 ~ –450 g	Pyrolysis locks carbon + syngas fuels kiln
Larvae feed 🟢 ~ –300 g	Larvae emit less GHG and replace soy-based animal feed

*Note: Numbers are estimates (ranges) to show how measurable the impacts can be.

How Much CO₂ Does 1 kg of Orange Peel Emit or Save?

> Positive = adds pollution

> Negative = avoids

or stores carbon

🟢

🔴

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Every Path Has Trade-Offs

Landfill: Low effort

→ highest GHG emissions, no resource recovery.

Compost: Low cost, nutrient return

→ slower process, can’t handle all scraps.

Bokashi/Digester: Processes more waste types, produces fertilizer/energy

→ needs airtight setup, extra finishing step.

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Every Path Has Trade-Offs

Biochar: Long-term carbon storage, soil health gains

→ high heat & equipment needed.

Insect Bioconversion: Produces feed & fertilizer

→ requires ongoing care, possible “yuck factor.”

No single “perfect” pathway – each balances climate benefit, cost, speed, and usability differently. But together, they close the landfill loop!

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Which Path Shrinks Emissions Most?

Different Paths with Different Needs

Context Matters

Insects produce more usable protein than biochar.
Bokashi works well for a wider range of food scraps.
Compost is easiest to set up at low cost.

Image: Google Gemini, 2025

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Carbon Math

But How Do We Compare Accurately?

What Is Carbon Math?

Equation: ΔCO₂-eq = mgas x GWPgas

Define Terms:

ΔCO₂-eq (equivalent): Change in emissions compared to landfill baseline
mgas: Mass of gas released (grams)
GWP: Global Warming Potential (how strongly a gas traps heat vs. CO₂)

Trade-offs are complex — to compare them on the same scale, scientists use Carbon Math.

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Carbon Math

How to Use Δ CO₂-eq?

Step 1: Start with a baseline (usually landfill)

Step 2: Calculate emissions of the new pathway

Step 3: Subtract: Δ = CO₂-eq - Landfill CO₂-eq

Interpretation:

Positive Δ → Adds more emissions (worse than landfill)
Negative Δ → Avoids emissions or stores carbon (better than landfill)

The more negative the number, the better for the climate!

Carbon math works like a recipe: start with a baseline, calculate the emissions for a new pathway, and then compare the two.

🔴

🟢

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Carbon Math

Step 1: Know your values and givens.

Equation: ΔCO₂-eq = mgas x GWPgas

ΔCO₂-eq (equivalent): Change in emissions compared to landfill baseline
mgas: Mass of gas released (grams)
GWP: Global Warming Potential (how strongly a gas traps heat vs. CO₂)

Step 2: Plug in your values into the equation.

Guided Calculation*

*We are using CH₄ (Methane) here in the example instead of CO₂ (Carbon Dioxide), as CH₄ is the gas that is produced most in landfills!

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Carbon Math

Step 1: Know your values and givens

Equation: ΔCO₂-eq = mgas x GWPgas

ΔCO₂-eq (equivalent): Change in emissions compared to landfill baseline
mgas: Mass of gas released (grams)
GWP: Global Warming Potential (how strongly a gas traps heat vs. CO₂)

Step 2: Plug in your values into the equation

Guided Calculation

Step 1: Landfill ΔCO₂-eq Values

mCH4, old: 24.51 g CH₄
mCH4, new: 6.1275 g CH₄ GWP
CH₄ GWP₁₀₀: 27.2

Step 2: Equations

CO2-eqold= 24.51 × 27.2

= 666.672 g CO₂-eqCO₂

CO2-eqnew = 6.1275 × 27.2

=166.668 g CO₂-eqCO₂

ΔCO2-eq = 166.668−666.672

=−500.004 g CO₂-eq≈−500 g

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Looking At An Impact of Carbon Math

School generates 50 kg of lunch scraps/day

30 kg → Compost for garden
10 kg → Bokashi, then → Larvae
5 kg woody waste → Biochar for raised beds
Fryer oil → Biodiesel coop

Result: 95% diversion from landfill! ♻️ Cafeteria waste becomes power, protein, and plant food

Campus Scenario

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Case Study: Turning Campus Waste into Plant Power

10% Bokashi + 10% Biochar → Half the fertilizer, healthier citrus
50% less fertilizer still led to increased seedling height & germination rates
Bokashi delivers quick nutrients & beneficial microbes
Biochar improves water retention, nutrient holding, & soil structure
Both made from campus organic waste streams

Lavagi et al., Sustainability (2024)

Campus Organic Waste

Bokashi & Biochar

Greenhouse Soil

Bigger, Healthier Plants!

