Rot Renew Workbook
Rot & Renew
Soil Ecology & Biogeochemical Systems
Student Lab Investigation
Middle School Science Core
Student Name:
Period / Lab Group:
Date:
1
The Decomposition Engine & Carbon Flow
Composting is controlled, aerobic bio-oxidation. In a healthy pile, billions of micro-organisms (aerobic bacteria, actinomycetes, and fungi) and macro-organisms (earthworms, mites, springtails) break down complex organic polymers—such as cellulose and proteins—into stable humus, water vapor, microbial biomass, and carbon dioxide.
Matter & Energy Transfer Model
System Inputs
- Organic Waste (C & N)
- Atmospheric \(O_2\) (Oxygen)
- \(H_2O\) (Moisture 40–60%)
Compost Bioreactor
Cellular Respiration
\(C_6H_{12}O_6 + 6O_2 \rightarrow\)
\(6CO_2 + 6H_2O + \text{Heat}\)
Decomposer Web Active
System Outputs
- Finished Humus / Compost
- Water Vapor (\(H_2O\))
- Carbon Dioxide (\(CO_2\))
- Thermal Energy (Heat)
Question 1.1: Law of Conservation of Mass in Decomposition
After 10 weeks, a school compost pile loses over 50% of its physical volume and total mass. Explain where that mass went, citing the chemical respiration equation above.
Question 1.2: Aerobic vs. Anaerobic Microbes
Why must a compost operator periodically turn (aerate) the pile? Contrast the gas byproducts of oxygen-rich composting with oxygen-depleted landfill environments.
Unit: Biogeochemical Cycles & Soil Ecology Page 1 of 4
The Golden Ratio
Balancing Browns & Greens (Carbon to Nitrogen)
Stoichiometry & Diet
Optimal Formula: 30:1
CARBON ("Browns") — Energy Source
Provides carbohydrates for microbial respiration and porous structure for airflow. Excess carbon slows decomposition dramatically ("cold pile").
NITROGEN ("Greens") — Cell Building
Supplies amino acids, enzymes, and proteins needed for microbial reproduction. Excess nitrogen creates ammonia gas (\(NH_3\)) and bad odors.
Common Feedstock C:N Benchmarks Target Blend C:N = 25:1 to 30:1
| Feedstock Material | Classification | Typical C:N Ratio | Decomposition Rate |
|---|
| Fresh Vegetable/Fruit Scraps | Green (Nitrogen) | 15:1 | Very Fast (1–2 weeks) |
| Used Coffee Grounds | Green (Nitrogen) | 20:1 | Moderate (3–4 weeks) |
| Dry Autumn Leaves | Brown (Carbon) | 60:1 | Slow (4–8 months) |
| Cardboard & Newsprint (Shredded) | Brown (Carbon) | 350:1 | Very Slow (6–12 months) |
| Wood Chips & Sawdust | Brown (Carbon) | 500:1 | Extremely Slow (1–2 years) |
2
Lab Challenge: Diagnosing the School Compost Pile
Scenario A: The "Slime & Stench" Pile
A student club loaded the bin with 40 kg of apple cores, cafeteria melon rinds, and coffee grounds, but added zero dry leaves or cardboard.
Identify the limiting factor & formulate the correction:
Scenario B: The "Sleeping Giant" Pile
A gardener filled a 1 m³ bin entirely with dry cedar shavings and pine needles. After 6 weeks, the pile remains at ambient temperature (18°C).
Identify the limiting factor & formulate the correction:
Calculation: Practical Volume Rule of Thumb
Because "Browns" are light and bulky while "Greens" are dense and wet, compost scientists recommend a practical volume recipe of 2 to 3 buckets of brown materials for every 1 bucket of green materials. If your cafeteria generates 6 five-gallon buckets of vegetable scraps per week, calculate how many buckets of shredded leaves you must supply:
Unit: Biogeochemical Cycles & Soil Ecology Page 2 of 4
Thermal Ecology
Microbial Succession & Temperature Dynamics
Field Data Analysis
14-Day Thermophilic Cycle
Phase 1: Mesophilic
20°C – 40°C (Days 1–3)
Acid-producing bacteria rapidly consume soluble, easily degraded sugars and starches, generating initial metabolic heat.
Phase 2: Thermophilic
45°C – 65°C (Days 4–9)
Heat-tolerant bacteria (*Bacillus*, *Thermus*) break down proteins and fats. High temps sanitize pathogens and weed seeds.
Phase 3: Curing / Maturation
Cooling < 30°C (Weeks 3+)
Fungi and actinomycetes digest tough lignin and cellulose. Earthworms re-enter to finish humus humification.
School Bioreactor 14-Day Temperature Log
Critical Threshold: 55°C (Weed & Pathogen Kill)
55°C (Sanitation Standard)
40°C (Thermophilic Boundary)
20°C (Ambient Air)
Turned & Aerated (Day 8)
D1 (22°) D2 (34°) D4 (48°) D6 (62°) D8 (38°) D9 (58°) D11 (49°) D14 (30°)
Question 3.1: Biological Mechanism of Temperature Rise
What cellular process directly causes the pile to heat up from 22°C to 62°C between Days 1 and 6? Why doesn't the pile catch fire?
Question 3.2: Interpreting the Day 8 Turning Event
Notice that temperature dipped briefly on Day 8, then rebounded sharply to 58°C by Day 9. Explain why introducing fresh oxygen provoked a rapid microbial resurgence.
Question 3.3: Food Safety & Vector Control
Agricultural safety standards require compost to sustain at least 55°C for a minimum of 72 consecutive hours. Based on the data log, did this school pile meet the safety standard? Justify your claim.
Unit: Biogeochemical Cycles & Soil Ecology Page 3 of 4
Climate & Campus
Methane Abatement & Sustainability Decision Matrix
Action Plan & Audit
Middle School Eco-Civics
Landfill Fate vs. Compost Fate
Municipal Landfill (Anaerobic)
Food waste buried under tons of trash is deprived of oxygen. Methanogenic archaea digest the waste, producing Methane (\(CH_4\))—a greenhouse gas with 28× the heat-trapping power of carbon dioxide over a 100-year timescale.
Aerobic Compost System
With active aeration, aerobic microbes emit biogenic Carbon Dioxide (\(CO_2\)) and sequester substantial organic carbon into rich humus that restores topsoil microbiology and retains water.
School Audit: Quantifying Campus Impact
Your middle school cafeteria serves 450 lunches daily. A 1-day waste audit reveals an average of 0.12 kg of compostable food scraps discarded per student lunch.
Daily Scraps
54 kg / day
450 students × 0.12 kg
Annual Scraps (180 days)
9,720 kg / yr
~9.7 metric tons
Methane Diverted
~6,000 kg \(CO_2e\)
Equal to 14,800 miles driven
Action Policy Proposal: Designing Our School Composting System
You are presenting to the School Board to request funding for a three-bin campus composting station. Formulate three concrete operational guidelines that will prevent odors and rodent pests while ensuring student volunteers remain safe and engaged.
Personal Reflection: Closing the Nutrient Loop
How does transforming food waste into finished garden compost challenge the traditional linear "extract $\rightarrow$ consume $\rightarrow$ discard" economic model?
Unit: Biogeochemical Cycles & Soil Ecology Page 4 of 4
