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Effects of Compost Material on Various Degradable Lawn Bags
Joe Mautino
9th Grade
Central Catholic High School
Problem
• Plastic bags are used frequently and add to pollution problems
• Plastic bags are not thought to readily decompose
• Composting has been implied as an effective means of recycling organic materials
• Can composting degrade plastic bags as readily as paper?
Background (Composting)• Composting is the transformation of organic waste into
compost • Main components of composting
– Organic matter• Brown (leaves, twigs, manure) supply Carbon• Green (grass, fruit rinds) supply Nitrogen
– Bacteria• Mesophilic Bacteria Range (10 C° - 40 C° ) • Thermophilic Bacteria Range (40 C° - 65 C°) most desirable
– Oxygen• Oxygen is used up quickly by the microbes as they metabolize the
organic matter • Less oxygen, slower composting
– Moisture• Ideal range is 40% to 60% moisture• High moisture causes anaerobic conditions, low moisture inhibits
activity
Background (Plastic)
• Americans throw away approximately 100 billion polyethylene plastic bags a year
• Made from crude oil– Accounts for 4% of the worlds total oil usage
• The process of making plastic bags requires large amounts of electricity
• Does not readily decompose
Background (Paper)Paper production impacts the environment in many
ways• Collection of timber for production is long and
environmentally taxing• Water usage
– Thousands of gallons of clean H2O used to wash and bleach pulp
– Paper = 1 part pulp to 400 part H2O
Disposition of used paper• Landfills
– Takes many years to decompose
• Recycle– Requires extensive process to return to pulp
Background (BioPlastic)• New biodegradable & compostable
plastics derived from cornstarch, Mater-Bi– Made from starch, biodegradable polyester,
other natural plasticizers – Claim to biodegrade in 10-45 days– Biodegradable: degrade from composting into
carbon dioxide, water, and inorganic biomass
• Compostable: Meets ASTM -6400-99– Biodegradable– Disintegrate– Low eco-toxicity
Purpose
To determine the garbage bag that will decompose the most rapidly in a compost pile.
Hypothesis
In the test compost, Mater-Bi plastic bags will decompose more than polyethylene plastic bags. The paper bags will undergo the greatest degree of decomposition.
Null: No significant variation in decomposition rate will be composted between Mater-Bi, polyethylene plastic and paper.
Materials
• 10 Mater-Bi plastic 127 mm * 127 mm bag pieces
• 10 polyethylene plastic 127 mm * 127 mm bag pieces
• 10 paper 127 mm * 127 mm bag pieces
• Digital scale (.000) grams • 5 L of organic potting mix• 15 L of cut grass• 900 ml of cheese
• 500 ml of yogurt• 500 ml of cucumber • 700 ml of green pepper• 400 ml of broccoli • 1 22 L metal bucket• A small electric heater• 1 155 L insulated bucket• 1 measuring cup• Appropriate PPE
Procedure• Collected and used appropriate PPE• Cut 10 127 mm * 127 mm pieces of each bag
(Polyethylene plastic, Paper, and Mater-Bi plastic bags)
• Weighed each sample and recorded initial mass of each piece
• Created compost mixture with the organic materials (Approximately 20 L)
• Placed the compost into a 22L bucket.• Mixed all 30 samples (Plastic, paper, and Mater-
Bi plastic) into the compost mixture• Used a small heater under the bucket and set to
25°C
Procedure• Covered the small bucket with the 155L
insulated can to keep a constant temperature • Used a small shovel to mix compost weekly• After 4 weeks removed sample bags from the
compost• Cleaned bag samples by brushing all excess dirt
from bags• Let the samples dry overnight• Weighed final mass
Polyethylene Plastic Experiment Samples (Control)
Before After
Paper Experiment Samples
Before After
Mater-Bi Plastic Experiment Samples
Before After
Data
Average Polyethylene Plastic Bag
Average Paper
Bag
Average Mater-Bi
Plastic Bag
Initial Weight (grams) 0.3884 1.3416 0.3746
Finial Weight (grams) 0.3827 0.1038 0.3579
Weight Loss (grams) 0.0057 1.2378 0.0167
Percentage of Weight Loss 1.47% 92.26% 4.46%
Anova Single Factor calculations for the
Average Weight Loss For the 3 Bag Types Anova: Single
Factor
SUMMARY
Groups Count Sum Average Variance
Mater-Bi Plastic 10 44.89 4.489 1.352121111
Polyethylene Plastic 10 16.33 1.633 0.278801111
Paper 10 924.61 92.461 157.6407656
ANOVA
Source of Variation SS df MS F P-value F crit
Between Groups 53323.18 2 26661.5918 502.1907951 4.39E-22 3.354131
Within Groups 1433.445 27 53.0905626
Total 54756.63 29
Percentage Weight Loss for the Average of Each Sample Bag
92.26
4.461.47
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Polyethylene Plastic Bag
Paper Bag
Mater-Bi plastic Bag
Observations
• All elements in the compost biodegraded to rich black soil
• Mater-Bi plastic showed indications that decomposition had started
• The Polyethylene plastic did not show any signs of biodegradation
• Only little pieces of the paper bags were left
Future Improvements
• Fill actual bags with organic material
• Improve final cleaning to reduce residual compost on the samples
• Add additional composting bacteria to accelerate decomposition
Conclusion
• My alternate hypothesis was proven correct, that in the test compost, Mater-Bi plastic bags will decompose more than polyethylene plastic bags. The paper bags will undergo the greatest degree of decomposition.
• My null hypothesis was rejected, shown by the P value stated in the Anova calculations.