Pagliaccia et al., Sci Hortic. (2024)

Image: Cai, 2025

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Group Analysis Activity

Students will work in groups to fill in the table
You will:

Use realistic examples
Decide a pathway for a school cafeteria waste stream
Defend your choice

Activity Corner: Toolkit Trade-Offs Discussion

Think-Pair-Share

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Review Questions

What does a negative ΔCO₂-eq value mean when comparing waste-treatment pathways?
Order the following pathways from most to least climate-friendly: landfill, biochar, insect bioconversion, compost, Bokashi.
If a digester has higher upfront costs but produces renewable energy, in what situations might it still be the best choice?

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Review Answers

It means the process prevents or offsets more greenhouse gases than it emits (a climate benefit).
Biochar (most climate-friendly) → Insect bioconversion → Bokashi/Digester → Compost → Landfill (least climate-friendly).
When long-term operation offsets costs via renewable energy production (biogas) and nutrient-rich digestate, especially in communities with year-round waste streams.

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Lesson C - Measuring Waste & Calculating CO₂ Impact

How can implementing multiple waste-valorization methods together create a more sustainable, closed-loop campus or community?

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Data helps identify biggest problems (“hotspots”).
Knowing quantities = choosing best solutions.
Without numbers → solutions are guesswork.

Why Measure Waste?

Why should we care about the data and how do we calculate it?

Image: ChatGPT, 2025

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Various Methods Used

Visual estimation – comparing to known sizes (e.g., a standard bin).
Counting bins – how many bins get filled per day/week.
Weighing samples – weigh one full bin, use it as an average.
Frequency – how often bins are emptied.

How to Measure Waste?

Step 1: Estimating Waste Volumes

Image: ChatGPT, 2025

SLIDE 42 Spoken Dialogue:

“The first step is figuring out how much waste you actually have. We don’t need perfection; we need enough accuracy to make smart choices. One way is visual estimation: compare your waste to something familiar, like a standard trash bin or a milk crate. Another way is to count how many bins are filled over a week—that gives you a volume estimate without touching the waste. For more precision, you can weigh one bin to get an average, then apply that across all bins. Even the frequency of emptying bins is data—if they’re emptied daily, you know the waste load is high; if weekly, it’s lower. Let’s try a quick thought experiment: picture your cafeteria’s trash bins. How many do you think are filled every day? That’s the start of volume estimation.”

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Use density (kg/L) to convert volume → mass.
Shortcut: weigh 1 bin once, use that number for similar bins.
Example:

Bin volume = 50 L
Density of food waste ≈ 0.4 kg/L
Mass = 50 × 0.4 = 20 kg per bin.

Why Measure Waste?

Step 2: Converting Volume to Mass

Image: ChatGPT, 2025

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Formula:

Weekly Waste (kg) = Mass per bin (kg) ✕ empties per week

Example:

Mass per bin = 20 kg
Emptied 3×/week
Weekly total = 20 × 3 = 60 kg/week

Why Measure Waste?

Step 3: Calculating Weekly Totals

Image: ChatGPT, 2025

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Formula:

CO2-e = Mass of waste (kg) ✕ Emission factor (kg CO2-e/kg waste)

Emission factors (simplified table):

Food waste → 1.9 kg CO₂-e/kg
Paper waste → 1.5 kg CO₂-e/kg
Yard waste → 0.6 kg CO₂-e/kg

Why Measure Waste?

Step 4: From Waste to CO₂-equivalent

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Case Study: Dorm Kitchen Food Waste

Meet Juan and Katie

Meet Juan and Katie! They are college roommates living in a dorm, and we want to measure the amount of food waste they generate. By tracking their waste, we can see how small daily choices add up over time. This gives us a closer look at where leftovers go and how they might be turned into useful resources.

Image: Google Gemini, 2025

SLIDE 46 Spoken Dialogue:

“Let’s ground all of our measurement skills in a real story. Meet Juan and Katie, who share a small dorm kitchen. Like most students, they cook some meals, save leftovers, and toss scraps. Today we’ll use their kitchen as a mini-lab: we’ll measure their food waste, see how quickly it adds up, and connect it to CO₂-equivalent so we can talk about climate impact with numbers, not guesses. Before we jump into the math, picture the bin in their kitchenette: what fills it in a typical week — wilted greens, coffee grounds, leftover rice? Hold that mental picture. In a moment, you’ll estimate the weekly amount, then we’ll scale it to a year and translate it into emissions. This case links directly to what we covered on landfill methane and avoided emissions — now we’ll quantify it for one ordinary kitchen.”

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What We Have

Dorm kitchen has 1 bin = 25L volume.
Density = 0.4kg/L → 10kg food waste/bin.
Emptied 2 × per week (2/week).
Emission factor for food = 1.9kg CO₂-e/kg.

Case Study: Dorm Kitchen Food Waste

Step-by-Step Solution

Guided Calculation

Mass/week:

10kg/bin × 2/week

CO₂-e/week:

(Mass/week) × 1.9kg CO₂-e/kg

CO₂-e/year:

(CO₂-e/week) × 52 weeks

Formula:

Weekly Waste (kg) = Mass per bin (kg) ✕ empties per week

Don’t Forget!

SLIDE 47 Spoken Dialogue:

“Let’s work the numbers together and show our steps so everyone can follow. If the bin is 25 liters and we use a typical density for mixed food scraps of 0.4 kilograms per liter, that comes out to about 10 kilograms per full bin. Since Juan and Katie empty that bin twice per week, that adds up to roughly 20 kilograms of food waste each week. Using a food-waste emission factor of 1.9 kilograms of CO₂-equivalent per kilogram of waste, that translates into about 38 kilograms of CO₂-e every week if their scraps were landfilled. Over the course of a year, multiplying by 52 weeks, this amounts to nearly 1,976 kilograms of CO₂-e—almost two tonnes. That’s the climate footprint of just one small dorm kitchen bin! As we calculate, be sure to double-check units as we convert liters into kilograms and weeks into years, and compare your results with your partner. Notice how these simple measurements—bin size and emptying frequency—quickly become a clear picture of both waste mass and emissions.”

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Impact

2 tonnes CO₂-e/year ≈ emissions from driving a car ~5,000 miles.
Even a small kitchen bin of waste adds up quickly.

Case Study: Dorm Kitchen Food Waste

Interpreting the Result

Results

Mass/week:

20 kg/week

CO₂-e/week:

38 kg CO₂-e/week

CO₂-e/year:

1,976 kg CO₂-e/year (~2 tonnes)

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Optional Activity Corner: Mini Waste-to-Resource Pilot Think-Pair-Share

Group Design Activity

Pick 1 cafeteria waste item (e.g., banana peels, leftover fries)
Design a mini blueprint:

Choose best valorization method (compost, bokashi, larvae, etc.)
Assign who manages it
Estimate CO₂ reduction
Write 2-sentence justification

Image: Google Gemini, 2025

Spoken Dialogue:

“Time to design a mini pilot. Choose one cafeteria waste item—maybe banana peels, coffee grounds, or leftover fries—and match it to the best-fit pathway such as compost, Bokashi, insects, biochar, or a digester. As a group, sketch out a simple one-page blueprint that explains who would collect and manage the waste, where it would go and what equipment or space would be needed, and what change in CO₂-equivalent you’d expect, supported with a quick calculation. Think about the co-products you’d generate, whether that’s compost, Bokashi mash or tea, larvae and frass, or biochar. Then add a short two-sentence justification that explains why this option makes sense in terms of both carbon savings and practical considerations. Use a floor map or sticky notes to mark out hotspots, and include a simple before-and-after sketch or even a tiny CO₂ thermometer to show the impact. When everyone is finished, we’ll compare pilots and talk about which ideas could realistically scale up to a school-wide system.”

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Review Questions

Which location on campus produces the highest CO₂-e emissions from food waste, and how do you know?
If you implemented insect bioconversion at your largest hotspot, what would happen to CO₂-e emissions and what co-products would you generate?
Why might using multiple waste-valorization methods together be more effective than relying on a single solution?

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Review Answers

Likely the cafeteria or dining hall — data shows it generates the largest volume of food waste; multiplying volume × emission factor gives the highest total CO₂-e.
CO₂-e emissions decrease (avoiding methane from landfill), and you produce high-protein feed (larvae meal) and organic fertilizer (frass).
Different waste streams suit different processes, spreading risk, maximizing recovery, and balancing trade-offs (e.g., speed, nutrient retention, scalability).

SLIDE 50 Spoken Dialogue:

“Let’s check. The cafeteria or dining hall is usually the top emitter, because it generates the largest mass of scraps daily, and we know this from bin counts and weights combined with emission factors. Insect bioconversion would lower CO₂-e significantly—around minus 300 grams of CO₂-e per kilogram avoided—and at the same time it would produce two valuable co-products: larvae, which can be used as animal feed to replace soy or fishmeal, and frass, which is a nutrient-rich fertilizer. Using multiple methods is better than relying on a single one because different wastes are best suited to different systems. A mix maximizes resource recovery, minimizes emissions, and adds resilience when one pathway reaches its limit. That’s how measurement and carbon math guide smarter designs—by allowing us to target hotspots, choose the right tools, and prove the impact.”

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Module 2 Key Takeaways

Image: Google Gemini, 2025

Image: ChatGPT, 2025

Waste has many pathways

Food-waste strategies differ in process, outputs, and environmental impact.

Carbon math matters

CO₂ calculations reveal which options deliver the biggest climate benefits.

Design for circularity

Data-driven solutions transform waste into resources, building circular food systems.

SLIDE 51 Spoken Dialogue:

“As we wrap up Module 2, let’s take a step back and look at the big picture. We started by asking how food waste could be redefined as a resource, and we explored five different pathways — landfill, composting, Bokashi, anaerobic digestion, and biochar — each with unique benefits and trade-offs. We also practiced doing the carbon math, learning how to compare emissions across systems and identify which pathways deliver the biggest climate benefits. Then, we moved into measurement, seeing how simple tools like bin counts and density estimates can generate powerful data for planning solutions. The key takeaway here is that waste isn’t just something to throw away; it’s a material flow that can either worsen climate change or help us build circular systems. By using systems thinking, we can see how waste connects to carbon, soil health, energy, and even economic opportunities, and we can design smarter strategies that close loops instead of breaking them.”

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What You’ll Learn: Mindmap

Image: Cai, 2025

SLIDE 52 Spoken Dialogue:

“Before we move forward, let’s visualize how everything we’ve learned in this module connects. Imagine a mindmap that links the five waste-valorization pathways, the carbon math that measures their impact, and the tools we use to track waste in real-world settings. At the center is organic waste, and branching from it are the strategies that transform it: compost brings nutrients back to soil, Bokashi and digesters recycle food into fertilizer and energy, biochar locks carbon away while improving soil, and insect bioconversion creates both feed and fertilizer. Around the edges, you see the supporting ideas we’ve practiced: data collection, CO₂-equivalent calculations, trade-off analysis, and systems thinking. This mindmap is your toolkit — it shows how different approaches don’t stand alone, but interlock to form a circular economy. Keep this structure in mind as we move into future modules, because the skills you built here will connect to water, energy, and farming systems more broadly.”

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Career Pathways

Technical & Engineering Careers

Waste Management Engineer
Environmental Engineer
Bioenergy Plant Technician
Agricultural Machinery Designer
Water & Wastewater Treatment Operator

Science & Research Careers

Soil Scientist
Environmental Scientist
Microbiologist
Food Waste Researcher
Climate Data Analyst

Policy, Education & Community Careers

Sustainability Coordinator
Environmental Policy Advisor
Community Compost Program Manager
Agri-Food Systems Educator
Corporate Sustainability Officer

SLIDE 53 Spoken Dialogue:

“Now let’s shift to thinking about your future. The knowledge and skills from this module don’t just live in the classroom; they connect to real career paths in sustainability, agriculture, science, and engineering. If you’re interested in policy, you might work on designing food-waste reduction programs or advising governments on climate-smart agriculture. If you lean toward science and technology, you could become a researcher in composting microbes, a biochar systems engineer, or a data analyst mapping carbon footprints. Innovation and business offer other opportunities — developing circular food companies, upcycling products, or working on sustainable packaging. And of course, careers in farming, urban agriculture, or nonprofit advocacy all benefit from understanding waste-to-resource strategies. As you consider these pathways, think about how your own strengths — whether in science, communication, design, or leadership — might fit into building a more circular food system.”

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Sneak Peek on Hands-On Activities

Cafeteria Waste

Audit

DIY Bokashi

Bucket Setup

Biochar Experiment

Image: ChatGPT, 2025

SLIDE 54 Spoken Dialogue:

“To close, here’s a preview of what’s coming next. In our upcoming sessions, you’ll have a chance to apply these ideas through hands-on activities that bring waste-to-resource strategies to life. You might measure and sort actual cafeteria waste, calculate the CO₂-equivalent of your school’s scraps, or design small-scale pilots using compost bins, Bokashi buckets, or even insect larvae systems. You’ll also practice presenting solutions, just like a real sustainability consultant would do for a school or city. The point of these activities is not just to test your knowledge, but to give you the confidence to turn ideas into action. When you leave this module, you’ll be ready to look at waste differently — not as a problem to hide, but as a resource you can measure, calculate, and transform. That mindset shift is the first step toward becoming a leader in building sustainable food systems.”